10.1021/ja063717g
The study focuses on the development and analysis of hafnocene catalysts for the selective oligomerization of propylene to produce 4-methyl-1-pentene, a branched olefin used in the production of polymers with desirable properties. A series of hafnocene complexes with varying substituents were tested as catalyst precursors. Upon activation with methylaluminoxane (MAO) or [Ph3C][B(C6F5)4]/AliBu3, these complexes catalyzed the dimerization of propylene, with selectivities for 4-methyl-1-pentene ranging from 23.9 to 61.6 wt%. The selectivity was found to depend on the nature of the substituents R1 and R2, with the highest selectivity observed for the complex (η5-C5Me4iBu)2HfCl2 (12). The study also investigated the influence of steric effects on the selectivity and the mechanism of propylene oligomerization, including the rate constants for propagation, β-hydride elimination, and β-methyl elimination. The purpose of these chemicals was to evaluate their catalytic performance in producing 4-methyl-1-pentene and to understand the underlying reaction mechanisms that govern the selectivity and activity of the catalysts.
10.1016/j.poly.2011.03.028
The research investigates the stereogenic properties of cyclotriphosphazene derivatives with two different chiral centers. The purpose is to explore the geometric isomers and racemic forms of these compounds, which have potential applications in various fields due to their chirality. Key chemicals used include hexachlorocyclotriphosphazene (N3P3Cl6) and gem-disubstituted cyclotriphosphazene derivatives (N3P3Cl4X2, where X = Ph, PhS, PhNH), which were reacted with N-methyl-1,3-propanediamine and 3-amino-1-propanol to produce compounds with two different stereogenic phosphorus atoms. The geometric isomers were separated and characterized using techniques such as X-ray crystallography, 31P and 1H NMR spectroscopy, and chiral HPLC. The study confirmed that these compounds exist as cis and trans geometric isomers and as two different racemic isomers. The enantiomers of the racemic compounds were analyzed using a chiral solvating agent (CSA) and chiral HPLC methods developed for this study. The conclusions highlight the successful synthesis and characterization of these chiral cyclotriphosphazene compounds, providing insights into their stereogenic properties and potential uses in chiral chemistry.