ic502670x_si_002.pdf (3.36 MB)
Protonolysis and Amide Exchange Reactions of a Three-Coordinate Cobalt Amide Complex Supported by an N‑Heterocyclic Carbene Ligand
journal contribution
posted on 2015-05-18, 00:00 authored by Christopher B. Hansen, Richard
F. Jordan, Gregory L. HillhouseA three-coordinate cobalt species,
IPrCoCl{N(SiMe3)2} [1; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene],
was synthesized by the reaction of {IPrCoCl2}2 with NaN(SiMe3)2. Compound 1 is
a useful starting material for low-coordinate (IPr)Co species. 1 reacts with 2,6-di-tert-butyl-4-methylphenol
(BHT-H) via aminolysis of the Co–N bond to generate a three-coordinate
phenoxide complex, IPrCoCl(O-2,6-tBu2-4-MeC6H2) (2). The reaction of 1 with 2,6-diisopropylaniline (NH2DIPP) generates IPrCoCl(NHDIPP)
(4), which undergoes disproportionation to form a mixture
of 4, {IPrCoCl2}2, and IPrCo(NHDIPP)2 (3). The same product mixture is formed by the
reaction of 1 with Li[NH(DIPP)], which unexpectedly proceeds
by amide exchange. Compound 3 was synthesized independently
by the reaction of {IPrCoCl2}2 with 4 equiv
of Li[NH(DIPP)]. The reaction of 1 with the bulkier lithium
2,6-dimesitylanilide (LiNHDMP) also proceeds by amide exchange to
generate IPrCoCl(NHDMP) (5), which is stable toward disproportionation.
Compounds 1 and 2 exhibit trigonal-planar
geometries at cobalt in the solid state. The solid-state structure
of 3 also contains a trigonal-planar cobalt center and
exhibits close Co---H contacts involving the methine hydrogen atoms
of the NH(DIPP) groups in the axial positions. The solid-state structure
of 5 features an interaction between cobalt and a flanking
aryl group of the anilide ligand, resulting in pyramidalization of
the cobalt center.
