1080
On the basis of the above data, we conclude that compound I1 is the trans isomer and I11 the cis isomer, The mechanism by which 111 is formed lends support to these assignments, since only with yellow mercuric oxide has it been found possible to isolate the cis compound. It is believed that there is a high degree of steric control involved with this unique polymeric'O oxidant in that it is able to form a highly ordered stereospecific intermediate chelate, of which one possible form is suggested by structure V. Under these conditions, the oxidation and coupling of molecules of I occur while they are held in the syn position, resulting in the formation of the cis azo structure. With the other oxidants, the uncomplexed aminonitrene (diazene)11-14 intermediate species VI is probably formed, which due to the lack of any induced stereochemistry collapses by dimerization to the thermodynamically favored trans structure.
well documented in the In many cases thus far studied the complexed metal ion has a closedshell configuration, so that extensive mixing of metal and ligand orbitals in the wave function of the unpaired electron is unlikely. It has recently been suggested5 that several planar anionic complexes, bis(maleonitri1edithio1ato)nickel (Ni(mnt)z-, I), bis(toluene-3,4-dithio1ato)nickel (Ni(tdt),-, II), and glyoxalbis(2-mercaptoani1)nickel (Ni(gma)-, 111), are all most appropriately described as containing diamagnetic d8 Ni(I1) with the unpaired electron localized on the ligands. This description was based on the asserted close similarity among the g tensors of these specie^.^ Such a sug-
CH~J
I1
111
These observations suggest a whole new approach to stereospecific oxidation of 1,l-disubstituted hydrazines. The possibility of designing hydrazines with suitable ligands for complexation and oxidation with yellow mercuric oxide offers the potential of tailor-making a variety of new isomeric azo compounds. Acknowledgments. This research was supported by the Advanced Research Projects Agency, Propellant Chemistry Office, and was monitored by the Bureau of Naval Weapons, RMMP, under Contract NOrd 18728. We are indebted to N. B. Colthup for assistance in interpretation of the infrared and Raman spectra, J. E. Lancaster for assistance in interpretation of the nmr spectra, and T. E. Mead for the mass spectrographic determinations. (10) The crystal structure of yellow HgO is an infinite planar zig-zag chain in which the Hg-0-Hg angle is 109" and the 0-Hg-0 angle is 179"; see D. GrdeniC, Quart. Rev. (London), 19,316 (1965). for leading references. (1 1) W. H. Urry, H. W. Ruse and W. R. McBride, J. Am. Chem. Soc., 79, 6568 (1957), ref 3; W. R. McBride and E. M. Bens, ibid., 81, 5546 (1959). (12) C. G. Overberger, Record Chem. Progr., 21, 21 (1960); C. G. Overberger, N. P. Marullo, and R. G. Hiskey, J . Am. Chem. SOC.,83, 1374 (1961); C. G. Overberger and L. P. Herin, J. Org. Chem., 27, 2423 f~~. 1962). .~, (13) L. A. Carpino, A. A. Santilli, and R. W. Murray, J. Am. Chern. SOC.,82, 2728 (1960). (14) D. M. Lemal, F. Menger, and E. Coats, ibid., 86, 2395 (1964), and references therein. ~
~~
Peter S. Forgione, G. Sidney Sprague
Howard J. Troffkin American Cyanamid Company, Central Research Division Stamford, Connecticut Received January 17, 1966
Concerning Cation-Stabilized Anion Free Radicals Sir: The occurence and the paramagnetic resonance properties of cation-stabilized free radicals are now Journal of the American Chemical S o c i e t y / 88:5
gestion is at variance with the large g-value anisotropy observed for the complexes6J and the demonstration' that the Ni(II1) d7configuration is pragmatically useful in interpreting the oriented single crystal epr properties of Ni(mnt)r. The postulated lack of involvement of metal orbitals in the unpaired electron wave functions of these complexes has prompted our extensive paramagnetic resonance investigation of I11 and related systems. From the point of view of paramagnetic resonance, the ultimate validity of the above postulate hinges upon what is the expected g tensor for a system unambiguously described as a cation-stabilized free radical. Significant deviations of g values from that of a free electron spin (g = 2.0023) may be expected from extensive involvement of sulfur orbitals in the wave function.8 We have interpreted the g and hyperfine tensor of I in terms of a b,, ground-state wave function, which is roughly 50% delocalized over the 7r system of the ligand^.^ The spin-orbit coupling was assumed to be entirely caused by the nickel atom, and the contribution of sulfur was not considered. Hiickel molecular orbital calculations on I9 predict considerably less metal (1) I. M. Brown and S. I. Weissman, J . Am. Chem. Soc., 85, 2528 (1963). (2) D. R. Eaton, I n o r g . Chem., 3 , 1268 (1964). (3) A. Davison, N. Edelstein, R. H. Holm, and A. H. Maki, J . Am. Chern. Soc., 86, 2799 (1964). (4) A. Davison, N. Edelstein, R. H. Holm, and A. H. Maki, I n o r g . Chem., 4, 5 5 (1965). ( 5 ) E. I. Steifel, J. H. Waters, E. Billig, and H. B. Gray, J. Am. Chem. Soc., 87, 3016 (1965). (6) A. Davison, N. Edelstein, R. H. Holm, and A. H. Maki, ibid., 85, 2029 (1963). (7) A. H. Maki, N. Edelstein, A. Davison, and R. H. Holm, ibid., 86, 4580 (1964). (8) W. G. Hodgson, S. A. Buckler, and G. Peters, ibid., 85, 543 (1963): J. J. Windle. A. I
