N‐Heterocyclic Carbene and Cyclic (Alkyl)(amino)carbene Adducts of Antimony(III)

Abstract

A systematic study on Lewis‐acid/base adducts of N‐heterocyclic carbenes (NHCs) and the cyclic (alkyl)(amino)carbene cAACMe (1‐(2,6‐di‐iso‐propylphenyl)‐3,3,5,5‐tetramethyl‐pyrrolidin‐2‐ylidene) with antimony(III) chlorides of the general formula SbCl2R (R=Cl, Ph, Mes) is presented. The reaction of the NHCs Me2ImMe (1,3,4,5‐tetra‐methyl‐imidazolin‐2‐ylidene), iPr2ImMe (1,3‐di‐isopropyl‐4,5‐dimethyl‐imidazolin‐2‐ylidene), Mes2Im, Dipp2Im (R2Im=1,3‐di‐organyl‐imidazolin‐2‐ylidene; Mes=2,4,6‐trimethylphenyl, Dipp=2,6‐di‐isopropylphenyl) and cAACMe with antimony(III) compounds SbCl2R (R=Cl (1), Ph (2) and Mes (3)) yields the adducts NHC ⋅ SbCl2R (R=Cl (4), Ph (5) and Mes (6); NHC=Me2ImMe (a), iPr2ImMe (b), Dipp2Im (c) and Mes2Im (d)) and cAACMe ⋅ SbCl2R (R=Cl (4 e) and Ph (5 e)). Thermal treatment of (Dipp2Im) ⋅ SbCl2Ar (Ar=Ph (5 c) and Mes (6 c)) in benzene leads to isomerization to the backbone coordinated aNHC‐adduct aDipp2Im ⋅ SbCl2Ar (Ar=Mes (7) and Ph (8)) (“a” denotes “abnormal” coordination mode of the NHC) in high yields. One of the chloride substituents at antimony of 7 can be abstracted by GaCl3 or Ag[BF4] to obtain the imidazolium salts [aDipp2Im ⋅ SbClMes][BF4] (9) and [aDipp2Im ⋅ SbClMes][GaCl4] (10).

Carbene chemistry of arsenic, antimony, and bismuth: origin, evolution and future prospects

“…15a). 40 The solid-state structures of 35–47 are essentially isostructural and adopt a distorted see-saw geometry at antimony, a feature that is commonly found in these carbene–pnictogen adducts (Fig. 15b).…”

A Versatile Route To Cyclic (Alkyl)(Amino)Carbene‐Stabilized Stibinidenes

“…cAAC Cy ⋅SbCl: 205.6 ppm in toluene‐d 8 , [11] DAC Mes ⋅SbPh: 205.6 ppm, C 6 D 6 ) [12] ). These resonances were remarkably shifted compared to free carbene (cAAC Me : 313.6 ppm, and cAAC Cy : 316.2 ppm)., and also in a different region as compared to the chlorostibane(III) adduct cAAC Me ⋅SbCl 2 Ph (225.8 ppm) [15] …”

“…[19] We have demonstrated previously on several occasions that these partially dissociated substituents can be easily transferred to Lewis acids. [15,19] The Lewis acid used here is SbCl 2 Mes, and chloride transfer from cAAC Me •SbCl 2 Mes to SbCl 2 Mes should form a contact ion pair [cAAC Me •SbClMes][SbCl 3 Mes] (3). The next step is chlorine abstraction from the cationic part of 3, either by simple chloride transfer to the carbene carbon atom of the cAAC or by cAAC addition to cationic [cAAC Me •SbClMes] + and subsequent elimi- formal transfer of "Cl + " from [cAAC Me •SbClMes] + to the cAAC, which makes in total the carbene carbon atom of cAAC Me the reducing reagent.…”

“…Furthermore, the characteristic septet of the cAAC methine protons (2 a, iPr-CH, 3.05 ppm; 2 b, iPr-CH, 3.06 ppm) is shifted compared to either the free carbene (cAAC Me : iPr-CH, 3.13 ppm; cAAC Cy : iPr-CH, 3.15 ppm) or to the Lewis acid/base adduct cAAC Me •SbCl 2 Ph (iPr-CH, 3.25 ppm). [15] The 13 C{ 1 H} NMR resonances of the carbene carbon atom at 238.7 ppm and 239.4 ppm were also indicative for the formation of the cAACstabilized stibinidenes 2 a and 2 b (cf. cAAC Cy •SbCl: 205.6 ppm in toluene-d 8 , [11] DAC Mes •SbPh: 205.6 ppm, C 6 D 6 ) [12] ).…”

N-heterocyclic carbene and cyclic (alkyl)(amino)carbene adducts of plumbanes and plumbylenes

“…1 i ,2 Our group has been interested in NHC coordination chemistry and reactivity of the p-block elements over years, 3 lately especially in the chemistry of the heavier p-block elements such as gallium, 4 tin 5 and antimony. 6 Investigations on NHC-supported group 14 elements in general led to a plethora of new compounds and reactivities in recent years, 1 g – i ,2 c ,7 for example various group 14 element motifs in the oxidation state 0, such as monomeric (cAAC R ) 2 E (R = Me, Cy; E = Si, 8 Ge 9 ), the dimeric (Dipp 2 Im) 2 E 2 (E = Si, 10 Ge, 11 Sn 12 ) (1,3-bis-(2,6-di-isopropylphenyl)-imidazolin-2-ylidene), (cAAC R ) 2 Si 2 13 (R = Me, Cy) and the trimeric (cAAC Me ) 3 Si 3 . 14 In contrast, the chemistry of carbene ligated lead compounds is remarkably underdeveloped.…”