Synthesis and characterization of Ru(arene) complexes of bispyrazolylazines: Catalytic hydrogen transfer of ketones q M. Laura Soriano a , Félix A. Jalón a, * , Blanca R. Manzano a , Miguel Maestro b a Departamento de Química Inorgánica, Orgánica y Bioquímica, Facultad de Químicas-IRICA, UCLM, Avda. Camilo J. Cela 10, 13071 Ciudad Real, Spain b Departamento de Química Fundamental, Universidade da Coruña, 15071 A Coruña, Spain article info Article history: Received 29 January 2009 Received in revised form 1 April 2009 Accepted 16 April 2009 Available online 23 April 2009 Dedicated to Prof. Jerry Trofimenko Keywords: Ruthenium Pyrazole Catalysis Hydrogen transfer N-donor ligands Arene derivatives abstract The bis(pyrazol-1-yl)azine ligands 2,3-bis(pyrazol-1-yl)quinoxaline (bpzqnx), 2,3-bis(pyrazol-1-yl)pyra- zine (bpzprz) and 3,6-bis(3,5-dimethylpyrazol-1-yl)pyridazine (bpz*pdz) were prepared by the reaction of pyrazolate salts and the corresponding azine dichloride derivatives. The reaction of these ligands with Ru(arene) precursors led to the mononuclear complexes [RuCl(arene)(L)]BPh 4 (arene = p-cymene, L = bpzqnx, 1, bpzprz, 5, bpz*pdz, 7; arene = C 6 H 6 , L = bpzqnx, 2, bpzprz, 6, bpz*pdz, 8) with the N-donor ligand coordinated in a bidentate chelate way. In general, the ligands coordinate through one pyrazole ring and the azine, except in the cases of 1 and 2 where the two pyrazolyl rings are coordinated to the metal in a symmetrical way. When the reactions between the ruthenium precursors and bpzqnx are car- ried out in MeOH, the complexes [RuCl(arene)(OMepzqnx)]BPh 4 with partially methanolyzed ligands are isolated (arene = p-cymene, 3;C 6 H 6 , 4). In this process a methoxy group has replaced one of the pyrazole groups in the ligand. The X-ray structures of 6 and 7 have been determined. These compounds have a three-legged piano-stool structure with cations and anions packed through weak interactions. Complexes 1–8 are active in ketone hydrogenation transfer processes even in the absence of base. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction Ru(arene) derivatives constitute a family of interesting precur- sors in a variety of catalytic processes [1]. Noyori and other authors have designed very active systems with basic centres (N-donor mainly) in the asymmetric catalytic reduction of ketones using alcohols as the hydrogen source [2]. This situation has raised inter- est in the preparation of systems bearing N-donor centres that could participate in one or more steps of these hydrogenation pro- cesses [3]. However, the use of arene ruthenium derivatives with heterocyclic auxiliary ligands as polypyridines in catalytic hydro- genation processes has not been explored very much [4]. Our expe- rience in the preparation of Ru(arene) complexes with N-donor ligands and their use in hydrogen transfer reactions [5] inspired the work described here, which focuses on the study of the effect that uncoordinated basic centres could have in hydrogen transfer catalytic processes. With this aim in mind, a family of bis(pyra- zol-1-yl)azines, which are easily prepared, have been chosen. The preparation of mononuclear [RuCl(arene)(L)]BPh 4 derivatives was carried out and these compounds were used as precursors in hydrogen transfer reaction processes with and without a base as co-catalyst. 2. Experimental 2.1. General procedures All manipulations were carried out under an atmosphere of dry oxygen-free nitrogen using standard Schlenk techniques. Elemen- tal analyses were performed with a Carlo Erba Instruments EA 1108 CHNS/O microanalyzer. IR spectra were recorded on a Shima- dzu IRPRESTIGE-21 spectrophotometer deposing a pure solid sam- ple over an ATR device (4000–700 cm 1 range). FAB+ mass spectra (position of the peaks in Da) were recorded with a VG Biotech Quattro Spectrometer. NMR spectra were recorded at room tem- perature (25 °C) on Varian Unity Inova-400 (400 MHz for 1 H; 100.6 MHz for 13 C) and Varian Inova FT-500 (500 MHz for 1 H; 125 MHz for 13 C) spectrometers. 1 H shifts (ppm) were recorded using the residual proton signal of the solvent as an internal stan- dard (see numbering of protons and carbons in Scheme 1). For the acquisition of the COSY, g-HMBC and g-HMQC spectra the standard VARIAN pulse sequences were used (VNMR 6.1 C software). The fol- lowing parameters were used for COSY: acquisition time 0.214 s, pulse width 10 ls, relaxation delay 1 s, 16 scans, 512 increments. For the g-HMBC and g-HMQC the spectra were acquired using 7996-Hz ( 1 H) and 25133.5-Hz ( 13 C) widths; 16 transients of 2048 data points were collected for each of the 128 increments. The nOe difference spectra were recorded with 5000 Hz, acquisition time 3.27 s, pulse width 90°, relaxation delay 4 s, and irradiation power 5–10 dB. All the 13 C{ 1 H} NMR resonances are singlets. 0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2009.04.011 q In memoriam of our friend and master Jerry Trofimenko. * Corresponding author. Tel.: +34 926295300; fax: +34 926295318. E-mail address: Felix.Jalon@uclm.es (F.A. Jalón). Inorganica Chimica Acta 362 (2009) 4486–4492 Contents lists available at ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica