Alkynylcyclohexanol chairs and twist-boats: Co-2(CO)(6) as a conformational switch

Treatment of 1-[axial]-(trimethylsilylethynyl)cyclohexan-1-ol with dicobalt octacarbonyl results in a conformational ring flip such that the bulky dic obalt-alkyne cluster moiety now occupies the favored equatorial site. Howev er, when a 4-tert-butyl substituent is present, the coordinated alkynyl gro up retains its original axial or equatorial position. Complexation of trans -[diaxial]-1,4-bis(triphenylsilylethynyl)cyclohexane-1,4-diol brings about a chair-to-chair conformational inversion such that both cluster fragments now occupy equatorial sites. In contrast, cis-1,4-bis(triphenylsilylethynyl )cyclohexane-1,4-diol reacts with CO2(CO)(8) to yield the twist-boat confor mer in which the two axial hydroxy substituents exhibit intra-molecular hyd rogen bonding. Likewise, the corresponding reaction of cis-1,4-bis(trimethy lsilylethynyl)cyclohexane-1,4-diol with CO2(CO)(8) leads to a twist-boat, b ut in this case, the molecules are linked through inter-molecular hydrogen bonds. Eight of these cobalt clusters have been characterized by X-ray crys tallography, and the potential use of twist-boats in synthesis is discussed .