Platinum(II), palladium(II) and rhodium(I) complexes of o-, m- and p-Ph2PC6H4PO(OEt)2. PtCl2–SnCl2 Hydroformylation catalysts modified with phosphonated triarylphosphines

Abstract

An improved route to the bulky phosphine o-Ph₂PC₆H₄PO(OEt)₂o-1 has been elaborated. The isomers [PtCl₂L₂], L = o- (2), m- (3) or p-1 (4), were made by treatment of [PtCl₂(cod)] with the appropriate phosphine. Complex 2 has a trans configuration whereas the m and p isomers, 3 and 4 are cis, reflecting the greater bulk of the o isomer. Crystal structure analyses of o-1 and its platinum complex 2 indicated normal dimensions for the tertiary phosphine in both and the considerable asymmetric steric bulk of o-1. Abstraction of the chloro ligands in 2 occurs upon addition of AgSbF₆ and the resulting dicationic bis P,O-chelate 5 has a cis geometry. The palladium complexes [PdCl₂L₂], L = o- (6), m- (7), or p-1 (8) were made by treatment of [PdCl₂(NCPh)₂] with the appropriate phosphine but, in contrast to the platinum analogues, the o isomer 6 has a cis configuration and the m and p isomers 7 and 8 are predominantly trans. Complex 6 is fluxional: variable temperature ³¹P NMR spectroscopy is consistent with hemilabile behaviour of the ligand with reversible co-ordination of the PO of the phosphonate functionality. Treatment of [Rh₂Cl₂(CO)₄] with o-1 gave the mononuclear chelate [RhCl(CO)(o-1)] (9) which upon addition of further o-1 gave predominantly the fluxional species trans-[RhCl(CO)(o-1)₂]. The platinum complexes 2, 3 and 4 when combined with SnCl₂ catalyse the hydroformylation of but-2-ene and but-1-ene.