The N-acylated derivatives of parent complex [{(μ-SCH₂) ₂NH}Fe₂(CO)₆] as active site models of fe-only hydrogenases: Synthesis, characterization, and related properties

A series of N-acylated diiron azadithiolate complexes as H-cluster models was synthesized and structurally characterized. Treatment of parent complex [{(μ-SCH₂)₂NH}Fe₂(CO)₆] (A) with 2-chloroacetic acid in the presence of dicyclohexylcarbodiimide or with 2-chloroacetyl chloride in the presence of Et₃N gave N-chloroacetyl complex [{(μ-SCH₂)₂NC(O)CH₂Cl}Fe ₂(CO)₆] (1). Further treatment of 1 with MeC(O)SK afforded N-acetylthioacetyl complex [{(μ-SCH₂)₂NC(O)CH ₂SC(O)Me}Fe₂(CO)₆] (2). N-Ethoxylcarbonylacetyl complex [{(μ-SCH₂)₂NC(O)CH₂CO ₂Et}Fe₂(CO)₆] (3) and N-heterocyclic complexes [{(μ-SCH₂)₂NC(O)C₄H₃Y-2}Fe ₂(CO)₆] (4, Y = O; 5, Y = S) were produced by reactions of A with EtO₂CCH₂C(O)Cl, 2-furancarbonyl chloride, and 2-thiophenecarbonyl chloride in the presence of pyridine or Et₃N. Similarly, N-malonyl complex [{Fe₂(CO)₆(μ-SCH ₂)₂NC(O)}₂CH₂] (6) and N-carbonylbenzaldehyde complex [{(μ-SCH₂)₂NC(O)C ₆H₄CHO-P}Fe₂(CO)₆] (7) could be obtained by reaction of A with malonyl dichloride in the presence of pyridine and with p-CHOC₆H₄C(O)Cl in the presence of Et ₃N. More interestingly, further reaction of 7 with PhCHO and pyrrole in a 1:3:4 molar ratio in the presence of BF₃·OEt₂ followed by p-chloranil yielded the first light-driven type of model complex containing an N-carbonylphenylporphyrin moiety [{(μ-SCH₂) ₂NC(O)(TPP)}Fe₂(CO)₆] (8, TPP = tetraphenylporphyrin group). Whereas the molecular structures of 2, 5, and 7 were established by X-ray crystallography, the electrochemical properties of 2-5 as well as the proton reduction to hydrogen gas catalyzed by 2 and 3 were studied by CV techniques.