1 3 Bimetallic nano-Pd/PdO/Cu system as a highly effective 4 catalyst for the Sonogashira reaction 5 6 7 Mateusz Korzec a , Piotr Bartczak a,c , Anna Niemczyk a,⇑ , Jacek Szade b , Maciej Kapkowski a , 8 Paulina Zenderowska a , Katarzyna Balin b , Józef Lela ˛tko d , Jaroslaw Polanski a,⇑ 9 a Institute of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, Poland 10 b Institute of Physics, University of Silesia, 75 Pulku Piechoty 1A, 41-500 Chorzów, Poland 11 c NANO-CHEM-TECH Ltd, Ligocka 90A/14, 40-568 Katowice, Poland 12 d Institute of Materials Science, University of Silesia, 75 Pulku Piechoty 1A, 41-500 Chorzów, Poland 13 14 15 17 article info 18 Article history: 19 Received 4 January 2014 20 Revised 9 February 2014 21 Accepted 14 February 2014 22 Available online xxxx 23 Keywords: 24 Pd nanoparticles 25 Sonogashira reaction 26 Bimetallic Pd/Cu 27 Heterogeneous catalysis 28 Sonogashira coupling 29 Palladium oxide 30 31 abstract 32 A copper-supported nanopalladium catalyst obtained by an innovative method of nanoparticle transfer 33 from the intermediate carrier SiO 2 to the target Cu carrier was a highly efficient and selective catalyst, 34 giving as much as quantitative conversion and yield in a series of Sonogashira reactions. Comparisons 35 with other Pd systems, especially Pd/SiO 2 , indicated substantial advantages for this novel catalytic sys- 36 tem. X-ray photoelectron spectroscopy (XPS) studies of the prepared Pd/Cu catalyst revealed the devel- 37 opment of a PdO species in the Pd/Cu system and illustrated for the first time the importance of the 38 resulting Pd/PdO/Cu system for efficient Sonogashira coupling. 39 Ó 2014 Published by Elsevier Inc. 40 41 42 43 1. Introduction 44 Catalytic C–C bond forming reactions provide attractive syn- 45 thetic routes to a variety of important chemicals and pharmaceuti- 46 cals or their building blocks. Palladium is one of the most 47 frequently transition metal used for catalytic Heck, Sonogashira, 48 Suzuki or Stille cross-couplings [1–4]. Although there has been tre- 49 mendous progress in recent years in this area, a number of prob- 50 lems remain to be solved [5]. More efficient catalysts are still 51 sought to allow us to run the reactions in higher yields under 52 milder conditions [6]. Easier catalyst separation, reuse, and lower 53 contamination of the final products are other important issues to 54 be addressed. Additionally, commercial availability at low cost is 55 required for industrial applications guided by economic efficiency. 56 The Pd-catalyzed Sonogashira C–C cross-couplings can be per- 57 formed under both heterogeneous and homogenous conditions 58 [7,8]. In general, homogeneous Pd catalysts are complexes of Pd(II) 59 salts such as chloride or acetate with such organic ligands as phos- 60 phines and phosphites. They display high activity, but are rela- 61 tively difficult to separate from reaction mixtures, especially for 62 reuse [8]. Moreover, numerous investigations have indicated that 63 in coupling reactions, the catalytic active state is a Pd 0 species 64 and where Pd(II) is used, in situ reduction to Pd 0 occurs during 65 the reaction [9–17]. 66 This rationalizes the application of heterogeneous catalysts con- 67 sisting of an active catalytic Pd species supported on solid materi- 68 als such as silica, polymers or carbon [18–21]. These types of 69 catalysts usually are easier for separation and reuse; however, they 70 often exhibit lower activity compared with many of their homoge- 71 neous counterparts [8]. Moreover, heterogeneous palladium- 72 catalyzed cross-couplings follow a mechanism in which palladium 73 is leached from the support in the oxidative addition step [22]. 74 Although palladium re-precipitates later during the reductive 75 elimination, the activity of the catalyst significantly suffers from 76 this process [22]. Such a mechanism, termed quasi-heterogenous 77 catalysis, severely complicates the design of efficient fully hetero- 78 geneous nano-Pd systems for the demanding cross-couplings, 79 especially the Sonogashira reaction. One of the solutions is the 80 use of water as a solvent in which the mechanism was believed 81 to take the form of a fully heterogeneous process [23]. In another 82 approach, Choi et al. applied Pd 2+ exchanged mesoporous sodalite 83 and NaA zeolite for catalyzing various C–C couplings and observed 84 that reactions were catalyzed by a Pd 0 species, which was gener- 85 ated in situ under the reaction conditions [9]. This species seemed http://dx.doi.org/10.1016/j.jcat.2014.02.008 0021-9517/Ó 2014 Published by Elsevier Inc. ⇑ Corresponding authors. Fax: +48 32 2599978. E-mail addresses: anna.niemczyk@us.edu.pl (A. Niemczyk), jaroslaw.polanski@ us.edu.pl (J. Polanski). Q1 Journal of Catalysis xxx (2014) xxx–xxx Contents lists available at ScienceDirect Journal of Catalysis journal homepage: www.elsevier.com/locate/jcat YJCAT 11421 No. of Pages 9, Model 5G 5 March 2014 Please cite this article in press as: M. Korzec et al., Bimetallic nano-Pd/PdO/Cu system as a highly effective catalyst for the Sonogashira reaction, J. Catal. (2014), http://dx.doi.org/10.1016/j.jcat.2014.02.008