SYNTHESIS AND CRYSTAL-STRUCTURE OF MOCP(CL)I(PME3)2 (CP=ETA-5-C5H5) AND EQUILIBRIUM OF HALIDE REDISTRIBUTION TO MOCPCL2(PME3)2 AND MOCPI2(PME3)2

The mixed halide MoCp(Cl)I(PMe3)2 compound has been synthesized by selective halide exchange from MoCpCl2(PMe3)2. It slowly establishes a halide redistribution equilibrium in solution to a mixture containing the two homogeneous halide compounds, MoCpCl2(PMe3)2 and MoCpI2(PMe3)2. The equilibrium position has been determined in both CH2Cl2 and THF media at different I/Cl ratios in the temperature range 22-35-degrees-C. The value of the redistribution equilibrium constant is close to the expected statistical value but it slightly favours the mixed halide species, which is estimated to be ca. 0.5 kcal more stable than the average enthalpy of the two homogeneous halide compounds. The crystal structure of MoCpICl(PMe3)2 has been determined: monoclinic, space group P2(1)/c, a = 12.310(3), b = 10.551(3), c = 13.682(3) angstrom, beta = 105.04(2)-degrees, V = 1716.2(8) angstrom 3, Z = 4, D(calc) = 1.840 g cm-3, mu (Mo K-alpha) = 28.9 cm-1, R = 0.0388, R(w) = 0.0425 for 145 parameters and 2926 observed reflections. The compound has a four-legged piano stool geometry and its structural parameters are compared with those of the two homogeneous halide systems.