Development of Highly Efficient Bond Dissociation and Bond Formation Reactions Utilizing Group 6 Organometallic Complexes

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Transition metal polyhydrido complexes are known to be potent precursors of the coordinatively unsaturated species because they often release dihydrogen via reductive elimination on light irradiation or heating in solution. In view of the highly reactive nature of the coordinatively unsaturated intermediate thus generated toward oxidative addition reactions, the research program utilizing [MH_4 (Ph_2PCH_2CH_2PPh_2)_2](1, M=Mo, W) and [MH_2 (η^5-C_5H_5)_2](2, M=Mo, W) as starting complexes for the selective bond cleavage and bond formation was undertaken. Complex 1 affords coordinatively unsaturated intermediate {MoH_2 (Ph_2PCH_2CH_2PPh_2)_2} and/or {Mo (Ph_2P-CH_2CH_2PPh_2)_2} on irradiation or heating in solution by releasing one or two moles of dihydrogen. The reactive intermediates thus formed were found to react with (1) methacrylic esters to cause olefinic C-H bond activation, (2) allyl carboxylates to give an η^2-carboxylato complex and propene as a result of C-O bond activation, (3) β-diketones and catechols to give chelated diketonato and catecholato derivatives, respectively, (4) cyclic imines and amides to cleave their N-H bonds to give N-acylamido complexes, or finally (5) aryl silanes or germanes to give a novel hydrido-silyl or-germyl complex which has a quinquedentate ligand comprising of a P〜P〜Si/Ge〜P〜P framework. The last complex was further investigated in view of the reactivity resulting from its unique structure. Complex 2 gives, on protonation with the acid such as p-toluene sulfonic acid, cationic trihydirdo complex, which exhibits selective reduction of organic functional group such as carbonyl and imine. The system was found also to reduce allylic alcohols to propane. Finally synthesis of the hitherto unknown carbene derivatives of molybdenocene was attempted and some new complex of such type were obtained.