Bis(benzonitrile)dichloroplatinum(II)

[14873-63-3]  · C14H10Cl2N2Pt  · Bis(benzonitrile)dichloroplatinum(II)  · (MW 472.25) (cis)

[15617-19-3] (trans)

[51921-56-3]

(catalyst for hydrogenation of nitro compounds5,7a and hydroformylation of alkenes;13 versatile starting material for complexes of platinum3)

Physical Data: mp 224 °C (dec).

Solubility: sol dichloromethane.

Form Supplied in: yellow crystalline solid.

Preparative Methods: prepared as a mixture of cis and trans complexes. The reaction of Palladium(II) Chloride in benzonitrile at room temperature for 7 h yields a mixture that can be separated chromatographically to yield 26% trans- and 58% cis-PtCl2(PhCN)2.1 An alternate route requires stoichiometric amounts of potassium tetrachloroplatinate(II) and benzonitrile stirred at room temperature for one week. Trituration of the product with hot benzene yields pure cis-PtCl2(PhCN)2 in 60% yield; the cooled benzene solution yields pure trans-PtCl2(PhCN)2 in 20% yield.2a,b

Purification: chromatography on silica gel with dichloromethane as eluant,1 or trituration with hot benzene.2a,b

Introduction.

The title reagent is frequently used as the starting material for preparation of organometallic complexes of platinum.3 The labile ligand, PhCN, can be easily displaced with various phosphorus(III) ligands, thereby modifying or improving the activity of the catalyst. Polymer-supported platinum catalysts are prepared by treating phosphole-containing copolymers with the title reagent. The resulting heterogeneous catalyst can be used in the presence of Tin(II) Chloride dihydrate to catalyze the hydroformylation of a variety of alkenic substrates.4

Hydrogenations.

The homogeneous hydrogenation of aliphatic nitro compounds is catalyzed by platinum metal phosphine complexes. These complexes are formed in situ by treating the title reagent, which possesses the labile ligand PhCN, with a phosphine reagent, for example (R)-N,N-Dimethyl-1-[(S)-2-(diphenylphosphino)ferrocenyl]ethylamine (PPFA) at 1000 psi (eq 1).5

Platinum catalysts have also been utilized in the reductive N-acylation of nitro compounds. The catalyst system requires the platinum catalyst, carbon monoxide, a Lewis acid (Tin(IV) Chloride), and a phosphorus(III) ligand. For example, the title reagent, when used in conjunction with Triphenylphosphine, SnCl4, acetic acid, and CO at 60 atm, yields acetanilide in 89% yield from nitrobenzene (eq 2).7a When ethanol is used in place of the acetic acid, the resulting product is the carbamate.7b

Carbonylations, Rearrangements, and N-Alkylations.

Platinum catalysts have been used for the carbonylation of alkyl, alkenyl, and alkynyl iodides under carbon monoxide pressure. The title reagent, when used in the presence of Tri-n-butylphosphine and Triethylamine, shows good catalytic activity in the methoxycarbonylation of 1-iodo-1-octyne (eq 3).6

The transformation of a primary amine to a secondary amine has also been catalyzed by the title reagent.8 Similar transformations have been reported with ruthenium9a,b and palladium10 catalysts. The title reagent, in the presence of the Lewis acid SnCl2.2H2O (Sn:Pt = 2.5:1), catalyzes the reaction of n-butylamine to give N,N-dibutylamine in 65% yield (eq 4). Other Lewis acids such as SnCl4, FeCl3, AlCl3 are not effective in this reaction.

Rearrangements of oxocyclopropanes to vinyl ethers can be accomplished using the title reagent.12a,b The rearrangement of cyclopropanes containing the combination of vicinal alkoxy and alkoxy-carbonyl substituents is facile when using PtCl2(PhCN)2 as the catalyst (eq 5). Other transition metal complexes, e.g. Tetracarbonyl(di-m-chloro)dirhodium and [Ru(CO)3Cl2]2, are also active catalysts in this system, as are Copper Bronze and Copper(I) Chloride.

N-Alkylation and N-allylation can be catalyzed by the title reagent in conjunction with SnCl2.2H2O.11 Reaction of aniline with an allylic alcohol gives N-allylated products (eq 6). The platinum catalyst does not catalyze isomerization of the allylic alcohol to the corresponding aldehyde.

The hydroformylation of 1-pentene is catalyzed by the title reagent, SnCl2.2H2O, and a bidentate phosphine ligand under carbon monoxide pressure. When the bidentate ligand is (-)-DIOP ((2,3-O-Isopropylidene)-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane) the reaction proceeds in 5 h at 100 °C, yielding 75% hexanal, 9% pentane, and 16% 2-pentene.13


1. Uchiyama, T.; Nakamura, Y.; Miwa, T.; Kawaguchi, S.; Okeya, S. CL 1980, 337.
2. (a) Maresca, L.; Natile, G.; Intini, F. P.; Gasparrini, F.; Tiripicchio, A.; Tiripicchio Camellini, M. JACS 1986, 108, 1180. (b) Hofmann, K. A.; Bugge, CB 1907, 40, 1772.
3. Hartley, F. R., The Chemistry of Platinum and Palladium; Applied Science: London, 1973; p 462.
4. Stille, J. K.; Deschenaux, R.; Parrinello, G. JOC 1986, 51, 4189.
5. Harsy, S. G. T 1990, 46, 7403.
6. Takeuchi, R.; Tsuji, Y.; Fujita, M.; Kondo, T.; Watanabe, Y. JOC 1989, 54, 1831.
7. (a) Watanabe, Y.; Tsuji, Y.; Kondo, T.; Takeuchi, R. JOC 1984, 49, 4451. (b) Watanabe, Y.; Tsuji, Y.; Takeuchi, R.; Suzuki, N. BCJ 1983, 56, 3343.
8. Tsuji, Y.; Shida, J.; Takeuchi, R.; Watanabe, Y. CL 1984, 889.
9. (a) Khai, B. Tl; Concilo, C.; Porzi, G. JOM 1981, 208, 249. (b) Jung, C. W.; Fellmann, J. D.; Garrou, P. E. OM 1983, 2, 1042.
10. Murahashi, S.; Yoshimura, N.; Tsumiyama, T.; Kojima, T. JACS 1983, 105, 5002.
11. Tsuji, Y.; Takeuchi, R.; Ogawa, H. Watanabe, Y. CL 1986 293.
12. (a) Doyle, M. P.; Van Leusen, D. JACS 1981, 103, 5917. (b) Doyle, M. P.; Van Leusen, D. JOC 1982, 47, 5326.
13. Hayashi, T.; Kawabata, Y.; Isoyama, T.; Ogata, I. BCJ 1981, 54, 3438.

Janet S. Plummer

Parke-Davis Pharmaceutical Research, Ann Arbor, MI, USA



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