[29933-60-6; 15614-66-1]  · C36H30O2P2Pd  · Peroxybis(triphenylphosphine)palladium  · (MW 663.02)

(an oxygen carrier for mild oxidation of alkenes,1 sulfur compounds,2 and oximes3)

Alternate Name: dioxygenbis(triphenylphosphine)palladium.

Physical Data: described as green crystalline solid; mp 105 °C (darkens); 140-143 °C (melts);4 also described as pale blue powder; mp 100 °C (dec).5

Solubility: sol CH2Cl2.

Preparative Methods: prepared by bubbling oxygen through a solution of Tetrakis(triphenylphosphine)palladium(0) in a carbon dioxide-free mixture of CH2Cl2 and diethyl ether4 or benzene,6 or by bubbling oxygen through a carbon dioxide-free solution of bis(triphenylphosphine)palladium in benzene.5

Purification: recrystallization from a 1:1 mixture of CH2Cl2 and ether with oxygen bubbling through continuously.4

Handling, Storage, and Precautions: the solid and its solutions decompose in a few days to metallic palladium and oxygen or phosphine oxide.

Oxygenation of Alkenes.

Electron-deficient alkenes and a,b-unsaturated carbonyl compounds react with (PPh3)2PdO2 to form five-membered ring dioxapalladacycles in high yields below room temperature (eq 1).1 At temperatures above 25 °C these dioxapalladacycles break down to a ketone and an oxapalladacyclopropane, where the lone carbon in the heterocyclopropane is the carbon of the alkene bearing the electron-withdrawing groups (eq 2).1 If the dioxapalladacycle is treated with Trifluoroacetic Acid, an epoxide is obtained in high yield and with high stereoselectivity where applicable (eq 2).1

Electron-rich alkenes are epoxidized by (PPh3)2PdO2 only in the presence of acid derivatives (eq 3).2 The need for the acid derivative has been suggested to imply that a peroxy acid-palladium complex is the active oxidizing agent. The O2 of (PPh3)2PdO2 adds to reactive dienes under thermal or photochemical conditions to give endoperoxides which can break down to diketones.7 For example, 1,3-diphenylisobenzofuran reacts with (PPh3)2PdO2 to give a mixture of endoperoxide and o-dibenzoylbenzene (eq 4). 9,10-Diphenylanthracene, however, is unreactive under thermal conditions, but on irradiation gives an endoperoxide which breaks down to o-dibenzoylbenzene (eq 5). Photochemical reactions involving (PPh3)2PdO2 must avoid the presence of alkyl halides and the use of alkyl halogenated solvents, because zerovalent palladium species that may be present react with aliphatic halides to give (PPh3)2PdX2 and the oxygen atoms of the peroxy complex are diverted to the formation of phosphine oxide under these conditions.8

Other Oxygenation Reactions.

(PPh3)2PdO2 effectively converts base- and acid-sensitive ketoximes to ketones (eq 6).3 In the presence of acid derivatives, sulfides are oxidized to sulfoxides and sulfoxides are oxidized to sulfones in good yield (eq 7).2

1. Osborne, R. B.; Ibers, J. A.; Sheldon, R. A.; Van Doorn, J. A. JOM 1975, 94, 115.
2. Mashino, T.; Nagano, T.; Hirobe, M. CPB 1988, 36, 1997.
3. Maeda, K.; Moritani, I.; Hosokawa, T.; Murahashi, S-I. TL 1974, 797.
4. Nyman, C. J.; Wymore, C. E.; Wilkinson, G.; JCS(A) 1968, 561.
5. Urata, H.; Suzuki, H., Moro-Oka, Y., Ikawa, T., JOM 1989, 364, 235.
6. Wilke, G.; Schatt, H.; Heimbach, P. AG(E) 1967, 6, 92.
7. Dagonneau, M.; Fauvarque, J. F. JOM 1983, 241, 113.
8. Deal, D.; Zink, J. I. IC 1981, 20, 3995.

Godson C. Nwokogu

Hampton University, VA, USA

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