Synthesis and structure of cubane-type tetrairon clusters possessing μ _3-isonitrile ligands. reductive coupling of two isonitriles on redox-responsive tetrairon reaction sites

摘要

A 3:1 molar ratio mixture of [(η ~5-C _5H _4Me) _4Fe _4(HCCBr) _2](PF _6) (1a) and [(η ~5-C _5H _4Me) _4Fe _4(HCCH)(BrCCBr)](PF _6) (1b) was converted to [(η ~5-C _5H _4Me) _4Fe _4(μ _3-CH) _2(μ _3-CNPh) _2](PF _6) _2 (2) upon treatment with aniline, followed by N iPr _2Et and finally [Cp _2Fe](PF _6). The X-ray diffraction analysis revealed that 2 can be described as a cubane-type tetrairon cluster possessing two μ 3-CH and two μ 3-isonitrile ligands. Treatment of 2 with 2.5 equiv of [Cp _2Co] gave the neutral form 3, formulated as [(η ~5- C _5H _4Me) _4Fe _4(HCCH) _2(μ _3-CNPh) _2]. The redox reactions were chemically reversible; treatment of 3 with [Cp _2Fe](PF _6) reproduced 2 quantitatively. The structure of 3 was determined by X-ray diffraction analysis. The molecule exhibits a butterfly geometry resulting from the scission of one of the iron-iron bonds of the tetrahedron in 2. In accordance with the conversion of the core structure from tetrahedron to butterfly, the coupling of two μ _3-CH ligands occurs to form an acetylene ligand. Further treatment of 3 with LiAlH _4 followed by air-oxidation resulted in reductive coupling of two isonitrile ligands to give a bis(acetylene) cluster, [(η ~5-C _5H _4Me) _4Fe _4(HCCH) _2](PF _6) (6).