A New Route to the Synthesis of Phosphine-Substituted Diiron Aza- and Oxadithiolate Complexes

Diiron dithiolate
complexes have received special attention because
of their structural similarity to the active site of [FeFe]-hydrogenases,
which are the most efficient and fastest catalysts for the generation
of dihydrogen in nature. Recently, we established a novel and efficient
way to prepare phosphine-substituted diiron aza- and oxadithiolate
complexes. Reaction of Fe2(μ-SCH2OH)2(CO)6 and several phosphine ligands L (L = PPh3, PPh2(2-C5H4N), P­(C6H4-4-CH3)3) affords the intermediate
Fe2(μ-SCH2OH)2(CO)5L, while the intermediate in situ reacts with primary
amines RNH2 (R = CH2CH2CH­(CH3)2, CH2CH2CH2SCH3, C6H4-4-CH3) to produce
the target phosphine-substituted diiron azadithiolate complexes Fe2[(μ-SCH2)2NCH2CH2CH­(CH3)2]­(CO)5(PPh3) (1), Fe2[(μ-SCH2)2NCH2CH2CH­(CH3)2]­(CO)5[PPh2(2-C5H4N)]
(2), Fe2[(μ-SCH2)2NCH2CH2CH­(CH3)2]­(CO)5[P­(C6H4-4-CH3)3] (3), Fe2[(μ-SCH2)2NCH2CH2CH2SCH3]­(CO)5(PPh3) (4), Fe2[(μ-SCH2)2NCH2CH2CH2SCH3]­(CO)5[PPh2(2-C5H4N)] (5), Fe2[(μ-SCH2)2NCH2CH2CH2SCH3]­(CO)5[P­(C6H4-4-CH3)3] (6), Fe2[(μ-SCH2)2N C6H4-4-CH3]­(CO)5[PPh2(2-C5H4N)]
(7), and Fe2[(μ-SCH2)2N C6H4-4-CH3]­(CO)5[P­(C6H4-4-CH3)3] (8) in moderate yields. A novel complex Fe2[(μ-SCH2)2NCH2CH2PPh2]­(CO)5 (9) can be obtained by reaction of Fe2(μ-SCH2OH)2(CO)6 and Ph2PCH2CH2NH2. In addition,
according to the same strategy, phosphine-substituted diiron oxadithiolate
complexes Fe2[(μ-SCH2)2O]­(CO)5[P­(C6H4-4-F)3] (10), Fe2[(μ-SCH2)2O]­(CO)5[P­(C6H4-4-CH3)3] (11), and Fe2[(μ-SCH2)2O]­(CO)5(Ph2PCH2CH3) (12) have been successfully synthesized. All of the
new complexes 1–12 were fully characterized
by elemental analysis, IR, and NMR spectroscopy, and particularly
for 1–4, 6, 7, and 9–11 by X-ray single diffraction
analysis. Moreover, complexes 1 and 10 were
found to be catalysts for H2 production under electrochemical
conditions.