COMMUNICATIONS TO THE EDITOR
996
Vol. 83
We thank Dr. George A. Wiley for preparing the crystals which we used. Further refinement of this structure is in progress.
with the structurally related b o r a t e ~ . ~While .~ pentacoordinate complexes of various halosilanes have been reported,6 the triptych-siloxazolidines herein described are believed to be the first examples DEPARTMENT OF CHEMISTRY AND LAWRENCE RADIATION LABORATORY of pentacoordinate alkoxysilanes. Their marked UNIVERSITY OF CALIFORNIA THOMAS N. MARGULIS stability despite the weakly basic nature of triBERKELEY 4, CALIFORNIA DAVIDH. TEMPLETON alkanolamines' and the apparent failure of triRECEIVED DECEMBER 27, 1960 methoxysilane to complex with an amine as nucleophilic as piperidine ( o d e infra) underscores the importance of steric factors in such interactions. TRIPTYCH-SILOXAZOLIDINES: PENTACOORDINATE BRIDGEHEAD SILANES Brownk based his assignment of a triptych RESULTING FROM TRANSANNULAR INTERACTION structure to triethanolamine borate upon the inertOF NITROGEN AND SILICON ness of the nitrogen atom toward methyl chloride Sir. and its sluggish neutralization by methanesulfonic We have found the alcoholysis of trialkoxysilanes acid in nitrobenzene solution. Similarly, we have by trialkanolamines to lead to the exclusive forma- found that triptych-siloxazolidines are not neution of crystalline monomeric products.' tralized immediately by perchloric acid in a glacial ZSi(OR)s (HOCHRCH2)aN + acetic acid medium, thereby supporting a structure ZSi( OCHRCH&N -I-3ROH wherein the nitrogen's basic pair of electrons is not This is in striking contrast to the polymeric prod- available for immediate protonation. The silicon system provides the means for a unique ucts one might reasonably have anticipated from the condensation of such highly functional react- test of the triptych model. Smith and Angeants. A series of such derivatives has been prepared lotti8 studied the effect of molecular structure upon and representative members are shown in Table I. the Si-H stretching frequency, showing clearly that
+
TABLE I TRIPTYCH-SILOXAZOLIDINES "fP.'" C.
Substituents
Molecular formula
None 5-Methylb
----Silicon, Calcd.
%Found
--Neut. Calcd.
equiv.-Found
253-256 CeH1.O8SiN 16.02 16.23 175 123-125 C7HI6O0SiN 14.84 14.66 189 151-153" 3,5-Dimethyl 9597 CsH1701SiN 13.82 13.60 203 5-Octadecyl 6.73 428 85-86 GHtoO&iri 6.57 5-a-Phenethyl 192-194 CllHniOaSiN 10.05 10.16 279 5-Vinyl 163-165 CsHjsO&iN 13.96 14.14 20 1 5-Phenyl 11.24 251 CI2H17O3SiN 11.18 208-209 3-Methyl-5-phenyl 10.48 265 ClaHloO&3iN 10.58 85-87 5-Ethoxyd 100-102 CBH1,OSiN 12.72 2 19 12.81 5-( - )-Menthoxy 152-154 C16HS1O4SiN 8.52 8.32 330 a Uncorrected. B.p. 174" (31 mm.). Apparent polymorphism; the lower-melting form was obtained by the melt a t about 100". B.p. 180" (0.6 mm.).
