Influence of gold nanoparticles applied to catalytic hydrogenation of acetophenone with cationic complexes containing ruthenium

Abstract

Herein the catalytic activity of cationic ruthenium(II) complexes [Ru]⁺ is described in the presence of gold nanoparticles (AuNPsⁿ⁻) in the transfer hydrogenation of acetophenone, to produce phenylethanol. The catalytic activity of the complexes, with a general formula cis-[RuCl(CH₃OH)(P–P)(N–N)]⁺ or cis-[RuCl(CH₃OH)(P)₂(N–N)]⁺ {where: P = triphenylphosphine (PPh₃); P–P = 1,1-bis(diphenylphosphino)methane (dppm); 1,2-bis(diphenylphosphino)ethane (dppe); 1,3-bis(diphenylphosphino)propane (dppp), 1,4-bis(diphenylphosphino)butane (dppb); N–N = 2,2′-bipyridine; 4,4′-dimethyl-2,2′-bipyridine} was investigated in the presence of AuNPsⁿ⁻. The interaction between [Ru]⁺ and AuNPsⁿ⁻ citrate capped is an electrostatic interaction, by a self-assembly processes, to produce a supramolecular species, labeled as [Ru]⁺/AuNPsⁿ⁻. This non-covalent interaction has no effect over the chemical and physical chemical parameters of the complexes, which provides a good point of comparison in the presence and absence of AuNPsⁿ⁻. The AuNPsⁿ⁻ alone have no catalytic activity in the transfer hydrogenation of acetophenone within 24 h of reaction. However, the AuNPsⁿ⁻ have improved the catalytic activity of the complexes that have biphosphines with tensioned or large bite angle, while for the complexes that have biphosphines with a strong chelate effect a decrease in the catalytic activity was observed. The evidence is supported by experimental values of the yields of the hydrogenated product and DFT calculations of the “RuP–P” intermediates. Suitable crystals of cis-[RuCl₂(dppe)(bipy)], cis-[RuCl₂(dppp)(bipy)] and cis-[RuCl(CH₃OH)(dppb)(bipy)](PF₆) were obtained and the X-ray structures are presented here.