The infrared spectra of N,N-dimethylformamide (DMF) and N,N-dimethylthioformamide (DMTF) have been investigated in the range 4000–250 cm−1. Assignment of the frequencies of DMF has been made on the basis of normal coordinate analysis for DMF, DMF-15N, and DMF-d7 using Urey-Bradly, modified Urey-Bradley, and symmetrized valence force fields. Calculations have been extended to N,N-dimethylthioformamide and N,N-dimethylselenoformamide, using the Urey-Bradley and symmetrized valence force fields. The assignments for DMF from the modified Urey-Bradley field are found to be more satisfactory. The frequency shifts on isotopic substitution and on complexation have been explained. The results of the calculations are discussed in comparison with other related molecules.
We have investigated the coordination modes of NNS Schiff base, thioether ligands to manganese (I) carbonyls. The ligands contain ortho substituted pyridines (H, CH 3 , OCH 3 , fluorophenyl) and varying substituents (H, CH 3 ) at the Schiff base linkage. In general, reaction of [Mn(CO) 5 Br] with a tridentate NNS ligand in CH 2 Cl 2 affords species in which the thioether-S may be bound or unbound to the manganese center, depending on the steric and electronic substitution in the ligand framework; as a result, the complexes exhibit two or three carbonyl ligands, respectively. Aldehyde-derived ligand frames ( tricarbonyl motif. We highlight that coordination of these NNS ligands to Mn(I) carbonyls occurs on a soft conformational landscape, and that ligand substituents can be rationally employed to favor the desired coordination mode.
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 Fe-C(NH)(═O) bond (carbamoyl) as a mimic of the active site iron acyl. The reaction of [((O═)C(HN)N(py)S(Me))Fe(CO)2(Br)] (1) with NaHBEt3 generates the iron hydride intermediate [((O═)C(HN)N(py)S(Me))Fe(H)(CO)2] (2; δFe-H = -5.08 ppm). Above -40 °C, the hydride species extrudes CH3S(-) via intramolecular hydride transfer, which is stoichiometrically trapped in the structurally characterized dimer μ2-(CH3S)2-[((O═)C(HN)N(Ph))Fe(CO)2]2 (3). Alternately, when activated by base ((t)BuOK), 1 undergoes desulfurization to form a cyclometalated species, [((O═)C(NH)NC(Ph))Fe(CO)2] (5); derivatization of 5 with PPh3 affords the structurally characterized species [((O═)C(NH)NC)Fe(CO)(PPh3)2] (6), indicating complex 6 as the common intermediate along each pathway of desulfurization.
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