Tetrakis(pyridine)copper(I) Perchlorate

(py)4Cu+ ClO4-

[21465-66-7]  · C20H20ClCuN4O4  · Tetrakis(pyridine)copper(I) Perchlorate  · (MW 479.44)

(catalyst for the decomposition of diazonium salts)

Physical Data: light yellow crystals;2,7 d 1.47 g cm-3;7 IR n 1085 (ClO4-), 616 (py) cm-1.2,8

Solubility: sol pyridine, MeCN.

Form Supplied in: prepared as needed.

Analysis of Reagent Purity: iodometric determination of Cu.2

Preparative Methods: conveniently prepared from the tetrakis(acetonitrile) complex1 by reaction with Pyridine in a 1:4 molar ratio under nitrogen.2

Purification: drying in vacuo at rt.

Handling, Storage, and Precautions: irritant; moisture sensitive; handle under inert atmosphere. Occasional mild explosions have been reported with dry organic perchlorate salts.9 Use in a fume hood.

Decomposition of Aryl Diazonium Salts.

The homolytic decomposition of aryl diazonium salts can be catalyzed effectively by copper(I) salts. For example, Copper(I) Oxide accelerates homolytic carbon-nitrogen bond scission and eliminates the competitive heterolytic pathway in the decomposition of 2-diazobenzophenone tetrafluoroborate at 45 °C.5,6 However, Cu2O has the disadvantage of being effective only in highly acidic media, due to its insolubility in neutral water. The title reagent was shown3,4 to be an effective catalyst for diazonium salt decomposition in less acidic media (pH = 6.2). Similar complexes, e.g. Tetrakis(acetonitrile)copper(I) Perchlorate and Tetrakis(acetonitrile)copper(I) Tetrafluoroborate, disproportionated to CuII species too rapidly to be useful; nitrate complexes were too unstable to react with the diazonium salt. Many common cuprous salts, as well as CuH, failed to catalyze the reaction.3

The nature and concentration of the copper complexes significantly affect the distribution of products shown in eq 1. In the presence of CuII ions, high yields of 2-hydroxybenzophenone (1) could be obtained; with hydrogen-donating solvents such as ethanol, the major product was benzophenone (2). A similar heterocyclic amine complex, tris(2-picoline)copper(I) perchlorate, also proved useful as a catalyst, giving a dibenzoylbiphenyl dimer and 9-fluorenone (3) as the major products.

A kinetic study showed the relative rate constants for reduction, phenol formation, and cyclization of the intermediate radical to be 4, 2, and 1, respectively; in solutions containing 15% or more dioxane, however, the rate constant for phenol formation is drastically reduced by micelle formation. A pH-dependent competition between dimerization and cyclization was also observed.4

1. Hathaway, B. J.; Holah, D. G.; Postlethwaite, J. D. JCS 1961, 3215.
2. Chen, K-L.; Iwamoto, R. T. Inorg. Nucl. Chem. Lett. 1968, 4, 499.
3. Lewin, A. H.; Michl, R. J. JOC 1973, 38, 1126.
4. Lewin, A. H.; Michl, R. J. JOC 1974, 39, 2261.
5. Lewin, A. H.; Cohen, T. JOC 1967, 32, 3844.
6. Lewin, A. H.; Cohen, T.; Dinwoodic, A. H. T 1966, 22, 1527.
7. Lewin, A. H.; Michl, R. J.; Ganis, P.; Lepore, U.; Avitabile, G. CC 1971, 1400.
8. Chen, K-L. H.; Iwamoto, R. T. ICA 1971, 5, 97.
9. Kubota, M.; Johnston, D. L. J. Inorg. Nucl. Chem. 1967, 29, 769.

Edward J. Parish & Shengrong Li

Auburn University, AL, USA

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