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

Herein the catalytic activity of cationic ruthenium(II) complexes [Ru](+) is described in the presence of gold nanoparticles (AuNPs(n-)) 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 AuNPs(n-). The interaction between [Ru](+) and AuNPs(n-) citrate capped is an electrostatic interaction, by a self-assembly processes, to produce a supramolecular species, labeled as [Ru](+)/AuNPs(n-). 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 AuNPs(n-). The AuNPs(n-) alone have no catalytic activity in the transfer hydrogenation of acetophenone within 24 h of reaction. However, the AuNPs(n-) 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.