Intramolecular versus intermolecular mechanism of metallotropic rearrangements of chiral chromium tricarbonyl complexes of substituted naphthalenes and other polyaromatic compounds investigated by chiral HPLC of its racemic mixtures

Pure enantiomers of chromium tricarbonyl complexes of α- and β-monosubstuted naphthalenes RC10H7Cr(CO)3 (R=Cl, Me, SiMe3, SnMe3) were separated as pure enantiomers by chiral phase HPLC on a Chiracel OD column. Inter-ring haptotropic rearrangements (IRHRs) (process in which metal shifts between substituted and non-substituted rings) of pure enantiomers were investigated in different solvents in the presence or absence of some solvating additives. It was shown that IRHR proceeds at 85°C in noncoordinative and noncomplexing solvents such as hexafluorobenzene or decane through an intermolecular mechanism without racemization. In aromatic toluene, which can bind with the organometallic group, it proceeds through a partially intramolecular mechanism, leading to considerable racemization (ca. 20%) of the complexes. In the presence of solvating additives (THF, dibutyl ether), almost complete racemization (>90%) was observed.