First stepwise Dotz reaction: Isolation and characterization of a chelatedmetallatriene intermediate. Influence of its pattern of substitution in product partition

A series of chelated tetracarbonyl aminovinyl carbene complexes 5 are prepa red by high-yielding decarbonylation reaction. gamma-Alkyl-substituted comp lexes 5a-d are stable in solid form while gamma-aryl-substituted analogues 5e-g are stable only in solution. NMR studies determined that complexes 5 u ndergo a dynamic process in solution, in which the unsaturated eta(1) speci es an present in low concentration. Reaction of complexes 5 with electron-d eficient alkynes under controlled conditions afforded the 1,4,5-eta(3)-dien ylcarbene complexes 9 arising from the insertion of the alkyne in the metal -carbon bond. The stability and behavior of these complexes were studied an d found to be related to their electronic structure and pattern of substitu tion. Thermal decomposition of carbenes 9 produced either cyclopentadienes 13 or phenol derivatives 15, the major products in the Dotz reaction, thus demonstrating that they can be the actual intermediates in this reaction. T he overall process can be considered a Dotz reaction carried out in three s eparate steps at low temperature.