That even a fourth substituent on the silicon may be functional is illustrated by the monomeric products derived from such silanes as trimethoxysilane and ethyl orthosilicate. For reasons cited below, these silanes are believed to be pentacoordinate as a result of transannular dative bonding between the nitrogen and silicon atoms (I). They have been
I
designated as triptych-siloxazolidines2~3 by analogy (1) Subsequent to completion of this work, an account of t h e independent preparation of CaHsSi(0CHzCHz)aN and CHaCHzOSi(OCHzCHdsN appeared in U. S. Patent 2,953,545 granted to Arnold B. Finestone, Sept. 20, 1960. The melting point of the latter compound (35-37') differs significantly from our value (100-102°). ( 2 ) This nomenclature is best illustrated by a specific example such as the naming of CzHaOSi(0CHCHz)aN. Using the numbering scheme shown (I), one obtains the name 5-ethoxytriptychsiloxazolidine. This compares favorably with the precise but unwieldy
177 189 203 428 282 202 250 267 218 333 crystallizing
increased electron supply a t the silicon displaces the absorption to lower energy regions. Although showing some solvent dependency, the position of v(SiH) for HSi(OCH2CH2)3Nwas displaced from the region characteristic of silanes bearing three Si-0 bonds to a lower energy region wherein silanes systematic' name 4,6,11,1,5-trioxazasila-5-ethoxytricyrlo[3.3.3.O'~slundecane. (3) IUPAC 1957 Rules, J. Am. Chcm. Soc., 89, 5573 (1960). (4) (a) A. A. Schleppnik and C. D. Gutsche. J. Org. Chcm., 9 6 , 1378 (1960); (b) H. Steinberg and D. L. Hunter, J. Am. Chem. Soc., 88, 853 (1960); (c) H. C. Brown and E. A. Fletcher, i b i d . , 73, 2808 (1951); (d) C. A. Rojahn, German Patent 582,149 (Chem. Zenlr., 104, 11, 2704 (1933)). (5) It seems likely t h a t similar compounds containing such elements as AI, Fe, Ti, S n , Ge, P , etc., might be feasible. In this connection, preliminary studies have shown sublimable material of the anticipated composition to result from the reaction of triisopropanolamine and aluminum isopropylate. T h e importance of atomic size and/or the presence of relatively low-lying vacant orbitals was demonstrated by the condensation of ethyl orthoformate and triethanolamine to form a cross-linked polymer rather than a monomeric species. ( 6 ) (a) C. Eaborn, "Organosilicon Compounds," Butterworths Scientific Publications, 1960, p. 92: (b) F. G. A. Stone and D. Seyferth, J. I n o r g . and S u c l . Chcm., 1, 112 (1955). (7) H. K. Hall, J . Am. Chem. SOL.,79, 5441 (1957). (8) A. L. Smith and K. C. Angelotti, Sbectrochim. Acfa. 16. 412 (19591.
COMMUNICATIONS ‘ro THE EDITOR
Feb. 20, 1961 bearing three Si-C bonds are found. lustrating the shift are listed : Compound
HSi(OCHs)a
HSi( OCH&Ha)s HSi[OCH( CH&] J HSi( OCH2CH2)rN HSi(CsH& HSi( CHzCH8)a
997
Data8 il-
v(SiH)
2203 (CClr) 2201 (Piperidine) 2202 (Pyridine) 2196 ( c a d 2191 (CClr) 2137 (HCC18) 2117 (CHsOH) 2126 (CCL) 2097 (cc14)
This shift is consistent with the triptych model which would certainly appear to involve increased electron supply a t the silicon atom. Observations of solute association made in the course of our molecular weight determinationsg are not inconsistent with the triptych structure. Whereas a polar solvent such as acetonitrile yielded ideal solutions over a wide concentration range, the relatively non-polar toluene did not. lo Such associative propensities could result from the dipolar nature implied by the intramolecular dative bond. The hybridization of the silicon in the triptychsiloxazolidines is probably of the sp3d type, wherein the oxygens are coplanar with the silicon and situated a t the three equatorial positions ( L o s i o = 120°), while the nitrogen and 2, the remaining substituent, occupy the axial positions. X-Ray studies now in progress should permit a more precise description of the actual disposition of atoms. Since the silicon atom in such a structure (I) is a t once pentacoordinate and a bridgehead site, its reactivity as well as that of 2, the “fifth” substituent, may be altered considerably. Studies dealing with these aspects will be reported a t a later date.
I
// 4
PH Fig. 1.-Spectrophotometric titration of OH-group iii ITP in 0.05 M (CH3)rNCl a t 263 mp.
