Dihydroxybipyridine complexes of ruthenium and iridium for water oxidation and hydrogenation

Abstract

Ruthenium and iridium cationic complexes [ArM(Y)(L2)]A [1, M = Ru, Ar = η6-arene, Y = anionic ligand, L2 = 6,6'-dihydroxy-2,2'-bipyridine, 4,4'-dihydroxy-2,2'-bipyridine, 2,2'-En[[C5H2N]PX]2, where En = bond, CO, O, CH2, CHSO3-, P = alkyl, phosphate, sulfonate in 4-, 5-, 6-positions, X = hydrogen-bonding group, such as OH, in 4- or 6-positions; M = Ir, Ar = η5-cyclopentadienyl, same Y, L2; A = anionic group], useful as pH-dependent catalysts for water oxidn., and (transfer) hydrogenation of ketones and carbon dioxide, were prepd. by reductive coupling of 2-chloro-6-methoxypyridines and subsequent complexation with metal precursors and examd. in catalytic reactions of water oxidn. with (NH4)2Ce(NO3)6 (CAN) yielding O2, and hydrogenation of ketones into alcs. In an example, water oxidn. by 0.1 M soln. of (NH4)2Ce(NO3)6 catalyzed by 17 μM aq. soln. of [Cp*IrCl[4,4'-(HO)2-2,2'-bpy]]Cl (1a) resulted in O2 formation with a rate of 600 μM/L in 10 min. In another example, hydrogenation of acetophenone at 75 psi of H2 in 10:90 MeOH/water at reflux for 16-18 h catalyzed by 1 mol% of [(η6-p-cymene)RuCl[6,6'-(HO)2-2,2'-bpy]]Cl (1b) gave the 1-phenylethanol product with 97% conversion, 16.7 h-1 turnover frequency and 97 TON. [on SciFinder(R)]