Nitrogenases and Model Complexes in Bioorganometallic Chemistry

This article focuses on organometallic aspects of nitrogenase enzymes. After an introduction to the metalloclusters involved in electron and energy transfer, the predominant focus of the chapter is on the active sites for reduction of N2 and other small molecules, which are carbide-containing iron-sulfur clusters called FeMoco, FeVco, and FeFeco. These clusters harness reducing equivalents and protons to reduce N2, as well as other small molecules like CO2, CN−, and CO. Aspects of the structure, redox, protonation state, mechanism, substrates and products are discussed, highlighting areas where more remains to be learned. It is evident that this organometallic cofactor has much to teach reaction chemists about the multistep pathways for reducing small molecules under mild conditions. After this description of the enzyme, we describe various model complexes which have been used to gain insight into the structure, bonding, and/or reactivity of this cofactor. These complexes mimic aspects such as sulfur/carbon donors, active hydrides, and N2Hx reduction, and form a distinct area of ongoing research that mixes bioinorganic chemistry and organometallic chemistry.