Bis-nickel-bridged p-terphenyl dianion – Synthesis and structures

Nature of the Short Rh–Li Contact between Lithium and the Rhodium ω-Alkenyl Complex [Rh(CH2CMe2CH2CH═CH2)2]−

“…Especially interesting are compounds in which the metal–metal bonds involve two metals of different electronegativity: such compounds are able to activate small molecules such as H 2 and N 2 . − As the electronegativity difference between the metals increases, the bonding necessarily becomes less covalent. Compounds that combine very electropositive metals, such as Li and Mg, with very electronegative metals, such as electron-rich late transition metals, show potential as catalysts for organic reactions such as cross-coupling − and cycloaddition reactions. , Understanding the interactions between these metal centers is important for the development of the chemistry of these complexes …”

“…Several dozen compounds are known that exhibit relatively short M–M distances between a group 8 transition metal and a Li − ,− or a Mg − center. In some of these compounds, the two metal centers are best described as noninteracting and are held in close proximity by electron-rich anionic ligands. ,, In other compounds, the M–M interaction has been described in a variety of ways: ion pairing, ,, dative bonding (coordinate bonding), p–d π bonding, and three-center bonding mediated by an anionic ligand. ,, In a few cases, covalent interactions have been suggested. , Despite this variety in the description of the M–M interaction, modern computational studies generally suggest that the interactions between Li or Mg and late transition metals are predominantly ionic and that covalent (dative) interactions play a minor role at best. ,,,, …”