Synthesis of Square-Planar Aluminum(III) Complexes

The synthesis of two four-coordinate and square planar (SP) complexes of aluminum(III) is presented. Reaction of a phenyl-substituted bis(imino) pyridine ligand that is reduced by two electrons, Na-2((I2P2-)-I-Ph), with AlCl3 afforded five-coordinate [((I2P2-)-I-Ph)Al(THF)Cl] (1). Square-planar [((I2P2-)-I-Ph)AlCl] (2) was obtained by performing the same reaction in diethyl ether followed by lyphilization of 2 from benzene. The four-coordinate geometry index for 2, tau(4), is 0.22, where 0 would be a perfectly square-planar molecule. The analogous aluminum hydride complex, [((I2P2-)-I-Ph)AlH] (3), is also square-planar, and was characterized crystallographically and has tau(4) = 0.13. Both 2 and 3 are Lewis acidic and bind 2,6-lutidine.