Journal of Molecular Catalysis A: Chemical 410 (2015) 26–33 Contents lists available at ScienceDirect Journal of Molecular Catalysis A: Chemical jou rnal h om epa ge: www.elsevier.com/locate/molcata Nitrile hydration to amide in water: Palladium-based nanoparticles vs molecular catalyst W. Oberhauser a,∗ , Mattia Bartoli b , Giorgio Petrucci b , Damiano Bandelli b , Marco Frediani b , Laura Capozzoli c , Cinzia Cepek d , Sunil Bhardwaj d , Luca Rosi b a Istituto di Chimica dei Composti Organometallici (CNR-ICCOM), Via Madonna del Piano 10, 50019 Sesto Fiorentino, Italy b Dipartimento di Chimica, Università Degli Studi di Firenze, Via della Lastruccia 13, 50019 Sesto Fiorentino, Italy c Istituto di Fisica Applicata Nello Carrara CNR, Via Madonna del Piano 10, 50019 Sesto Fiorentino, Italy d IOM-CNR Laboratorio TASC, Area Science Park, s.s. 14 km 163.5, Basovizza, Trieste, Italy a r t i c l e i n f o Article history: Received 7 August 2015 Received in revised form 1 September 2015 Accepted 4 September 2015 Available online 8 September 2015 Keywords: Poly(ethyleneglycol) Nitriles Amides Palladium Nanoparticles a b s t r a c t The catalytic performance of small Pd-nanoparticles (NPs) (2.0 nm), partially covered by chemisorbed oxygen atoms, and of Pd-acetate, both stabilized by 2,2 ′ -bipyridine-end functional- ized poly(ethyleneglycol) monomethylether was compared in the selective hydration of nitriles to amide in water under mild reaction conditions (353 K). Regardless of the nitrile substrate employed, the Pd-NP-based catalyst showed much higher normalized TON-values (i.e. refereeing to the amount of surface Pd atoms) compared to the Pd(II) macrocomplex, as far as the first catalytic run was considered. Deactivation of the Pd-NP-based catalyst was significant due to the formation of a hydroxide-water layer on the NPs’ surface. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Amide bonds are fundamental for the composition of biolog- ically active systems, since they are the key link between amino acids in proteins. Moreover many marketed drug molecules con- tain amide bonds [1,2], for instance Atorvastatin [3], a top selling drug worldwide which blocks the production of cholesterol or Dil- tiazem a calcium channel blocker used for treatment of angina and hypertension [4]. The majority of amide bond syntheses involve the use of stoichiometric amounts of coupling reagents [5], making this approach expensive and not sustainable from an environmental point of view. Hence atom-efficient catalytic amide bond forming reactions are highly desired [6]. Four different types of metal- catalyzed primary amide synthesis procedures of relevance have been described, namely: (i) the dehydrogenative coupling of pri- mary alcohols with ammonia in water [7–9]; (ii) the primary amide synthesis from aldoximes or aldehydes [10,11]; (iii) the palladium- catalyzed aminocarbonylation of halide compounds either in the presence of ammonia [12] or formamide [13] and (iv) the metal cat- alyzed hydration of nitriles [14] in the homogeneous [15,16] and ∗ Corresponding author. Fax: +39 55 5225203. E-mail address: werner.oberhauser@iccom.cnr.it (W. Oberhauser). heterogeneous phases [17–24], with [25] and without the presence of metal nanoparticles (NPs) [26–28]. Excellent homogenous cata- lysts for this latter reaction were designed based on the concept of bifunctional catalysis, where the metal centre acts as a Lewis acid, activating the nitrile functional group and the ligand as Brønsted base, providing the nucleophilic hydroxide group which attacks the metal-coordinated nitrile group [16,29–31]. This latter catalytic concept has been also applied to heterogeneously-catalyzed nitrile hydration reactions, where the nitrile functional group is activated by the surface atoms of metal NPs and chemisorbed oxygen atoms function as Brønsted base [32–34]. Indeed, it has been found that the percentage of the NPs’ oxygen atom coverage is a key parameter for the observed catalytic activity [17,18]. Herein we compare the catalytic performance of small Pd-NPs with that of Pd(OAc) 2 (OAc = acetate) in the hydration of nitriles to amide in water. In order to solubilize both catalysts in the reaction medium, we stabilized both Pd-based catalysts with 2,2 ′ -bipyridine end-functionalized poly(ethyleneglycol) (PEG) monomethylether. PEG is an amphiphatic polymer and functions itself as a unique solvent [35,36]. The high water solubility of PEG combined with its insolubility in diethyl ether and hexane was exploited to separate the organic reaction compounds from catalyst. http://dx.doi.org/10.1016/j.molcata.2015.09.003 1381-1169/© 2015 Elsevier B.V. All rights reserved.