CYCLOPENTADIENYL OXIDES OF MOLYBDENUM

An improved preparation of CpMoC12(O) (Cp = η-C5H5) from [MoCl3(O)]n and Bun3Sn(C5H5) is described. X-ray diffraction revealed that CpMoCl2(O) has a piano-stool structure similar to Cp*VCl2(O) and Cp*ReCl2(O) (Cp* = η-C5(CH3)5). The major difference between the three compounds is the Cl-M-Cl angle, 104.6 (2)° in Cp*VCl2(O) (d0), 93.4 (1)° in CpMoCl2(O) (d1), and 85.4 (1)° in Cp*ReCl2(O) (d2). Extended Hückel molecular orbital calculations showed that the decrease in the Cl-M-Cl angle as the number of d electrons increased is due to occupation of an orbital that is π-antibonding between M and Cl at high Cl-M-Cl angles but weakly σ-bonding at low angles. Reduction of CpMoCl2(O) with zinc powder in tetrahydrofuran (THF) gave diamagnetic {[CpMoCl]4(µ-O)6}(ZnCl(THF))2, formally containing two Mo(IV) and two Mo(V) centers. Reoxidation of {[CpMoCl]4(µ-O)6}(ZnCl(THF))2 with O2 gave green [CpMoCl-(O)]2(μ-O) (containing two Mo(V) centers), colorless [ZnCl(THF)(µ-Cl)]∞, and a third black product that could not be identified. X-ray diffraction showed that [CpMoCl(O)]2(µ-O) was centrosymmetric with a linear Mo-O-Mo bridge and was diamagnetic. The relation between the center of symmetry and the diamagnetism is discussed. © 1990, American Chemical Society. All rights reserved.