The biological reduction of nitrogen to ammonia may occur via one of two predominant pathways in which nitrogenous NxHy intermediates including hydrazine (N2H4), diazene (N2H2), nitride (N3-) and imide (NH2-) may be involved. To test the validity of hypotheses concerning iron’s direct role in the stepwise reduction of N2, iron model systems are needed. Such systems can test the chemical compatibility of iron with various proposed NxHy intermediates, and the reactivity patterns of such species. Here we describe a TBP (SiPR3)Fe-L scaffold (SiPR3 represents [Si(o-C6H4PR2)3]−; R = Ph and iPr) where the apical site is occupied by nitrogenous ligands such as N2, N2H4, NH3 and N2R. The system accommodates terminally bound N2 in the three formal oxidation states (iron(0), +1, and +2). N2 uptake is demonstrated via displacement of its reduction partners NH3 and N2H4, and N2 functionalizaton is illustrated via electrophilic silylation.

Reversible, heterolytic addition of H2 across an iron-boron bond in a ferraboratrane with formal hydride transfer to the boron gives iron-borohydrido-hydride complexes. These compounds catalyze the hydrogenation of alkenes and alkynes to the respective alkanes. Notably, the boron is capable of acting as a shuttle for hydride transfer to substrates. The results are interesting in the context of heterolytic substrate addition across metal-boron bonds in metallaboratranes and related systems, as well as metal-ligand bifunctional catalysis.

A series of monocarbonyl iron complexes in the formal oxidation states 0, þ1, and þ2 are accessible when supported by a tetradentate tris(phosphino)silyl ligand (SiP iPr 3 = [Si(o-C 6 H 4 PiPr 2 ) 3 ] -). X-ray diffraction (XRD) studies of these carbonyl complexes establish little geometrical change about the iron center as a function of oxidation state. It is possible to functionalize the terminal CO ligand of the most reduced carbonyl adduct by addition of SiMe 3 þ to afford a welldefined iron carbyne species, (SiP iPr 3 )FetC-OSiMe 3 . Single-crystal XRD data of this iron carbyne derivative reveal an unusually short FetC-OSiMe 3 bond distance (1.671(2) Å) and a substantially elongated C-O distance (1.278(3) Å), consistent with Fe-C carbyne character. The overall trigonal bipyramidal geometry of (SiP iPr3 )FetC-OSiMe 3 compares well with that of the corresponding carbonyls, (SiP iPr 3 )Fe(CO) -, (SiP iPr 3 )Fe(CO), and (SiP iPr 3 )Fe(CO) þ . Details regarding the electronic structure of the carbyne complex have been explored via the collection of comparative M€ ossbauer data for all of the complexes featured and also via DFT calculations. In sum, these data point to a strongly π-accepting Fischer-type carbyne ligand that confers stability to a lowvalent iron(0) rather than high-valent iron(IV) center.

The tetradentate tris(phosphino)silyl ligand [SiP(iPr)(3)] ([SiP(iPr)(3)] = [Si(o-C(6)H(4)P(i)Pr(2))(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 [SiP(iPr)(3)]M-Cl (M = Fe, Co, Ni), as well as the monovalent dinitrogen adducts [SiP(iPr)(3)]M-N(2) (M = Fe, Co, Ir), which are compared with related [SiP(Ph)(3)]M-Cl and [SiP(Ph)(3)]M-N(2) 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 [SiP(R)(3)]M-N(2) precursors affords the divalent iron triflate [SiP(Ph)(3)]Fe(OTf) and trivalent cobalt triflate {[SiP(iPr)(3)]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.

A T-shaped Ni complex was synthesized using a rigid acridane-based pincer ligand to prepare a metalloradical center. Structural data displays a nickel ion is embedded in the plane of a PNP ligand. Having a sterically exposed half-filled dx2-y2 orbital, this three-coordinate Ni species reveals unique open-shell reactivity including the homolytic cleavage of various σ-bonds, such as H-H, N-N, and C-C.