Catalytic deoxygenation of terminal-diols under acidic aqueous conditions by the ruthenium complexes [(η6-arene)Ru(X)(N ∩ N)](OTf)n, X = H2O, H, η6-arene = p-Me-iPr-C6H4, C6Me6, N ∩ N = bipy, phen, 6,6′-diamino-bipy, 2,9-diamino-phen, n = 1, 2): Influence

A series of ruthenium complexes of the general composition [(η6-arene)(N ∩ N)Ru(X)](Y)n, (arene = p-Me-iPr-C6H4, C6Me6; N ∩ N = bipy, phen, 6,6′-diamino-2,2′-bipyridine, 2,9-diamino-1,10-phenanthroline; X = Cl, H, H2O; Y = Cl, OTf) was synthesized and the new compounds exhaustively structurally characterized by standard techniques (NMR, IR, elemental analysis, single-crystal X-ray crystallography). The single-crystal X-ray structures of [(p-Me-iPr-C6H4)Ru(dabipy)Cl][Cl] (3Cl[Cl]), [(p-Me-iPr-C6H4)Ru(daphen)Cl][Cl] (4Cl[Cl]), [(C6Me6)Ru(dabipy)Cl][Cl] (7Cl[Cl]), [(C6Me6)Ru(daphen)Cl][Cl] (8Cl[OTf]), [(p-Me-iPr-C6H4)Ru(bipy)(H2O)][OTf]2 (1O[OTf]2), [(p-Me-iPr-C6H4)Ru(dabipy)(H2O)][OTf]2 (3O[OTf]2), [(p-Me-iPr-C6H4)Ru(dabipy)(H2O)][SO4] (3O[SO4]), [(p-Me-iPr-C6H4)Ru(daphen)(H2O)][OTf]2 (4O[OTf]2), [(C6Me6)Ru(daphen)(MeOH)][OTf]2 (8(MeOH)[OTf]2), [(p-Me-iPr-C6H4)Ru(dabipy)(H)][OTf] (3H[OTf]), [(p-Me-iPr-C6H4)Ru(daphen)(H)][OTf] (4H[OTf]), [(C6Me6)Ru(dabipy-BH2-OTf)(H)] (7H[-NH2-BH2-OTf]) have been determined. Under 750–1100 psi (5–7.5 MPa) of hydrogen pressure at 110 °C in the presence of acid and water in sulfolane solvent the aquo complexes form active catalysts for the selective deoxygenation of terminal diols, notably 1,2-hexanediol, to the corresponding primary alcohol, i.e., 1-hexanol in up to 60% yield. The presence of amino functions on the ortho-positions of the chelating ligands results in lower catalyst activity. Under the same reaction conditions the catalysts fail to convert glycerol to GC-detectable products. At the higher temperatures (T > 150 °C) possibly required for glycerol activation the catalysts show increasing decomposition with increasing temperature.

Graphical abstractIn sulfolane solvent at 110 °C under 5–7.5 MPa H2(g) and the presence of free HOTf the complexes [(η6-arene)Ru(X)(N ∩ N)](OTf)n form acid and water-tolerant catalysts for the selective deoxygenation of terminal diols, notably 1,2-hexanediol, to the corresponding primary alcohol, i.e., 1-hexanol in up to 60% yield.Figure optionsDownload full-size imageDownload as PowerPoint slide