Jack Bobinski Picatinny Arsenal Dover, N e w Jersey
The Discovery of a New Class of Compounds:
The first member of a new class of carborane compounds, 1-isopropenylcarborane, was discovered during a broad-scale investigation of the use of boron hydrides as propellants for the US.Air Force. This work was conducted a t Reaction Motors, then a subsidiary of Olin Mathieson Chemical Corp., Denville, N. J. (at present a division of Thiokol Chemical Corp.) about seven years ago and recently has been declassified. At the time of investigation, it was known that decaborane interacts with acetonitrile to produce bis-(acetonitrile)-decaborane (1) as presented in equation (1). The structure (g) of bis-(acetonitrile)-decaborane is shown in Figure 1. Chemical evidence indicated that the reaction of nitrile compounds occurs via nucleophilic attack a t the 6 and 9 boron atoms. During this study, interaction of the 6,Q-bis-(acetonitrile)-decaborane with the olefinic double bonds was observed.
Figure 1. Structure of 6.9-bir-(acetanitrileldecorborone. 0, Boron; 0, Hydrogen.
500 / Journal of Chemical Education
Figure
2.
0,Boron, a;
Carboranes
Analysis of the product of the reaction of 6,9-bis(acetonitrile)-decaborane with 1-hexene indicated that one mole of 6,9-bis-(acetonitri1e)decaborane reacts with one mole of hexene. The product contains no double bond. The reaction of one mole of 6,9-bis(acetonitrile)-decaborane with one mole of a diolefin was then investigated with the hope of preparing a molecule which would contain decaborane and a double bond. However, the products of these reactions did not contain any double bond which could be utilized for polynlerization. The author of this article approached the synthesis of a boron hydride monomer as follows: If a decaborane molecule, which would contain a double bond, cannot be re pared by the reaction of a diligand of decaborane with a diolefin, perhaps this goal could be achieved by the reaction of 6,9-bis-(acetonitrile)-decaboranewith a molecule which would have both a double and a triple bond, so that decaborane would react with the double bond of the organic molecule leaving the triple bond umtouched.
Structure of carborone Hydrogen; *,Carbon.
nucleus.
Figure 3.
Slrueture of carborone.
o, Hydrogen; *,Carbon.
0, Boron;
The subsequent. controlled hydrogenation would reduce the acetylenic bond to the double bond and the resulting product, an organoboron compound containing a double bond could then be polymerized. With this in mind, 6,9-bis-(acetonitrile)-decaborane was reacted with isopropenylacetylene, CH,=C-C=CH. I
and internal niono- and diacetylenes (4-10). In addition to 6,9-bis-(acetonitrile)decaborane, other diligand derivatives of decaborane of the general formula Bl0H& (where L is a Lewis base) were employed for the reaction with the acetylenic compounds to produce carboranes. The following examples illustrate the scope and broad applicability of the carborane reaction. HC--CH
The reaction was carried out by dissolving both ingredients in benzene and heating the resultant solution to promote the reaction. Since isopropenylacetylene had a relatively low boiling point, the decision was made to carry out the reaction in a closed container. A pressure bottle was used which was heated in a water bath a t 8OoC. After cooling the reaction mixture and evaporating the volatile ingredients, a solid product was obtained which, unlike 6,9-bis-(acetonitrile)-decaborane, was noncrystalline, soluble in benzene, and melted without deconipositiun. This product contained a small amount of nitrogen, evidently an impurity. The main surprise, though, was still to come. Infrared analysis showed that this crude material contained a double bond but no triple bond. It was evident that 6,9-bis-(acetonitrile)-decaborane had reacted with the triple bond of isopropenylacetylene in preference to the double bond. The course of the reaction was later established to be:
Following the recommendation of the I.U.P.A.C. Committee on Nomenclature, the product of this reaction is identified as 1-isopropenylcarborane. The name "carborane" is used for the ClBm nucleus. Figure 2 shows the icosahedral structure for the carborane nucleus, which has not been completely elucidated so far. Probably the valence electrons of the acetylenic bond are used to form a carbon-carbon sigma bond and the remainder of the valence electrons are used in threecentered boron-to-boron bonds. The bridge hydrogens of the decaborane structure (3) are no longer found in the structure of the carborane nucleus. Because of this, carboranes do not possess the monoprotonic character of decaborane. The structure for carborane is shown in Figure 3. After the discovery of 1-isopropenylcarboraneelthe chemistry of carboranes was rapidly developed. I n addition to this author, a number of other workers have conducted research on these new compound^.^ A variety of carboranes were obtained by the reaction of 6,9-bis-(acetonitrile)-decaborane with terminal A patent application was submitted by Jack Bobinski, Marvin Fein and Nathan Mayes of Reaction Motors, Division of Thiokol, covering the discovery of the first carborane, l-isopropenylcarbornne. =Murray S. Cohen, Marvin Fein, Daniel Grafstein, Nathan Mayes, Joseph Dvorak, J m p h Green, Nelson Sohv:artz, John Paustian, Bernard Lichtstein, Harry Smith of Reaction Motors, Sehroeder of Olin Mathieson Theodore L. Heving. . -. Hanaiurmn . Chemical Corp., as well as many others.
-
+ (CHICN)~B,~HIS
HC=CCH,CHSCHI
+ (CHSCN)~B,,H,,
HC-CH
(3)
