Fast Transfer Hydrogenation(TH) in Aerobic Condition and Oxidation of Alcohols with N‐Methylmorpholine‐N‐oxide Catalyzed by Ru(II) Ligated with Chalcogenated Pyridines and PPh₃

Abstract

The transfer hydrogenation (TH) of aldehydes / ketones (at mmol level), using propan‐2‐ol as a H‐source is complete within 15 min when catalyzed by 0.1 mol% of [Ru(L)(PPh3)Cl2]] (1–4; L=L1–L4; L1/L2=(E)‐2‐(phenylthio/seleno)‐N‐(pyridin‐2‐ylmethyene)ethan‐amine, L3/L4=2‐(phenylthio/seleno)‐N‐(pyridin‐2‐ylmethyl)ethan‐ amine). The 1–4 were prepared by treating [Ru(PPh3)3Cl2] with L1–L4 respectively.The L1–L4 and 1–4 were characterized by 1H, 13C{1H} and 77Se{1H} NMR spectra. Single crystal structures of 1–4 determined by X‐ray diffraction revealed distorted octahedral geometry of Ru in each complex and bond lengths (Å) as: Ru−S, 2.3441(1) and 2.335(3) and Ru−Se, 2.4497(2) and 2.4518(4). Each of 1–4 (0.1 mol%) is almost equally efficient as catalyst for TH and oxidation of alcohols with N‐methylmorpholine‐N‐oxide (NMO). The optimum amount of oxidant NMO was found 3 mmol for 1 mmol of alcohol. In ambient conditions both the catalytic reactions by the four complexes appear to be homogeneous. The scope of substrates for both the reactions is reported.

Nucleophilic substitution reaction as an important tool in the synthetic protocol for selenium donor containing Schiff bases: applications of metal complexes in homogeneous catalysis

“…RuCl 2 (PPh 3 ) 3 is used for the synthesis of complex 4 . 27 It is added directly as a solid (Scheme 5) to the solution of L9 in benzene under a nitrogen environment. The complex 4 has a distorted octahedral geometry around ruthenium.…”

“…Complexes of Se donor containing Schiff bases are used 26–29 to catalyse the TH reactions of various aldehydes and ketones including benzaldehyde, 4-nitrobenzaldehyde, 4-bromobenzaldehyde, 4-chlorobenzaldehyde, 4-fluorobenzaldehyde, 4-anisaldehyde, 4-methylbenzaldehyde, 2-bromobenzaldehyde, 3-anisaldehyde 2-pyridinecarboxaldehyde, acetophenone, propiophenone, 4-methylacetophenone, octan-2-one, benzophenone, cyclopentanone, 4-chloroacetophenone, pentan-2-one, butan-2-one, and 2-pyridine carboxaldehyde.…”

“…9 In the recent past, such selenium containing ligands have been used to develop interesting and highly competent homogeneous catalytic systems for various organic transformations. 10,12,[16][17][18][19][22][23][24][25][26][27][28][29][30][31][32][33][34][35] This article aims at covering the utility of nucleophilic substitution reaction as a tool in the synthetic methodologies for selenium containing Schiff base ligands and their metal complexes, and also analyzing their applications in catalysis of various organic transformations such as Suzuki coupling, Heck coupling, Sonogashira coupling, C-O coupling, oxidation of alcohols and transfer hydrogenation reactions.…”

“…26,29 At room temperature, 2-(phenylseleno)ethylamine and pyridine 2-carboxaldehyde combine (Chart 2) to produce the ligand L9. 27 Ligand L10 is synthesized (Chart 2) by mixing a solution of 2-(phenylseleno)ethylamine and 2-methylthiobenzaldehyde in dry CH 3 OH, 28,30,31 followed by stirring. For the synthesis of ligand L11, 2-(phenylseleno)ethylamine and o-hydroxyacetophenone (Chart 2) are stirred 18 together in dry ethanol at room temperature.…”

“…Compounds such as propan-2-ol, and glycerol 85-93 are used as hydrogen donors in 4) of aliphatic and aromatic carbonyl compounds. [26][27][28][29] Hydrogenation of such compounds can be done using propan-2-ol (iPrOH) as the source of hydrogen. Such reactions produce acetone as the by-product, which can be easily eliminated from the mixture during the work-up.…”