High-temperature reaction of a Co2(CO)6-complexed propargyl cation

The novel high-temperature reaction of Co2(CO)6-complexed propargyl cations, occurring in the spontaneous and stereoselective (90–97% d ,l- ) manner and yielding the radical dimers, d ,l- 3,4-diaryl-1,5-hexadiynes (2, 11, 14), is described. Despite the alleged thermal lability and delicate nature of the requisite Co2(CO)6-complexed propargyl cations, the reaction temperature can be elevated from 20 °C to 147 °C, shortening the reaction time from 660 min to less than 1 min. Isotopic enrichment experiments detected (MS TOF/ESI/APCI) an incorporation of upto, eight 13CO ligands into the metal core, suggesting a single electron, cluster-to-cluster reduction along the reaction coordinate. The reaction kinetics is found to be sensitive toward the electronic nature of the substituents (H, OMe) and to the substitution pattern (0-, 4-, 3,4,5-) on the periphery of the aromatic ring. Calculation data suggest that the spontaneous transfer of a single electron from the metal cluster, onto a π-bonded propargyl moiety, is dependent upon the negative charge on aromatic C1′C1′ carbon atom, located alpha to the cationic center. The spontaneous conversion of diamagnetic species (propargyl cation) to paramagnetic counterparts (propargyl radical) indicates that the π-bonded organometallic cations can act as the prototypes for transition metal-based thermal sensors. Their application in photochemical research, electronic devices, molecular electronics, and biomedical fields can also be envisioned.