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)]

The compound [Rh2(η-C5H5) 2(μ-CO)(μ-dppm)] (1) was obtained from the reaction of [Rh 2(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)-CH 2-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-C5H 5)2(μ-SO2)(μ-dppm)] and with SnCl 2 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-C5H 5)2Br4(μ-dppm)]. Initial oxidative addition to one rhodium atom occurs in the reaction of I2 with (1) and [Rh2(η-C5H5)2(CO)l 2(μ-dppm)] was isolated. Compound (1) does not react with Mel or with diphenylacetylene in diethyl ether.