A model for the CO-inhibited form of [NiFe] hydrogenase: synthesis of (CO) ₃ Fe( μ -S ^t Bu) ₃ Ni{SC ₆ H ₃ -2,6-(mesityl) ₂ } and reversible CO addition at the Ni site

Abstract

A [NiFe] hydrogenase model compound having a distorted trigonal-pyramidal nickel center, ðCOÞ 3 Feðμ-S t BuÞ 3 NiðSDmpÞ, 1 (Dmp¼ C 6 H 3 -2;6-ðmesitylÞ 2 ), was synthesized from the reaction of the tetranuclear Fe-Ni-Ni-Fe complex ½ðCOÞ 3 Feðμ-S t BuÞ 3 Ni 2 ðμ-BrÞ 2 , 2 with NaSDmp at −40°C. The nickel site of complex 1 was found to add CO or CN t Bu at −40°C to give ðCOÞ 3 FeðS t BuÞðμ-S t BuÞ 2 NiðCOÞ ðSDmpÞ, 3, or ðCOÞ 3 FeðS t BuÞðμ-S t BuÞ 2 NiðCN t BuÞðSDmpÞ, 4, respectively. One of the CO bands of 3, appearing at 2055cm −1 in the infrared spectrum, was assigned as the Ni-CO band, and this frequency is comparable to those observed for the CO-inhibited forms of [NiFe] hydrogenase. Like the CO-inhibited forms of [NiFe] hydrogenase, the coordination of CO at the nickel site of 1 is reversible, while the CN t Bu adduct 4 is more robust.iron | nickel | thiolates B iological hydrogen evolution and uptake are mediated by hydrogenase enzymes (1-7). The most prevalent family are the [NiFe] hydrogenases, and various forms have been identified (8)(9)(10)(11)(12)(13)(14)(15). A unique feature of the [NiFe] hydrogenase is the common organometallic dinuclear Ni-Fe frame at the active site ( Fig. 1), which has attracted inorganic and organometallic chemists attempting to model both the structure and physicochemical properties. Thiolate-bridged Ni-Fe complexes have been synthesized as structural models of the active site (16-26), and sulfurligated mono-and dinuclear transition metal complexes have been reported to promote H 2 activation mimicking the function of [NiFe] hydrogenase (27-41). However, synthesis of better structural/functional models remains challenging.One interesting aspect of the [NiFe] hydrogenase is the reversible inhibition of the active site by CO. According to a crystallographic analysis of the CO-inhibited form of the [NiFe] hydrogenase obtained from Desulfovibrio vulgaris Miyazaki F (D. v. Miyazaki F), a CO molecule is coordinated at the nickel center (42). It has been suggested that this nickel-bound CO can be liberated and the catalytic activity recovered, upon flushing with a stream of N 2 (43), or by white-light irradiation at 20 K (44). Herein we report the synthesis of a thiolate-bridged dinuclear Ni-Fe complex ðCOÞ 3 Feðμ-S t BuÞ 3 NiðSDmpÞ, 1, carrying a bulky thiolate SDmp (Dmp¼C 6 H 3 -2;6-ðmesitylÞ 2 ) at Ni, and its CO and CN t Bu adducts, ðCOÞ 3 FeðS t BuÞðμ-S t BuÞ 2 NiðCOÞðSDmpÞ, 3, and ðCOÞ 3 FeðS t BuÞðμ-S t BuÞ 2 NiðCN t BuÞðSDmpÞ, 4. The reaction of 1 with CO occurs reversibly to give 3, while the analogous CN t Bu adduct 4 is robust. We also report the x-ray crystal structures of 1, 3, and 4. Results and DiscussionSynthesis and Structure of ðCOÞ 3 Feðμ-S t BuÞ 3 NiðSDmpÞ, 1. We have reported that a linear tetranuclear Fe-Ni-Ni-Fe complex ½ðCOÞ 3 Feðμ-S t BuÞ 3 Ni 2 ðμ-BrÞ 2 , 2, which was synthesized from FeBr 2 ðCOÞ 4 þNaðS t BuÞþNiBr 2 ðEtOHÞ 4 (1∶2∼3∶1), serves as a convenient precursor for the synthesis of thiolate-bridged dinuclear Ni-Fe complexes (17). The penta-coo...

Thiolate‐Bridged Iron–Nickel Models for the Active Site of [NiFe] Hydrogenase

“…We synthesized a dinuclear complex having a bulky thiolate, [(CO) 3 Fe(StBu) 3 Ni(SDmp)] {65; Dmp = 2,6-di(mesityl)phenyl}, from the reaction of Fe-Ni-Ni-Fe complex 58 with NaSDmp at -40°C. [63] The nickel site of 65 was found to bind CO at -40°C to give the adduct [(CO) 3 (tBuS)Fe(StBu) 2 Ni-(CO)(SDmp)] (66a), the molecular structure of which was identified by X-ray crystallography (Scheme 7). Its Ni-CO band appearing at 2055 cm -1 is comparable to those observed for the CO-inhibited form of [NiFe] hydrogenases from C. vinosum and D. fructosovorans.…”

Synthesis and characterization of ruthenium heterocyclic-thiocarboxylate complexes

“…For (1a), disorder was observed for the thiophene group. Two preferred orientations were refined resulting in site occupancies of 65 (2) and 35(2)%. For the disordered structure parts, a number of restraints were applied (DFIX, ISOR, SADI and SAME) with the aim to model correct thiophene group.…”

“…This is due to the fact that many metalloenzymes contain M-SH functionalities in their active sites [1][2][3][4] and several industrial processes such as hydrodesulfurization (HDS) of fossil fuels use these complexes as catalysts [5][6][7][8][9][10]. The reaction of hydrogensulfido complexes with sulfur dioxide has been proposed as a key step in the Claus process [11,12].…”

“…Consequently, CpRu(PPh 3 ) 2 SH was synthesized from the metathesis reaction of CpRu(PPh 3 ) 2 Cl with excess of NaSH [13][14][15]. Insertion of elemental sulfur into the Ru-H bond of CpRu(PPh 3 ) 2 H offers an alternative route to the same complex [13].…”

Synthetic Analogues of the Active Sites of Nitrogenase and [NiFe] Hydrogenase

“…66 The nickel-bound CO liberates to recover the catalytic activity, upon flushing with a stream of N 2 to D. v. Miyazaki F 67 or white-light irradiation to Chromatium vinosum (C. vinosum) at 20 K. 68 The reversible binding of CO at the nickel site was found to occur with the (CO) 3 FeNi complex carrying a bulky thiolate ligand. 69 The reaction precursor [(CO) 3 Fe(¯-S (25) is more robust, and the CN t Bu ligand on nickel remains intact under reduced pressure. One of the CO bands of 24, appearing at 2055 cm ¹1 in the infrared spectrum, was assigned as the NiCO band based on an isotope labeling experiment with 13 CO.…”