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

Abstract

An efficient method for the synthesis of the first N-heterocyclic carbene (NHC)-stabilized halosilylidyne complexes is reported that starts from SiBr(4). In the first step, SiBr(4) 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 [SiBr(3)(SIdipp)]Br (1-Br), which then was reduced with potassium graphite to afford the silicon(II) dibromide-NHC adduct SiBr(2)(SIdipp)(2-Br) in good yields. Heating 2-Br with Li[CpCr(CO)(3)] afforded the complex [Cp(CO)(2)Cr=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 SiCl(2)(SIdipp) (2-Cl) with Li[CpCr(CO)(3)] gave the analogous chloro derivative [Cp(CO)(2)Cr=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 (IMe(2)iPr(2)) to give the complex [Cp(CO)(2)CrSiBr(IMe(2)iPr(2))(2)] (4-Br). Compound 4-Br features a distorted-tetrahedral four-coordinate silicon center. Bromide abstraction occurs readily from 4-Br with Li[B(C(6)F(5))(4)] to give the putative silylidene complex salt [Cp(CO)(2)Cr=Si(IMe(2)iPr(2))(2)][B(C(6)F(5))(4)], which irreversibly dimerizes by means of an Si-promoted electrophilic activation of one carbonyl oxygen atom to yield the dinuclear siloxycarbyne complex [Cp(CO)Cr{(μ-CO)Si(IMe(2)iPr(2))(2)}(2-)Cr(CO)Cp][B(C(6)F(5))(4)](2) (5). All compounds were fully characterized, and the molecular structures of 2-Br-5-Br were determined by single-crystal X-ray diffraction. DFT calculations of 3-Br and 3-Cl and their carbene dissociation products [Cp(CO)(2)Cr=Si-X] (X=Cl, Br) were carried out, and the electronic structures of 3-Br, 3-Cl and [Cp(CO)(2)Cr=Si-X] were analyzed by the natural bond orbital method in combination with natural resonance theory.

An Air‐Stable Heterobimetallic Si2M2 Tetrahedral Cluster

“…The IR spectra of 2 and 3 each show two ν (CO) absorption bands at 1782 and 1864 cm −1 ( 2 ), and at 1770 and 1849 cm −1 ( 3 ). The positions of these bands agree well with previously reported metal arylsilylidene complexes and our predictions by density functional theory (DFT) calculations ( 3 : 1837 and 1892 cm −1 ) . Single crystals of 2 and 3 were obtained from a toluene/pentane (1:3) mixture at ambient temperature, and the structure in the solid state was determined by X‐ray diffraction analysis (Figure ).…”

London Dispersion Interactions in Pnictogen Cations [ECl2]+ and [E=E]2+ (E=P, As, Sb) Supported by Anionic N‐Heterocyclic Carbenes

“…As noted above, compounds of the latter type can be formally regarded as NHC adducts of pnictenium ions [EX 2 ] + , and accordingly, the compounds 2 – 4 represent neutral zwitterionic analogues, in which the negative charge is localized intramolecularly in the borate moiety. Similarly, 2 – 4 are also closely related to neutral NHC‐tetrylene adducts (NHC)EX 2 (E=Si, Ge, Sn) such as (IDipp)SiCl 2 , (IDipp)SiBr 2 , (IDipp)GeCl 2 , (IDipp)SnCl 2 , and related species . All these compounds exhibit similar trigonal‐pyramidal geometries, but differ in the orientation of the EX 2 units from that in 2 – 4 , since one of the E−X bonds is generally aligned with the imidazole plane.…”

Recent Advances in Silylene Chemistry: Small Molecule Activation En-Route Towards Metal-Free Catalysis

“…See: [55] Finally an NHC-stabilised dibromosilylene, similar to 63 with the exception that the NHC is saturated in the backbone (63-b), has also been reported to engage in interesting chemistry with Cr precursors [64]. Accordingly, reaction of this silylene with Li[CpCr(CO) 3 ] afforded the novel halo-substituted NHC-stabilised silylene complex [Cp(CO) 2 ¼ {SiBr(SIDipp)}] (68) with concomitant LiBr formation (Scheme 20).…”