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

Abstract

Abstract The novel high-temperature reaction of Co 2 (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 Co 2 (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 13 CO 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 C 1 ′ 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.