[77933-52-9]  · C4H6ClN3O2Pd  · Bis(acetonitrile)chloronitropalladium(II)  · (MW 269.98)

(reagent capable of catalyzing the oxidation of alkenes to ketones,2 aldehydes,3 or epoxides4)

Physical Data: yellow solid, mp 107-109 °C.2

Solubility: sol chloroform, benzene, acetonitrile.

Analysis of Reagent Purity: 1H NMR (CDCl3) 2.19 (s).2

Preparative Method: prepared from the reaction of Pd(MeCN)2Cl2 (formed from Palladium(II) Chloride and acetonitrile) with 1 equiv of Silver(I) Nitrite in Acetonitrile.2 Removal of the silver chloride after 1 h by filtration and evaporation of the solvent gives the required complex in quantitative yield.

Handling, Storage, and Precautions: the complex should be stored under an inert atmosphere. Palladium compounds are reported to be mildly toxic. Acetonitrile is highly flammable and lachrymatory.

Reactions of Alkenes.

Bis(acetonitrile)chloronitropalladium(II) can act as an efficient catalyst for the oxidation of alkenes to ketones.2 The reaction frequently gives good yields and high selectivity, even for acid sensitive substrates such as 2-methyl-3-buten-2-ol (eq 1).5

Occasionally the rate for the reaction can be too low. In such situations the rate can be dramatically increased by making the catalyst a cationic palladium complex.6 This can be achieved by the addition of a silver salt. For instance, if Silver(I) Hexafluoroantimonate is added to the palladium complex the rate of oxidation of oct-1-ene to octan-2-one in THF shows a 20-fold rate increase over the neutral palladium species. Under these conditions and over longer periods of time, the resultant ketone can undergo oxydehydrogenation to give the a,b-unsaturated ketone. In the case of cyclohexene the reaction can proceed even further to form phenol (eq 2).

If bis(acetonitrile)chloronitropalladium(II) is treated with Copper(II) Chloride in t-butanol at 55 °C, a new catalyst is formed which will catalyze the oxidation of terminal alkenes to aldehydes (60-70% yields) with reasonable selectivity (eq 3).3

These conditions also enhance the rate of reaction and by carrying out the reaction in a 1:1 mixture of t-butanol and N,N-diethylpivaloylamide,7 instead of just t-butanol, the selectivity can be changed to favor formation of the ketone (generally with >90% selectivity).

If the alkene being oxidized is more sterically constrained, the hydrogen migration necessary to produce the ketone becomes disfavored and an epoxide is formed instead (eq 4).8 For this reaction to be efficient, the transformation must be carried out at low-to-moderate concentration. If the epoxidation of norbornene is attempted at high concentration, dimerization occurs to give a tetrahydrofuran adduct.9

1. (a) Beck, I. E.; Gusevskaya, E. V.; Stepanov, A. G.; Libholobov, V. A.; Nekipelov, V. M.; Yermakov, Y. I.; Zamaraev, K. I. J. Mol. Catal. 1989, 50, 167. (b) Chauvet, F.; Heumann, A.; Waegell, B. JOC 1987, 52, 1916.
2. Andrews, M. A.; Kelly, K. P. JACS 1981, 103, 2894.
3. Feringa, B. L. CC 1986, 909.
4. Heumann, A.; Chauvet, F.; Waegell, B. TL 1982, 23, 2767.
5. Derdar, F.; Martin, J.; Martin, C.; Brégeault, J. M.; Mercier, J. JOM 1988, 338, C21.
6. Wenzel, T. T. CC 1989, 932.
7. Kiers, N. H.; Feringa, B. L.; Van Leeuwen, P. W. N. M. TL 1992, 33, 2403.
8. Andrews, M. A.; Cheng, C. W. P. JACS 1982, 104, 4268.
9. Wong, P. K.; Dickson, M. K.; Sterna, L. L. CC 1985, 1565.

Kevin J. Smith

The Ohio State University, Columbus, OH, USA

Copyright 1995-2000 by John Wiley & Sons, Ltd. All rights reserved.