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 [Ru2(CO)4(μ-H)(μ-PBut2)(μ-L2)] (1) (Rudouble bond; length as m-dashRu) with nitric oxide afforded four new trans-hyponitrito complexes of the general formula [Ru2(CO)4(μ-H)(μ-PBut2)(μ-L2)(μ-η2-ONNO)] (2) in good yields. Thus the complexes 2a–e were obtained using the following bridging biphosphane ligands (μ-L2): dppm (2a, dppm = Ph2PCH2PPh2), dppen (2b, dppen = Ph2PC(double bond; length as m-dashCH2)PPh2), dpppha (2c, dpppha = Ph2PN(Ph)PPh2), dpppra (2d, dpppra = Ph2PN(Prn)PPh2), and dppbza (2e, dppbza = Ph2PN(CH2Ph)PPh2). 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.