Carbonyl clusters rhodium, complexes

Mononuclear ruthenium complexes were found to be superior to carbonyl clusters during a comprehensive comparison of a variety of catalysts in the reduction of acetone [49]. Without solvent, most catalysts were highly selective, although the activity was quite low. The addition of water to the system vastly increased yields, in agreement with Schrock and Osborrfs observations into rhodium-catalyzed hydrogenations (Table 15.9) [41],... 

Rhodium carbonyl complexes catalyze the silane-initiated cascade cyclization of 1,6,11-triynes to form fused aromatic tricyclic compounds. For example, reaction of 83 [X = G(G02Et)2] with methyldiphenylsilane catalyzed by the tetrarhodium carbonyl cluster Rh4(GO)i2 in toluene at room temperature gave an 88 12 mixture of the silylated and unsilylated fused tricycles 84a and 84b [X = G(G02Et)2] in 85% combined yield (Equation (55)). The ratio of silylated to unsilylated tricyclic product formed in the reaction of 1,6,11-triynes was dependent on the nature of the substrate (Equation (55)). For example, Rh4(GO)i2-catalyzed reaction of diaminotriyne 83 (X = NBn) with methyldiphenylsilane gave unsilylated tricycle 84b (X = NBn) in 92% yield as the exclusive product (Equation (55)). 

Under mild conditions, hydroformylation of olefins with rhodium carbonyl complexes selectively produces aldehydes. A one-step synthesis of oxo alcohols is possible using monomeric or polymeric amines, such as dimethylbenzylamine or anion exchange resin analog to hydrogenate the aldehyde. The rate of aldehyde hydrogenation passes through a maximum as amine basicity and concentration increase. IR data of the reaction reveal that anionic rhodium carbonyl clusters, normally absent, are formed on addition of amine. Aldehyde hydrogenation is attributed to enhanced hydridic character of a Rh-H intermediate via amine coordination to rhodium. 

Homogeneous Catalytic Oxidation with Phosphine-Substituted Complexes of Rhodium Carbonyl Clusters... 

Formal silylcarbonylation and silylformylation reactions are mainly catalyzed by cobalt and rhodium complexes (clusters) yet, Chatani et al. [158] have found a new type of carbonylation of diynes with trialkylsilanes leading to catechols (Eq. 100). 

Our Interest In understanding the behavior of rhodium carbonyl clusters in systems which catalytlcally convert CO H2 Into alcohols 3. prompted us to test the potential presence of mononuclear and bI nuclear rhodium carbonyl complexes In these systems. A positive characterization of these species under these circumstances would show a previously unknown behavior of rhodium carbonyl clusters under high pressure of carbon monoxide. It could also show the existence of a parallel behavior between the chemistry of these species under ambient and high pressures of carbon monoxide, and it may shed some light on the catalytic reactions occurring in those systems. 3. ... 

Rhodium carbonyl clusters with encapsulated heteroatoms, e.g., CRh6(C0)i5C]2 , [RhgPtCO l12 and [Rhi7S2(C0)32]3 , have been observed to be more resistant to fragmentation under 500-1000 atm of C0 H2 than homometal lie rhodium clusters. Polynuclear species account for 95-98 and 80-85 percent, respectively, of the total rhodium content of those systems, while the greatest catalyst activity has been noted with the latter complexes. CRh(C0>4l]— Is the only fragmentation product detected In both Instances. . ... 

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)... 

A few homometallic HNCC have also been produced by the condensation reactions of anionic carbonyl clusters with cationic complexes. For instance, sequential buildup of rhodium HNCC via incorporation of Rh(CO)2 fragments has been achieved by reacting [Rh(CO)2(MeCN)2] in acetonitrile with a series of anionic rhodium clusters as illustrated by the reactions shown in Eqs. (11) and (12) (223). 

Adams RD, Captain B, Smith JL Jr, Hall MB, Beddie CL, Webster CE (2004) Superloading of tin ligands into rhodium and iridium carbonyl cluster complexes. Inorg Chem 43 7576... 

Si 3H CP/MAS-NMR was used to probe interactions of transition metal carbonyl clusters (Ru3H(CO)M, Os2FI(CO)ii, Co(CO)4 ) deposited in the mesoporous aluminosilicate material MCM-41.637 A 29Si MAS-NMR study has been made of rhodium-amine complexes on Si02 surfaces.638 31P CP/MAS-NMR spectroscopy was able to characterise Cu6(TePh)6(PPh2Et)5 clusters in the pores of MCM-41.639... 

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