Synthesis, Structures, and Characterizations of [ArTi(O-i-Pr)3]2and Efficient Room-Temperature Aryl−Aryl Coupling of Aryl Bromides with [ArTi(O-i-Pr)3]2Catalyzed by the Economic Pd(OAc)2/PCy3System

Abstract

The series of aryltris(2-propoxo)titanium reagents [ArTi(O-i-Pr)3]2 (Ar = Ph (1a), 2-MeC6H4 (1b), 4-MeC6H4 (1c), 4-ClC6H4 (1d), 4-TMSC6H4 (1e), 4-CF3C6H4 (1f), 3,5-Me2C6H3 (1g)) was synthesized from reactions of the in situ prepared ClTi(O-i-Pr)3 with ArMgBr in THF. All compounds were characterized by NMR spectroscopy and elemental analyses. A variable-temperature 1H NMR study of 1c suggested that compounds 1 are dimeric species in solution. The structures of complexes 1b,g were further determined by single-crystal X-ray analyses. X-ray diffraction studies confirmed that the aryltris(2-propoxo)titanium complexes have a dimeric structure with a Ti2O2 core bridging through the oxygen atom of two 2-propoxide groups. The application of aryltris(2-propoxo)titanium reagents to cross-coupling with aryl bromides catalyzed by the catalytic system of 1 mol % Pd(OAc)2 and 2 mol % PCy3 was studied. Results show that aryltris(2-propoxo)titanium compounds are excellent reagents for aryl−aryl coupling reactions at room ...