Carbon-13 nuclear magnetic resonance spectra of σ,η-binuclear complexes prepared from dodecacarbonyltri-iron and acetylenes

Abstract

The binuclear complexes [Fe₂(CR¹:CR²·CR³:CR⁴)(CO)₆], (I), and [Fe₂(µ-CR¹:CR²·CO·CR³:CR⁴)(CO)₆], (II), have been investigated by ¹³C n.m.r. spectroscopy (R¹, R², R³, R⁴= H, Me, Bu^t, Ph, or CH₂:CH·CH:CH₂). Low-field absorptions observed for carbon atoms σ- and η-bonded to two iron atoms are discussed for the two classes of complex. Variable-temperature ¹³C n.m.r. spectra show that these complexes are stereochemically non-rigid; steric effects are important in the fluxional behaviour of the Fe(CO)₃ moiety in complexes (II).