REACTIONS OF COORDINATED LIGANDS .55. MOLYBDENUM-MEDIATED ADDITION OFALKYNES TO CYCLOOCTATETRAENE - ONE-ELECTRON OXIDATION AND PROTONATIONOF A(3)-ALLYL(ETA(4)-1,3-DIENE)-(ETA-CYCLOPENTADIENYL OR ETA(5)-INDENYL) MOLYBDENUM COMPLEXES, AND CRYSTAL-STRUCTURES OF [MO(ETA(3),ETA(4)-C12H13)(ETA-C5H5)], [MO(ETA(2),ETA(4)-C14H17)(ETA-C5H5)][BF4] AND ,ETA(4)-C12H13)-(MU(MO,C)-H)(ETA(5)-C9H7)][CF3SO3]

Reaction of [Mo(NCMe)(eta2-MeC2Me)2(eta-C5H5)][BF4] with cyclooctatetr aene (cot) in acetonitrile in the presence of the proton scavenger Na2 CO3 affords the neutral complex [Mo(eta3,eta4-C12H13)(eta-C5H5)] 1. An alogous reactions between cot and (Mo(NCMe)(eta2-EtC2Et)2(eta-C5H5)][B F4], [Mo(NCMe)(eta2-MeC2Me)2(eta5-C9H7)][BF4] and (Mo(NCMe)(eta2-EtC2E t)2(eta5-C9H7)][BF4] give [Mo(eta3,eta4-C14H17)(eta-C5H5)] 2, [Mo(eta3 ,eta4-C12H13)(eta5-C9H7)] 3, and [Mo(eta3,eta4-C14H17)(eta5-C9H7)] 4 i n good yield. A single-crystal X-ray diffraction study on 1 establishe d the presence of an unusual bicyclo[4.2.2]decane ligand, to which a M o(eta-C5H5) fragment is eta3,eta4-bonded. Although this structure sugg ests that these complexes are formed via a (6 + 2)pi addition reaction , it is proposed that a stepwise process is involved. The chemical rea ctivity of the complexes 1-4 has been explored. Reaction of 1 or 3 wit h [CPh3][BF4] affords respectively the cations (Mo(eta4,eta4-C12H12)(e ta-C5H5)][BF4] 7 and [Mo(eta4,eta4-C12H12)(eta5-C9H7)][BF4] 8. Reactio n of these bis(1,3-diene) cations with the nucleophiles 'H-' and 'Ph-' leads to regioselective attack on the exo-eta4-1,3-diene moiety. Trea tment of 1, 2 and 3 with AgBF4 leads to a one-electron oxidation react ion and formation of the 17-electron species [Mo(C12H13)(eta-C5H5)][BF 4] 10, [Mo(C14H17)(eta-C5H5)][BF4] 11, and [Mo(C12H13)(eta5-C9H7)[BF4] 12. A single crystal X-ray diffraction study on 11 indicates the abse nce of agostic Mo(mu-H)C interactions, the radical cation being best d escribed as a carbon-centred radical eta2,eta4-bonded to a 16-electron cationic molybdenum centre. Finally, the protonation of 1-4 has been studied, being shown to afford cationic species which adopt different structures in the solid state and in solution. An X-ray crystallograph ic study on [Mo(eta6-C12H13)(mu(Mo,C)-H)(eta5-C9H7)][CF3SO3], which is formed on reaction of 3 with CF3SO3H, established the presence of an agostic Mo(mu-H)C interaction between a carbon-hydrogen bond beta to a n alkene moiety, representing an arrested 1,3-hydrogen shift of the ty pe postulated in the initial stage of a metal-assisted isomerisation o f an alkene.