Inorganic Chemistry, VoZ. 10,No. 10,1971 ' 2363
NOTES
Experimental Section Methods and Materials.-Standard vacuum-line techniques were used in the manipulation of volatile materials. Nonvolatile materials were transferred in a drybox in a nitrogen atmosphere. 4NHpC1 f 4(CHa)zPCla ----f [P(CHs)*N]4.2HCl+ 14HC1 Pentaborane(9) and diborane(6) were obtained from the Callery Our work indicates that i t is crucial in order to obtain Chemical Co. and used directly. Solutions of LiCH3 in diethyl ether were purchased from Foote Chemical Co. and had known good yields that this HC1 be efficiently removed. concentrations in the range 1.5-1.7 M . Reagent grade diethyl Hence the continuous sweeping with nitrogen followed ether was dried over LiAlH4 and distilled and stored under by pumping are of vital importance. The removal of vacuum in a glass bulb equipped with a Fisher-Porter Teflon the remaining HC1 by treatment with triethylamine is valve. Dimethyl ether was obtained in a cylinder from the Matheson Co. and used directly. then very facile Preparation of LiB6H8Solutions .-In typical syntheses, 30[P(CHs)zN]a*nHCl n(CzH,),N+ mmol quantities of LiB& were prepared in (CH&O or (CzH6)zO solutions. I n a drybox, a carefully measured volume of LiCH3[P(CHa)zNl44- n(CzH6)aNHCl ethyl ether solution (about 20 ml of a 1.5 M solution) was syringed It is also worth stressing that method I has the into a 100-ml reaction flask which contained a Teflon-covered advantage of giving pure tetramer, uncontaminated stirring bar (this vessel must be of adequate volume to contain the foam produced by the rapid evolution of methane in the with trimer. reaction). The flask was fitted with a stopcock, placed on the Method 11.-This method is new although the apvacuum line, cooled to - 196", and evacuated. In cases where proach was suggested by previously reported direct am(CH3)tO was used, the (CZHS)ZO was pumped away and an equal monolysis reaction^.^*^ It provides an efficient route volume of (CH3)a0was then distilled into the vessel. An amount of BsHo, equimolar to the LiCH3 present, was condensed into the to the intermediate (CH3)2(NHz)zPC1which can then be used as previously described by Sisler and FrazierS2 reaction vessel a t - 196'. The vessel was opened to an evacuated section of the vacuum line of sufficient volume to contain The equations are the anticipated gas evolution and then warmed to 78'. With (C2Hs)zO as the solvent, it was sometimes necessary t o warm (CHa)zPCla 4- 4s" ----f (CH3)z(NHz)zPCl 2NHaC1 the reaction mixture to about -50" in order to melt the B ~ H Q n(CHs)z(NHz)zPCl+ which was frozen to the side of the bulb. On such occasions, the solution was then quickly cooled t o -78" in order to prevent x[P(CHs)zN13 I(% - 3x)/41 [P(CHa)zN14 f nNHaCl excessive foaming. By observing the increasing pressure in the This route differs from that in method I by providing, system the extent of reaction was followed; as it neared completion, the mixture was stirred and allowed to warm briefly in in roughly equimolar quantities, both the trimer and order to hasten completion of the reaction. While it is not posthe tetramer, which can be separated by fractional sible to isolate LiBoHs free of solvent, solutions thus produced crystallization. appeared to be stable a t room temperature for periods up to S hr. For the preparation of LiB,Hs in greater than 30-mmol quantiAcknowledgment.-We are grateful to the National ties, the required amount of LiCH3 solution was syringed into the Science Foundation for financial support. reaction bulb, but it was prudent to add BGHO in 20-30-mmol (8) C. P. Haber, D . L. Herring, and E. A. Lawton, J . Amer. Chem. Soc., 80, increments and allow complete reaction before the addition of 2116 (1958). each successive increment. (9) A. J. Bilbo, 2. Nalurfovsch B , 16, 330 (1960). Preparation of B6Hlo.