Nine N,O-ligands L¹~L⁹ have been synthesized. L¹~L⁴ each reacted with half equivalent Co₂(CO)₈ by redox coordination to produce neutral mononuclear cobalt compounds 1~4. Reactions of L⁵~L⁹ each with equivalent Co₂(CO)₈ occurred by disproportionation and redox coordination to afford 5~7. When the reaction of L⁸, 5/6 equiv. of Co₂(CO)₈, 1.2 equiv. of MeOH, and 0.4 equiv. of H₂O took place via disproportionation and redox coordination to give compound 8, L⁹ and 0.5 equiv. of Co₂(CO)₈ happened through disproportionation coordination to form compound 9. Compounds 5~9 are all the ionic species with the same anion [Co(CO)₄]^–, but coupled by mononuclear cobalt cation for 5~7 and 9 whereas trinuclear cation for 8. Compounds 1~9 have been characterized by FT-IR spectroscopies and elemental analysis, of which 1 and 8 were further determined by X-ray crystallography. The catalytic property of propylene oxide (PO) carbonylation hydroesterification using 1~9 was investigated, achieving PO conversions of 42.6%~99.0% and β-hydroxy methylbutyrate (HMB) yields of 34.1%~88.6%. The time-traced reactions were carried out for both catalysts 8 and 9, and the catalytic reaction mechanism based on cooperative interplay by the homonuclear cobalt ion pair was discussed as well.

Key words: N, O-ligand cobalt compounds, carbonylation hydroesterification catalytic property, propylene oxide (PO), β-hydroxy methylbutyrate, homonuclear cobalt ion pair catalytic mechanism