Pincer and Diamine Ru and Os Diphosphane Complexes as Efficient Catalysts for the Dehydrogenation of Alcohols to Ketones

Abstract

The ruthenium and osmium complexes [MCl(2)(diphosphane)(L)] (M=Ru, Os; L=bidentate amino ligand) and [MCl(CNN)(dppb)] (CNN=pincer ligand; dppb=1,4-bis-(diphenylphosphino)butane), containing the N−H moiety, have been found to catalyze the acceptorless dehydrogenation of alcohols in tBuOH and in the presence of KOtBu. The compounds trans-[MCl(2)(dppf)(en)] (M=Ru 7, Os 13; dppf=1,1'-bisdiphenylphosphino)ferrocene; en=ethylenediamine) display very high activity and different substrates, including cyclic and linear alcohols, are efficiently oxidized to ketones by using 0.8-0.04 mol % of catalyst. The effect of the base and the comparison of the catalytic activity of the Ru versus Os complexes are reported. The ruthenium complex 7 generally leads to a faster conversion into ketones with respect to the osmium complex 13, which displays better activity in the dehydrogenation of 5-en-3β-hydroxy steroids. The synthesis of new Ru and Os complexes [MCl(2)(PP)(L)] (PP=dppb, dppf; L=(±)-trans-1,2-diaminocyclohexane,2-(aminomethyl)pyridine, and 2-aminoethanol) of trans and cis configuration is also reported.

Ruthenium and osmium complexes containing 2-(aminomethyl)pyridine (Ampy)-based ligands in catalysis

“…For the asymmetric TH catalyzed by cisRuCl 2 (PP)(Ampy) based complexes, a further improvement was achieved by isolation the derivatives cis-RuCl 2 (PP)(R-Ampy) containing a chiral diphosphine (PP) correctly matched with a chiral 2-(aminomethyl)pyridine derivative (R-Ampy) displaying a substituent on the carbon connecting the pyridine and amino group of Ampy (R-Ampy: (±)-19a-c in Scheme 12). [19].…”

“…Treatment of RuCl 2 (PPh 3 ) 3 with 1,1-bis(diphenylphosphino)ferrocene (dppf) and Ampy in toluene at 50 • C gave in 92% yield the derivative 17 with trans-configuration, which by heating in toluene at reflux temperature for 24 h afforded the thermodynamically more stable cis-isomer 18 (Scheme 10) [19]. The Ru-complex 18 catalyzed efficiently the selective TH of aldehydes and ketones to alcohols [18].…”

Dehydrogenative Oxidation of Alcohols Catalyzed by Highly Dispersed Ruthenium Incorporated Titanium Oxide

“…The surface area of samples was measured by Brunauer-Emmett- The turnover frequency (TOF) based on Ru for benzyl alcohol oxidation using Ru 0.01 TiO 2 amounts to 130 h −1 where the total amount of ruthenium obtained from Inductively coupled plasma mass spectrometry (ICP) data are used for TOF calculation. In comparison with other heterogeneous catalytic systems in oxidant-free conditions (Au/CeO 2 , (TOF = 125 h −1 ) [7], Ag/Al 2 O 3 (>2 h −1 ) [9], Ru/AlO(OH) (7 h −1 ) [39], Cu/hydrotalcite (1.5 h −1 ) [40], Cu/Al 2 O 3 (8.3 h −1 ) [41]), our value is higher except for the silver nanoparticles on the hydrotalcite system (590 h −1 ) [11].…”

“…In comparison with other heterogeneous catalytic systems in oxidant-free conditions (Au/CeO2, (TOF = 125 h −1 ) [7], Ag/Al2O3 (>2 h −1 ) [9], Ru/AlO(OH) (7 h −1 ) [39], Cu/hydrotalcite (1.5 h −1 ) [40], Cu/Al2O3 (8.3 h −1 ) [41]), our value is higher except for the silver nanoparticles on the hydrotalcite system (590 h −1 ) [11].…”

“…Moreover, there have been lots of studies seeking the novel oxidation catalytic systems of alcohols in which alcohol oxidation is accomplished by a dehydrogenation pathway under oxidant-free conditions. In homogeneous catalytic systems, iridium complexes, osmium, or ruthenium pincer-type complexes, and Grubbs' catalyst were commonly applied for the dehydrogenative oxidation [4][5][6][7]. Recently, nickel complexes were also reported [8].…”