Bridging diphosphine ligands

Scheme 8.4 Mechanism for the hydrogenation of alkenes catalyzed by ruthenium clusters stabilized by edge-bridging diphosphine ligands (CO ligands omitted for clarity).

For catalysts which promote the formation of low molecular weight products, the anion might make the difference, as in the case of the catalyst with C2-bridged diphosphine ligand 23 (Fig. 5), which gives a low molecular weight polymer or MP when the counter-anion is MsO or propanoate, respectively [101]. 

Steric bulk has a similar effect also for the methylamino-bridged diphosphines ligands 14 in CH2CI2, which give catalysts even of superior performances [ 105,109,110], again with poor activity in MeOH. 

The most effective palladium catalysts are those in which a PdFe bimetallic compound carries a bridging diphosphine ligand, when the reaction is thought to occur at the palladium centre with the iron playing an important role.25 Optically active methyl-phenylneophyltin hydride, [a] +28.9°, reacts with palladium on charcoal to give the optically active distannane, [a] +13.2°, which is optically stable for several weeks.28... 

The chelated complex [HRh((-)-diop)2] is active for the hydrogenation of terminal olefins or unsaturated carboxylic acids. " " From kinetic data and spectroscopic evidence an active intermediate containing a monoden-tate (-)-diop ligand has been postulated, " " analogous to a known carbonyl complex. Polymeric species containing bridging diphosphine ligands were postulated to explain inhibition of catalytic activity in the presence of added (-)-diop or dppb, but not added However, proof of... 

In the studies on the Rh-fdpp-Cp3 catalyst system,the effects of H2 and CO partial pressures and total reaction pressure (1 1 H2/CO) indicate that CO, rather than the bridging diphosphine ligand, dissociates... 

Reactions with phosphines are the central theme in papers dealing with P-C bond cleavage in CH2(PPh2)2 a new low-pressure synthesis of Co2(CO)g(PR3)2 complexes and cobalt carbonyl complexes with bridging diphosphine ligands ... 

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