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Journal of Organometallic Chemistry (v.692, #21)

Editorial Board (pp. ifc).
Contents (pp. v-xvi).
Insertion chemistry of the metal–carbon bond: A tribute to Gerhard Erker by Timothy H. Warren Guest Editor (pp. xvii-xix).

How to synthesize a constrained geometry catalyst (CGC) – A survey by Jesus Cano; Klaus Kunz (pp. 4411-4423).
Since the early 1990s constrained geometry complexes of group 4 metals have been studied as catalysts in olefin polymerizations and are now of major industrial importance. This article describes the development of this structurally highly diverse catalyst family providing a concise overview on synthetic entries to these organometallic complexes.Since the discovery of titanium- and zirconium complexes with linked cyclopentadienyl amido ligands, this new polymerization catalyst class (constrained geometry catalysts “CGCs”) has attracted the interest of many research groups in industry and academia. In order to improve or modify the catalytic and polymer properties, numerous changes in the environment of the catalyst have produced a huge family of CGCs. The aim of this contribution is to provide a concise overview on synthetic entries to these structurally highly diverse catalysts – an organometallic guide to CGCs.

Keywords: Constrained geometry catalysts; Cyclopentadienyl amido ligands; Titanium; Zirconium; Polymerization


Reactivity of the metal–cyclopentadienyl (indenyl, fluorenyl and cycloheptatrienyl) bonds by Ruiting Liu; Xigeng Zhou (pp. 4424-4435).
The focus of this review concerns the reactivity patterns of metal–cyclopentadienyl (indenyl, fluorenyl and cycloheptatrienyl) bonds. The advances in metal–carbon(η5) insertion chemistry have demonstrated that the π-bonding character provides additional reaction opportunities which are not shown by metal–alkyl compounds and these differences are highlighted.The focus of this review concerns the reactivity patterns of metal–cyclopentadienyl (indenyl, fluorenyl and cycloheptatrienyl) bonds. The advances in the metal–carbon(η5) insertion chemistry have demonstrated that the π-bonding character provides additional reaction opportunities which are not shown by metal–alkyl compounds and these differences are highlighted.

Keywords: Insertion; Coupling reaction; Organometallic complexes; Cyclopentadienyl; Indenyl; Fluorenyl; Cycloheptatrienyl


On the insertion processes of unsaturated molecules into the Nb–X σ-bond of“Cp2′NbX” moieties (Cp′=η5-C5H4SiMe3; X=H, C, P) by Antonio Antiñolo; Santiago García-Yuste; Antonio Otero; Elena Villaseñor (pp. 4436-4447).
The Nb–X σ-bond of the formally 16-electron moieties“Cp2′NbX” (Cp′=η5-C5H4SiMe3; X=H, C, P) undergoes insertion processes of different types of unsaturated molecules, namely CO, CO2, isocyanates, isothiocyanates, isonitriles, olefins and activated alkynes.In this article, we have reviewed a series of insertion processes of different types of unsaturated reagents, namely carbon monoxide, carbon dioxide, isocyanates, isothiocyanates, isonitriles, alkenes and activated alkynes, in the Nb–X σ-bond, X=H, C and P, of“Cp2′NbX” moieties, Cp′=η5-C5H4SiMe3.

Keywords: Niobocene; Insertion


Synthesis and reactivity of di(silylamido)cyclopentadienyl titanium and zirconium complexes by Jesús Cano; María Sudupe; Pascual Royo (pp. 4448-4459).
A short account of our recent contributions to the synthesis and reactivity of doubly silylamido-bridged cyclopentadienyl titanium and zirconium chelates is presented with particular emphasis on the insertion reactions of isocyanides into their M–N and M–C bonds and the efficiency of their alkyl-free cationic species as ethene polymerization catalysts and their deactivation pathways.We present in this account the synthesis and recent developments of a new class of group 4 metal complexes with the tridentate di(silylamido)cyclopentadienyl ligand. These doubly silyl-bridged group 4 metal amido chelates are receiving increasing interest as they are efficient catalysts for ethene polymerization when activated with MAO despite generating 14-electron d0 cationic species free of the alkyl group required for the first insertion reaction in the polymerization process.

Keywords: Silylamido; Cyclopentadienyl; Titanium; Zirconium


Edge-bridged half-open zirconocenes: Synthesis, characterization, and reaction with diphenylacetylene by Benjamin G. Harvey; Vichien Kulsomphob; Atta M. Arif; Richard D. Ernst (pp. 4460-4466).
The synthesis and characterization of the half-open zirconocene, Zr(C5H5)( c-C8H11)(PEt3) ( c-C8H11=cyclooctadienyl), is described. The compound shows shorter Zr–C distances for the cyclooctadienyl ligand, in accord with expectations of stronger Zr–C bonding relative to C5H5. This compound reacts with two equivalents of diphenylacetylene to yield a bicyclic coupling product.The synthesis and characterization of the new, 16 electron half-open zirconocenes, Zr(C5H5)( c-C8H11)(PR3) (R=Me, Et) are reported, together with a structural study of the PEt3 complex. As with other low valent half-open zirconocenes, the Zr–C distances are significantly shorter on average for the electronically open dienyl ligand than those for the C5H5 ligand, 2.343 vs. 2.512Å. Reaction of either of these compounds with PhC2Ph led to the incorporation of two equivalents of the alkyne, resulting in a formally 14 electron complex with coordination from cyclopentadienyl, allyl, σ-alkyl, and σ-vinyl units.

Keywords: Pentadienyl; Coupling reaction; Zirconium complex


High-nuclearity ruthenium carbonyl cluster chemistry. 8: Phosphine activation, CO insertion, and deruthenation at a phosphido cluster – X-ray structures of [ppn][Ru88-P)(μ-CO)2(CO)20] and [ppn][Ru77-P)(μ-η2-OCPh)(μ-PPh2)(μ-CO)(CO)17] by Michael D. Randles; Anthony C. Willis; Marie P. Cifuentes; Mark G. Humphrey (pp. 4467-4472).
Reaction of [ppn][Ru88-P)(μ-CO)2(CO)20] with triphenylphosphine proceeds by loss of one cluster core vertex, phosphine P–C cleavage, and CO insertion into the putative Ru–phenyl bond to afford [ppn][Ru77-P)(μ-η2-OCPh)(μ-PPh2)(μ-CO)(CO)17] in low yield.Reaction of the square antiprismatic cluster [ppn][Ru88-P)(μ-CO)2(CO)20] [ppn=bis(triphenylphosphoranylidene)ammonium] with triphenylphosphine proceeds by loss of one cluster core vertex, phosphine P–C cleavage, and CO insertion into the putative Ru–phenyl bond to afford [ppn][Ru77-P)(μ-η2-OCPh)(μ-PPh2)(μ-CO)(CO)17] in low yield, the first heptaruthenium μ7-phosphido-ligated cluster.

Keywords: Crystal structure; Ruthenium; Phosphido; Interstitial; Cluster


Hydrogen sensitivity – A systematic computational study of electronic effects by Peter H.M. Budzelaar; Betty B. Coussens; Nic Friederichs (pp. 4473-4480).
DFT studies for model polymerization catalysts indicate hydrogen sensitivity decreases with increasing electrophilicity (measured as NH3 complexation energy) of the metal centre.Hydrogen sensitivity, defined as the preference of a metal alkyl for hydrogenolysis over olefin insertion, was studied computationally (DFT) for a series of simple model catalysts, including some metallocenes and a few basic models of heterogeneous catalysts. As a measure of electrophilicity, we have used the complexation energy to the probe molecule ammonia. For isolated species in the gas phase, complexation energies appear to dominate the chemistry. Ethene complexes more strongly than hydrogen, and with increasing electrophilicity of the metal centre this difference grows; the hydrogen sensitivity decreases accordingly. This result seems to agree both in broad terms with the experimental lower hydrogen sensitivity of heterogeneous catalysts, and more specifically with the increased hydrogen sensitivity of highly alkylated or fused metallocenes. The opposite conclusion reached by Blom et al. [R. Blom, O. Swang, R.H. Heyn, Macromol. Chem. Phys. 203 (2002) 381] is due to the use of a very different measure of electrophilicity, rather than to different experimental data.

Keywords: Hydrogen sensitivity; Hydrogen response; Metallocenes; Electrophilicity; DFT


Reactions of the titanium-carbide species CpTi(μ2-Me)(μ2-NP i-Pr3)(μ4-C)(AlMe2)3 by Todd W. Graham; Christopher Ong; Pingrong Wei; Douglas W. Stephan (pp. 4481-4485).
Reaction of CpTi(μ2-Me)(μ2-NP i-Pr3)(μ4-C)(AlMe2)3 with ClSnMe3 and MeO3SCF3 afford the species [CpTi(μ2-Cl)(μ2-NP i-Pr3)(μ4-C)(μ2-Cl)(AlMe)(AlMe2)2]1 and [CpTi(μ2-Me)(μ2-NP i-Pr3)(μ4-C)(μ2-O3SCF3)(AlMe)(AlMe2)2]2, respectively.The reaction of CpTi(μ2-Me)(μ2-NP i-Pr3)(μ4-C)(AlMe2)3 with ClSnMe3 and MeO3SCF3 affords the species CpTi(μ2-Cl)(μ2-NP i-Pr3)(μ4-C)(μ2-Cl)(AlMe)(AlMe2)21 and CpTi(μ2-Me)(μ2-NP i-Pr3)(μ4-C)(μ2-O3SCF3)(AlMe)(AlMe2)22, respectively. Both1 and2 have been structurally characterized.

