Synthesis, characterization, and dynamic behaviour of pseudoferrocene complexes

Abstract

Carbanion sources (organolithium and Grignard reagents) react with [(mesitylene)2Fe]2+ and [(mesitylene)(Ch)Fe]+ cations (Ch = cyclohexadienyl) to afford neutral Ch2Fe and ChCh′Fe ("pseudoferrocene") complexes, respectively. Addition of R− (R− = methyl, phenyl, benzyl, and t-butyl) occurs stereospecifically via exo addition at an unsubstituted carbon atom of the arene ring. The synthesis and characterization of these complexes is detailed and the structure of bis(η5-exo-6-phenyl-1,3,5-trimethylcyclohexadienyl)iron(II), 3b, has been determined by single crystal X-ray diffraction analysis. 3b crystallizes in the triclinic space group [Formula: see text], with a = 11.947(2), b = 12.784(1), c = 8.865(2), α = 108.59(1)°, β = 108.19(1)°, γ = 84.91(1)°, and Dcalcd 1.227 g cm−3 for Z = 2. Least-squares refinement gave a conventional R value of 0.0452 for 2080 independent observed reflections. The structure reveals that the complex adopts a gauche-eclipsed conformation. The variable temperature (vt) 1H NMR spectra of pseudoferrocenes are interpreted in terms of restricted ring rotation around the ligand—metal—ligand axis. Keywords: arene, cyclohexadienyl, pseudoferrocene, variable temperature NMR, X-ray diffraction.