Magnesium and calcium complexes bearing mono-oxidized or monoprotonated acenaphthylenebisamido ligand: Structure features and ROP activity

Acenaphthylenebisamido metal complexes (dpp-bian)Mg(thf)3 and (dpp-bian)Ca(thf)4 by reaction with azobenzene and dicumyl peroxide, respectively, give paramagnetic species [(dpp-bian)Mg(thf)NPh]2 (3) and (dpp-bian)CaOCMe2Ph(dme) (4) containing monoanionic dpp-bian ligand. Treating the parent compounds with 1 equiv of 2,6-di-tert-butyl-4-methylphenol leads to formation of amino/amidoacenaphthylene-supported complexes (dpp-bianH)MgO(tBu2MeC6H2)(thf) (5) and (dpp-bianH)CaO(tBu2MeC6H2)(thf)2 (6) featuring ancillary bulky phenoxido ligand. As NMR studies confirm, a sterically demanding moiety in the magnesium coordination sphere hinders the intramolecular shuttle proton transfer in 5, whereas calcium complex 6 maintains typical dynamics in solution. Compounds obtained show a modest activity in ROP of L-lactide in toluene. In particular, 3 and 4 prove to be active for moderate-controlled polymerization, whereas 5 and 6 give broadly dispersed PLAs.