Arene ruthenium(II) p-chloroacetophenone phenylthiosemicarbazone complex mediated transfer hydrogenation of ketones Mathiyazhagan Ulaganatha Raja, Elangovan Sindhuja, Rengan Ramesh ⁎ School of Chemistry, Bharathidasan University, Tiruchirappalli 620 024, India abstract article info Article history: Received 6 June 2010 Accepted 21 July 2010 Available online 29 July 2010 Keywords: Synthesis Ruthenium(II)-p-cymene Phenylthiosemicarbazone ligands Structural characterization Transfer hydrogenation A series of cationic half-sandwich arene ruthenium(II) complexes of general formula [Ru(η 6 -p-cymene)Cl (L)]Cl have been synthesized from the reaction of [Ru(η 6 -p-cymene)Cl 2 ] 2 with thiosemicarbazone derivatives (L). Characterization of the complexes were accomplished by analytical and spectral (FT-IR, UV–Vis, 1 H NMR) methods. Single crystal structure determination reveals the presence of a pseudooctahe- dral three-legged piano stool conformation. All the complexes exhibit a quasi-reversible one electron reduction in the range from -0.75 to -0.85 V. Further, the catalytic activity of the titled complex has been investigated in the transfer hydrogenation of ketones in the presence of isopropanol/NaOH. © 2010 Elsevier B.V. All rights reserved. There has been much interest in the chemistry of half-sandwich arene ruthenium(II) complexes [1,2] since the development of useful synthetic precursors with the general formula [RuCl 2 (η 6 -arene)] n . Syntheses of new and highly active transition-metal based catalysts derived from arene ligands are used in different catalytic reactions including addition of carboxylic acids to alkynes [3], transfer hydrogenation of ketones [4], polymerization of olefins [5] and isomerization of alkenes [6]. Further, several arene ruthenium complexes are found in applications as anticancer drugs [7,8]. The reduction of carbonyl compounds is an important transfor- mation in organic synthesis from both academic and industrial points of view [9]. Transfer hydrogenation of ketones by using an alcohol, preferably isopropyl alcohol, is an interesting alternative to the classical hydrogenation process requiring the use of dihydrogen gas [10]. Homogeneous ruthenium complexes are considered to be the most attractive catalysts for transfer hydrogenation reactions, though other metal complexes have also been used successfully [11]. Transfer hydrogenation of unsaturated compounds like ketones, imines etc. by using isopropanol/NaOH as hydrogen source is a widely investigated reaction that is promoted by many transition metal complexes [12]. Cationic arene ruthenium(II) complexes containing 2,2'-bipyrimi- dine ligands are used as active catalysts for transfer hydrogenation of ketones in water in the presence of HCOOH/HCOONa [13]. Similarly, asymmetric transfer hydrogenation of ketones carried out by [RuCl 2 (p-cymene)] 2 in the presence of NaOH and t-BuOK has been described [14]. Bimetallic ruthenium(II) complexes bearing bis(aminopho- sphine) and bis(phosphinite) monodentate ligands were used as catalyst in the transfer hydrogenation of substituted acetophenone [15]. Transfer hydrogenation of benzophenone and acetophenone by arene ruthenium(II) complexes containing bis(pyrazolylazines) ligands has also been described [16]. Further, the catalytic activity of conformationally rigid diphosphine arene ruthenium(II) complexes in the transfer hydrogenation of various ketones has been reported [17]. Furthermore, transfer hydrogenation of aromatic ketones were successfully achieved by water-soluble arene ruthenium complexes containing an N,N-chelating 2,2'-dipyridylamine ligands [18]. As a part of ongoing efforts to synthesize novel ruthenium complexes and to study their catalytic efficiency in transfer hydroge- nation reactions [19], herein we describe the synthesis and char- acterisation of a series of cationic arene ruthenium(II) complexes containing thiosemicarbazones along with their catalytic activity in transfer hydrogenation of ketones. The substituted acetophenone thiosemicarbazone ligands (L1–L5) were prepared by modification of the reported procedure [20]. The general procedure for the preparation of the complexes is as follows. To a solution of 0.1 mmol of [{(η 6 -p-cymene)RuCl} 2 (μ-Cl) 2 )] in dry benzene (25 ml) was added 0.2 mmol thiosemicarbazone ligand (mole ratio of ruthenium complex and ligand is 1:2 respectively) and the mixture was refluxed for 2–3h(Scheme 1). The solution was concentrated to about 3 ml, pet. ether (15 ml) was added to precipitate the cationic η 6 -p-cymene ruthenium(II)phenylthiosemi- carbazone complexes. The resulting complexes were recrystallized from CH 2 Cl 2 /pet.ether and dried under vacuum. The overall yield obtained for all the complexes were 66–80%. All the newly synthesized η 6 -p-cymene ruthenium(II)phenylthio- semicarbazones complexes are colored, stable in air, non-hygroscopic in Inorganic Chemistry Communications 13 (2010) 1321–1324 ⁎ Corresponding author. Tel.: +91 431 2407020; fax: +91 431 2407045. E-mail address: ramesh_bdu@yahoo.com (R. Ramesh). 1387-7003/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2010.07.026 Contents lists available at ScienceDirect Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche