Gaia Urciuoli, Francesco Zaccaria, Cristiano Zuccaccia, Roberta Cipullo, Leonardo Tensi, Peter H.M. Budzelaar, Antonio Vittoria, Christian Ehm, Alceo Macchioni, Vincenzo Busico
{"title":"Al-alkyl Borate Salt Cocatalysts for Olefin Polymerization: Exploration of N-donor Ligand Variations","authors":"Gaia Urciuoli, Francesco Zaccaria, Cristiano Zuccaccia, Roberta Cipullo, Leonardo Tensi, Peter H.M. Budzelaar, Antonio Vittoria, Christian Ehm, Alceo Macchioni, Vincenzo Busico","doi":"10.1039/d4qi01874e","DOIUrl":null,"url":null,"abstract":"The well-defined Al-alkyl borate (AAB) salt {[iBu2(PhNMe2)Al]2(μ-H)}+[B(C6F5)4]- (AlHAl) has been recently identified as a promising “complete” cocatalyst for olefin polymerization. Herein, we explore structural variations of AlHAl obtained by replacing the PhNMe2 (DMA) donor with a variety of anilines, amines, and N-heterocycles. Of the 18 investigated N-donors, twelve provided stable AAB salts; those were tested as cocatalyst in ethylene/1-hexene copolymerization with a archetypical metallocene catalyst. In the other six cases, occurring side reactions were thoroughly analyzed by NMR spectroscopy. For instance, addition of an o-Me substituent on the DMA ligand triggers C–H activation leading to five-membered cyclometalated species; increasing steric bulk directly at the N-donor atom leads to tricoordinate mononuclear Al-alkyl cations, which could be isolated, fully characterized and tested in polymerization when using PhNEt2 (DEA). Cocatalytic performance of aniline- and amine-based systems varies only marginally with respect to the benchmark AlHAl_DMA. N-heterocyclic AAB salts perform worse; only the two least electron donating donors, namely difluoropyridine (Py-3,5-F) and quinoline (QUI) provide noticeable productivity. A simple quantitative-structure activity relationship, correlating steric bulk and stabilizing ability of the N-donor to productivity (R2 = 0.88), has been identified.","PeriodicalId":79,"journal":{"name":"Inorganic Chemistry Frontiers","volume":null,"pages":null},"PeriodicalIF":6.1000,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Inorganic Chemistry Frontiers","FirstCategoryId":"92","ListUrlMain":"https://doi.org/10.1039/d4qi01874e","RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"CHEMISTRY, INORGANIC & NUCLEAR","Score":null,"Total":0}
引用次数: 0
Abstract
The well-defined Al-alkyl borate (AAB) salt {[iBu2(PhNMe2)Al]2(μ-H)}+[B(C6F5)4]- (AlHAl) has been recently identified as a promising “complete” cocatalyst for olefin polymerization. Herein, we explore structural variations of AlHAl obtained by replacing the PhNMe2 (DMA) donor with a variety of anilines, amines, and N-heterocycles. Of the 18 investigated N-donors, twelve provided stable AAB salts; those were tested as cocatalyst in ethylene/1-hexene copolymerization with a archetypical metallocene catalyst. In the other six cases, occurring side reactions were thoroughly analyzed by NMR spectroscopy. For instance, addition of an o-Me substituent on the DMA ligand triggers C–H activation leading to five-membered cyclometalated species; increasing steric bulk directly at the N-donor atom leads to tricoordinate mononuclear Al-alkyl cations, which could be isolated, fully characterized and tested in polymerization when using PhNEt2 (DEA). Cocatalytic performance of aniline- and amine-based systems varies only marginally with respect to the benchmark AlHAl_DMA. N-heterocyclic AAB salts perform worse; only the two least electron donating donors, namely difluoropyridine (Py-3,5-F) and quinoline (QUI) provide noticeable productivity. A simple quantitative-structure activity relationship, correlating steric bulk and stabilizing ability of the N-donor to productivity (R2 = 0.88), has been identified.