Abstract

Utilizing the bulky guanidinate ligand [L-Ar*](-) (L-Ar* = (Ar*N)(2)C(R), Ar* = 2,6-bis(diphenylmethyl)-4-tert-butylphenyl, R = (NCBu2)-Bu-t) for kinetic stabilization, the synthesis of a rare terminal Fe(IV) nitride complex is reported. UV irradiation of a pyridine solution of the Fe(II) azide [L-Ar*]FeN3(py) (3-py) at 0 degrees C cleanly generates the Fe(IV) nitride [L-Ar*]FeN(py) (1). The N-15 NMR spectrum of the 1(15N) (50% FO N-15) isotopomer shows a resonance at 1016 ppm (vs externally referenced CH3NO2 at 380 ppm), comparable to that known for other terminal iron nitrides. Notably, the computed structure of 1 reveals an iron center with distorted tetrahedral geometry, tau(4) = 0.72, featuring a short Fe N bond (1.52 angstrom). Inspection of the frontier orbital ordering of 1 shows a relatively small HOMO/LUMO gap with the LUMO comprised by Fe(d(xz,yz))N(p(x,y)) pi*-orbitals, a splitting that is manifested in the electronic absorption spectrum of 1 (lambda = 610 nm, epsilon = 1375 L center dot mol(-1)center dot cm(-1); lambda = 613 run (calcd)). Complex 1 persists in low-temperature solutions of pyridine but becomes unstable at room temperature, gradually converting to the Fe(II) hydrazide product [kappa(2)-((Bu2CN)-Bu-t)C(eta(6)-NAr*)(N-NAr*)]Fe (4) upon standing via intramolecular N-atom insertion. This reactivity of the Fe N moiety was assessed through molecular orbital analysis, which suggests electrophilic character at the nitride functionality. Accordingly, treatment of 1 with the nucleophiles PMe2Ph and Ar-N C (Ar = 2,6-dimethylphenyl) leads to partial N-atom transfer and formation of the Fe(II) addition products [L-Ar*]Fe(N=PMe2Ph)(py) (5) and [L-Ar*]Fe(N=C=NAr)(py) (6). Similarly, 1 reacts with PhSiH3 to give [L-Ar*]Fe[N(H)(SiH2Ph)](py) (7) which Fukui analysis shows to proceed via electrophilic insertion of the nitride into the Si-H bond.