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) (RuRu) 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(CH2)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.

Graphical abstractThe synthesis and crystal structures of new trans-hyponitrito complexes [Ru2(CO)4(μ-H)(μ-PBut2)(μ-L2)(μ-η2-ONNO)] (L2 = biphosphanes or aminobiphosphanes) are reported. The compounds were obtained by the reaction of the coordinatively unsaturated complexes [Ru2(CO)4(μ-H)(μ-PBut2)(μ-L2)] (RuRu) with NO. The latter species couple in their coordination sphere two NO molecules to trans-hyponitrite and offer the possibility for the elimination of N2O.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The synthesis of four new trans-hyponitrito diruthenium complexes was reported. ► These compounds can serve as model complexes in NO reductase processes. ► The molecular structures of all new compounds were determined by X-ray crystallography.