5434
WALTERR . HERTLER,WALTERH . KNOTH,AND EARLL. MUETTERTIES
[CONTRIBUTION S o 1004 FROM
THE
Vol. 86
CENTRAL RESEARCH DEPARTMENT, EXPERIMENTAL STATION, E . I. DU PONT DE NEMOURS AND COMPAXY, \.\’ILMINGTON
Chemistry of Boranes.
XXII.’
98,
DELAWARE]
Polyhedral Rearrangement of Derivatives of BloHIo2and B12H122-
BY WALTERR. HERTLER,L
%
7 H .~ KNOTH, ~ ~ A N~ D EARL ~ L. MUETTERTIES
RECEIVED AUGUST19, 1964 Individual isomers of bis( trimethylamine) decaborane ( 8 ) , B,,,Hs[ X( CH,),] 2, undergo isomerization a t 3000 to give an equilibrium mixture of isomers. Characterization of the rearrangement of C14-labeled 1,6- isomer yielded thermodynamic estimates; e.g., the enthalpy change for 1 , l O $ 2,7(8) isomerization is 0.77 kcal./rnole. The 1,6- isomer is the sole product from 2J-rearrangement a t 220”. Activation parameters for this isomerization are AH* = 37 kcal./mole and ASk = f 2 . 4 e.u. The 1,lO-isomer of B ~ O H ~ ( C Nrearranges )?~above 350’ to a predom-inantly equatorially substituted isomeric mixture. Rates of isomerization of the 1,2- and 1,6- isomers are comparable. These structural interconversions are discussed in terms of an intraof ( CH3)?SBlIIHaN( molecular “polyhedral rearrangement” mechanism. The vicinal isomer of B12H10[ N(CHl),]%undergoes degradation at 3 2 5 ” . The 1,12- isomer does not isomerize a t -530” and the 1 , i - isomer is mostly unchanged a t 400 O
Introduction Rearrangement reactions have long provided intriguing and fruitful areas of research in both organic and inorganic chemistry. Of particular interest to us was the possibility of rearrangement of clovoboranes (closed polyhedral boranes). Recent work? has shown that icosahedral 1,2-C2B10H12undergoes rearrangement a t -5W0 to 1,7-CzBloHiz. Hoffmann, Lipscomb, Kaczmarczyk, and D ~ b r o t thave ~ ~ ,discussed ~ this and related hypothetical rearrangements in some detail in terms of stabilities of various isomers as estimated from LCAO-blO calculations.4 A specific mechanism was proposed3” for the isomerization of C2BlaH12,2 and it was predicted that 1 2 - and 1,i-B12HloX22would undergo isomerization by the same mechanism. The proposed mechanism involves isomerization without breaking any bonds external to the polyhedral “cage.” A cuboctahedron was proposed as an intermediate in the lowest energy pathway for isomerization of C2H1aHl2 or B12HloX2?-. However, a recent demonstration5 of the thermal isomerization of neocarborane to p-carborane indicates that a rearrangement pathway which does not involve a cuboctahedron intermediate is also available in this system. Kaczmarczyk, Dobrott, and L i p ~ c o m b suggested ~~ that substituted derivatives of BloHlo2-should undergo polyhedral rearrangement and reported the isomerization of l-BloHgOH2- to %-BloH90H2-.This work, however, has been shown to be erroneous.6 Since earlier studies have made available to us four isomers of B,oH8[I\j(CH3)a]z( l ) , 7 - gall three isomers of Bl2H1o[N(CH3)3]2 (Z),’ and a variety of other substituted derivatives of BloHlo2-l o of known configuration, a (1) Paper- XXI: P;.E. Miller, J , A , Forstner, a n d E. I,. IvIuetterties, Znorg C h e m , 3, 1690 (1964). (2) H . Schi-oeder and G. D. Vickers, i b i d . , 2 , 1317 (19631, see also D. Grafstein and J. Dvorak, i b r d . , 2, 1128 (1963). (3) (a) R . Hoffmann and W. K. Lipscomb, i b i d . , 2 , 231 (19631, ( b ) A . Kaczrnal-czyk. R . D. D o b r o t t , and \T. S . Lipscomb, Pvoc. S o l i . Acad. Sci. 5 . S.,48, 729 (1962). ( 4 ) (a) I
