Investigations on the, active site models of [FeFe]-hydrogenases: Synthesis, structure, and properties of N-functionalized azadithiolatodiiron complexes containing mono- and diphosphine ligands

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 [(mu-SCH2N(Fun)]Fe-2(CO)(6) (A, Fun= C6H4CHO-p; B, Fun= C6H4CO2Me-p; C, Fun= CH2CH2O2CCH2C10H7-1; D, Fun = CH2CH2OH) and [(mu-SCH2)(2)N(Fun)]Fe-2(CO)(5)(Ph2PH) (E, Fun = C6H4OMe-p). Treatment of A and B with 1 equiv of Me3NO center dot 2H(2)O followed by 1 equiv of Ph3P or Ph2PH affords the corresponding monophosphine-substituted complexes [(mu-SCH2)(2)N(C6H4CHO-p)]Fe-2(CO)(5)(Ph3P) (1) and [(mu-SCH2)(2)N(C6H4CO2Me-p)]Fe-2(CO)(5)L (2, L = Ph3P; 3, Ph2PH). Further treatment of B with ca. 1 equiv of Ph2PC2H4PPh2 (dppe) produced the diphosphine dppe-bridged single model [(mu-SCH2)(2)N(C(6)H(4)CO(2)Mep)]Fe-2(CO)(4)(dppe) (4), whereas C reacts with 1 equiv of Me3NO center dot 2H(2)O followed by 0.5 equiv of (eta(5)-Ph2PC5H4)(2)Fe (dppf) to give the diphosphine dppf-bridged double model [(mu-SCH2)(2)N(CH2CH2O2CCH2C10H7-1)Fe-2(CO)(5)](2)(dppf) (5). While D reacts with 1 equiv of n-BuLi followed by 1 equiv of Ph2PCl or directly reacts with 1 equiv of Ph2PCl in the presence of Et3N to generate N-alkoxyphosphine-substituted complex [(mu-SCH2)(2)N(CH2CH2OPPh2-eta(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 [(mu-SCH2)(2)N(C6H4OMe-p)]Fe-2(CO)(5)[Ph2PFe(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 spectroelectrochernical studies, an ECEC mechanism is proposed for this electrocatalytic reaction.