Mononuclear ruthenium catalysts for the direct propargylation of heterocycles with propargyl alcohols

A new family of mononuclear ruthenium catalysts for the catalytic direct propargylation by propargylic alcohols of heterocycles is presented. The catalyst activity can be improved by tuning the ligand's influence and electronic properties at the metal centre. Whereas [(p-cymene)RuCl(PR3)][OTf] (PR3 = PCy3, PPh3) complexes catalyse the propargylation of furan or 2-methylfuran by the alkynol HC=CCH(OH)Ph in moderate yield, mononuclear [(p-cymene)RuCl(CO)(PR3)][OTf] complexes are more active to achieve the same reaction. Low temperature NMR experiments performed on the stoichiometric reaction of the parent [(p-cymene)RuCl(PR3)][B(Ar-F)(4)] and the alkynol show the unexpected in situ formation, via allenylidene and hydroxycarbene intermediates, of the carbonyl complexes [(p-cymene)RuCl(CO)(PR3)][B(Ar-F)(4)] [Ar-F=3,5-(CF3)(2)C6H3] that appear to be the best catalyst precursors.