--In a typical procedure, a 30-mmol quantity of B2H6 was allowed to expand into a reaction bulb a t -78' which contained a dimethyl ether solution of 30 mmol of LiBsHs that had been prepared by the method described above. The B& was completely absorbed in 1-2 hr when the solution CONTRIBUTION FROM THE EVANSLABORATORY OF CHEMISTRY, was stirred vigorously. Then the reaction vessel was opened to a U trap a t - 196' and the bulk of the solvent distilled from THEOHIOSTATEUNIVERSITY, COLUMBUS, OHIO 43210 A t this point the remaining matethe reaction vessel a t -78". rial was white and solid at -78". While constantly pumping through the U trap a t -196", this solid was stirred and slowly The Preparation of Hexaborane(l0) warmed to -15" over a period of several hours. The solid from Octahydropentaborate(1-) Salts liquefied and thickened, first turning yellow and then yellowbrown, as HZ was given off. The mixture was maintained at - 15.3" (benzyl alcohol slush) until removal of volatile material BY R A. GEANANGEL, H. D. JOHNSON 11, AND S. G. SHORE* to the U trap became prohibitively slow (several hours for the scale of reaction described herein). Then the mixture was Received April 8, 1971 slowly warmed to room temperature over several additional hours while continuously pumping volatile material into the U trap a t The preparation and characterization of alkali metal - 196'. The nonvolatile residue which remained consisted of octahydropentaborate(1 -) salts have been described. l--? LiBH4 (identified by X-ray powder diffraction and boron-SS Addition of B2H6 to LiB5H8 is a potentially useful renmr), plus unidentified material. Hexaborane(l0) was isolated from the material which was action in that i t can yield B ~ H I and o BloH14.~ We decollected in the U trap. This was accomplished by warming scribe herein the preparation of in a procedure the trap to -45' and slowly distilling its contents through a which offers substantial advantages over previously series of traps which were maintained a t -78, -95, and - 196". published methods.8-13 The fractionation process was continued until the material which collected in the -78" trap was shown to have a constant vapor (1) D. F. Gaines and T. V. Iorns, J. Amer. Chem. Soc., 89, 3375 (19673. pressure, 7.5 mm a t O " , in excellent agreement with an earlier (2) D. F. Gaines and T. V. Iorns, ibid., 89, 4249 (19671, 92, 4571 (1970). from the -78" trap was report for B ~ H ~ The o . ~yield ~ of (3) R. A. Geanangel and S. G. Shore, ibid., 89, 6771 (1967); U. S. Patent about 6.5 mmol. The fraction which collected in the -95" trap 3,489,517 (Jan 13, 1970). consisted primarily of BsH9 but also contained some B6H10. (4) T. Onak, G. B . Dunks, I. W. Searcy, and J. Spielman, Inoug. Chem., 6 , 1465 (1967). Fractionating this material at -78" yielded another 1.0 mmol (5) A. B. Burg and H. Heinen, ibid., 7 , 1021 (1968). of B6Hl0, giving a total yield of 25y0 of the theoretical yield.
very cryptic.' In this reaction an enormous amount of HC1 is produced, viz.
+
-
+
+
(6) H. D. Johnson 11, R . A. Geanangel, and S. G. Shore, ibid., 9, 908 (1970). (7) V. T. Brice and S. G. Shore. Chem. Commun.. 1312 (19701 (8) A. Stock, "Hydrides of Boron and Silicon." Cornell University Press, Ithaca, N.Y.,1933. (9) P. L. Timms and C. S.G. Phillips, Inoug. Chem., 8 , 297 (1964).
(lo) (11) (12) (13) (14)
J. L. Boone and A. B. Burg, J . Amer. Chem. Sac., 80, 1519 (1958). J. L. Boone and A. B. Burg, ibid., 81, 1766 (1959). W. V. Kotlensky and R. Schaeffer, $bid., 80, 4517 (1958). H. A. Beall and W. N. Lipscomb, Inoug. Chem., 8 , 1783 (1964). A. B. Burg and R . Kratzer, ibid., 1, 725 (1962).
CORRESPONDENCE
2364 Irtorganic Chemistry, Vol. 10, No. 10, 1971 TABLE I REPRESENTATIVE YIELDSOF BeHloFROM REACTION LiBsHs BIHB
+
Solvent
(C~HS)ZO (C2HaLO (CHsIzO (CH3)zO (CH3)zO
Scale, mmol
BBHIO yield, mmol ( % j
7 2 30 30 30 150
1 56 (21.7) 6 45(21 5 ) 9 20 (30 7 ) 7 50(25 0 ) 37 e ( 2 5 1)
THE
BlOH14 yield, mmol
0 16 Not measd 2 0 16 8 96
The identity and purity of the product were established by its molecdar weight by vapor density (calcd for BeH10, 75.95; found, 76.3), vapor pressure,I4 mass spectrum,15 infrared spectrum,”
and boron-11 nmr spectrum,Ieall of which were in excellent agreement with published reports. Decaborane(l4) was isolated from the fraction remaining a t -46” by warming to room temperature and fractionating through a U trap maintained a t -15’ (benzyl alcohol slush). Decaborane(l4) was identified by its melting point8 and its boron-11 nmr spectrum.16 The preparation of BBHlO can be conveniently scaled up. Typical yields fbr several scale reactions are given in Table I.
