仿生不對稱銅催化劑對萘酚與其衍生物進行具鏡像選擇性氧化偶合反應之研究

Abstract

本研究設計一個C2對稱且含有兩個掌性中心的三牙配位基BDPPP，藉由BDPPP成功地合成出兩種二價銅錯合物[Cu(BDPPP)(H2O)](OTf)2 (1)與[Cu(BDPPP)Cl]Cl (2)，利用X-ray單晶繞射儀解析可得錯合物1與錯合物2的分子結構皆為平面四邊形。利用錯合物1對3-羥基-2-萘甲酯進行氧化偶合的催化反應，ee值可達到39%，但是由於錯合物1的金屬中心太過擁擠，嘗試許多方法皆無法改善產率過低的問題。 為了增進受質的轉化率，我們將含氮三牙配位基BDPPP修飾成含氮二牙配位基DPPP並僅含有一個掌性中心。利用DPPP與CuCl2可以合成幾何結構為平面四邊形的Cu(DPPP)Cl2 (3)。另外，也可將DPPP修飾成DXPP，DXPP是以兩個3,5-二甲基苯基來取代DPPP上的苯基。Cu(DXPP)Cl2 (4)可以藉由合成錯合物3的方法得到。在催化反應的探討中，我們利用修飾後的配位基DPPP及DXPP與不同的含銅金屬鹽類形成各種催化劑，再對3-羥基-2-萘甲酯進行催化反應，我們發現利用修飾後的配位基DPPP (10 mol%)與Cu(OTf)2 (10 mol%)所形成的催化劑在含有TMEDA (10 mol%)的條件下，產率為65%，藉由條件最佳化，將20 mol%的催化劑加上20 mol%的TMEDA，此反應的ee值可達到63%，產率最高還可達75%。A C2-symmetric tridentate ligand BDPPP, which contains two identical chiral centers was designed and prepared to synthesize two Cu(II) mononuclear complexes, [Cu(BDPPP)(H2O)](OTf)2 (1) and [Cu(BDPPP)Cl]Cl (2). The molecular structures of complexes 1 and 2 determined by X-ray crystallography were rerealed to possess a square planar geometry at Cu(II) centers. Complex 1 was employed as a catalyst for the oxidative coupling reaction of 2-naphthol or methyl 3-hydroxy-2-naphthaloate. When methyl 3-hydroxy-2-naphthaloate was chosen as a substrate, the ee value of the oxidative coupling product can reached to 39%. However, due to the bulky ligand of complexes 1 and 2, the yield of the oxidative coupling reaction was low in many reaction conditions. In order to improve the conversion of the substrate, the tridentate ligand BDPPP was modified, and a bidentate ligand DPPP, which contains one chiral center, was prepared. The square planar complex, Cu(DPPP)Cl2 (3), was successfully synthesized by reacting DPPP with CuCl2. Inaddition, a bulkier bidentate ligand, DXPP containing two 3,5-dimethylphenyl group, was also prepared, and Cu(DXPP)Cl2 (4) was synthesized. In the catalytic study, DPPP and DXPP were added into different copper salts, respectively, to form several catalysts for the catalyzation of the oxidative coupling reaction of methyl 3-hydroxy-2-naphthaloate. Notably, the yield of the reaction was 65% while using 10 mol% of DPPP with 10 mol% of Cu(OTf)2 as the catalyst in the presence of 10 mol% of TMEDA. The ee value could reach to 63% and the yield went up to 75% as the reaction condition was optimized to 20 mol% of catalyst loading with 20 mol% of TMEDA.