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)Å, 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]⁺.