Facilely synthesized benzotriazole phenolate zirconium complexes as versatile catalysts for copolymerization of carbon dioxide with cyclohexene oxide and lactide polymerization1

A family of zirconium complexes containing bis-, tri- or tetra-BTP ligands (BTP = benzotriazole phenolate) were synthesized and structurally characterized. Treatment of Zr((OPr)-Pr-i)(4)((PrOH)-Pr-i) with 2.0 molar equivalents of 2-(2H-benzotriazol-2-yl)-4-(2,4,4-trimethylpentan-2-yl) phenol ((BTP)-B-C8-H) or 2-(2H-benzotriazol- 2-yl)-4,6-di-tert-butylphenol (t-BuBTP-H) afforded zirconium alkoxide ([((BTP)-B-C8)(2)Zr((OPr)-Pr-i)(2)] (1); [(t-BuBTP)(2)Zr((OPr)-Pr-i)(2)] (2)) in good yield. Similarly, the bis-adduct Zr amide [(t-BuBTP)(2)Zr(NMe2)(2)] (3) resulted from amine elimination of Zr(NMe2)(4) as the metal precursor and t-BuBTP-H as the pro-ligand under a similar synthetic method with a metal to ligand precursor ratio of 1 : 2 at 0 degrees C. The reaction of Zr(NMe2)(4) with (BTP)-B-C8-H or t-BuBTP-H (4.0 mol equiv.) gave the tetra-adduct zirconium complex ([((BTP)-B-C8)(4)Zr] (4); [(t-BuBTP)(4)Zr] (5)) in. 70% yield. Interestingly, the tri-adduct Zr amide [(t-BuBTP)(3)Zr-( NMe2)] (6) could be prepared by treatment of 3 with a stoichiometric amount of t-BuBTP-H. The solid-state structure of 6 reveals a monomeric Zr(IV) amide with three t-BuBTP ligands and one -NMe2 group, and the bonding modes between the BTP moiety and the metal centre adopt both N, O-bidentate and O-monodentate types. Zr complexes 1 and 4 incorporating sterically less bulky (BTP)-B-C8 ligands were demonstrated to efficiently catalyse not only copolymerization of epoxide with CO2 but also lactide polymerization. The tetra-BTP Zr catalyst 4 was able to copolymerize cyclohexene oxide and CO2 in a controllable manner, generating the high-molecular-weight copolymer (M-w > 10 000 g mol(-1)) and a high degree of carbonate linkages (> 90%). Single-site zirconium alkoxide 1 is the most active catalyst for living lactide polymerization in solution among these complexes, giving poly(lactide) s with the expected molecular weights and narrow molecular weight distributions (PDI <= 1.25). This is a successful example of utilizing versatile benzotriazole phenolate Zr(IV) catalysts for either the production of biodegradable poly( lactide) or poly(cyclohexene carbonate-co-cyclohexene oxide).