KINETICS AND MECHANISM OF THE REDUCTIVE ELIMINATION OF CYCLIC TITANOCENE IMINOACYLS

1,1-Dicyclopentadienyltitanaindan (1)reacts with isocyanides (RNC) to give cyclic iminoacyl complexes 2 (R = t-Bu) and 5a-e (R = p-R'C6H4, R ' = Et(2)N, MeO, Me, H, and Cl) where the isocyanide has inserted into the Ti-CH2 bond. The X-ray crystal structure of 2 has been determined . Complex 2 crystallizes in a monoclinic space group P2(1) with a = 14 .353(1), b = 8.556(2), c = 15.652(2) Angstrom; beta = 88.95(5); and Z = 4. Compounds 2 and 5a-e decompose in solution with formation of imin es and paramagnetic Ti species. The decomposition follows first-order kinetics, with Delta C-double dagger = 24.5 +/- 0.2 Kcal mol, Delta H- double dagger = 24.3 +/- 0.2 Kcal mol, and Delta S-double dagger = -0. 4 +/- 2 eu in the case of 2. The rate of imine elimination depends on the nature of the substituent on the nitrogen atom, higher rates are o bserved for electron-withdrawing substituents (Hammet theta = +1.59 +/ - 0.04 for 5a-e), and the rate is little affected by the solvent or by the presence of PMe(3). These results are consistent with a concerted reductive elimination mechanism that initially leads to an unstable e ta(1)-imine complex which subsequently converts to the observed produc ts.