SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF PYRAZOLE AND PYRAZOLYL NIOBOCENE COMPLEXES

Nb(eta(5)-C(5)H(4)SiMe(3))(2)H-3 1 was treated with pyrazole (Hpz) and 3-methylpyrazole (Hpz') in a 1:2 molar ratio to the give dihydrogen a nd (eta(1)-pyrazole-N)(eta(1)-pyrazol-N) niobocenes, (5)-C(5)H(4)SiMe( 3))(2)(eta(1)-Hpz-N)(eta(1)-pz-N) 2, and )-C(5)H(4)SiMe(3))(2)(eta(1)- Hpz'-N)(eta(1)-pz'-N) 3, respectively. A kinetic study of the formatio n of 2 is discussed. Protonation of 2 gave the cationic bis-pyrazole c omplex, Nb(eta(5)-C(5)H(4)SiMe(3))(2)(eta(1)-Hpz-N)(2)](+) 4. 4. The p yrazole in 2 was replaced by pi-acid ligands, CO, (t)BuNC, RC=CR', to give the related pyrazolylniobocenes, Nb(eta(5)-C(5)H(4)SiMe(3))(2)(CO )(eta(1)-pz-N) 5, b(eta(5)-C(5)H(4)SiMe(3))(2)(CN(t)Bu)(eta(1)-pz-N) 6 and Nb(eta(5)-C(5)H(4)SiMe(3))(2)(RC=CR) (eta(1)-pz-N) 7, respectivel y. Finally, complex 1 was reacted with a molar equivalent of the proto nated form of bis(pyrazol-1-il)methane, [Hbpzm]BF4, to generate dihydr ogen and the bpzm containing cationic complex b(eta(5)-C(5)H(4)SiMe(3) )(2)(eta(2)-bpzm-N,N')]BF4 8. 8.