Coordination Chemistry Reviews (v.255, #1-2)

by Peter M.H. Kroneck (1-2).

This is a review of papers published in the year 2009 that focus on the synthesis, reactivity, or properties of compounds containing a carbon-transition metal double or triple bond.
Keywords: Carbene complexes; Alkylidene complexes; Metathesis; Carbyne complexes; Alkylidene complexes; Vinylidene complexes; Allenylidene complexes;

Synthesis, structure and reactivity of complexes containing a transition metal–bismuth bond by Holger Braunschweig; Paul Cogswell; Katrin Schwab (101-117).
The transition metal chemistry of bismuth has attracted significant interest since the 1970s. The low cost and high abundance of bismuth(III) reagents, such as the trihalides, makes them ideal starting materials and the size of the bismuth centre allows three- and higher-coordinate complexes to be synthesised, in which the bismuth atom is linked to one or more transition metal fragments. The ability to vary these metal fragments gives access to a plethora of available structures, with cyclopentadienylcarbonyl, metal carbonyl and sandwich compounds of bismuth in existence. Significant recent study has focused on applications in catalysis, where bismuth species can act as cross-coupling agents in carbon–carbon, carbon–nitrogen and carbon–oxygen bond forming reactions. Another striking feature is the variation in bonding situations that can be observed when studying the organometallic chemistry of bismuth. For example, dative and covalent interactions have been reported, in addition to cases of dibismuth acting as a two-, four- or six-electron donating ligand. This review aims to demonstrate the multi-faceted nature of the transition metal chemistry of bismuth and provide a detailed coverage of this topic.
Keywords: Bismuth; Transition metal; Dibismuth; Bismuthine; Cluster compounds;

Applications of transition metal amidinate [RC(NR′)2], guanidinate and amidopyridine complexes to olefin coordination polymerization are reviewed. In addition, the use of complexes, featuring closely related ligands, such as phosphonamide or iminophosphonamide [R2P(NR′)2], in olefin polymerization is highlighted. Some of these complexes have also been investigated in the stereoregular polymerization of styrene and conjugated dienes, whereas more recent work has focused on controlled ring-opening polymerization of lactones and lactides.
Keywords: Metal; Amidinate; Polymerization; Olefin; Diene; Lactone;

Cyclocarbonylation reactions proceed mainly by the coupling reactions of carbonylation components with cyclization components having an unsaturated π-electron bond, in the presence of transition metal compounds. The representative reactions are cyclocarbonylation of alkynes by carbon monoxide such as Pauson–Khand reactions, hetero Pauson–Khand reactions, cyclocarbonylation of alkynyl alcohols, cyclocarbonylation of alkynyl amines, cyclocarbonylative alkyne–alkyne coupling reactions, and reductive cyclocarbonylation of alkynes. The other reactions are cyclocarbonylation of alkenes by carbon monoxide such as alkene–alkene coupling reactions, cyclocarbonylation with aldehydes, ketones, amines or imines, cyclocarbonylation of alkenyl alcohols. Carbonylation via cyclometalation, carbonylative ring expansion reactions, cyclocarbonylation by aldehydes, carboxylic acids or carboxylic acid esters are also cyclocarbonylation reactions. These reactions are conveniently used for organic syntheses, especially, for the syntheses of pharmaceutical intermediates.
Keywords: Transition metals; Cyclocarbonylation; Coupling reactions; Carbonylation; Cyclization; Carbon monoxide;

Bis(oxalato)chromium(III) complexes: Versatile tectons in designing heterometallic coordination compounds by Gabriela Marinescu; Marius Andruh; Francesc Lloret; Miguel Julve (161-185).
The mononuclear oxalato-containing chromium(III) complexes of general formula [Cr(AA)(C2O4)2] (AA = α-diimine type ligand) are able to produce a large variety of heterometallic complexes by acting as ligands towards either fully solvated metal ions or preformed cationic complexes with available coordination sites. This review focuses on the structural diversity of the polynuclear complexes (oligonuclear and coordination polymers) which are generated by the bis(oxalato)chromate(III) species, with a special emphasis to their magnetic properties.
Keywords: Chromium(III) complexes; Oxalato complexes; Heterometallic complexes; Magnetic properties;

This review analyzes the currently available data on true and purported FeMn enzymes with a particular emphasis on their specific physical properties. The characterization of the purple acid phosphatase from sweet potato and the current view of the hydrolysis mechanism are presented. The controversy associated with the discovery of the class Ic ribonucleotide reductase from Chlamydia trachomatis is discussed in the light of its extensive reactivity and physical studies. The amine oxygenase AurF is presented also albeit it is not exactly an FeMn enzyme but its case is particularly enlightening of the difficulties in assessing which is the right metal of an enzyme. Then, the very recent emergence of a new class of FeMn oxidases is highlighted. Lastly, examination of potential model compounds reveals the paucity of reported examples and therefore the need to develop this area. General considerations on biologically active metals and their substitution in hydrolases and redox active proteins are provided and possible reasons for the choice of the peculiar FeMn active site over the more classical diiron center are considered.
Keywords: Purple acid phosphatase; Ribonucleotide reductase; Amine oxygenase; Bimetallic sites; Fe–Mn center;

