N-Heterocyclic carbene and cyclic (alkyl)(amino)carbene ligated half-sandwich complexes of chromium(ii) and chromium(i)

Abstract

The synthesis and characterization of a series of Cr(II) N-Heterocyclic Carbene (NHC) complexes of the type [{Cr(NHC)Cl(μ-Cl)}₂] and [(Cyp)Cr(NHC)X] (Cyp = η⁵-C₅H₅, cyclopentadienyl; η⁵-C₅Me₅, pentamethylcyclopentadienyl; X = Cl, η³-C₃H₅; NHC = IMe^Me, IiPr^Me, IMes, IDipp) as well as the cyclic (alkyl)(amino)carbene cAAC^Me ligated complexes [(η⁵-C₅H₅)Cr(cAAC^Me)X] (X = Cl, NPh₂), [(η⁵-C₉H₇)Cr(cAAC^Me)Cl] (C₉H₇ = Ind, indenyl) and [(η⁵-C₁₃H₉)Cr(cAAC^Me)Cl] (C₁₃H₉ = Fl, fluorenyl) are reported. The reduction of [(η⁵-C₅Me₅)Cr(IMe^Me)Cl] with KC₈ in the presence of CO afforded the NHC ligated Cr(I) metallo-radical [(η⁵-C₅Me₅)Cr(IMe^Me)(CO)₂]. Quantum chemical calculations performed on [(η⁵-C₅Me₅)Cr(IMe^Me)(CO)₂] confirm for this complex a predominantly chromium centered radical.