对[Ta(=CHtBu)(CH2tBu)3]和[Cp*TaMe4]在700摄氏度下部分脱羟基的二氧化硅上的接枝进行详细的结构研究，以及接枝配合物对烷烃复分解反应的活性。

Detailed structural investigation of the grafting of [Ta(=CHtBu)(CH2tBu)3] and [Cp*TaMe4] on silica partially dehydroxylated at 700 degrees C and the activity of the grafted complexes toward alkane metathesis.

作者信息

Le Roux Erwan, Chabanas Mathieu, Baudouin Anne, de Mallmann Aimery, Copéret Christophe, Quadrelli E Alessandra, Thivolle-Cazat Jean, Basset Jean-Marie, Lukens Wayne, Lesage Anne, Emsley Lyndon, Sunley Glenn J

机构信息

Laboratoire de Chimie Organométallique de Surface, UMR 9986 CNRS/ESCPE Lyon, Villeurbanne, France.

出版信息

J Am Chem Soc. 2004 Oct 20;126(41):13391-9. doi: 10.1021/ja046486r.

DOI:10.1021/ja046486r

PMID:15479095

Abstract

The reaction of [Ta(=CHtBu)(CH2tBu)3] or [CpTa(CH3)4] with a silica partially dehydroxylated at 700 degrees C gives the corresponding monosiloxy surface complexes [([triple bond]SiO)Ta(=CHtBu)(CH2tBu)2] and [([triple bond]SiO)Ta(CH3)3Cp] by eliminating a sigma-bonded ligand as the corresponding alkane (H-CH2tBu or H-CH3). EXAFS data show that an adjacent siloxane bridge of the surface plays the role of an extra surface ligand, which most likely stabilizes these complexes as in [([triple bond]SiO)Ta(=CHtBu)(CH2tBu)2([triple bond]SiOSi[triple bond])] (1a') and [([triple bond]SiO)Ta(CH3)3Cp*([triple bond]SiOSi[triple bond])] (2a'). In the case of [(SiO)Ta(=CHtBu)(CH2tBu)2([triple bond]SiOSi[triple bond])], the structure is further stabilized by an additional interaction: a C-H agostic bond as evidenced by the small J coupling constant for the carbenic C-H (JC-H = 80 Hz), which was measured by J-resolved 2D solid-state NMR spectroscopy. The product selectivity in propane metathesis in the presence of [([triple bond]SiO)Ta(=CHtBu)(CH2tBu)2([triple bond]SiOSi[triple bond])] (1a') as a catalyst precursor and the inactivity of the surface complex [([triple bond]SiO)Ta(CH3)3Cp*([triple bond]SiOSi[triple bond])] (2a') show that the active site is required to be highly electrophilic and probably involves a metallacyclobutane intermediate.

摘要

[Ta(=CHtBu)(CH2tBu)3] 或 [CpTa(CH3)4] 与在700℃下部分脱羟基的二氧化硅反应，通过消除一个σ键合配体生成相应的烷烃（H-CH2tBu或H-CH3），得到相应的单硅氧基表面配合物 [([三键]SiO)Ta(=CHtBu)(CH2tBu)2] 和 [([三键]SiO)Ta(CH3)3Cp]。扩展X射线吸收精细结构（EXAFS）数据表明，表面相邻的硅氧烷桥起着额外表面配体的作用，这很可能像在 [([三键]SiO)Ta(=CHtBu)(CH2tBu)2([三键]SiOSi[三键])] (1a') 和 [([三键]SiO)Ta(CH3)3Cp*([三键]SiOSi[三键])] (2a') 中那样稳定这些配合物。对于 [(SiO)Ta(=CHtBu)(CH2tBu)2([三键]SiOSi[三键])]，该结构通过额外的相互作用进一步稳定：一种C-H agostic键，如通过J分辨二维固态核磁共振光谱测量的卡宾C-H的小J耦合常数（JC-H = 80 Hz）所证明。在 [([三键]SiO)Ta(=CHtBu)(CH2tBu)2([三键]SiOSi[三键])] (1a') 作为催化剂前体存在下丙烷复分解反应中的产物选择性以及表面配合物 [([三键]SiO)Ta(CH3)3Cp*([三键]SiOSi[三键])] (2a') 的无活性表明，活性位点需要具有高亲电性，并且可能涉及金属环丁烷中间体。