Carbonyl Diiron Azadithiolate Complexes with Azadiphosphine Chelates Related to the Active Site of [FeFe]-Hydrogenases: Protonation and Redox Behaviour
- 1Laboratoire de Chimie, Electrochimie Moléculaire et Chimie Analytique, UMR 6521 CNRS-Université de Bretagne Occidentale, CS 93837–6 Avenue Le Gorgeu, CEDEX 3, 29238 Brest, France
- 2Department of Biotechnology and Biosciences, University of Milano-Bicocca, Piazza della Scienza 2, 20126 Milan, Italy
Abstract
Bimetallic systems with several protonation sites are used for modelling the activity of polymetallic active sites such as the H-cluster of [FeFe]-hydrogenases or nitrogenases. In order to examine the behaviours of multi-proton sites dinuclear systems, the syntheses of the complexes [Fe2(CO)4(k2-PPh2NR2)(μ-adtBn)] (PPh2NR2 = {PhPCH2NRCH2}2, R = Bn (1), Ph (2); adtBn = {SCH2}2NCH2Ph) were carried out by reacting the hexacarbonyl precursor [Fe2(CO)6(µ-adtBn)] with cyclic diphosphines PPh2NR2. Investigation of the reactivity towards proton (CH3SO3H/CF3SO3H) and of the redox properties of these complexes featuring several amine functions in proximity of a diiron site was performed using spectroscopic and electrochemical methods. The experimental results were rationalized by DFT calculations. The protonation sites in such clusters are discussed on the basis of the strength of the acid and the R groups carried by the diphosphine PPh2NR2. The similarities and differences with analogues [Fe2(CO)4(k2-PPh2NR2)(μ-pdt)] and [Fe3(CO)5(k2-PPh2NR2)(μ-adtBn)(µ-pdt)] are highlighted. The main results show that protonations depend on the substituted group R of the PPh2NR2 chelate and of the strength of the acid used (CH3SO3H vs. CF3SO3H). With CH3SO3H, complexes are protonated once, at the PPh2N2Bn diphosphine in 1 and at the diiron site in 2. This latter observation suggests that the coordination of the amine-functionalized-diphosphine PPh2NPh2 assists a competitive pathway for the protonation of the diiron site versus NBn group of the adtBn group. With CF3SO3H, the protonation of two NBn sites is observed in 1, which shows that the protonation of the diiron core bearing an azadithiolate bridge is unfavoured. In 2, the protonation with CF3SO3H arises at the diiron site or the adtBn bridge. This shows the stabilization of the N-protonated forms when a fluorinated counter-anion, such as CF3SO3−, is used.
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BibTeX
@article{hobballah2026carbonyl,
title = {{Carbonyl Diiron Azadithiolate Complexes with Azadiphosphine Chelates Related to the Active Site of [FeFe]-Hydrogenases: Protonation and Redox Behaviour}},
author = {Ahmad Hobballah and Rachid Motei and Federica Arrigoni and Catherine Elleouet and Philippe Schollhammer and Giuseppe Zampella},
journal = {Inorganics},
year = {2026},
month = oct,
doi = {10.3390/inorganics14110270},
url = {https://www.mdpi.com/2304-6740/14/11/270},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Carbonyl Diiron Azadithiolate Complexes with Azadiphosphine Chelates Related to the Active Site of [FeFe]-Hydrogenases: Protonation and Redox Behaviour
AU - Ahmad Hobballah
AU - Rachid Motei
AU - Federica Arrigoni
AU - Catherine Elleouet
AU - Philippe Schollhammer
AU - Giuseppe Zampella
PY - 2026
DA - 2026/10/23
JO - Inorganics
DO - 10.3390/inorganics14110270
UR - https://www.mdpi.com/2304-6740/14/11/270
AB - Bimetallic systems with several protonation sites are used for modelling the activity of polymetallic active sites such as the H-cluster of [FeFe]-hydrogenases or nitrogenases. In order to examine the behaviours of multi-proton sites dinuclear systems, the syntheses of the complexes [Fe2(CO)4(k2-PPh2NR2)(μ-adtBn)] (PPh2NR2 = {PhPCH2NRCH2}2, R = Bn (1), Ph (2); adtBn = {SCH2}2NCH2Ph) were carried out by reacting the hexacarbonyl precursor [Fe2(CO)6(µ-adtBn)] with cyclic diphosphines PPh2NR2. Investigation of the reactivity towards proton (CH3SO3H/CF3SO3H) and of the redox properties of these complexes featuring several amine functions in proximity of a diiron site was performed using spectroscopic and electrochemical methods. The experimental results were rationalized by DFT calculations. The protonation sites in such clusters are discussed on the basis of the strength of the acid and the R groups carried by the diphosphine PPh2NR2. The similarities and differences with analogues [Fe2(CO)4(k2-PPh2NR2)(μ-pdt)] and [Fe3(CO)5(k2-PPh2NR2)(μ-adtBn)(µ-pdt)] are highlighted. The main results show that protonations depend on the substituted group R of the PPh2NR2 chelate and of the strength of the acid used (CH3SO3H vs. CF3SO3H). With CH3SO3H, complexes are protonated once, at the PPh2N2Bn diphosphine in 1 and at the diiron site in 2. This latter observation suggests that the coordination of the amine-functionalized-diphosphine PPh2NPh2 assists a competitive pathway for the protonation of the diiron site versus NBn group of the adtBn group. With CF3SO3H, the protonation of two NBn sites is observed in 1, which shows that the protonation of the diiron core bearing an azadithiolate bridge is unfavoured. In 2, the protonation with CF3SO3H arises at the diiron site or the adtBn bridge. This shows the stabilization of the N-protonated forms when a fluorinated counter-anion, such as CF3SO3−, is used.
SN - 2304-6740
ER -