om9b00875_si_002.xyz (18.3 kB)
Reactivity of a Two-Coordinate Cobalt(0) Cyclic (Alkyl)(amino)carbene Complex
dataset
posted on 2020-02-25, 17:37 authored by Jingzhen Du, Wenwei Chen, Qi Chen, Xuebing Leng, Yin-Shan Meng, Song Gao, Liang DengCyclic (alkyl)(amino)carbenes
(cAACs) are the merely known ligand
set being capable of stabilizing two-coordinate cobalt(0) complexes.
While two complexes of the type [(R2-cAAC)2Co]
[R2-cAAC = 5,5-dialkyl-3,3-dimethyl-2-(2′,6′-diisopropylphenyl)pyrrolidine-1-ylidene,
R = Me, Et] have been reported for years, little is known regarding
their reactivity. In this Article, we present the investigation on
the reactivity of [(Me2-cAAC)2Co] (2). Complex 2 can be synthesized in a high yield from
the reaction of [(Me2-cAAC)2CoCl] (1) with MeLi. The interaction of 2 with 1 equiv of ArBr
(Ar = phenyl, mesityl) or n-C8H17X (X = Br, Cl) in THF affords the corresponding cobalt(I) complex
[(Me2-cAAC)2CoX] (X = Cl, 1; Br, 3). The formation of ArH and n-C8H18 in these reactions and the relatively high half-wave
potential of [(Me2-cAAC)2Co]0/1+ over
that of [ArBr]0/1+ indicate an inner-sphere electron-transfer
character of the C–X bond cleavage reactions mediated by 2. The two-coordinate cobalt(I) complex [(Me2-cAAC)2Co][BArF4] (4) has been
synthesized from the reaction of 2 with [Cp2Fe][BArF4]. Complex 2 reacts with
the diazo compounds (p-tolyl)2CN2 and DmpCHN2 (Dmp = 2,6-dimesitylphenyl) to form [(Me2-cAAC)Co((η6-p-tolyl)(p-tolyl)CNN(Me2-cAAC))] (5) and
[(Me2-cAAC)2Co(σ-NNCHDmp)] (6), respectively. The formation of the azine ligand in 5 indicates the reactivity of the Co–C(carbene) bond in 2. In addition, the reaction of 2 with 4 equiv
of 2,6-dimethylphenyl isocyanide (XylNC) gives the ligand-substitution
product [(Me2-cAAC)Co(CNXyl)3] (7) and a ketenimine Me2-cAACCNXyl (8) in good
yields, and the interaction of 2 with 3-hexyne yields
a three-coordinate cobalt(0) complex bearing η2-alkyne
ligand [(Me2-cAAC)2Co(η2-EtCCEt)]
(9). The diversified reactivity of 2 arises
from the coordination–unsaturation and electron-rich (d9) nature of the cobalt center and demonstrates the promising
synthetic utility of cobalt(0) cAAC complexes.