Low-Valent Aminopyridinato Chromium Methyl Complexes via Reductive Alkylation and via Oxidative Addition of Iodomethane by a Cr–Cr Quintuple Bond

The reaction of 1 equiv of the deprotonated
(sterically demanding)
aminopyridine Ap*-H (Ap*-H = (2,6-diisopropylphenyl)-[6-(2,4,6-triisopropylphenyl)­pyridin-2-yl]­amine)
with [CrCl3(thf)3] led selectively to the monomeric
complex [Ap*CrCl2(thf)2]. Methylation of [Ap*CrCl2(thf)2] by methyllithium gave rise to a mixture
of a dichromium methylidene and a dichromium methyl complex. Alkylation
of [Ap′CrCl2(thf)2] (Ap′-H = (2,6-diisopropylphenyl)-[6-(2,6-dimethylphenyl)­pyridin-2-yl]­amine)
afforded selectively the dimethyl complex [Ap′2CrCr­(CH3)2]. In addition to reductive alkylation, oxidative
addition can be used to synthesize chromium methyl complexes. Selective
oxidative addition was observed when CH3I was reacted with
the quintuply bonded CrI dimer [Ap′CrCrAp′].
Here, the Grignard-like Cr2 compound [Ap′2CrCr­(μ-I)­(μ-CH3)] was formed. DFT calculations
were performed to investigate the electronic structure of the organometallic
complexes.