| Cobalt-clusters are versatile reagents in organometallic chemistry. Their ability to protect an alkyne allows one to selectively manipulate a ligand without undergoing a competitive reaction from the alkyne. Cobalt-clusters geometrically modify linear alkynes to 136--145° degrees, thereby allowing for some non-traditional alkynyl chemistry to occur. In particular, the focus of this dissertation lies upon the chemistry of cobalt-complexed propargyl alkynols, the ability of cobalt to stabilize neighbouring cations generated from these alcohols, and the chemistry that can be accomplished by altering the steric and electronic effects. We have chosen to study the possibility of inducing migration of various substituents from one terminus of the cobalt-complexed alkyne to the alcoholic site of the propargyl group via protonation of the desired complex. While examining various silanes, and altering the propargyl alcohol itself, we have considered both steric and electronic effects, thereby determining the idealized conditions for such transfers to occur. Furthermore, in our attempts to successfully apply these migrations to several systems, we have acquired a diverse synthetic knowledge of propargyl cobalt-clusters and their intricate reactivity.; An examination of the potential for allyl migrations in norbornyl derivatives revealed several fascinating transformations. Upon protonation with HBF 4, [(2-endo-allyldimethylsilyl)ethynylborneol]Co 2(CO)6, 63, suffers elimination of water or propene, to yield [(2-allyldimethylsilyl)ethynylborn-2-ene]Co2(CO) 6, 68, [(2-endodimethylfluorosilyl)ethynylborneol]Co 2(CO)6, 69, respectively, and, surprisingly, the tricobalt complex (2-norbornylidene)CHCCo3(CO)9, 70. In contrast, protonation of the terminal alkyne (2-endo -ethynylborneol)Co2(CO)6, 76, an anticipated precursor to 70, led instead to (2-ethynyl-2-bornene)Co 2(CO)6, 78, and the ring-opened species (2-ethynyl-4-isopropyl-1-methylcyclohexa-1,3-diene)Co 2(CO)6, 79. However, conversion of 76 to 70 was achievable upon prolonged heating at reflux in acetone, thereby also affording the corresponding alcohol, [2-(2-hydroxybornyl)]CH2CCo3(CO) 9, 77. A mechanistic rationale is offered for the formation of RCH2CCo3(CO)9 clusters upon protonation of alkyne complexes of the type (RC≡CH)CO2(CO)6. (Abstract shortened by UMI.)... |
