Synthesis and properties of calcium tetraorganylalanates with [Me4-nAlPhn]- anions

Triphenylalane yields in THF or Et2O the corresponding ether complexes [(thf)AlPh3] (1a) and [(Et2O)-AlPh3] (1b). The reaction of these triphenylalanes with phenylcalcium iodide in THF yielded quantitatively [(thf)(5)CaI][AlPh4] (2), which can be recrystallized from diethyl ether/THF mixtures without ether exchange reactions. The reaction of PhCa(thf)(4)I with trimethylalane in THF in an equimolar ratio leads to the formation of solvent-separated [(thf)(6)Ca][AlMe3Ph](2) (5). which immediately shows ligand redistribution. Therefore, a fractionated crystallization gives [(thf)(6)Ca][AlMe2Ph2](2) (4) at 4 degrees C, [(thf)(4)CaI2] at -20 degrees C, and after reduction of the volume of the mother liquor [(thf)(6)Ca][AlMe3Ph](2) (5) at -40 degrees C and [(thf)(6)Ca][AlMe4](2) (6) at -78 degrees C. The formation of (thf)(4)CaI2 confirms that a Schlenk equilibrium is operative besides the ligand redistribution reactions. A solution of crystalline [(thf)(6)Ca][AlMe2Ph2](2) (4) in THF shows 4 as the major component besides [(thf)(6)Ca][AlMe3Ph](2) (5) and [(thf)(6)Ca][AlMePh3](2) (3). With an increasing number of methyl groups the melting points decrease from 210 degrees C for the tetraphenylalanate 2 to 20 degrees C for the tetramethylalanate 6.