(1) (-)-cis

[12084-44-5]  · C10H15Cl2NPt  · (-)-Dichloro(ethylene)(a-methylbenzylamine)platinum(II)  · (MW 415.22) (2) (-)-trans


(determination of % ee of alkenes and allenes via 195Pt NMR;1 resolution of alkenes;2 asymmetric epoxidation of alkenes3)

Physical Data: trans isomer: mp 71 °C, [a]21D + 15.5-16.9° (c 1.0, CH2Cl2), usually obtained as a viscous oil but can be crystallized upon further purification;2g cis isomer: mp 164 °C, [a]25D -54.5° (c 1.3, acetone), obtained as pale green-yellow needles.4

Solubility: both the cis and trans isomers are sol acetone and dichloromethane.

Analysis of Reagent Purity: trans isomer: 1H NMR (CD2Cl2) d 7.39 (s, 5H), 4.62 (t, J = 30.5 Hz, 4H), 1.78 (d, J = 6.5 Hz, 3H);2g for 13C and 195Pt NMR data see Pregosin et al.5

Preparative Methods: trans isomer: synthesized from Zeise's salt [K2PtCl3(ethylene)] by adding (+)- or (-)-a-methylbenzylamine under acidic conditions;2g cis isomer: synthesized by adding 2 equiv of (+)- or (-)-a-methylbenzylamine to an aqueous solution of K2PtCl4 and then exposing this material to ethylene under pressure.4

Purification: trans isomer: chromatography over silica with CH2Cl2 as eluent;2g cis isomer: recrystallization from 1:1 acetone/n-heptane or toluene.4

Handling, Storage, and Precautions: both isomers are air and water stable.

Determination of % ee via 195Pt NMR.

The cis chiral complex has been used to determine enantiomeric purity of asymmetric allenes1a and allylic alcohols and ethers1b via complexation and 195Pt NMR spectroscopy. The complexes (3) and (4) are generated by displacement of ethylene from (1) by the alkene; recovery of the alkene and (1) is effected by the reverse sequence employing excess ethylene.1b

Resolving Agent.

A variety of chiral alkenes have been resolved via complexation and crystallization including alkenes (5)-(7) (via 1),2a cis,trans-1,5-cyclooctadiene (8) (via 2),2b 2-vinyltetrahydropyran (9) (via 1),2c,d 1,2-cyclononadiene (10) (via 2),2e trans-cyclooctene (11) (via 2),2f and spiro[3.3]hepta-1,5-diene (12) (via 2).2g

Asymmetric Epoxidation.

McKervey and co-workers have effected the asymmetric epoxidation of humulene. Complexation of humulene with (2) in a 1:2 ratio followed by peracid oxidation gave (-)-humulene 1,2-epoxide in 37% ee (eq 1).3

1. (a) Salvadori, P.; Uccello-Barretta, G.; Lazzaroni, R.; Caporusso, A. M. CC 1990, 1121. (b) Salvadori, P.; Uccello-Barretta, G.; Bertozzi, S.; Settambolo, R.; Lazzaroni, R. JOC 1988, 53, 5768.
2. (a) Lazzaroni, R.; Salvadori, P.; Pino, P. TL 1968, 9, 2507. (b) Cope, A. C.; Hecht, J. K.; Johnson, H. W., Jr.; Keller, H.; Winkler, H. J. S. JACS 1966, 88, 761. (c) Lazzaroni, R.; Uccello-Barretta, G.; Pini, D; Pucci, S.; Salvadori, P. JCR(S) 1983, 286. (d) Lazzaroni, R.; Uccello-Barretta, G.; Bertozzi, S.; Bertucci, C.; Marchetti, F. JCR(S) 1984, 286. (e) Cope, A. C.; Moore, W. R.; Bach, R. D.; Winkler, H. J. S. JACS 1970, 92, 1243. (f) Cope, A. C.; Ganellin, C. R.; Johnson, H. W., Jr.; Van Auken, T. V.; Winkler, H. J. S. JACS 1963, 85, 3276. (g) Hulshof, L. A.; McKervey, M. A.; Wynberg, H. JACS 1974, 96, 3906.
3. Chamberlain, T. R.; McKervey, M. A. CC 1969, 366.
4. Paiaro, G.; Panunzi, A. TL 1965, 6, 441.
5. Pregosin, P. S.; Sze, S. N.; Salvadori, P.; Lazzaroni, R. HCA 1977, 60, 2514.

Steven D. Paget

The Ohio State University, Columbus, OH, USA

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