ISOLATION AND STRUCTURAL CHARACTERIZATION OF MIXED CARBONYL-BIS(DIMETHYLPHOSPHINO)METHANE COMPLEXES OF DIRHENIUM(II)

The triply bonded dirhenium(II) complex Re2Cl4(mu-dMPM)3 (dmpm = Me2PC H2PMe2) reacts with CO and xylNC in deoxygenated acetone in the presen ce of TIPF6 to form the salts [Re2Cl3(L)(mu-dmpm)3]PF6 (L = CO, xylNC) in which one of the equatorial chloride ligands has been displaced by a pi-acceptor ligand L. A crystal structure determination of the carb onyl complex shows that a very short Re-Re bond distance is still pres ent (2.3565(7) A), in accord with the retention of a Re=Re bond. The d icarbonyl complexes [Re2X2(CO)2(dMPM)3](H2PO4)2 are produced upon the reaction of [Re2(mu-O2CCH3)X2(mu-dmpm)3]PF6 (X = Cl, Br) with CO in de oxygenated acetone/HPF6(aq) mixtures. These compounds have a structure in which two of the bridging dmpm ligands have switched to a chelatin g mode and the two halide ligands are now bridging the two metal cente rs, i.e. [Re2(mu-X)2(mu-dmpm)(CO)2(dmpm)2](H2PO4)2. A crystal structur e determination of the chloro complex has revealed that the Re-Re dist ance is quite long (2.918(2) angstrom); this distance is consistent wi th the presence of a Re-Re single bond. Crystal data for [Re2Cl3(CO)(d MPM)3]PF6 (+20-degrees-C): orthorhombic space group P2(1)2(1)2, (No. 1 9), a = 12.270(2) angstrom, b = 15.389(2)angstrom, c = 17.147(2)angstr om, V = 3237(1)angstrom3, Z = 4. The structure was refined to R = 0.02 3(R(w) = 0.027) for 2091 data with I > 3.0sigma(I). Crystal data for [ Re2Cl2(CO)2(dmPM)3](H2PO4)2(+20-degrees-C): orthorhombicspace group P2 (1)2(1)2 (No.18), a = 12.576(1)angstrom, b = 14.374(2)angstrom, c = 10 .872(2), V = l965.3(8)angstrom3, Z = 2. The structure was refined to R = 0.052 (R(w) = 0.064) for 1232 data with I > 3.0sigma(I).