Mechanism of aryl chloride oxidative addition to chelated palladium(0) complexes

Moshe Portnoy, David Milstein

Research output: Contribution to journalArticle

173 Citations (Scopus)

Abstract

The mechanism of oxidative addition of aryl chlorides to Pd(dippp)2 (1) has been studied in depth. 31P NMR monitoring of the reaction of 1 with chlorobenzene in dioxane reveals that cis-(dippp)Pd(Ph)Cl (2) and trans-(η1-dippp)2Pd(Ph)Cl (3) are formed in parallel pathways and are also in equilibrium with each other, 2 being favored both kinetically and thermodynamically. The reaction is first order in chlorobenzene and approximately first order in Pd(0), the deviation resulting from a parallel equilibrium between 1 and the binuclear complex (dippp)Pd(μ-dippp)-Pd(dippp). Strong rate retardation by added dippp is observed, the reaction being approximately reciprocal first order in dippp. 1 undergoes reversible dissociation of dippp, followed by rate-determining oxidative addition of chlorobenzene to the 14-electron complex (dippp)Pd (5), whose existence was demonstrated directly by inversion transfer NMR experiments using (dippp)-PdPiPr2 nBu. The trans complex 3 is formed directly from the 14-electron complex (η1-dippp)2-Pd. Rate constants for oxidative addition of substituted aryl chlorides show an excellent fit to the Hammet σ1 constants, ρ = +5.2, whereas the fit to σ is poor. Activation parameters of ΔH obs = 28 ± 3 kcal/mol and ΔS obs = -2 ± 8 eu were measured; since ΔS obs = ΔS°diss + ΔS OA and ΔS°diSS ≫ 0, then ΔS OA, ≪ 0. These observations taken together provide strong evidence for an SNAr-type charged transition state, probably stabilized by partial chloride coordination.

Original languageEnglish
Pages (from-to)1665-1673
Number of pages9
JournalOrganometallics
Volume12
Issue number5
Publication statusPublished - 1993

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chlorobenzenes
Palladium
Chlorides
palladium
chlorides
Service oriented architecture (SOA)
Nuclear magnetic resonance
nuclear magnetic resonance
Electrons
Rate constants
electrons
Chemical activation
activation
dissociation
inversions
deviation
Monitoring
chlorobenzene
Experiments

ASJC Scopus subject areas

  • Inorganic Chemistry
  • Organic Chemistry

Cite this

Mechanism of aryl chloride oxidative addition to chelated palladium(0) complexes. / Portnoy, Moshe; Milstein, David.

In: Organometallics, Vol. 12, No. 5, 1993, p. 1665-1673.

Research output: Contribution to journalArticle

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