We are studying the reduction of N2 and the oxidation of NH3 by addition/removal of protons and electrons, which often occur by proton-coupled electron transfer pathways. Our focus is on the use of bidentate and polydentate phosphine ligands that enhance the stability of the metal complexes. All three hydrogen atoms are removed from [CpMo(CO)(PPh2NtBu2)(15NH3)]+ by the organic radical 2,4,6-tri-tert-butylphenoxyl, giving an alkylimido ([Mo=NR]+) complex. Reduction with KC8 gives a Mo(IV)-nitride, CpMo(15N)(PPh2NtBu2), which can be protonated at the nitride to generate [CpMo(15NH)(PPh2NtBu2)]+. Iron complexes with a tetradentate P4N2 ligand were characterized for Fe(0), Fe(I), and Fe(II). Fe0(N2)(P4N2) catalyzes the conversion of N2 to N(SiMe3)3 at room temperature, giving up to 65 equiv N(SiMe3)3 per Fe. N2 binding is reversible in [FeI(N2)(P4N2)]+ but much more strongly bound in Fe0(N2)(P4N2). The reaction of H2 with [FeI(P4N2)]+ will be described. A 16-membered tetraphosphine macrocycle binds to Cr, and [Cr(N2)2(PPh4NBn4)] is the first molecular Cr catalyst for reduction of N2. It catalyzes the reduction of N2 to N(SiMe3)3 using Me3SiCl and Na, giving up to 34 equivalents of N(SiMe3)3 per Cr.

Adding or removing protons and electrons in metal-mediated reduction of N2 and oxidation of NH3

255th National Meeting (2018)

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