Rhodium hydride complexes structure

In 2004 Caporali investigated the hydroformylation of 1-hexene and cyclohexene using HRh(CO)(PPh3)3 [61]. The collected data indicated that the rate-determining step in the hydroformylation cycle depends upon the structure of the olefin. With an alpha-olefin like 1-hexene, the slowest step seems to be the hydrogenolysis of the acyl rhodium complex. In the presence of cyclohexene as a model for an internal olefin, the rate-determining step is the reaction of the olefin with the rhodium hydride complex (intermediate II in Fig. 6). 

Reactions of soluble metal complexes, whose mechanisms of catalysis appear to be reasonably well known, can serve as a guide to the main reaction paths followed on heterogeneous catalysts. Mononuclear complexes catalyze syn addition of H2 to alkynes to yield initially only cis isomers, as in equation (25). 5 More recently, Muetterties and coworkers showed that the dinuclear rhodium hydride complex ( yi-H)Rh[P(OPr )3]2 2 (38) converts alkynes to trans isomers as initial products (equation 26). The alkyne addition compound (39) was isolated its structure shows the vinyl group bonded to one rhodium atom by a a-bond and to the other by a ir-bond, while the substituents on the vinyl group are trans to one another. This structure resembles ones hypothesized earlier to explain the formation of trans isomers and alkanes. Hydrogenations of alkynes which are catalyzed by the dinuclear rhodium hydride are much slower than the hydrogenation of an alkene catalyzed by the dinuclear tetrahydride (40), which is formed rapidly from (38) in the presence of H2 (equation 11). ... 

Hydride Complexes of Ruthenium, Rhodium, and Iridium G. L. Geoffroy and J. R. Lehman Structures and Physical Properties of Polynuclear Carboxylates Janet Catterick and Peter Thornton... 

In the case of terminal C=C (1,2 addition units), i.e. when R=R =H and R" (or R111) = polymer chain, two types of hydride migration are possible, namely (i) The Markownikoff s addition which would lead to the formation of B type repeating units and (ii) The anti Markownikoff s addition which would result in the formation of the observed repeating units C. In the case of Markownikoff s type addition the hydride transfer occurs to Ca and results in the formation of branched alkyl-rhodium intermediate complex shown by Structure 2. Whereas when anti Markownikoff s addition occurs, the resulting intermediate alkyl-rhodium complex has linear alkyl ligand as shown by Structure 3. 

RhHClIBu CH HgCHCHaCH BuJ ], and a small amount of an olefinic diphosphine-rhodium(I) complex (vide infra). The 16-atom chelate exists in solution as predominantly one rotamer, with about 10% of a second rotamer (P-31 and H-l NMR evidence) (34). The probable structures of these two rotamers are Complexes IX and X or vice versa. The cyclometallated hydride complex [ithHClIBu CI CH2CHCH2CI12PBU2 ] has the configuration of Structure XI by X-ray... 

The X-ray structure of the latter complex (Fig. 5) shows that it contains a [HRh(/A-H)2RhH] core. Both complexes may be considered classical rhodium hydride species, although they are of a less common variety in that the ancillary amine ligands are purely room temperature, the complex of 4 is fluctional whereas that of 3 is rigid. 

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