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-butylphosphany l)ethyl] cyclopentadienylcobalt(I) chelate system were investigated. Ethene complex 2 reacts with diphenylcyclopropenone under cobalt insertion to giv e cobaltacyclobutenone chelate complex 6 in 91% yield. 6 was characterized crystallographically and shows a structure similar to that of a known plati nacyclobutenone. Thermoanalysis of 6 indicated a reaction at elevated tempe rature, which was shown to be a cycloreversion at 60 degrees C leading to k nown diphenylethyne and carbonyl complexes 7 and 9. Attempts to reduce the metallacyclobutenone with lithium tetrahydridoaluminate resulted in the cyc loreversion reaction at a temperature as low as -100 to -90 degrees C, the lithium cation acting as a Lewis acid. The reaction of dimethoxycyclopropen e complex 4 with zinc triflate unexpectedly resulted in the formation of me thyl acrylate complex 13, which was characterized crystallographically.