Monophosphine‐substituted diiron azadithiolate complexes: New syntheses, characterization and electrochemical properties

Abstract

Investigating the synthesis and properties of diiron azadithiolate complexes is one of the key topics for mimicking the active site of [FeFe]‐hydrogenases, which might be very useful for the design of new efficient catalysts for hydrogen production and the development of a future hydrogen economy. A series of new phosphine‐substituted diiron azadithiolate complexes as models for the active site of [FeFe]‐hydrogenases are described. A novel and efficient way was firstly established for the preparation of phosphine‐substituted diiron azadithiolate complexes. The reaction of Fe 2 (μ‐SH) 2 (CO) 6 and phosphine ligands L affords the intermediate Fe 2 (μ‐SH) 2 (CO) 5 L ( A ). The intermediate reacts in situ with a premixed solution of paraformaldehyde and ammonium carbonate to produce the target phosphine‐substituted diiron azadithiolate complexes Fe 2 [(μ‐SCH 2 ) 2 NH](CO) 5 L ( 1a – 1f ) (L = P(C 6 H 4 –4‐CH 3 ) 3 , P(C 6 H 4 –3‐CH 3 ) 3 , P(C 6 H 4 –4‐F) 3 , P(C 6 H 4 –3‐F) 3 , P(2‐C 4 H 3 O) 3 , PPh 2 (OCH 2 CH 3 )). Furthermore, reactions of the intermediate A with I‐4‐C 6 H 4 N(CH 2 Cl) 2 in the presence of Et 3 N give the phosphine‐substituted diiron azadithiolate complexes Fe 2 [(μ‐SCH 2 ) 2 NC 6 H 4 –4‐I](CO) 5 L ( 2a – 2e ) (L = P(C 6 H 4 –4‐CH 3 ) 3 , P(C 6 H 4 –3‐CH 3 ) 3 , P(C 6 H 4 –4‐F) 3 , P(C 6 H 4 –3‐F) 3 , P(2‐C 4 H 3 O) 3 ). All the complexes were fully characterized using elemental analysis, IR and NMR spectroscopies and, particularly for 1a , 1c – 1e , 2a and 2c , single‐crystal X‐ray diffraction analysis. In addition, complexes 1a – 1f and 2a – 2e were found to be catalysts for H 2 production under electrochemical conditions. Density functional theory calculations were performed for the reactions of Fe 2 (μ‐SH) 2 (CO) 6 + P(C 6 H 4 –4‐CH 3 ) 3 .