Reactions of co-ordinated ligands. Part 27. Formation of η 3 -allyl and σ-vinyl complexes by nucleophilic attack on cationic molybdenum monoacetylene complexes. Molecular structures of [Mo(CO)(PEt 3 )(η 3 -anti-1-MeC 3 H 4 )(η 5 -C 9 H 7 )] and [Mo{P(OMe) 3 } 3 {σ-(E)-CHCHBu t }(η-C 5 H 5 )]

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[BHBus3] 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-HC2But)(η-C5H5)][BF4] with NaBH4 or K[BHBus3] in the presence of excess P(OMe)3 gives the σ-vinyl complex [Mo{P(OMe)3}3{σ-(E)–CHCHBut}(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[BHBus3] 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.