α-Methyl-benzylcalcium complexes: syntheses, structures and reactivity

α-Methyl-benzylcalcium complexes were prepared analogue to α-Me3Si-benzylcalcium complexes for which procedures were reported earlier. The crystal structures of homoleptic bis(2-Me2N-α-Me-benzyl)calcium·(THF)2 and heteroleptic (9-Me3Si-fluorenyl)(2-Me2N-α-Me-benzyl)calcium·(THF) were determined. For both compounds only one of the two diastereomers crystallized. Barriers for inversion of the chiral benzylic carbon were estimated by variable temperature NMR spectroscopy. The α-methyl-benzylcalcium compounds are less stable and show a higher reactivity and faster initiation of styrene polymerization than the analogue α-Me3Si-benzylcalcium complexes. Intramolecular CH activation in a heteroleptic α-methyl-benzylcalcium complex was observed and the product, a calcium complex with a dianionic alkyl/fluorenyl ansa-ligand, was characterized by crystal structure determination.