Silica-Grafted Diethylzinc and a Silsesquioxane-Based Zinc Alkyl Complex as Catalysts for the Alternating Oxirane−Carbon Dioxide Copolymerization

Abstract

A novel zinc silsesquioxane complex ([(c-C5H9)7Si7O11(OSiMePh2)]2Zn4Me4 (1)) has been used as a model compound for silica-grafted zinc catalysts in the copolymerization of cyclohexene oxide and CO2. Complex 1 exists as a dimer in the solid state and is moderately active in the copolymerization, and polycyclohexene carbonates have been obtained with a carbonate content of 79−98%. Polymerizations with ZnEt2-treated silica particles resulted in polymer particles with M̄ n and M̄ w values and carbonate contents comparable to those of the polymers obtained with 1. It was further demonstrated that CO2 consumption can be followed online by monitoring the decrease of system pressure during the reaction. CO2 consumption has been interpreted in relation to both polycarbonate and cyclic carbonate formation. These measurements represent the intrinsic kinetics of this reaction, which appear to be directly related to CO2 pressure.

1,2‐Addition of Diethylzinc to a Bis(Imidazolyl)ketone Ligand

“…As mentioned before the Zn 2 (µ‐O) 2 planar core observed here is quite a common structural motif. The majority of structures containing this motif are obtained from coordination reactions of amino alcohols with alkylzinc compounds , , , . The formation of such a Zn 2 O 2 ‐motif is often thermodynamically favored, e.g.…”

“…it also forms in the reaction of O 2 with alkylzinc reagents and an external ligand; in the latter reaction O 2 is activated leading to the selective oxygenation of one Zn–C bond , . Furthermore, complexes with a planar Zn 2 (µ‐O) 2 ‐core are known to be active as initiator and catalyst in ring opening polymerization (ROP) reactions,, , and catalytically active in, e.g., enantioselective addition of dialkylzinc compounds to aldehydes, and the asymmetric alternating copolymerization of cyclohexene oxide or oxirane and CO 2 , , …”

Modern concepts and methods in the chemistry of polyhedral metallasiloxanes

“…LiMe, LiMH 4 , and Na[Et 2 MH 2 ] are used as coreagents for the simultaneous introduction of both polyvalent and alkali metal ions into polyhedral molecules. Using various reagent ratios and types of ligands leads to the formation of polyhedrons with different shapes from the same polyvalent metal ion (48)(49)(50)(51) 3 . Indeed, the prismatic polyhedra 52-53 (Fig.…”

“…When one of the Si-OH groups is blocked by OЕR х fragments (Е denotes non-metal), several unusual metal-containing compounds can be obtained based on modified cubane synthones ( Fig. 5; 9, R = c-C 5 H 9, [44]; 10, R = c-C 5 H 9 , [42]; 11, R = c-C 5 H 9 , X =, B(C 6 F 5 ) 2 [45], X = SiMeVin 2 [46]; 12, R = c-C 5 H 9, X = Me 3 , MePh 2 [47]; 13, R = c-C 6 H 11 , [48]; 14, R = c-C 5 H 9 , [49]; 15, R = c-C 6 H 11 , [35] [44] 10 [42] 11 [45] 12 [47] A c c e p t e d M a n u s c r i p t 7 13 [48] 14 [49] 15 [35] This synthetic approach was developed by using a method to obtain an "open" siloxane cage with two Si-OH-groups instead of three. Compound 16 was synthesized in three steps starting with acidic splitting of the closed cubic structure (Scheme 3) [50].…”

Polynuclear alkoxy–zinc complexes of bowl-shaped macrocycles and their use in the copolymerisation of cyclohexene oxide and CO2

“…25,[84][85][86][87][88] While higher nuclearity zinc catalysts have been reported, it is not yet understood if dinuclear catalysts are optimum. [89][90][91][92][93] As such, we reasoned that the tetranuclear alkyl-zinc macrocyclic complexes 1 and 2 could be activated by alcoholysis and that the resulting zinc alkoxide complexes could act as catalysts for ROCOP of CO 2 and epoxides.…”