2862 R-NHZ
+ NOCl +R-N=NOH + HC1 e
chloride-nitromethane (A1C1,-CH3NO,), vvhich was found more satisfactory than concentrated sulfuric acid R-N=N-OH NOCl --f R-N=N-ON0 for producing a number of cation radicals. Although A1C13-CH3N02 is known to produce cation radical^,^ R-NzN-ONO +R . + NS + NO2 except for p,p'-dimethoxybipheny16 the method does R . + C1-NO +R C 1 + NO not appear to have been used for the investigation of Re + solvent other products hyperfine structure. Further, we have not been able to find any comparisons of the two systems in the Decomposition of diazonitrite might be either spontaneliterature. ous or one step in a chain reaction, again by analogy For a number of radicals, such as the cation radicals with proposals of Buchholz and Powell. of 1,4-dimethoxybenzene and 1,4-diethaxybenzene, Whatever the mechanism, our results demonstrate the radical concentration obtained with A1C13-CH3N02 that a free-radical path for the decomposition of aliapproximates to 100 %, whereas the radical concentraphatic diazonium salts (or diazohydroxides) is energetition obtained in concentrated sulfuric acid was concally accessible and may compete with the usual carsiderably less than 1%.' Sometimes, the low radical bonium ion process whenever the latter is relatively unconcentration obtained in sulfuric acid solution does favorable. The formation of triptycene in the deaminanot permit analysis of the hyperfine structure. This tion of 9-aminotriptycene with nitrosyl chloride in was found to be the case for 1,4-di-n-butcixybenzene, etherlbsc and the formation of unrearranged chloride in where again the A1Cl3-CH3NO2 system gave a satisthe deamination of 3 '-amino-l,2-cyclopropanoacenaphfactory spectrum. The increased radical concentratheneI5 may be examples of such free-radical processes. tion of these compounds permits a spectral analysis We are investigating the latter possibility as well as to be made in terms of cis and trans isomerism.' For continuing our study of the chemistry of amine 1. these and other compounds, A1C13-CH,N0.2 was there(15) R. Pettit, J . Am. Chem. Soc., 82, 1972 (1960); see C. H. DePuy, fore found to be an oxidizing agent supeirior to sulL. G. Schnack, J. W. Hawser, and W. Wiedemann, ibid.,87,4006 (1965), furic acid. for an alternative explanation. (16) National Science Foundation Predoctoral Fellow, 19641965; Different spectra are sometimes obtained for the two NASA Predoctoral Fellow, 1965-1966. systems as illustrated by the spectrum of dimethoxyKirby V. Scherer, Jr., Robert S . Lunt, LIP durene.8 The esr signal in A1C13-CH3N01 (Figure 1) Department of Chemistry, University of California affords narrow lines (half-width ca. 70 mgauss) and Berkeley, California 94720 analyses for UCH, = 2.11 gauss and U O C H ~= 2.76 gauss Receiced Febrkiary 3, 1966 14". Moreover, the dimethoxydurene cation at radical showed a marked temperature deptendence of the -OCH3 splitting constant, which is being further The Use of Aluminum Chloride-Nitromethane for the investigated. In sulfuric acid solution ani esr signal Production of Cation Radicals' was obtained which was identical with that observed on dissolving duroquinol in sulfuric acid.9' Hence in Sir: this case only the A1Cl3-CH3NO2 system gives rise to Positive ion free radicals have been investigated with the appropriate cation radical without furtlier chemical esr spectroscopy by Weissman, Carrington, and reaction. others, usually by dissolving the appropriate neutral Since A1C13-CH3N02 is less viscous than concensubstance in concentrated sulfuric acid. Although trated sulfuric acid, effects due to the anisotropic dipolar g tensor interaction terms of the line-width I equations'o are of little importance. For example, the duroquinol cation radical can be studied to -95" in the former, whereas in the latter system determinations below O o are marred by line-width variations. Studies at -95" allow observation of the cis and trans isomers of the duroquinol cation radical. Sometimes, A1Cl3-CH3NO2 permits oxidation beyond the one-electron stage. For example, p,p'biphenol gave a blue paramagnetic soliition which analyzed as a4H = 1.95 gauss, a2H = 1.64 gauss, and a 4 = ~ 0.73 gauss. Using excess A1CI3, the solution Figure 1. The esr spectrum of dimethoxydurene at -24" in became yellow in color and was diamagnetic. This AlC13-CHaN02. further oxidation was reversed by diluting tor by adding more starting material. other chemical methods for producing cation radicals are Experimentally, the chemicals used were Fisher known (e.g., ref 4), concentrated acid oxidation has become the most frequently used method. The purpose of (5) H. M. Buck, W. Bloemhoff, and L. J. Oosterhoff, Terrahedron Letters, No. 9, 5 (1960). this communication is to report on the use of aluminum RNi+
+
+ H20 + C1+ HCl
+
(6) D. L. Allara, B. C. Gilbert, and R. 0. C. Norman, Chem. Com-
(1) This research was supported by the National Research Council of Canada. (2) S. I. Weissman, E. De Boer, and J. J. Conradi, J. Chem. Phys., 26, 963 (1957). ( 3 ) A. Carrington, F. Dravnieks, and M. C. R. Symons, J . Chem. Soc., 947 (1959). (4) I. C. Lewis and L. S. Singer, J. Chem. Phys., 43, 2712 (1965).
