Aminophosphine-substituted Fe/E (E = S, Se) carbonyls related to [FeFe]-hydrogenases: Synthesis, protonation, and electrocatalytic proton reduction

To develop the chemistry of Fe/E (E = S, Se) carbonyls related to [FeFe]-hydrogenases, four types of aminophosphine substituted Fe/E carbonyls were successfully prepared. That is, treatment of amin-odiphosphine ligands (PNP ligands) (Ph2P)2NR (R = C6H5 and C6H4-3CCH) with Fe2(mu-EBn)2(CO)6 (Bn = CH2C6H5) in the presence of Me3NO.2H2O at room temperature gave target PNP-chelated complexes Fe2(mu-EBn)2(CO)4(K2-Ph2P)2NR ( 2a -2d) . The more interesting finding is that unexpected aminophosphine monosubstituted complexes Fe2(mu-EBn)2(CO)5{K1-Ph2PNH(R)}(1a-1d) were also iso-lated. Alternately, 1a -1d could also be readily produced by using the Me3NO-assisted substitution of Fe2(mu-EBn)2(CO)6 with 1 equivalent of Ph2PNHR (hereinafter abbreviated as HNP ligand) at room temperature. Further, treatment of Fe2(mu-SBn)2(CO)6 with 2 equivalents of HNP ligands gave target HNP-disubstituted complexes Fe2(mu-SBn)2(CO)4{Ph2PNH(R)}2 ( 3a and 3b ) in moderate yields, whereas treatment of Fe2(mu-SeBn)2(CO)6 with 2 equivalents of HNP ligands afforded mononuclear species Fe(SeBn)2(CO)2{Ph2PNH(R)}2 ( 3c and 3d ) in low yields. In control tests, dppm substituted models Fe2(mu-EBn)2(CO)5(K1-dppm) ( 4a and 4b ) were prepared by treatment of Fe2(mu-EBn)2(CO)6 and dppm (dppm = Ph2PCH2PPh2) in the presence of Me3NO.2H2O at room temperature, in which the dppm be-haves as a monodentate ligand. All the new complexes obtained above were fully characterized by various spectroscopic techniques and particularly by X-ray crystallography except 1d . Meanwhile, protonation of 2a by HBF4.Et2O afforded mu-hydride diiron complex (mu-H)Fe2(mu-SBn)2(CO)4{(K2-Ph2P)2NPh}BF4 ( 5 ). Crys-tal structure reveals that two P atoms of (Ph2P)2NPh occupy the basal/basal position. Additionally, the electrochemical properties of complexes 1a, 2a, 2c and 3a are studied by cyclic voltammetry, indicating that they are active for electrocatalytic proton reduction to hydrogen (H 2 ).(c) 2023 Elsevier B.V. All rights reserved.

Automated summary

Researchers successfully prepared four types of aminophosphine substituted Fe/E (E = S, Se) carbonyls related to [FeFe]-hydrogenases. These compounds have interesting structures and can be used for electrocatalytic hydrogen production.