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

Abstract

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 Fe 2 (μ-SCH 2 OH) 2 (CO) 6 and several phosphine ligands L (L = PPh 3, PPh 2 (2-C 5 H 4 N), P(C 6 H 4 -4-CH 3 ) 3 ) affords the intermediate Fe 2 (μ-SCH 2 OH) 2 (CO) 5 L, while the intermediate in situ reacts with primary amines RNH 2 (R = CH 2 CH 2 CH(CH 3 ) 2, CH 2 CH 2 CH 2 SCH 3, C 6 H 4 -4-CH 3 ) to produce the target phosphine-substituted diiron azadithiolate complexes Fe 2 [(μ-SCH 2 ) 2 NCH 2 CH 2 CH(CH 3 ) 2 ](CO) 5 (PPh 3 ) ( 1 ), Fe 2 [(μ-SCH 2 ) 2 NCH 2 CH 2 CH(CH 3 ) 2 ](CO) 5 [PPh 2 (2-C 5 H 4 N)] ( 2 ), Fe 2 [(μ-SCH 2 ) 2 NCH 2 CH 2 CH(CH 3 ) 2 ](CO) 5 [P(C 6 H 4 -4-CH 3 ) 3 ] ( 3 ), Fe 2 [(μ-SCH 2 ) 2 NCH 2 CH 2 CH 2 SCH 3 ](CO) 5 (PPh 3 ) ( 4 ), Fe 2 [(μ-SCH 2 ) 2 NCH 2 CH 2 CH 2 SCH 3 ](CO) 5 [PPh 2 (2-C 5 H 4 N)] ( 5 ), Fe 2 [(μ-SCH 2 ) 2 NCH 2 CH 2 CH 2 SCH 3 ](CO) 5 [P(C 6 H 4 -4-CH 3 ) 3 ] ( 6 ), Fe 2 [(μ-SCH 2 ) 2 N C 6 H 4 -4-CH 3 ](CO) 5 [PPh 2 (2-C 5 H 4 N)] ( 7 ), and Fe 2 [(μ-SCH 2 ) 2 N C 6 H 4 -4-CH 3 ](CO) 5 [P(C 6 H 4 -4-CH 3 ) 3 ] ( 8 ) in moderate yields. A novel complex Fe 2 [(μ-SCH 2 ) 2 NCH 2 CH 2 PPh 2 ](CO) 5 ( 9 ) can be obtained by reaction of Fe 2 (μ-SCH 2 OH) 2 (CO) 6 and Ph 2 PCH 2 CH 2 NH 2 . In addition, according to the same strategy, phosphine-substituted diiron oxadithiolate complexes Fe 2 [(μ-SCH 2 ) 2 O](CO) 5 [P(C 6 H 4 -4-F) 3 ] ( 10 ), Fe 2 [(μ-SCH 2 ) 2 O](CO) 5 [P(C 6 H 4 -4-CH 3 ) 3 ] ( 11 ), and Fe 2 [(μ-SCH 2 ) 2 O](CO) 5 (Ph 2 PCH 2 CH 3 ) ( 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.