Diphosphine bridging

B(3,5-(CF3)2C6H3)4-.512 Palladium complexes with a hemilabile terdentate carbene ligand, 1,3-bis(pyl)imidazol-2-ylidene, were active toward the catalytic polymerization of CO/norbornylene.513 Palladium complexes of cz s-bidentate C4-bridged diphosphines cis- and trans- 1,2-bis [(diphenylphosphino)methyl]cyclohexane, e fl o,e fl o-2,3-bis[(diphenylphosphino)methyl] norbornane,... 

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. 

Differently from the dtbpp or the dtbpx systems, in the case of the dtbpe after the formation of intermediate 3, insertion of a second molecule of ethene wins over termination by methanolysis to MP as, possibly, a consequence of the larger space at the vacant side because of the smaller bite angle of the C2-bridged diphosphine. 

By replacing the f-Bu groups with the smaller s-Bu in the C3-bridged diphosphine, the selectivity changes from MP to DEK. Keeping the same sub-... 

The dehalogenation by Fe2(CO)9 of binuclear arene ruthenium(II) derivatives 293 and 296 depends on the nature of the bridging diphosphine. With Ph2PCH2CH2PPh2, complexes with Ru2Fe [294 (20%)] and Ru3 [295 (12%)] are formed. With Ph2PCH2PPh2 complete dehalogenation is favored, and complexes 297 (37%) and 298 (15%) are obtained. The X-ray structure of the latter shows that the phosphorus ligand is located almost in the Ru3 plane (169) [Eqs. (37) and (38)]. 

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... 

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