Palladium(0) complexes of N-heterocyclic carbene ligands with dangling NMeCO functionalities: Synthesis, reactivity and application in Mizoroki–Heck reactions

A series of new Pd(0) complexes of N-heterocyclic carbene (NHC) ligands with dangling NMe(CO) functionalities (LMe) is reported, with yields in the range 56–73%. The reactivity of one of the Pd(0) complexes, bearing bulky N-mesityl groups, towards the oxidative addition of pentafluoroiodobenzene was studied, revealing the formation of decafluorobiphenyl, a diiodo Pd(II) NHC complex and an intriguing Pd(II) complex with four carbon-donor ligands coordinated to the metal center. The latter complex contains two new NHC ligands derived from LMe. One of the NHC ligands is a bidentate ligand, resulting from an addition reaction between LMe and the coordinated maleic anhydride. The other NHC ligand is derived from the N-protonation of LMe. A pentafluorophenyl ligand completes the fourth coordination site. A mechanism for the formation of this intriguing Pd(II) complex is proposed. The structures of these two new Pd(II) complexes were established by single-crystal X-ray diffraction studies. The catalytic activities of the new Pd(0) complex with LMe in the Mizoroki–Heck coupling reaction between 4-chloroacetophenone and styrene were compared and they contrast with those reported for the Pd(0) NHC complex with dangling NH(CO) groups (LH).

A series of new Pd(0) NHC complexes with dangling NMe(CO) functionalities is reported. The reactivity of one of the Pd(0) complexes towards the oxidative addition of pentafluoroiodobenzene was studied, revealing the formation of an intriguing Pd(II) complex. The catalytic activities of the new complexes in the Mizoroki–Heck coupling reaction were investigated.Figure optionsDownload as PowerPoint slide