TMPMgnBu(L), where L = THF, 2-MeTHF, pyridine and dimethylaminopyridine and TMP = 1,5,9-trimesityldipyrromethene: Reaction with lactide and ε-caprolactone

Abstract

The compounds TMPMgnBu(L), where L = THF, 2-MeTHF, pyridine (py) and dimethylaminopyridine (DMAP) and TMP = 1,5,9-trimesityldipyrromethene, have been synthesized and allowed to initiate polymerization with rac-lactide (rac-LA) and ε-caprolactone (ε – CL). Both the rate of rac-LA polymerization and the tacticity were found to be solvent dependent, with CH2Cl2 being faster than THF and yielding heterotactic polylactic acid with Pr ∼70% and 95%, respectively. For ε-CL, rates of polymerization were in the inverse order with THF being faster than CH2Cl2. In CH2Cl2 the reactions showed a dependence on the coordinating ligand with rates, 2-MeTHF > THF > py > DMAP in the polymerization of rac-LA and ε-CL. The molecular structure of TMPMgnBu(2-MeTHF) was shown to contain a trigonally distorted tetrahedron of TMPMg(nBu) with a weak axial Mg—-2-MeTHF bond.