COMPETITIVE CHAIN TRANSFER BY BETA-HYDROGEN AND BETA-METHYL ELIMINATION FOR THE MODEL ZIEGLER-NATTA OLEFIN POLYMERIZATION SYSTEM [ME2SI(ETA(5)-C5ME4)2]SC(CH2CH(CH3)2)(PME3)

The reaction of OpSc(H)(PMe3) (Op = {(eta-C5Me4)2SiMe2}) with isobutene produces OpSc(CH3)(PMe3) along with isobutene, 2-methylpentane, isobutene, 2-methyl-1-pentene, propane, and n-pentane. These products arise from a series of reactions involving olefin insertion, beta-CH3 and (faster) beta-H elimination which proceed until only the 2-methyl-1-alkenes (C4H8, C6H12, etc.) and the predominant organoscandium product OpSc(CH3)(PMe3) remain. A transient observed in the reaction sequence has been unambiguously characterized as OpSc(CH2CH2CH3)(PMe3). Slower sigma bond metathesis involving the methyl C-H bonds of PMe3 and the Sc-C bonds of the scandium alkyls accounts for the observation of saturated alkanes (2-methylalkanes (C4H10, C6H14, etc.), normal alkanes (C3H8, C5H12, etc.), and a minor organoscandium product OpScCH2-PMe2 in the product mixture. Beta-ethyl migration is not observed for the closely related 2-ethylbutyl derivative, OpSc{CH2CH(C2H5)CH2CH3}(PMe3), obtained from reaction of 2-ethyl-1-butene with OpSc(H)(PMe3).