ORGANOMETALLIC OXIDES - OXIDATION OF (ETA-C5ME5)2V WITH O-2 TO FORM [(MU-ETA-3-C5ME5O3)V(O)]2, [(ETA-C5ME5)V]4(MU-O)6, AND (ETA-C5ME5)6V8O17

The reaction between (eta-C5Me5)2V (1) and O2 (1:2 mole ratio) in hexane at -30-degrees-C for 12 h gave [(mu-eta-3-C5Me5O3)V(O)]2 (3) in 20% yield. In this reaction three oxygen atoms were inserted into adjacent V-C bonds in an all-cis fashion. The reaction between 1 and traces of O2 in hexane at 20-degrees-C for 24 h gave [(eta-C5Me5)V]4(mu-O)6 (4). Cluster 4 was more conveniently prepared by oxidation of 1 with N2O (85% yield) and was also formed on reduction of [(eta-C5Me5)V(O)(mu-O)]3 with PMe2Ph. Oxidation of 1 or 4 with a large excess of O2 in toluene at 20-degrees-C for 48 h gave (eta-C5Me5)6V8O17 (5) in 80% yield. Reaction of (eta-C5Me4H)2V with O2 gave the eta-C5Me4H analogues of 4 and 5, but the analogue of 3 was not formed. Treatment of 5, or its C5Me4H analogue, with SOCl2 gave (eta-C5Me5)VCl2(O) (2) in 70% yield. The structures of 3 and 4 were previously determined by X-ray crystallography. Compound 3 is an alkoxide in which each V(V) atom has five-coordinate, square-pyramidal, (RO)4V(O) coordination. Cluster 4 has an adamantane-like V4(mu-O)6 core (T(d) symmetry) and a magnetic moment of 2.90-mu-B at 295 K. The electronic structure of 4 has been investigated by extended Huckel molecular orbital methods; the core has the a1(2)e(2)1t2(0)t1(0)2t2(0) configuration. Cluster 5 is proposed, on the basis of chemical and spectroscopic evidence, to contain two [V(O)(mu-O)]4 units linked by a bridging oxygen.