The Milstein Bipyridyl PNN Pincer Complex of Ruthenium Becomes a Noyori-Type Catalyst under Reducing Conditions.

Hydrogenation of the dearomatized PNN ligand of the Milstein bipyridyl complex RuH(CO)[PNN] () gives a square-pyramidal Ru(II) product RuH(CO)[pPNN] (). The central ring of the pPNN ligand is a piperidine. A minor byproduct of the hydrogenation reaction is complex which has a dimeric structure made of two Ru(II) fragments each possessing a partly hydrogenated PNN ligand.