Interplay between Terminal and Bridging Diiron Hydrides in Neutral and Oxidized States

Abstract

Graphical Abstract This study describes the structural, spectroscopic, and electrochemical properties of electronically unsymmetrical diiron hydrides. The terminal hydride Cp*Fe(pdt)Fe(dppe)(CO)H ([1(t-H)]0, Cp*− = Me5C5−, pdt2− = CH2(CH2S−)2, dppe = Ph2PC2H4PPh2) was prepared by hydride reduction of [Cp*Fe(pdt)Fe(dppe)(CO)(NCMe)]+. As established by X-ray crystallography, [1(t-H)]0 features a terminal hydride ligand. Unlike previous examples of terminal diiron hydrides, [1(t-H)]0 does not isomerize to the bridging hydride [1(μ-H)]0. Oxidation of [1(t-H)]0 gives [1(t-H)]+, which was also characterized crystallographically as its BF4− salt. Density functional theory (DFT) calculations indicate that [1(t-H)]+ is best described as containing an Cp*FeIII center. In solution, [1(t-H)]+ isomerizes to [1(μ-H)]+, as anticipated by DFT. Reduction of [1(μ-H)]+ by Cp2Co afforded the diferrous bridging hydride [1(μ-H)]0. Electrochemical measurements and DFT calculations indicate that the couples [1(t-H)]+/0 and [1(μ-H)]+/0 differ by 210 mV. Qualitative measurements indicate that [1(t-H)]0 and [1(μ-H)]0 are close in free energy. Protonation of [1(t-H)]0 in MeCN solution affords H2 even with weak acids via hydride transfer. In contrast, protonation of [1(μ-H)]0 yields 0.5 equiv of H2 by a proposed protonation-induced electron transfer process. Isotopic labeling indicates that μ-H/D ligands are inert.

Carbon monoxide substitutions by trimethyl phosphite in diiron dithiolate complex: Fe-Fe bond cleavage, selectivity of the substitutions, crystal structures and electrochemical studies

“…The binuclear complexes of iron whose structures are close to those of the [FeFe] hydrogenase complexes have been known for more than 80 years [3]. Since [FeFe] hydrogenase crystal structure publication [1], some complexes containing a Fe2S2 core have attracted the interest of chemists [4][5][6][7][8]. These complexes are easily synthesized and have been studied as structural and functional mimics of enzyme active site [9].…”

Insertion of BH3 into a Cobalt–Aryl Bond: Synthetic Routes to Arylborohydride and Borane-Amino Hydride Complexes

“…The Co–C distance is 1.937(3) Å, which is 0.053 Å shorter than 1.990(3) Å found in Co­(2-Ph 2 PC 6 H 4 )­(PMe 3 ) 3 . The magnetic moment of 1 , a paramagnetic compound, was determined to be 1.84 μ B in benzene . The experimental μ eff value corresponds to a low-spin 17-electron cobalt system …”

“…30 The magnetic moment of 1, a paramagnetic compound, was determined to be 1.84 μ B in benzene. 31 The experimental μ eff value corresponds to a lowspin 17-electron cobalt system. 32 Organometallic compounds with metal−carbon (M−C) bonds usually allow the insertion of small molecules, and this provides a wide range of remarkable new complexes.…”

Reactions of Fe2(μ‐odt)(CO)6 (odt = 1, 3‐oxadithiolate) with small bite‐angle diphosphines to afford the monodentate, chelate, and bridge diiron complexes: Selective substitution, structures, protonation, and electrocatalytic proton reduction

“…The asymmetrically substituted diiron complexes could be regarded as a desirable candidate for the active site models of [FeFe]‐hydrogenases, the diiron subunit of which has a key function to bind protons in natural enzyme . Thus, the reactivity of the chelate complex 2 toward acid proton is explored via the in situ protonations of 2 with five equivalents of CH 3 CO 2 H (HOAc) or CF 3 CO 2 H (TFA), respectively, which was monitored by IR ( ν CO ) and NMR ( 1 H, 31 P) techniques.…”