Aminodiphosphine substituted 2Fe2Se complex as new precursor to single and double butterfly Fe/Se models related to FeFe hydrogenase models

Abstract

A convenient way to synthesize the aminediphosphine (PNP) substituted Fe/Se models with [Fe2(µ-Se2)(CO)4(μ-PNP)] as a new precursor was described. Firstly, treatment of [Fe2(µ-SeR)2(CO)6] (R = C6H5 and CH2C6H5) with (Ph2P)2NBui in refluxing xylene gave [Fe2(μ-SeR)2(CO)4(μ-Ph2P)2NBui] (R = C6H51 and CH2C6H52). Further debenzylation reaction was found in complex 2 after long-time heating, and precursor complex [Fe2(μ-Se2)(CO)4(μ-Ph2P)2NBui] (3) was isolated with satisfactory yield. GC–MS analysis showed that the reaction involved the formation of (C6H5CH2)2. Further, the “open” single butterfly complex 2 and “closed” butterfly complex [Fe2(µ-pdSe)(CO)4(μ-Ph2P)2NBui] (pdSe = Se(CH2)3Se) (4) were conveniently prepared via a new synthetic route involving the reaction of 3 with 2 equiv of Et3BHLi, followed by treatment of the resulting [Fe2(μ-SeLi)2(CO)4(μ-Ph2P)2NBui] with BzBr (Bz = CH2C6H5) and Br(CH2)3Br, respectively. On the other hand, to obtain a double butterfly complex [{Fe2(μ-SeEt)(CO)4(μ-Ph2P)2NBui}2(μ-Se2)] (5), the first Fe4Se4 carbonyl model containing two PNP substituents, successive reactions were performed, including treating precursor complex 3 with EtMgBr, protonation with CF3CO2H (TFA), and air-direct oxidation. All the complexes were well characterized by various spectral techniques and particularly by X-ray crystallography. Moreover, a comparison of the electrochemical and electrocatalytic properties of single and double clusters 4 and 5 is also presented.