Hydrogenation of α,β‐unsaturated carbonyl compounds over covalently heterogenized Ru(II) diphosphine complexes on AlPO4‐sepiolite supports

Abstract

In this work, the covalent immobilization of two ruthenium(II) complexes, i.e., [RuIICl (bpea){(S)(‐)(BINAP)}](BF4), 1, and [RuIICl(bpea)(DPPE)](BF4), 2, where BINAP = 2,2'‐bis(diphenylphosphino)‐ 1,1'‐binaphthyl and DPPE = 1,2‐bis(diphenylphosphino)ethane, have been obtained (AlPO4‐Sepiolite@1 and AlPO4‐Sepiolite@2) by using a N‐tridentate ligand N,N‐bis‐(2‐pyridylmethyl) ethylamine (bpea), linked to an amorphous AlPO4‐Sepiolite (20/80) inorganic support. This AlPO4‐sepiolite support is able to immobilize the double amount of ruthenium complex (1.65%) than the amorphous AlPO4 (0.89%). Both heterogenized complexes have been assessed as catalysts in the liquid phase hydrogenation of several substrates with carbonyl and/or olefinic double bonds using methanol as solvent, attaining good catalytic activity and high enantioselectivity (99%). The highest Turn Over Number (TON) value (748.6) was obtained over the [RuII Cl (bpea)(DPPE)](BF4) 2 catalyst, although the [RuIICl(bpea){(S)(‐)(BINAP)}](BF4) 1 exhibits better reusability. In fact, the [RuIICl(bpea){(S)(‐)(BINAP)}](BF4) immobilized on AlPO4‐Sepiolite maintained the activity throughout 14 successive runs. Furthermore, some findings on hydrogenation mechanisms of the α,β‐unsaturated carbonyl compounds over Ru catalysts have been also obtained