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 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.

The two noVel diiron propanedithiolate model compounds [Fe 2 (µ-CH 2 SMe)(µ-SCH 2 )(CO) 6 ][Fe 2 (µ-SCH 2 ) 2 CMe-(CO) 6 ] (3) and [Fe 2 (µ-CH 2 CHdCH 2 )(µ-SCH 2 )(CO) 6 ][Fe 2 (µ-SCH 2 ) 2 CMe(CO) 6 ] ( 4) haVe been unexpectedly obtained through a "one-pot" route by reaction of the trithiol MeC(CH 2 SH) 3 with Fe 3 (CO) 12 in the presence of Et 3 N, followed by treatment with MeSCH 2 Cl and CH 2 dCHCH 2 Br, respectiVely. The structures of 3 and 4 haVe been fully characterized, and the possible pathway for formation of 3 and 4 is suggested. In addition, some electrochemical properties of 3 related to the H 2 eVolution function of Fe-only hydrogenases are also reported.Fe-only hydrogenases are a naturally occurring class of metalloenzymes, which catalyze hydrogen evolution or uptake at rapid rates in a wide variety of microorganisms. 1 Recent studies on structures of two Fe-only hydrogenases isolated from C. pasteurianum and D. desulfuricans have revealed 2 that the active site (so-called H cluster) consists of a butterfly 2Fe2S cluster core that bears three unusual ligands, CO, CN -, and the cysteine-S-substituted cubic 4Fe4S cluster; in addition, a less defined three-atom linker bridges between two S atoms of the 2Fe2S cluster core. This structural information has greatly stimulated synthetic studies aimed at obtaining model compounds which can perform catalytic activities similar to those found in natural systems. 3 So far, numerous models have been synthesized, which can be classified into three major types according to the three-atom linker: namely, diiron propanedithiolate (PDT) complexes, 4 diiron azadithiolate (ADT) complexes, 5 and diiron oxadithiolate (ODT) complexes. 6 Among the three

As the new H-cluster models, a series of N-functionalized azadithiolatodiiron complexes containing mono-and diphosphine ligands 1-7 have been prepared by various methods from complexes [(µ-SCH 2 N(Fun)]Fe 2 (CO) 6 (A, Fun ) C 6 H 4 CHO-p; B, Fun ) C 6 H 4 CO 2 Me-p; C, Fun ) CH 2 CH 2 O 2 CCH 2 C 10 H 7 -1; D, Fun ) CH 2 CH 2 OH) and [(µ-SCH 2 ) 2 N(Fun)]Fe 2 (CO) 5 (Ph 2 PH) (E, Fun ) C 6 H 4 OMe-p). Treatment of A and B with 1 equiv of Me 3 NO • 2H 2 O followed by 1 equiv of Ph 3 P or Ph 2 PH affords the corresponding monophosphine-substituted complexes [(µ-SCH 2 ) 2 N(C 6 H 4 CHO-p)]Fe 2 (CO) 5 (Ph 3 P) (1) and [(µ-SCH 2 ) 2 N(C 6 H 4 CO 2 Me-p)]Fe 2 (CO) 5 L (2, L ) Ph 3 P; 3, Ph 2 PH). Further treatment of B with ca. 1 equiv of Ph 2 PC 2 H 4 PPh 2 (dppe) produced the diphosphine dppe-bridged single model [(µ-SCH 2 ) 2 N(C 6 H 4 CO 2 Mep)]Fe 2 (CO) 4 (dppe) ( 4), whereas C reacts with 1 equiv of Me 3 NO • 2H 2 O followed by 0.5 equiv of (η 5 -Ph 2 PC 5 H 4 ) 2 Fe (dppf) to give the diphosphine dppf-bridged double model [(µ-SCH 2 ) 2 N(CH 2 CH 2 O 2 CCH 2 C 10 H 7 -1)Fe 2 (CO) 5 ] 2 (dppf) (5). While D reacts with 1 equiv of n-BuLi followed by 1 equiv of Ph 2 PCl or directly reacts with 1 equiv of Ph 2 PCl in the presence of Et 3 N to generate N-alkoxyphosphine-substituted complex [(µ-SCH 2 ) 2 N(CH 2 CH 2 OPPh 2 -η 1 )]Fe 2 (CO) 5 ( 6), treatment of E with 1 equiv of n-BuLi followed by 1 equiv of CpFe(CO) 2 I yields organometallic phosphine-substituted complex [(µ-SCH 2 ) 2 N(C 6 H 4 OMep)]Fe 2 (CO) 5 [Ph 2 PFe(CO) 2 Cp] (7). All the new model complexes 1-7 are fully characterized by elemental analysis, spectroscopy, and particularly for 1, 3, 4, 6, and 7 X-ray crystallography. More interestingly, 2 is found to be a catalyst for HOAc proton reduction to hydrogen under CV conditions. In addition, according to electrochemical and spectroelectrochemical studies, an ECEC mechanism is proposed for this electrocatalytic reaction.

The preparation, characterization, and some properties of the C2Co2 cluster-bridged bipyridine ligand (4-C5H4N)2C2Co2(CO)6 (1), diphosphine-chelated Pd(II)/Pt(II) complexes [M(dppb)(H2O)2][OTf]2 (dppb = 1,4-bis(diphenylphosphino)butane, OTf = SO3CF3; 2, M = Pd; 3, M = Pt), and the unique cationic cluster-containing Pd(II)/Pt(II) macrocycles {[M(dppb)]-μ-[(4-C5H4N)2C2Co2(CO)6]}2[OTf]4 (4, M = Pd; 5, M = Pt) and {[M(dpab)]-μ-[(4-C5H4N)2C2Co2(CO)6]}2[OTf]4 (dpab = 1,4-bis(diphenylarsino)butane; 6, M = Pd; 7, M = Pt) are reported. While ligand 1 is prepared by reaction of bis(4-pyridyl)acetylene with Co2(CO)8 in 61% yield, complexes 2 and 3 are prepared by reaction of M(dppb)Cl2 with silver triflate followed by hydrolysis of the intermediates M(dppb)(OTf)2 in 96% and 94% yields, respectively. Particularly interesting is that the self-assembly of ligand 1 with 2 and 3 results in formation of the C2Co2 cluster-containing macrocycles 4 and 5 in 62% and 65% yields, whereas 6 and 7 can be produced by self-assembly of 1 with diarsine-chelated complexes [Pd(dpab)(H2O)(OTf)][OTf] and [Pt(dpab)(H2O)2][OTf]2 in 79% and 68% yields, respectively. 1−7 have been fully characterized by elemental analysis, spectroscopy, and particularly for 2−7 X-ray crystallography, and for 1, 4, and 7 by cyclic voltammetric techniques.