Note Ortho-metallation of a phenyl ring with antimony(V) Nicola Dinsdale, John C. Jeffery, Richard J. Kilby, Stephen M. Mansell, Oliver C. Presly, Christopher A. Russell * School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, UK Received 16 June 2006; received in revised form 26 July 2006; accepted 26 July 2006 Available online 10 August 2006 Inorganic Chemistry – The Next Generation. Abstract Reaction of Ph 3 SbCl 2 with LiN@CPh 2 produces [Ph 3 Sb–N=C(C 6 H 4 )Ph] via ortho metallation of one of the phenyl groups of the imino functionality. This is the first reported example of ortho metallation of a phenyl ring by a pnictogen. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Antimony; Imino; Structure elucidation; Ortho-metallation 1. Introduction Activation of C–H bonds is one of the most important academic and industrial topics in modern chemistry. One aspect of this work that has aroused widespread interest concerns ortho-metallation of aromatic rings. The origins of this work date back to the pioneering work of Wittig [1] and Gilmann [2] who showed that aromatic rings substi- tuted with certain heteroatom groups (often N- or O-donor substituents) undergo specific lithiation in the ortho posi- tion. The products have enormous utility in selectively forming new C–C bonds. More recent literature focuses on similar reactivity of the transition elements. [3] How- ever, despite the intense research conducted in the area, this valuable property remains almost exclusively associated with the s- and d-block metals. In this current report, we describe the unprecedented ortho-metallation of a phenyl ring using a Sb(V) centre. Reaction of Ph 3 SbCl 2 with two equivalents of LiN@CPh 2 in tetrahydofuran followed by workup and recrystalli- sation (À18 °C) of the toluene-soluble material afforded, in good yield, colorless crystals of [Ph 3 Sb–N=C(C 6 H 4 )Ph] Æ {C 6 H 5 Me} 0.5 (1 Æ {C 6 H 5 Me} 0.5 ) (see Scheme 1). As expected, the 1 H NMR spectrum showed a large number of peaks in the aromatic region, but it was not until we managed to obtain the crystal structure of 1 (see Fig. 1) that the real intri- cacies of the reaction became apparent. Rather than forming the expected diimino-triphenyl antimony, which would have been a very rare example of an imino-antimony complex, one of the phenyl rings of the imino group has been metal- lated in the ortho position to generate a product that con- tains a five-membered C 3 SbN heterocycle. To our knowledge, such an observation is without precedent. Complex 1 crystallises in the triclinic space group P  1 with half a molecule of toluene in the lattice. The molecular structure of 1 showed a distorted trigonal bipyramidal anti- mony centre coordinated by three phenyl groups, a nitrogen atom from the imino functionality and the ortho carbon of a C 6 H 4 group. Complex 1 is a very rare example of a structur- ally characterised antimony imino complex; indeed there are only three other reports of such compounds 1 (Scheme 2) – the Sb(III) complex, Sb(N@CPh 2 ) 3 (2) [4], the Sb(V) 0020-1693/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2006.07.091 * Corresponding author. Tel.: +44 117 928 7599; fax: +44 117 929 0509. E-mail address: chris.russell@bristol.ac.uk (C.A. Russell). 1 We note that there are many more examples where Sb is bonded to macrocyclic oligo-imine units; in all of these the imine is acting as a neutral Lewis base donor rather than being formally r-bonded to the Sb centre as in 1–3. www.elsevier.com/locate/ica Inorganica Chimica Acta 360 (2007) 418–420