STUDY OF THE GAS-PHASE CHEMISTRY OF YCH3(+) - SIGMA-BOND METATHESIS AND MIGRATORY INSERTION OF C=C BONDS INTO THE Y+-METHYL BOND

The gas-phase chemistry of YCH3+ is studied, with particular emphasis on C-H activation via a multicentered intermediate. This activation pathway is observed for the benzyl-hydrogen bond and allylic C-H bonds but not for the H-H bond, C-H bonds in simple alkanes, vinylic C-H bonds, and phenyl-H bonds. The reaction of YCH3+ with toluene generates (benzyl)yttrium ion and methane, exclusively. The reaction of YCH3+ with ethylene occurs by migratory insertion of the C=C double bond into Y+-CH3, followed by H-2 elimination to give Y+-allyl. Labeling experiments indicate facile reversible steps in the reaction mechanism, resulting in rapid isomerization of the Y+-propyl intermediate to Y+-isopropyl, which occurs prior to H-2 loss. In contrast, for propene, such C=C bond migratory insertion accounts for only a minor amount of the reaction and leads to the formation of YC4H7+ consisting of about 80% (2-methylallyl)yttrium ion and 20% (1-methylallyl)yttrium ion. The majority of the reaction proceeds by methane elimination involving an allylic hydrogen and the methyl group originally attached to the yttrium center, leading to the formation of (allyl)yttrium ion. (1-Methylallyl)yttrium ion and (2-methylallyl)yttrium ion are formed from the linear butenes and isobutene, respectively, and they yield distinctive CID patterns and reactivities. (eta-5-Cyclopentadienyl)yttrium ion, (eta-5-cyclohexadienyl)yttrium ion, (eta-7-cycloheptatrienyl)yttrium ion, and (eta-7-cyclooctatrienyl)yttrium ion are formed from 5-, 6-, 7-, and 8-membered cyclic alkenes, respectively.