N-Heterocyclic carbene and cyclic (alkyl)(amino)carbene ligated half-sandwich complexes of chromium(II) and chromium(I).

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