title: Effect of Bridgehead Steric Bulk on the Intramolecular C-H Heterolysis of [FeFe]-Hydrogenase Active Site Models Containing a P2N2 Pendant Amine Ligand.
abstract: A series of pendant amine-containing [FeFe]-hydrogenase models, [X(CH2S-μ)2{Fe(CO)3}{Fe(CO)(P2(Ph)N2(Bn))}] (1H, X = CH2; 2Me, C(CH3)2; 3Et, C(CH2CH3)2; and P2(Ph)N2(Bn) = 1,5-dibenzyl-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane) with different groups at the bridgehead carbon of the S-to-S linker were synthesized. The oxidations of these complexes as well as the reverse reduction reaction were studied by cyclic voltammetry and in situ IR spectroscopy. Regardless of the bridgehead steric bulk, all three complexes demonstrate intramolecular iron-mediated C(sp(3))-H bond heterolytic cleavage with the assistance of the pendant amine base within the chelating diphosphine ligand in the two-electron oxidation process. X-ray crystallographic analysis shows that the doubly oxidized products, [1'H](+), [2'Me](+), and [3'Et](+), all have a rigid FeSC three-membered ring at the open apical site of the rotated iron center. The most noticeable difference in structures of the oxidized complexes is that the single CO ligand of the rotated Fe(P2(Ph)N2(Bn))(CO) unit in [1'H](+) and [2'Me](+) is found below the Fe···Fe vector, while in [3'Et](+) an unusually rotated Fe(P2(Ph)N2(Bn))(CO) moiety positions one of the P donors within the bidentate ligand under the Fe···Fe vector. The starting Fe(I)Fe(I) complexes can be recovered from their corresponding doubly oxidized complexes by reduction in the presence of Brönsted acid.
authors.affiliation: State Key Laboratory of Fine Chemicals, DUT-KTH Joint Education and Research Center on Molecular Devices, Dalian University of Technology (DUT) , Dalian 116024, China.
authors.forename: Dehua
authors.initials: D
authors.lastname: Zheng
authors.affiliation: State Key Laboratory of Fine Chemicals, DUT-KTH Joint Education and Research Center on Molecular Devices, Dalian University of Technology (DUT) , Dalian 116024, China.
authors.forename: Mei
authors.initials: M
authors.lastname: Wang
authors.affiliation: School of Chemistry and Chemical Engineering, Henan University of Technology , Zhengzhou 450001, China.
authors.forename: Ning
authors.initials: N
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Fine Chemicals, DUT-KTH Joint Education and Research Center on Molecular Devices, Dalian University of Technology (DUT) , Dalian 116024, China.
authors.forename: Minglun
authors.initials: M
authors.lastname: Cheng
authors.affiliation: State Key Laboratory of Fine Chemicals, DUT-KTH Joint Education and Research Center on Molecular Devices, Dalian University of Technology (DUT) , Dalian 116024, China.|Department of Chemistry, KTH Royal Institute of Technology , Stockholm 10044, Sweden.
authors.forename: Licheng
authors.initials: L
authors.lastname: Sun
mesh_terms: D000588:Amines / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry*; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D006859:Hydrogen / Q000737:chemistry*; D006864:Hydrogenase / Q000737:chemistry*; D007506:Iron-Sulfur Proteins / Q000737:chemistry*; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular
chemical_list: D000588:Amines; D007506:Iron-Sulfur Proteins; D008024:Ligands; D002244:Carbon; D006859:Hydrogen; C118830:iron hydrogenase; D006864:Hydrogenase