Oxidation of carbon monoxide cocatalyzed by palladium(0) and the H(5)PV(2)Mo(10)O(40) polyoxometalate probed by electron paramagnetic resonance and aerobic catalysis.
The H(5)PV(2)Mo(10)O(40) polyoxometalate and Pd/Al(2)O(3) were used as co-catalysts under anaerobic conditions for the activation and oxidation of CO to CO(2) by an electron transfer-oxygen transfer mechanism. Upon anaerobic reduction of H(5)PV(2)Mo(10)O(40) with CO in the presence of Pd(0) two paramagnetic species were observed and characterized by continuous wave electron paramagnetic resonance (CW-EPR) and hyperfine sublevel correlation (HYSCORE) spectroscopic measurements. Major species I (65-70%) is assigned to a species resembling a vanadyl cation that is supported on the polyoxometalate and showed a bonding interaction with (13)CO. Minor species II (30-35%) is attributed to a reduced species where the vanadium(IV) atom is incorporated in the polyoxometalate framework but slightly distanced from the phosphate core. Under aerobic conditions, CO/O(2), a nucleophilic oxidant was formed as elucidated by oxidation of thianthrene oxide as a probe substrate. Oxidation reactions performed on terminal alkenes such as 1-octene yielded a complicated mixture of products that was, however, clearly a result of alkene epoxidation followed by subsequent reactions of the intermediate epoxide. The significant competing reaction was a hydrocarbonylation reaction that yielded a approximately 1:1 mixture of linear/branched carboxylic acids.
Goldberg
Hila
H
Department of Organic Chemistry, Weizmann Institute of Science,Rehovot, Israel 76100.
Kaminker
Ilia
I
Goldfarb
Daniella
D
Neumann
Ronny
R