Sandwich structured aryl-diimine Pd (II)/Co (II) monolayer—Fabrication, catalytic performance, synergistic effect and mechanism investigation

Abstract

Self-assembled sandwich structured aryl-diimine Pd/Co catalytic monolayers linked with graphene oxide (GO@DiI-PdxCo1-x) were fabricated and characterized. The catalytic performance in Suzuki coupling reactions was systematically investigated, and GO@DiI-Pd0.01Co0.99 exhibited higher catalytic activity with a Turn Over Number (TON) and Turn Over Frequency (TOF) (TON = 32,204, TOF = 6441 h−1) than monometallic catalysts when water was used as the solvent. The occurrence of heterogeneous catalysis was confirmed by hot filtration experiments, poisoning experiments, and dynamic studies using ReactIR. The synergistic effects between the different metals were investigated, and the catalytic activity could be enhanced by the palladium active center formed by the synergy between Pd2+ and Co2+, which also involved in the diimine ligands and graphene oxide. The special symmetric coordination sites of the aryl-diimine ligand accelerated electron transfer from GO to the metals or Co2+ to Pd2+, thereby making the palladium active center more negative and oxidative addition easier. A detailed catalytic mechanism was proposed based on the analysis of various experiments and theoretical calculations.