Journal of the American Chemical Society
I
88:12
mun., 1, 319 (1965).
(7) W. F. Forbes and P. D. Sullivan, Can. J . Chem., in press, and unpublished in format ion. (8) We are indebted to Drs. H. G. Cassidy and M. Hashimoto for a sample of this compound. (9) J. R. Bolton and A. Carrington, Mol. Phys., 5 , 161 (1962). (10) J. H. FreedandG. K. Fraenke1,J. Chem. Phys., 39, 326(1963).
I June 20,1966
2863
reagent grade. Nitromethane was dried over calcium hydride and deoxygenated by passing dry nitrogen gas through the solution, followed by degassing under vacuum. The oxidation was carried out in an inverted U-tube, one arm of which was filled with anhydrous aluminum chloride and the compound to be oxidized (ca. 20 and 5 mg, respectively). This U-tube was connected to a vacuum line and nitromethane (1 ml) was distilled into the reaction mixture. The reaction proceeded at room temperature and the solutio n was subsequently transferred under vacuum into the capillary tube, which was then placed in the esr cavity. The spectra were run on a JES-3BX spectrometer using a field-selector unit. Values of splitting constants are believed accurate to k 0.5 %.
(A)
2500
3500
3000
400
3 Log &
\ 2
t1
W. F. Forbes, P. D. Sullivan Department of Chemistry, University of Waterloo Waterloo, Ontario, Canada Receiued March 24, 1966
.------.
E[-&,)
. .......... .....
0'
............. -, ...........,4*-*. ....................... E -.- 0 .
/."
0
/--.
02
/
,/'
#.##
-1
1nducl:ion of Asymmetry in cis-Dicchloro(olefin)(amine)platinum(II) Complexes Sir : In previous publications we have described a number of plsttinum(I1) complexes of olefins, containing a dissymm#etricamine [(I?)- or (a-a-phenethylamine], trans or cij): coordinated with respect to the olefin, of the general types I and 11.
c1
c1
I
amine-At-olefin
amine-Pt-C1 I
I
olefin
C1
I
I1
If the ethylene complex is allowed t o equilibrate with an olefin having a symmetry different from Czvor D2h, two diastereoisomers are formed. For the trans-coordin ated complexes no evidence has been found for the induction of asymmetry during the course of the exchange reaction. Fo I- the cis-coordinated complexes we now report data showing that the equilibrium constant of the react ion
c1 amine(S+Jt-CI I
e
c1
amine(+Pt-c1I I
olefiA(R) I11
is generally different from unity. A s noted previously, the deviation of the molecular rota tion of an olefin complex (I) from that of the corresponding ethylene complex affords an indication that asyrnmetric induction occurs in the coordination of the olefin. A probable origin of the effect is a steric interacti on between the amine and the cis-coordinated olefin. In fact, the deviation is Darticularlv marked in the case of the complexes with blefins of t h e type transR--CH=CH-R. (1 ) (a) G . Paiaro, P. Corradini, R. Palumbo, and A. Panunzi, Mukromol.. Chem., 71, 184 (1964); (b) G. Paiaro and A. Panunzi,J. Am. Chem. SOC.,86, 5148 (1964). ( z 2 ) G . Paiaro and A. Panunzi, Tetrahedron Letters, 8, 441 (1965).
-
I
40
35
y
I
I
30
25
(103~~-~)
Figure 1. The electron absorption and circular dichroism spectra of cis-dichloroolefin-(S)-cu-phenethylamineplatinum(II) complexes in ethanol solution: (A) the absorption spectrum, and (B) the circular dichroism spectrum of the ethylene complex; the circular dichroism spectra of (C) the cis-2-butene complex, (D) the (+) diastereoisomer and (E) the (-) diastereoisomers of the propylene complex, (F) the equilibrium mixture of diastereoisomers, and (G) the (-) diastereoisomer of the trans-2-butene complex.
The molecular rotations should indicate (Table I) that for the complexes with trans-2-butene, trans-3hexene, and trans-l,Cdichlorobutene,there is a 25 % Table 1.0 Data of the Optical Activityb of cis-Dichloro(olefin)-(S)-a-phenethylamineplatinum(II)Complexes
MD
