CHEMISTRY OF NEW ELECTROPHILIC METAL ALKYL-COMPOUNDS

The reaction of the neutral carborane C2B9H13 with CP*M(CH3)3 (M = Zr (a), Hf (b); Cp* = eta5-C5Me5) yields [CP*(C2B9H11)M(CH3)]n (3a,b). Complexes 3a,b form THF adducts Cp*(C2B9H11)M(CH3)(THF) 4, insert 2-butyne to yield Cp*(C2B9H11)M{C(Me=CMe2) 5, and undergo methane elimination upon thermolysis to yield methylene-bridged complexes [CP*(C2B9H11)M]2(mu-CH2) (6). These chemical studies, and companion structural and theoretical studies establish that 3a,b are neutral analogues of the cationic CP2M(R)+ species (1; Cp = eta5-C5H5) and CP2M(R)(L)+ (2) which are believed to be active in Cp2MX2-based Ziegler catalysts. Despite the lower metal charge, 3-6 exhibit characteristic ''electrophilic metal alkyl'' properties including agostic M-H-C and M-H-B interactions, high insertion and intramolecular C-H activation reactivity, and high ethylene polymerization and propene oligomerization activity. These observations suggest that the key requirement for high insertion/polymerization activity in metallocene systems is high metal unsaturation (i.e. two empty metal-centered orbitals) rather than charge.