The
N-heterocyclic carbene supported three-coordinate Ni(I) complex
(IPr)Ni(κ1-N-N(
i
Pr)C(O)
t
Bu)(CNXyl) ([2-CNXyl]; CNXyl = 2,6-dimethylphenyl isocyanide) undergoes disproportionation
with 1 equiv of CNXyl to afford an equimolar mixture of Ni(0) and
Ni(II) complexes (IPr)Ni(CNXyl)3 ([3-CNXyl]) and (IPr)Ni(κ2-N,O-N(
i
Pr)CO(
t
Bu))2 ([4]), respectively. Complexes [3-CNXyl] and [4] are also produced when 2 equiv of the isonitrile
CNXyl is added to (IPr)Ni(κ3-N,bis(H
2
CMe)-N(
i
Pr)C(O)
t
Bu) ([1]).
Furthermore, we show that reactions with π-acceptors CO and
select alkenes also result in disproportionation. In the case of CO
we show that reactions in the solid state afford selectivity for and
isolation of the reaction intermediate (IPr)Ni(κ1-N-N(
i
Pr)C(O)
t
Bu)(CO) ([2-CO]), which is not isolable
by solution methods. Kinetic analysis of the disproportionation reaction
with alkenes suggests that the reaction is first order in both nickel
and alkene. Preliminary trapping experiments rule out amidyl radicals
as intermediates in these reactions. We propose instead that a bimolecular
ligand transfer is operative, in part due to the hemilabile nature
of amidate ligands.
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