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

The μ-(amino)alkylidyne complex [Fe 2 Cp 2 (CO) 2 (μ-CO){μ-CNMe(CH 2 CHCH 2 )}]CF 3 SO 3 , [1]CF 3 SO 3 , reacted with NBu 4 CN in dichloromethane affording the μ-(cyano)(amino)alkylidene [Fe 2 Cp 2 (CO) 2 (μ-CO){μ-C(CN)N(Me)(CH 2 CHCH 2 )}], 2, in 91% yield. Decarbonylation of 2 by using Me 3 NO in acetone at room temperature yielded [Fe 2 Cp 2 (CO)(μ-CO){μ-κ 3 C -C(CN)N(Me)(CH 2 CHCH 2 )}], 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 [Fe 2 Cp 2 (CN)(CO)(μ-CO){μ-CN(Me)(CH 2 CHCH 2 )}], 4. The reaction of the μ-(amino)alkylidyne imine complex [Fe 2 Cp 2 (CO)(μ-CO)(NHCPh 2 ){μ-CN(Me)(CH 2 CHCH 2 )}]CF 3 SO 3 , [7]CF 3 SO 3 , with NBu 4 CN 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 PPh 3 . The previously unknown compounds 2, 3, 4 and [7]CF 3 SO 3 were fully characterized by analytical and spectroscopic techniques and the structure of 3 was elucidated by single crystal X-ray diffraction.