Applying Le Chatelier's Principle for a Highly Efficient Catalytic Transfer Hydrogenation with Ethanol as the Hydrogen Source

Abstract

While isopropanol or formic acid derivatives are mainly applied as hydrogen sources in catalytic transfer hydrogenation reactions, there are only a few reports on the use of primary alcohols. In the present communication we report that ecologically benign and cheap ethanol can be applied with a ruthenium(II) that is completely stable against moisture and oxygen. Catalytic transfer hydrogenation is an equilibrium reaction. Therefore, a rapid removal of acetic aldehyde being formed as the product of ethanol oxidation is the key for high conversions. The reaction shows a broad substrate scope and allows the hydrogenation of ketones, aldehydes and imines.

Electronic Fine‐tuning of Ruthenium(II) Transfer Hydrogenation Catalysts with Ethanol as the Hydrogen Source

“…Only bulky phosphines such as triphenylphosphine, triphenylphosphite and tricyclohexyl- 7, Ru1-N1 2.008(2), Ru1-N2 2.123(2), Ru1-N4 2.141(2), I1-Ru1-I2 87.31(2), I1-Ru1-P1 175.74(2), I1-Ru1-N1 91.83 6, I1-Ru1-N2 88.60 6, I1-Ru1-N4 88.79 6, I2-Ru1-P1 89.10(2), I2-Ru1-N1 179.10 7, I2-Ru1-N2 103.41 6, I2-Ru1-N4 102.68 6, P1-Ru1-N1 91.77 7, P1-Ru1-N2 90.00 6, P1-Ru1-N4 94.24 6, N1-Ru1-N2 76.84(9), N1-Ru1-N4 77.02(9), N2-Ru1-N4 153.62(9). 8, Ru1-N1 2.044(3), Ru1-N2 1.952(2), Ru1-N4 2.154(2), Ru1-C12 2.204(3), Ru1-C13 2.245(3), C12-C13 1.415 5, C24-C25 1.293 7, Cl1-Ru1-Cl2 176.00(3), Cl1-Ru1-N1 90.75 7, Cl1-Ru1-N2 97.33 8, Cl1-Ru1-N4 86.07 7, Cl1-Ru1-C12 84.01 8, Cl1-Ru1-C13 94.00(9), Cl2-Ru1-N1 88.60 7, Cl2-Ru1-N2 86.32 8, Cl2-Ru1-N4 89.94 7, Cl2-Ru1-C12 98.67 (8), Cl2-Ru1-C13 86.46(9), N1-Ru1-N2 75.27(10), N1-Ru1-N4 76.07(10), N1-Ru1-C12 146.76 11, N1-Ru1-C13 174.46 12, N2-Ru1-N4 151.17 11, N2-Ru1-C12 72.92 11, N2-Ru1-C13 106.90 13, N4-Ru1-C12 1.…”

“…Reacting 7, Cl2-Ru1-N2 91.65(6), Cl2-Ru1-N4 91.57(6), P1-Ru1-N1 165.73 7, P1-Ru1-N2 106.53(6), P1-Ru1-N4 101.51 7, N1-Ru1-N2 76.21 (8), N1-Ru1-N4 76.53(8), N2-Ru1-N4 151.96(9); 3 b-D Ru1-Cl1 2.4246(9), Ru1-Cl2 2.4071(9), Ru1-P1 2.2557(8), Ru1-N1 2.064(3), Ru1-N2 2.121(3), Ru1-N4 2.111(2), Cl1-Ru1-Cl2 173.85(3), Cl1-Ru1-P1 98.99(3), Cl1-Ru1-N1 91.31 7, Cl1-Ru1-N2 87.67 7, Cl1-Ru1-N4 87.48 7, Cl2-Ru1-P1 87. 13(3), Cl2-Ru1-N1 82.56 7, Cl2-Ru1-N2 91.42 7, Cl2-Ru1-N4 90.47 7, P1-Ru1-N1 169.63 7, P1-Ru1-N2 105.01 7, P1-Ru1-N4 103.18 (8), N1-Ru1-N2 76.47(10), N1-Ru1-N4 75.90(10), N2-Ru1-N4 151.80(10); 3 b-E Ru1-Cl1 2.4177(5), Ru1-Cl2 2.4194 5 17, Cl1-Ru1-N1 88.06 5, Cl1-Ru1-N2 88.98(4), Cl1-Ru1-N4 90.25(4), Cl1-Ru1-N6 92.33 5, Cl2-Ru1-N1 88.35 5, Cl2-Ru1-N2 89.77(4), Cl2-Ru1-N4 89.49(4), Cl2-Ru1-N6 91.27(5), N1-Ru1-N2 77.49(6), N1-Ru1-N4 78.18(6), N1-Ru1-N6 178.02(6), N2-Ru1-N6 104.46(6), N2-Ru1-N4 155.68(6), N4-Ru1-N6 99.87 (6). 6 a with a second equivalent of silver(I) acetate gave the acetato complex b, while treatment of 6 a with an second equivalent of silver(I) hexafluorophosphate led to the dicationic compound 6 c.…”

“…Since compound 3 b had turned out to be an excellent catalyst for the transfer hydrogenation of ketones and aldehydes, even with ethanol as the hydrogen source, [7,8] it seemed reasonable to also investigate the other above introduced ruthenium(II) complexes for this transformation, since they are structurally closely related. We chose acetophenone (Scheme 9) as the model substrate and took the reaction conditions we recently had published for the transfer hydrogenation with ethanol.…”

“…[7] The same catalyst is also very active in the presence of ethanol as long as the oxidation product acetaldehyde is removed continuously from the reaction mixture. [8] In terms of sustainable chemistry, the replacement of isopropanol by ethanol that can simply be obtained by…”

Two Simple and Highly Efficient Variants of the Griffith‐Ley Oxidation of Alcohols

“…For this, we applied ruthenium complex 1 (Scheme 2), which we recently developed for the transfer hydrogenation of ketones, aldehydes and imines. [13] Compound 1 is highly active in these conversions.…”