Synthesis And Characterization Of Zinc Complexes And Their Catalytic Behavior Toward Hydroboration And Hydrosilylation Of Unsaturated Compounds

Zinc ethyl complexes 1 and 2 bearing polydentate phenolato ligands were synthesized.Complexes 1 and 2 were characterized by 1H and 13C NMR spectroscopy,elemental analyses and single crystal X-ray diffraction analysis.Zinc ethyl complexes were applied in hydroboration and hydrosilylation of N-heterocycles,and dehydrogenative borylation of terminal alkynes.1.Zinc ethyl complexes 1 and 2 were synthesized in 85-90%yields by treating ligand precursors L1H and L2H with ZnEt2,and their catalytic properties in hydroboration and hydrosilylation of N-heterocycles were studied.The optimal conditions were confirmed as follows:10 mol%of complex 2 as catalyst,C6D6 as solvent,30℃.Hydroboration of benzo-fused N-heterocycles with HBpin gave almost exclusively 1,2-addition products in 80-97%yields.At 70℃,reactions of pyridines afforded a mixture of 1,2-,1,4 and 1,6-products in yields of 55-95%.Bis-hydrosilylation were observed for quinoline derivatives,generating bis-1,2-hydrosilylation products in 76-96%yields.Kinetic studies suggested that catalyst,quinoline and pinacolborane are all first-order dependent.Based on literature survey and a series of control experiments,a possible mechanism involving zinc hydride intermediate was proposed.2.The catalytic properties of zinc ethyl complexes in dehydrogenative borylation of terminal alkynes were studied,and the optimal conditions were confirmed.In the presence of 10 mol%complex 2,terminal alkynes reacted with HBpin to afford alkynyl boronic esters with excellent selectivity in 57%-99%yields.