Jeffrey A. Rahn

Redistribution reactions of platinum(II) and palladium(II) phosphine complexes

Abstract Anion redistribution equilibria of the type (R 3 P) 2 MX 2 + (R 3 P) 2 MY 2 ⇆ 2(R 3 P) 2 MXY (X, Y = Cl, Br, I, CN, N 3 ; R 3 P = Me 2 PhP, MePh 2 P, (Bzl) 3 P, (CH 2 CH) 2 PhP, (CH 2 CH)Ph 2 P and 1-phenyl-3,4-dimethylphosphole; M = Pd, Pt) have been studied by 31 P{ 1 H} and in some cases 195 Pt{ 1 H} NMR spectroscopy. It was found that except for the two cases when R 3 P = MePh 2 P, M = Pd, X = Cl, Y = Br and R 3 P = Me 2 PhP, M = Pd, X = Cl, Y = Br, redistribution was in general instantaneous. The (R 3 P) 2 PdCl 2 + (R 3 P) 2 Pd(CN) 2 reactions were slow but proceeded to completion. In contrast, when one of the anions is CN − no anion redistribution was observed for the platinum complexes even after a month. The thermodynamic stabilities of the mixed anion species relative to the symmetric species is anion dependent showing that these are not random processes. The (R 3 P) 2 PdXY complexes possess the trans geometry. The (R 3 P) 2 PtXY complexes are generally cis but in some cases both the cis and trans isomers are present in solution. A mechanism is proposed for these reactions. Phosphine redistribution of the type (R 3 P) 2 MX 2 +(R′ 3 P) 2 MX 2 ⇇ 2(R 3 P)(R′ 3 P) 2 MX 2 is general for palladium. It did not occur for platinum unless one or more of the R and R′ groups on each phosphine was unsaturated (allyl, vinyl or the butadiene moiety of a phosphole). In most of these cases the (R 3 P)(R′ 3 P)MX 2 complexes underwent intramolecular [4+2] Diels-Alder cycloaddition reactions.