Synthesis, Structure, and Photoinduced Catalysis of [FeFe]-Hydrogenase Active Site Models Covalently Linked to a Porphyrin or Metalloporphyrin Moiety

A series of novel light-driven-type models, which contain a single diiron- ADT(azadithiolate) unit or two and four diiron-ADT units covalently bonded to a photosensitizer porphyrin or metalloporphyrin, have been synthesized and structurally characterized. Reaction of complex [(μ-SCH2)2NC6H4CHO]Fe2(CO)6 (A) with PhCHO, pyrrole, and CF3CO2H in CH2Cl2 followed by treatment with p-chloranil gave light-driven models 5-[(μ-SCH2)2NFe2(CO)6phenyl]-10,15,20-triphenylporphyrin (1), 5,15-[(μ-SCH2)2NFe2(CO)6phenyl]2-10,20-diphenylporphyrin (2), and 5,10-[(μ-SCH2)2NFe2(CO)6phenyl]2-15,20-diphenylporphyrin (3). While light-driven model 5,10,15,20-[(μ-SCH2)2NFe2(CO)6phenyl]4porphyrin (4) could be similarly prepared by reaction of complex A with pyrrole and CF3CO2H followed by treatment with p-chloranil, model 1 could also be prepared by another new method involving a final cyclization step of (μ-HOCH2S)2Fe2(CO)6 with (p-aminophenyl)triphenylporphyrin. In addition, the PPh3-substituted model 5-[(μ-SCH2)2NFe2(CO)5(PPh3)phenyl]-10,15,20-triphenylporphyrin (5) was prepared by reaction of 1 with PPh3 in the presence of Me3NO, whereas treatment of 1 with Zn(OAc)2 afforded the metalloporphyrin-containing model 5-[(μ-SCH2)2NFe2(CO)6phenyl]-10,15,20-triphenylporphyrinozinc (6). X-ray crystallographic studies confirmed that (i) model 3 consists of two diiron-ADT units, which are connected to the two ortho-benzene rings of the porphyrin macrocycle, and (ii) model 6 contains one molecule of MeOH, which is axially coordinated to the Zn atom of the metalloporphyrin macrocycle. Particularly noteworthy is that model 1 was found to be a photoactive catalyst for photoinduced H2 production, and a possible pathway for such H2 production is suggested.