Structural and rotational isomerism in diaminocarbene complexes of iron

Primary amines react with a variety of cationic and neutral iron isocyanide complexes to yield structural and rotational diaminocarbene isomers characterized by variable temperature ¹H and ¹³C NMR spectra. Structural isomers result from the conversion of amines to isocyanide ligands via the base-catalyzed nucleophilic attack of initially formed diaminocarbenes on $\text{cis}$ isocyanides substituents, the effect on isomer populations is often marked. Factors influencing structural and rotational isomeric preferences are discussed.