[29964-62-3]  · C28H28Cl2P2Pd  · Dichloro[1,4-bis(diphenylphosphino)butane]palladium(II)  · (MW 603.80)

(useful for the catalysis of styrene carbonylation,1 coupling of alkyl Grignard reagents with organic halides,2 selective monoalkylation of organic polyhalides,3 and modification of the dihalovinyl moiety of synthetic pyrethroids4)

Solubility: commonly used in ethanol, benzene, and ethereal solvents.

Form Supplied in: cream colored powder.

Preparative Methods: can be prepared conveniently in situ by mixing the bidentate phosphine ligand and (PhCN)2PdCl2 in either benzene or chloroform.1 The preparation of (dppb)PdCl2 is also possible through the reaction of PdCl2 with dppb in acetone, a process that slowly forms the catalyst as a white precipitate which can be isolated in 51% yield.5 Preparation of the hydrate complex is possible via the reaction of Na2[PdCl4] with dppb in a mixture of CH2Cl2 and water.5

Handling, Storage, and Precautions: hygroscopic.

Carbonylation of Styrene.

One of the earliest uses of (dppb)PdCl2 was for the catalytic carbonylation of styrene (eq 1).1 The product distribution from this reaction depends on the nature of the phosphine ligand, Ph2P(CH2)nPPh2, and was examined for n = 1-6 and 10 (the n = 2 ligand did not show catalytic activity). The selectivity appears to depend on the coordinating power of the phosphine ligand, where strongly coordinating bidentate ligands (n = 3 or 4) create a steric environment that suppresses formation of the branched ester (2). The highest selectivity for the formation of (2) is obtained with a derivative of the dppb ligand, DIOP ((2,3-O-Isopropylidene)-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane).

Coupling Reactions.

Investigation of the activity of various bisphosphine-Pd and -Ni complexes in the coupling of s-butylmagnesium chloride with aryl or vinyl bromides shows that (dppb)PdCl2 is relatively selective (eq 2).2 In comparison, Dichloro[1,1-bis(diphenylphosphino)ferrocene]palladium(II), (dppf)PdCl2, is far more effective. The increased selectivity of the dppf ligand is attributed to the larger P-Pd-P angle and smaller Cl-Pd-Cl angle imposed by the presence of the ligand. Overall, the selectivity for the ligands is: (dppf)PdCl2 >> (dppb)PdCl2 &egt; (dppp)PdCl2 > (PPh3)4Pd > (PPh3)2PdCl2 > (dppe)PdCl2. Although (dppp)NiCl2 is the most selective nickel catalyst for such transformations, (dppf)PdCl2 is even more effective. The use of these catalysts allows for coupling with secondary alkyl groups and with alkyl groups containing b-hydrogens.2

The use of (dppb)PdCl2 promotes selective monoalkylation of organic polyhalides to produce 1-substituted (Z)-1-chloroalkenes from 1,1-dichloro-1-alkenes and either Grignard or organozinc reagents (eq 3).3 Alkyl, aryl, and heteroaryl Grignard or zinc reagents are effective in this coupling reaction. Even trichloroethylene undergoes this coupling reaction at the expected position. The regioselectivity of this reaction depends upon the presence of substituent R1.3 In addition, the use of (PPh3)2PdCl2 rather than (dppb)PdCl2 gives mainly diarylation products. This procedure provides a viable alternative to Wittig alkenation for the preparation of unsymmetrically trisubstituted alkenes since aldehydes can easily be transformed into 1,1-dichloroalkenes.

Work toward modification of the dihalovinyl moiety of synthetic pyrethroids such as permethrin, cypermethrin, and deltamethrin, which are present in many household and agricultural insecticides, has progressed due to the application of similar palladium catalyzed coupling reactions.4 The reaction of an organozinc complex in the presence of (dppb)PdCl2 provides a pathway for the direct stereoselective transformation of (2,2-dihalovinyl)dimethylcyclopropanecarboxylates into [(Z)-2-substituted 2-halovinyl]dimethylcyclopropanecarboxylates (eq 4).4

Similar reactions are known for the catalytic system formed from Pd(OAc)2 and dppb. This system is used for affecting regioselective hydrocarboxylation of alkenes,6 and for regioselective arylation of unsymmetrical alkenes7 and acyclic enol ethers.8

In addition, the combination of (dppb)PdCl2 and CuO has been shown to be a useful catalytic system for the Stille cross coupling of 2-tributylstannylpyridine with halobenzenes and aromatic heterocyclic halides.9

Related Reagents.

Dichloro[1,4-bis(diphenylphosphino)butane]palladium(II); Dichloro[1,2-bis(diphenylphosphino)ethane]palladium(II); Dichloro[1,1-bis(diphenylphosphino)ferrocene]palladium(II); Tetrakis(triphenylphosphine)palladium(0).

1. Sugi, Y.; Bando, K.-I. CL 1976, 727.
2. Hayashi, T.; Konishi, M.; Kobori, Y.; Kumada, M.; Higuchi, T.; Hirotsu, K. JACS 1984, 106, 158.
3. Minato, A.; Suzuki, K. JACS 1987, 109, 1257.
4. Minato, A. JOC 1991, 56, 4052.
5. Sanger, A. R. JCS(D) 1977, 1971.
6. (a) Ali, B. E.; Alper, H. J. Mol. Catal. 1992, 77, 7. (b) Ali, B. E.; Alper, H. JOC 1993, 58, 3595.
7. Cabri, W.; Candiani, I.; Bedeschi, A.; Santi, R. JOC 1992, 57, 3558.
8. Cabri, W.; Candiani, I.; Bedeschi, A.; Penco, S.; Santi, R. JOC 1992, 57, 1481.
9. Gronowitz, S.; Björk, P.; Malm, J.; Hömfeldt, A.-B. JOM 1993, 460, 127.

Nancy S. Barta & John R. Stille

Michigan State University, East Lansing, MI, USA

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