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Oxidative C–C Bond Formation Reactivity of Organometallic Ni(II), Ni(III), and Ni(IV) Complexes

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posted on 2016-12-20, 00:00 authored by Michael B. Watson, Nigam P. Rath, Liviu M. Mirica
The use of the tridentate ligand 1,4,7-trimethyl-1,4,7-triazacyclononane (Me3tacn) and the cyclic alkyl/aryl C-donor ligand -CH2CMe2-o-C6H4- (cycloneophyl) allows for the synthesis of isolable organometallic NiII, NiIII, and NiIV complexes. Surprisingly, the five-coordinate NiIII complex is stable both in solution and the solid state, and exhibits limited C-C bond formation reactivity. Oxidation by one electron of this NiIII species generates a six-coordinate NiIV complex, with an acetonitrile molecule bound to Ni. Interestingly, illumination of the NiIV complex with blue LEDs results in rapid formation of the cyclic C-C product at room temperature. This reactivity has important implications for the recently developed dual Ni/photoredox catalytic systems proposed to involve high-valent organometallic Ni intermediates. Additional reactivity studies show the corresponding NiII species undergoes oxidative addition with alkyl halides, as well as rapid oxidation by O2, to generate detectable NiIII and/or NiIV intermediates and followed by C-C bond formation.

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