Synthesis and structures of rac-Me2Si(eta(5)-1-indenyl)(2)Hf(NMe2)(2) and {Me2Si(eta(5)-1-indenyl)(eta(3)-2-indenyl)}Hf(NMe2)(2)

The amine elimination reaction of Me2Si(1-indenyl)(2) (1, (SBI)H-2) and Hf(NMe2)(4) (2) affords rac-Me2Si(eta(5)-1-indenyl)(2)Hf(NMe2)(2) (rac-3, rac-(SBI)Hf(NMe2)(2)) in 20% isolated yield. This reaction proceeds by initial formation of a mono(indenyl) intermediate, (eta(5)-C9H6SiMe2C9H7)Hf(NMe2)(3) (4), which reacts reversibly with a second equivalent of 2 to form a binuclear complex, {mu-eta(5):eta(5)-Me2Si(1-indenyl)(2)}(Hf(NMe2)(3)}(2) (5), and undergoes reversible intramolecular amine elimination to form rac-3 and meso-3. The novel C-1-symmetric ansa-metallocene {Me2Si(eta(5)-1-indenyl)(eta(3)-2-indenyl))Hf(NMe2)(2) (6), in which one of the indenyl groups is bridged through the 2-position, is observed as a side product in the synthesis of 3. Complex 6 has been prepared in 21% isolated yield by thermolysis of 4 (or mixtures of 1 and 2) at 160 degrees C and can be converted to {Me2Si(eta(5)-1-indenyl)(eta(3)-2-indenyl)}HfMe2 (7, 100% NMR) by reaction with AlMe3. The molecular structures of rac-3 and 6 have been determined by X-ray crystallography.