d6‐Metal Complexes of 4,4′‐Bipyrimidine, an Ambident Ligand with High π‐Acceptor Ability

The highest π-acidity of all bidiazines, which have the possibility of forming α-diimine chelates (1–4), is not exhibited by 2,2′-bipyrazine 3 but rather by the 4,4′-bipyrimidine 2, which has not been used up to now in complex chemistry. This result was obtained from a theoretical analysis as well as an investigation of the corresponding d6 metal complexes.