Diiminopyrrolide Copper Complexes: Synthesis, Structures, and rac-Lactide Polymerization Activity

作者：Daneshmand Pargol; Fortun Solene; Schaper Frank^*

来源：Organometallics, 2017, 36(19): 3860-3877.

DOI：10.1021/acs.organomet.7b00609

2,5-Diiminopyrrole ligands with N-xylyl (L3), N-naphthyl (L4), N-cyclohexyl (L5), N-diphenylmethyl (L6), and N-p-bromobenzyl (L7), as well as the 5-R-2-iminopyrroles with N-S-methylbenzyl (L8, R = H; L10, R = Me; L11, R = Cl) and N-benzyl (L9, R = H) were reacted with Cu(OMe)(2) and pyridylmethanol ((ROH)-O-1) or dimethylaminoethanol ((ROH)-O-2) to yield the corresponding dinuclear complexes L2Cu2(mu-OR)(2). Reactions in the absence of chelating (ROH)-O-1 or (ROH)-O-2 only yielded homoleptic L2Cu or L2Cu2. Complexes with (ROH)-O-2 were obtained with all ligands but L4, complexes with (ROH)-O-1 for all ligands but L3, L4, and L6. All complexes but those with L7 displayed dinuclear crystal structures with pentacoordinated copper centers and bridging alkoxy groups. The alkoxy group and the pyrrolide ligand were consistently found in equatorial positions. Imine, pyridine, or amine occupied the axial position. L7 coordinated both imino groups to copper, yielding a distorted-octahedral coordination geometry. All complexes containing (ROH)-O-1, with the exception of L7, showed an isotactic bias in the polymerization of rac-lactide, with a maximum P-m value of 0.7. Complexes containing (ROH)-O-2 provided atactic PLA or, in the case of L3 and L6, heterotactic PLA. Reduced stereocontrol in monoiminopyrrolide copper complexes and lack of stereocontrol with octahedrally coordinated L7 indicate that the catalytic site needs to adapt to chain-end chirality and is participating in enantiomer selection.

• 出版日期2017-10-9