Nucleophilic Activation of Carbon Monoxide: Synthesis, Characterization and Reactivity of Intramolecular Group VI Metallaesters

Citation

Coolbaugh, Thomas Smith (1985) Nucleophilic Activation of Carbon Monoxide: Synthesis, Characterization and Reactivity of Intramolecular Group VI Metallaesters. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/aps3-bk95. https://resolver.caltech.edu/CaltechTHESIS:12172018-123100783

Abstract

An investigation of the design and reactivity of bifunctional transition metal complexes pertinent to homogeneous reduction of carbon monoxide is presented. Oxygen nucleophiles were incorporated into Group VI metal carbonyl complexes via cyclopentadienyl ligands.

Neutral molybdenum dimers yield no intramolecular nucleophilic interaction between an alcohol, attached by different bridging arm lengths, and the metal carbonyl fragment. A crystal structure of the propanol substituted cyclopentadienyl molybdenum tricarbonyl dimer (space group P1, a = 7.487 Å, b = 7.713 Å, c = 10.902 Å, α = 99.3600°, β = 81.460°, γ = 115.260°, V = 563.0 ų, Z = 1) indicates only an intermolecular hydrogen bond between alcohols.

The synthesis of the cationic compounds, [CpRM(CO)₃L]⁺BF^-₄ is reported, where M = Mo, W and R = -(CH₂)_η - OH with n = 1-3. Deprotonation of the alcohols leads to intramolecular metallaester formation for the methylene and ethylene bridged compounds. The equilibria established upon reaction with external alcohols are reported as are the thermodynamic parameters associated with the process.

Crystal structures of the metallaesters bridged by a methylene (space group P2₁/n, a = 7.867 Å, b = 17.083 Å, c = 17.768 Å, β= 100.959°, V = 2344.4 ų, Z = 4) and ethylene group (space group P2₁/n, a = 8.127 Å, b = 16.823 Å, c = 17.623 Å, β = 101.980°, V = 2357.1 ų, Z = 4) are presented. A comparison of the structures is given.

Reaction of the intramolecular metallaesters with molecular hydrogen produces no volatile products. Reaction with stoichiometric hydride sources yields compounds of relevance to carbon monoxide reduction. Reactions with Me⁺ and water are presented, the latter giving rise to a stoichiometric analog of the water-gas shift reaction.

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