The organometallic chemistry of iron has been dominated by strong-field supporting ligands such as CO, CN, and phosphines, and by macrocyclic N ligands like porphyrins. The active sites of hydrogenase enzymes incorporate S-based ligands, and these are low-spin due to the influence of carbonyl and cyanide donors. However, the interesting reactions of nitrogenase enzymes, and a new generation of low-valent iron catalysts, have predominantly weak-field ligands and have led to increasing interest in organometallic iron complexes with higher spin states. We focus here on iron coordination environments that result from a mixture of C and S donors -choices that are particularly compelling since the six "belt" iron atoms in the ironmolybdenum cofactor (FeMoco) of nitrogenase have a mixed C/S coordination sphere. This unusual combination of potentially strong-field C donors and weak-field S donors could lead to changes in spin states during catalysis, which has been linked to changes in barriers and selectivity. Thus, the study of C-and S-ligated iron has relevance for both fundamental coordination chemistry and bioinorganic mechanisms. However, CO-free iron complexes with supporting ligands that coordinate through only carbon and sulfur donors are rare. Of these examples, only one multidentate C/S ligand is known to support N2 binding. In addition, Qu has provided important studies on Cp*-supported iron dimers bridged by dithiolates, and this C/S ligand sphere can bind and facilitate the reduction of nitrogenase-relevant NxHy substrates. Our group's recent work on SCS systems began with a dithiolate ligand having a central arene that can interact with iron through backbonding into its π-system in low oxidation states. While this hemilabile interaction stabilizes the reduced complexes, complete dissociation of the SCS ligand occurred in the presence of Brønsted acids, and backbonding into N2 competed with backbonding into the arene. In order to address this instability, we then moved to tridentate pincer 4 Chart 1. Typical palladium SCS pincer complexes and closely-related iron complexes with SNS and SCS pincers. In the bottom pictures, the square represents a coordination site with various ligands.