Triggering N2 uptake via redox-induced expulsion of coordinated NH3 and N2 silylation at trigonal bipyramidal iron

Abstract

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.

Cationic silyldiazenido complexes of the Fe(diphosphine)2(N2) platform: structural and electronic models for an elusive first intermediate in N2fixation

“…13 The Fe-N bond lengths (see Table 1) are appreciably shorter, and N-N bond lengths notably longer, than in 1 (cf. 1.748 (8) 8,15 Collectively these data correlate with an enhanced transfer of electron density from Fe into the NN fragment upon electrophilic attack at the terminal nitrogen (N β ), which results in an increased Fe-N bond order attendant with a reduction in the N-N bond order. Recently, the borane adduct Fe(depe) 2 (NN·B(C 6 F 5 ) 3 ) has been structurally verified, 16 which permits a valuable comparison between electrophiles of differing Lewis acidity upon the extent of electron transfer from Fe to N 2 , using the same parent system 1.…”

“…Notably, silylium ions (R 3 Si + ) are valid proton mimics in this regard since they are isolobal and isocharged with H + , yet impart an enhanced kinetic stability to the resultant silyldiazenides, which greatly facilitates the detailed characterisation of complexes relative to their protonated counterparts. 3,6 However, structurally verified examples resulting from the direct monosilylation of FeN 2 species remain limited [7][8][9] and, despite the proven competence of 1 in catalytic N 2 fixation, none have yet been reported for this system. 10 Figure 1).…”

Iron-catalysed transformation of molecular dinitrogen into silylamine under ambient conditions

“…In this reaction system, up to 34 equiv. of N(SiMe 3 ) 3 Recently, the preparation of Fe-N 2 complexes and their stoichiometric reactivity have been intensively studied [24][25][26][27] , but the Fe-catalysed transformation of N 2 by using Fe-N 2 complexes has not yet been reported until now 28 . We believe that the results described here provide valuable and useful information to develop the Fe-catalysed transformation of N 2 .…”

Ruthenium and Osmium Metalloradicals

“…A key to further stabilize the construct could be the incorporation of the anionic function into the tetradentate ligand to yield a M(XL 3 ) moiety. On the basis of this idea, Peters has recently developed tris(o-phosphinophenyl)silyl ligands (their relationship to the Sacconi system is illustrated in Scheme 1), and shown that they are capable of stabilizing dinitrogen complexes of Fe [6][7][8] More recently, the same ligand (with R = iPr) has successfully been used to generate the first stable mononuclear ruthenium(I) and osmium(I) metalloradicals (see Scheme 2).[9] The precursor complexes [(SiP The two dinitrogen complexes (1 and 2) were also investigated electrochemically, revealing a reduction and an oxidation. The reduction process is reversible for both compounds and the stable M 0 products could be generated by stoichiometric reductions with KC 8 , isolated, and crystallographically characterized.…”