Synthesis, structure, and catalytic studies of mixed lithium-magnesium and sodium-magnesium complexes: Highly isospecific initiators for polymerization of methyl methacrylate

Abstract

The unusual lithium n-butylmagnesium complex [(EDBP)Mg(mu(2)-Bu-n)Li(Et2O)](2) (2) and sodium n-butylmagnesium complex [(EDBP) Na(Et2O) (MgBu)-Bu-n](2) (5), lithium-magnesium enolate, {(EDBP) Mg[ mu(2)-OC(Mes) CH2] Li(Et2O)}(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 (BuLi)-Bu-n in diethyl ether gives [(EDBP-H) Li(Et2O) 3] (1). The dimeric lithium n-butylmagnesium complex 2 was obtained from the reaction of 1 with a stoichiometric amount of Mg(n)B(u)2. Alternatively, 2 can also be prepared by the reaction of [(EDBP) Mg(Et2O)](2) (A) with a stoichiometric amount of (BuLi)-Bu-n in Et2O. Furthermore, the reaction of 2 with 2', 4', 6'-trimethylacetophenone (MesC(O)CH3, Mes = 2,4,6-Me3C6H2) produces 3. Reaction of EDBP-H-2 with excess sodium metal in Et2O furnishes compound 4. In the presence of a stoichiometric amount of (MgBu2)-Bu-n in Et2O, 4 can be converted to the dimeric sodium-magnesium mixed-metal complex [(EDBP) Na(Et2O) (MgBu)-Bu-n](2) (5). Experimental results show that 2, 3, and 5 efficiently initiate the anionic polymerization of methyl methacrylate.