Dinitrogen Complexes Supported by Tris(phosphino)silyl Ligands

The tetradentate tris(phosphino)silyl ligand [SiPiPr3] ([SiPiPr3] = [Si(o-C6H4PiPr2)3]−) has been prepared, and its complexation with iron, cobalt, nickel, and iridium precursors has been explored. Several coordination complexes have been thoroughly characterized and are described. These include, for example, the divalent trigonal bipyramidal metal chlorides [SiPiPr3]M−Cl (M = Fe, Co, Ni), as well as the monovalent dinitrogen adducts [SiPiPr3]M−N2 (M = Fe, Co, Ir), which are compared with related [SiPPh3]M−Cl and [SiPPh3]M−N2 species (M = Fe, Co). Complexes of this type represent the first examples of terminal dinitrogen adducts of monovalent iron, and the ligand architecture allows examination of a unique class of dinitrogen adducts with a trans-disposed silyl donor. Oxidation of the appropriate [SiPR3]M−N2 precursors affords the divalent iron triflate [SiPPh3]Fe(OTf) and trivalent cobalt triflate {[SiPiPr3]Co(OTf)}{OTf} complexes, which are of interest for group transfer studies because of the presence of a labile triflate ligand. Comparative electrochemical, structural, and spectroscopic data are provided for these complexes.