Comparison of the reactions of some bisphosphines with two related dinuclear rhodium complexes

Article abstract of DOI:10.1016/S0022-328X(96)06535-7

The reactions of some phosphines and bisphosphines with the dirhodium complexes (η⁵-C₅H₅)₂Rh₂(μ-CO)(μ₂-n²-CF₃C₂CF₃) (I) and (η⁵:η⁵-C₅H₄CH₂C₅H₄)Rh₂(CO)₅(μ₂-η¹:η¹-CF₃C₂CF₃) (II) have been compared. The complexes (n⁵-C₅H₅)₂Rh₂(CO){η¹-Ph₂P(CH₂)_nPPh₂}(μ₂-η¹:η¹-CF₃C₂CF₃) (III, n = 1-4), which are formed from (I) and the appropriate bisphosphine, all have a trans arrangement of the carbonyl and bisphosphine ligands. When left in solution, the complex (III, n = 1) loses CO to form (η⁵-C₅H₅)₂Rh₂(μ₂-η¹:η¹-dppm)(μ₂η¹:η¹-CF₃C₂CF₃) (IV), but the other complexes are stable. The complex (II) was prepared to force a change of stereochemistry on the products of the addition reactions. Treatment of (II) with the phosphines P(p-MeC₆H₄)₃ and PPh₂H, and the bisphosphines Ph₂P(CH₂)_nPPh₂ (n = 1-4) gave (η⁵:η⁵-C₅H₄CH₂C₅H₄)₂Rh₂(CO)(L)(μ₂-η¹:η¹-CF₃C₂CF₃) in which CO and L adopt a cis configuration on the Rh-Rh bond. UV irradiation of (η⁵:η⁵-C₅H₄CH₂C₅H₄)Rh₂(CO)(PPh₂H)(μ₂-η¹:η¹-CF₃C₂CF₃) (VII) results in formal insertion of the alkyne into the P-H bond to give (η⁵:η⁵-C₅H₄CH₂C₅H₄)Rh₂(CO){μ₂-PPh₂C(CF₃)C(CF₃)H} (VIII). Unlike (III, n= 1), (η⁵:η⁵-C₅H₄CH₂C₅H₄)Rh₂(CO)(η¹-dppm)(μ₂-η¹:η¹CF₃C₂CF₃) (IX n = 1) shows no tendency to lose CO in solution. Some bis(dinuclear) complexes [(η⁵-C₅H₅)₂Rh₂(CO)(μ₂η¹:η¹-CF₃C₂CF₃)]₂(μ₂-η¹:η¹-Ph₂P(CH₂)_nPPh₂}) (V, n = 2-4) and [(η⁵:η⁵-C₅H₄CH₂C₅H₄)Rh₂(CO)(μ₂-η¹:η¹-CF₃C₂CF₃)]₂(μ-η¹:η¹-dppb) (X) were formed when two equivalents of (I) or (II) were treated with the bisphosphine. The crystal and molecular structures of (III, n = 2), (IV) and (IX, n = 1) were determined by X-ray crystallography.