Palladium Carbene Complexes for Selective Alkene Di- and Oligomerization

详细信息    查看全文

• 作者：Vsevolod Khlebnikov ; Angelo Meduri ; Helge Mueller-Bunz ; Tiziano Montini ; Paolo Fornasiero ; Ennio Zangrando ; Barbara Milani ; Martin Albrecht
• 刊名：Organometallics
• 出版年：2012
• 出版时间：February 13, 2012
• 年：2012
• 卷：31
• 期：3
• 页码：976-986
• 全文大小：453K
• 年卷期：v.31,no.3(February 13, 2012)
• ISSN：1520-6041

文摘

A series of palladium complexes were synthesized that comprise three sterically different C,N-bidentate coordinating NHC-pyridine ligands (NHC = N-heterocyclic carbene). In one set, the pyridine and the carbene are linked by a flexible CH₂ group (a); in the other two sets, the two ligand units are directly linked and feature a shielding mesityl substituent on the carbene and either an unsubstituted pyridine (b) or a xylyl-substituted pyridine unit (c). Investigation of the reactivity of cationic complexes [Pd(CN)Me(NCMe)]⁺ (6), analogues to Brookhart鈥檚 伪-diimine system, toward alkenes showed a strong correlation between the catalytic activity and selectivity and the ligand setting. While 6a was inactive in ethylene conversion, 6b afforded low-molecular-weight olefins (oligomerization), and 6c produced exclusively butene (dimerization). With styrene as substrate, exclusive dimerization occurred with all three complexes. Steric and electronic factors were identified that govern the disparate activity and selectivity and that allow for efficient tailoring of the catalytic performance.