Steric Effects on the Structures, Reactivity, and Coordination Chemistry of Tris(2‐pyridyl)aluminates

AbstractIntroducing substituents in the 6‐position of the 2‐pyridyl rings of tris(pyridyl)aluminate anions, of the type [EtAl(2‐py′)3]− (py′=a substituted 2‐pyridyl group), has a large impact on their metal coordination characteristics. This is seen most remarkably in the desolvation of the THF solvate [EtAl(6‐Me‐2‐py)3Li⋅THF] to give the monomer [EtAl(6‐Me‐2‐py)3Li] (1), containing a pyramidal, three‐coordinate Li+ cation. Similar monomeric complexes are observed for [EtAl(6‐CF3‐2‐py)3Li] (2) and [EtAl(6‐Br‐2‐py)3Li] (3), which contain CF3 and Br substituents (R). This steric influence can be exploited in the synthesis of a new class of terminal AlOH complexes, as is seen in the controlled hydrolysis of 2 and 3 to give [EtAl(OH)(6‐R‐2‐py)2]− anions, as in the dimer [EtAl(OH)(6‐Br‐2‐py)2Li]2 (5). Attempts to deprotonate the AlOH group of 5 using Et2Zn led only to the formation of the zincate complex [LiZn(6‐Br‐py)3]2 (6), while reactions of the 6‐Br substituted 3 and the unsubstituted complex [EtAl(2‐py)3Li] with MeOH give [EtAl(OMe)(6‐Br‐2‐py)2Li]2 (7) and [EtAl(OMe)(2‐py)2Li]2 (8), respectively, having similar dimeric arrangements to 5. The combined studies presented provide ke