Group 8 and 10 hyponitrite and dinitrosyl complexes

cis-Hyponitrite complexes LnM(N2O2) (M = Ni, Pt; Ln = PPh3, PPh2Me, dppe, and dppf) of divalent group 10 metals have been previously shown to be readily prepared by treating the corresponding LnMCl2 derivatives with sodium-(Z)-1-{4-(2,6-di-tert-butyl-4-methoxycyclohexadienonyl)}diazen-1-ium-1,2-diolate. These complexes adopt a diamagnetic square planar geometry with oxygen bound chelating planar cis-hyponitrite ligands. They are readily prepared at room temperature but thermally decompose above 90 °C with release of nitrous oxide. Electrophiles such as iodine, methyltriflate, and hydrochloric acid also react rapidly with the cis-hyponitrite complexes to give nitrous oxide. The structure of one of these previously prepared complexes, (PPh3)2Pt(N2O2), has been redetermined at −100 °C as a dichloromethane solvate with improved precision. The related tetrahedral group 8 dinitrosyl complexes, (PPh3)2M(NO)2 (M = Ru, Os; Ln = PPh3, dppe, and dppf) have been reexamined and new derivatives with chelating phosphines have been prepared by ligand substitution on the corresponding (PPh3)2M(NO)2. The structures of Ru(dppf)(NO)2 and Os(dppe)(NO)2 have been determined. These two analogous families of cis-hyponitrite and dinitrosyl complexes illustrate the balance of metal dn electron count and nitrosyl redox state with one having linear nitrosyls bound to low valent metal centers, and the former having coupled N2O22- ligands bound to a higher oxidation state metal center.

Group 8 and 10 complexes bind two NO’s in very different ways; either as a pair of linear dinitrosyls for group 8, or as coupled hyponitrtie in the case of group 10. Thus for polynitrosyl complexes the redox state of pairs of NO ligands need to be considered in addition to their bent/linear or the metal’s oxidation state.Figure optionsDownload as PowerPoint slide