Carbonyl adducts of bis(1,4-bis(diphenylphosphino)butane)rhodium(I) cation. Crystal and molecular structure of [Rh2(Ph2P(CH2)4PPh2)3(CO)4](PF6)2

The reaction of CO with CH2Cl2 solutions of [Rh(dppb)2]+X−, where X = BF4 or PF6 and dppb = Ph2P(CH2)4PPh2, yields the binuclear complex [Rh2(dppb)3(CO)4]2+ and uncoordinated dppb. This complex was isolated in the solid state as the PF6 salt and characterized by single crystal X-ray diffraction. The structure consists of two trigonal bipyramidal RhP3(CO)2 cores bridged by a dppb ligand via axial coordination sites. The CO ligands are cis and occupy equatorial sites and the chelating dppb ligands span equatorial and axial sites of their respective coordination cores. One binuclear molecule (Rh2(dppb)3)(CO)4](PF6)2 is contained in the P1 unit cell such that an inversion center exists in the center of the backbone of the bridging dppb ligand. The unit cell dimensions are a = 12.385(2), b = 15.286(2), c = 12.353(4) Å, α = 99.77(2), β = 107.03(2), γ = 103.66(1)°, and V = 2100 Å3. Atotal of 5780 observed reflections were used to solve the structure and the final R value was 0.060. The formation of the binuclear complex in acetone solution was monitored by 31P{1H} NMR. The complex is fluxional at 25°C but exhibits a complicated pattern at −65°C in addition to a sharp singlet due to uncoordinated dppb ligand.