Reductive NO dimerization to trans-hyponitrite in diruthenium complexes: Intramolecular attack of hyponitrite on a CO ligand

The reaction of the electronically and coordinatively unsaturated compounds [Ru 2 (CO) 4 ( μ -H)( μ -PBu t 2 )( μ -L 2 )] ( 1 ) (Ru Ru) with nitric oxide afforded four new trans -hyponitrito complexes of the general formula [Ru 2 (CO) 4 ( μ -H)( μ -PBu t 2 )( μ -L 2 )( μ - η 2 -ONNO)] ( 2 ) in good yields. Thus the complexes 2a – e were obtained using the following bridging biphosphane ligands ( μ -L 2 ): dppm ( 2a , dppm = Ph 2 PCH 2 PPh 2 ), dppen ( 2b , dppen = Ph 2 PC( CH 2 )PPh 2 ), dpppha ( 2c , dpppha = Ph 2 PN(Ph)PPh 2 ), dpppra ( 2d , dpppra = Ph 2 PN(Pr n )PPh 2 ), and dppbza ( 2e , dppbza = Ph 2 PN(CH 2 Ph)PPh 2 ). The molecular structures of the complexes 2a – e were determined by X-ray diffraction. Furthermore the molecular structure of the known compound 2a was reinvestigated in light of a better refinement of the short intramolecular contact between the hyponitrite O atom in close vicinity to the C atom of a neighbouring carbonyl group. This unusual effect in crystals of all compounds 2a – e can be interpreted as a nucleophilic intramolecular attack of a hyponitrito ligand towards an electrophilic carbon center of a carbonyl ligand.