Taking advantage of two N-heterocyclic carbenes (NHCs), novel silyliumylidene ions 1a and 1b are prepared by a facile one-pot reaction of the corresponding dichlorosilanes with three equivalents of NHCs. For the first time, a C–H insertion reaction of phenylacetylene by a novel silyliumylidene ion is reported. The treatment of m-terphenyl substituted silyliumylidene ion 1a with three equivalents of phenylacetylene results in the formation of m-terphenyl substituted 1-alkenyl-1,1-dialkynylsilane 2.

The silicon analogues of an acylium ion, namely, sila-acylium ions 2a and 2b [RSi(O)(NHC)2]Cl stabilized by two N-heterocyclic carbenes (NHC = 1,3,4,5-tetramethylimidazol-2-ylidene), and having chloride as a countercation were successfully synthesized by the reduction of CO2 using the donor stabilized silyliumylidene cations 1a and 1b [RSi(NHC)2]Cl (1a, 2a; R = m-Ter = 2,6-Mes2C6H3, Mes = 2,4,6-Me3C6H2 and 1b, 2b; R = Tipp = 2,4,6-iPr3C6H2). Structurally, compound 2a features a four coordinate silicon center together with a double bond between silicon and oxygen atoms. The reaction of sila-acylium ions 2a and 2b with water afforded different products which depend on the bulkiness of aryl substituents. Although the exposure of 2a to H2O afforded a stable silicon analogue of carboxylate anion as a dimer form, [m-TerSi(O)O]2(2-)·2[NHC-H](+) (3), the same reaction with the less bulkier triisopropylphenyl substituted sila-acylium ion 2b afforded cyclotetrasiloxanediol dianion [{TippSi(O)}4{(O)OH}2](2-)·2[NHC-H](+) (4). Metric and DFT (Density Functional Theory) evidence support that 2a and 2b possess strong Si═O double bond character, while 3 and 4 contain more ionic terminal Si-O bonds. Mechanistic details of the formation of different (SiO)n (n = 2, 3, 4) core rings were explored using DFT to explain the experimentally characterized products and a proposed stable intermediate was identified with mass spectrometry.

Heavier analogues of silaacylium ions 2-4 ([m-TerSiE(NHC)]Cl; m-Ter = 2,6-MesCH; Mes = 2,4,6-MeCH; 2 (E = S), 3 (E = Se), 4 (E = Te)) were synthesized by the reaction of the NHC-stabilized silyliumylidene cation 1 with elemental chalcogens. Fascinating regeneration of 1 from the reaction of 2-4 with AuI was achieved, as successful recovery of a parent Si(ii) species from a silachalcogen Si(iv) compound. Furthermore, unique chalcogen exchange reactions from 4 → 3 → 2 were observed in line with the calculated silicon-chalcogen bond energies.

Depending on the reaction conditions, the base hydrolysis of (2,6-Mes2C6H3In)2(μ-Cl)2Cl2 (1) in a two-layer system of aqueous NaOH/diethyl ether or toluene afforded 2,6-Mes2C6H3InCl2·H2O (2), (2,6-Mes2C6H3In)2(μ-OH)2Cl2 (3), (2,6-Mes2C6H3In)3(μ-OH)4Cl2 (4), and (2,6-Mes2C6H3In)4(μ-OH)8 (5), respectively, in high yields. The indoxane 5 can be regarded as a heavier and aggregated congener of arylboronic acids. An attempt at preparing (2,6-Mes2C6H3Tl)2(μ-Cl)2Cl2 (6) by the chlorination of 2,6-Mes2C6H3Tl (prepared in situ from 2,6-Mes2C6H3Li and TlCl) using SO2Cl2 provided the isomeric diarylthallium cation [(2,6-Mes2C6H3)2Tl]TlCl4 (7). The exposure of crude reaction mixture consisting of 2,6-Mes2C6H3Tl and LiCl to moist air surprisingly produced (2,6-Mes2C6H3Tl)2(μ-OH)2Cl2 (8), which reacted with hydrochloric acid to give 6. Base hydrolysis of 8 in a two-layer system of aqueous NaOH/CHCl3 proceeded with partial cleavage of the m-terphenyl substituents and yielded the thalloxane cluster (2,6-Mes2C6H3Tl)4Tl2(μ3-O)4(μ-OH)6 (9) in moderate yield. Compounds 1−9 were characterized by X-ray crystallography.

COMMENTThe tin atom in Ph 2 Sn(S 2 CN(CH 2 ) 5 )Cl (Fig. 1) is fivecoordinated within a C 2 ClS 2 donor set that is best described as trigonal bipyramidal with the S1 and chlorine in the axial positions (Cl-Sn-S1 is 154.68(2)• ) as for the literature precedent.