Synthesis and structural aspects of M-allyl (M = Ir, Rh) complexes Akella Sivaramakrishna, Emma Hager, Feng Zheng, Hong Su, Gregory S. Smith, John R. Moss * Department of Chemistry, University of Cape Town, Rondebosch 7701, Cape Town, South Africa Received 10 May 2007; received in revised form 23 July 2007; accepted 23 July 2007 Available online 8 August 2007 Abstract The synthesis, characterization and chemistry of novel g 3 -allyl metal complexes (M = Ir, Rh) are described. The structures of com- pounds (C 5 Me 4 H)Ir(PPh 3 )Cl 2 (1), (C 5 Me 4 H)Ir(PPh 3 )(g 3 -1-methylallyl)Br (3a), (C 5 Me 4 H)Ir(g 4 -1,3,5-hexatriene) (8), and (C 5 Me 5 )Rh- (g 3 -1-ethylallyl)Br (5d) have been determined by X-ray crystallography. Structural comparisons among these complexes are discussed. It is found that the neutral metal allylic complex [Cp * IrCl(g 3 -methylallyl)] (5) ionizes in polar solvents to give [Cp * Ir(g 3 -methyl- allyl)] + Cl  (6) and reaches equilibrium (5  6) at room temperature. Addition of tertiary phosphine ligands to neutral complexes such as [Cp * Ir(g 3 -methylallyl)Cl], results in the formation of stable ionic phosphine adducts. Factors such as solvent, length of carbon chain, temperature and light are discussed with respect to the formation, stability and structure of the allyl complexes. Ó 2007 Elsevier B.V. All rights reserved. Keywords: Metal-(g 3 -allyl) complexes; Transmetalation reactions; Ligand addition reactions; Structure comparison; Thermolysis studies 1. Introduction Transition metal g 3 -allyl compounds display a rich chemistry [1] and are widely encountered both as synthetic reagents and in catalysis. There has also been much interest shown in elucidating the structures and stereodynamic behaviour of g 3 -allyl metal complexes in solution [2]. Investigations on potential applications of these types of complexes in asymmetric synthesis as well as in heteroge- neous catalysis have been carried out [3]. For example, tris(allyl)rhodium complexes with a variety of metal oxide supports have been reported as catalysts [4]. g 3 -Allyl palla- dium complexes have been studied extensively, partly because of the extremely useful palladium-catalyzed reac- tions of nucleophiles with allylic substrates [5]. It has also been shown that the bulky ligand substituents can cause modifications to the structure and solution behaviour of the stable allylic metal complexes [6]. The reactivity of rho- dium and iridium allylic complexes with various substrates as reactants has been reported [7]. The catalytic asymmetric hydrogenation of a-functionalized ketones using chiral Ru(II)-allyl complexes has also been reported [8]. A good knowledge of the structural aspects of these compounds is important in understanding the reactivity patterns in detail. The present work describes the synthesis, structural characterization and reactivity of some allylic iridium(III) and rhodium(III) complexes. 2. Results and discussion Our original efforts were aimed at preparing and charac- terizing a series of iridium and rhodium alkenyl com- pounds with an M–C r-bond and a pendant alkene group. However, some of the products of the reactions of 1 with 1-alkenyl Grignard reagents were shown to be the metal allyl complexes. It has been found that the com- pound 2 is air-sensitive in the solid state and decomposes rapidly in solution, particularly in chlorinated solvents (Eq. (1)) [9]. The analogous reaction involving the rhodium precursor with 1-alkenyl Grignard reagent showed that the PPh 3 ligand was eliminated from the metal sphere (as 0022-328X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jorganchem.2007.07.053 * Corresponding author. Tel.: +27 21 650 2535; fax: +27 21 689 7499. E-mail address: John.Moss@uct.ac.za (J.R. Moss). www.elsevier.com/locate/jorganchem Journal of Organometallic Chemistry 692 (2007) 5125–5132