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

Metal-mediated reaction between equimolar amounts of cis -[MCl 2 (C≡NR) 2 ] [M = Pd, R = cyclohexyl (Cy) 1, t Bu 2, 2,6-Me 2 C 6 H 3 (Xyl) 3, 4-MeOC 6 H 4 4; M = Pt, R = cyclohexyl (Cy) 5, 2,6-Me 2 C 6 H 3 (Xyl) 7, 4-MeOC 6 H 4 8 ] and benzophenone hydrazone, H 2 N−N═CPh 2, proceeds in CHCl 3 under reflux for 8 h. The subsequent workup provides the carbene species cis -[MCl 2 { C (N(H)N═CPh 2 )═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 ( 1 H, 13 C{ 1 H}) and 2D ( 1 H, 1 H-COSY, 1 H, 13 C-HMQC/ 1 H, 13 C-HSQC, 1 H, 13 C-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-R 2 C 6 H 4 Br (R 2 = H, Me, OMe, and NO 2 ) with phenylboronic acid (in EtOH as a solvent, K 2 CO 3 as a base, 80 °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 × 10 6 ).