Keywords: Carbide; Titanium; Aluminum; Crystal structure


Synthesis and reactions of heterodinuclear organopalladium complex having an unsymmetrical PN ligand by Nobuyuki Komine; Susumu Tsutsuminai; Masafumi Hirano; Sanshiro Komiya (pp. 4486-4494).
Reactions of novel heterodinuclear organopalladium–cobalt complexes having an unsymmetrical PN ligand (Et2NC2H4PPh22 N, P)RPd–ML n (ML n=Co(CO)4; R=Me, Ph) with CO yield corresponding acyl complexes (Et2NC2H4PPh22 N, P)(RCO)Pd–Co(CO)4 (R=Me, Ph). Rate of CO insertion was significantly faster than those for mononuclear methylpalladium complex, PdMeI(Et2NC2H4PPh22 N, P) and methylpalladium–cobalt complex with a 1,2-bis(diphenylphosphino)ethane (dppe) ligand, (dppe-κ2 P, P′)MePd–Co(CO)4.Novel heterodinuclear organopalladium complexes having an unsymmetrical PN ligand (Et2NC2H4PPh22 N, P)RPd–ML n (ML n=Co(CO)4; R=Me (2a), Ph (2b), ML n=MoCp(CO)3; R=Ph (3b)) are synthesized by metathetical reactions of PdRX(Et2NC2H4PPh22 N, P) (X=I, NO3) with Na+[ML n]. Reversible dissociation of the Pd–N bond in3b is revealed by variable temperature NMR studies. Reactions of2a and2b with CO yield corresponding acyl complexes (Et2NC2H4PPh22 N, P)(RCO)Pd–Co(CO)4 (R = Me (5a), Ph (5b)). Rate of CO insertion for2a and2b is significantly faster than those for mononuclear methylpalladium complex, PdMeI(Et2NC2H4PPh22 N, P) (1a), and methylpalladium–cobalt complex with a 1,2-bis(diphenylphosphino)ethane (dppe) ligand, (dppe-κ2 P, P′)MePd–Co(CO)4 (6a).5a smoothly reacts with nucleophiles such as diethylamine, methanol and benzenethiol to give corresponding amide, ester and thioester, respectively. These reactions of5a are also significantly faster than those of corresponding mononuclear analogues and the similar heterodinuclear complexes with symmetrical bidentate ligands such as 1,2-bis(diphenylphosphino)ethane or N, N, N′, N′-tetramethylethylenediamine ligand.

Keywords: Heterodunuclear organopalladium complex; Unsymmetrical PN ligand; CO insertion


Optically active rhodium complexes with indenyl-linked phosphane ligands by Angelino Doppiu; Ulli Englert; Vera Peters; Albrecht Salzer (pp. 4495-4505).
The complexation of ( S)-[2-(4,7-dimethyl-3 H-inden-1-yl)-1-phenylethyl]diphenylphosphane with [Rh(μ-Cl)(η2-CH2CH2)2]2 affords the two diastereomers ( S, R pl)-Rh3 and ( S, S pl)-Rh4 in a ratio that depends strongly on the solvent. The complexes undergo oxidative addition of CH3I with high diastereoselectivity.The optically active indenyl-linked phosphane ligands ( S)-[2-(3 H-inden-1-yl)-1-phenylethyl]diphenylphosphane (L1) and ( S)-[2-(4,7-dimethyl-3 H-inden-1-yl)-1-phenyl-ethyl]diphenylphosphane (L2) were synthesized in three steps from ( R)-1-phenylethane-1,2-diol in excellent yields. Their lithium salts reacted with [Rh(μ-Cl)(η2-CH2CH2)2]2 at −78°C in THF affording the planar chiral complexes ( S, R pl+ S pl)-[Rh(η5-indenyl-CH2CH(Ph)PPh2- kP)(η2-CH2CH2)] and ( S, R pl+ S pl)-[Rh(η5-4,7-dimethylindenyl-CH2CH(Ph)PPh2- kP)(η2-CH2CH2)] as 61:39 and 15:85 mixtures of diastereomers. The complexes were isolated in optically pure form by column chromatography. The stereochemical configuration of one of the diastereomers was determined by X-ray crystallography. The complexation ofL2 was studied in different solvents and with several Rh precursors and diastereomeric excesses up to 76% were achieved. The ability of the chiral ligands to control the stereochemistry at the metal center was tested by oxidative addition of methyl iodide. Diastereomeric excesses greater than 98% were observed.

Keywords: Rhodium; Constrained geometry ligands; P ligands; Chirality; Oxidative addition; X-ray diffraction


Synthesis and characterization of iron and cobalt dichloride bearing 2-quinoxalinyl-6-iminopyridines and their catalytic behavior toward ethylene reactivity by Wen-Hua Sun; Peng Hao; Gang Li; Shu Zhang; Wenqing Wang; Jianjun Yi; Maliha Asma; Ning Tang (pp. 4506-4518).
The 2-quinoxalinyl-6-iminopyridines and their iron(II) and cobalt(II) complexes were synthesized and full characterized. The molecular structures of ( E)- N-(1-(6-(quinoxalin-2-yl)pyridin-2-yl)ethylidene)benzenamine and their metal complexes indicates rotations of the quinoxalinyl and imino-groups of ligand backbone during coordination, which suggests that the ligands form sterically-favored coordination with the metal center with the distorted trigonal-bipyramidal geometry. Upon activation with MAO, all iron complexes showed good catalytic activity for ethylene reactivity; while their cobalt analogues gave moderate to good activity for ethylene reactivity in the presence of MMAO.The 1-(6-(quinoxalin-2-yl)pyridin-2-yl)ethanone was synthesized in order to prepare a series of N-(1-(6-(quinoxalin-2-yl)pyridine-2-yl)ethylidene)benzenamines (L1L7), which provided new alternative NNN tridentate ligands coordinating with iron(II) and cobalt(II) dichloride to form complexes of general formula LFeCl2 (17) and LCoCl2 (814). All organic compounds were fully characterized by NMR, IR spectroscopic and elemental analysis along with and magnetic susceptibilities and metal complexes were examined by IR spectroscopic and elemental analysis, while their molecular structures (L1,L4,1,4,10,13) were confirmed by single crystal X-ray diffraction analysis. Upon activation with methylaluminoxane (MAO), all iron complexes gave good catalytic activities for ethylene reactivity (oligomerization and polymerization), while their cobalt analogues showed moderate activities toward ethylene oligomerization with modified methylaluminoxane (MMAO). Various reaction parameters were investigated for better catalytic activities, the higher activities were observed at elevated ethylene pressure. The iron and cobalt complexes with para-methyl substituents of aryl group linked on imino group showed highest activity.

Keywords: 2-Quinoxalinyl-6-iminopyridines; Iron and cobalt complex; Ethylene oligomerization; Ethylene polymerization


Regiochemistry of propene insertion with group 4 polymerization catalysts from a theoretical perspective by Andrea Correa; Giovanni Talarico; Luigi Cavallo (pp. 4519-4527).
Steric and electronic effects in the regiochemistry of monomer insertion in propene polymerization promoted by various metallocene, CGC and octahedral group 4 metal catalysts has been investigated by using DFT methods.The regiochemistry of monomer insertion in propene polymerization promoted by group 4 metal catalysts has been investigated by using DFT methods. We calculated primary and secondary propene insertion on metallocenes, constrained geometry catalysts and post-metallocene systems analyzing the effects of ligand framework, growing chain and metal. Our study supports the concept that for metallocene-based catalysts the regiochemistry of propene is mainly originated by steric effects. Instead, for octahedral systems a delicate balance between steric and electronic effects is found. This allows to play with the electronic properties of the ligand framework to tune finely the regiochemistry of polymerization.

