Co-ordination, isomerisation and disruption of the ligands Ph2PO2C(CH2)nCHCH2(n= 0 or 1). X-Ray crystal and molecular structure of chloro(tetraphenyldiphosphoxane-κ2P,P′)(triphenylphosphine)rhodium(I)–tetrahydrofuran (1/1)

Abstract

Reaction of Ph₂PCl with CH₂CHCO₂H and CH₂CHCH₂CO₂H in the presence of triethylamine produces Ph₂PO₂CCHCH₂(L) and Ph₂PO₂CCH₂CHCH₂(L′) respectively. Both are found to undergo further intermolecular reaction to produce Ph₂PP(O)Ph₂. Reaction of L with [RhCl(PPh₃)₃], 1 mol L per 1 mol Rh, produces [RhCl(PPh₃)L] which reverts back to [RhCl(PPh₃)₃] if left in solution. The compound [RhCl(PPh₃)L] contains a bidentate L ligand co-ordinated via the phosphorus atom and the double bond. A similar reaction of L′ with [RhCl(PPh₃)₃] produces [RhCl(PPh₃)(Ph₂PO₂CCHCHMe)], involving metal-promoted double-bond migration in the L′ ligand. Reaction of 2 mol of L per mol of rhodium produces [RhCl(PPh₃)(Ph₂POPPh₂)] involving a metal-promoted disruption of the L ligand to bidentate tetraphenyldiphosphoxane. Reaction of [RhCl(PPh₃)(Ph₂POPPh₂)] with TlPF₆ produces [Rh(PPh₃)₂(Ph₂POPPh₂)][PF₆]. However addition of TlPF₆ to the reaction solution of the above 2:1 reaction of L and [RhCl(PPh₃)₃] results in the isolation of [Rh(PPh₃)₃(O₂CCH₂CH₂PPh₃)][PF₆], a complex containing a triphenylphosphoniopropionate ligand, the formation of which involves a major alteration of the L ligand. Reaction, 1 mol ligand per 1 mol Rh, of L and L′ with [{RhCl(C₈H₁₄)₂}₂] produces complexes of the form [(RhClL″)₂], where L″= L or L′ in which the mixed anhydride ligand is co-ordinated via the phosphorus atom and the double bond. Reaction of 2 mol of L per mol of Rh with [{RhCl(C₈H₁₄)₂}₂] produces [RhClL₂] and [(RhClL)₂(Ph₂POPPh₂)] as its major products. The former is a five-co-ordinate complex containing two bidentate L ligands, the later a binuclear complex containing a tetraphenyldiphosphoxane bridge between the metal centres each of which has a bidentate L ligand co-ordinated to it. All L ligands in these complexes are co-ordinated via the phosphorus atom and the double bond. The complexes have been characterised by spectroscopic means and by an X-ray crystal structure of [RhCl(PPh₃)(Ph₂POPPh₂)]·thf (thf = tetrahydrofuran). The crystals are triclinic, space group P with a= 11.294(4), b= 11.475(6), c= 17.144(9)Å, α= 102.31(4), β= 102.71(4), γ= 74.11(4)°, and Z= 2. The structure was obtained from 2329 reflections measured on an automatic diffractometer and refined to an R′ value of 0.075. The RhPOP ring is essentially planar with very small angles at Rh (68.4°) and O (95.4°) so that the two ring phosphorus atoms are brought very close together (2.457 Å). Calculations confirm that, despite this short P ⋯ P distance, there is no bonding interaction.