Mechanistic Insights into C−S Cross-Coupling Reactions Catalyzed by Nickel Bis(phosphinite) Pincer Complexes
作者:Jie Zhang、Christopher M. Medley、Jeanette A. Krause、Hairong Guan
DOI:10.1021/om100816d
日期:2010.12.13
these catalytic reactions, such as nickel thiolate complexes [2,6-(Ph2PO)2C6H3]NiSAr (Ar = Ph, 2a; Ar = p-MeC6H4, 3a; Ar = p-MeOC6H4, 4a), have been synthesized and spectroscopically characterized. The reaction between 2a and PhI in DMF-d7 is slow enough to argue against 2a being directly involved in the C−S bond-forming step. NMR studies suggest that the pincer ligand framework in complexes 1a, 3a
双(次膦酸酯)镍钳形配合物[2,6-(R 2 PO)2 C 6 H 3 ] NiCl(R = Ph,1a ; R = Me,1b ; R = i Pr,1c ; R = t Bu,1d)在芳基碘化物和芳基硫醇的交叉偶联中显示催化活性。最佳的催化条件包括在80°C的DMF中含有1 mol%的1a和2当量的KOH(相对于芳基硫醇),并能承受底物中的各种官能团。这些催化反应中的潜在中间体,例如硫醇镍络合物[2,6-(Ph 2 PO)2 C 6 H3 ]尼萨尔(AR = PH,图2a ; Ar为p -MeC 6 ħ 4,图3a ; Ar为p -MeOC 6 ħ 4,图4a),已经合成和光谱表征。DMF- d 7中2a和PhI之间的反应足够缓慢,足以证明2a直接参与了CS键形成步骤。NMR研究表明,配合物1a,3a和4a中的钳位配体骨架通过POH键的裂解被KOH破坏,从而释放出Ph 2POK,进一步分解会生成Ph