Published: August 01, 2011 r2011 American Chemical Society 4475 dx.doi.org/10.1021/om200477a | Organometallics 2011, 30, 4475–4478 COMMUNICATION pubs.acs.org/Organometallics Synthesis and Characterization of Octakis(3-propyl ethanethioate)- octasilsesquioxane Vuthichai Ervithayasuporn,* ,†,‡ Thapakorn Tomeechai, † Nobuhiro Takeda, § Masafumi Unno, § Arada Chaiyanurakkul, † Rangsinee Hamkool, † and Tanakorn Osotchan ‡,^ † Department of Chemistry, Faculty of Science, Mahidol University, Rama VI Road, Ratchathewi, Bangkok 10400, Thailand ‡ Capability Building Unit for Nanoscience and Nanotechnology, Faculty of Science, Mahidol University, Rama VI Road, Ratchathewi, Bangkok 10400, Thailand § Department of Chemistry and Chemical Biology, Graduate School of Engineering, Gunma University, Kiryu, Gunma 376-8515, Japan ^ Department of Physics, Faculty of Science, Mahidol University, Rama VI Road, Ratchathewi, Bangkok 10400, Thailand b S Supporting Information A lkyl ethanethioates (R-SAc) have been widely used as precursors for alkyl thiols (R-SH), 1,2 alkyl sulfides (R-S- R 0 ), 3 and alkyl sulfonic acids (R-SO 3 H). 4 These compounds are usually prepared from primary halides and potassium thioacetate through a nucleophilic substitution, and numerous methods have been developed to optimize the yield of alkyl ethanethioates. 57 Dijs et al. reported on the modification of alkyl surface-function- alized silica by thioacetate substitution and its subsequent oxidation to a sulfonic acid group; they have also presented a novel synthetic route for obtaining a heterogeneous acid catalyst on a silica base. 8 Alternative methods for the preparation of alkyl ethanethioates utilize a radical elongation method on the double bond with thioacetic acid. 9 Polyhedral oligomeric silsesquioxanes can act as nanobuilding blocks that, at the molecular level, consist of a hybrid inorganic SiO core or silsesquioxane cage; these compounds are externally covered with a variety of organic func- tional groups. 10 Recently, applications for these compounds have been found in catalysis, 11 biomedicine, 12 molecular machines, 13 and electronic materials. 14 Simple routes to synthesize T 8 deriva- tives, possibly starting from either trichloro or trialkoxy alkylsi- lanes via the hydrolysis and condensation reactions, usually suffer from very poor yield due to unselective conditions, with the major products being random polymeric structures. 10c,j,15 Octakis- (3-chloropropyl)octasilsesquioxane (1) with the T 8 structure is a pro- mising silsesquioxane material because of its reactive hyperbranched dendrimer. 15 This material has eight functional alkylchloride groups, which have attracted considerable attention for use in organic modification via nucleophilic substitution. 16,18 However, vigorous substitution reactions on T 8 reduce the product yield and can result in side reactions on multiple functional groups. This together with the highly sensitive nature of the silsesquioxane T 8 cage against nucleophiles or bases can make isolation of the intended product difficult. 16,19 We previously reported on cage rearrangement 16 and cage decomposition 17 under particular reaction conditions. Performing specific substitution reactions without cage perturba- tion is quite challenging, as it is difficult to obtain the desired T 8 product with high yield under mild conditions. To date, only one study has reported on the preparation of an alkyl sulfide T 8 deriva- tive via nucleophilic substitution from 1. However, the substitu- tion reaction was carried out at high temperature under strong basic conditions and was found to result in a poor yield. 18 Here, the novel octakis(3-propyl ethanethioate)octasilsesquioxane (2) was synthesized with high yield by using the strong nucleophi- licity and stability of the thioacetate ion (SAc  ) under ambient conditions. The nucleophilic substitution on the primary chloride site of 1 against nucleophiles in the S N 2 type does not proceed efficiently in the absence of heating. 16,18 Even though the chlorine atom is considered to be a good leaving group, the nucleophilicity and solubility of the salt in organic solvents appear to play a major role in accelerating the reaction rate. The nature of the function- alized T 8 derivative is not clearly understood, and we hypothe- sized that the starting material and product may undergo a cage rearrangement 16,19 and cage decomposition. 17 A soft nucleophile of SAc  and the high solubility of KSAc in dipolar aprotic solvents Received: June 3, 2011 ABSTRACT: A novel octakis(3-propyl ethanethioate)octa- silsesquioxane was successfully synthesized via nucleophilic substitution on octakis(3-chloropropyl)octasilsesquioxane using potassium thioacetate in aprotic dimethylformamide as a sol- vent. Complete substitution proceeded at room temperature within a day to produce a crystalline product in high yield. The reaction products were characterized by 1 H, 13 C, and 29 Si NMR spectroscopy; ESI-MS; and single-crystal X-ray diffraction, confirming the structure of the cubic T 8 cage and demonstrating that the substitution reaction on eight side chains progressed smoothly under ambient conditions without any cage rearrangement or cage decomposition.