NC palladacycles in the Heck arylation of ethylene: Synthesis, structure and their reactivity Shashi B. Atla a , Ashutosh A. Kelkar a, * , Vedavati G. Puranik b , Wolfgang Bensch c , Raghunath V. Chaudhari d, * a Chemical Engineering and Process Development Division, National Chemical Laboratory, Pune 411 008, India b Center for Materials Characterization, National Chemical Laboratory, Pune 411 008, India c Institut für Anorganische Chemie, University of Kiel, Olshausenstrasse 40-60, 24098 Kiel, Germany d Center for Environmentally Beneficial Catalysis, The University of Kansas, 1501 Wakarusa Dr., Lawrence, KS 66047-1803, USA article info Article history: Received 9 September 2008 Received in revised form 24 November 2008 Accepted 25 November 2008 Available online 7 December 2008 Keywords: Arylation Palladacycle a-Aryl propionic acids abstract Monomeric cyclopalladated complexes with NC coordination using ligands 2-phenylpyridine, 2-phenyl- quinoline, 8-methylquinoline have been synthesized and the structures have been determined by single crystal X-ray structure analysis. The crystal structures of monomeric palladacycles prepared using ben- zophenone oxime, and 2-phenylpyridine have also been determined. The use of these complexes in the Heck arylation of ethylene with 2-bromo-6-methoxynaphthalne (BMN) to give 2-vinyl-6-methoxy- napthalene which is an intermediate for the synthesis of anti-inflammatory drug Naproxen has been examined and also arylation of ethylene with 3-bromo-benzophenone and 4-bromo-isobutylbenzene was investigated. These palladacycles with NC coordination show excellent catalytic activity with a TOF > 4000 h 1 . Ó 2008 Elsevier B.V. All rights reserved. 1. Introduction Palladium catalyzed Heck reaction is considered as one of the landmark developments in the organic synthesis. During the last decade, homogeneously catalyzed Heck reaction has been investi- gated extensively and the details are summarized in recent review articles [1]. The palladium catalyzed coupling reaction of organic halides with olefins allows a one step synthesis of aromatic olefins, which are of considerable importance [2] as fine organics, specialty monomers, pharmaceuticals, UV absorbers and precursors of active compounds. Major emphasis of the work during recent times has been on the development of catalysts that are more stable com- pared to the classical palladium(0) phosphine complexes [3]. Typ- ical examples are palladacycles [4], which remain active at higher temperatures (100–140 °C) leading to higher reaction rates and thus allow lower catalyst loadings and high turnovers (>200 000). There are many types of palladacycles, particularly those with nitrogen [5], phosphorus [6], sulfur [7] and oxygen [8] containing donor ligands. They can also be found in pincer forms [9]. Arylation of ethylene provides an easy and general method for the synthesis of vinyl aromatic compounds. Also, it may allow replacing [10] the classical Friedel and Crafts chemistry and other classical organic chemistry involved in the production of most aro- matic compounds and form the basis for environmentally friendly production processes. However, there are very few reports on the arylation of ethylene. Aryl halides [11] and other pseudo-halides [12] (acid chlorides, diazonium salts and triflates) have been used as substrates in the arylation reactions using Pd(OAc) 2 as the cata- lytic system. Activity of the catalyst was generally found to be low (turnover frequency <15 h 1 ) and high catalyst loading (1–5 mol% of palladium salt based on halide) was essential for good activity. a-Aryl propionic acids such as Ibuprofen, Naproxen, Ketoprofen, Fenoprofen, Indoprofen have emerged as important non-steroidal anti-inflammatory agents during the past three decades [13]. While many synthetic routes [14] for these products are known, a catalytic route involving a two step synthesis [15] (viz Heck reac- tion followed by carbonylation [16]) is one of the recent develop- ments to achieve an environmentally cleaner route (Scheme 1). The catalytic systems proposed previously for the arylation of ethylene with 2-bromo-6-methoxynaphthalene (BMN) to produce 2-vinyl-6-methoxynaphthalene (VMN) include the Herrmann pal- ladacycle [17] and PdCl 2 /NMDP [18] (neomenthyldiphenylphos- phine) [19]. However, the activity of these catalysts was found to be very low (TOF: 85 h 1 and 444 h 1 , respectively). The perfor- mance of the colloids [Pd(CH 3 CN) 2 Cl 2 ]  6Ph 4 PCl [20] has also been described for these reactions (TOF: 75 h 1 ). From the literature it was observed that there are very few reports on the arylation of ethylene particularly for the important substrates having potential applications in the synthesis of important drugs such as Ibuprofen, 0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jorganchem.2008.11.065 * Corresponding authors. Tel.: +91 20 25902544; fax: +91 20 25902621 (A.A. Kelkar); tel.: +1 785 864 1634; fax: +1 785 864 6051 (R.V. Chaudhari). E-mail addresses: aa.kelkar@ncl.res.in (A.A. Kelkar), rvc1948@ku.edu (R.V. Chaudhari). Journal of Organometallic Chemistry 694 (2009) 683–690 Contents lists available at ScienceDirect Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem