[2,6-Bis[(bis(1-methylethyl)phosphino-P]methyl]-3,5 dimethylphenyl]methyl-C]tri-fluoroacetato-O)palladium1

[198414-94-7]  · C25H41F3O2P2Pd  · (MW 598.94)

(reagent used as an efficient, stable catalyst for the coupling of aryl halides with alkenes [the Heck reaction])

Solubility: soluble in benzene, toluene, chloroform, THF, dioxane, DMF, and NMP.

Form Supplied in: yellow crystals; not commercially available.

Analysis of Reagent Purity: 1H NMR (C6D6): d = 0.73 (dd, 3JH,H;H,P = 7.1 and 6.7 Hz, 6H, CH3), 0.88 (dd, 3JH,H;H,P = 7.3 and 8.1 Hz, 6H, CH3), 1.05 (dd, 3JH,H;H,P = 7.1 and 6.7 Hz, 6H, CH3), 1.15 (dd, 3JH,H;H,P = 7.3 and 8.1 Hz, 6H, CH3), 1.76, 1.96 (m, 2H, CH), 2.11 (s, 6H, CH3), 2.33 (t, 3JH,P = 9.6 Hz, 2H, Pd-CH2), 2.36 (d, 2JH,H = 14.9 Hz, 2H, right part of a AB quartet, P-CH2), 2.63 (dt, 2JH,H = 14.9 Hz, 2JH,P = 4.6 Hz, 2H, left part of a AB quartet, P-CH2), 6.51 (s, 1H, Ar-H); 13C NMR (C6D6): d = 9.8 (brs, Pd-CH2), 16.8 (brs, CH3), 17.5 (vt, JP,C = 1.9 Hz, CH3), 18.0 (brs, CH3), 18.2 (vt, JP,C = 3.0 Hz, CH3), 19.5 (s, Ar-CH3), 21.3 (vt, JP,C = 8.3 Hz, CH2), 25.4 (vt, JP,C = 6.5 Hz, CH), 25.7 (vt, JP,C = 6.4 Hz, CH), 125.1 (s, Cp), 130.0 (s, Cm), 132.1 (vt, JP,C = 1.6 Hz, Co), 142.4 (vt, JP,C = 4.7 Hz, Ci); 31P NMR (C6D6): d = 86.6 (s).

Handling, Storage, and Precautions: although the compound is air stable, it is recommended to keep it under nitrogen for long-term storage. Incompatible with acids, oxidizing and reducing agents.

Preparation

To a solution of 60 mg (0.18 mmol) of Pd(OCOCF3)2 in 8 ml of THF under a nitrogen atmosphere were added 76 mg (0.2 mmol) of 1,3-bis(diisopropylphos-phinomethyl)-2,4,6-trimethyl-benzene. After stirring at 60 °C for 4 h, all volatile compounds were removed in vacuo and the yellow-brown residue was recrystallized from a THF/pentane mixture at -20 °C. The yellow crystalline product was isolated by separation from the solvent and was dried in vacuo. Yield: 86 mg (80%) of the clean Pd(II) complex (yellow crystals).

Catalysis of the Heck Reaction

The Pd complex is an efficient catalyst for the Heck reaction1,2 using aryl bromides or iodides and acrylate esters or styrene derivatives (1). The reactions can be run under air.

A sealed vessel is used when substrates boiling below 140 °C are employed. Very low catalyst loading is required and various bases and polar solvents can be used. The catalyst remains active after the reaction is complete and upon addition of more substrates catalysis is resumed. Shorter reaction times are required with higher catalyst loading. The reaction tolerates various functional groups on the arene and is faster with electron-withdrawing substituents. Aryl chlorides are not reactive.

Reaction of bromobenzene with methyl acrylate using N-methyl-pyrrolidone (NMP) solvent and sodium carbonate as base is a typical example (2). The analogous catalyst which contains two five-membered chelating rings and an aryl-Pd bond is less efficient with aryl bromides.1


1. (a) Ohff, M.; Ohff, A.; van der Boom, M. E.; Milstein, D., J. Am. Chem. Soc. 1997, 119, 11687. (b) Corriganda: J. Am. Chem. Soc. 1998, 120, 3273.
2. (a) Heck, R. F., Palladium Reagents in Organic Synthesis, Academic Press: London, 1985. (b) de Meijere, A.; Meyer, F. E., Angew. Chem. Int. Ed. 1994, 33, 2379. (c) Cabri, W.; Candiani, I., Acc. Chem. Res. 1995, 28, 2. (d) Beletskaya, I.-P.; Chepkarov, A. V., Chem. Rev. 2000, 100, 3009. (e) de Vries, J. G., Can. J. Chem. 2001, 79, 1086.

David Milstein

The Weizmann Institute of Science, Rehovot, Israel



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