Synthetic and Structural Studies of Butterfly Fe/S/P Cluster Complexes Related to the Active Site of [FeFe]-Hydrogenases. Proton Reduction to H₂ Catalyzed by (η¹-Ph₂PS-η¹)₂Fe₂(CO)₆

Abstract

The butterfly Fe/S cluster anions (µ-RS)(µ-S -)Fe 2 (CO) 6 (A, R ) Et, p-MeC 6 H 4 ), (µ-S -) 2 Fe 2 (CO) 6 (C), [(µ-S -)Fe 2 (CO) 6 ] 2 (4-µ-SC 6 H 4 C 6 H 4 S-µ-4′) (D), and [(µ-S -)Fe 2 (CO) 6 ] 2 [4-µ-SC 6 H 4 OCH 2 CH 2 OC 6 H 4 Sµ-4′] (E) (generated in situ via reactions of (µ-S 2 )Fe 2 (CO) 6 with RMgBr, Et 3 BHLi, 4-LiC 6 H 4 C 6 H 4 Li-4′, and 4-LiC 6 H 4 OCH 2 CH 2 OC 6 H 4 Li-4′) were found to react with Ph 2 PCl to give a series of novel butterfly Fe/S/P cluster complexes. Treatment of monoanions A (R ) Et, p-MeC 6 H 4 ) with 1 equiv of Ph 2 PCl in THF from -78 °C to room temperature gave the single-butterfly Fe 2 S 2, whereas dianions C, D, and E reacted with 2 equiv of Ph 2 PCl to give single-butterfly Fe 2 S 2 P 2 complex (η 1 -Ph 2 PS-η 1 ) 2 Fe 2 (CO) 6 ( 11) and double-butterfly Fe 4 S 4 P 2 complexes [(η 1 -Ph 2 PS-η 1 )Fe 2 (CO) 6 ] 2 (4-µ-SC 6 H 4 C 6 H 4 S-µ-4′) ( 12) and [(η 1 -Ph 2 PS-η 1 )Fe 2 (CO) 6 ] 2 [4-µ-SC 6 H 4 OCH 2 CH 2 OC 6 H 4 S-µ-4′] (13), respectively. More interestingly, the novel µ 4 -S-containing doublebutterfly Fe 4 S 2 P complexes [(µ-RS)Fe 2 (CO) 6 ](µ 4 -S)[(µ-Ph 2 P)Fe 2 (CO) 6 ] (14, R ) Me; 15, R ) Ph; 16, R ) Et) could be prepared by reactions of single-butterfly complexes (µ-RS)(η 1 -Ph 2 PS-η 1 )Fe 2 (CO) 6 (1, R ) Me; 3, R ) Ph; 7 R ) Et) with excess Fe 2 (CO) 9 in THF at room temperature, whereas the quadruplebutterfly Fe 8 S 4 P 2 complexes [(µ-Ph 2 P)Fe 2 (CO) 6 (µ 4 -S)Fe 2 (CO) 6 ] 2 (4-µ-SC 6 H 4 C 6 H 4 S-µ-4′) ( 17) and [(µ-Ph 2 P)Fe 2 (CO) 6 (µ 4 -S)Fe 2 (CO) 6 ] 2 [4-µ-SC 6 H 4 OCH 2 CH 2 OC 6 H 4 S-µ-4′] (18) were similarly prepared by reactions of the corresponding double-butterfly complexes 12 and 13 with excess Fe 2 (CO) 9 , respectively. All the new complexes 7-18 have been characterized by elemental analysis, by spectroscopy, and for 9, 11, and 14 by X-ray crystallography. In view of the structural similarity of these Fe/S/P complexes to the [FeFe]-hydrogenase active site, they might be regarded as H-cluster models. As a representative, model complex 11 was found to be able to catalyze proton reduction to hydrogen under CV conditions.

Carbon- and Sulfur-Bridged Diiron Carbonyl Complexes Containing N,C,S-Tridentate Ligands Derived from Functionalized Dibenzothiophenes: Mimics of the [FeFe]-Hydrogenase Active Site

“…The steric environment and the oxidation state of the diiron center can be controlled by substitution of CO with other strong σ-donor ligands, and mixed-valent Fe II Fe I dithiolate complexes with phosphines or N-heterocyclic carbenes were reported as a model for the diiron unit in the H OX state. , The active site models with the cubane cluster have been synthesized by using tripod thiolate ligands . On the other hand, diiron model complexes with different bridging atoms such as P, N, and Se have been explored. − Electrocatalytic activity of the diphosphido-, diimido-, and diselenido-bridged complexes for proton reduction was also reported.…”

Diiron Complexes with Pendant Phenol Group(s) as Mimics of the Diiron Subunit of [FeFe]‐Hydrogenase: Synthesis, Characterisation, and Electrochemical Investigation

“…Since the revelation of the detailed structural information of the enzyme, mimicking of the diiron centre has attracted tremendous attention because of the relevance of hydrogen to energy, and a good collection of model complexes containing either a {2Fe2S} or {2Fe3S} core have been reported. [6][7][8][9][10][11][12][13][14][15] Some of those reported synthetic analogues duplicated delicately key structural features found in the Hcluster. [16][17][18] But attempts of preparing models to mimic the bonding feature Fe-OH 2 (OH -) had not been successful [19][20][21][22][23] because such a bond is doomed to be labile as it is necessary for this bond to be readily cleaved for substrate binding in the enzymatic catalysis.…”

Reactions of Monoanions [(μ-RE)(μ-E)Fe2(CO)6]− and Dianions [(μ-E)2Fe2(CO)6]2− (E = Se, S) with N-Substituted Benzimidoyl Chlorides, Leading to Novel Butterfly Fe/E Cluster Complexes

“…It is well known that the [MgX] + salts of monoanions A and B , and the dilithium salts of dianions C and D − can be prepared in nearly quantitative yields by reductive cleavage of the E−E bond of cluster (μ-E 2 )Fe 2 (CO) 6 with Grignard reagents and Super-Hydride (Et 3 BHLi), respectively, in THF at −78 °C (Scheme ). In addition, these anions have been also demonstrated to be versatile reagents for synthesis of a wide variety of novel butterfly Fe/E cluster complexes. − Recently, we published two papers that described the unexpected production of the butterfly Fe/S/P cluster complexes from reactions of the butterflyFe/S cluster anions B and D with a P-based electrophile, Ph 2 PCl. , Closely related to such studies, we further carried out a study on reactions of anions A − D with another type of electrophile, namely, the N-substituted benzimidoyl chlorides PhC(Cl)NR′, in order to find new reaction modes and to prepare the corresponding butterfly cluster complexes. Interestingly, through this study we found that the Se-centered anions A and C reacted with PhC(Cl)NR′ to give the expected butterfly Fe/Se cluster complexes, whereas reactions of the S-centered anions B and D afforded the unexpected novel butterfly Fe/S cluster complexes.…”