Synthetic[FeFe]-hydrogenase Models Bearing P-S Chelating Ligands

As one class of organometallic enzymes,[FeFe]hydrogenases(H2ase)can catalyze the reversible interconvertion of hydrogen with electrons and protons,which dramatically high efficiency have spawned intense scrutiny of the[FeFe]-H2ase structure and mechanism.Hundreds of related diiron complexes based on[Fe2S2]type of structure have been reported to date.Notably,there is a cysteine thiolate in the active site of[FeFe]-H2ases.However,synthetic[Fe2S3]models have been rarely reported relative to the models using phosphine ligands.In this paper,we report a series of[Fe2S3]models,as well as exploring their reactions toward protons.In the first part,[Fe2(Me2pdt)(1,2-Cy2PC6H4SMe)(CO)4](2,pdt = CH2(CH2S)2)was synthesized on the basis of[1,2-Cy2PC6H4SMe]and[Fe2(Me2pdt)(CO)6].Variable-temperature 31P NMR spectra showing coalescences and decoalescences suggest the rapid interconversion between a(P),b(S)-2 and a(P),b(S)-2 for the apical-basal isomers.Treatment 2 with HBF4·Et2O afforded[H2]BF4,as well as some electron transfer product[2]?.Based on the oxidation of 2 to[2]?,the tri-substituted[Fe(I)Fe(II)]+ cationic complex[Fe2(Me2pdt)(1,2-Cy2PC6H4SMe)(PPh3)(CO)3]BF4([3]BF4)was synthesized.Reduction of[3]BF4 provided the neutral tri-substituted Fe(I)Fe(I)compound 3.Most importantly,this substitution also leads to 2 and 3 with large Lewis basicity difference,i.e.?pKaMeCN-10.The thioether group can not be protonated in our models.In the second part,we selected more basic ligand[PPh2PC6H4-2-SH]and[Fe2(pdt)-(CO)4(dppbz)](dppbz = 1,2-bis(diphenylphosphino)benzene).Through the oxidative addition of a S-H bond at iron,[Fe2(pdt)(CO)2(?-H)(dppbz)(PS)](4)was synthesized.The thiolate sulfur in[P,S]ligand of 4 is proved to be a basity site.Protonation of 4 afforded[Fe2(pdt)(CO)2(?-H)(dppbz)(PS-H)]BF4 5 with pKa-3.6...