University of Illinois Urbana-Champaign

Base Catalysis of Ligand Substitution in Metal Carbonyls

Bellus, Peter Alexander

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Description

Title
Base Catalysis of Ligand Substitution in Metal Carbonyls
Author(s)
Bellus, Peter Alexander
Issue Date
1980
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Inorganic
Language
eng
Abstract
  • Manganese(I) carbonyls can undergo substitution by a variety of mechanisms. Three different mechanisms have been found for the substitution reactions of Mn(CO)(,5)CH(,3)CN('+).
  • Mn(CO)(,5)CH(,3)CN('+) reacts with P(C(,6)H(,5))(,3) in CH(,3)CN by a dissociative process. CH(,3)CN dissociates and P(C(,6)H(,5))(,3) takes its place to form Mn(CO(,5))P(C(,6)H(,5))(,3)('+). First order overall, and first order in metal carbonyl, kinetics are observed.
  • Mn(CO)(,5)CH(,3)CN('+) reacts with pyridine in CH(,3)CN by an associative process that is best explained by a carbonyl base-attack mechanism, whereby a pyridine attacks the carbon of a CO to generate an adduct-ligand of the formula, ('-)C(O)NC(,5)H(,5). This adduct ligand labilizes the complex toward loss of the ligands cis to it. Pyridine or CH(,3)CN can fill the vacancy thus generated. The substitution process continues until the adduct-ligand breaks up, regenerating free pyridine and a coordinated CO, in the observed product, Mn(CO)(,3)(CH(,3)CN) (pyridine)(,2)('+). The kinetics observed are second order overall and first order each in metal carbonyl and pyridine.
  • Mn(CO)(,5)CH(,3)CN('+) reacts with pyridine in CH(,3)NO(,2) also by a base-attack mechanism. The nucleophile is CH(,2)NO(,2)('-), formed by the deprotonation of CH(,3)NO(,2) by pyridine. The adduct-ligand formed is C(O)ON(O)CH(,2), which labilizes the complex towards loss of ligand cis to it, and substitution occurs. The adduct ligand breaks down to give CO(,2) and, presumably, CH(,2)NO('-). Mn(CO)(,3)(pyridine)(,3)('+) is the metal containing product. The kinetics show first order dependences on both the metal carbonyl and pyridine, and an inverse dependence on pyridinium ion.
  • Mn(CO)(,5)CH(,3)CN('+) also undergoes a complex series of reactions in CH(,3)CN containing both pyridine and water. Mn(O) binuclear species, Mn(CO)(,5)('-), Mn(II) species and Mn(I) carbonyls are among the products. Formation of a hydroxycarbonyl species is thought to be the key step, leading to substitution by virtue of the cis-labilizing ability of the COOH moiety, and leading to Mn(CO)(,5)('-) formation via the hydroxycarbonyl. Electron transfer steps involving these species generate Mn(O) radicals and Mn(II).
  • The application of the base-attack mechanism of ligand substitution to other metal carbonyl systems is discussed.
Graduation Semester
1980
Type of Resource
text
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http://hdl.handle.net/2142/67219

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