Cobalt Carbonyls Stabilized by N,P-Ligands: Synthesis, Structure, and Catalytic Property for Ethylene Oxide Hydroalkoxycarbonylation.

Abstract

Reactions of N,P-Ligands as Ph2 P(o-NMe2 C6 H4 ) (1 L), 2,6-iPr2 C6 H3 NHC(Ph)=NC6 H4 (o-PPh2 ) (2 L), and Ph2 PN(R)PPh2 (R=iPr (3 L), cyclo-C6 H11 (4 L), tBu (5 L), CH2 C4 H7 O (6 L)) each with dicobalt octacarbonyl produced complexes [1 LCo(CO)3 ]2 (1), [2 LCo(CO)(μ-CO)2 Co(CO)3 ] (2), [3 LCo(CO)3 ]+ [Co(CO)4 ]- (3), [3 LCo(CO)2 ]2 (4), [4 LCo(CO)2 ]2 (5), [5 LCo(CO)2 ]+ [Co(CO)4 ]- (6), and [6 LCo(CO)2 ]+ [Co(CO)4 ]- (7). Complexes 1-7 have all been structurally characterized by X-ray crystallography, IR and NMR spectroscopies, and elemental analysis. Catalytic tests on transformation of ethylene oxide (EO), CO and MeOH into methyl 3-hydroxypropionate (3-HMP) indicate that complexes 1-7 are active, where ion-pair complexes 3 and 6-7 behave more excellently (by achieving 88.4-93.6% 3-HMP yields) than the neutral species 1-2 and 4-5 (35.0-46.5% 3-HMP yields) when the reactions are all operated at 2 MPa CO pressure and 50 °C in MeOH solvent. Density functional theory (DFT) study by selecting 3 as a model suggests a cooperative catalytic reaction mechanism by [Co(CO)4 ]- and its counter cation [3 LCo(CO)3 ]+ . The cobalt-homonuclear ion-pair catalyzed hydroalkoxycarbonylation of EO is present herein.