ChromiumSilicon Multiple Bonds: The Chemistry of Terminal N‐Heterocyclic‐Carbene‐Stabilized Halosilylidyne Ligands

AbstractAn efficient method for the synthesis of the first N‐heterocyclic carbene (NHC)‐stabilized halosilylidyne complexes is reported that starts from SiBr4. In the first step, SiBr4 was treated with one equivalent of the N‐heterocyclic carbene 1,3‐bis[2,6‐bis(isopropyl)phenyl]imidazolidin‐2‐ylidene (SIdipp) to give the 4,5‐dihydroimidazolium salt [SiBr3(SIdipp)]Br (1‐Br), which then was reduced with potassium graphite to afford the silicon(II) dibromide–NHC adduct SiBr2(SIdipp) (2‐Br) in good yields. Heating 2‐Br with Li[CpCr(CO)3] afforded the complex [Cp(CO)2CrSiBr(SIdipp)] (3‐Br) upon elimination of CO. Complex 3‐Br features a trigonal‐planar‐coordinated silicon center and a very short CrSi double bond. Similarly, the reaction of SiCl2(SIdipp) (2‐Cl) with Li[CpCr(CO)3] gave the analogous chloro derivative [Cp(CO)2CrSiCl(SIdipp)] (3‐Cl). Complex 3‐Br undergoes an NHC exchange with 1,3‐dihydro‐4,5‐dimethyl‐1,3‐bis(isopropyl)‐2H‐imidazol‐2‐ylidene (IMe2iPr2) to give the complex [Cp(CO)2CrSiBr(IMe2iPr2)2] (4‐Br). Compound 4‐Br features a distorted‐tetrahedral four‐coordinate silicon center. Bromide abstraction occurs readily from 4‐Br with Li[B(C6F5)4] to give the putative sil