Phosphine/polyphosphine ligands

More recent work on the hydrogenation of thiophenic molecules catalyzed by water-soluble metal complexes is pursuing the use of polyphosphine ligands (cf. Section 3.2.2). These studies follow the success obtained with the tridentate phosphine MeC (CH2PPh2)3 (TRIPHOS), which forms rhodium and iridium catalysts for the hydrogenation, hydrogenolysis, and desulfurization of various thiophenic... 

The clean introduction of clusters onto the termini of polyphosphine dendrimers is a real challenge because of the current interest of dendritic clusters in catalysis and the mixtures usually obtained in thermal reactions of [Ru3(CO)i2] with phosphines.37 The diphosphine CH3(CH2)2N(CH2PPh2)2 (abbreviated P-P) was used as a simple, model ligand. The reaction between P-P and [Ru3(CO)i2] (molar ratio 1/1.05) in the presence of 0.1 equiv. [Fe p 6-C6Me6)] in THF at 20°C led to the complete disappearance of [Ru3(CO)i2] in a few minutes and the appearance of a mixture of chelate [P-P. Ru3(CO)i0], monodentate [P-P. Ru3(CO)n], and bis-cluster [P-P. (Ru3(CO)n 2]. These reactions were reported by Bruce et al. with simple diphosphines.38 On the other hand, the reaction of P-P with [Ru3(CO)i2] in excess (1/4) and only 0.01 equiv. [FeICp(r 6-C6Me6)] in THF at 20°C led, in 20 minutes, to the formation of the air-stable, light-sensitive bis-cluster [P-P. Ru3(CO)n 2] as the only reaction product. Given the simplicity of this characterization of the reaction product by 31P NMR and the excellent selectivity of this model reaction when excess [Ru3(CO)i2] was used, the same reaction between Reetz s dendritic phosphines,39 derived from DSM s dendritic amines,40 and... 

Keiter s data suggest that the best results are obtained by building the polyphosphine from a vinylphosphine ligand bonded to the transition metal complex of interest. This approach should be limited only by the lability of the complex and the susceptibility of other attached ligands to reaction under the experimental conditions employed. It should also lead to syntheses of new cyclic and acyclic tri- and tetra-phosphines coordinated to the metal (or cluster) used for the template. 

Hughes, O.R. and Unruh, J.D. (1981) Hydroformylation catalyzed by rhodium complexes with diphosphine ligands. Journal of Molecular Catalysis, 12,71 Sanger, A.R. (1977) Hydroformylation of 1-hexene catalysed by complexes of rhodium(I) with di- or tritertiary phosphines. Journal of Molecular Catalysis, 3,221 Sanger, A.R. and Schallig, L.R. (1977) The structures and hydroformylation catalytic activities of polyphosphine complexes of rhodium(l), and related complexes immobilised on polymer supports. Journal of Molecular Catalysis, 3, 101 Pittman, C.U. and Hirao, A. (1978) Hydroformylation catalyzed by cis-chelated rhodium complexes - extension to polymer-anchored cis-chelated rhodium catalysts. The Journal of Organic Chemistry, 43, 640. 

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