Diverse Reactivity of an Iron–Aluminium Complex with Substituted Pyridines

Abstract

The reaction of an Fe–Al complex with an array of substituted pyridines is reported. Depending on the substitution pattern of the substrate site-selective sp2 or sp3 C–H bond activation is observed. A series of reaction products are observed based on (i) C–Al bond formation, (ii) C–C bond formation by nucleophilic addition or (iii) deprotonation of the β-diketiminate ligand. A divergent set of mechanisms involving a common intermediate is proposed.

Cooperative activation of carbon–hydrogen bonds by heterobimetallic systems

“…Secondly, the regioselectivity and stereospecificity of the reaction directly arise from the decisive last transition state and therefore require the participation of both metal centers. 111 While the previous examples are stoichiometric activations, the group of Nakao reported a Rh-Al complex 114 able to catalyze the C2-selective functionalization (silylation or alkylation) of pyridines. 112,113,115 The Rh center is coordinated by an X-type PAlP pincer ligand and provides a catalytic site for the regioselective oxidative insertion into the C2-H bond of pyridine.…”

“…26 Cooperative C-H activation of vinyl derivatives by a Fe/Al complex. 111 Fig. 27 Proposed mechanism for the selective C2-silylation or alkylation of pyridines catalyzed by a Rh/Al complex.…”

“…26 ). 111 The reaction pathway involves the formation of a pseudo [2 + 2] cycloadduct from the reaction of the alkene with the metal–metal bond. This cycloaddition intermediate is then converted into the hydrido vinyl product in a rate-determining C–H cleavage step, a highly unusual oxidative addition of a non-aromatic C (sp 2 ) –H bond across two adjacent metal centers.…”

“…Secondly, the regioselectivity and stereospecificity of the reaction directly arise from the decisive last transition state and therefore require the participation of both metal centers. 111 …”