This review begins with a brief introduction to pyrazole and to spin crossover. The focus then moves to a detailed consideration of the synthesis and magnetic properties of structurally characterized iron(II) spin crossover (SCO) active complexes of pyrazole- and pyrazolate-based ligands that also contain at least one pyridine or pyrazine unit within the ligand motif. The syntheses and crystallization methods reported in the original publications are emphasized in this review. The reason for this is that these factors often affect the exact nature of the final product, including the amount and nature of the crystallization solvent molecules present and/or what polymorph is obtained, and hence they can impact strongly on the SCO properties of the resulting materials, as can be seen in this review.
Keywords: Iron(II); Spin crossover; Pyrazole; Synthesis; Structure; Magnetic; Mössbauer;

Homoleptic transition metal acetylides by Roy Buschbeck; Paul J. Low; Heinrich Lang (241-272).
The synthesis, structure, bonding motifs, reaction chemistry, and some potential applications of homoleptic metal alkynides, as well as current trends in this field of chemistry, are reported.
Keywords: Homoleptic; Alkynide; Cyanide; Transition metals; Cluster;

N,O-donating spacers are members of a class of ambidentate donors used in supramolecular self-assemblies. The skeletal adaptability and coordination flexibility of these ligands enable them to support a myriad of discrete molecular systems and extended network materials. This review focuses on pyridinecarboxylates as a representative of N,O-hetero-donating spacers and describes their recent developments in the coordination assemblies and highlights their functions and potential applications.
Keywords: Pyridylcarboxylate; Supramolecular; MOF (Metal-Organic-Framework); Assembly; Spacer; Polymer; Oligomer;

Display Omitted▶ A review of 2,2-pyridine-2,6-diylbis(1Hbenzimidazole) chemistry. ▶ Coordination ability and structural properties of title compounds. ▶ Spin crossover phenomenon of iron complexes in solid and liquid phase. ▶ Modelling compounds for biological activity investigation. ▶ Spectral characteristics of transition metal complexes with title ligands. ▶ The role of the metal ion, the counterion and hydrogen bonding in spin crossover complexes.A review of papers up to 2008 dealing with all branches of chemistry of the compounds containing 2,2′-pyridine-2,6-diylbis(1H-benzimidazole) and 2,2′-pyridine-2,6-diylbis(1,3-benzothiazole) is presented. The review summarizes the preparation procedures and properties of free organic compounds, as well as their different protonated and/or deprotonated forms. A summary of complex compounds of the considered ligands is presented together with the review of the most important properties such as spectroscopic properties, structures, magnetic properties or biological and electrochemical activity. From this review the blind spots can be identified which might suggest more points of potential interest. Also missing is a promising investigation of, at present unknown, analogues.
Keywords: 2,6-Bis-(benzimidazol-2-yl)-pyridine (bzimpy); 2,6-Bis-(benzthiazol-2-yl)-pyridine (bztpy); Complexes; Magnetic properties; Spin crossover; Structure; Spectra;

▶ MOFs with sulfur-containing heterocycles have been constructed by three types of in situ methods as (i) in situ S–S function reactions, (ii) in situ C–S bond cleavage, and (iii) in situ thiol-S atom reactions. ▶ 4,4′-dipyridinedisulfide (4-dpds) and 2,2′-dipyridinedisulfide (2-dpds) are mostly investigated for in situ S-S function reactions. ▶ The type of organic ligand, HOOC-CH2-S-Het (Het = heterocycle), is employed mainly for in situ C-S bond cleavage. ▶In situ thiol-S atom reactions offer a promising tool coupled with the rich sulfur chemistry.This review outlines three types of in situ methods used for constructing metal–organic sulfur-containing heterocycle frameworks, viz., in situ S–S function reactions, in situ C–S bond cleavage and in situ thiol-S atom reactions. Each method is described in detail in three respects, namely (i) reaction parameters, (ii) the organic transformation and coordination modes involved, and (iii) fascinating structures and functional properties of those in situ-generated metal-coordination compounds.
Keywords: In situ methods; Sulfur-containing heterocycle; S–S function reaction; C–S bond cleavage; Thiol-S atom reaction;

Coordination chemistry of 1,3,5-triazapentadienes by Maximilian N. Kopylovich; Armando J.L. Pombeiro (339-355).
▶ 1,3,5-Triazapentadienes are also known as imidoylamidines. ▶ 1,3,5-Triazapentadienes exhibit a rich coordination chemistry. ▶ The synthetic methods for 1,3,5-triazapentadienes and their complexes are reviewed.The methods of synthesis of 1,3,5-triazapentadienes (also known as imidoylamidines), as well as the preparation of their complexes, are reviewed. The former methods include mainly the Pinner, Ley and Muller syntheses, the amination of N-imidoylimidoates or of nitriles bearing strong electron-withdrawing groups, the desulfurizing amination of N-tiobenzoylbenzamidines and the reaction of perfluoro-5-aza-4-nonene with primary amines. The synthetic procedures for the complexes involve not only the coordination of a pre-formed 1,3,5-triazapentadiene but also the generation in situ of such a species, namely by condensation of amidines, by direct one-pot template synthesis from nitriles, by nucleophilic addition of amidines or related reagents to coordinated nitriles, by nucleophilic additions to dicyanamidate or hydrolytic conversion of triazines.
Keywords: 1,3,5-Triazapentadienes; Imidoylamidines; Amination; Amidines; Nitriles; Dicyanamidate; Triazines; Template synthesis;