Synthesis, Structure, and Catalytic Studies of Mixed Lithium−Magnesium and Sodium−Magnesium Complexes:  Highly Isospecific Initiators for Polymerization of Methyl Methacrylate

The unusual lithium n -butylmagnesium complex [(EDBP)Mg(μ 2 - n Bu)Li(Et 2 O)] 2 ( 2 ) and sodium n -butylmagnesium complex [(EDBP)Na(Et 2 O)Mg n Bu] 2 ( 5 ), lithium−magnesium enolate, {(EDBP)Mg[μ 2 -OC(Mes)CH 2 ]Li(Et 2 O)} 2 ( 3 ), and the sodium aggregate, [(EDBP)Na 2 ] 4 ( 4 ), have been synthesized and structurally characterized. Among them, 2, 3, and 5 have been used as initiators for the polymerization of methyl methacrylate. The reaction of 2,2‘-ethylidenebis(4,6-di- tert -butylphenol) (EDBP-H 2 ) with n BuLi in diethyl ether gives [(EDBP-H)Li(Et 2 O) 3 ] ( 1 ). The dimeric lithium n -butylmagnesium complex 2 was obtained from the reaction of 1 with a stoichiometric amount of Mg n Bu 2 . Alternatively, 2 can also be prepared by the reaction of [(EDBP)Mg(Et 2 O)] 2 ( A ) with a stoichiometric amount of n BuLi in Et 2 O. Furthermore, the reaction of 2 with 2‘,4‘,6‘-trimethylacetophenone (MesC(O)CH 3, Mes = 2,4,6-Me 3 C 6 H 2 ) produces 3 . Reaction of EDBP-H 2 with excess sodium metal in Et 2 O furnishes compound 4 . In the presence of a stoichiometric amount of Mg n Bu 2 in Et 2 O, 4 can be converted to the dimeric sodium−magnesium mixed-metal complex [(EDBP)Na(Et 2 O)Mg n Bu] 2 ( 5 ). Experimental results show that 2, 3, and 5 efficiently initiate the anionic polymerization of methyl methacrylate.