Novel Metal-Mediated (M = Pd, Pt) Coupling between Isonitriles and Benzophenone Hydrazone as a Route to Aminocarbene Complexes Exhibiting High Catalytic Activity (M = Pd) in the Suzuki−Miyaura Reaction
作者:Konstantin V. Luzyanin、Alexander G. Tskhovrebov、M. Carolina Carias、M. Fátima C. Guedes da Silva、Armando J. L. Pombeiro、Vadim Yu. Kukushkin
DOI:10.1021/om900682v
日期:2009.11.23
Metal-mediated reaction between equimolar amounts of cis-[MCl2(C NR)(2)] [M = Pd, R = cyclohexyl (Cy) 1, tBu 2, 2,6-Me2C6H3 (Xyl) 3, 4-MeOC6H4 4; M = Pt, R = cyclohexyl (Cy) 5, 2,6-Me2C6H3 (Xyl) 7,4-MeOC6H4 8] and benzophenone hydrazone, H2N-N=CPh2, proceeds in CHCl3 under reflux for 8 h. The subsequent workup, provides the carbene species cis-[MCl2C(N(H)N=CPh2)=N(H)R}(C NR)] (M = Pd, 9-12; M = Pt, 13-15) in good (80-85%) isolated yields. Complexes 9-15 are air- and moisture-stable in the 20-80 degrees C temperature range and were characterized by elemental analyses (C, H, N), ESI+-MS, IR, and ID (H-1,C-13H-1}) and 2D (H-1,H-1-COSY, H-1,C-13-HMQC/H-1,C-13-HSQC, H-1,C-13-HMBC) NMR spectroscopies. In addition, the structures of two metallacarbenes, 11 and 14, were elucidated by single-crystal X-ray diffraction. The catalytic properties of 9-15 in the Suzuki-Miyaura cross-coupling of the aryl bromides 4-(RC6H4Br)-C-2 (R-2 = H, Me, OMe, and NO2) with phenylboronic acid (in EtOH as a solvent, K2CO3 as a base, 80 degrees C), yielding biaryl species, were evaluated, and it was found that the palladium-aminocarbene species 9-12 exhibit a high catalytic activity (yields up to 97%, TONS up to 1.4 x 10(6)).