NOTES
Oct., 1960
1583
trum of triethylborane is found at lowest field by a considerable margin and consists of a broad singlet suggesting perhaps unresolved proton-boron coupling. (The boron-boron coupling of the single bond in tetraborme5 had been found to be about 23 c./s.). The possibility of detecting boron-boron coupling in diborane and its derivatives had long been considered to be of interest. These questions led to a Bll n.m.r. survey of the various methyldiboranes, B-deuteriomethyldiboranes, some ethyldiboranes, the trimethyl- and triethylboranes, as well a,s trimethylborane-&. The system triethylboranesodium hydride also was investigated. The various samples were prepared by mixing the isotopically appropriate trialkylborane with isotopically appropriate diborane6 and placed 2 3.01 I the in 5 mm. 0.d. tubes for B1l 1i.m.r. study at 12.8 mc. I The chemical shifts were measured in parts per 0 20 40 60 million from BFI etherate as zero. Compounds (1 - 1/z~2St)t1/,(sec.)'/l. Fig, 1.-Extrapolation of ( H / A ) ( l - 1/&St)--It1/~ to were isolated by vapor-liquid partition chromatography. The column consisted of 20 ft. of 10 mm. t = 0 for bovine serum albumin. Data of Baldwin2 at Co = 0.67 g./lOO ml. (filled circles) and a t C, = 1.35 g./100 i.d. Pyrex tubing, coiled to fit into a large dewar, ml. (half-filled circles). packed with a 30Oj, Kel-F 90 on 30 mesh firebrick. Separatioiis were carried out at -15" to 5" with a As a test,, the method has been applied to the same data of Baldwin2 which were used by Fujita.3 helium flow rate of 60 cc. per minut,e. Trialky1boranes.-The chemical shift of triThe protein is bovine serum albumin, sedimenting in buffer, a t protein concentrations of 0.67 g./100 methylborane has a value of - 84 compared to - 85 ml. and 1.35 g./100 ml. Graphs according to equa- for t,riethylborane and tripropylborane. The halftion 8 are shown in Fig. l. Within experimental width of the resonance of triethylborane-dlb and of error, the data seem to lie on straight lines. The the isot'opically normal triethylborane are found to constants evaluated from the intercept and slope be identical (70 c./s.). Since deuterium-boron coupling would spread the Bll n.m.r. spectrum only are recorded in Table I. one third of the equivalent proton-boron coupling TABLE I the width of the Bll 1i.m.r. spectrum of txiethylborane must, therefore, result from factors other COMPARISON OF D AND k VALUES than proton-boron coupling (possibly quadrupole relaxation). 0 67 6 72 6 79 6 85 0 055 0 057 Alky1diboranes.-The spectra of the va,rious iso135 6 85 6 93 6 94 0.073 0.059 topically normal methyldiboranes are shown in From equation 8. Units of D are cm.e/sec., units of li Fig. 1; the chemical shift values (6) are represented (g./100 ml.) -1. * By Fujita's method, ref. 3. Evaluated as dots, the spin coupling constants between boron by Baldwin from free diffusion data of Gosting.6 From S and terminal prot.ons (Jt)and between boron and us. Co graph; Baldwin.2 bridge protons ( J b ) are recorded along the right,. It is felt that in the region of small Em and 7, the The methyldiboranes prepared from deuteriodibomethod outlined here yields results for D which rane showed essentially identical chemical shift compare favorably with those of Fujita's method. values (in parentheses) at 12.8mc. S o deuteriumThe value obtained for k is presumably more sensi- boron coupling mas resolved. The chemical shifts tive to assumptions in the theory. of the few et,hyldiboranes studied did not differ In conclusion, it should be noted that pronounced detectably from hheir methyl analogs. heterogeneity should lead to marked deviations All of the above spectra were obtained in the from the simple straight line extrapolation. liquid phase. Those of the mono- and trialkyldiThis investigation was supported in part by a bomnes were obtained at reduced temperature bePHS research grant No. ,43096, from the Kational cause of rapid disproportionation. In Fig. l it is -Advisory Council on Arthritis and Metabolic Dis- shown that 1,2-dimetjhyldiborane (U)rapidly apeases, Public Health Service. pears in the methyldiborane by disproportionation. ( 5 ) Values qiiuted hy Fuiita, ref. 3 In the trimethyldiborane spect,rum an impurity arising during the synt,hesis of trialkylboraite is representred by (Z). Satisfactory spect,ra of tet,ra~ 1 N1 . n m SPECTRA OF ALKYLDIBORANES, (1) N o w affiliaterl with National Engineering Pc.ienve (10.. I'asaTRIALKY1,RORASES AND NaBHEta
--
BY
ROBERT
E. J 1 r ~ ~H. ~DTVIGHT ~ ~ ~FISHER^ ~ , lAND CHARLES 0. WILSON'
Olzn Sfntiiieson Research Laboralory,1 Pasadena, Calzfornaa Receibed A p r z l 19, 1960
Boron-11 chemical shift values of a large number The spec-
of compound^^.^ have been compiled.
dena, California. (2) Hughes Tool Co., Culver City, California. (3) T. . ' l Onak, €I. Landosman, R. E. Williams and I. Shapirr,, THISJOURNAL,63, 1533 (1959). (4) W. D. Phillips, H. C. Miller and E. L. Muetterties, J. B m . Chem. Soc., 81,4496 (1959). ( 5 ) R. E. Williams, S. G . Gibbins and I. Shapirn, ibid., 81, 01G4
(1959).
