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 phosphinesubstituted diiron aza- and oxadithiolate complexes. Reaction of Fe-2(mu-SCH2OH)(2)(CO)(6) and several phosphine ligands L (L = PPh3, PPh2(2-C5H4N), P(C6H4-4-CH3)(3)) affords the intermediate Fe-2(mu-SCH2OH)(2)(CO)(5)L, 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 Fe-2[(mu-SCH2)(2)NCH2CH3CH(CH3)(2)](CO)(5)(PPh3) (1), Fe-2[(mu-SCH2)(2)NCH2CH2CH(CH3)(2)](CO)(5)[PPh2(2-C5H4N) (2), Fe-2[(mu-SCH2)(2)NCH2CH2CH(CH3)(2)](CO)(5)[P(C6H4-4-CH3)(3)] (3), Fe-2[(mu-SCH2)(2)NCH2CH2CH2SCH3](CO)(5)(PPh3) (4), Fe-2[(mu-SCH2)(2)NCH2CH2CH2SCH3](CO)(5)[PPh2(2-C5H4N) (5), Fe-2[(mu-SCH2)(2)NCH2CH2CH2SCH3](CO)(5)[P(C6H4-4-CH3)(3)] (6), Fe-2[(mu-SCH2)(2)N C6H4-4-CH3](CO)(5)[PPh2(2-C5H4N)] (7), and Fe-2[(mu-SCH2)(2)N C6H4-4-CH3](CO)(5)[P(C6H4-4-CH3)(3)] (8) in moderate yields. A novel complex Fe-2[(mu-SCH2)(2)NCH2CH2PPh2](CO)(5) (9) can be obtained by reaction of Fe-2(mu-SCH2OH)(2)(CO)(6) and Ph2PCH2CH2NH2. In addition, according to the same strategy, phosphine-substituted diiron oxadithiolate complexes Fe-2[(mu-SCH2)(2)O](CO)(5)[P(C6H4-4-F)(3)] (10), Fe-2[(mu-SCH2)(2)O](CO)(5)[P(C6H4-4-CH3)(3)] (11), and Fe-2[(mu-SCH2)(2)O](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 H-2 production under electrochemical conditions.