Synthesis, characterisation and reactivity of oxodiperoxo-[2-(1-pyrazolyl)-6-menthylpyridine]molybdenum(VI): The first chiral 2-(1-pyrazole)pyridineoxodiperoxomolybdenum(VI) complex Elisabete da Palma Carreiro, Guo Yong-En, Anthony J. Burke * Departamento de Quı ´mica and Centro de Quı ´mica de E ´ vora, Universidade de E ´ vora, Rua Roma ˜o Romalho 59, 7000 E ´ vora, Portugal Received 25 September 2005; accepted 8 November 2005 Available online 4 January 2006 Abstract We have obtained a novel chiral enantiomerically pure molybdenum complex of the type MoO(O 2 ) 2 LL 0 which has been fully char- acterised, including structural determination by X-ray crystallography and screened in a series of epoxidation reactions with simple ole- fins giving satisfactory conversions, but low enantioselectivities. It’s mode of epoxidation has been investigated. Ó 2005 Elsevier B.V. All rights reserved. Keywords: Oxodiperoxomolybdenum(VI) complex; Asymmetric catalysis; Epoxidation; Pyridine–pyrazole ligand 1. Introduction The chiral epoxide functionality is a key structural unit present in a number of important natural products and bio- active compounds [1]. Amongst the various methods for the installment of such an important motif in a molecule, asymmetric catalysis represents an extremely elegant and efficient method to achieve this goal [2]. Despite the tremendous advances made using transition metal catalysts incorporating titanium [3] and manganese [4], a general highly selective catalytic epoxidation method remains elusive. One alternative catalytic system with potential to achieve this goal is the molybdenum based Mimoun-type peroxo complex system [MoO(O 2 ) 2 L n , L = ligand, n = 1, 2] [5] available from cheap molybdenum trioxide and which has been demonstrated to be highly cat- alytic and efficient [5,6]. Thiel et al. [7a,7b,7c,7d,7e] success- fully prepared a molybdenum based Mimoun-type peroxo complex incorporating a bidentate pyridine–pyrazole ligand and they demonstrated its effectiveness in the cata- lytic epoxidation of a number of simple, yet unreactive ole- fins. In 1998, this group reported the synthesis of an optically pure complex [8]. Several years ago Kagan et al. [9,10] reported the prep- aration of a chiral molybdenum(VI) oxo–peroxo-N,N- dimethylacetamide complex giving enantioselectivities up to 35% ee. Later Park et al. [11] obtained enantioselectivi- ties of 26–81% ee for the epoxidation of cis- and trans-b- methylstyrene using the molybdenum(VI) oxo–peroxo complexes derived from (R)-piperidinylmandelamide and (R)-piperidinylphenylacetamide, respectively. However, these were the only olefins examined. Unfortunately, these complexes were characterised by infra-red spectroscopy and elemental analysis only, and no information was given regarding the structure of these interesting molybde- num(VI) oxo–peroxo complexes. Schurig et al. [12] and Bartollini et al. [13] have reported enantioselective epoxida- tions using chiral Mimoun-type peroxo complex systems but the ees reported were low. Very recently Go ´mez’s group [14,15] reported the preparation of the very first chi- ral molybdenum(VI) oxo–peroxo–oxazoline complex, 0020-1693/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2005.11.021 * Corresponding author. Tel.: +351 266745310; fax: +351 266744971. E-mail address: ajb@dquim.uevora.pt (A.J. Burke). www.elsevier.com/locate/ica Inorganica Chimica Acta 359 (2006) 1519–1523