Chiral salenCo(iii) complexes with bulky substituents as catalysts for stereoselective alternating copolymerization of racemic propylene oxide with carbon dioxide and succinic anhydride. Issue 12 (4th March 2021)

• Record Type: Journal Article
• Authors: Wang, Zhou; Mu, Ying
• Is Part Of: Polymer chemistry. Volume 12:Issue 12(2021)
• Page Start: 1776
• Page End: 1786
• Publication Date: 2021-03-04
• Subjects: Polymers -- Periodicals; Macromolecules -- Periodicals; Polymerization -- Periodicals; 547.705
• DOI: 10.1039/d0py01562h
• Languages: English
• ISSNs: 1759-9954

Abstract

Abstract : Stereoregular poly(propylene carbonate)s and poly(propylene succinate- block -carbonate)s were synthesized with new chiral salenCo(iii ) catalysts carrying bulky substituents. Abstract : A series of new chiral salenCo(iii )X complexes [salen = ( R, R )- N, N ′-bis(3-R-5- tert -butylsalicylidene)-1, 2-cyclohexanediamine, X − = OAc −, R = CMe2 CHMe2 (4a ), CPhMe2 (4b ), CPh2 Me (4c ); X − = 2, 4-dinitrophenoxide anion (DNP), R = CMe2 CHMe2 (5a ), CPhMe2 (5b ), CPh2 Me (5c ); X − = Br −, R = CMe2 CHMe2 (6a ), CPhMe2 (6b ), CPh2 Me (6c )] with bulky substituents at the 3, 3′-positions of the salicylidene moiety were synthesized and investigated as catalysts in the copolymerization of CO2 /propylene oxide (PO) and the sequential copolymerization of succinic anhydride/PO and CO2 /PO. The effects of the reaction conditions were examined by using complex 4b as a representative catalyst for the copolymerization of CO2 /PO. It was found that catalysts with different ligands and axial coordinating groups show remarkable differences in their catalytic properties. The catalysts with relatively small R groups show relatively high catalytic activity and produce copolymers with relatively high molecular weights, while the catalysts with relatively bulky R groups show relatively high stereoselectivity. Catalyst systems employing 4-(dimethylamino)pyridine (DMAP) as the cocatalyst show relatively low catalytic activity but high stereoselectivity in comparison with the ones observed in the systems with bis(triphenylphosphoranylidene) ammonium chloride (PPNCl) or PPNDNP as the cocatalyst. With the catalyst system of 5c /DMAP, a high kinetic resolution coefficient ( K rel ) of 10.6 for the insertion of ( S )-PO over ( R )-PO was obtained at 25 °C. High molecular weight PPCs ( M w > 100 kg mol −1 ) were prepared with 5a /PPNCl and 5a /PPNDNP catalyst systems. Stereoregular block copolymers poly(propylene succinate- block -carbonate) were obtained from sequential copolymerization via catalytic kinetic resolution.