Reactions of co-ordinated ligands. Part 27. Formation of η3-allyl and σ-vinyl complexes by nucleophilic attack on cationic molybdenum monoacetylene complexes. Molecular structures of [Mo(CO)(PEt3)(η3-anti-1-MeC3H4)(η5-C9H7)] and [Mo{P(OMe)3}3{σ-(E)-CHCHBut}(η-C5H5)]

Abstract

Reaction of [MoLL¹(η-MeC₂R)A][BF₄][R = Me, Et, or Prⁱ; L = L¹= P(OMe)₃; LL¹= Ph₂PCHCHPPh₂; L = PEt₃, L¹= CO; A =η-C₅H₅ or η⁵-C₉H₇] with NaBH₄ or K[BHBu^s₃] in tetrahydrofuran affords the anti-substituted η³-allyl complexes [MoLL¹(η³-CH₂CHCHR)A]. The structure of the complex [Mo(CO)(PEt₃)(η³-anti-1-MeC₃H₄)(η⁵-C₉H₇)] was established by single-crystal X-ray crystallography. Crystals are monoclinic, space group P2₁/n with a= 10.038(2), b= 17.291(4), c= 11.346(3)Å, β= 95.000(18)°, and Z= 4. Using 3 887 reflections measured on a four-circle diffractometer at room temperature, the structure has been refined to R 0.0344, R′ 0.0459. The molecule adopts an exo-conformation with the methyl substituent of the allyl ligand in an anti-position cis to the carbonyl ligand. Treatment of the complex [Mo{P(OMe)₃}₂(η-HC₂Bu^t)(η-C₅H₅)][BF₄] with NaBH₄ or K[BHBu^s₃] in the presence of excess P(OMe)₃ gives the σ-vinyl complex [Mo{P(OMe)₃}₃{σ-(E)–CHCHBu^t}(η-C₅H₅)], structurally identified by n.m.r, spectroscopy and X-ray crystallography. Crystals are monoclinic, space group P2₁/c with a= 11.731(3), b= 12.796(3), c= 18.827(4)Å, β= 92.33(2)°, and Z= 4. Using 7 437 intensity data, measured at 195 K on a four-circle diffractometer, the structure has been refined to residuals R= 0.026, R′= 0.026. The molecule shows typical four-legged ‘piano-stool’ geometry with the vinyl group adopting E stereochemistry, σ-bonded to the molybdenum atom. In contrast, the reaction of K[BHBu^s₃] with [Mo{P(OMe)₃}₂(η-HC₂Prⁱ)(η-C₅H₅)][BF₄] in tetrahydrofuran at low temperature affords the allyl complex [Mo{P(OMe)₃}₂(η³-1,1-Me₂C₃H₃)(η-C₅H₅)]. The n.m.r. spectra and mechanism of formation of these compounds are discussed.