Ketone transfer hydrogenation has become a versatile and powerful method for the production of secondary alcohols. We have recently reported the synthesis and chemical properties of a series of 18e and 16e half-sandwich arene ruthenium iminophosphonamide (NPN) complexes of type [(arene)Ru{(R2P(NR’)2}(X)] (X = Cl-, PF6-, BAr4-), structural analogues of Noyori’s catalyst [(arene)RuCl(Ts-DPEN)] (DPEN = 1,2-diamino-1,2-diphenylethane). The zwitterionic NPN ligand is a strong σ,π-donor and can efficiently stabilize coordinatively unsaturated 16e NPN complexes. We shall present here the first examples of catalytic transfer hydrogenation of acetophenone with these complexes (arene = p-cymene, C6Me6; R = p-Tol; R’ = Ph) in isopropanol. In the absence of added base, only the 18e NPN-complexes (X = Cl) show moderate catalytic activity (TOF ~ 10 h-1). However, addition of a strong base makes both the 18e and the 16e complexes active (TOF ~ 200 h-1). Mechanistic studies have revealed the nature of catalytic intermediates through isolation or spectroscopic characterization.

Transfer hydrogenation of ketones catalyzed by novel arene ruthenium iminophosphonamides

254th National Meeting (2017)

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