Efficient catalytic transfer hydrogenation reactions of carbonyl compounds by Ni(II)-diphosphine complexes

Dehydrogenation of 1-Phenylethanol Catalyzed by Nickel(II)diphosphine Complexes

“…It has recently been shown that nickel(II)diphosphine complexes are very good catalysts in transfer hydrogenation, where various substituted ketones were converted nearly quantitatively to the corresponding alcohols using isopropanol as a sacrificial hydrogen donor as well as a solvent. 31 However, in the current acceptorless conditions, in spite of our attempts with varying reaction stoichiometry and conditions, we were not able to improve the conversion. Gradual disintegration of the catalyst under the reaction conditions is envisaged to be the main cause for the deterioration of catalytic activity.…”

“…[34][35][36][37][38] Continuous bubbling of dry nitrogen/argon gas throughout the reaction period is found to be key to expel the molecular hydrogen produced and to access the better conversions. 16 A drastic decrease in the yield (~8%) was observed, otherwise, due to the superseding backword, hydrogenation reaction 31 (Entry 1, Table 2). Since alcohol dehydrogenation is a thermodynamically uphill process, 39 continuous removal of hydrogen gas will have a positive thermodynamic contribution and can favour the forward reaction.…”

“…However, the dominant backword hydrogenation reaction could also have some key role to play. 16,31 During the course of the catalytic dehydrogenation reaction, a change in the colour of the reaction mixture from yellow to dark brown was observed, which is a typical indication for the formation of Ni(0) related nanoclusters. 31,44 In order to investigate if the Ni(0) nanoclusters have any role to play in the catalysis, a mercury poisoning test (Entry 15, Table 2), 16,47 as well as a carbon disulphide poisoning test (Entry 16, Table 2) 46 were performed.…”

“…16,31 During the course of the catalytic dehydrogenation reaction, a change in the colour of the reaction mixture from yellow to dark brown was observed, which is a typical indication for the formation of Ni(0) related nanoclusters. 31,44 In order to investigate if the Ni(0) nanoclusters have any role to play in the catalysis, a mercury poisoning test (Entry 15, Table 2), 16,47 as well as a carbon disulphide poisoning test (Entry 16, Table 2) 46 were performed. However, both tests turned out to be negative, as no significant difference in the catalytic reactivity/ conversion was observed, thus, ruling out any contribution from a metal nano-particle mediated heterogeneous pathway.…”

“…Ligands, bis(dimethylphosphaneyl)ethane (L1), bis(diethylphosphaneyl)ethane (L2), bis(diphenylphosphaneyl)ethane (L4), triphenylphosphine (L5), bis(diphenylphosphaneyl)methane (L6), 1,3-bis(diphenylphosphaneyl)propane (L7) were purchased from Sigma Aldrich (Merck). Ligand, bis(diisopropylphosphaneyl)ethane (L3) 27 and the nickel(II)catalysts, [1,2-bis(dimethylphosphino)ethane]dichloronickel(II) (C1), 28 [1,2-bis(diethylphosphino)ethane]dichloronickel(II) (C2), 28,29 [1,2 bis(diisopropylphosphino)-ethane] dichloronickel(II) (C3), 30 [1,2-bis(diphenylphosphino) ethane]dichloronickel(II) (C4), 28,31 dichlorobis(triphenylphosphine)nickel(II) (C5), 32 bis(diphenylphosphino) methane] dichloronickel(II) (C6) 31 and bis(diphenylphosphino)propane]dichloronickel(II) (C7) 31 , were prepared by following the reported protocols.…”