Keywords: Propene polymerization; Regiochemistry; DFT calculations


Acylzirconocene chloride: Formation of carbocycles by palladium-catalyzed cascade reaction by Yuji Hanzawa; Yusuke Oka; Masaya Yabe (pp. 4528-4534).
Acylzirconocene chloride complex as an acyl group donor reacts with ω-carbonyl α,β-enones or with bis-enones to give carbocyclic compounds under 10mol% Pd(OAc)2-catalyzed conditions, and each reaction was accelerated by the addition of a stoichiometric amount of Me2Zn.Acylzirconocene chloride complex as an acyl group donor reacts with ω-carbonyl α,β-enones or with bis-enones to give carbocyclic compounds under 10mol% Pd(OAc)2-catalyzed conditions, and each reaction was accelerated by the addition of a stoichiometric amount of Me2Zn. The formation of the carbocycles from ω-carbonyl α,β-enones was considered to be a result of a series of reactions; (i) the formation of Pd(II)-intermediate by an electron transfer from the Pd(0)-catalyst to an α,β-enone function in an initial step, (ii) an acyl group transfer from the acylzirconocene complex to the Pd(II)-intermediate (transmetalation), (iii) the reductive elimination of Pd(0)-metal, and (iv) an intramolecular addition of metal enolate to ω-carbonyl group. On the other hand, the reaction of bis-enones with acylzirconocene chloride under the identical condition afforded reductive cyclization product, bicyclo[3.3.0] octane derivatives, in which acyl group from acylzirconocene complex was not incorporated.

Keywords: Acylzirconocene chloride; Palladium catalyst; Cascade reaction; Reductive cyclization


Remarkable Lewis acid effects on polymerization of functionalized alkenes by metallocene and lithium ester enolates by Yalan Ning; Hongping Zhu; Eugene Y.-X. Chen (pp. 4535-4544).
Drastic Lewis acid effects on polymerization of functionalized alkenes mediated by metallocene and lithium ester enolates are observed as well as elucidated.Drastic effects of Lewis acids E(C6F5)3 (E=Al, B) on polymerization of functionalized alkenes such as methyl methacrylate (MMA) and N, N-dimethyl acrylamide (DMAA) mediated by metallocene and lithium ester enolates, Cp2Zr[OC(O iPr)CMe2]2 (1) and Me2CC(O iPr)OLi, are documented as well as elucidated. In the case of metallocene bis(ester enolate)1, when combined with 2equiv. of Al(C6F5)3, it effects highly active ion-pairing polymerization of MMA and DMAA; the living nature of this polymerization system allows for the synthesis of well-defined diblock and triblock copolymers of MMA with longer-chain alkyl methacrylates. In sharp contrast, the1/2B(C6F5)3 combination exhibits low to negligible polymerization activity due to the formation of ineffective adduct Cp2Zr[OC(O iPr)CMe2]+[OC(O iPr)CMe2B(C6F5)3] (2). Such a profound Al vs. B Lewis acid effect has also been observed for the lithium ester enolate; while the Me2CC(O iPr)OLi/2Al(C6F5)3 system is highly active for MMA polymerization, the seemingly analogous Me2CC(O iPr)OLi/2B(C6F5)3 system is inactive. Structure analyses of the resulting lithium enolaluminate and enolborate adducts, Li+[Me2CC(O iPr)OAl(C6F5)3] (3) and Li+[Me2CC(O iPr)OB(C6F5)3] (4), coupled with polymerization studies, show that the remarkable differences observed for Al vs. B are due to the inability of the lithium enolborate/borane pair to effect the bimolecular, activated-monomer anionic polymerization as does the lithium enolaluminate/alane pair.

Keywords: Metallocene catalysts; MMA polymerization; Anionic polymerization; Block copolymers; Enolaluminates; Enolborates


Synthesis and characterization of half-sandwich iridium complexes containing 2,6(7)-bis(4-pyridyl)-1,4,5,8-tetrathiafulvalene and ancillary ortho-carborane-1,2-dichalcogenolato ligands by Ying-Feng Han; Jia-Sheng Zhang; Yue-Jian Lin; Jie Dai; Guo-Xin Jin (pp. 4545-4550).
Binuclear half-sandwich dichalcogenolate carborane iridium complexes5a and5b, connected with 2,6(7)-bis(4-pyridyl)-1,4,5,8-tetrathiafulvalene ligands, have been synthesized and characterized structurally.The binuclear half-sandwich iridium complexes {CpIrCl2}2(μ-2,6(7)-bis(4-pyridyl)-1,4,5,8-tetrathiafulvalene) (3) and {CpIr[E2C2(B10H10)]}2(μ-2,6(7)-bis(4-pyridyl)-1,4,5,8-tetrathiafulvalene) (E=S(5a), Se(5b)) were prepared from the reaction of [CpIrCl(μ-Cl)]2 or the “ pseudo-aromatic” half-sandwich iridium complex CpIr[E2C2(B10H10)] (E=S(4a), Se(4b)) with a tetrathiafulvalene (TTF) derivative 2,6-bis(4-pyridyl)-1,4,5,8-tetrathiafulvalene (2) at room temperature. The complexes (3,5a and5b) have been fully characterized by IR and NMR spectroscopy, as well as elemental analysis. And the molecular structures of2 and5a were established through X-ray crystallography. It is interesting that infinite tunnels are created by repeating ‘buckled bowl’ molecules of5a.

Keywords: Iridium; Half-sandwich complexes; Carborane; Tetrathiafulvalene; Molecular structures


Computational study of methane functionalization by a multiply bonded, Ni-bis(phosphine) complex by Thomas R. Cundari; Aaron W. Pierpont; Sridhar Vaddadi (pp. 4551-4559).
Theoretical study of methane functionalization by a multiply bonded, Ni-bis(phosphine) complex: [2+2] vs [1+2] pathways.A computational chemistry study of nickel-catalyzed group transfer to methane is presented. Analysis of the reaction energetics implies a possible competition between two mechanisms for carbene transfer, while for nitrene transfer, the [1+2] pathway is predicted to be the preferred route. For phosphinidene transfer, a [2π+2σ] mechanism is preferred. Regeneration of the active species via a group transfer reagent XE is highly exothermic. The calculations indicate that (P∼P)NiE complexes deserve consideration as plausible starting points in the search for improved hydrocarbon functionalization catalysts.A computational chemistry study of nickel-catalyzed group transfer to methane is presented. Two mechanisms were evaluated: a one-step mechanism involving [1+2] insertion of E into the C–H bond of methane, and a two-step [2π+2σ] mechanism involving addition of the C–H bond of methane across the NiE bond to a square planar NiII intermediate, followed by C–E reductive elimination. Analysis of the energetics for the different mechanistic steps implies a possible competition between the two mechanisms for carbene transfer. For nitrene transfer, the [1+2] pathway is predicted to be the preferred route. Finally, for phosphinidene transfer, the [2π+2σ] mechanism is calculated to be the preferred mechanism. The two mechanisms studied – [1+2] and [2π+2σ] – entail exothermic individual reactions, coupled with reasonable enthalpic barriers. Furthermore, regeneration of the catalyst active species by reaction with a group transfer reagent XE is highly exothermic. The calculations thus indicate that (P∼P)NiE (P∼P denotes a chelating bis-phosphine ligand) deserve consideration as plausible starting points in the search for improved hydrocarbon functionalization catalysts.

Keywords: Nickel; Catalysis; Density functional theory; Methane activation; Multiply bonded complexes; Group transfer catalysis


Chiral, bridged bis(imidazolin-2-ylidene) complexes of palladium by Sabine K. Schneider; Jürgen Schwarz; Guido D. Frey; Eberhardt Herdtweck; Wolfgang A. Herrmann (pp. 4560-4568).
A systematic study of chiral bis(imidazolin-2-ylidene)palladium(II) complexes is presented, bearing the chiral group on the ring nitrogens. A structural proof of the chiral palladium(II) complexes is represented by a X-ray diffraction study.Varieties of chiral, bridged bisimidazolium salts as well as the synthesis of palladium complexes of general formula[bridge{NC(H)C(H)N(R∗)C¯}2PdBr2] with the corresponding chelating N-heterocyclic carbene ligands is reported. This is the first systematic study of chiral bis(imidazolin-2-ylidene)palladium(II) complexes bearing chiral groups on the endocyclic nitrogens. Structural proof of such a chiral palladium(II) complex is presented by way of an X-ray diffraction study of complex3a.

