Carbonyl anion and hydride clusters

Carbon tetrabromide, irradiation of, 5 152 Carbon tetrachloride, ionization, 9 230-231 Carbonyl anion and hydride clusters, 13 478-480, 482, 483... 

Hieber and his school have carried out a systematic investigation of the transition metal carhonyl anions and derivative hydrides 169), and have synthesized many carbonyl anion and hydride clusters, particularly of the first row transition metals. The preparations of these clusters were all based on the reduction of a carbonyl compound. More recently a number of heteronuclear carbonyl anion and hydride clusters have been produced by condensation reactions. 

Many of these reduction reactions have been used in the preparation of carbonyl anion and hydride clusters (Section II, C). 

Lewis bases or organic ligands containing multiple carbon-carbon bonds. Other derivatives of the simple carbonyl clusters are the carbonyl anion and carbonyl hydride clusters. Other clusters have been prepared in which the principal Tr-acceptor ligands are 7r-cyclopentadienyl, nitrosyl, or phosphine groups. 

Data for the known carbonyl anion and carbonyl hydride clusters are collected in Table III, along with their methods of preparation and references to mass spectral and structural studies. Although many of the compounds listed have not been shown conclusively to be clusters, on the basis of comparative evidence and application of the noble gas rule, it is considered that all the compounds have a closed cluster structure. 

There are three important routes to the formation of the mercury-transition metal bond (a) displacement of halogen or pseudohalogen from mercury(II) salts with carbonyl metallate anions (b) reaction of a halo-phenylmercury compound with a transition metal hydride and (c) oxidative addition of a mercury halide to neutral zero valent metals.1 We report here the syntheses of three compounds containing three-centre, two-electron, mercury-ruthenium bonds utilizing trinuclear cluster anions and mercury(II) halides.2-4... 

A number of simple and inexpensive materials catalytically promote the cobalt-carbonylation (Reaction 2) in aqueous solution. These include ion-exchange resins, zeolites, or special types of activated carbon. Formation of the active catalyst in a separate reactor is thus economically feasible. The mechanism of this catalysis has not yet been elucidated and seems to differ for each promoter mentioned. After an induction period during which the cobalt fed to the reactor is partially retained by the promoter, fully active materials have absorbed cobalt carbonyl anion Co(CO)4 (ion exchange resins), Co2+ cation (zeolites), or a mixture of Co2+, cobalt carbonyl hydride, and cluster-type cobalt carbonyls (activated carbon). This can be shown by analytical studies (extraction, titration, and IR studies) of active material withdrawn from the reactor. 

The reaction of a carbonylmetalate with a neutral metal carbonyl has been labeled a redox condensation by Chini et al. (40, 41) and has been as widely used as a pyrolysis reaction for synthesizing mixed-metal clusters. Carbonylmetalates usually react rapidly with most neutral carbonyls, even under very mild conditions. A large number of mixed-metal hydride clusters have been formed via this type of reaction, primarily because the initial products are anionic clusters that in many cases may be protonated to yield the neutral hydride derivative. 

These studies have Indicated that simple rhodium carbonyl complexes, e.g., mono- and binuclear species are Involved in the fragmentation and aggregation reactions of rhodium carbonyl clusters under high pressures of carbon monoxide and hydrogen. They indicate that it is possible to write formal equations for such reactions in the case of rhodium carbonyl anionic hydrido clusters (equation 25) and for the more particular situation when there are not hydrides present (equation 26)... 

As a consequence of the recency of the development of cluster chemistry, most research in this field has been directed toward preparation of clusters and subsequent determination of their structure by X-ray studies. Sufficient preliminary studies of the reactivity of clusters, however, have been made to show that in a number of classes of reactions the closed cluster structure considerably affects the course of the reaction. The maj ority of reactivity studies have been made on the simple carbonyl clusters. A few reactions of carbonyl anion, carbonyl hydride, and substituted carbonyl clusters have also been reported. The intermediates and products of many reactions of clusters are air-sensitive and special techniques must be used to carry out reactions 347). 

Several surface-mediated reactions leading to metal carbonyl clusters start from hydrated metal chlorides on wet silica it is also known that the presence of water can result in the formation of cluster anions at the expense of coordinated carbonylsJ l Hydridic cluster anions can be active in the water-gas shift reaction (WGSR), the Fischer-Tropsch and other reactions, as discussed belowJ ... 

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