1,2-Azolylamidino ruthenium(II) complexes with DMSO ligands: electro- and photocatalysts for CO reduction.

New 1,2-azolylamidino complexes -[RuCl(DMSO)(NHC(R)az*-κN,N)]OTf [R = Me (2), Ph (3); az* = pz (pyrazolyl, a), indz (indazolyl, b)] are synthesized chloride abstraction from their corresponding precursors ,-[RuCl(DMSO)(az*H)] (1) after subsequent base-catalyzed coupling of the appropriate nitrile with the 1,2-azole previously coordinated. All the compounds are characterized by H NMR, C NMR and IR spectroscopy. Those derived from MeCN are also characterized by X-ray diffraction. Electrochemical studies showed several reduction waves in the range of -1.5 to -3 V. The electrochemical behavior in CO media is consistent with CO electrocatalytic reduction. The catalytic activity expressed as [(CO)/(Ar)] ranged from 1.7 to 3.7 for the 1,2-azolylamidino complexes at voltages of . -2.7 to -3 V ferrocene/ferrocenium. Controlled potential electrolysis showed rapid decomposition of the Ru catalysts. Photocatalytic CO reduction experiments using compounds 1b, 2b and 3b carried out in a CO-saturated MeCN/TEOA (4 : 1 v/v) solution containing a mixture of the catalyst and [Ru(bipy)] as the photosensitizer under continuous irradiation (light intensity of 150 mW cm at 25 °C, > 300 nm) show that compounds 1b, 2b and 3b allowed CO reduction catalysis, producing CO and trace amounts of formate. The combined turnover number for the production of formate and CO is 100 after 8 h and follows the order 1b < 2b ≈ 3b.