A 13C NMR study of some derivatives obtained from iron carbonyls and diphenylacetylene

The molecule Fe₂(CO)₇(PhC₂Ph)₂ has been studied by ¹³C NMR and is static at ?40°C with a spectrum which is consistent with the known structure observed in the crystals. In the range ?40 to +41°C the three carbonyl resonance coalesce possibly by a single carbonyl averaging process. At room temperature violet Fe₃(CO)₈(PhC₂Ph)₂ is found to be static by ¹³C NMR having a spectrum consistent with the known solid state structure. Dark green Fe₃(CO)₈(PhC₂Ph)₂ is static via ¹³C NMR at ?62°C with a spectrum consistent with the known solid state structure. Between ?62 and +96°C a fluxional process occurs which scrambles the bridge carbonyls and four of the six terminal carbonyl groups. In this process the bridging carbonyls appear to be preferentially moving toward the iron atoms with which they have the shortest iron-carbon bond as observed in the solid state structure.