Mechanism of thermal decomposition of dineopentylbis(triethylphosphine)platinum(II): formation of bis(triethylphosphine)-3,3-dimethylplatinacyclobutane
The thermal decomposition of dineopentylbis(triethylphosphine)platinum(II) (1) in cyclohexane solution at 157/sup 0/C yields bis(triethylphosphine)-3,3-dimethylplatinacyclobutane (4) by a reaction which involves dissociation of 1 equiv of triethylphosphine, intramolecular oxidative addition of the C-H bond of a neopentyl methyl group to platinum (3), and reductive elimination of neopentane. Carbon-carbon bond formation resulting in production of dineopentyl is a detectable side-reaction. The overall reaction has Arrhenius activation parameters: E/sub a/ approximately equal to 49 kcal mol/sup -1/, log A approximately equal to 20. The activation energy for phosphine dissociation is 27 to 35 kcal mol/sup -1/. Transfer of a hydrogen atom from the triethylphosphine group to a neopentyl moiety occurs at a rate approximately 3% that of transfer of hydrogen from the methyl of one neopentyl group to the methylene of the other. Any processes which abstract ..cap alpha..-methylene hydrogens from the neopentyl group occur at less than 1% the rate of processes which abstract hydrogens from the neopentyl methyl groups. Substitution of deuterium for hydrogen in either the neopentyl methyl groups or the triethylphosphine groups slows the decomposition reactions (k/sub H//k/sub D/ approximately equal to 3.0). The mechanism proposed for generation of 4 is based in part on deuterium-labeling experiments: comparison of results by using different labeling patterns for 1 demonstrates the special utility of inverted experiments in which hydrogen transfer from a specific site is examined in a system which is otherwise perdeuterated. The driving force for the conversion of 1 to 4 is not obvious; it may be relief of steric strain in 1, changes in electronic energy due to reorganization of ligands around platinum, or changes in entropy.
- Research Organization:
- Massachusetts Inst. of Tech., Cambridge
- OSTI ID:
- 6800564
- Journal Information:
- J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 102:22; ISSN JACSA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400302* -- Organic Chemistry-- Isotope Effects-- (-1987)
ACTIVATION ENERGY
ALKANES
ARRHENIUS EQUATION
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
COMPLEXES
CYCLOALKANES
CYCLOHEXANE
DECOMPOSITION
DEUTERIUM
ENERGY
EQUATIONS
HIGH TEMPERATURE
HYDROCARBONS
HYDROGEN ISOTOPES
ISOTOPE EFFECTS
ISOTOPES
KINETICS
LIGANDS
LIGHT NUCLEI
NUCLEI
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
PHOSPHINES
PHOSPHORUS COMPOUNDS
PLATINUM COMPLEXES
PLATINUM COMPOUNDS
PYROLYSIS
RADICALS
REACTION KINETICS
STABLE ISOTOPES
THERMOCHEMICAL PROCESSES
TRANSITION ELEMENT COMPLEXES
TRANSITION ELEMENT COMPOUNDS