Synthesis, Structures, and Reactivity of Diazabutadiene-Ligated Rare-Earth Radical Complexes Bearing Adaptable Auxiliary Ligands

Bis­(diazabutadiene) rare-earth diradical complexes [(MesDAD)2 REL] (1–4) were synthesized, of which the auxiliary ligand L could be borohydride, alkyl, alkoxide, or aminoxide ligands. The synthetic approach was utilized by a one-pot reaction, including reduction of DAD and salt metathesis of ligands. Single-crystal X-ray diffraction results showed that complexes 1–4 maintained similar distorted square-pyramidal coordination spheres, and the DAD ligands were all traditional DAD radical anions. When the auxiliary ligand was changed to a less bulky N-pyrrolyl ligand, a partial ligand redistribution product [(MesDAD)Lu(NC4H4)2]2 (5) was found. The redox reactivity of DAD ligands in rare-earth diradical complexes was also studied. The single-electron reduction of 1 yielded [Lu(MesDAD•–)­(MesDAD2–)­(THF)]­(6), and the disproportionation reaction of [(MesDAD)2 ScCl­(THF)] in tetramethylethylenediamine (TMEDA) gave a 1:1 product of MesDAD and [(MesDAD)ScCl­(TMEDA)] (7). Furthermore, the reaction of MesDAD with SmI2 resulted in an unexpected C–C coupling product 8, which is a new reaction mode for DAD radicals.