a-Methyl-benzylcalcium complexes: syntheses, structures and reactivity.
a-Methyl-benzylcalcium complexes were prepd. analog to a-Me3Si-benzylcalcium complexes for which procedures were reported earlier. The crystal structures of homoleptic bis(2-Me2N-a-Me-benzyl)calcium.(THF)2 and heteroleptic (9-Me3Si-fluorenyl)(2-Me2N-a-Me-benzyl)calcium.(THF) were detd. For both compds. only one of the two diastereomers crystd. Barriers for inversion of the chiral benzylic carbon were estd. by variable temp. NMR spectroscopy. The a-methyl-benzylcalcium compds. are less stable and show a higher reactivity and faster initiation of styrene polymn. than the analog a-Me3Si-benzylcalcium complexes. Intramol. C-H activation in a heteroleptic a-methyl-benzylcalcium complex was obsd. and the product, a calcium complex with a dianionic alkyl/fluorenyl ansa-ligand, was characterized by crystal structure detn.
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