Phosphines carbon donor ligands

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). 

Palladium(0)-catalysed coupling reactions of haloarenes with alkenes, leading to carbon-carbon bond formation between unsaturated species containing sp2-hybridised carbon atoms, follow a similar mechanistic scheme as already stated, the general features of the catalytic cycle involve an oxidative addition-alkene insertion-reductive elimination sequence. The reaction is initiated by the oxidative addition of electrophile to the zero-valent metal [86], The most widely used are diverse Pd(0) complexes, usually with weak donor ligands such as tertiary phosphines. A coordinatively unsaturated Pd(0) complex with a formally d° 14-electron structure has meanwhile been proven to be a catalytically active species. This complex is most often generated in situ [87-91],... 

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. 

Most of the catalysis using iridium compounds has typically exploited iridium with neutral, soft donor ligands such as phosphines, arsines, olefins, and carbon monoxide. Recent investigations into the chemistry of iridium in atypical environments has shown that oxygen ligand environments can support some very active iridium catalysts and may actually be more akin to the environment that exists around a metal when it is supported on an oxide support (see Water 0-donor Ligands and Oxides Solid-state Chemistry). 

Besides the numerous studies already mentioned on the reactions of [Mn(R)(CO)5] with phosphines, amines, isocyanides, and carbon monoxide, there have been extensive investigations into the reactions of [Mn(R)(CO)5] compounds with other neutral donor ligands. A brief description of these now follows. 

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