Synthetic and Structural Investigations of Organomagnesium Complexes of Hybrid Boraamidinate/Amidinate Ligands and Their Use in the Polymerization of <i>r</i><i>ac</i>-Lactide

Abstract

The complexation chemistry of the protio and lithium bamam complexes (H)bamam-1 and (Li)bamam-1 [bamam-1 = {DippN(Ph)B(NtBu)CnBu(NtBu)}, Dipp = 2,6-diisopropylphenyl] with magnesium is explored. Emphasis is placed on the preparation and characterization of both solvated and unsolvated aryl/alkylmagnesium bamam complexes (RMgL)bamam-1 (1, R = tBu, L = none; 2, R = Mes, L = none; 3, R = Me, L = OEt2; 4, R = Ph, L = THF; 5, R = iPr, L = THF; 6, R = nBu, L = OEt2). X-ray structural analyses reveal that the Mg bamam-1 complexes are six-membered rings, which adopt a distorted boat structure as a result of a transannular Mg−N interaction (2.39−2.85 Å). Variable-temperature NMR spectra indicate this interaction is maintained in solution. Preliminary studies of the polymerization of rac-lactide with complexes 3−6 revealed that 3 and 4 promote the polymerization process producing hetero-biased polylactide, whereas 5 and 6 are inactive.