A tert-butyl/cyano substituted (1,2,3,5-dithiadiazolyl)benzene and g 2 p complexes with CpCr(CO) 2 q Rene ´ T. Boere ´ a, * , Lai-Yoong Goh b, * , Chwee Ying Ang b , Seah Ling Kuan b , Hiu Fung Lau b , Victor Wee Lin Ng b , Tracey L. Roemmele a , Sonja D. Seagrave a a Department of Chemistry and Biochemistry, The University of Lethbridge, Lethbridge, Alberta, Canada T1K 3M4 b Department of Chemistry, National University of Singapore, Kent Ridge 119260, Singapore Received 13 October 2006; received in revised form 24 November 2006; accepted 24 November 2006 Available online 9 December 2006 Abstract A rational synthesis for 5-tert-butyl-3-cyano-1-(1,2,3,5-dithiadiazolyl)benzene, which was first observed from thermal cleavage of the bis-dithiadiazolyl, has been developed. Voltammetry and electron paramagnetic resonance (EPR) spectra for this radical are reported and its X-ray structure is described. Despite the bulky t Bu substituent, the cyano supramolecular synthon is still able to maintain links to a single neighbouring sulfur atom of the S 2 unit, as previously observed in cyano-substituted dithiadiazolyls. In the g 2 complex with CpCr(CO) 2 , no such interactions are observed; the nitrile group forms a centrosymmetric dimer through weak contacts with the para H atom on the aryl ring of the partner molecule. This behaviour is contrasted to similar complexes of less bulky dithiadiazolyls, where inter- molecular interactions are retained in the crystalline lattice. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Chromium–sulfur complexes; Main-group heterocycles; Free-radicals; EPR spectroscopy; Electrochemistry 1. Introduction We have recently communicated the first bona fide p-complexes of unsaturated electron-rich C,N,S heterocy- les [1,2]. The reaction of two different 1,2,3,5-dithiadiazol- yls, 1, with the radical released from [CpCr(CO) 3 ] 2 , 2 (Cp = g 5 -C 5 H 5 ) led to synthesis in ca. 50% yield of new complexes with g 2 coordination across S–S bonds, which crystallize in either exo (3a) or endo (3b) isomeric forms (Scheme 1) [1]. Reaction of two different 1,2,4,6-thiatriazi- nyls (4a,b) with the same organometallic radical likewise yielded new complexes with either g 1 , 5, or g 2 , 6, coordina- tion across S@N bonds (Scheme 2) [2]. The novelty in all of these reactions is the suppression of oxidative addition which normally results from the reaction of unsaturated S–N bonds with low-valent transition metal complexes [3]. We attribute the success of our method to the employ- ment of radical coupling reactions under mild conditions. Our strategy is an alternative to the recently reported use of b-pyridyl groups in the building of multi-spin magnetic complexes incorporating C,N,S radicals [4]. Previous studies on the reactivity of [CpCr(CO) 3 ] 2 , 2, towards polyatomic main group elements [5] or various classes of organic substrates [6] containing P–P and S–S bonds, have shown that the reactions were initiated by the 17-electron radical [CpCr(CO) 3 Æ] 2a, into which 2 readily dissociates in solution (Chart 1) [7]. Thus, the resulting pri- mary products, A, from dibenzothiazolyl disulfide [(C 6 H 4 )- NSCS] 2 [8], B, tetraalkylthiuram disulfanes (R 2 NC(S)S) 2 [9], C, tetraalkyldiphosphine disulfide [10], D and E, diphe- nyl dichalcogenide Ph 2 E 2 (X = S, Se, Te) [11], F, thiophos- phorus compounds bis(diphenylthiophosphinyl)disulfane 0022-328X/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jorganchem.2006.11.049 q This article is based on the oral presentation by Rene ´ T. Boere ´ (Abstract 61) at the 11th International Symposium on Inorganic Ring Systems, Oulu, Finland, July 30–August 4, 2006. * Corresponding authors. Tel.: +1 403 329 2045; fax: +1 403 329 2057 (Rene ´ T. Boere ´); fax: +65 6779 1691 (Lai-Yoong Goh). E-mail addresses: boere@uleth.ca (R.T. Boere ´), chmgohly@nus.edu.sg (L.-Y. Goh). www.elsevier.com/locate/jorganchem Journal of Organometallic Chemistry 692 (2007) 2697–2704