Keywords: Chelating ligands; Chiral ligands; Bisimidazolium salts; Palladium


Highly active/selective and adjustable zirconium polymerization catalysts stabilized by aminopyridinato ligands by Winfried P. Kretschmer; Bart Hessen; Awal Noor; Natalie M. Scott; Rhett Kempe (pp. 4569-4579).
Sterically very demanding aminopyridinato ligands stabilize thermally robust, highly active and selective zirconium ethylene polymerization catalysts. Small changes in the bulky ligand periphery can be used to fine tune the nature of the formed polymers and even “living” ethylene polymerization at elevated temperatures (50°C) can be observed.This paper describes a substantial enhancement of the aminopyridinato ligand stabilized early transition metal chemistry by introducing the sterically very demanding 2,6-dialkylphenyl substituted aminopyridinato ligands derived from (2,6-diisopropylphenyl)-[6-(2,6-dimethylphenyl)-pyridin-2-yl]-amine (1aH, ApH) and (2,6-diisopropylphenyl)-[6-(2,4,6-triisopropylphenyl)-pyridin-2-yl]- amine (1bH, ApH). The corresponding bis aminopyridinato zirconium dichloro complexes, [Ap2ZrCl2] (3a) and [Ap2ZrCl2] (3b) and the dimethyl analogues, [Ap2ZrMe2] (4a) and [Ap2ZrMe2] (4b) (Me=methyl) were synthesized, using standard salt metathesis routes. Single-crystal X-ray diffraction was carried out for the dichloro derivatives. Both zirconium metal centers have a distorted octahedral environment with a cis-orientation of the chloride ligands in3a and a closer to trans-arrangement in3b. The dimethyl derivatives are proven to be highly active ethylene polymerization catalysts after activation with [R2N(Me)H][B(C6F5)4] (R=C16H33–C18H37). During attempted co-polymerizations of α-olefins (propylene) and ethylene high activity and selectivity for ethylene and nearly no co-monomer incorporation was observed. Increasing the steric bulk of the ligand going from (2,6-dimethylphenyl) to (2,4,6-triisopropylphenyl) substituted pyridines, switches the catalyst system from producing long chain α-olefins to polymerization of ethylene in a living fashion. In contrast to the dimethyl complexes only [Ap2ZrCl2] in the presence of MAO at elevated temperature gave decent polymerization activity. NMR investigations of the reaction of dichloro complexes with 25equiv. of MAO or AlMe3 at room temperature revealed, that [Ap2ZrCl2] decomposes under ligand transfer to aluminum and formation of [ApAlMe2], while [Ap2ZrCl2] remains almost unreacted under the same conditions. The aminopyridinato dimethyl aluminum complexes, [ApAlMe2] (5a) and [ApAlMe2] (5b) were synthesized independently and structurally characterized. The aluminum complexes5a andb show no catalytic activity towards ethylene, when “activated” with[R2N(Me)H][B(C6F5)4].

Keywords: Aluminum; Aminopyridinato ligands; N-ligands; Olefin polymerization; Zirconium


Influence of the para-substitution in bis(arylimino)pyridine iron complexes on the catalytic oligomerization and polymerization of ethylene by Christian Görl; Helmut G. Alt (pp. 4580-4592).
A series of nine iron complexes with halogen or alkynyl functionalized bis(arylimino)pyridine ligands was synthesized and characterized. After activation with methylalumoxane (MAO), these catalysts oligomerize or polymerize ethylene to give highly linear products. The influence of substituents in the para-position of the iminophenyl rings was investigated.A series of nine bis(arylimino)pyridine iron complexes containing halogen or alkynyl substituents in their ligand frameworks was synthesized and characterized. After activation with methylalumoxane (MAO), these catalysts oligomerize or polymerize ethylene to give highly linear products. The introduction of halogen or alkynyl substituents in the para-position of the iminophenyl rings has a great influence on the polymerization activities of the corresponding iron complexes.

Keywords: Bis(arylimino)pyridine iron complexes; Ethylene polymerization; Oligomerization; Polyethylene


Carbohydrate-containing N-heterocyclic carbene complexes by Friederike Tewes; Andreas Schlecker; Klaus Harms; Frank Glorius (pp. 4593-4602).
Novel carbohydrate bearing imidazolium salts have been synthesized and used for the in situ generation of the corresponding N-heterocyclic carbenes1. These compounds were successfully used as catalysts of the conjugate umpolung of cinnamaldehyde to form γ-butyrolactones. In addition, silver and palladium complexes of these N-heterocyclic carbenes were synthesized and structurally characterized.Novel carbohydrate bearing imidazolium salts have been synthesized and used for the in situ generation of the corresponding N-heterocyclic carbenes. These compounds were successfully used as catalysts of the conjugate umpolung of cinnamaldehyde to form γ-butyrolactones. In addition, silver and palladium complexes of these N-heterocyclic carbenes were synthesized and structurally characterized.

Keywords: N-Heterocyclic carbenes; Carbohydrates; Palladium complex; Silver complex; Catalysis


Mixed-ligand iminopyrrolato-salicylaldiminato group 4 metal complexes: Optimising catalyst structure for ethylene/propylene copolymerisations by Lewis M. Broomfield; Yann Sarazin; Joseph A. Wright; David L. Hughes; William Clegg; Ross W. Harrington; Manfred Bochmann (pp. 4603-4611).
Mixed-ligand titanium (iminopyrrolato)(salicylaldiminato) complexes activated with MAO are highly effective ethylene/propylene copolymerisation catalysts. Activities and comonomer incorporation significantly exceeds those of either (N–N)2Ti or (N–O)2Ti systems.Treatment of MCl3(OC6H3-2- tBu-6-CHNC6F5)(THF) (M=Ti, Zr) with a variety of different potassium iminopyrrolate salts (K+[RNCHC4H3N]), (R=phenyl, cyclo-hexyl, ethyl) afforded the corresponding titanium and zirconium mixed-ligand complexes MCl2(N–O)(N–N). The molecular structures of TiCl2(OC6H3-2- tBu-6-CHNC6F5)(C2H5NCHC4H3N) (1c), TiCl2(OC6H3-2- tBu-6-CHNC6F5)(C6H11NCHC4H3N) (1b) and ZrCl2(OC6H3-2- tBu-6-CHNC6F5)(C6H11NCHC4H3N) (2b) show distorted octahedral geometries with trans-O,N/ cis-Cl2 arrangements. On activation with MAO the titanium (iminopyrrolato)(salicylaldiminato) complexes show excellent activities in ethylene polymerisation and are significantly more effective ethylene/propylene copolymerisation catalysts, both in terms of activity and propene incorporation, than either of the parent complexes. The ethylene–propylene copolymers show ca. 80% 1,2 regioselectivity and at high propylene incorporation tend towards an alternating structure.

Keywords: Titanium; Zirconium; Ethene; Copolymerization; Salicylaldiminate; Iminopyrrolate


Zirconocene-promoted coupling reaction of terminal acetylenes to geminal enediynes in the presence of p-chloranil by Chanjuan Xi; Yuanyuan Liu; Xiaoyu Yan; Chao Chen (pp. 4612-4617).
Zirconocene-promoted trimerization of terminal acetylenes to zirconoenediynes in the presence of p-chloranil. Moreover, the resulting zirconoenediynes could be transformed into a variety of geminal enediynes through coupling reaction with electrophiles.Reaction of alkynyllithium with zirconocene dichloride in the presence of quinones afforded zirconoenediynes in good yields. Treatment of the zirconoenediyne with p-chloranil in the presence of CuCl afforded 1,1,4,4-tetraethynyl-1,3-diene in good yield. In the presence of CuCl and/or Pd(PPh3)4, the zirconoenediynes could be transformed into various enediyne derivatives through coupling reaction with electrophiles.

Keywords: Coupling reactions; Alkynes; Zirconium; Quinones; Enediynes


Synthesis of functionalized isoindolinones: Addition of in situ generated organoalanes to acyliminium ions by Joshua G. Pierce; David L. Waller; Peter Wipf (pp. 4618-4629).
Addition of in situ generated di- or trisubstituted alkenylalanes to N-acyliminium ions provides rapid access to functionalized isoindolinones. Subsequent ring closing metathesis leads to tricyclic products. These transformations proceed under mild conditions and allow for the convergent synthesis of biologically significant scaffolds from readily available starting materials.Addition of in situ generated di- or trisubstituted alkenylalanes to N-acyliminium ions provides rapid access to functionalized isoindolinones. Subsequent ring closing metathesis leads to tricyclic products. These transformations proceed under mild conditions and allow for the convergent synthesis of biologically significant scaffolds from readily available starting materials.Display Omitted

Keywords: Isoindolinone; Aluminum; Zirconium; Hydrozirconation; Carbometallation; N; -Acyliminium ion


Coordination compounds of N, N′-olefin functionalized imidazolin-2-ylidenes by Ekkehardt F. Hahn; Beate Heidrich; Alexander Hepp; Tania Pape (pp. 4630-4638).
Palladium and nickel complexes with imidazolin-2-ylidene ligands bearing N-olefin substituents have been prepared from Pd(OAc)2 or [Ni(NCCH3)6](BF4)2. X-ray diffraction studies revealed formation of cis or trans square-planar complexes. Bromine abstraction from monocarbene cyclopentadienyl nickel complexes gave the trigonal-pyramidal nickel(II) complexes featuring N-allyl double bond coordination. N-Heterocyclic carbene ligands (NHC) were metalated with Pd(OAc)2 or [Ni(CH3CN)6](BF4)2 by in situ deprotonation of imidazolium salts to give the N-olefin functionalized biscarbene complexes [MX2(NHC)2]37 (3: M=Pd, X=Br, NHC=1,3-di(3-butenyl)imidazolin-2-ylidene;4: M=Pd, X=Br, NHC=1,3-di(4-pentenyl)imidazolin-2-ylidene;5: M=Pd, X=I, NHC=1,3-diallylimidazolin-2-ylidene;6: M=Ni, X=I, NHC=1,3-diallylimidazolin-2-ylidene;7: M=Ni, X=I, NHC=1-methyl-3-allylimidazolin-2-ylidene). Molecular structure determinations for47 revealed that square-planar complexes with cis (5) or trans (4,6,7) coordination geometry at the metal center had been obtained. Reaction of nickelocene with imidazolium bromides afforded the η5-cyclopentadienyl (η5-Cp) monocarbene nickel complexes [NiBr(η5-Cp)(NHC)]8 and9 (8: NHC=1-methyl-3-allylimidazolin-2-ylidene;9: NHC=1,3-diallylimidazolin-2-ylidene). The bromine abstraction in complexes8 and9 with silver tetrafluoroborate gave complexes [NiBr(η5-Cp)(η3-NHC)]10 and11. The X-ray structure analysis of10 and11 showed a trigonal-pyramidal coordination geometry at the nickel(II) center and coordination of one N-allyl substituent.

