Deciphering the direct heterometallic interaction in κ³-bis(donor)ferrocenyl-transition-metal complexes

Ligands featuring a 1,1'-bis(donor)ferrocene motif can adopt various binding modes. Among them, the κ³ binding mode, which involves interaction between the iron center of the ferrocene unit and the transition metal is the most unique. Although various examples highlight the interaction itself, the exact quantification of its strength remains uncertain. In our computational study, we systematically investigate the nature of this unique heterometallic bond, demonstrating that the electron density at the transition metal primarily governs the heterobimetallic interaction. On the other hand, the contribution of the ipso-carbon atoms of the cyclopentadiene ring is not negligible. We demonstrated that isodesmic reactions provide the most quantifiable data regarding the interaction. If the transition metal center is complexed with good electron-donor ligands or its positive charge is compensated by the negative charge of the ligands, the interaction with the electron-rich iron center recedes into the background. Finally, we highlighted the importance of the accurate computational description of these systems.