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

Introducing 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 key synthetic methods for the functionalization and elaboration of tris(pyridyl)aluminate ligands.