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. 2008 Jan;64(36):8271-8278.
doi: 10.1016/j.tet.2008.04.105.

A Colorimetric Chemodosimeter for Pd(II): A Method for Detecting Residual Palladium in Cross-Coupling Reactions

Ronald J T Houk  1 , Karl J Wallace, Himali S Hewage, Eric V Anslyn
Affiliations

A Colorimetric Chemodosimeter for Pd(II): A Method for Detecting Residual Palladium in Cross-Coupling Reactions

Ronald J T Houk et al. Tetrahedron. 2008 Jan.

Abstract

A colorimetric chemodosimeter (SQ1) for the detection of trace palladium salts in cross-coupling reactions mediated by palladium is described. Decolorization of SQ1 is affected by nucleophilic attack of ethanethiol in basic DMSO solutions. Thiol addition is determined to have an equilibrium constant (K(eq)) of 2.9 × 10(6) M(-1), with a large entropic and modest enthalpic driving force. This unusual result is attributed to solvent effects arising from a strong coordinative interaction between DMSO and the parent squaraine. Palladium detection is achieved through thiol scavenging from the SQ1-ethanethiol complex leading to a color "turn-on" of the parent squaraine. It was found that untreated samples obtained directly from Suzuki couplings showed no response to the assay. However, treatment of the samples with aqueous nitric acid generates a uniform Pd(NO(3))(2) species, which gives an appropriate response. "Naked-eye" detection of Pd(NO(3))(2) was estimated to be as low as 0.5 ppm in solution, and instrument-based detection was tested as low as 100 ppb. The average error over the working range of the assay was determined to be 7%.

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Figures

Figure 1
Figure 1
1H-NMR of SQ1 with ethanethiol in the presence of DBU in CHCl3-d. [SQ1]0 = 37 mM; [DBU]0 = 37 mM; [EtSH]0 = 185 mM.
Figure 2
Figure 2
Van’t Hoff analysis of SQ1:SEt at 1.2 × 10-5 M. A) Spectral data of free SQ1 at tempuratures from 288.5 K to 317.8 B) van’t Hoff plot of lnKeq vs. 1/T.
Figure 3
Figure 3
Titration of Pd(OAc)2 into a solution of SQ1:SEt at 2.35 × 10-5 M in DMSO. SQ1:SEt complexation was facilitated with 1 equivalent of ethanethiol and 2 equivalents of DBU.
Figure 4
Figure 4
Titration of Pd(PPh3)2Cl2 into a solution of SQ1:SEt at 2.35 × 10-5 M in DMSO. SQ1:SEt complexation was facilitated with 1 equivalent of ethanethiol and 2 equivalents of DBU
Figure 5
Figure 5
Titration data for Pd(NO3)2 into SQ1:SEt (1.18 × 10-5 M in DMSO) formed with ethanethiol and 2 equivalents DBU. A) Spectra. B) Isotherm showing apparent 2:1 thiol:palladium interaction. Dotted line—extrapolation of initial slope; dotted and dashed line—absorbance at full recovery.
Figure 6
Figure 6
Titration of Pd(NO3)2 into 8.8 × 10-6 M SQ1:SEt in DMSO formulated with ethanethiol and Verkade base VB. Titration was conducted after 4 hours reaction time between squaraine SQ1 and ethanethiol.
Figure 7
Figure 7
Titration of Pd(NO3)2 into 8.8 × 10-6 M SQ1:SEt in DMSO formulated with ethanethiol and Verkade base VB. Titrations were conducted after 12-15 hours reaction time between squaraine SQ1 and ethanethiol
Figure 8
Figure 8
A) Normalized kinetic traces of calibration curve data using a series of samples of increasing palladium concentration. Below 1 equivalent shown in black, above shown in red. The inset shows the half-time. [SQ1:SEt] = 1.2 × 10-5; [Pd] range = 9 × 10-7 to 1.5 × 10-5
Figure 9
Figure 9
Isotherm and curve fit of kinetically monitored titration. Isotherm was fit using a sigmoidal Richards type 1 function with the Origin graphing software.
Scheme 1
Scheme 1
Decolorization of SQ1 with ethanethiol followed by palladium(II) scavenging.
Scheme 2
Scheme 2
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References

    1. Liesen PJ, Varma RS, Naicker KP. Tetrahedron Lett. 1999;40:2075–2078.
    1. Liu W-J, Xie Y-X, Liang Y, Li J-H. Synthesis. 2006:860–864.
    1. Baxter JM, Steinhuebel D, Palucki M, Davies IW. Org Lett. 2005;7:215–218. - PubMed
    1. Buchwald SL, Mauger C, Mignani G, Scholzc U. Adv Synth Catal. 2006;348:23–39.
    1. Arvela Riina K, Leadbeater NE, Collins Michael J., J Tetrahedron. 2005;61:9349–9355.

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