The biomimetic chemistry of single and double oxadithiolatodiiron-containing model compounds for the active site of Fe-only hydrogenases (FeHases) has been systematically studied. The simplest such model, Fe2(μ-SCH2OCH2S-μ)(CO)6 (1), was prepared by reaction of (μ-S2)Fe2(CO)6 with 2 equiv of Et3BHLi followed by direct treatment with excess (ClCH2)2O or by successive treatment with 2 equiv of CF3CO2H and excess (ClCH2)2O in the presence of Et3N. Further reaction of 1 with 1 equiv of Me3NO in MeCN at room temperature followed by treatment of the intermediate Fe2(μ-SCH2OCH2S-μ)(CO)5L (L = MeCN or Me3N) with 1 equiv of Et4NCN, PPh3, or Cp(CO)2FeSPh gave the single models Fe2(μ-SCH2OCH2S-μ)(CO)5La (2, La = (CN)(Et4N); 3, PPh3; 4, Cp(CO)2FeSPh) in 62−93% yields, whereas the in situ treatment of the intermediate Fe2(μ-SCH2OCH2S-μ)(CO)5L with 0.5 equiv of 1,4-(CN)2C6H4, (η 5-Ph2PC5H4)2Fe (dppf), or (η 5-Ph2PC5H4)2Ru (dppr) afforded the double models [Fe2(μ-SCH2OCH2S-μ)(CO)5]2Lb (5, Lb = 1,4-(CN)2C6H4; 6, dppf; 7, dppr) in 57−90% yields. However, in contrast to 5−7, the double models [Fe2(μ-SCH2OCH2S-μ)(CO) n ]2Lc (8, n = 5, Lc = (Ph2PCH2CH2OCH2)2; 9, n = 4, Lc = [(Ph2PCH2)2NCH2]2) could be prepared by direct reaction of 1 in toluene at reflux with 0.5 equiv of diphosphine (Ph2PCH2CH2OCH2)2 and tetraphosphine [(Ph2PCH2)2NCH2]2 in 86% and 56% yields, respectively. 1−9 were characterized by elemental analysis and spectroscopy, and particularly for 1, 2, and 4−9 by X-ray diffraction analysis. The structural features of some model compounds are compared with those of the active site of FeHases. While the cyclic voltammetric behavior of 1 and 5 was studied, 1 was found to be a catalyst for proton reduction of acetic acid to give hydrogen under the corresponding electrochemical conditions. An EECC mechanism for such electrocatalytic H2 production is preliminarily suggested.

The series of diiron oxadithiolate model complexes for the active site of [Fe] 4), and [Fe 2 (µ-SCH 2 OCH 2 S-µ) (CO) 5 ] 2 [(η 5 -Ph 2 PC 5 H 4 ) 2 Fe] ( 5) have been synthesized and fully characterized by elemental analysis, spectroscopy, and X-ray diffraction analysis. The structural features for some of the model complexes are compared with the corresponding features for the active site of [Fe]-only hydrogenases.

Efficient communication: The first porphyrin‐photosensitizer‐containing biomimetic model for the active site of Fe‐only hydrogenases has been synthesized and structurally characterized (see picture). Its fluorescence spectrum reveals that an efficient electronic communication occurs between the porphyrin unit and the covalently linked diiron–azadithiolate moiety.

