Tuning coordination modes of pyridine/thioether Schiff base (NNS) ligands to mononuclear manganese carbonyls

Manganese carbonyls are ligated by pyridine/thioether Schiff base (NNS) ligands. Coordination of the thioether-S donor to the Mn(i) center is determined by subtle steric changes at the ligand periphery.

Synthesis, structural characterization, and some properties of 2-acylmethyl-6-ester group-difunctionalized pyridine-containing iron complexes related to the active site of [Fe]-hydrogenase

The first four acylmethyl/ester group-disubstituted pyridine-containing models for [Fe]-hydrogenase have been synthesized and crystallographically characterized.

Hydrogen-activation mechanism of [Fe] hydrogenase revealed by multi-scale modeling

A complete atomistic model of [Fe] hydrogenase reveals important details of its mechanism.

Kinetic modeling of hydrogen conversion at [Fe] hydrogenase active-site models

By means of density functional theory, we investigate the catalytic cycle of active-site model complexes of [Fe] hydrogenase and study how ligand substitutions in the first coordination sphere of the reactive Fe center affect the free-energy surface of the whole reaction pathway. Interestingly, dispersion interactions between the active site and the hydride acceptor MPT render the hydride transfer step less endergonic and lower its barrier. Substitution of CO by CN(-), which resembles [FeFe] hydrogenase-like coordination, inverts the elementary steps H(-) transfer and H2 cleavage. A simplified kinetic model reveals the specifics of the interplay between active-site composition and catalysis. Apparently, the catalytic efficiency of [Fe] hydrogenase can be attributed to a flat energy profile throughout the catalytic cycle. Intermediates that are too stable, as they occur, e.g., when one CO ligand is substituted by CN(-), significantly slow down the turnover rate of the enzyme. The catalytic activity of the wild-type form of the active-site model could, however, be enhanced by a PH3 ligand substitution of the CO ligand.

The reactions of pyridinyl thioesters with triiron dodecacarbonyl: their novel diiron carbonyl complexes and mechanistic investigations

Reaction of Fe(3)(CO)(12) with pyridinyl thioester ligand PyCH(2)SCOCH(3) (L(1), Py = pyridin-2-yl) produced complex, [Fe(2)(κ-COCH(3))(μ-SCH(2)Py)(CO)(5)] (1) (PyCH(2)S = pyridin-2-ylmethanethiolate). When complex 1 reacted with PPh(3), a monosubstituted complex, [Fe(2)(κ-COCH(3))(μ-SCH(2)Py)(CO)(4)PPh(3)] (2), was derived. Reaction of the same precursor with analogous thioester ligand PyCH(2)SCOPy (L(2)) generated three novel diiron complexes, [Fe(2)(κ-Py)(μ-SCH(2)Py)(CO)(5)] (3), [Fe(2)(κ-Py)'(μ-SCH(2)Py)(CO)(5)] (4), and [Fe(2)(κ-Py)(μ-SCH(2)Py)(CO)(6)] (5). Complexes 3 and 4 are structural isomers. Complex 5 could be converted into complex 4 but the conversion from complex 5 to the isomer 3 was not observed. All the five complexes were fully characterised using FTIR, NMR, and other techniques. Their structures were determined using X-ray single crystal diffraction analysis. The oxidative formation of complexes 1, 3, 4, and 5 involved C-S and/or C-C bonds cleavages. To probe possible mechanisms for these cleavages, DFT calculations were performed. From the calculations, viable reaction pathways leading to the formation of all the isolated products were delineated. The results of the theoretic calculations also allowed rationalisation of the experimental observations.