Synthesis and atropisomeric stability of 2,2 '-bis(ferrocenylhydroxymethyl)-1,1 '-biphenyl

Nickel(0)-mediated homocoupling of (2-bromobenzoyl)ferrocene gave in high yield diketone 4 possessing a biphenyl unit. Its chemical reduction afforded the title compound in three diastereomeric forms 1a-c with sufficient atropisomeric stability to allow their detection and purification. By rotation around the biphenyl bond, enantiomers of 1a suffered racemization whereas diol 1c isomerized to 1b, which resulted in being atropisomerically stable since the reverse process from 1b to 1c did not occur. Activation parameters for both these atropisomerizations were also determined. The observed conformational stability can be explained by both hydrogen bonding and steric interactions.