Polyfluorophenyl derivatives of the group v elements and their metal complexes.

The Introduction is a critical review of the evidence for back-bonding in transition metal phosphine complexes. The compounds (C6F5)nPh3-nM (M = P, As, Sb; n = 1, 2 or 3) have been prepared in high yield by an improved method using pentafluorophenyllithium. The reactions of these ligands with various rhodium, palladium and platinum compounds have been investigated and displacement reactions indicate that the complexes L2PtC12 increase in stability in the order of ligands (L), Me2S < (C6F5)3P < (C6F5)Ph2As < (C6F5)2PhP < tris(2,6 difluoropheny1) phosphine < cycloocta-l,5-diene < Ph3As < (C6F5)Ph2P < Ph3P < (Ph0)3P. The reaction of (C6F5)3P with RhC13.xH20 gives the dark green complex [(C6F5)3P]4Rh2C12. Similar chloro- and bromo- complexes are obtained with (C6F5)2PhP and (C6F5)Ph2P. Carbon monoxide readily cleaves the halogen bridge present in these complexes to yield trans [(C6F5)xPh3-xP] 2RhC0C1. x = 1, 2 or 3. The reactions of trispentafluorophenylphosphine rhodium complexes with cycloocta-1,5-diene, triphenylphosphine, and triphenylphosphite show that these ligands readily displace the (C6F5)3P. Treatment of the Rh(I) complexes of (C6F5)3P with chlorine or methyl iodide gives ill defined Rh(III) materials. The 19F n.m.r. of the complexes is consistent with d?-d? bonding between the metal and the phosphorus. Infrared spectra are also reported. High resolution 19F n.m.r. studies have been carried out on the compounds (C6F5)nPh3-nM (M = P, As, Sb; n = 1, 2, 3). A loss in resolution is observed when more than one pentafluorophenyl group is present. The low temperature n.m.r. studies suggest that the phosphine (C6F5)3P is rotating about the metal-phosphorus bond in its platinum or palladium complexes at room temperature. The production of the carbonyl complexes L2RhCOC1 from high temperature (120C) experiments involving fluoro-olefins and the complexes L4Rh2C12 (L = (C6F5)nPh3-nP, n = 1, 2 or 3) and (PH3P)3 RhC1 has been investigated. The reaction has been shown to involve hydrolysis of an intermediate fluoro-olefin complex, and some tentative mechanisms are proposed.