Isolation, characterization, and stability of α-[(ethynyl)dicobalt hexacarbonyl] carbonium ions

Abstract

Stable carbonium ion salts of the type [(HCCC +R 1R 2)Co 2(CO) 6]Z − (R 1 = R 2 = CH 3, Z = SbF 6; R 1 = R 2 = C 6H 5, Z = SbF 6; R 1 = CH 3, R 2 = H, Z = BF 4; R 1 = R 2 = H, Z = BF 4) were isolated upon treatment of the corresponding alcohol complexes with HF·SbF 5 or HBF 4·Et 2O at −45°C. Extensive charge delocalization onto the Co 2(CO) 6 moiety of the cations was evidenced in the IR by an increase in v(CO) and in the proton NMR spectra which exhibited very small downfield shifts relative to the alcohol precursors (Δδ). The p K R+ values for the cations were essentially the same regardless of other substituents at the carbonium ion center and were approximately equal to that of the triphenylmethyl cation.