Transfer Hydrogenation of Unsaturated Substrates by Half-sandwich Ruthenium Catalysts using Ammonium Formate as Reducing Reagent

Abstract

A series of half‐sandwich phosphine‐ and NHC‐supported complexes were screened in catalytic transfer hydrogenation of nitriles, N‐heterocycles, olefins, and carbonyls by using ammonium formate as the reductant. Complex [Cp(iPr3P)Ru(NCCH3)2][PF6] (3) was found to be the most efficient catalyst. Mechanistic studies suggested that the formate complexes Cp(iPr3P)Ru(κ2‐O2CH) and Cp(iPr3P)Ru(κ1‐O2CH)(NCCH3) could be the true catalysts in these reactions. An inner‐sphere monohydride mechanism was suggested. Excess free phosphine impedes the catalysis by forming the catalytically inactive bis(phosphine) complex Cp(iPr3P)2RuH.

Cyclopentadienyl–Ru(II)–Pyridylamine Complexes: Synthesis, X-ray Structure, and Application in Catalytic Transformation of Bio-Derived Furans to Levulinic Acid and Diketones in Water

“…Tremendous interest toward the development of a wide range of stable cyclopentadienyl–Ru­(II) (η 5 -Cp–Ru) complexes has been observed over the past five decades. , Consequently, due to the unique structural properties, stability, and chemical reactivity of the η 5 -Cp–Ru­(II) complexes, these complexes find application in various fields (Scheme ), including small-molecule activation, transfer hydrogenation, and biology. − In the particular context of catalysis, one of the prominent η 5 -Cp–Ru­(II)-based transfer hydrogenation catalysts is Shvo’s catalyst, which demonstrated the involvement of both the metal and the ligand to control the selectivity. , Nikonov’s group also demonstrated the application of [(η 5 -C 5 H 5 )­Ru­( i Pr 3 P)­(NCCH 3 ) 2 ] in the transfer hydrogenation of ketones, nitriles, esters, and N-heterocycles. , Studies demonstrated the formation of (η 5 -C 5 H 5 )­Ru–H (ruthenium hydride) as an important intermediate species, which facilitated the transfer hydrogenation of these unsaturated groups. − Moreover, mechanistic studies by NMR also revealed the presence of the trihydride species [(η 5 -C 5 H 5 )­Ru­(NHC)­(H) 3 ] (NHC is a carbene ligand) as the catalyst resting stage for the transfer hydrogenation reaction . Weissensteiner et al also demonstrated the catalytic reactivity of the η 5 -Cp–Ru­(II) aminophosphine (PN) complexes [(η 5 -C 5 H 5 )­Ru­(κ 2 -PN)­CH 3 CN] + and [(η 5 -C 5 H 5 )­Ru­(κ 2 -PN)­Br] for the transfer hydrogenation of a wide range of ketones to secondary alcohols .…”

Production of Methane by Catalytic Decarboxylation of Methyl Formate as a Liquid Surrogate

“…In acetonitrile, the reaction did not form methane or methyl iodide, and only methanol as well as unidentified peaks were detected (Table 1, entry 9), which may arise from the decomposition of acetonitrile. 66 In DMF-d 7 , methane was formed in 73% yield, albeit together with 24% of methanol after 3 days of reaction (Table 1, entry 10).…”

“…The influence of the solvent was then tested: replacing THF with an apolar solvent, benzene- d 6 , led to a very low (12%) conversion, and mostly methyl iodide was observed (Table , entry 8). In acetonitrile, the reaction did not form methane or methyl iodide, and only methanol as well as unidentified peaks were detected (Table , entry 9), which may arise from the decomposition of acetonitrile . In DMF- d 7 , methane was formed in 73% yield, albeit together with 24% of methanol after 3 days of reaction (Table , entry 10).…”

Production of Methane by Catalytic Decarboxylation of Methyl Formate as a Liquid Surrogate

“…In acetonitrile, the reaction did not form methane or methyl iodide, and only methanol as well as unidentified peaks were detected (Table 1, Entry 9), which may arise from the decomposition of acetonitrile. 23 In DMF-d7, methane was formed in 73 %yield, albeit together with 24 % of methanol after three days of reaction (Table 1, Entry 10).…”