STRUCTURAL CHARACTERIZATION OF THE 1ST CYCLOTETRAMOLYBDENUM DIYNES WITH BIDENTATE PHOSPHINES, MO4CL4(MU-CL)2(MU-OME)2(MU-DPPM)2 AND MO4CL4(MU(4)-O)(MU-CL)3(MU-OME)3(MU-DMPM)2

The first cyclotetramolybdenum diynes with bidentate phosphines, namely, Mo4Cl4(mu-Cl)2(mu-OMe)2(mu-dppm)2 (1) and Mo4Cl4(mu4-0)(mu-Cl)3(mu-OMe)3(mu-dmpm)2 (2), have been synthesized by cycloaddition of K4Mo2Cl8 in methanol followed by the reaction with dppm or dmpm ligand. The molecules of 1 reside on the crystallographic 2-fold axes in the centrosymmetric space group C2/c. The planar rectangular Mo4 ring has bond lengths of 2.224(l) and 2.814(1) angstrom, which fall within the ranges established for Mo-Mo triple-, and single-bond distances, respectively. For compound 2, there is an 0 atom capping the planar Mo4 ring and the Mo-Mo bond distances are 2.449(3) and 2.452(3) angstrom for the short edges and 2.706(3) and 2.648(3) angstrom for the long edges of the rectangular unit. The arrangements of the Cl, OMe, and phosphine ligands are such as to give idealized C2v symmetry in complex 1 and C(s) symmetry in compound 2. The crystal structures of 1 and 2 are fully described. Crystallographic data for these compounds are as follows: 1.2C6H6, monoclinic, space group C2/c, with a = 27.180(6) angstrom, b = 9.768(l) angstrom, c = 26.553(4) angstrom, beta = 114.49(1)-degrees, V= 6415(4) angstrom3, Z = 4, R = 0.0474, and R(w) = 0.0761; 2.C6H6.C4H8O orthorhombic, space group P2(1)2(1)2(1). with a = 13.895(4) angstrom, b = 16.490(6) angstrom, c = 18.181(4) angstrom, V = 4166(4) angstrom3, Z = 4, R = 0.0526, R(w) = 0.0616.