Keywords: Carbene; N; -Olefin substituent; Palladium(II); Nickel(II); Structure determination


Theoretical investigation on the model active site for isotactic polypropylene in heterogeneous Ziegler–Natta catalyst: A density functional study by Jin Woo Lee; Won Ho Jo (pp. 4639-4646).
The reaction mechanism of the stereoselective insertion of propylene monomer into the model active site created by Ti2Cl7 adsorption on the (100) surface of MgCl2 has been investigated by using DFT calculations.The stereoselectivity of the model active site formed by the adsorption of Ti2Cl7 on the (100) surface of MgCl2 was investigated by density functional calculations. The analysis of energetics for successive propylene insertions into the model active site reveals that the insertion of propylene into the model active site is energetically more favorable when a growing chain and one chlorine atom (that makes the active site chiral) are on the opposite side rather than on the same side. From this result, it is realized that the model active site is highly stereoselective. It is also observed that the Cl atoms near the growing chain significantly affect the activation energy barrier through the interaction with the growing chain.

Keywords: Theoretical methods; Density functional theory; Ziegler–Natta catalyst; Isotactic polypropylene; Stereoselectivity


The epimetallation and carbonation of carbonyl and imino derivatives: Epivanadation route to 2-amino and 2-hydroxy acids by John J. Eisch; Paul O. Fregene; John N. Gitua (pp. 4647-4653).
The feasibility of hydrocarboxylating carbonyl and imino derivatives by a two-step process of epimetallation and carbonation has been demonstrated with 9-fluorenone and 9-fluorenone anil. With LiVH2 as the epimetallating agent, the process yielded 75% of 9-hydroxy-9-fluorenecarboxylic acid and 65% of 9-( N-phenylamino)-9-fluorenecarboxylic acid. Epimetallating reagents of vanadium and titanium also show promise.The feasibility of hydrocarboxylating carbonyl and imino derivatives by the two-step process of epimetallation and carbonation has been demonstrated with the model substrates of 9-fluorenone and 9-fluorenone anil. With lithium vanadium dihydride as the epimetallating agent, such hydrocarboxylation has led to a 75% yield of 9-hydroxy-9-fluorenecarboxylic acid and a 65% yield of 9-( N-phenylamino)-9-fluorenecarboxylic acid, respectively. Some initial success in extending the scope of this reaction to other substrates, such as benzophenone, has been achieved by using other epimetallating agents, like the presumed LiV(CH3)2 and Ti(OPr i)2. A brief review of the processes and organic synthetic applications of epimetallation and transfer epimetallation of C–C π-bonds is offered as background.

Keywords: Hydrocarboxylation; Epimetallation of C; E bond (E; =; O, N–R); Carbonation; Lithium vanadium(I) dihydride; Presumed lithium dimethylvanadate(I)


Synthesis and structural characterization of [(C5H4)SiMe2(N- t-Bu)]Ti[( o-C6H4)C(Ph)C(Ph)], generated via an alkyne-Ti benzyne coupling reaction by Shawn M. Nettles; Jeffrey L. Petersen (pp. 4654-4660).
The thermolysis of [(C5H4)SiMe2(N- t-Bu)]TiPh2 in the presence of diphenylacetylene proceeds at 80°C in cyclohexane solution with the formation of the titanacyclic complex [(C5H4)SiMe2(N- t-Bu)]Ti[( o-C6H4)C(Ph)C(Ph)], which has been characterized by NMR and X-ray crystallography.The thermolysis of [(C5H4)SiMe2(N- t-Bu)]TiPh2 in the presence of diphenylacetylene proceeds at 80°C in cyclohexane solution with the sole formation of the titanacyclic complex [(C5H4)SiMe2(N- t-Bu)]Ti[( o-C6H4)C(Ph)C(Ph)], which has been characterized by solution NMR measurements and X-ray crystallographic analysis. This reaction is accompanied by the elimination of benzene and presumably occurs via coupling of a titanium benzyne intermediate with diphenylacetylene. The two chemically inequivalent Ti–C bonds of 2.081(7) and 2.103(6)Å in [(C5H4)SiMe2(N- t-Bu)]Ti[( o-C6H4)C(Ph)C(Ph)] reflect the increased electrophilicity of the d0 Ti(IV) center arising from the presence of the bifunctional ansa-cyclopentadienyldimethylsilylamido ligand.

Keywords: Ti-benzyne intermediate; Coupling reaction; Titanacyclic complex


Ion pair symmetrization in metallocenium cations partnered with diborane derived borate counteranions by Lee D. Henderson; Warren E. Piers (pp. 4661-4668).
The thermodynamics of ion pair symmetrization in a series of metallocenium species generated fromCp2″ZrMe2(Cp″=1,2-Me2C5H3) were studied using a variety of dynamic NMR techniques.The thermodynamics of ion pair symmetrization in a series of metallocenium species generated fromCp2″ZrMe2(Cp″=1,2-Me2C5H3) were studied using a variety of solution dynamic techniques including line broadening, 2D-EXSY, and 1D-DPFGSE-NOE. Ion pairs were generated by methide abstraction using the corresponding trityl salts [1-A] to yield[Cp2″ZrMe]+[A]- (A={C6F4-1,2-[B(C6F5)2]2(μ-O(C6F5))},2-O(C6F5); {C6F4-1,2-[B(C6F5)2]2(μ-OPh)},2-OPh; {C6F4-1,2-[B(C6F5)2]2(μ-OMe)},2-OMe; and [B(C6F5)4],2-B(C6F5)4). The observed activation parameters were interpreted on the basis of a solvent-assisted mechanism of ion pair symmetrization.

Keywords: Metallocenes; Ion pair symmetrization; Weakly coordinating anions; Fluoroarylborates


Exploring reactivity of a bis-sulfonium zirconocene-ate dimer: Synthesis of various zwitterionic phosphonium anionic zirconocene complexes by Esteban Ortega; Nadine Pirio; Philippe Richard; Philippe Meunier (pp. 4669-4674).
A new class of stable zwitterionic phosphonium anionic zirconocene complexes containing at least one group 16 atom directly bonded to zirconium was prepared from reactions of a bis-sulfonium zirconocene-ate dimer with methylpropiolate, benzaldehyde, carbon disulfide and more simply with elemental sulfur and heavier chalcogens.Formal [3+2] cycloaddition reactions between the bis-sulfonium zirconocene-ate dimer ▪1a and methylpropiolate, benzaldehyde and carbon disulfide afforded stable zwitterionic phosphonium zirconocene-ate complexes24, respectively, with two orthocondensed five-membered heterocycles. X-ray crystal structure of4 has been determined. Elemental chalcogens (S, Se, Te) gave rise also to a new variety of five-coordinate zirconium(IV) complexes (57) by a formal [3+1] cycloaddition reaction. In these bicyclic zirconates, sulfur is included in a five-membered ring while the second chalcogen is in a four-membered one.

