Three series of new Ni/Fe/S cluster complexes have been prepared and structurally characterized. One series of such complexes includes the linear type of (diphosphine)Ni-bridged double-butterfly Fe/S complexes [(μ-RS)(μ-S═CS)Fe(2)(CO)(6)](2)[Ni(diphosphine)] (1-6; R = Et, t-Bu, n-Bu, Ph; diphosphine = dppv, dppe, dppb), which were prepared by reactions of monoanions [(μ-RS)(μ-CO)Fe(2)(CO)(6)](-) (generated in situ from Fe(3)(CO)(12), Et(3)N, and RSH) with excess CS(2), followed by treatment of the resulting monoanions [(μ-RS)(μ-S═CS)Fe(2)(CO)(6)](-)with (diphosphine)NiCl(2). The second series consists of the macrocyclic type of (diphosphine)Ni-bridged double-butterfly Fe/S complexes [μ-S(CH(2))(4)S-μ][(μ-S═CS)Fe(2)(CO)(6)](2)[Ni(diphosphine)] (7-9; diphosphine = dppv, dppe, dppb), which were produced by the reaction of dianion [{μ-S(CH(2))(4)S-μ}{(μ-CO)Fe(2)(CO)(6)}(2)](2-) (formed in situ from Fe(3)(CO)(12), Et(3)N, and dithiol HS(CH(2))(4)SH with excess CS(2), followed by treatment of the resulting dianion [{μ-S(CH(2))(4)S-μ}{(μ-S═CS)Fe(2)(CO)(6)}(2)](2-) with (diphosphine)NiCl(2). However, more interestingly, when dithiol HS(CH(2))(4)SH (used for the production of 7-9) was replaced by HS(CH(2))(3)SH (a dithiol with a shorter carbon chain), the sequential reactions afforded another type of macrocyclic Ni/Fe/S complex, namely, the (diphosphine)Ni-bridged quadruple-butterfly Fe/S complexes [{μ-S(CH(2))(3)S-μ}{(μ-S═CS)Fe(2)(CO)(6)}(2)](2)[Ni(diphosphine)](2) (10-12; diphosphine = dppv, dppe, dppb). While a possible pathway for the production of the two types of novel metallomacrocycles 7-12 is suggested, all of the new complexes 1-12 were characterized by elemental analysis and spectroscopy and some of them by X-ray crystallography.
The first phthalocyanine (Pc) macrocycle-containing [FeFe]-hydrogenase model complex, (i-BuO)8PcRu(CO)(μ-PDT)[(Ph2P)2NCH2C5H4N]Fe2(CO)4 (6), has been prepared by a multistep synthetic route. The treatment of 4-picolylamine with Ph2PCl/Et3N in CH2Cl2 at room temperature gave 4-picolyl-substituted azadiphosphine (Ph2P)2NCH2C5H4N (1), whereas further treatment of 1 with diiron complex (μ-PDT)Fe2(CO)6 in refluxing o-xylene produced the 4-picolylazadiphosphine-chelated diiron complex (μ-PDT)[(Ph2P)2NCH2C5H4N]Fe2(CO)4 (2). While 3,6-dihydroxyphthalonitrile reacted with i-BuBr/K2CO3 in DMF at 80 °C to give 3,6-diisobutoxyphthalonitrile 3, further reaction of 3 with lithium wire in refluxing i-BuOH afforded isobutoxyphthalocyanine (i-BuO)8PcH2 (4). Furthermore, 4 reacted with Ru3(CO)12 in refluxing PhCN to give ruthenium phthalocyanine (i-BuO)8PcRu(CO)2 (5). Finally, CO substitution reaction of 5 with diiron complex 2 in the presence of Me3NO in CH2Cl2 resulted in formation of the targeted model complex 6. While all the new compounds 1–6 were structurally characterized, complex 6 was found to be a catalyst for photoinduced H2 generation.
