Formation of Binuclear Ruthenium(II) Aqua Complexes and a Mononuclear Ammonia Complex Bearing P−P−O Facial Tridentate Ligands and Oxametallacycle Moieties

The reaction of Ru(η6-cot)(dmfm)2 (1; cot = 1,3,5-cyclooctatriene, dmfm = dimethyl fumarate) with
water and dppe derivatives (dppe = 1,2-bis(diphenylphosphino)ethane) having two or four methoxy groups
at the ortho positions of the phenyl rings, (S,S)-DIPAMP or o-MeO-dppe, afforded the unique binuclear
Ru(II) aqua complexes 4a,b, where two oxaruthenacycles are combined and hold a water molecule by
coordination and hydrogen bonding, as revealed by X-ray crystallography. Although complex 4b has a
binuclear form in the solid state, disintegration occurred in solution to give the mononuclear aqua complex
4b‘. Complex 4b was further treated with ammonia, resulting in the formation of the mononuclear Ru(II)
ammonia complex 5 via ligand displacement with water. The water oxygen atom and ammonia nitrogen
atom in these complexes can be regarded as chiral centers in the solid state, since they have four different
groups, distinguished by coordination to ruthenium and nonequivalent hydrogen bondings.