REACTIONS OF CP(2)TA(CH2)(CH3) WITH SUBSTITUTED AND UNSUBSTITUTED METAL-CARBONYLS (GROUP-7, GROUP-8, AND GROUP-9) - EVIDENCE FOR INTERMEDIATES INVOLVED IN THE CARBON-CARBON BOND-FORMING STEPS OF THE REDUCTION AND DEOXYGENATION OF CO

The mechanisms of surface-catalyzed reactions that deoxygenate carbon monoxide (CO) and convert it into longer chain hydrocarbons are not we ll understood. Homogeneous models involving soluble, well-characterize d organometallic complexes would be helpful in developing an understan ding of these reactions. Reported here are transformations in which CH 2, CO, alkyl, and aryl fragments incorporated in soluble metal complex es undergo a variety of changes that lead to new multicarbon ligands. In one example, treatment of the tantalum methylene complex Cp(2)Ta(CH 2)(CH3) (1, Cp = eta(5)-C5H5) With the methyl- or phenylrhenium pentac arbonyl complexes R-Re(co) (CO)(5) (R = CH3 (2a), Ph (2b)) above 0 deg rees C leads to >90% yields of the bridging oxo complexes Cp(2)(CH3)Ta (mu-O)Re(CR=CH2)(CO)(4) (R = Me (3a) and Ph (3b)). Low-temperature NMR monitoring and use of a perfluoroalkyl ligand has provided informatio n about the initial steps in these transformations. These demonstrate the first observation of ''Wittig-like'' attack of a metal alkylidene group on a CO ligand to give a zwitterion (e.g., fully characterized 1 6) followed by cleavage to oxometal and vinylidene complexes. In anoth er example, the tantalum-methylene complex 1 reacts with the dinuclear metal carbonyls Co-2(CO)(8) and Fe-2(CO)(9) to yield new complexes (1 7 and 18) that incorporate a C3H2O2 ligand bridging three metal center s. Reaction of the tantalum-methylene complex with Re-2(CO)(10), Mn-2- (CO)(10), or Fe(CO)(5) leads to 19, 20, and 21, requiring even more de ep-seated changes in which extensive rearrangement along with three-ca rbon coupling occurs. In this process, an oxygen atom is removed from one CO group, leading to the oxotantalum compound Cp(2)(CH3)Ta = O. Th e carbon atom from the transformed CO couples with two CH2 groups init ially bound to tantalum, and the CH2 hydrogens are simultaneously rear ranged to produce a CH3-C=C- ligand. This C-3 fragment is stabilized b y binding to a tantalum-late-metal chain. These products also contain the first examples of tantalum-carbon monoxide bridges. A reaction bet ween 1 and Ru-3(CO)(12) that results in CO deoxygenation along with co upling of the CO carbon to methylidene groups and other CO carbons to yield the cluster complex Cp(2)(CH3)Ta(mu-O)Ru-3(C4H4)(CO)(9) (23) and the unstable free tantalum oxo species Cp(2)Ta(=O)-(CH3) is also repo rted. The TaRu3 product contains a 4-carbon cumulene ligand that bridg es the three late-metal centers. The crystal structures of complexes 3 b, 16, 17, 18, 19, 20, 21, and 23 are reported.