Palladium salicylaldimine complexes derived from 2,3-dihydroxybenzaldehyde Eric G. Bowes a , Graham M. Lee a , Christopher M. Vogels a , Andreas Decken b,⇑⇑ , Stephen A. Westcott a,⇑ a Department of Chemistry and Biochemistry, Mount Allison University, Sackville, Canada NB E4L 1G8 b Department of Chemistry, University of New Brunswick, Fredericton, Canada NB E3B 5A3 article info Article history: Received 5 April 2011 Received in revised form 26 July 2011 Accepted 27 July 2011 Available online 4 August 2011 Keywords: Cross-coupling Green chemistry Palladium Salicylaldimines Schiff base Suzuki–Miyaura abstract Schiff bases derived from condensation of 2,3-dihydroxybenzaldehyde with various primary amines, such as 1-adamantanamine hydrochloride, 2,6-dimethylaniline, 2,6-diethylaniline and 2,6-diisopropylaniline, react with palladium(II) acetate to give the corresponding bis(N-arylsalicylaldiminato)palladium(II) com- plexes. These complexes have been found to be active catalyst precursors for the Suzuki–Miyaura cross- coupling of aryl bromides and iodides with aryl boronic acids using water as a solvent. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction The use of palladium complexes to catalyze the coupling of organoboron compounds with aryl or vinyl halides has become one of the most widely used tools in organic synthesis. The scope and utility of the Suzuki–Miyaura reaction has been the subject of several excellent reviews [1–3]. Indeed, the Suzuki–Miyaura cross-coupling reaction has become an attractive route to generat- ing biaryls, compounds with vast applications ranging from materials science to pharmaceutical chemistry. The use of boronic acids in this cross-coupling process is especially advantageous, compared to the analogous organotin species, as these boron compounds are relatively nontoxic and thermally, air- and moisture-stable [4]. The use of aryl chlorides as substrates and the ability to conduct this cross-coupling reaction at low temperatures and at low catalyst loading have greatly increased the versatility of the Suzuki–Miyaura cross-coupling reaction. Catalyst development has also played a significant role in improving this reaction [5–12] as traditional palladium complexes used to catalyze this transformation contain air-sensitive phosphine ligands. In recent years, however, the use of catalysts containing N-heterocyclic carbenes [13–15], oxazolines [16–18], and ‘ligandless’ systems [19–21], as well as heterogeneous systems [22–24], have also been employed. A considerable amount of research has also focused on designing water-soluble catalysts to provide a greener and more environmentally benign alternative to this reaction [25–30]. In a recent elegant study by Hong et al., it was found that (N-aryl- salicylaldiminato)palladium(II) complexes are active catalysts for the Suzuki–Miyaura cross-coupling reaction of a wide array of aryl bromides [31]. However, reactions were carried out in organic solvents (THF and toluene) and high yields were only achieved after several days. Likewise, trinuclear triphenylphosphine Au(I) complexes with N,N,O-tridentate unsymmetrical Schiff base li- gands catalyzed the Suzuki cross-coupling reaction to afford nonsymmetrical biaryls in good yields, whereas the Au(III) com- plexes gave only arylboronic homocoupling products [32]. As part of our ongoing investigation into designing new metal Schiff base complexes, we have prepared several palladium complexes derived from the condensation of 2,3-dihydroxybenzaldehyde with various primary amines, such as 1-adamantanamine hydrochlo- ride, 2,6-dimethylaniline, 2,6-diethylaniline and 2,6-diisopropyl- aniline and examined their ability to be used as catalysts for the green Suzuki–Miyaura cross-coupling reaction. 2. Experimental 2.1. General procedures Reagents and solvents used were purchased from Aldrich Chemicals. Palladium(II) acetate was purchased from Precious Metals Online Ltd. (Melbourne, AU). Schiff base 1c was synthesized as previously reported [33]. NMR spectra were recorded on a JEOL 0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2011.07.051 ⇑ Corresponding author. ⇑⇑ Corresponding author regarding X-ray crystallography. E-mail addresses: adecken@unb.ca (A. Decken), swestcott@mta.ca (S.A. West- cott). Inorganica Chimica Acta 377 (2011) 84–90 Contents lists available at SciVerse ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica