Ancillary Ligand Effects on Organo-f-Element Reactivity. ansa-Metallocenes with Bridge-Tethered Donors

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• 作者：Peter W. Roesky ; Charlotte L. Stern ; and Tobin J. Marks
• 刊名：Organometallics
• 出版年：1997
• 出版时间：October 14, 1997
• 年：1997
• 卷：16
• 期：21
• 页码：4705 - 4711
• 全文大小：286K
• 年卷期：v.16,no.21(October 14, 1997)
• ISSN：1520-6041

文摘

The synthesis and reactivity of ansa-metallocenes basedupon the new ligand systemR(Me)SiCp''₂^2- (Cp'' =C₅Me₄ and R =(CH₂)_nOMe, n =3-5) is reported. The tethered donorfunctionality, which is appended via varying chain lengths to thesilicon bridge, is introducedto examine possible intramolecular reactivity modifications. Thekey step of the ligandsynthesis is the hydrosilylative fusion of the donor functionality R tothe silicon center. Thecomplexes[R(Me)SiCp''₂]LnCH(SiMe₃)₂(Ln = Y, Sm) were synthesized to investigate theinfluence of the tethered ether group on the reactivity and catalyticproperties. Catalyticreactions in which the substrate is a relatively weak donor, such as inolefin hydrogenation,exhibit depressed turnover frequencies, presumably reflectingcompetition between thesubstrate and donor functionality for the empty coordination site atthe metal center. Incontrast, for amino-alkene hydroamination/cyclization in which astrong amine donor isthe substrate, catalytic activity is significantly enhanced whilediastereoselectivity isessentially unchanged. The molecular structure of the precatalyst[MeO(CH₂)₅(Me)SiCp''₂]YCH(SiMe₃)₂ has been determined by X-raydiffraction.