1218922-85-0Relevant articles and documents
Correlating reactivity and selectivity to cyclopentadienyl ligand properties in Rh(III)-catalyzed C-H activation reactions: An experimental and computational study
Piou, Tiffany,Romanov-Michailidis, Fedor,Romanova-Michaelides, Maria,Jackson, Kelvin E.,Semakul, Natthawat,Taggart, Trevor D.,Newell, Brian S.,Rithner, Christopher D.,Paton, Robert S.,Rovis, Tomislav
, p. 1296 - 1310 (2017)
CpxRh(III)-catalyzed C-H functionalization reactions are a proven method for the efficient assembly of small molecules. However, rationalization of the effects of cyclopentadienyl (Cpx) ligand structure on reaction rate and selectivity has been viewed as a black box, and a truly systematic study is lacking. Consequently, predicting the outcomes of these reactions is challenging because subtle variations in ligand structure can cause notable changes in reaction behavior. A predictive tool is, nonetheless, of considerable value to the community as it would greatly accelerate reaction development. Designing a data set in which the steric and electronic properties of the CpxRh(III) catalysts were systematically varied allowed us to apply multivariate linear regression algorithms to establish correlations between these catalyst-based descriptors and the regio-, diastereoselectivity, and rate of model reactions. This, in turn, led to the development of quantitative predictive models that describe catalyst performance. Our newly described cone angles and Sterimol parameters for Cpx ligands served as highly correlative steric descriptors in the regression models. Through rational design of training and validation sets, key diastereoselectivity outliers were identified. Computations reveal the origins of the outstanding stereoinduction displayed by these outliers. The results are consistent with partial η5-η3 ligand slippage that occurs in the transition state of the selectivity-determining step. In addition to the instructive value of our study, we believe that the insights gained are transposable to other group 9 transition metals and pave the way toward rational design of C-H functionalization catalysts.
Propylene polymerization to high molecular weight atactic polypropylene and copolymerization with 1-hexene using monocyclopentadienyl titanium catalysts
Wu, Qiaolin,Su, Qing,Ye, Ling,Li, Guanghua,Mu, Ying
experimental part, p. 2525 - 2535 (2010/05/15)
A number of cyclopentadienyltitanium aryloxide complexes, 1-Ar-2,3,4,5-Me4-Cp(2,6-iPr2C6H 3O)TiCl2 (Ar = 4-Me3SiPhenyl (5), 4- iPrPhenyl (6), 4-MePhenyl (7), 3,5-(CF3)2Phenyl (8)) and (1-Ar-2,3,4,5-Me4CpTiCl2)2(OAr′ O) (Ar′ = 4,4′-(3,3′,5,5′-iPr 4C6H2-C6H2), Ar = 4-SiMe3Phenyl (9), 4-MePhenyl (10)) were synthesized from the reaction of a corresponding cyclopentadienyl titanium trichloride derivative with the lithium salt of a relevant phenol. The molecular structures of complexes 6, 7 and 8 were determined by X-ray crystallography. Upon activation with iBu3Al and Ph3CB(C6F 5)4, all mononuclear complexes 5-8 exhibit good catalytic activities for propylene polymerization, whereas the binuclear complexes 9 and 10 show lower catalytic activities under the same polymerization conditions. 13C NMR, DSC and GPC analysis indicates the produced polymers are atactic polypropylene with relatively high molecular weight. It was found that the substituents on both the cyclopentadienyl and aryloxy ligands of these complexes show obvious influence on the molecular weight of the resultant polymers with complex 5 producing the highest molecular weight atactic polypropylene. Complexes 5, 6 and 7 were also tested as catalysts for copolymerization of propylene with 1-hexene and copolymers with 1.2-10.1% comonomer incorporation were obtained in reasonable catalytic activity. The Royal Society of Chemistry 2010.
