Evidence for the activation of unstrained carbon-carbon bonds by bare transition metal ions M+ (M = Fe, Co) without prior C-H bond activation

Abstract

The metastable ion (MI) decompositions of RNH 2 /M + complexes (R = (C 2 H 5 ) 2 CHCH 2 , C 2 H 5 C(CH 3 ) 2 CH 2 ; M=Fe, Co) in the gas phase have been studied by tandem mass spectrometry with a four-sector instrument of BEBE configuration. The analyses of the MI spectra of isotopically labeled complexes uncover processes which inter alia demonstrate that the loss of C 4 H 8 corresponds to a reaction in which site-specific oxidative addition of an unstrained C-C bond to the «anchored» transition-metal ion M + takes place without prior C-H bond activation. The intramolecular methyl migration preceding the elimination of C 4 H 8 is subject to a secondary kinetic isotope effect of k H /k D = 1.33 for M + = Fe + and k H /k D = 1.15 for M + = Co + per D atom. Additional processes observed correspond to the generation of molecular hydrogen, methane, ethylene and ethane. All reactions are highly specific, and mechanisms are suggested that are in keeping with the labeling data