Photo-promoted Carbonylation Of Olefins With Methyl Formate Under Ambient Conditions

Carbonylation is one of the most important organic synthesis which usually takes place at high temperatures and high pressure with precious catalysts. In recent years, more and more attention has been paid to the photo-promoted carbonylation under ambient conditions.It is well known that carbon monoxide gas is the most commonly employed C1 source in the carbonylation. However, the use of carbon monoxide gas is limited due to high toxicity and complicated operation. The recent attention has been paid to the researches of using C1 source in liquid or solid state in place of CO gas.In this paper, the photo-promoted carbonylation of olefins with methyl formate catalyzed by non-precious metal catalysts has been studied under ambient conditions.The cobalt complexes catalysts show high catalytic activities for the photo-promoted carbonylation of olefins. Weak basicity is beneficial to this reaction and NaOAc is the most efficient additive. In addiation, NaI also can promote the reaction. The results indicate that the reaction activities of olefins increase with the increasing temperature under the catalysis of cobalt complexes. However, as for the carbonylation of straight chain terminal olefins, the ratio of n/i is not good as we expected.On the basis of the carbonylation with cobalt complexes catalysts, copper complexes are investigated. The catalytic activities of copper complexes are lower than cobalt complexes but the selectivity of ester for straight chain terminal olefins is high, the major product is isomeric ester. Base additives have no promoted effects on this reaction. On the other hand, halides have different promoted effects on different olefins. The activities of cyclohexene and 1-octene can be improved by additition of NaI and NaBr, respectively.The mechanism of methyl formate participating in the carbonylation is verified by the IR analysis and the labeling experiments of CD)3OD and CH₃¹⁸OH. The results indicate that methyl formate decomposes into CO and CH₃OH firstly under irradiation, and then the carbonylation of olefins proceed.The influences of some factors on the photo-promoted carbonylation of olefins are studied. The results are obtained that double bond with groups of donating electrons are beneficial to this reaction and double bond with groups of withdrawing electrons are unfavorable to this reaction. The space configuration of olefins also have some effects on the reaction, the activitiy of terminal olefin is better than branched olefin. The activity sequence of the alcohols is as follows: primary alcohol, secondary alcohol and tertiary alcohol. As for primary alcohol, the activity decreases with the increasing length of carbon chain.The mechanism of photopromoted carbonylation of olefin with carbon monoxide catalyzed by Co(OAc)₂ is investigated by UV and IR spectrograph. It is preliminary considered that Co₂(CO)₈ maybe is not the intermediate as some literature reported, Co(OAc)₂ is assumed to initiate the reaction via another catalytic cycle.