We report the identification and reactivity of an iron hydride species in a synthetic model complex of monoiron hydrogenase. The hydride complex is derived from a phosphine-free CNS chelate that includes a FeCNH(=O) bond (carbamoyl) as a mimic of the active site iron acyl. The reaction of [(O=(CNSMe)-N-HN-S-py)Fe(CO)(2)(Br)] (1) with NaHBEt3 generates the iron hydride intermediate [(O=(CNpySMe)-N-HN)Fe(H)(CO)(2)] (2; delta(Fe)-H = -5.08 ppm). Above -40 degrees C, the hydride species extrudes CH3S via intramolecular hydride transfer, which is stoichiometrically trapped in the structurally characterized dimer mu 2-(CH3S)(2)-[(O=(CNPh)-N-HN)Fe(CO)(2)](2) (3). Alternately, when activated by base (tBuOK), 1 undergoes desulfurization to form a cyclometalated species, [((CNCPh)-C-O=-N-NH)Fe(CO)(2)] (5); derivatization of 5 with PPh3 affords the structurally characterized species [((CNC)-C-O=-N-NH)Fe(CO)(PPh3)(2)] (6), indicating complex 6 as the common intermediate along each pathway of desulfurization.