Synthesis and Structures of the Amino-Linked N-Heterocyclic Carbenes and C-N Bond Cleavage of its by a Tetrakis(benzyl) Zirconium Complex

• Main Authors: Yu-Cheng Hu, 胡育誠
• Other Authors: 陳建添
• Format: Others
• Language: en_US
• Online Access: http://ndltd.ncl.edu.tw/handle/05691431648391441619

碩士 === 國立臺灣師範大學 === 化學系 === 97 === Treatment of [HC{(R)N(CHCH)N(CH2CH2NHtBu}]Br•HBr, R = MES (1-MES) or tBu (1-tBu) with an excess of NaOH afforded the organic-soluble imidazolium salt 2,[HC{(R)N(CHCH)N(CH2CH2NH tBu}]Br. We also modified an alkyl of amino pendant arm group using bulkier 2,6-diisopropylaniline to afford the [2,6-(CH3)2(C6H3)] NHCH2CH2[HC{MESN(CHCH)N}]Br, (2-MES-Anilian). Deprotonation of imidazolium salt 2 by NaN(SiMe3)2 yielded the amino-linked free carbene, 3. The molecular structure of 3-MES was determined by X-ray single-crystal analysis, revealing an unexpectedly close intermolecular contact associated with the carbene and amine through an N-H • • • C interaction. Treatment of 3-tBu with n-BuLi gave the more stable Li carbene adduct 3-tBu.Li, which serves as an effective carbene transfer agent to stabilize high oxidation early transition metal and added the ZrCl4 to afford the ZrCl3-NHC, 7 in high yield. X-ray diffraction studies of ZrCl3-NHC confirmed the formation of distorted square planar Zr species, in which the NHC binds via conventional σ-donation of the lone pair to the electrophilic metal center. The reaction of Zr(Bz)4 with 3-MES with 3-tBu resulted to a unique meta-stable Zr complex, 6-MES and 6-tBu, possessing an aza-allyl and an η2-N,C-imidazolyl carbene moiety. The crystal structure of 5-MES exhibits an unexpected β-agostic interaction with kinetic investigation believed to involve C-H activation and unprecedented C-N cleavage of the amino-carbene moiety.