Electronic Effects on the β-Alkyl Migratory Insertion Reaction of para-Substituted Styrene Methyl Palladium Complexes

Abstract

The β-methyl migratory insertion chemistry of a series of cis-coordinated styrene methyl complexes of palladium [(phen)Pd(CH3)(p-X-C6H4CHCH2)+Ar‘4B- (2X) (phen = 1,10-phenanthroline; X = CF3, Cl, H, CH3, OCH3; Ar‘ = 3,5-(CF3)2C6H3)] has been investigated. Complexes 2X are prepared in situ from the addition of p-X-styrene to CD2Cl2 solutions of (phen)Pd(CH3)(OEt2)+Ar‘4B- (1). The X-ray structure of 1 has been determined [P21/c; a = 16.460(4) A, b = 18.911(3) A, c = 17.374(3) A; β = 117.996(14)°; V = 4775.2(15) A3; Z = 4] at −78 °C. The rearrangement of 2X, via β-CH3 migratory insertion then arene coordination, to yield (phen)Pd(η3-CH(CH2CH3)(C6H4-p-X)+Ar‘4B- (3X) has been studied by 1H NMR spectroscopy. The rearrangement is accelerated by electron-withdrawing groups; a Hammett analysis at −29.2 °C reveals that log k values are best fit by σp parameters: ρp = 1.1 ± 0.1, r = 0.992. The anti-isomer of 3H has been structurally characterized: P21/n; a = 13.950(4) A, b = 15.582(5) A, c = 24.004(8) A; β = 101.9...