Investigations on the Active Site Models of [FeFe]-Hydrogenases: Synthesis, Structure, and Properties of N-Functionalized Azadithiolatodiiron Complexes Containing Mono- and Diphosphine Ligands

Abstract

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.

Synthesis, characterization, and electrochemical properties of diiron azadithiolate complexes related to the active site of [FeFe]-hydrogenases

“…The reduction peaks of A (-1.59 V vs. Fc/Fc ? ), 1 (-1.77 V), and 2 (-1.79 V) can be assigned to the one-electron reduction processes from Fe I Fe I to Fe I Fe 0 (supported by bulk electrolysis at controlled potential, as reported in the literature [5]), and the oxidation peaks of A (0.54 V), 1 (0.28 V), and 2 (0.22 V) should be attributed to the one-electron oxidation processes from Fe I Fe I to Fe I Fe II because their peak currents were close to those of the respective one-electron reduction processes [11,12]. It should be noted that the reduction and oxidation peaks of 1 and 2 are apparently shifted toward more negative potentials than those corresponding to their parent complex A, which is consistent with the phosphine ligands having stronger electron-donating character than CO [11].…”

“…Diiron azadithiolate complexes of the type [(l-SCH 2 ) 2 -NR]Fe 2 (CO) 5 (L), such as [(l-SCH 2 ) 2 NH]Fe 2 (CO) 5 (PPh 3 ) [4], [(l-SCH 2 ) 2 N(C 6 H 4 CO 2 Me-p)]Fe 2 (CO) 5 (PPh 3 ) [5], and [(l-SCH 2 ) 2 N(C 6 H 4 C : CC 6 H 4 NO 2 -4)]Fe 2 (CO) 5 (PPh 3 ) [6], were prepared by the substitution of carbonyl ligands with PPh 3 in the presence of Me 3 NO, and their properties were studied by cyclic voltammetric techniques. On the basis of this previously reported work, we have successfully synthesized two new diiron azadithiolate complexes containing PPh 3 or PPh 2 H ligands.…”

Synthesis, characterization and electrocatalysis of diiron propanediselenolate derivatives as the active site models of [FeFe]-hydrogenases

“…Since the successful structural elucidation regarding the two types of [FeFe]Hases, a great variety of biomimetic models (for example, diiron PDT-type [14][15][16][17][18][19][20][21], diiron ADT-type [22][23][24][25][26][27][28][29][30][31][32], diiron ODT-type [33], and diiron TDT (thiodithiolate)-type [34,35] models) have been prepared and structurally characterized. It is worthy of note that among these models, diiron PDT-type models are actually the earliest and most extensively studied, which have played a key role in the development of biomimetic chemistry of [FeFe]Hases [36][37][38][39][40].…”

“…It is worthy of note that among these models, diiron PDT-type models are actually the earliest and most extensively studied, which have played a key role in the development of biomimetic chemistry of [FeFe]Hases [36][37][38][39][40]. On the basis of our previous modelling studies [19][20][21][27][28][29][30][31][32][33][34] we launched a study on the synthesis, structures and properties of a series of diiron propanediselenolate (PDS) derivatives. The purposes that we launched such a study are: (i) to prepare the first examples of diiron PDS-type H-cluster models (note that some diiron azadiselenolate (ADS)-type models were recently reported [41]), and (ii) to make a comparison of biomimetic chemistry between these selenium-containing PDS-type models and their sulfur analogs, the diiron PDT-type models.…”

Synthesis, characterization and electrocatalysis of mono- and di-nickel tetraiminodiphenolate macrocyclic complexes as active site models of [NiFe]-hydrogenases

“…A typical mechanism of proton reduction involves the following steps: a) reduction of the metal center concomitant with proton transfer from the acid to the pendant base; b) protonation of the metal ion in low oxidation state generating of a metalehydride complex; c) release of molecular hydrogen parallel with a second electron transfer and recovery of the catalyst. In the absence of the pendant base, the second protonation is simultaneous with the dihydrogen evolution [3,19].…”