Addition of Aluminum and Gallium Species to Aromatic and Alkyl-Substituted 1,4-Diaza-1,3-butadiene Ligands

Abstract

In this report, we investigate the interactions of Me_<i>x</i>MCl_3–<i>x</i> (<i>x</i> = 0–3, M = Al, Ga) with various aromatic and alkyl-substituted 1,4-diaza-1,3-butadiene ^RDAB ligands (or α-diimine ligands) to give a variety of structures in solution and in the solid state. In combination with other previously reported structures, certain general trends of reactivity of these species can be deduced, although there are still some unexplained modes of reactivity. The methylated Al species react with aromatic-substituted ^RDAB ligands to provide final products that result from CN insertion into the Al–CH₃ group followed by rearrangement reactions. The addition of methyl groups onto the backbone of the ^RDAB ligand is insufficient to stop the insertion and rearrangement processes from occurring. In the case of MeAlCl₂ with the bulky ^DiPPDAB ligand, the reaction could be followed spectroscopically from the monoadduct through the inserted/rearranged final product. Methylated Ga species, however, are much less predictable in their behavior with aromatic-substituted ^RDAB ligands. Depending on the exact species and ratios used, coordinated adducts can be formed and identified, or inserted/rearranged products similar to the aluminum reactions can be obtained. Quite interestingly, cation/anion pairs can also be formed in which GaCl₃ or MeGaCl₂ act as a chloride acceptors. This behavior was unique and substantially different from the analogous Al reactions which formed either a dicoordinated adduct or an inserted/rearranged complex. When the stronger-donating alkyl-substituted ^RDAB ligands were used with Me₂GaCl, only cation/anion pairs were obtained. Surprisingly, when the same reactions were performed using Me₂AlCl as a reagent, irreproducible results were obtained