Preparation and Characterization of Homologous Diiron Dithiolato, Diselenato, and Ditellurato Complexes: [FeFe]-Hydrogenase Models

Abstract

In order to elucidate the influence of the bridging chalcogen atoms in hydrogenase model complexes, diiron dithiolato, diselenolato, and ditellurolato complexes have been prepared and characterized. Treatment of Fe3(CO)12 with 3,3-bis(thiocyanatomethyl)oxetane (1) or a mixture of 2-oxa-6,7-dithiaspiro[3.4]octane (2a) and 2-oxa-6,7,8-trithiaspiro[3.5]nonane (2b) in toluene at reflux afforded the model compound Fe2(μ-S2C5H8O)(CO)6 (3). The analogous diselenolato and ditellurolato complexes, Fe2(μ-Se2C5H8O)(CO)6 (4) and Fe2(μ-Te2C5H8O)(CO)6 (5), were obtained from the reaction of Fe3(CO)12 with 2-oxa-6,7-diselenaspiro[3.4]octane (6) and 2-oxa-6,7-ditelluraspiro[3.4]octane (7), respectively. Compounds 3−5 were characterized by spectroscopic techniques (NMR, IR, photoelectron spectroscopy), mass spectrometry, single-crystal X-ray analysis, and computational modeling. The electrochemical properties for the new compounds have been studied to assess their ability to catalyze electrochemical reduction of protons to give dihydrogen, and the catalytic rate is found to decrease on going from the sulfur to selenium to tellurium compounds. In the series 3−5 the reorganization energy on going to the corresponding cation decreased from 3 to 4 to 5. Spectroscopic and computational analysis suggests that the increasing size of the chalcogen atoms from S to Se to Te increases the Fe−Fe distance and decreases the ability of the complex to form the structure with a rotated Fe(CO)3 group that has a bridging carbonyl ligand and a vacant coordination site for protonation. This effect is mirrored on reduction of 3−5 in that the rotated structure with a bridging carbonyl, which creates a vacant coordination site for protonation, is disfavored on going from the S to Se to Te complexes.

Diiron Dichalcogenolato (Se and Te) Complexes: Models for the Active Site of [FeFe] Hydrogenase

“…The computational methodology utilized by Weigand and co-workers to investigate these catalysts (12, 13, 23-27) has previously been shown to give good quantitative agreement with the structures, CO stretching frequencies (νCO), oxidation and reduction potentials, bond energies, and pK a values of a variety of catalysts inspired by [FeFe] hydrogenase active sites. [56,59,60,[101][102][103] The optimized geometries and computed νCO values agree very well with the experimental values, suggesting that the computations are able to yield sufficiently reasonable electron distributions and energies for catalysts 12, 14, and 23-27.…”

“…In a recent study, Weigand and co-workers extended the current investigations on [FeFe] hydrogenase model complexes containing the higher homologues by using the concept of a fixed backbone and prepared complexes 23, 24, and 25 with dithiolato, diselenolato, and ditellurolato ligands, respectively (Scheme 9). [59] Scheme 9. Models of [FeFe] hydrogenases containing dichalcogenolato ligands.…”

“…[56,[58][59][60] These active site catalysts typically exhibit extensive overlap of six Fe 3d orbitals and range up to about 9 eV with a weak shoulder on the low ionization energy side corresponding to ionization from the HOMO. The HOMO is calculated to be predominantly the Fe-Fe σ bond (vide infra), with an adiabatic ionization (IE A ) energy around 7.5 eV.…”

Reactions of Selected Aromatic Thioketones with Dodecarbonyltriiron

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] The Fe-S bond lengths are found to be within the same range observed for the hydrogenase model complexes. [10][11][12][13][14][15][16][17][18][24][25][26] The C-S average bond length (1.83 Å) is within the same range for a C-S single bond (1.80-1.85 Å) [40] and is significantly longer than the corresponding bond of Fe(PMe 3 ) 3 (Me)(κ,S,C-Ph 2 C=S) [1.675(4) Å] [38] , which contains a C=S bond. The bite angles of the butterfly shape are within the same ranges observed for the hydrogenase model complexes indicating a distorted octahedral geometry around each iron center.…”

Synthesis and Characterization of [FeFe]‐Hydrogenase Models with Bridging Moieties Containing (S, Se) and (S, Te)

“…pounds containing dithiolato, diselenolato, [33][34][35][36][37][38] or ditellurolato [33,[39][40][41] bridging ligands have been prepared, characterized, and evaluated for the electrocatalytic production of H 2 from weak acids.…”