Tetrakis(acetonitrile)palladium Tetrafluoroborate


[21797-13-7]  · C8H12B2F8N4Pd  · Tetrakis(acetonitrile)palladium Tetrafluoroborate  · (MW 444.28)

(catalyst for isomerization and rearrangement of alkenes1 and strained carbocycles,1,2 polymerization of vinyl monomers1,2 and reagent for preparation of more stable Pd2+ complexes3)

Physical Data: yellow to bright yellow solid; mp 230 °C (dec).

Solubility: sol polar solvents such as MeCN, MeNO2; insol less polar solvents.

Preparative Methods: commercially available but it is easily prepared from either spongy palladium metal4,5 or Palladium(II) Chloride.5b,6

Handling, Storage, and Precautions: air and moisture sensitive.

Double Bond Isomerization and Skeletal Rearrangements.

Double bond isomerizations catalyzed by [Pd(MeCN)4](BF4)2 occur mostly at room temperature. Most often, the thermodynamically most stable alkene predominates,1 but an example has been noted where the product ratio is kinetically controlled (eq 1).7 The efficacy of this electrophilic catalyst in isomerizations is illustrated by fast skeletal rearrangements of alkenes (eq 2),1,5b substituted cyclopropanes (eq 3),1,5b and cyclopropenes (eq 4)5b at 25 °C.

Oligomerization and Polymerization of Vinyl Compounds.

[Pd(MeCN)4](BF4)2 has been found to be a very effective catalyst for highly regioselective dimerization of acrylic esters (eq 5) in the presence of Lithium Tetrafluoroborate.8 It catalyzes the polymerization of vinyl monomers and alkynes at room temperature.1,5b,9 In the polymerization of norbornene (eq 6)2,5b,9 and norbornadiene5b,9 by this catalyst, the bicyclic structure is retained intact. Both cationic1,5b and insertion2 mechanisms have been suggested for these Pd2+-catalyzed processes.

In the presence of ligands which bind more strongly to palladium than MeCN, [Pd(MeCN)4](BF4)2 catalyzes the copolymerization of CO with alkenes. The addition of two styrene molecules to CO is highly regiospecific when a solution of this catalyst and styrene in THF is placed under CO and H2 pressure in the presence of 1,3-diphenylphosphinopropane (dppp) (eq 7).10 Similarly, CO and ethylene give a polyketone when treated with [Pd(MeCN)4](BF4)2 in the presence of a phosphine ligand at room temperature.11 Cotelomerization of CO2 with butadiene using the same catalyst and other ligand additives has been reported to give d-lactones with high selectivity.12

Preparation of More Stable Pd2+ Complexes.

Because of the lability of the acetonitrile ligands of [Pd(MeCN)4](BF4)2, other cationic and neutral Pd2+ complexes are conveniently prepared from it either in a separate step3 or in situ.10-12

1. Sen, A.; Lai, T-W. JACS 1981, 103, 4627.
2. (a) Mehler, C.; Risse, W. Macromolecules 1992, 25, 4226; (b) Mehler, C.; Risse, W. Makromol. Chem., Rapid Commun. 1991, 12, 255; (c) Mehler, C.; Breunig, S.; Risse, W. Polym. Prepr., ACS Div. Polym. Chem. 1991, 32, 337.
3. DuBois, D. L.; Miedaner, A. JACS 1987, 109, 113.
4. Wayland, B. B.; Schramm, R. F. IC 1969, 8, 971.
5. (a) Sen, A.; Lai, T-W. IC 1984, 23, 3257. (b) Sen, A.; Lai, T-W.; Thomas, R. R. JOM 1988, 358, 567. (c) Sen, A.; Thomas, R. R. Inorg. Synth. 1989, 26, 128.
6. Werner, H.; Bertleff, W. ICA 1980, 43, 199.
7. McKinney, R. J. OM 1985, 4, 1142.
8. (a) Nugent, W. A.; Hobbs, Jr., F. W. JOC 1983, 48, 5364; (b) Nugent, W. A.; Hobbs, Jr., F. W. OS 1988, 66, 52.
9. Sen, A.; Lai, T-W. OM 1982, 1, 415.
10. Pisano, C.; Mezzetti, A.; Consiglio, G. OM 1992, 11, 20.
11. Sen, A.; Lai, T-W. OM 1984, 3, 866.
12. Braunstein, P.; Matt, D.; Nobel, D. JACS 1988, 110, 3207.

Godson C. Nwokogu

Hampton University, VA, USA

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