Acknowledgment.-We wish to acknowledge, gratefully, the support of this work by the National Science Foundation. H . D. J. is grateful for support from The Ohio State University Graduate School in the form of a dissertation fellowship.
~
(15) I. Shapiro, C. 0. Wilson, J. F. Ditter, and W. J. Lehnian, Aduan. Chem. Sev., No.82, 127 (1961).
(18) T. P. Onak, H Landesman, R. E. Williams, and I. Shapiro, J. Phys Chem., 65, 1533 (1959).
Correspondence Reply to the Paper by F. A. Cotton and T. J. Marks, “Interpretation of a Spin-Tickling Experiment oh(Monohuptocyclopentadieny1)(methyl)(dichloro)silane’’l
MH,.l*Z For example, phenylarsine is a stronger acid than arsine, and diphenylarsine is a stronger acid than phenylarsine.2 However, germane and the phenylgermanes constitute a puzzling exception to this rule. The phenylgermanes are weaker acids than germanethe weakness increasing with increasing phenyl subSir : stitution.3,4 Although the exceptional acidities of the The assignment made by Cotton and Marks while phenylgermanes have been cited as evidence for pr-dn analyzinz our spin-tickling data for the compound b ~ n d i n g no , ~ explanation was offered for the implied C5HaSiCH8Cla2is absolirtely correct However, 3 greater importance of such bonding in the phenylmonths before Cotton and Marks published their paper germanes than in, say, the phenylarsines. The purwe published the correction in ref 3, in which this corpose of this communication is to show that the data rect assignment was already made. Perhaps Cotton may be explained in terms of two opposing effects of and Marks were not aware of our correction phenyl substitution : an acid-weakening effect (which (1) F A Cotton and T J Marks, Inovg Chem , 9 , 2802 (1070) we ascribe to pT-dn bonding) and an acid-strengthen(2) N M Sergeyev, G I Avramenko, and Yu A Ustynyuk J Ovganoing effect (mainly due to p7r-pn bonding). metal Chem , 22 (3), 79 (1970) (3) N M Sergeyev, G I Avrarnenko, and Yu A Ustynyuk, tbzd , 2 4 ( 9 j , The phenyl group in the molecule C6H&fH, can c 3 a (1970) exert an acid-weakening effect if the atom M has empty KMR LABORATORY, CHEMICAL D E P A R T M E ~ST M SERGEYEV* valence d r orbitals which interact with the filled pn Moscow STATE UNIVERSITY G I A ~ R A M E N K O molecular orbitals of the phenyl ring. Such dn- orbitals M O S C O W B-234, U S S R Yu rl USTYXYUK are available when M is from the second or third row RECEIVED MARCH 26, 1971 of the periodic table.6 The acid-weakening effect may
The Acidities of Germane and the Phenylgermanes Sir : Generally, a phenyl derivative of a nonmetal hydride, C$H&fi-I,-l, is more acidic than the parent hydride,
(1) G. E. K. Branch and M. Calvin, “The Theory of Organic Chemistry,” Prentice-Hall, Englewood Cliffs, N. J., 1941, p 240 ff; J. B. Hendrickson, D. J. Cram, and G. S. Hammond, ”Organic Chemistry,” 3rd ed, McGrawHill, New York, N. Y., 1970, p p 304-318. (2) K. Issleib and R. Kumrnel, J. OrganometaL. Chem., 8, 84 (1965). (3) T. Birchalland W. L . Jolly, Inorg. Chem., 6, 2177 (1966). (4) T. Birchall and I. Drummond, J. Chem. SOC. A , 1401 (1970). ( 5 ) M. D . Curtis and A. L. Allred, J . Amev. C h e w Soc., 87, 2554 (1965); J. A. Bedford, J. R . Bolton, A. Carrington, and R . H. Prince, P a n s . Favaday SOC.,59, 53 (1963); C. Glidewell, D . W. H . Rankin, and A. G. Robiette, J . Chem. Soc., 2935 (1970).
