CHEMISTRY OF DINUCLEAR FULVALENE COMPLEXES - DIHYDRIDES, ZWITTERIONS, AND RING-SLIPPAGE COMPLEXES DERIVED FROM FVM2(CO)6 (M=MO, W)

Reduction of the metal-metal-bonded complex FvW2(CO)6 generated the dianion FvW2(CO)62-. An X-ray crystallographic analysis of [Et4N+]2[FvW2(CO)6]2- (monoclinic space group P2(1)/c, a = 7.687(2) angstrom, b = 13.752(4) angstrom, c = 16.297(5) angstrom, beta = 94.80(2)-degrees, V = 1716.8(8) angstrom3, Z = 4) showed the dianion to contain a planar Fv ring system bonded to the two metal centers in an anti fashion. The dianion reacted with a number of electrophiles to yield the neutral species FVW2(CO)6E2 (E = H, Me, Et, sigma-C3H5, CH2Ph). The pK(a) values for the two consecutive deproteinations of FvW2(CO)rH2 were determined as 14.0 and 16.6 by equilibrium measurements in acetonitrile. Thermolysis and photolysis of FvW2(CO)6H2 yielded FvW2(CO)6 and H-2. Unlike Cp2W2(CO)6, FvW2(CO)6 underwent protonation at the W-W bond by HBF4-Et2O in acetonitrile. Reactions of FvW2(CO)6 and FvMo2(CO)6 with PMe3 and Me2PCH2PMe2 (dmpm) resulted in generation of the dinuclear zwitterions FvM2(CO)5(PMe3)2 and FvM2(CO)5)(dmpm), respectively. An X-ray crystallographic analysis of FvMo2(CO)5 (orthorhombic space group P2(1)2(1)2(1), a = 9.1049(8) angstrom, b = 12.2598(14) angstrom, c = 20.1606(18) angstrom, V = 2250.4(7) angstrom3, Z = 4) showed an anti coordination of the MO(CO)3- and Mo(CO)2(dmpm)+ moieties at a planar Fv ligand. Electrophiles added at the anionic part of the zwitterions, whereas LiAlH4 effected reduction of coordinated CO to CH3 at the cationic center of FvMo2(CO)5(PMe3)2. Excess PMe3 caused the conversion of FvMo2(CO)5(PMe3)2 and FvMo2(CO)5)(dmpm) to Mo(CO)3(PMe3)3 along with FvMo(CO)2(PMe3)2 and FvMo(CO)2(dmpm), respectively. These reactions constitute the first ring-slippage reactions that have been observed in fulvalene metal complexes. When treated with Mo(CO)3(NCMe)3, FvMo(CO)2(PMe3)2 cleanly regenerated FvMo2(CO)5(PMe3)2.