The catalytic activation and functionalization of carbon-hydrogen bonds. Aldimine formation by the insertion of isonitriles into aromatic carbon-hydrogen bonds

Abstract

Many examples of the activation of aromatic and aliphatic carbon-hydrogen bonds by homogeneous transition-metal complexes have appeared over the past few years, offering attractive new routes to organometallic species. While several of these reports involve oxidative addition of low valent metal complexes to alkanes or arenes, these new adducts have not proven to be useful for the generation of functionalized hydrocarbon products. Reports of successful metal-based alkane functionalization include free radical oxidations, intramolecular cyclizations of alkyl carbenoid species to given cyclopentanones, aromatic isonitrile insertion to give indoles, and alkane dehydrogenation to produce olefins. Arene functionalization reactions commonly depend upon the presence of tethering groups, although the production of benzaldehyde, benzoic acid, styrene, and phenylsiloxane insertion products have been recently reported. They report here a new type of iron catalyzed insertion of isonitrile into the C-H bond of arenes to produce aldimines (eq 1). RNC + C/sub 6/H/sub 6/ (Fe) ..-->.. ..delta..G/sup 0/ approx. = -11 Kcal/mol C/sub 6/H/sub 5/ - CH = NR (1).