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. 2009 Aug 12;131(31):11234-41.
doi: 10.1021/ja904116k.

Synthetic and mechanistic studies of Pd-catalyzed C-H arylation with diaryliodonium salts: evidence for a bimetallic high oxidation state Pd intermediate

Nicholas R Deprez  1 , Melanie S Sanford
Affiliations

Synthetic and mechanistic studies of Pd-catalyzed C-H arylation with diaryliodonium salts: evidence for a bimetallic high oxidation state Pd intermediate

Nicholas R Deprez et al. J Am Chem Soc. .

Abstract

This contribution describes the substrate scope and mechanism of Pd-catalyzed ligand-directed C-H arylation with diaryliodonium salts. This transformation was applied to the synthesis of a variety of different biaryl products, using directing groups including pyridines, quinolines, pyrrolidinones, and oxazolidinones. Electronically and sterically diverse aryl groups (Ar) were transferred in high yield using iodine(III) reagents of general structure [Mes-I-Ar]BF(4). Mechanistic investigations have been conducted that establish the kinetic order of the catalytic reaction in each component, determine the resting state of the catalyst and the iodine(III) reagent, quantify the electronic influence of the arylating reagent on the reaction rate, and establish the intra- and intermolecular 1 degree H/D kinetic isotope effect. On the basis of these studies, this transformation is proposed to proceed via turnover-limiting oxidation of the Pd dimer [Pd(N~C)(OAc)](2) (N~C = 3-methyl-2-phenylpyridine) by [Mes-I-Ph]BF(4). This mechanism implicates a bimetallic high oxidation state Pd species as a key catalytic intermediate. The significance of this and other aspects of the proposed mechanism are discussed in detail.

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Figures

Figure 1
Figure 1
Plot of Initial Rate (Δ[2]/Δt) versus [IIII] Showing 1st Order Kinetics in IIII Reagent
Figure 1
Figure 1
Plot of Initial Rate (Δ[2]/Δt) versus [IIII] Showing 1st Order Kinetics in IIII Reagent
Figure 2
Figure 2
Plot of Initial Rate (Δ[2]/Δt) versus [Pd]2 Showing 2nd Order Kinetics in [Pd]
Figure 3
Figure 3
Plot of Initial Rate (Δ[2]/Δt) versus [1]−3 Showing Inverse 3rd Order Kinetics in 1
Figure 4
Figure 4
Job plot of Δδ•χ (mole fraction of substrate) versus χ at 110 °C
Figure 5
Figure 5
δ as a Function of [4] at 110 ºC
Figure 6
Figure 6
Hammett for Pd-Catalyzed C–H Arylation of 1 with [Mes–I–Ar]BF4
Figure 6
Figure 6
Hammett for Pd-Catalyzed C–H Arylation of 1 with [Mes–I–Ar]BF4
Figure 7
Figure 7
Two Alternative Formulations for Intermediate 9: PdIV/PdII (9a) versus PdIII∼PdIII (9b)
Figure 8
Figure 8
Related PdIII∼PdIII and PtIII∼PtIII Complexes from the Literature
Scheme 1
Scheme 1
Originally Proposed Catalytic Cycle for Pd-Catalyzed C–H Arylation
Scheme 2
Scheme 2
Observation of 7 Under the Catalytic Reaction Conditions
Scheme 3
Scheme 3
Proposed Mechanism for C–H Arylation of 3-Methyl-2-phenylpyridine
See this image and copyright information in PMC

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    1. Kalyani D, Deprez NR, Desai LV, Sanford MSJ. Am. Chem. Soc. 2005;127:7330. - PubMed
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