Cyanide–alkene competition in a diiron complex and isolation of a multisite (cyano)alkylidene–alkene species

Abstract

The μ-(amino)alkylidyne complex [Fe₂Cp₂(CO)₂(μ-CO){μ-CNMe(CH₂CHCH₂)}]CF₃SO₃, [1]CF₃SO₃, reacted with NBu₄CN in dichloromethane affording the μ-(cyano)(amino)alkylidene [Fe₂Cp₂(CO)₂(μ-CO){μ-C(CN)N(Me)(CH₂CHCH₂)}], 2, in 91% yield. Decarbonylation of 2 by using Me₃NO in acetone at room temperature yielded [Fe₂Cp₂(CO)(μ-CO){μ-κ³_C-C(CN)N(Me)(CH₂CHCH₂)}], 3, containing a multidentate alkylidene−alkene ligand occupying both a bridging site and a terminal site, in admixture with the μ-(amino)alkylidyne cyanide product [Fe₂Cp₂(CN)(CO)(μ-CO){μ-CN(Me)(CH₂CHCH₂)}], 4. The reaction of the μ-(amino)alkylidyne imine complex [Fe₂Cp₂(CO)(μ-CO)(NHCPh₂){μ-CN(Me)(CH₂CHCH₂)}]CF₃SO₃, [7]CF₃SO₃, with NBu₄CN gave 3 with an optimized yield of 75% via imine elimination. According to DFT calculations, 3 is less stable than its geometric isomer 4 by 13.4 kcal mol⁻¹ and quantitative conversion to 4 was achieved by refluxing a THF solution of 3 for 2 hours. No replacement of alkene coordination occurred upon treating 3 with CO or PPh₃. The previously unknown compounds 2, 3, 4 and [7]CF₃SO₃ were fully characterized by analytical and spectroscopic techniques and the structure of 3 was elucidated by single crystal X-ray diffraction.