Phosphorus trifluoride complexes of rhodium

Abstract

The chlorine-bridged rhodium@) complex [RhCl(PF3)2]2 is conveniently obtained by treatment of [RhCl(CO)2]2 with PF, in solution. In the solid state, the CO groups are not completely displaced. Recent reports by Nixon et al. that in solution there is rapid ligand exchange between [RhC1(C0)2]2 and [RhCI(PF3)2]2, and between [RhCI(C2H4)2]2 and [RhCl(PF3)2]2, are confirmed. The dimers [RhX(PF,),], (X = C1, Br, or I) react reversibly with an excess of PF, at low temperature to give RhX(PF,),, which are probably five-coordinate and which increase in stability in the order C1 < Br < I. There is no evidence for the analogous carbonyl complex RhCI(CO),. Triphenyl phosphite and 1,2-bis(dipheny1phosphino)ethane (diphos) displace all the PF, groups from [RhC1(PF3),I2, but triphenylphosphine, triphenylarsine, and tris(dimethy1amino)phosphine give complexes of the type RhCl(PF,)(ligand),, and triphenylphosphine also forms a dimeric complex [RhC1(PF3)(PPh3)l2. These complexes are generally more air-sensitive and thermally unstable than the analogous carbonyl complexes. Anomalously low molecular weights determined osmometrically for the complex RhC1(PF3)(PPh3)2 are attributed to oxidation in solution. This complex forms adducts with chlorine, hydrogen halides, and sulphur dioxide which are thermally less stable than the analogous 1 : 1 adducts formed by RhC1(CO)(PPh3)2. The complex RhCl(PF3){P(NMe2)3}2 loses one molecule of tris(dimethy1amino)- phosphine at room temperature and undergoes exchange of substituents on the coordinated ligands to give mixtures containing coordinated PF,NMe2 and PF(NMe2)2. 19F n.m.r. and infrared data are given. The trends in P-F stretching frequencies [v(P-F)] are like those in v(C0) in analogous carbonyl complexes and can be interpreted in terms of metal-to-PF, n-bonding.