New Ruthenium Nitrosyl Pincer Complexes Bearing an O sub(2) Ligand. Mono-Oxygen Transfer

We report on Ru( super(II))( mu super(2)- O sub(2)) nitrosyl pincer complexes that can return to their original Ru(0) state by reaction with mono-oxygen scavengers. Potential intermediates were calculated by density functional theory (DFT) and a mechanism is proposed, revealing a new type of metal-ligand cooperation consisting of activation of the O sub(2) moiety by both the metal center and the NO ligand. Reaction of the Ru(0) nitrosyl complex 1 with O sub(2) quantitatively yielded the crystallographically characterized Ru super((II)) ( mu super(2)-O sub(2)) nitrosyl complex 2. Reaction of 2 with the mono-oxygen scavengers phosphines or CO gave the Ru(0) complex 1 and phosphine oxides, or the carbonyl complex 3 (1 trapped by CO) and CO sub(2), respectively. Reaction of 2 with 1 equiv of phosphine at room temperature or -40 [degrees]C resulted in immediate formation of half an equivalent of 1 and 1 equiv of phosphine oxide, while half an equivalent of 2 remained unchanged. Overnight reaction at room temperature of 2 with excess CO (> or =3 equiv) resulted in 3 and CO sub(2) gas as the only products. Reaction of 1 with 1 equiv of mono-oxygen source (dioxirane) at -78 [degrees]C yielded the Ru super((II))( mu super(2)- O sub(2)) complex 2. Similarly, reaction of the Ru(0) dearomatized complex 4 with O sub(2) led to the crystallographicaly characterized Ru super((II))( mu super(2)- O sub(2) complex 5. Further reaction of 5 with mono-oxygen scavengers (phosphines or CO) led to the Ru(0) complex 4 and phosphine oxides or complex 6 (4 trapped by CO) and CO sub(2). When instead only 1 equiv of 5 was reacted with 1 equiv of phosphine at room temperature, immediate formation of half an equivalent of 4 and 1 equiv of phosphine oxide took place, while half an equivalent of 5 remained unchanged. When 5 reacted with an excess of CO (> or =3 equiv), complex 6 and CO sub(2) gas were the only products obtained. DFT studies indicate a new mode of metal-ligand cooperation involving the nitrosyl ligand in the oxygen transfer process.