Uridate/pyridyl Pd(II) complexes: Phosphine-free high turnover catalysts for the Heck reaction of deactivated aryl bromides Pottabathula Srinivas a , Keesara Srinivas a , Pravin R. Likhar a, * , Balsubramanian Sridhar b , Kakita Veera Mohan c , Suresh Bhargava d , Mannepalli Lakshmi Kantam a, * a I & PC Division, Indian Institute of Chemical Technology, Hyderabad 500607, India b X-ray Crystallography Center, Indian Institute of Chemical Technology, Hyderabad 500607, India c NMR Center, Indian Institute of Chemical Technology, Hyderabad 500607, India d School of Applied Sciences, RMIT University, Melbourne, Australia article info Article history: Received 20 July 2010 Received in revised form 29 September 2010 Accepted 30 September 2010 Available online 12 October 2010 Keywords: Heck reaction N-Ligand Phosphine-free Palladium High turnover abstract The synthesis and structure of palladium(II) complexes bearing uridato/pyridyl ligands as an anionic N-donor coordination sites are reported. The complexes have been shown to be highly active catalysts for the Heck reaction of aryl bromides (TON 4.010 4 e9.110 4 ) and moderate activity for the activation of aryl chlorides under phosphine-free conditions. Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction The Heck reaction [1], since its popularity started to flourish in the mid 1980 0 s, has become not only one of the most exciting organic transformations for CeC bond formation but also a bench- mark to estimate the efficiency of a catalytic system [2]. This powerful reaction has received considerable attention due to its functional group tolerance and its application to a broad range of endeavors, ranging from synthetic organic chemistry to materials science [3]. Therefore, several goals have to be achieved for its industrial application, such as the use of inexpensive starting materials, achievement of high turnover numbers (TON’s) with less reactive aryl bromides and aryl chlorides, and the use of stable and inexpensive ligands. In this context, the design of new ligands and their palladium complexes that can catalyze the Heck reaction of less reactive aryl bromides and aryl chlorides with both high activity and high efficiency is a current important topic of research. As the choice of ligand plays a major role in the efficiency of the catalyst, phosphine ligands are the first choice to catalyze the Heck reaction more actively and efficiently [4]. However, they are often toxic, air-sensitive or quite expensive. Moreover, there is no need to use electron-rich phosphines to generate nucleophilic Pd(0) species for promoting the oxidative-addition step in the catalytic cycle [5]. Therefore, the development of phosphine-free Pd-catalysts has become another equally important topic of research [6]. Although palladacycles [7], N-heterocyclic [8] and carbocyclic [9] carbene Pd-catalysts are well performing phosphine-free cata- lysts, their tedious multi-step synthesis, inert atmosphere or dry conditional catalytic performance and the use of various additives, limit their use in industrial applications. In addition, alternative catalytic systems such as N-, O- and S-centered ancillary ligand complexes of Pd have appeared with moderate catalytic activity and efficiency [10]. Recently, we have shown that anionic carbox- yamide is a good supporting N-donor functional group which increases the thermal stability and activity of the palladium complexes for CeC bond-formation reactions [11]. We now report the synthesis and structure of new palladium(II) complexes bearing uridato/pyridyl ligands as an anionic N-donor coordinating site, together with its performance in the Heck reaction. * Corresponding authors. Tel.: þ91 40 27193510; fax: þ91 40 27160921. E-mail addresses: plikhar@iict.res.in (P.R. Likhar), mlakshmi@iict.res.in (M.L. Kantam). Contents lists available at ScienceDirect Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem 0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jorganchem.2010.09.075 Journal of Organometallic Chemistry 696 (2011) 795e801