Keywords: Zwitterionic complexes; Zirconocene-ate; Anionic zirconocene; Phosphonium; Sulfonium; Chalcogens


Effect of ketimide ligand for ethylene polymerization and ethylene/norbornene copolymerization catalyzed by (cyclopentadienyl)(ketimide)titanium complexes–MAO catalyst systems: Structural analysis for CpTiCl2(NCPh2) by Kotohiro Nomura; Junji Yamada; Wei Wang; Jingyu Liu (pp. 4675-4682).
Effects of the ketimide substituents for ethylene polymerization and ethylene/norbornene (NBE) copolymerization by Cp′TiCl2(NCR1R2) [Cp′=Cp (1), Cp (2); R1,R2= tBu, tBu (a), tBu,Ph (b), Ph,Ph (c)]–MAO catalysts were investigated, and the structure of2c was determined by X-ray crystallography.Ligand effects on the catalytic activity [and norbornene (NBE) incorporation] for both ethylene polymerization and ethylene/NBE copolymerization using half-titanocenes (titanium half-sandwich complexes) containing ketimide ligand of type Cp′TiCl2[NC(R1)R2] [Cp′=Cp (1), C5Me5 (Cp,2); R1,R2= tBu, tBu (a), tBu,Ph (b), Ph,Ph (c)]–methylaluminoxane (MAO) catalyst systems have been investigated. CpTiCl2[NC( tBu)Ph] (1b) CpTiCl2(NCPh2) (1c), and CpTiCl2(NCPh2) (2c) were prepared and identified; the structure of CpTiCl2(NCPh2) (2c) was determined by X-ray crystallography. The catalytic activity for ethylene polymerization increased in the order:1a>1b>1c, suggesting that an electronic nature of the ketimide ligand affects the activity. However, molecular weight distributions for resultant (co)polymers prepared by1b,c and by2c–MAO catalyst systems were bi- or multi-modal, suggesting that the ketimide substituent plays a key role in order for these (co)polymerizations to proceed with single catalytically-active species. CpTiCl2(NC tBu2) (1a) exhibited both remarkable catalytic activity and efficient NBE incorporation for ethylene/NBE copolymerization.

Keywords: Titanium; Polymerization; Homogeneous catalysis; Ethylene; Norbornene; Copolymerization


Regio- and stereospecific syntheses and structural characterization of alkyl-substituted 1,3-diene complexes of cyclopentadienylzirconium amidinates of the general formula: (η5-C5Me5)Zr[N( iPr)C(Me)N( iPr)](σ2,π-C4H5R) (R=Me or Et) by Philip P. Fontaine; Albert Epshteyn; Peter Y. Zavalij; Lawrence R. Sita (pp. 4683-4689).
New synthetic methods have been developed that provide several derivatives of the titled family of compounds in regio- and stereospecific fashion and for which structural characterization support a Zr(IV) σ2,π-metallacyclopent-3-ene limiting resonance form.Alkylation of CpZr[N( iPr)C(Me)N( iPr)](Cl)2 (Cp5-C5Me5) (4) with 2 equiv. of n-hexyllithium in diethylether at −30°C provided CpZr[N( iPr)C(Me)N( iPr)]( n-C6H13)2 (5) in excellent yield. In solution,5 undergoes thermally induced loss of “C6H16” to provide a 35% isolated yield of the 1,3-hexadiene complex, CpZr[N( iPr)C(Me)N( iPr)](C4H5Et) (6), in regio- and diastereochemically pure form. Ligand substitution of the η2-styrene group in CpZr[η2-CH2CH(C6H5)][N( iPr)C(Me)N( iPr)] (3) was achieved using an excess of 2-methyl-1,3-butadiene (isoprene) in toluene at 25°C to provide CpZr[N( iPr)C(Me)N( iPr)](isoprene) (7) in regio- and stereochemically pure form. In similar fashion, an excess of cis, trans-1,3-pentadiene was used to separately prepare the isomeric diene complex CpZr[N( iPr)C(Me)N( iPr)](1,3-pentadiene) (8), once again in regio- and stereospecific fashion. Detailed experimental investigations of the molecular and electronic structures of68, as performed in solution by 1D and 2D NMR spectroscopy and in the solid state by single-crystal X-ray analysis, revealed that the best structural description for these compounds is that of the Zr(IV) σ2,π-metallacyclopent-3-ene limiting resonance form rather than as a Zr(II) η4-diene complex.

Keywords: Group 4 metals; Conjugated dienes; Regiospecific; Stereospecific; Olefin polymerization catalysts


(+)-Neomenthyl- and (−)-phenylmenthyl-substituted cyclopentadienyl and indenyl yttrocenes as catalysts in asymmetric hydroamination/cyclization of aminoalkenes (AHA) by Daniela V. Vitanova; Frank Hampel; Kai C. Hultzsch (pp. 4690-4701).
The synthesis of chiral terpenoid-substituted yttrocene complexes, in particular the yttrium analogue of Erker’s neomenthylindenyl zirconocene is reported. The application of these complexes in asymmetric hydroamination/cyclization of aminoalkenes was investigated.The chiral, terpenoid-substituted yttrocene [(η5-neomenthylCp)2Y{ o-C6H4CH2NMe2}] (1) can be prepared via facile arene elimination starting from [Y( o-C6H4CH2NMe2)3]. Compound1 retains a C1-symmetric structure in solution on the NMR time scale, due to tight binding of the amine donor. The (−)-phenylmenthyl-substituted complexes [(η5-(−)-phenylmenthylCp)2Y(μ-Cl)2Li(OEt2)2] (5) and [(η5-(−)-phenylmenthylCp)2YN(SiMe3)2] (6) were prepared via salt metathesis. Reaction of YCl3 with the planar chiral (1-neomenthylindenyl)lithium predominantly produced a single, C2-symmetric, racemic-like diastereomer. The X-ray crystal structure analysis confirmed that [(η5-(+)-NMInd)2Y(μ-Cl)2Li(Et2O)2] (7) represents the same p- S, p- S metallocene diastereomer and adopts a very similar conformation as observed by Erker in his zirconocene complexes. Complex7 reacts with LiN(SiMe3)2 to form [(η5-(+)-NMInd)2YN(SiMe3)2] (8) with retention of configuration. Complexes1,6 and8 showed moderate to good catalytic activity in asymmetric hydroamination/cyclizations of aminoalkenes, but enantioselectivities were limited to a maximum of 38% ee for the sterically most hindered catalyst8. The indenyl complex8 is prone to protolytic loss of an indenyl ligand at low (⩽0.5%) catalyst loading, if sterically undemanding aminoalkene substrates are applied.

Keywords: Asymmetric catalysis; Hydroamination; Yttrium; Metallocene complexes


Half-sandwich dibenzyl complexes of scandium: Synthesis, structure, and styrene polymerization activity by Julia Hitzbleck; Klaus Beckerle; Jun Okuda (pp. 4702-4707).
Half-sandwich dibenzyl complexes of scandium have been synthesized, structurally characterized and tested as syndiospecific styrene polymerization catalysts upon cationization.Half-sandwich dibenzyl complexes of scandium have been prepared by stepwise treatment of scandium trichloride with lithium derivatives of silyl-functionalized tetramethylcyclopentadienes (C5Me4H)SiMe2R (R=Me, Ph) and benzyl magnesium chloride. The resulting complexes [Sc(η5-C5Me4SiMe3)(CH2Ph)2(THF)] and [Sc(η5-C5Me4SiMe2Ph)(CH2Ph)2(1,4-dioxane)] show structure related to that of the corresponding bis(trimethylsilylmethyl) compounds [Sc(η5-C5Me4SiMe2R)(CH2SiMe3)2(THF)]. The four-coordinate complexes display η1-coordinated benzyl ligands without significant interaction of the ipso-carbon of the phenyl moiety. Conversion of [Sc(η5-C5Me4SiMe3)(CH2Ph)2(THF)] into the cationic species by treatment with triphenylborane in THF led to the formation of a stable charge separated complex [Sc(η5-C5Me4SiMe3)(CH2Ph)(THF) x][BPh3(CH2Ph)]. Benzyl cation formed using [Ph3C][B(C6F5)4] in toluene resulted in a moderately active syndiospecific styrene polymerization catalyst.

Keywords: Scandium; Benzyl complexes; Styrene polymerization; Metallocene catalysis


Insertion vs. site epimerization with singly-bridged and doubly-bridged metallocene polymerization catalysts by Stephen A. Miller (pp. 4708-4716).
A statistical model has been employed to determine the unidirectional site epimerization probability, ε, during propylene polymerization with singly-bridged and doubly-bridged C1-symmetric metallocenes activated with methylaluminoxane. Generally, the probability of site epimerization increased as follows: carbon singly-bridged catalystsε, during propylene polymerization with the following C1-symmetric metallocene precatalysts activated with MAO (MAO=methylaluminoxane): doubly-bridged rac-(1,2-SiMe2)25-C5H2-4-(CHMe(CMe3))}{η5-C5H-3,5-(CHMe2)2}ZrCl2 (1) and (1,2-SiMe2)25-C5H2-4-(1 R,2 S,5 R-menthyl)}{η5-C5H-3,5-(CHMe2)2}ZrCl2 (2); and singly-bridged Me2C(3-(2-adamantyl)-C5H3)(C13H8)ZrCl2 (3) and Me2Si(3-(2-adamantyl)-C5H3)(C13H8)ZrCl2 (4). For1/MAO a steep tacticity dependence on monomer concentration was found, as ε increased from 0.114 to 0.909 as [C3H6] decreased from 12.5M to 0.5M; similarly, ε increased for2/MAO from 0.177 to 0.709. For3/MAO, ε was moderately responsive to an increase in polymerization temperature, as ε increased from 0.000 to 0.485 from Tp=0–90°C ([C3H6]=1.1M). Similarly, ε increased for4/MAO from 0.709 to 0.913 from Tp=0–40°C; at higher temperatures, bidirectional site epimerization was implicated.

