An Oligosilsesquioxane Cage Functionalized with Molybdenum(II) Organometallic Fragments

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• 作者：Newton L. Dias Filho ; F谩tima C. M. Portugal ; J. M. F. Nogueira ; Paula Brand茫o ; Vitor F茅lix ; Pedro D. Vaz ; Carla D. Nunes ; Luis F. Veiros ; Maria J. Villa de Brito ; Maria Jos茅 Calhorda
• 刊名：Organometallics
• 出版年：2012
• 出版时间：June 25, 2012
• 年：2012
• 卷：31
• 期：12
• 页码：4495-4503
• 全文大小：410K
• 年卷期：v.31,no.12(June 25, 2012)
• ISSN：1520-6041

文摘

A silsesquioxane cage polymer functionalized with eight chloropropyl arms (<b>1b>, Tb>8b>-PrCl) reacted with 2,2鈥?dipyridiylamine (DPA) to afford a new derivative with eight pendant linear chains (<b>2b>, Tb>8b>-Pr-DPA). Further reaction with [Mo(畏³-Cb>3b>Hb>5b>)Br(CO)b>2b>(NCMe)b>2b>] afforded another derivative containing three molybdenum units (<b>3b>, Tb>8b>-Pr-DPA-Mo), after substitution of the two nitrile ligands in each complex. These are the first silsesquioxane species containing DPA and the Mo(畏³-Cb>3b>Hb>5b>)Br(CO)b>2b> fragment. The three materials were characterized by ¹H, ¹³C, ²⁹Si, and ⁹⁵Mo NMR, FTIR, XRD, and elemental analysis, and Tb>8b>-PrCl (<b>1b>) was also structurally characterized by single-crystal X-ray diffraction. It was identified as a low-temperature polymorph of this material. Elemental analysis indicated that all Cl atoms in the parent material Tb>8b>-PrCl (<b>1b>) were substituted by the deprotonated DPA group in Tb>8b>-Pr-DPA (<b>2b>). However, only three [Mo(畏³-Cb>3b>Hb>5b>)Br(CO)b>2b>(DPA)] units were detected in Tb>8b>-Pr-DPA-Mo (<b>3b>). A comprehensive NMR study, complemented with DFT calculations, was carried out in order to detect the effect of Mo coordination on the cage silicon and on the protons and carbons of the propyl chain, but no significant effects were observed. Both ¹H and ²⁹Si chemical shifts vary upon introducing DPA but remain the same after reaction with the Mo(II) precursor. The ⁹⁵Mo NMR data reveal that the metal is not sensitive to the cage. The catalytic activity of <b>3b> was tested as a precursor in the epoxidation of cyclooctene and styrene in the presence of TBHP. Despite the high selectivity toward the epoxides, the conversion and turnover frequencies were low, reflecting the behavior of the [Mo(畏³-Cb>3b>Hb>5b>)Br(CO)b>2b>(DPA)] complex.