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. 2010 Mar 24;132(11):3793-807.
doi: 10.1021/ja909371t.

Mechanism of C-F reductive elimination from palladium(IV) fluorides

Takeru Furuya  1 , Diego Benitez, Ekaterina Tkatchouk, Alexandra E Strom, Pingping Tang, William A Goddard 3rd, Tobias Ritter
Affiliations

Mechanism of C-F reductive elimination from palladium(IV) fluorides

Takeru Furuya et al. J Am Chem Soc. .

Erratum in

  • J Am Chem Soc. 2010 Apr 28;132(16):5922

Abstract

The first systematic mechanism study of C-F reductive elimination from a transition metal complex is described. C-F bond formation from three different Pd(IV) fluoride complexes was mechanistically evaluated. The experimental data suggest that reductive elimination occurs from cationic Pd(IV) fluoride complexes via a dissociative mechanism. The ancillary pyridyl-sulfonamide ligand plays a crucial role for C-F reductive elimination, likely due to a kappa(3) coordination mode, in which an oxygen atom of the sulfonyl group coordinates to Pd. The pyridyl-sulfonamide can support Pd(IV) and has the appropriate geometry and electronic structure to induce reductive elimination.

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Figures

Figure 1
Figure 1
Pd(IV) fluoride complexes 1–3 analyzed in this study.
Figure 2
Figure 2
ORTEP diagram of the Pd(IV) difluoride 3 (left) and characteristic 13C–19F coupling constants (right). Selected bond lengths [Å] and angles [°]: Pd–F(1) 2.040(3), Pd–F(2) 1.955(3), Pd–C(35) 2.008(5), Pd–N(13) 2.019(4), Pd–N(1) 2.027(5), Pd–N(26) 2.012(5), F(1)–Pd–F(2) 88.27(13)°, F(2)–Pd–N(13) 173.48(15)°.
Figure 3
Figure 3
HOM2DJ spectrum and 1H–19F couplings. The 1H NMR is shown in the X axis and the 1H–1H coupling constants are shown in the Y axis. The doublet of doublets resulting from 1H–1H scalar coupling constants are resolved in the Y axis. Two coupling constants (2 Hz, 8 Hz) out of three shown in the Figure for the doublet of doublets of doublets are resolved in the Y axis. The one remaining coupling constant (18 Hz) is resolved only in the X-axis and, hence, corresponds to a 1H–19F coupling.
Figure 4
Figure 4
Characteristic NOE signals for configuration determination.
Figure 5
Figure 5
Considered structures for the cationic Pd(IV) fluoride complex. The data are consistent with structure 1.
Figure 6
Figure 6
Comparison of the temperature-dependent 1H NMR spectra of 1 and 2.
Figure 7
Figure 7
Energy minimized structure of 1. The computed energy difference (ΔH298) between 1 and 1b is 2.2 kcal·mol−1 favoring 1.
Figure 8
Figure 8
Methods employed in this mechanistic study.
Figure 9
Figure 9
Rate dependence on pyridine concentration.
Figure 10
Figure 10
Hammett study by independent modification of the sulfonamide, benzo[h]quinolyl, and pyridine ligand substitution.
Figure 11
Figure 11
Hammett plot for sulfonamide substitution.
Figure 12
Figure 12
Hammett Plot for pyridine (pyridyl-sulfonamide) substitution.
Figure 13
Figure 13
Hammett plot for benzo[h]quinoline substitution for complexes 8a–g.
Figure 14
Figure 14
Hammett Plots of benzo[h]quinoline substitution for pyridine complexes 10a–g.
Figure 15
Figure 15
Rate dependence on pyridine concentration for the three 7-substituted benzo[h]quinolyl Pd(IV) pyridine complexes 2, 10a, and 10g.
Figure 16
Figure 16
Kinetic data of C–F reductive elimination from 3.
Figure 17
Figure 17
Considered mechanisms for reductive elimination from 1. The data are consistent with mechanism (2b).
Figure 18
Figure 18
Two potential Y-shaped Pd(IV) transition states for C–F reductive elimination.
Figure 19
Figure 19
Computed transition state 1‡ for reductive elimination from 1 and predicted transition state based on Hammett analysis.
Scheme 1
Scheme 1
Fluorination of functionalized arylboronic acids via arylpalladium(II) complexes by the electrophilic fluorination reagent F-TEDA-BF4
Scheme 2
Scheme 2
Pd(II) product 11 after reductive elimination; ORTEP representation of Pd(II) fluoride complex 11 with ellipsoids drawn at 50% probability (hydrogen atoms omitted for clarity). Pd-F: 1.981 Å.
Scheme 3
Scheme 3
Proposed mechanism for C–F reductive elimination from 1.
Scheme 4
Scheme 4
Proposed rationale for the dependence of fluorination on solvent and reaction temperature.
Scheme 5
Scheme 5
Oxidation and reductive elimination supported by the pyridyl-sulfonamide ligand.
See this image and copyright information in PMC

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