Palladium biphenyl N-heterocyclic carbene complexes: Synthesis, structure and their catalytic efficiency in water mediated Suzuki–Miyaura cross-coupling reaction

Abstract

Synthesis of bis-N-heterocyclic carbene ligand with biphenyl backbone [MIBIPhen](Br)2 (L), [Ag(MIBIPhen)]2(PF6)2 (1) and palladium-NHC complexes, [Pd(MIBIPhen)(Cl)(H3C-CN)]PF6 (2), [Pd(MIBIPhen)(H3C-CN)2](PF6)2 (3) and [Pd(MIBIPhen)Br2] (4) {MIBIPhen=(3,3′-(biphenyl-2,2′-diylbis(methylene))bis(1-methyl-1H-imidazol-3-ium)bromide)} is reported. All complexes (1–4) are characterized by NMR, ESI-MS, elemental analysis and single crystal XRD. Complex 1 serves as an efficient NHC transfer agent for the preparation of complex 2. Treatment of complex 2 with AgPF6 drives the exchange of chloride by acetonitrile to result in complex 3. Complex 4 is prepared by in situ deprotonation of MIBIPhen with Pd(OAc)2. Complex 1 is molecular box type with silver in bent geometry. Complexes 2, 3 &4 exist as monomers with palladium in distorted-square-planar geometry. All Pd-NHC complexes are explored as catalyst in water mediated Suzuki-Miyaura cross coupling reaction where complex 3 shows efficient catalytic activity.