A quantum chemical study on the mechanism of S-coordinated tetrazole-thiolato formation by the reaction of organic isothiocyanates with metal azido complexes of Pt(II), Pd(II), and Sn Kunhye Lee, Yong-Joo Kim, Kyoung Koo Baeck * Department of Chemistry, Kangnung National University, Gangnung, Gangwon-do 210-702, Korea Received 11 May 2005; received in revised form 24 June 2005; accepted 4 July 2005 Available online 10 August 2005 Abstract The mechanism of the reaction of isothiocyanates with metal-azido complexes of Pt(II), Pd(II), and Sn as well as hydrazoic acid is studied using the density functional theory method. The relative stability between two possible product isomers (S-coordinated tetrazole-thiolato and N-coordinated tetrazolato complexes) does not directly relate to the experimentally synthesized product. The overall reaction proceeds via three steps. The first step is the approach of the S-atom of the organic isothiocyanate to the central metal atom followed by the nucleophilic attack of the coordinated N-atom of the azido group to the C-atom of the isothiocyanate. The activation barrier of this step is 22–24 kcal mol 1 , and the resulting intermediate has the imidoyl azide form. In the second reac- tion step, electrophilic attack of the terminal N-atom of the azido group to the N-atom of the isothiocyanate transforms the inter- mediate to the S-coordinated tetrazole-thiolato product with a barrier of about 11 kcal mol 1 . The N-coordinated tetrazole could be made from the S-coordinated tetrazole-thiolato complex only after the third step, in which the metal coordination migrates from the S- to the N-atom. Ó 2005 Elsevier B.V. All rights reserved. Keywords: S-coordinated tetrazole-thiolato; Metal azido complexes; Isothiocyanates; Hydrazoic acid; Reaction mechanism 1. Introduction Tetrazoles are an increasingly important functionality, not only as precursors to a variety of nitrogen-containing heterocycles [1] but also as materials with applications in diverse areas such as pharmaceuticals [2], explosives [3], information recording systems [4], and corrosion inhibi- tors [5]. The main route for the formation of tetrazoles, the reaction of organic azides with nitriles, is relatively well known and has been studied through many experi- ments [6]. The details of its reaction mechanism are also explained by recent theoretical studies [7]. Metal-azido complexes have long been considered to behave in a manner analogous to organic azides and azide salts [8]. The isothiocyanate group can also be an alternative source of the nitrile (CN) moiety that can be utilized for the synthesis of tetrazoles. As the re- sult, the reaction of organic isothiocyanates with metal- azido complexes is expected to generate a metal complex with tetrazole ligands, which can in turn be an alterna- tive source of tetrazoles. Several studies regarding the dipolar cycloaddition of organic isothiocyanates to the azido ligand of metal complexes have been reported [9–11], but the actual coordination of the tetrazole li- gand to the central metal was not clearly identified, ex- cept in just a few cases involving the formation of tetrazole-thiolato complexes with a direct tin–sulfur bond [12,13]. 0022-328X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jorganchem.2005.07.022 * Corresponding author. Tel.: +82 33 640 2307; fax: +82 33 647 1183. E-mail address: baeck@kangnung.ac.kr (K.K. Baeck). Journal of Organometallic Chemistry 690 (2005) 4319–4329 www.elsevier.com/locate/jorganchem