Rhodium-(I) and -(III) complexes of diphenylphosphinous acid and secondary phosphites

Abstract

After shaking [{RhCl(C8H12)}2](C8H12= cyclo-octa-1,5-diene) with PPh2Cl in methanol–water (7 : 1 v/v) for 15 min, addition of MCl gave high yields of the triple-chloride-bridged anionic complex M[Rh2Cl5{(PPh2O)2H}2][M = AsPh4+(2a) or PPh3(CH2Ph)+(2b)]. The structure of (2a)(CH2Cl2 trisolvate) has been verified by X-ray analysis. The crystals are triclinic, space group P with a= 12.157(4), b= 16.191(5), c= 20.523(8)A, α= 96.02(3), β= 99.88(2), γ= 96.10(2)°, and Z= 2. Variable-temperature 31P-{1H} n.m.r. spectroscopy indicates that (2a) undergoes facile intramolecular scrambling of the phosphorus nuclei at ambient temperature. Reaction of the anion (2) with BF3·Et2O leads to the formation of the [Rh2Cl5{(PPh2O)2BF2}2]– anion (3). In contrast, reaction of [{RhCl(C8H12)}2] with PPh2Cl in methanol–water (15 : 1 v/v) gives the cations [Rh{PPh2(OMe)}4]+ and [RhH(Cl){PPh2(OMe)}4]+, which do not undergo hydrolysis of the co-ordinated PPh2(OMe) ligand. The [Rh{PPh2(OEt)}4]+ cation is also formed by reaction of [RhL2(C8H12)]Y (Y = ClO4– or BPh4–; L2= Ph2AsCH2CH2AsPh2, PhSCH2CH2SPh, or 2,2′-bipyridyl) with PPh2(OEt) whereas with the [Rh(Ph2PCH2CH2PPh2)(C8H12)]+cation, [Rh(Ph2PCH2CH2PPh2){PPh2(OEt)}2][BPh4](4) is isolated. However, reaction of [RhL2(diene)][ClO4][L2= diphosphine or bis(phosphine)] with H2 followed by addition of P(OR)2(O)H (R = Me or Et) gives the unstable cations [RhL2{P(OR)2OH}2]+.