Synthesis and Structure of Cubane-Type Tetrairon Clusters Possessing μ 3 -Isonitrile Ligands. Reductive Coupling of Two Isonitriles on Redox-Responsive Tetrairon Reaction Sites

A 3:1 molar ratio mixture of [(eta(5)-C5H4Me)(4)Fe-4(HCCBr)(2)](PF6) (1a) and [(eta(5)-C-5-H4Me)(4)Fe-4(HCCH)-(BrCCBr)](PF6) (1b) was converted to [(eta(5)-C5H4Me)(4)Fe-4(mu(3)-CH)(2)(mu(3)-CNPh)(2)](PF6)(2) (2) upon treatment with aniline, followed by (NPr2Et)-Pr-i and finally [Cp2Fe](PF6). The X-ray diffraction analysis revealed that 2 can be described as a cubane-type tetrairon cluster possessing two mu(3)-CH and two mu(3)-isonitrile ligands. Treatment of 2 with 2.5 equiv of [Cp2Co] gave the neutral form 3, formulated as [(eta(5)-C5H4Me)(4)Fe-4(HCCH)(2)(mu(3)-CNPh)(2)]. The redox reactions were chemically reversible; treatment of 3 with [Cp2Fe](PF6) 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 mu(3)-CH ligands occurs to form an acetylene ligand. Further treatment of 3 with LiAlH4 followed by air-oxidation resulted in reductive coupling of two isonitrile ligands to give a bis(acetylene) cluster, [(eta(5)-C5H4Me)(4)Fe-4(HCCH)(2)](PF6) (6).