Synthesis, Properties, and Reactivity of a Linear NHC-Based Chromium(I) Silylamide

Abstract

We describe the synthesis of the linear N-heterocyclic carbene (NHC)-based chromium(I) silylamide [(IMes)Cr(N{Dipp}-Si i Pr 3 )] (IMes = 1,3-dimesityl-imidazol-2-ylidene, Dipp = 2,6-di-isopropylphenyl) via protolytic ligand displacement of the homoleptic chromium(I) silylamide [KCr(N{Dipp}Si i Pr 3 )] with the imidazolium salt IMes•HCl. This could also be extended to the bulkier NHC IDipp (IDipp = 1,3-bis(2,6-di-iso-propylphenyl)imidazol-2-ylidene). Analysis of the magnetic properties of [(IMes)Cr(N{Dipp}Si i Pr 3 )] reveals an isotropic high-spin S = 5/2 state. First reaction studies with this linear chromium(I) complex yields with CO the four-coordinate chromium dicarbonyl complex [(IMes)Cr(CO) 2 (N{Dipp}Si i Pr 3 )], with benzyl bromide oxidation to the trigonal chromium(II) bromide [(IMes)-Cr(Br)(N{Dipp}Si i Pr 3 )], and with DippN 3 the first three-coordinate chromium(III) imide ([(IMes)Cr(NDipp)(N{Dipp}Si i Pr 3 )]).

A Linear Two‐Coordinate Cr(II) Complex: Synthesis, Characterization, and Reactivity

“…It is worth noting that 4 and 5 are the rare three‐coordinate Cr imido complexes. Other related examples are the Cr(IV) imido complexes supported by two bulky siloxide [24] or alkoxide ligands, [25] Cr(OSi t Bu 3 ) 2 {N(2,6‐Ph 2 ‐C 6 H 3 )} and Cr(OC t Bu 2 Ph) 2 (NR) (R=Mesityl, Ad, 2,6‐Et 2 ‐C 6 H 3 ), reported by the Wolczanski group and the Groysman group, respectively, and the Cr(III) imido complex (IMes)Cr(NDipp){N(Si i Pr 3 )Dipp} supported by an N ‐heterocyclic carbene and a bulky amido ligand reported by Werncke and coworkers [18] . The effective magnetic moments ( μ eff ) measured using the Evans method by 1 H NMR spectroscopy in C 6 D 6 solutions are 2.91(1) μ B for 4 and 2.87(4) μ B for 5 , suggesting a d 2 Cr(IV) electron configuration.…”

“…However, reactivity studies on two‐coordinate Cr complexes are relatively rare, presumably due to the low number of such complexes reported. Representative examples include Tilley's chemical oxidation and reduction reactions of Cr{N(Si i Pr 3 )Dipp} 2 and Werncke's two‐coordinate Cr(I) complex (IMes)Cr{N(Si i Pr 3 )Dipp} 2 (IMes=1,3‐bis(1,3,5‐trimethylphenyl)imidazol‐2‐ylidene) [11,18] . We previously reported the reaction of an analogous Fe(II) complex, Fe{N( t Bu)Dipp} 2 , with organic azides to afford a Fe(III) imidyl complex [19] .…”

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

“…Since the first synthesis of a monodentate NHC ligated Cr( ii ) complex in 1997, 23 various NHC 24 and cAAC 25 ligated Cr( ii ) and Cr( iii ) complexes were reported, some of which already found application as catalysts 26 and represent a vibrant field of research to this date. 27 For example, in 2010 Zhu and coworkers reported the molecular structures of the di- and mononuclear complexes [{Cr(IiPr Me )Cl(μ-Cl)(thf)} 2 ] ( vide infra ) and [Cr(IiPr Me ) 2 Cl 2 ], yet a derivatization of the latter with NaC 5 H 5 proved to be unsuccessful ( vide infra ). 28 Shortly afterwards, Stasch, Jones and Stasch established the molecular structures of [Cr(IDipp) 2 Cl 2 ] (IDipp = 1,3-bis(2,6-diisopropylphenyl)-imidazolin-2-ylidene) and [Cr(IiPr Me ) 2 Cl 2 ], presented earlier by Zhu et al 24 d ,29…”