Functionalization of unsaturated molecules utilizing group 3 and organolanthanide metallocenes

Originally developed as olefin polymerization catalysts, the reactivity of organolanthanide and group 3 metallocenes has been exploited for the hydrogenation, hydrosilylation, hydroamination, hydroboration, and hydrophosphination of polyunsaturated molecules. A major consequence of their shared d0 electron configuration is that they typically do not exhibit redox chemistry. This results in a chemistry dominated by sigma-bond metathesis reactions. The orientation of the four-centered transition state is dictated predominantly by steric influences and provides excellent selectivity in appropriately designed systems. The transformations catalyzed by organolanthanide and group 3 organometallics are generally high yielding and highly selective, thereby enhancing their synthetic utility.; I. Hydrosilylation of alkynylsilanes. Alkynyl silanes are often used as surrogates for terminal alkynes. Surprisingly, the organolanthanide-catalyzed hydrosilylation of alkynylsilanes provided the (Z)-1,1- bis(silyl)alkene as the major regioisomer (Scheme 1). The ability to "tune" the reactivity of a given complex is demonstrated by the increased selectivity observed using lutetium catalyst 3. The observed selectivities can be rationalized by the alpha-directive effect of silicon.; Hydrosilylation of (phenylethynyl)dimethylsilane demonstrated an erosion of regioselectivity in comparison to alkylalkynylsilanes. The Lewis basic aryl moiety directs the lanthanide to the benzylic position. Competition between "aryl-directed" and "silyl-directed" processes results in a loss of selectivity.*; II. Nitrogen-heterocycle synthesis. Organolanthanide catalyzed cyclization-silylation of nitrogen containing polyunsaturated systems allows access to core structures commonly found in naturally occurring alkaloids. Nitrogen-containing dienes with various substitution patterns was investigated. Mono substitution at the allylic position provided a complete reaction within one hour (eq 1). Geminal substitution at the allylic position required the use of a less hindered precatalyst to accommodate the increased steric demands of the substrate (eq 2). Cyclization upon pendant 1,1-disubstituted olefins was not realized under various conditions.*; Interestingly, sterically hindered sulfonamides, which were thought to render the catalyst inactive, were compatible with the catalyst, thus affording the cyclized products after prolonged reaction times (eq 3). Variations using fused ring systems were also investigated (eq 4).*; *Please refer to dissertation for diagrams.