Synthesis and some reactions of binuclear η-cyclopentadienyl rhodium complexes containing bis(diphenylphosphino)methane and small molecules (CO, SO2, or SnCl2) as bridging ligands. Crystal and molecular structure of [Rh2(η-C5H5)2(µ-CO)(µ-Ph2PCH2PPh2)]

Abstract

The compound [Rh₂(η-C₅H₅)₂(µ-CO)(µ-dppm)](1) was obtained from the reaction of [Rh₂(η-C₅H₅)₂(µ-CO)(CO)₂] with bis(diphenylphosphino)methane (dppm). The X-ray structure determination of (1) shows it to crystallize in the space group C2/c with unit-cell dimensions a= 23.738(7), b= 11.731 (3), c= 26.883(7)Å, β= 123.2(1)°, and Z= 8. On the basis of 2 809 reflections with I 3σ(I), the structure has been refined to R= 0.050 and R′= 0.045. The molecule consists of two rhodium atoms bridged by a carbonyl group and a dppm ligand; a terminal η-C₅H₅ ligand completes the co-ordination sphere of each rhodium atom. The Rh(1)–CO–Rh(2) and P(1)–CH₂–P(2) fragments are folded on the same side. The cyclopentadienyl ligands are in cis position with an interplanar angle of 82.1°. Compound (1) reacts with SO₂ to give [Rh₂(η-C₅H₅)₂(µ-SO₂)(µ-dppm)] and with SnCl₂ to give [Rh₂(η-C₅H₅)₂(µ-CO)(µ-SnCl₂)(µ-dppm)]. For these reactions the possible site of attack at (1) is discussed. The oxidative addition of Br₂ and I₂ to (1) changes the CO bonding from bridging to terminal. From the reaction with Br₂ the cationic complex [(η-C₅H₅)Br₂Rh(µ-dppm)Rh(CO)Br(η-C₅H₅)]Br₃ was isolated; in solution it releases CO to form the neutral complex [Rh₂(η-C₅H₅)₂Br₄(µ-dppm)]. Initial oxidative addition to one rhodium atom occurs in the reaction of I₂ with (1) and [Rh₂(η-C₅H₅)₂(CO)l₂(µ-dppm)] was isolated. Compound (1) does not react with Mel or with diphenylacetylene in diethyl ether.