ORGANOMETALLIC OXIDES - OXIDATION OF [(ETA-C5ME5)MO(CO)2]2 WITH O2 TO FORM SYN-[(ETA-C5ME5)MOCL]2(MU-CL)2(MU-O), SYN-[(ETA-C5ME5)MOCL]2(MU-CL)(MU-CO3H)(MU-O), AND [C5ME5O][(ETA-C5ME5)MO6O18]

Oxidation of [(eta-C5Me5)Mo(CO)2]2 by air in CHCl3 gave [CrMe5O][(eta-C5Me5)Mo6O18], in an unprecedented reaction in which an oxygen atom was inserted into a C5 ring. The previously reported complexes [(eta-C5Me5)Mo(O)2]2(mu-O) and (eta-C5Me5)MoCl(O)2 were also obtained from the oxidation. The structure of [C5Me5O][(eta-C5Me5)Mo6O18] has been determined by X-ray diffraction (orthorhombic, a = 15.971 (1) angstrom, b = 16.825 (1) angstrom, c = 23.597 (1) angstrom, space group Pcab, Z = 8, R'= 0.051). The anion is a derivative of the Classic {[Mo(O)(mu-O)2]6(mu6-O)}2-, in which a terminal oxygen has been replaced by eta-C5Me5. The strong trans effect of Mo=O manifests itself across the Mo6(mu6-O) octahedron to the Mo-(eta-C5Me5) unit. Irradiation of [(eta-C5Me5)Mo(CO)2]2 in the presence of O2 gave syn-[(eta-C5Me5)MoCl]2(mu-Cl)2(mu-O) and syn-[(eta-C5Me5)MoCl]2(mu-Cl)(mu-CO3H)(mu-O), whose structures have been determined by X-ray diffraction. syn-[(eta-C5Mer)MoCl]2(mu-Cl)2(mu-O) is orthorhombic, with a = 8.581 (7) angstrom, b = 39.610 (6) angstrom, c = 56.650 (8) angstrom, space group F2dd, Z = 32, and R = 0.195. [(eta-C5Me5)MoCl]2(mu-Cl)(mu-CO3H)(mu-O) is monoclinic, with a = 8.451 (8) angstrom, b = 28.771 (16) angstrom, c = 10.925 (14) angstrom, beta = 107.2 (10)-degrees, space group P2(1)/c, Z = 4, and R = 0.073. These diamagnetic dinuclear compounds have long Mo-Mo distances (2.72 and 2.80 angstrom, respectively). Extended Huckel calculations show that there is very little Mo-Mo bonding, and the formal Mo-Mo description required by the 18-electron rule is incorrect.