Synergy of Theory and Experiment in the Remote Functionalization of Aliphatic Nitriles by “Bare” Fe(I) and Co(I) Cations in the Gas Phase

Abstract

The remote functionalization of aliphatic nitriles by the “bare” transition-metal ions Fe+ and Co+ has been investigated by means of extensive quantum chemical calculations and tandem mass spectrometry. The present investigation focuses on the chemo- and regioselectivity of bond activation, using an adequate computational strategy in conjunction with extensive labeling experiments. Nonanitrile, decanitrile, and undecanitrile have been studied experimentally; both metal ions exhibit an overall similar reactivity pattern, and molecular hydrogen, methane, and small olefins, respectively, are formed as major neutral fragments. In the theoretical study, structural and energetic aspects of the nonanitrile/M+ complexes have been investigated in great detail. For both Fe+ and Co+, the most favorable pathway of bond activation proceeds via initial C−H bond insertion at C(8), followed by exocyclic activation of a C−H bond and reductive elimination of molecular hydrogen via a multicentered transition structure. The calculated barriers lead to predictions with regard to the chemo- and regioselectivity of C−H and C−C bond activation pathways, and these predictions nicely agree with the findings of experiments performed afterward. In contrast to earlier experimental results, the present calculations reveal no evidence for the two metal ions Fe+ and Co+ to activate CH-bonds at different positions in the aliphatic chain. The implications of the present investigations are used to derive a more general mechanistic picture of remote functionalization in the gas phase.