Keywords: Metallocene catalysts; Polypropylene; Tacticity; Stereochemical model; ansa; -Metallocene; Doubly-bridged metallocene


Synthesis and characterization of titanium alkyl, oxo, and diene complexes bearing a SiMe2-bridged phenoxy-cyclopentadienyl ligand and their catalytic performance for copolymerization of ethylene and 1-hexene by Hidenori Hanaoka; Takahiro Hino; Masaaki Nabika; Tetsuya Kohno; Kazunori Yanagi; Yoshiaki Oda; Akio Imai; Kazushi Mashima (pp. 4717-4724).
A series of titanium alkyl, oxo, and diene complexes bearing a SiMe2-bridged phenoxy-cyclopentadienyl ligand were synthesized and characterized, and their catalytic behavior for copolymerization of ethylene and 1-hexene was investigated. X-ray analysis of 1,4-diphenyl-1,3-butadiene complex revealed that the diene ligand coordinates in s- cis fashion to titanium with a prone orientation. Polymerization study revealed that the alkyl complexes and the diene complexes showed higher activities than the starting dichloride at 130°C.A series of titanium complexes bearing a SiMe2-bridged phenoxy-cyclopentadienyl ligand were synthesized and characterized, and their catalytic behavior for copolymerization of ethylene and 1-hexene was investigated. Treatment of dimethylsilyl(2,3,4,5-tetramethylcyclopentadienyl)(3- tert-butyl-5-methyl-2-phenoxy)-titanium dichloride (1) with appropriate nucleophiles afforded dimethoxy complex2, dimethyl complex3, and dibenzyl complex4. Standing a toluene solution of2 in air afforded a dinuclear μ-oxo complex5 as a single isomer. 1,3-Diene complexes68 were prepared by reaction of1 with the corresponding 1,3-dienes in the presence of 2equiv. of n-BuLi. X-ray analysis of 1,4-diphenyl-1,3-butadiene complex6 revealed that the diene ligand coordinates to titanium in s- cis fashion with a prone orientation. The newly prepared titanium complexes were applied to copolymerization of ethylene and 1-hexene upon activation with Al iBu3 and [C6H5NMe2H][B(C6F5)4]. It was found that the alkyl complexes34 and the diene complexes68 showed higher activities than1 at elevated temperature.

Keywords: Titanium complex; Cyclopentadiene; Phenolate; Diene; Polymerization


Polymorphism of a nickel polymerization catalyst by Alexander Zeller; Georg Eickerling; Eberhardt Herdtweck; Martin U. Schmidt; Thomas Strassner (pp. 4725-4730).
Polymorphism of a nickel(II)salicylaldiminato polymerization catalyst is reported, the two structures differ significantly in the coordination geometry of the central metal atom. Lattice energy calculations were used to analyze the different solid state structures.Two polymorphs of an highly active nickel(II) salicylaldiminato polymerization catalyst are reported, which to our knowledge represent the first examples of polymorphism of catalytically active polymerization catalysts. The two structures differ significantly in the coordination geometry of the central metal atom. Lattice energy calculations were used to analyze the different solid state structures.

Keywords: Homogeneous catalysis; Solid state structure; Polymorphism; Nickel; N,O-ligands


Zirconium-catalyzed methylalumination of heterosubstituted arylethynes: Factors affecting the regio-, stereo-, and chemoselectivities by Guangwei Wang; Gangguo Zhu; Ei-ichi Negishi (pp. 4731-4736).
The Zr-catalyzed methylalumination of heterosubstituted arylethynes containing O, S, Cl, and Si can proceed in high yields (>70%) and in a highly regio- and stereoselective manner (⩾98–99%), although SO2Ph, Br, and Cl in a benzylic position present serious chemoselectivity-related problems. The low regioselectivity of 60% initially observed with o-ethynylphenol (1a) has been elevated to ⩾98% through the use of either a catalytic amount of Zr(ebi)Cl2 or Zr(2-Me-Ind)2Cl2 or, more conveniently, the stoichiometric amount of ZrCp2Cl2, ZrCp2MeCl, or ZrCp2Me2 in conjunction with the use of a deficient amount (0.9molar equiv.) of I2.The Zr-catalyzed methylalumination of heterosubstituted arylethynes containing O, S, Cl, and Si can proceed in high yields (>70%) and in a highly regio- and stereoselective manner (⩾98–99%), although SO2Ph, Br, and Cl in a benzylic position present serious chemoselectivity-related problems. The low regioselectivity of 60% initially observed with o-ethynylphenol (1a) has been elevated to ⩾98% through the use of either a catalytic amount of Zr(ebi)Cl2 or Zr(2-Me-Ind)2Cl2 or, more conveniently, the stoichiometric amount of ZrCp2Cl2, ZrCp2MeCl, or ZrCp2Me2 in conjunction with the use of a deficient amount (0.9molar equiv.) of I2 for subsequent iodinolysis.

Keywords: Methylalumination with Me; 3; Al; Heterosubstituted arylethynes; (; E; )-1-iodo-2-arylpropenes; ZrCp; 2; Cl; 2; and its derivatives; Regio- and stereoselectivities


Telomerization and dimerization of isoprene by in situ generated palladium–carbene catalysts by Ralf Jackstell; Anne Grotevendt; Dirk Michalik; Larbi El Firdoussi; Matthias Beller (pp. 4737-4744).
The palladium-catalyzed telomerization of isoprene with methanol and dimerization of isoprene has been studied in presence of palladium and imidazolium salts, which form in situ carbene ligands. A selectivity switch from the telomerization to the dimerization product occurred by using different substituted ligands.The palladium-catalyzed telomerization of isoprene with methanol and dimerization of isoprene have been studied in presence of in situ generated palladium–carbene catalysts. Unprecedented catalyst productivity has been observed for these two reactions. A selectivity switch from the telomer to the dimer product occurred by using different substituted carbene ligands. Among the imidazolium salts tested 1,3-dimesitylimidazolium mesylate (1), 1,3-dimesityl-4,5-dihydroimidazolium chloride (3) gave the best yields for telomerization reaction whereas 1,3-bis-(2,6-diisopropylphenyl)-4,5-dihydroimidazolium tetrafluoroborate (5) and 1,3-bis-(2,6-diisopropylphenyl)-4,5-dimethyl-4,5-dihydroimidazolium chloride (9) form dimers in high yield and good selectivity.

Keywords: Carbenes; Dimerization; Homogeneous catalysis; Isoprene; Palladium; Telomerization


A zwitterionic nickel–olefin initiator for the preparation of high molecular weight polyethylene by Yaofeng Chen; Brycelyn M. Boardman; Guang Wu; Guillermo C. Bazan (pp. 4745-4749).
Addition of 2equiv. B(C6F5)3 to [3-(2,6-diisopropylphenylimino)-but-1-en-2-olato](η1-benzyl)(trimethylphosphine)nickel (1) results in the formation of 2-tris(pentafluorophenyl)borate-3-(2,6-diisopropylphenylimino)-but-1-ene(η3-benzyl)nickel (2), in which the borane coordinates to the oxygen of the ligand and forces binding of the olefin to nickel. Compound2 can be used to initiate the homopolymerization of ethylene to obtain high molecular weight materials.The reaction of the sodium 3-(2,6-diisopropylphenylimino)-but-1-en-2-olato with Ni(PMe3)21-CH2C6H5)Cl provides 3-(2,6-diisopropylphenylimino)-but-1-en-2-olato(η1-benzyl)(trimethylphosphine) nickel (1), which was structurally characterized. The addition of 2equiv. of B(C6F5)3 to1 results in the formation of 2-tris(pentafluorophenyl)borate-3-(2,6-diisopropylphenylimino)-but-1-ene(η3-benzyl)nickel (2), in which the borane coordinates to the O site of the ligand and forces binding of the olefin unit to the nickel center. The solid-state structure of2 shows a zwitterionic structure with substantial positive charge at the nickel center. Compound2 can be used to initiate the homopolymerization of ethylene to yield high molecular weight polyethylene.

