Crystallization of 2 gave green blocks suitable for X-ray diffraction (Figure , top). The diffraction data showed an octahedral iron site with a meridional pincer ligand as expected. The Fe-C bond length is 1.9502(18) Å, and the average Fe-S length is 2.268(9) Å. The three Fe-P bonds are only slightly different, with a length of 2.2484(3) Å for the phosphine trans to C and lengths of 2.2553(4) Å and 2.2608(4) Å for the phosphines cis to C. There was disorder at the thioamide N-H site, which was satisfactorily modeled with each thioamide having 50% hydrogen atom occupancy, consistent with single protonation of the supporting ligand in 2. The Mössbauer spectrum of 2 has a doublet with δ = 0.21 mm/s and |ΔEQ| = 1.25 mm/s (Figure ). Proton NMR spectra in either C6D6 or THF-d8 show signals in the range expected for a diamagnetic complex of low-spin iron(II). The most downfield resonance integrates 1:1 with proton groups from each side of the molecule (Figure ). Adding D2O made this signal disappear, and therefore it is assigned as the thioamide proton. Based on the NMR spectra, 2 is unsymmetric in solution, and it is best described has having one neutral thioamide S donor and one anionic iminothiolate donor. The solid-state IR spectrum of 2 shows a broad peak centered at 3336 cm -1 (Figure , red trace), which is distinct from the analogous signal in free ligand 1 at 3136 cm -1 (Figure , gray trace), consistent with an N-H stretching vibration. We hypothesize that the thioamide arm is deprotonated during the synthesis of 2 by a transient iron hydride to form H2, which explains the effervescence during metalation. Electron and Proton Transfer in Phosphine Complexes. We serendipitously discovered that neutral, fully-deprotonated iron(III) compound 4 could also be prepared in one pot from 1 and Fe(PMe3)4 by simply exposing the crude product 2 to air after metalation was complete. Proton NMR and UV-visible spectroscopy of air-exposed 2 in situ demonstrates rapid and complete conversion to 4, with no monoprotonated iron(III) transient species observed. This one-pot procedure afforded 4 in 88% yield from 2, and this method was used to prepare 4 for subsequent experiments. Additional proton and electron transfer reactions were carried out on 2 and 4.