(6) C. 0. Wilson and I . Sctapiro, Anal. Chem.., 32, No. 1 , 78 (1960).
NOTES
1584 J r [3oron-i! spin-coupling w i t h J B E3oron-ii spin-coupling w i t h
6
Chemical s h i f t
(6) Chemical
shif! of onuloyues f r o n perdi:uterodiSorane
JB= 47.5 c/,
n JB=39.7
‘-24 8 ,(-23.5)
Ji = 125.5
4 1
J e = 49.7 BH2 -3 6 (-3.6)
Fig. l-BL1 nuclear magnetic resonance tlattt of methyldiborane.
wethyldiborane could only be obtained in the preseuce of a significant excess of trimet>hylboranc. The excess of hrimethylborane (X in Fig. 1) maintains the concentration of tetramethyldiborane. Without the influence of trimethylborane upon the various alkyldiborane equilibria the tetramethyldiborane rapidlj disproportionates to produce trimethylbcrarie and the lesser alkylated diboranes. The spectra of the methyldibornnes may best be interpreted by pointing out two effects that apparently determine the resulting B” chemical shifts. First, alkyl groups tend to shift the associated boron nuclei t 3 lower field. In the symmetrical series diboranca, 1,Zdimethyldiborane and tetra-
Vol. 64
methyldiborane, the trend is to lower field with alkylation; these molecules are made up of two identical “halves.” Second, unsymmctrical substitution promotes an even greater divergence of chemical shift values. When two “halves” of the molecule differ b y one alkyl group the shifts to lower aiid higher field are enhanced; when the “halves” differ by two alkyl groups, the divergent shifts are e ~ greater; ~ n ie., the chemical shifts of 1,l-dimethyldiborane, where the divergence of BH, and BRz groups is about doubled. Certain cyclic alkyldiboranes (1,2-tetramethylenediborane aiid 1C-methyltrimethyle1iediborane)~have chemical shift values similar to those of 1 J-dimethyldiborane. Similar chemical shift behavior upon alkylation mas also observed in 2,4-dimethylenetetrab0raiie.~~~ l\;o resolution of boron-boron coupling could be detected 111 the spectra of any of the diboranes and certainly cannot exceed a few cycles (Fig. 1). NaBHEt,-BEto Exchange.-Sodium hydride reacts lyith triethylborane and is known to form a liquid which is immiscible with additional triethylborane. This liquid, saturated with triethylborane, produced a broad peak in the B” spectrum; ac. the excess triethylborane was removed the peak shifted to higher field. Addition of diethyl ether reduced the viscosity and narrowed the peak. ?Then excess sodium hydride was introduced into the sample, the spectrum remained unchanged. However, upon re-examination, several months later, the singlet had changed iiito a doublet centered at the chemical shift position of the previous singlet. Apparently rapid intermolecular exchange of the protons takes place at room temperature in the presence of even a trace of BEt3; thus, the boron nuclei spend a portion of their time as BEtl arid a portion of the time as NaB€lEt3. Exchange evideiitly c a n i d take place in the absence of a trace of triethylborane as removed by several months’ contact n-ith NaI-I. (7) H. G. Weiss, W. .J. Lehiiiann and I. Shapiro, J An& Chem Sop. ( 8 ) R. C. Harrison I. J . Soloinon. R 1) Hites and hl. J Klein Abstracts of the 135th ACS illeettng, Boston, Maas. also (Inorgan2c and A - d e a r Chem , 1960). (9) S. G. Gibbins I. Sbapiro and R. E. JVilliams J P h w Chem
KINETICS OF THE KEACTIOS OF HYDROGEN IODIDE AND Di-1-BUTYL PEROXIDE 19 CAIRBONTETRA(’HI,ORIDE1 BY GEORGEA. Lo A N D WI:NDELI,11. GRAVEN Chemistry Department, L‘niueruity G’, Oregon, E u g e n e , Oregon I- chemical methods is difficult,? a,s a result o f their unreactive behavior toward the usual oxidat ion-reduction reagents. In contrast to the behavior of hydropcroxidcs, such as t-but,yl hydroperoxide, or diacyl peroxides, such as dibenzoyl peroxide, di-t-butyl peroxide is not reduced readily by alkali iodide in the preseiice (1) Taken from the hI.A. thesis of G. .%. 1.0, Uni\.rrsit) of Oregon.
19GO. (2)
G. J . Minkoff. Proe. R o y . Soc. ( L o n d o n ) , 8 2 2 4 , 17fj (1954).
