Ring Opening of a Cobalt-Stabilized Bornyl Cation: Mechanistic Study of the Alkyne−Dicobalt/Carbynyl−Tricobalt Cluster Transformation

Upon protonation with HBF4, [2-endo-((allyldimethylsilyl)ethynyl)borneol]Co2(CO)6 (2) suffers elimination of water or propene, to yield [2-((allyldimethylsilyl)ethynyl)born-2-ene]Co2(CO)6 (11) and [2-endo-((dimethylfluorosilyl)ethynyl)borneol]Co2(CO)6 (12), respectively, and, surprisingly, the tricobalt complex (2-norbornylidene)CHCCo3(CO)9 (13). In contrast, protonation of the terminal alkyne (2-endo-ethynylborneol)Co2(CO)6 (19), an …