Addition of Mg++ or e a + + to the un-ionized ring causes the same spectral shift as neutralization with OH-6; presumably in both cases protons are displaced from the ring. Spectral titration curves, enabling the determination of ring apparent pK as the pH of half ionization, were carried out a t the wave length of maximum shift: 263 mp for the 6-OH group of inosine nucleotides, 223 mp for the 6-NHe group in adenosine nucleotides, and 245 mp (9) We used a modified Swietoslawski differential ebulliometer as for the 4-NHz group of cytidine nucleotides. described by W. E . Barr and V. J. Anhorn in Instr. a?zd Automation, If ApK is the difference in ~ K ’ofs half titration 20, 822 (1947). (10) These apparent molecular weight values for CHsCHrOSiwithout and with metal, then, assuming one metal (OCHzCHdzN (calcd. mol. wt., 219) were obtained with toluene as solion bound per molecule of nucleotide, the metalvent and illustrate the increasing degree of association with increasing nucleotide affinit constant is K, = 2A (A- 1)/ { No molality: 257 ( 0 1 m): 306 (0.3m ) ; 342 (0.5m); 379 (0.7m). T h e A (2Mo - No) rwhere A = lOASK, Mo is the total other triptychsiloxazolidines displayed very similar associative tendencies. concentration of metal ion and No is the total conRESEARCH LABORATORIES CECILL. FRYE centration of nucleotide.’ Dow CORNING CORPORATION GEORGE E. VOGEL Table I shows that Kmof Mg++ for a ring containMIDLAND, MICHICAX JAMES A . HALL ing an OH group is greater than for a ring containing RECEIVED DECEMBER 29, 1960 an NH2 group. Also, e a + + and Mg++ do not shift the spectral titration curves of the corresponding EVIDENCE FOR INTERACTION BETWEEN bases or nucleosides, indicating that for interaction, MAGNESIUM AND PURINE OR PYRIMIDINE RINGS phosphate as well as ring is necessary, and sugO F 5’-RIBONUCLEOTIDES gesting that in solution N T P is partly in a curled Sir: ~ ~ ~Mg++ chelated between pyroThe evidence from ultraviolet spectra given here c o n f i g u r a t i ~ nwith phosphate structure and base. Apparent K m desupports suggestion^^-^ that Mg++ interacts with the purine or pyrimidine rings of NTP,’ possibly in pends strongly on both Mg++ and nucleotide concentration, suggesting that more than one M g f + enzymatic process. per nucleotide is bound.8-10 (1) The abbreviations used are: N T P , nucleosides triphosphates;
+
ATP, adenosine triphosphate: ITP, inosine triphosphate; CTP, cytidine triphosphate. (2) A. Szent-Gyorgyi in “Enzymes, Units of Biological Structure and Function,” Ed. 0. H. Gaebler, Academic Press, Inc., New York, N. Y., 1956, p. 393. (3) G. L. Eichhorn in “The Chemistry of the Coordination Compounds,” Ed. J. C. Bailar, Jr., Reinhold Publ. Co., New York, N. Y., 1956, p. 698. (4) W. G. McCormick and B. H. Levedahl, Biochem. et Bioghys. Acto, 34, 303 (1959). (6) J. J. Blum, Arch. Biochem. Biophys., 5 5 , 486 (1955); 87, 104
(1960).
(6) R. M. Bock, Nan-Sing Ling, S. A. Morrell and S. H. Lipton. ibdd., 62, 253 (1956). (7) If we suppose two kinds of equilibrium reaction
K, N fH
K,
“and
r*:
+M I -
NM,
with the masslaw equations, the equation for the conservation of mass and the condition N = N o / 2 a t half titration points, the equation K m in Lhe text is obtained. (8) R. Smith and R. Alberty, J . A m . Chem. Soc., 7 8 , 2376 (1956). (9) C. Liebecq and M. Jacquemotte-Louis, Bull. Soc. Chim. Biol., 40,
67 (1958). (10) J. M.Lowenstein, Biochem. Z..70, 222 (1958).