The first diiron thiadithiolates as active site models for the Fe-only hydrogenases were prepared. Treatment of Fe 3 (CO) 12 with excess 1,2,4-trithiolane in THF at reflux afforded parent model Fe 2 (µ-SCH 2 ) 2 S(CO) 6 (1) in 42% yield. Further treatment of 1 with Cp(CO) 2 Fe(BF 4 ) prepared in situ from Cp(CO) 2 FeI and AgBF 4 in CH 2 Cl 2 gave cationic model [Fe 2 (µ-SCH 2 ) 2 S(CO) 6 ][Cp(CO) 2 Fe](BF 4 ) (2) in 81% yield, while treatment of 1 with 2 equiv of Et 4 NCN in MeCN or with t-BuNC in CH 2 Cl 2 produced models (Et 4 N) 2 [Fe 2 (µ-SCH 2 ) 2 S(CO) 4 (CN) 2 ] (3) and Fe 2 (µ-SCH 2 ) 2 S(CO) 4 (t-BuNC) 2 (4) in 93% and 51% yields, respectively. All the new models 1-4 were characterized by elemental analysis and spectroscopy, as well as by X-ray crystallography for 1, 2, and 4. Furthermore, model 1 has been proved to be a catalyst for proton reduction of a weak acid Et 3 NHCl to give hydrogen under electrochemical conditions.

Treatment of the parent model [(μ-SCH2)2NH]Fe2(CO)6 (1) with 4-pyridinecarboxylic acid chloride or benzoyl chloride in the presence of Et3N afforded the simple model compounds [(μ-SCH2)2NC(O)C5H4N]Fe2(CO)6 (2) and [(μ-SCH2)2NC(O)Ph]Fe2(CO)6 (4). Further treatment of 2 with the photosensitizer zinc tetraphenylporphyrin (ZnTPP) produced the target model compound [(μ-SCH2)2NC(O)C5H4N]Fe2(CO)6(ZnTPP) (3), which is the first metalloporphyrin-containing active site model for the Fe-only hydrogenases.

A series of methoxyphenyl-functionalized diiron azadithiolate (ADT) complexes,

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.

The CO-bridged anions [(µ-RE)(µ-CO)Fe 2 (CO) 6 ] -reacted with S 8 to form the sulfur-centered anions (µ-RE)(µ-S -)Fe 2 (CO) 6 (4; E ) S, Se), whereas reaction of the anions with Se 8 yielded the selenium-centered anions (µ-RE)(µ-Se -)Fe 2 (CO) 6 (6; E ) S, Se). Interestingly, reaction of 4 with SO 2 Cl 2 afforded the S-S-bonded clusters [(µ-RE)Fe 2 (CO) 6 ] 2 (µ-S-S) (5), whereas reaction of 6 with SO 2 Cl 2 produced the µ 4 -Se clusters [(µ-RE)Fe 2 (CO) 6 ] 2 (µ 4 -Se) (8); clusters 8 could also be produced by the action of anions 6 on succinoyl chloride or p-phthaloyl chloride, while the µ 4 -S clusters [(µ-RE)Fe 2 (CO) 6 ] 2 (µ 4 -S) (9) were generated by reaction of anions 4 with the above organic bis acid chlorides under similar conditions. Also, reaction of 4 (E ) S) with p-MeC 6 H 4 SO 2 Cl gave the µ 4 -S clusters [(µ-RE)Fe 2 (CO) 6 ] 2 (µ 4 -S) (9; E ) S) and the expected Fe 2 S 2 butterfly clusters (µ-RE)(µ-p-MeC 6 H 4 SO 2 S)Fe 2 (CO) 6 ( 10), whereas anion 6 reacted with p-MeC 6 H 4 SO 2 Cl to afford the unexpected SdO-bridged complexes (µ-RE)(µ-p-MeC 6 H 4 SO 2 )Fe 2 (CO) 6 (11) and µ 4 -Se clusters 8. Clusters 11 could be also prepared through direct reaction of the precursor of 6, i.e. [(µ-RE)(µ-CO)Fe 2 (CO) 6 ] -, with p-MeC 6 H 4 SO 2 Cl. For some of these reactions the mechanisms were preliminarily proposed. The structures of 15 new cluster compounds have been characterized by C/H analysis and IR, 1 H NMR, and MS spectroscopy; those of [(µ-EtS)Fe 2 (CO) 6 ] 2 (µ 4 -Se) (8a) and (µ-EtS)(µ-p-MeC 6 H 4 SO 2 )Fe 2 (CO) 6 (11a) have been confirmed by X-ray diffraction analyses.