Chemistry of dinuclear fulvalene complexes. Dihydrides, Zwitterions, and ring-slippage complexes, derived from FvM2(CO)6 (M = Mo, W)

Article abstract of DOI:10.1021/om00020a032

Reduction of the metal - metal-bonded complex FvW₂(CO)₆ generated the dianion FvW₂(CO)₆^2-. An X-ray crystallographic analysis of [Et₄N⁺]₂[FvW₂(CO)₆^2- (monoclinic space group P2₁/c, a = 7.687(2) A, b = 13.752(4) A, c = 16.297(5) A, β = 94.80(2)°, V = 1716.8(8) A³, Z = 4) showed the dianion to contain a planar Fv ring system bonded to the two metal centers in an anti fashion. The diuanion reacted with a number of electrophiles to yield the neutral species FvW₂(CO)₆E₂ (E = H, Me, Et, σ-C₃H₆. CH₂Ph). The pK_a values for the two consecutive deprotonations of FvW₂(CO)₆H₂ 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 H₂. 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 Me₂-PCH₂PMe₂ (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 P2₁2₁2₁, a = 9.1049(8) A, b = 12.2598(14) A, c = 20.1606(18) A, V = 2250.4(7) A³, 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.