The Geometric and Electronic Structure of [(cyclam-acetato)Fe(N)]+: A Genuine Iron(V) Species with a Ground-State Spin S=1/2

摘要

High-valent transition-metal complexes play a crucial role as intermediates in the reaction cycles of metalloenzymes[1], [2] and, consequently, the synthesis of low-molecular-weight compounds that model the active sites is a major challenge in synthetic inorganic chemistry. Many of these observed heme- and non-heme enzyme intermediates contain terminal oxo ligands.[2] While in recent years a number of heme- and non-heme FeIVO complexes have been prepared and spectroscopically characterized,[3] much less is known about the corresponding high-valent iron-nitrido species despite their possible involvement in enzymes from the biogeochemical nitrogen cycle. However, over the course of the last few years a number of high-valent non-heme metal-nitrido species containing VV, CrV, MnV, and FeV ions have been prepared by atom and/or group-transfer reactions or by photolysis.[4], [5] We note that Wagner and Nakamoto[5c], [d] have previously reported the photochemical generation of [FeV(N)(TPP) (TPP2-=tetraphenylporphinate(2-)) and measured its resonance Raman spectrum. Most recently, Betley and Peters synthesized and characterized the distorted tetrahedrally coordinated terminal FeIV-nitrido species [PhBPiPr3]FeIVN ([PhBPiPr3]=[PhB(CH2PiPr2)3]-).[6] This compound was shown to be diamagnetic at room temperature and exhibit 15N NMR resonances near =952 ppm and a (FeN) stretching frequency of 1034 cm-1. Furthermore, density functional theory (DFT) calculations at the B3LYP level of theory predicted a very short FeN bond of 1.49 ?.