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

Abstract

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-[MCl2{C(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 °C temperature range and were characterized by elemental analyses (C, H, N), ESI+-MS, IR, and 1D (1H, 13C{1H}) and 2D (1H,1H-COSY, 1H,13C-HMQC/1H,13C-HSQC, 1H,13C-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-R2C6H4Br (R2 = H, Me, OMe, and NO2) with phenylboronic acid (in EtOH as a solvent, K2CO3 as a base, 80 °C), yielding biaryl...