Date of Award
Doctor of Philosophy (PhD)
Professor M. J. McGlinchey
Sterically demanding organometallic complexes, in which bulky clusters or large polyphenylated groups are incorporated, possess interesting structural character as well as molecular dynamics.
Trichloroacetate esters, p-C₆H₄(O₂C-CCI₃)₂ and C(CH₂-O₂C-CCI₃)4, can be utilized as templates in building multi-cobalt cluster systems such as p-C₆H₄(O₂C-CCo₃(CO)₉)₂ and C[CH₂-O₂C-CCo₃(CO)₉]₃(CH₂-O₂C-CCI₃). The crystal structure of C(CH₂-O₂C-CCI₃)₄ has been obtained and a molecular modelling study was performed on the tetra-cluster C[CH₂-O₂C-CCo₃(CO)₉]₄.
The 1,1,1-trichloroacetylacetonate complexes of Co(II), Co(IIl), or AI(III) can also be used as templates in the preparation of multi-cluster molecules by reaction with CO₂(CO)₈. The uncomplexed cluster ligand, CH₃C(O)CHC(OH)CCo₃(CO)₉, was structurally characterized. Its direction of enolization was studied by EHMO (Extended Huckel Molecular Orbital) calculations. The tendency to enolize is also found in (benzoylacetone)Cr(CO)₃ which was characterized by x-ray crystallography.
The Diels-Alder reaction of tetraphenylcyclopentadienone (tetracyclone) with triphenylcyclopropene yields a ketone adduct, C₇Ph₇HCO, with an endo hydrogen at the methine carbon; thermal elimanation of CO produces heptaphenylcycloheptatriene, C₇Ph₇H, a sterically crowded polyaryl system. This initially formed conformer with a pseudo-equatorial phenyl substituent at the sp³ position is sterically hindered and undergoes a conformational flip which allows the phenyl group to occupy the favored pseudoaxial site. However, the remaining phenyls are sterically encumbered and slowed rotation of these rings can be monitored by ¹H and ¹³C NMR spectroscopy. The intermediacy of the conformer is shown by the formation of isomers of C₇(p-tolyl)₂Ph₅H, arising via a series of [1,5] hydrogen shifts that are possible only for this conformer. Similarly, use of 2,5-dimethyl-3,4-diphenyl-cyclopentadienone yields C₇Me₂Ph₅H in which [1,5] hydrogen shifts also occur.
The heptaphenyltropylium ion, C₇Ph₇⁺Brˉ or C₇Ph₇⁺BF₄ˉ, has a planar central seven membered ring. The C₇Ph₇ˉK⁺ anion, which is prepared from C₇Ph₇⁺Brˉ and potassium metal, reacts with Me₃SnCI and SiMe₂HCI to form σ-bonded derivatives, C₇Ph₇-SnMe₃ and C₇Ph₇-SiMe₂H.
The reaction of Cr(CO)₆ with C₇Ph₇H, or C₇Me₂Ph₅H, leads to incorporation of a Cr(CO)₃ group on a peripheral phenyl ring rather than on the seven-membered ring. However, the tricyclic ketone, C₇Ph₇HCO, which is the precursor to C₇Ph₇H, reacts with Mo(CO)₆ to give the π-allyl complex, (η⁵-C₅Ph₄OH)Mo(CO)₂(η³-C₃Ph₃H₂), in which the triphenylcyclopropene ring has been opened as seen in its x-ray crystal structure.
Chao, Lisa Chen-Fang, "Sterically Demanding Organometallic Complexes Containing Multiple Clusters or Polyphenylated Ligands" (1995). Open Access Dissertations and Theses. Paper 1714.