INSERTION, ADDUCT FORMATION, AND ELIMINATION OF ALKENES IN GAS-PHASE REACTIONS OF BIS(ETA-5-CYCLOPENTADIENYL)METHYLZIRCONIUM(1+) WITH NITRILES

The gas-phase reactions of Cp2ZrCH3+, (1, Cp = cyclopentadienyl) with a number of alkyl nitriles and benzonitrile have been studied by using Fourier transform ion cyclotron resonance mass spectrometry. The formation of adducts occurs readily for all nitriles investigated, and the rate constants for adduct formation in the reaction of 1 with acetonitrile were determined. The rate constants range from 0.05kc to 0.15kc as buffer gas pressures are increased from 0 to ~1.5 ⨯ 10-6 Torr, where kc is the estimated ion/molecule collision rate (2.2 ⨯ 10-9 cm3 s-1). Insertion of nitriles is proposed to yield azomethine complexes, and in several cases the reverse reaction, deinsertion, produces Cp2ZrR+ and N≡CCH3, where R is the alkyl or phenyl portion of the nitrile substrate. Comparisons of reactivity of the gas-phase ion 1 to solution chemistry are considered, since both adduct formation and insertion have been observed for d0fn complexes in solution. Reactions of 1 with n-alkyl nitriles having alkyl groups larger than methyl result in elimination of alkenes producing Cp2ZrN̿C(H)(CH3)+, presumably by a mechanism involving deinsertion. Formation of Zr-allyl complexes is also observed for reaction of 1 with R-C≡N (R = propyl, butyl). Lower limits for relative Cp2Zr+-R bond disruption enthalpies are derived where possible and indicate that relative bond disruption\enthalpies for Cp2Zr-R+ complexes are similar to those reported for related neutral complexes in solution. The reactivity of 1 with nitriles is comparable to reactivity of analogous neutral and cationic d0fn metal complexes, but additional reaction pathways are observed in the gas phase. © 1990, American Chemical Society. All rights reserved.