STRUCTURAL STUDIES OF MONOCYCLOPENTADIENYL TITANIUM AND ZIRCONIUM COMPLEXES CONTAINING A DIISOPROPYLAMIDE LIGAND - EVIDENCE OF A BETA-AGOSTIC INTERACTION IN (C5H5)M[N((C3H7)-C-I)(2)]CL-2

The stoichiometric reaction of (C(5)R(5))MCl(3) or its THF adduct (R = H, Me; M = Ti, Zr) with one equivalent of [Li(N((C3H7)-C-i)(2))](n) i n toluene provides a convenient method for the preparation of a series of monocyclopentadienyl Group 4 diisopropylamido complexes (C(5)R(5)) M[N((C3H7)-C-i)(2)]Cl-2. The molecular structures of these four mononu clear, 14-electron complexes are characterized by a pseudotetrahedral geometry with the M-N bond distance being consistent with the presence of a double bond. The stereoelectronic influence of the replacement o f the C5H5 ring in (C5H5)M[N((C3H7)-C-i)(2)]Cl-2 (M = Ti(1), Zr(3)) by the stronger pi-donating and bulkier C(5)Me(5) ring in (C(5)Me(5))M[N ((C3H7)-C-i)(2)]Cl-2 (M = Ti(2), Zr(4)) is evidenced by a 10-15 degree s increase in the Cp(c)-M-N angle and by the loss of the beta-agostic interaction observed for the methine C-H bond of an isopropyl group in 1 and 3. A comparison of the structural parameters about the electrop hilic metal center of 1-4 with those of related bent metallocenes is c onsistent with the diisopropylamido ligand being a poorer pi-donor tha n either the C5H5 or C(5)Me(5) ring.