The first [Fe 2 SP] model complexes for the active site of [FeFe]-hydrogenases have been prepared. Thus, the μ-CO-containing complex salt [Et 3 NH][(μ-CO)(μ-SCH 2 CH 2 OH)Fe 2 (CO) 6 ] (m 1 ) formed from Fe 3 (CO) 12 , HSCH 2 CH 2 OH, and Et 3 N was treated in situ with PCl 3 and PPhCl 2 followed by treatment with Et 3 N/DBU to give the all-carbonyl complexes (μ-SCH 2 CH 2 OPR-μ)Fe 2 (CO) 6 (1, R = Cl; 3, Ph), whereas the functional transformation of 1 with PhOH/NaH and CO substitution of 3 with PPh 3 or PPh 2 H in the presence of Me 3 NO afforded the corresponding complexes (μ-SCH 2 CH 2 OPOPh-μ)Fe 2 (CO) 6 (2) and (μ-SCH 2 CH 2 OPPh-μ)Fe 2 (CO) 5 L (4, L = PPh 3 ; 5, PPh 2 H), respectively. Similarly, when complex salt [Et 3 NH][(μ-CO)(μ-SC 6 H 4 OH)Fe 2 (CO) 6 ] (m 4 ) generated from Fe 3 (CO) 12 , 2-HOC 6 H 4 SH, and Et 3 N was treated in situ with PCl 3 and PPhCl 2 followed by treatment with Et 3 N/DBU, the expected all-carbonyl complexes (μ-SC 6 H 4 OPR-μ)Fe 2 (CO) 6 (6, R = Cl; 8, Ph) were produced. In addition, further functional transformation of 6 with MeOH/Et 3 N and CO substitution of 8 with t-BuNC in the presence of Me 3 NO yielded the corresponding complexes (μ-SC 6 H 4 OPOMe-μ)Fe 2 (CO) 6 (7) and (μ-SC 6 H 4 OPPh-μ)Fe 2 (CO) 5 (t-BuNC) (9), respectively. However, it should be noted that when complex salt m 4 was treated with PBr 3 under similar conditions, [(μ-SC 6 H 4 OPO(CH 2 ) 4 Br-μ]Fe 2 (CO) 6 (10) was unexpectedly obtained. While the possible pathways for formation of the unexpected 10 were suggested, all complexes 1−10 were characterized by elemental analysis and spectroscopy and for some of them by X-ray crystallography. Interestingly, model complexes 1, 4, and 8 have been found to be catalysts for HOAc proton reduction to H 2 under CV conditions. ■ INTRODUCTION[FeFe]-Hydrogenases (hereafter denoted as [FeFe]Hases) are a class of natural enzymes that catalyze H 2 production at rapid rates in a broad range of prokaryotic and eukaryotic microorganisms. 1−5 The X-ray crystallographic 6−8 and FTIR spectroscopic 9−11 studies revealed that the active site of [FeFe]Hases consists of a butterfly [Fe 2 S 2 ] cluster core and a cubic [Fe 4 S 4 ] cluster core, which are connected together via a cysteine S atom. In addition, the two Fe atoms in the butterfly [Fe 2 S 2 ] core are bridged by a dithiolate ligand and coordinated by three CO and two CN − ligands. Recently, the dithiolate ligand has been identified as an azadithiolate μ-SCH 2 NHCH 2 S-μ ligand, evidenced by 14 N HYSCORE 12 and controlled metalloenzyme activation 13 (Figure 1a). Encouraged by the well-established active site structure, synthetic chemists have prepared a great number of models for the active site of [FeFe]Hases, such as the butterfly [Fe 2 E 2 ] (E = S, Se, Te) and [Fe 2 P 2 ]-type model complexes. 14−17 However, it is worth noting that up to now no butterfly [Fe 2 SP]-type model complex has been prepared, albeit some ordinary butterfly [Fe 2 SP] complexes are known. 18−21 Therefore, to further understand the active site struc...
Cysteine residue-containing [NiFe]-H2ase models 1–6 have been prepared for the first time and some of them were found to be catalysts for H2 production from HOAc under CV conditions.
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