215665-93-3Relevant academic research and scientific papers
On the Functional Group Tolerance of Ester Hydrogenation and Polyester Depolymerisation Catalysed by Ruthenium Complexes of Tridentate Aminophosphine Ligands
Fuentes, José A.,Smith, Samuel M.,Scharbert, M. Theresa,Carpenter, Ian,Cordes, David B.,Slawin, Alexandra M. Z.,Clarke, Matthew L.
, p. 10851 - 10869 (2015)
The synthesis of a range of phosphine-diamine, phosphine-amino-alcohol, and phosphine-amino-amide ligands and their ruthenium(II) complexes are reported. Five of these were characterised by X-ray crystallography. The activities of this collection of catalysts were initially compared for the hydrogenation of two model ester hydrogenations. Catalyst turnover frequencies up to 2400 h-1 were observed at 85 °C. However, turnover is slow at near ambient temperatures. By using a phosphine-diamine RuII complex, identified as the most active catalyst, a range of aromatic esters were reduced in high yield. The hydrogenation of alkene-, diene-, and alkyne-functionalised esters was also studied. Substrates with a remote, but reactive terminal alkene substituent could be reduced chemoselectively in the presence of 4-dimethylaminopyridine (DMAP) co-catalyst. The chemoselective reduction of the ester function in conjugated dienoate ethyl sorbate could deliver (2E,4E)-hexa-2,4-dien-1-ol, a precursor to leaf alcohol. The monounsaturated alcohol (E)-hex-4-en-1-ol was produced with reasonable selectivity, but complete chemoselectivity of C=O over the diene is elusive. High chemoselectivity for the reduction of an ester over an alkyne group was observed in the hydrogenation of an alkynoate for the first time. The catalysts were also active in the depolymerisation reduction of samples of waste poly(ethylene terephthalate) (PET) to produce benzene dimethanol. These depolymerisations were found to be poisoned by the ethylene glycol side product, although good yields could still be achieved. A simple catalyst for difficult reductions: Ruthenium complexes of P,N,N and P,N,O ligands catalyse the reduction of esters with high activities. The Ru complex of a phosphine-diamine ligand (see scheme) has been found to be a good catalyst for reducing alkene-, diene-, and alkyne-functionalised esters, displaying good activity and chemoselectivity. This catalyst was also active in the hydrogenation of waste poly(ethylene terephthalate) (PET).
