THE SYNTHESIS AND REARRANGEMENTS OF CYCLOPENTADIENYLCOBALT DIENE COMPLEXES.

摘要

The use of metals in organic chemistry has greatly enhanced the synthetic chemist's ability to effect selective reactions under extremely mild conditions. The prerequisite necessary for the application or extension of such metal-induced transformations, is a fundamental understanding of the mechanisms involved. Moreover, the organometallic reagents used should be both readily accessible and easily synthesized. This thesis describes both the facile preparation and rearrangements of cyclopentadienylcobalt diene complexes.;High temperature solution phase pyrolysis (200-300(DEGREES)C) of 2,3-disubstituted cyclopentadienylcobalt diene complexes was found to lead to positional isomerization, producing equivalent amounts of the E- and Z-1,2-disubstituted isomers. The data suggest that the formation of the Z-isomer was the result of a metal-assisted symmetry-controlled operation. Similar studies performed in the gas phase lead only to decomplexation.;Low temperature solution thermolysis of acyclic diene complexes was found to induce 1,3-prototropic shifts. The resulting product distribution of the complexed isomers was determined to reflect the relative thermodynamic stability of the free ligands.;The photochemically induced isomerization of (eta)('4)-1,3-(cis,cis-1,4-dideuterio-1,3-butadiene)cyclopentadienylcobalt gave a 1:1 mixture of starting material and (eta)('4)-1,3-(trans,trans-1,4-dideuterio-1,3-butadiene)cyclopentadienylcobalt. This process is believed to proceed via an envelope inversion mechanism. The corresponding thermal reaction produced a statistical mixture of the cis,cis-,cis, trans- and trans,trans-complexes.;The thermal and photochemistry of (eta)('4)-1,3-(trans-1,3,5-hexatriene)cyclopentadienylcobalt was also investigated. At concentrations below {C}(,o) = 1.0 x 10('-2)M a thermally induced "walk" process was observed (E(,a) = 26.75 kcal mol('-1); log A = 13.3). This mode of isomerization could also be photochemically induced. At higher concentrations facile metal-mediated {1,6} vinyl hydrogen shifts occurred, quantitatively furnishing a dinuclear pentadienylidene complex 12 and one equivalent of free trans-1,3,5-hexatriene. Complex 12 was found to unimolecularly isomerize to a more stable pentadienylidene complex 13 via {1,5} hydrogen shift on heating above 100(DEGREES)C (E(,a) = 29.1 kcal mol('-1); log A = 11.6). Laser irradiation of 13 at 514 nm was found to reverse the {1,5} hydrogen shift, producing an isomer 40 with opposite stereochemistry compared to 12. Compound 40 was found to thermally revert to 13 following first order kinetics (E(,a) = 19.4 kcal mol('-1); log A = 10.1).