Synthesis, structure and hydrogenation of η 3-benzyl diphosphine complexes of rhodium and iridium

Abstract

The preparation of (COD)Rh(η 3-CH 2Ph) is described starting from [(COD)Rh] 2(μ-Cl) 2 by the addition of either Zn(CH 2Ph) 2 or Mg(CH 2Ph) 2(THF) 2. The addition of the bulky chelating diphosphines tBu 2P(CH 2) 3P tBu 2, iPr 2P(CH 2) 3P iPr 2, iPr 2P(CH 2) 2-P iPr 2, iPr 2PCH 2P iPr 2 and Cy 2PCH 2PCy 2 to (COD)Rh(η 3-CH 2Ph) yields the coordinatively unsaturated, four-coordinate rhodium complexes of the form P 2Rh(η 3-CH 2Ph). Iridium complexes of the form P 2Ir(η 3-CH 2Ph) (where P 2 tBu 2P(CH 2) 3P tBu 2 and iPr 2P(CH 2) 3P iPr 2) can be prepared from [P 2Ir] 2(μ-Cl) 2 and Zn(CH 2Ph) 2 or Mg(CH 2Ph) 2(THF) 2. Reaction of the benzyl complexes with H 2 (1 atm) yields binuclear hydride derivatives of varying composition depending on the chelate ring size of the coordinated diphosphine. For the diphosphines with only a single methylene in the backbone, binuclear hexahydride complexes are formed in which the diphosphine is binucleating. The X-ray structure of { iPr 2P(CH 2) 3P iPr 2}Rh(η 3-CH 2Ph) shows a square planar geometry about rhodium with alternating single and double bonds in the η 3-coordinated benzyl fragment. Crystals of {1,3-bis(diisopropylphosphino)propane}rhodium(η 3-benzyl)are monoclinic, a = 10.540(3), b = 15.030(9), c = 14.858(5) Å, β = 92.91(3)°, Z = 4, D c = 1.329 g cm −3, space group P2 1/ n. The structure was solved by the Patterson method and was refined by full-matrix least-squares procedures to R = 0.036 and R w = 0.043 for 4152 reflections with I >- 3σ( I).