KURTMOEDRITZER AND JOHN R. VAN WAZER
2030
Cyclic Silthiazanes
by Kurt Moedritzer and John R. Van Wazer Central Research Department, Monsanto Company, St. Louis, Missouri
(Received January 18, 1966)
Proton nmr data are evaluated in terms of (1) two equilibrium constants which interrelate the four trimeric cyclic molecules resulting frdm permuting sulfur and methylimino bridges between three dimethylsilicon groups, and (2) a third const'ant which relates one of these structures to the dimeric cyclic molecule in which two dimethylsilicon groups are bridged by a pair of sulfur atoms. The trimeric cyclosilthiazanes (Le., those molecules involving both S and CH3N bridges) are new compounds.
Cyclic compounds of silicon in which silicon atoms alternate with heteroatoms, with the heteroatoms being of more than one kind, have recently attracted wide spread interest. Reports have appeared in the literature describing compounds derived from siliconnitrogen ring structures in which one or more of the nitrogen atoms are replaced by other bridging atoms. Four-membered silicon-nitrogen ring molecules were prepared with one of the nitrogens being replaced by boron or phosphorus.' In addition, six- and eightmembered silicon nitrogen ring structures have been reported in which one or more nitrogens are substituted by bridging oxygen atoms.2-8 In this paper we are reporting studies of the equilibria resulting from the exchange of the bridging -NCH3- groups of nonamethylcyclotrisilazane with the bridging sulfur atoms of hexamethylcyclotrisilthian to give sulfur-substituted cyclic trisilazanes.
Experimental Section Materials. Nonamethylcyclotrisila~aneg~lo and hexamethylcyclotrisilthian" were prepared according to the literature. The purified substances did not exhibit any proton-containing impurities detectable by proton nuclear magnetic resonance (nmr). Equilibration and Measurements. Various proportions of the hexamethylcyclotrisilthian and nonamethylcyclotrisilazane were heated at 120' in sealed 5-mm 0.d. precision nmr tubes. Equilibrium with respect to exchange of bridging sulfur with bridging methylimino groups was shown by pilot runs to be attained in less than 360 hr a t 120'. The reported equilibrium concentrations were determined after 404 hr a t this temperature. The The Journal of Physical Chemistry
equilibria a t room temperature were measured after the samples corresponding to 120' stood for 26 days a t 25'. From some analyses made a t shorter times, it appeared that the equilibrium corresponding to this temperature had been reached in less than 19 days. Proton nmr spectra were obtained on a Varian A-60 spectrometer. Peak areas were determined by cutting out and weighing Xerox copies of the spectra. The chemical shifts observed for various molecular segments in the cyclic molecules are presented in Table I. Well-resolved spectra were generally obtained; however, overlapping of the main peaks with satellite peaks due to spin coupling of the CH, protons by the Siz9isotope was observed and corrected for in the analytical measurements. The calculation of equilibrium constants was performed as previously d e ~ c r i b e d ' ~ (letting *'~ the hypo(1) W. Fink, Chem. Ber., 96, 1071 (1963). (2) N. N. Sokolov, J. Gen. Chem. U S S R , 29, 262 (1959). (3) N. N. Sokolov, Khim. i Prakt. Primenenie Kremneorgan. Soedin., Tr. x o n f . , Leningrad, No. 2, 130 (1958); Chem. Abstr., 54, 8603f (1960). (4) C. R. Krliger and E. G. Rochow, Angew. Chem., 74, 491 (1962). (5) C. R. Krtiger and E . G. Rochow, Inorg. Chem., 2, 1295 (1963). (6) 0. Schmita-DuMont, D. Merten, and D. Eiding, 2. Anorg. Allgem. Chem., 319, 362 (1963). (7) K. A. Andrianov, I. Khaiduk, and L. M. Khananashvili, J . Gen. Chem. U S S R , 33, 2717 (1963). (8) R. L. Elliot and L. W. Breed, Inorg. Chem., 4, 1455 (1965). (9) L. W. Breed and R. L. Elliot, ibid., 3 , 1622 (1964). (10) E. W. Abel and R. P. Bush, J. Inorg. Nucl. Chem., 26, 1685 (1965). (11) T. Nomura, N. Yokoi. and K. Yamasaki, Proc. Japan Acad., 29, 342 (1954); Chem. Abstr., 49, 12,274 (1955). (12) L. C. D . Groenweghe, J. R. Van Wazer, and A. W. Dickinson, Anal. Chem., 36, 303 (1964).
2031
CYCLIC SILTHIAZANES
Table I : Proton Nmr Chemical Shifts" Observed in an Equilibrated Sample Made from Equimolar Amounts of [( CHs)~%3]3and [(CH~)2SiNCH3]a Methyl resonance observed
CH3-?;
(NNW
(SNN)e
