[Fe]-hydrogenase is a methanogenic enzyme catalyzing the reversible reduction of H2. In its active site, the Fe center is ligated with several donor atoms—N from pyridone/pyiridinol, acyl C branching from the pyridone ring, S from cysteine, along with two carbonyl CO’s and a solvent (H2O) binding site. Notably, [Fe]-hydrogenase is (thus far) the only example exhibiting the metal-acyl moiety in nature. A CNSthioether ligand was synthesized by the Suzuki coupling of 2-bromo-6-methylpyridine with 2-(methylthio)phenylboronic acid using trans-Pd(II)Cl2(PPh3)2. Metalation of the ligand with Fe(CO)5 generates the acyl moiety and oxidation of the resulting complex with I2 affords the desired species [(acylCNSMe)Fe(CO)2(I)] (45%, selected IR bands: 2032, 1963, 1661 cm-1). The complex has been characterized by X-ray diffraction and 1H NMR spectroscopy (diamagnetic). The complex is highly sensitive towards light, moisture and temperature – complicating functional and reactivity studies. As a result, other ligand modifications have been investigated, including preparation of the analogous CNSthiophene and CNPPPh2 ligands. The complex derived from CNSthiophene – namely, [(acylCNSTh)Fe(CO)2(I)] – exhibits carbonyl stretches (C≡O) at 2070 and 2017 cm-1, as well as the acyl feature (C=O) at 1612 cm-1. The reactivity of the CNSthiophene and CNPPPh2 complexes with substrates, hydride sources and H2/D2 will be discussed.

Synthetic modeling of the organometallic active site of mono-iron hydrogenase: Fe-acyl complexes derived from CNS (S = thioether, thiophene) and CNP (P = RPPh2) chelates

251st National Meeting (2016)

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