Polycarbosilanes DOI: 10.1002/anie.200805840 Radical Polymerization of the Silene (Me 3 Si) 2 Si = CR 2 by Hydrogen Transfer from a Trimethylsilyl Group** Dmitry Bravo-Zhivotovskii,* Semyon Melamed, Victoria Molev, Nadejda Sigal, Boris Tumanskii, Mark Botoshansky, Gregory Molev, and Yitzhak Apeloig* Dedicated to Professor Armin de Meijere on the occasion of his 70th birthday Exciting progress has been achieved over the last two decades in the study of silenes — compounds with a Si =C bond –- and of other multiply bonded silicon compounds. [1] By analogy with the well-known polymerization of olefins, R 2 C = CR 2 , leading to polyolefins, it could be expected that silenes also polymerize to yield polycarbosilanes, (R 2 Si CR 2 ) n . Poly- carbosilanes have unique properties, and they are of signifi- cant practical interest. [2] It is therefore surprising that polymerization of a silene to form a polycarbosilane has not yet been reported. [3, 4] Herein, we report the polymerization of a silene, (Me 3 Si) 2 Si = Ad (1; Ad = 2-adamantylidene), which was gen- erated by thermal dissociation of its head-to-head dimer, the 1,2-disilacyclobutane 2. The polymerization product has a Si  Si C repeating moiety and 2-adamantyl side chains (structure P in Scheme 1). We provide evidence that the polymerization of 1 proceeds by a radical addition to the silicon terminus of the Si = C bond followed by hydrogen transfer from a trimethylsilyl group. We reported previously the generation of silene 1 by the thermal dissociation of 1,2-disilacyclobutane 2 in hydrocar- bons (Scheme 1, path a). [5] The conversion of 2 to 1 at 60 8C was demonstrated by NMR spectroscopy, [6] and by trapping 1 with various reagents. [7] Thermolysis at 150 8C of neat 2 yields a polymer P in 50 % yield (Scheme 1, paths a, b). Compound P was isolated by gel permeation chromatography (GPC) as an air- and water-stable white powder; a bimodal peak is observed in its chromatogram, corresponding to a molecular weight M w of 11 400 g mol 1 (Figure 1 a). [8] The 29 Si NMR spectrum of P (Figure 2) [9] has three broad signals: at 11.2 and 15.5 ppm, corresponding to a silicon atom bonded to one silicon and three carbon atoms [10] (Si b and Si g in P), and at 35.0 ppm, corresponding to a silicon atom bonded to two silicon and two carbon atoms [10] (Si a in P). According to this NMR spectrum, the structure of P is different from that expected for a polycarbosilane resulting from either a head-to-head (h-h, 3a) or a head-to-tail (h-t, 3b) polymerization of 1 (Scheme 1, paths c and d, respectively). First, 3a and 3b are expected to give rise to only two 29 Si NMR chemical shifts (not three, as observed); second, the backbone silicon atoms in 3a (each bonded to one carbon and Scheme 1. Possible polymerization modes of 1 and 2. See text for details. Figure 1. GPC curves (relative to a polystyrene standard) of a) polymer P obtained by thermolysis of neat 2 at 150 8C, and b) the crude mixture from the thermolysis of 2 in the presence of Na/K alloy. [*] Dr. D. Bravo-Zhivotovskii, S. Melamed, V. Molev, Dr. N. Sigal, Dr. B. Tumanskii, Dr. M. Botoshansky, G. Molev, Prof. Dr. Y. Apeloig Shulich Faculty of Chemistry and the Lise Meitner—Minerva Center for Computational Quantum Chemistry Technion—Israel Institute of Technology Haifa 32000 (Israel) Fax: (+ 972) 48294601 E-mail: chrbrzh@tx.technion.ac.il chrapel@tx.technion.ac.il [**] The authors thank the Israel Science Foundation administrated by the Israel Academy of Sciences and Humanities, the Minerva Foundation in Munich, and the Fund for the Promotion of Research at the Technion for financial support. D.B.-Z., B.T. and M.B. are grateful to the Ministry of Immigrant Absorption, State of Israel, for a “Kamea” scholarship. V.M. thanks the Israel Ministry of Science, Culture and Sport for a “Promotion of Women in Science” Scholarship. CR 2 = 2-adamantylidene. Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/anie.200805840. Communications 1834  2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. Int. Ed. 2009, 48, 1834 –1837