Keywords: Homogeneous catalysis; Polyethylene; Nickel; Olefin complexes


Cyclometalated group 4 complexes supported by tridentate pyridine-2-phenolate-6-(σ-aryl) ligands: Catalysts for ethylene polymerization and comparisons with fluorinated analogues by Ka-Ho Tam; Jerry C.Y. Lo; Zhengqing Guo; Michael C.W. Chan (pp. 4750-4759).
The pictured post-metallocene complexes (M=Ti, Zr, Hf) bearing the aromatic σ-carbanion as a chelating group have been prepared as olefin polymerization catalysts. The impact of different substituents on the σ-aryl moiety, especially at the R1 position, upon spectroscopic and polymerization characteristics have been examined.An adaptable synthetic methodology for the tridentate dianionic pyridine-2-phenolate-6-aryl [O,N,C] ligand framework, comprising the aromatic σ-carbanion moiety as a chelating component, has been developed. A series of non-fluorinated group 4 bis(benzyl) complexes supported by [O,N,C] auxiliaries, with halogen and alkyl groups at the ‘R1’ position ortho to the metal-C(σ-aryl) bond, have been prepared by exploiting the cyclometalation of the ligand. All derivatives have been characterized by NMR spectroscopy, and the spectral features concerning the metal-bound diastereotopic methylene groups have been highlighted. The capabilities of these complexes as catalysts for olefin polymerization have been tested, and comparisons with the recently reported fluorine-containing Ti-[O,N,C] analogues and related Hf-[N,N,C] derivatives are discussed. The titanium catalysts, in conjunction with MAO, displayed moderate to high activities for ethylene polymerization (up to 200gmmol−1h−1).

Keywords: Benzyl complexes; Cyclometalation; Olefin polymerization; Post-metallocenes; σ-Aryl ligand


A unique coplanar multi-center bonding network in doubly acetylide-bridged binuclear zirconocene complexes: A density functional theory study by Shuqiang Niu; Agnes Derecskei-Kovacs; Michael B. Hall (pp. 4760-4767).
A unique π-conjugative six-center-six-electron bonding network was revealed in the doubly acetylide-bridged binuclear group 4 metallocene complexes. The coplanar multi-center bonding interaction between the metal centers and acetylide ligands not only significantly stabilizes the doubly acetylide-bridged complexes but also lowers the isomerization barrier.A unique π-conjugative interaction pattern was experimentally revealed in the doubly acetylide-bridged binuclear group 4 metallocene complexes, which was involved in C–C coupling/cleavage reactions of acetylides and σ-alkynyl migrations. To elucidate how this multi-center bonding network affects the structural and reaction properties of these complexes, density functional theory (DFT) calculations and molecular orbital (MO) analysis were carried out on the electronic structure and σ-alkynyl migration mechanisms of the doubly acetylide-bridged binuclear Zr complexes, (L2Zr)2(μ-CCH)2 (L=Cp,Cl). The B3LYP calculations suggested that the doubly [σ,π] acetylide-bridged complex C2 h-(L2Zr)2(μ-CCH)2 was produced by the reaction of L2Zr(CCH)2 with L2Zr through a C2 v-(L2Zr)2(μ-CCH)2 intermediate followed by an isomerization process. In particular, the isomerization of C2 h- or C2 v-(L2Zr)2(μ-CCH)2 is almost thermoneutral through a low barrier of 15.3–17.0kcal/mol. The MO Walsh diagram revealed that the two isomers have a very similar six-center-six-electron bonding network. The coplanar π-conjunctive interaction by the electron donating and back-donating interactions between the metal centers and acetylide ligands significantly stabilizes the doubly acetylide-bridged binuclear group 4 metallocene complexes and the isomerization transition state.

Keywords: Density functional theory; C–C coupling; Coplanar multi-center bonding; Alkynyl migration mechanism; Isomerization transition state


Enantioselective methylalumination of α-olefins by Robby A. Petros; James M. Camara; Jack R. Norton (pp. 4768-4773).
The ability of various enantiopure zirconocenes to catalyze the asymmetric methylalumination of allylbenzene has been tested. The enantioselectivity of an ethylene(Ind)2ZrCl2/MAO system is the same as that of authentic methyl cation generated with Ph3C+ from ethylene(Ind)2ZrMe2, confirming that the methyl cation is the active catalyst from ethylene(Ind)2ZrCl2/MAO.The ability of various enantiopure zirconocenes to catalyze the asymmetric methylalumination of allylbenzene has been tested. The enantioselectivity of an ethylene(Ind)2ZrCl2/MAO system is the same as that of authentic methyl cation generated with Ph3C+ from ethylene(Ind)2ZrMe2, confirming that the methyl cation is the active catalyst from ethylene(Ind)2ZrCl2/MAO.

Keywords: Ansa-metallocenes; Asymmetric carboalumination; Insertion


Heterolytic CH-bond activation in the synthesis of Ni{(2-aryl-κC2)pyridine-κN}2 and derivatives by Emily C. Volpe; Andrew R. Chadeayne; Peter T. Wolczanski; Emil B. Lobkovsky (pp. 4774-4783).
When subjected to KO tBu in Et2O, the bromides (2-aryl-pyridine)BrNi{(2-aryl-κC2)pyridine-κN} (aryl=phenyl,2a; tolyl,2b) generated the entitled bis-cyclometalated compounds, Ni{(2-aryl-κC2)pyridine-κN}2 (aryl=phenyl,3a; tolyl,3b), whose low spin configuration and rippled geometry were confirmed by X-ray crystallography and a DFT study.Thermolysis of Ni(OTf)2 in 2-phenyl-pyridine or 2-tolyl-pyridine afforded the cationic chelate derivatives, [bis(2-aryl-pyridine)Ni{(2-aryl-κC2)pyridine-κN}]OTf (aryl=phenyl,1a; tolyl,1b). Addition of KBr to1a and LiBr to1b provided the bromides, (2-aryl-pyridine)BrNi{(2-aryl-κC2)pyridine-κN} (aryl=phenyl,2a; tolyl,2b). When subjected to KO tBu in Et2O, the bromides generated the entitled bis-cyclometalated compounds, Ni{(2-aryl-κC2)pyridine-κN}2 (aryl=phenyl,3a; tolyl,3b). These compounds insert diphenylacetylene into one cyclometalate arm to produce [(2-aryl-κC2)pyridine-κN]Ni[2-(2-(1,2-diphenylethenyl-κC2)aryl)pyridine-κN] (aryl=phenyl,4a; p-tolyl,4b). X-ray crystallographic studies were conducted on1a,2a,3a and4a, and a brief DFT study of3a confirmed its low spin configuration and rippled geometry.

Keywords: Nickel; CH-bond activation; Alkyne; Insertion; Triflate; Cyclometalation


Comparing propene polymerization with 1-butene polymerization catalyzed by MAO-activated C2- and C1-symmetric zirconocenes: An experimental and computational study on the influence of olefin size on stereoselectivity by Pierluigi Mercandelli; Angelo Sironi; Luigi Resconi; Isabella Camurati (pp. 4784-4791).
The propene and 1-butene polymerization behavior of a series of C2- and C1-symmetric zirconocenes has been reexamined. An attempt at rationalizing the observed influence of the olefin size on stereoselectivity on the basis of QM/MM calculations is reported.Polypropene and poly(1-butene) have been synthesized under very similar experimental conditions with a series of MAO-activated C2-symmetric and C1-symmetric ansa-zirconocenes. The C1-symmetric zirconocenes bearing the bilaterally symmetric fluorenyl or bis(2-methylthieno)cyclopentadienyl ligand connected through a dimethylsilyl bridge to substituted indenyl ligands produce isotactic polybutene of similar or higher molecular mass and with noticeably higher isotacticity, compared to isotactic polypropene prepared with the same catalysts under comparable conditions. Structural and mechanistic reasons for such behavior are discussed on the basis of QM/MM calculations.

Keywords: Isotactic polypropylene; Isotactic polybutene; QM/MM calculations; 13; C NMR; Metallocene catalysts; Stereoselective olefin polymerization


Synthesis and characterization of heteroleptic iron(II) thiolate complexes with weak iron–arene interactions by Shun Ohta; Yasuhiro Ohki; Yohei Ikagawa; Rie Suizu; Kazuyuki Tatsumi (pp. 4792-4799).
Selective preparation of a series of heteroleptic thiolate complexes of iron(II) have been achieved using acid–base reactions of an iron–amide complex Fe{N(SiMe3)2}2 with various bulky thiols. All new complexes have been identified by X-ray crystallography. The iron center weakly interacts with the aromatic ring of thiolate ligands.Selective preparation and characterization of a series of heteroleptic thiolate complexes of iron(II) are described. The compounds were synthesized by treatment of iron bis-amide Fe{N(SiMe3)2}2 (1) with 1equiv. of terphenyl thiols HS(2,6-(aryl)2C6H3) followed by addition of another equivalent of different thiol. An amide–thiolate intermediate [{(Me3Si)2N}Fe]2(μ-SDpp)2 (2; Dpp=2,6-Ph2C6H3) was isolated from the 1:1 reaction of1 and HSDpp. The X-ray crystal structures of all new thiolate complexes have been determined. The compounds crystallize as monomers or dimers, dependent on the substituents. They consist of distorted tetrahedral or trigonal-planar iron centers with weak interactions between the aromatic rings of thiolate ligands, where the Fe–C(arene) contact is 2.272(2)Å at shortest. The stronger iron–arene interaction appears to induce more pyramidalized geometry at the iron center.

Keywords: Iron; Thiolate; Heteroleptic complexes; Iron–arene interaction; Terphenyl group; Experimental methods

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