Coordination chemistry carbon donor

Structural aspects and coordination chemistry of metal porphyrin complexes with emphasis on axial ligand binding to carbon donors and mono- and di-atomic nitrogen and oxygen donors. P. D. Smith, B. R. James and D. H. Dolphin, Coord. Chem. Rev., 1981,39, 31-75 (170). 

In this chapter, the most efficient synthetic routes, the main stmctural features as well as reactivity patterns of odd-chain metallacumulene complexes bearing 7i-donor substituents, i.e., [M]=C(=C) =CR R ( = 1, 3, 5 R /R = NR2, OR, SR, SeR), are reviewed. In addition, the coordination chemistry of phosphonioace-tylides (R3P C=C ) and tricarbon monoxide (C3O) will also be discussed since these heteroatom-containing 77 -carbon ligands lead to closely related bonding situations, with participation of both neutral cumulenic and zwitterionic alkynyl-type mesomeric forms (Fig. 3). 

The coordination chemistry of macrocyclic ligands has been extensively studied and aspects of isomerism have been considered in numerous systems.241 Methods whereby two diastereomers of complexes of tetra- N-methylcyclam may be isolated have been discussed previously.184 This, however, is a relatively simple system and it is usually necessary to consider isomerism due to the presence of asymmetric atoms in the chelate arms, as well as that due to asymmetric donor atoms that may be rendered stable to inversion by coordination. An example of a system exhibiting this level of complexity is afforded by the nickel(II) complexes of the macrocyclic ligands generated by reduction of the readily prepared macrocycle (46). These ligands contain two asymmetric carbon atoms and four asymmetric nitrogen atoms but, because AT-inversion is rapid, it is conventional to consider that only three separable stereoisomers exist. There is an enantiomeric pair, (47a) and (47b), which constitutes the racemic isomer (R, R ), and an achiral (R, S ) diastereomer (47c), the meso isomer. 

The electronic influence of the other ligands in the metal s coordination sphere is a major consideration when exploring the coordination chemistry of carbon dioxide. Since the metal-C02 bond is stabilized mainly by back-donative interactions, it would be expected that good donor ligands (e.g., the ubiquitous phosphine ligands) would enhance the binding ability of C02 to the metal center. This has been verified both experimentally (10) and theoretically (20), and has as well been demonstrated to be of importance in C02 insertion processes (see below). 

The zero and lower oxidation states are relatively unimportant in the classical coordination chemistry of iron. With increased electron density on the iron, d-d and d-n interactions are particularly important, and systems with n acceptor orbitals are the dominant ligand species. Amongst the most common ligands encountered are carbon monoxide, phosphines, phosphites and unsaturated hydrocarbons. There are, however, a few relatively well-characterized iron(0) complexes derived from the reduction of higher oxidation state complexes containing N donor ligands possessing delocalized ji systems. 

The coordination chemistry of compounds containing phosphorus-carbon multiple bonds, such as phosphaalkynes, phosphaalkenes, phos-phaallenes, phosphaalkenyls, and phosphaallyls, has been studied extensively (349,350). The chemistry is dominated by the donor properties of the phosphorus atom, and, as far as we are aware, no examples of bimetallic or trimetallic compounds with bridging ligands which link metal centers by a carbon cr bond and a C=P or C P n bond have been recorded. Once the lone pair on the phosphorus atom is involved in bonding, the unsaturated bond becomes a possible site for further coordination. 

Those ligands with N, O, P and S donors, as well as the halogen anions, are particularly common. These donor atoms cover the large majority of ligands you are ever likely to meet, including in natural biomolecules. There are others, of course even carbon, as II3C, for example, is an effective donor, and there is an area of coordination chemistry (organometallic chemistry) devoted to compounds that include M—C bonds, addressed later in Section 2.5. 

CS2 can bind in monodentate end-on, bidentate chelate, bridging, or rj forms (Scheme 26). Most complexes of CS2 are low-valent electron-rich species, for example [Mo(Cp)(CO)2(/]2-CS2)] (51), [Ru(CO)2(PPh3)2( ] -CS2)] (52), and [Pt(PPh3)2 ( -CS2)] (53). Conversion of coordinated CS2 to CS and CS3 fragments can occur on coordination. The coordination chemistry of phosphine-carbon disulfide adducts (S2CPR3) has been reviewed these versatile ligands can act as 2 to 8 electron donors to metal centres. ... 

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