posted on 2016-12-20, 00:00authored byMichael
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.