Reactions of Cyclopropenone Derivatives with a Cyclopentadienylcobalt(I) Chelate:  Formation of a Cobaltacyclobutenone and a Transformation of 2,2-Dimethoxycyclopropenone to Methyl Acrylate at Cobalt

Reactions of cyclopropenone derivatives with the [2-(di-tert-butylphosphanyl)ethyl]cyclopentadienylcobalt(I) chelate system were investigated. Ethene complex 2 reacts with diphenylcyclopropenone under cobalt insertion to give cobaltacyclobutenone chelate complex 6 in 91% yield. 6 was characterized crystallographically and shows a structure similar to that of a known platinacyclobutenone. Thermoanalysis of 6 indicated a reaction at elevated temperature, which was shown to be a cycloreversion at 60 °C leading to known diphenylethyne and carbonyl complexes 7 and 9. Attempts to reduce the metallacyclobutenone with lithium tetrahydridoaluminate resulted in the cycloreversion reaction at a temperature as low as −100 to −90 °C, the lithium cation acting as a Lewis acid. The reaction of dimethoxycyclopropene complex 4 with zinc triflate unexpectedly resulted in the formation of methyl acrylate complex 13, which was characterized crystallographically.