DOI: 10.1002/chem.201203242 Reaction of N-Heterocyclic Silylenes with Thioketone: Formation of Silicon– Sulfur Three- (Si-C- S ) and Five- (Si-C-C-C- S ) Membered Ring Systems Ramachandran Azhakar, [a] Rajendra S. Ghadwal,* [a] Herbert W. Roesky,* [a] Ricardo A. Mata,* [b] Hilke Wolf, [a] Regine Herbst-Irmer, [a] and Dietmar Stalke* [a] Introduction Silylenes are divalent silicon atom containing species that contain silicon atoms and are considered to be silicon ana- logues of carbenes. [1] After the first report of stable N-heter- ocyclic silylene (NHSi) by West et al. [2] in 1994, many stable NHSi compounds as well as other substituted silylenes have been isolated. [1b–f, 3] Stable silylenes have been the subject of interest in terms of both theoretical and experimental as- pects. [4] The reactivities of NHSi compounds are to some extent comparable with those of N-heterocyclic carbenes (NHCs). The latter find widespread applications in different fields of chemistry. [5, 6] The reactivity of silylenes is associat- ed with the presence of both a lone pair of electrons and a vacant p orbital at the silicon atom. Thus, silylenes undergo reactions with Lewis acids and bases. [4] Owing to the ambi- philic nature of NHSi compounds, extensive research is being carried out on insertion, [7] addition reactions, [8] and metal complex formations. [9, 10] Silylenes are highly reactive and provide an alternative route to new, previously inacces- sible organosilicon compounds that are difficult to prepare by conventional methods. Furthermore, three-membered ring compounds that possess higher-coordinated silicon at the position adjacent to the heteroatom have attracted the attention of chemists because of their unique structure and their application in synthetic chemistry. [11] Three-membered ring compounds bearing a silicon atom are interesting on ac- count of their high strain and novel bonding arrangement within the ring. [12] In the case of the sulfur-supported Brook rearrangement, the transition state has been proposed as a three-membered ring compound bearing a pentacoordinate silicon at the position adjacent to the sulfur atom. [13] The first structurally characterized silathiacyclopropane was re- ported by Ando et al., obtained by the reaction of dimesityl- silylene with 1,1,3,3-tetramethyl-2-indanethione. [14a] In 1994, Brook et al. isolated silathiacyclopropane from the reaction of silene with elemental sulfur. [14b] Owing to the high ring strain of the three-membered ring, only a few silicon com- pounds with heteroatoms have been reported so far. [1b–f] Currently we are interested in the chemistry of silylenes. The diverse properties of LSiCl (1; L = PhCACHTUNGTRENNUNG(NtBu) 2 ) and L’Si (2 ; L’ = CHACHTUNGTRENNUNG{(C =CH 2 )ACHTUNGTRENNUNG(CMe)(2,6-iPr 2 C 6 H 3 N) 2 }) with or- ganic substrates inspired us to further explore their chemis- try. Among them, reactions with ketones are quite interest- ing, and the choice of silylene plays a key role in the prod- uct formation. [1b–f] We were curious to explore the reactivity of silylenes with thioketones. Herein, we report for the first time on the reactivity of a thioketone with stable N-hetero- Abstract: Three- and five-membered rings that bear the (Si-C- S ) and (Si-C- C-C- S ) unit have been synthesized by the reactions of LSiCl (1; L = PhC- ACHTUNGTRENNUNG(NtBu) 2 ) and L’Si (2 ; L’ = CHACHTUNGTRENNUNG{(C= CH 2 )ACHTUNGTRENNUNG(CMe)(2,6-iPr 2 C 6 H 3 N) 2 }) with the thioketone 4,4’-bis(dimethylamino)- thiobenzophenone. Treatment of 4,4’- bis(dimethylamino)thiobenzophenone with LSiCl at room temperature fur- nished the [1+2]-cycloaddition product silathiacyclopropane 3. However, reac- tion of 4,4’-bis(dimethylamino)thioben- zophenone with L’Si at low tempera- ture afforded a [1+4]-cycloaddition to yield the five-membered ring product 4. Compounds 3 and 4 were character- ized by NMR spectroscopy, EIMS, and elemental analysis. The molecular structures of 3 and 4 were unambigu- ously established by single-crystal X- ray structural analysis. The room-tem- perature reaction of 4,4’-bis(dimethyl- ACHTUNGTRENNUNGamino)thiobenzophenone with L’Si re- sulted in products 4 and 5, in which 4 is the dearomatized product and 5 is formed under the 1,3-migration of a hydrogen atom from the aromatic phenyl ring to the carbon atom of the C À S unit. Furthermore, the optimized structures of probable products were investigated by using DFT calculations. Keywords: cycloaddition · density functional calculations · silylenes · small-ring systems · thioketones [a] Dr. R. Azhakar, Dr. R. S. Ghadwal, Prof.Dr. H. W. Roesky, H. Wolf, R. Herbst-Irmer, Prof. Dr. D. Stalke Institut für Anorganische Chemie der Universität Gçttingen Tammannstrasse 4, 37077 Gçttingen (Germany) E-mail : rghadwal@uni-goettingen.de hroesky@gwdg.de dstalke@chemie.uni-goettingen.de [b] Prof. Dr. R. A. Mata Institut für Physikalische Chemie der Universität Gçttingen Tammannstrasse 6, 37077 Gçttingen (Germany) E-mail : rmata@gwdg.de Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201203242. Chem. Eur. J. 2013, 00,0–0 # 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim These are not the final page numbers! ÞÞ &1& FULL PAPER