anion in aqueous solution. The values of a and b in generic Formula 1 are, therefore, determined by the valence of M and they are the smallest whole numbers which satisfy the following equation:

is the substituent X, which is bonded to boron. The number of substituents which can be present in the group is not less than 1 or more than 12 and the substituents can be alike or different.

In its broadest aspects, X is a monovalent group which has the characterizing property of forming X-C bonds where C represents a carbon which is a nuclear member of a benzene ring and where the X-C bond is formed in place of an H-C bond. The property of forming X-C bonds, where C is nuclear carbon as defined above, is common to all the groups which are represented by X.

The group X can represent a substituent introduced into the B12H12-2 anion by direct reaction or it can represent a substituent obtained by subsequent chemical modification of a group which has been introduced by direct reaction, e.g., a substituent obtained by reduction, esterification, hydrolysis or amidation of directly introduced groups.

Compounds of the invention are obtained by processes which employ as a principal reactant a salt or acid having the B12H12-2 anion, i.e., a compound of the formula M. (B12H12) b, where M, a and b have the meanings given in previous paragraphs.

The salts or acid having the B12H122 anion (called dodecahydrododecaborates) are compounds whose infrared spectra consistently include strong absorption bands at 4.0μ±0.1 and 9.35μ±0.1. These bands are an identifying characteristic of dodecahydrododecaborate anions in which the absorption at 4.0μ ±0.1 is due to B-H stretching and at 9.35μ±0.1 is due to the dodecaborate cage.

The dodecaborate anion is referred to above as a dodecaborate cage. The Bl nuclear magnetic resonance spectra of dodecahydrododecaborate salts have been determined and the data indicate that the dodecahydrododecaborate anion contains one and only one type of boron atom, i.e., all the borons are chemically equivalent. The data further indicate that each boron atom is bonded to only one hydrogen atom and that all the hydrogen atoms are chemically equivalent. These data are best explained by assigning to the dodecahydrododecaborate anion a spatial configuration wherein the boron atoms form an icosahedron in which all the boron atoms are equal (in the same sense that all carbon atoms in benzene are equal) and each boron is bonded to one hydrogen. A complete analysis of infrared and Raman spectra show the dodecahydrododecaborate anion to have, in fact, I, symmetry. The spatial configuration of this dodecahydrododecaborate anion can be described most aptly as an icosahedron of boron atoms.

One or more hydrogens in the B12H122 anion can be replaced with groups or substituents to whatever degree desired. Substitution in the B2H122 anion can, of course, lead to a shift in the absorption bands and the characteristic bands for the substituted B12 anion may vary from the wavelengths given earlier for the unsubstituted B12H122 anion. Complete substitution of all 12 hydrogen atoms will, of course, result in the disappearance of the band at about 4.0μ which is due to B-H stretching.

The substituent X can be introduced directly or indirectly into the BH12-* anion. One or more groups can be introduced by direct reaction and these groups can be modified by subsequent chemical reactions. Groups which can be introduced by conventional processes and which employ readily available reactants form a preferred class. In this preferred group of compounds of Formula 1, the group X represents one or more of the following substituents: halogens (F,Cl, Br, I), hydrocarbon, carboxyl

where Y is F, Cl, Br, I), halomethyl (-CH2Y', -CHY'2 and CY'3, where Y' is F, Cl, Br, I), hydroxy (OH), hydrocarbonoxy (―OR'), monooxahydrocarbonoxy (R'OR'O) acetal [-CH(OR)2], ketal [-CR'(OR)2], hydrocarboncarbonyloxy [—OC(O) R'], hydrocarbonoxycarbonyl [—C(O)OR'], isocyanate (NCO), thiocyanate (SCN) isothiocyanate (NCS), hydrocarbonmercapto (-SR'), hydroxymethyl (-CH2OH), hydrocarbonoxymethyl (-CH2OR') aminomethyl (CH2NH2, —CH2NHR' and -CH2NR'2), cyano (CH), amino (-NHR', -NR'2), thiol (-SH), azido -N3), acyl

formyl

(C-R')

0
(-C-H)

nitro (NO2) nitroso (—NO), azo (—N-N-Ar), where Ar is an aromatic hydrocarbon group of up to 10 carbons), sulfo (—SO3H), sulfonyl (—SO2R'), and acetoxymercury

(-HgOČ

R', where used in the above substituents, is a monovalent organic group which is preferably a hydrocarbon group (alkyl, cycloalkyl, alkenyl, cycloalkenyl, aryl, alkaryl, aralkyl, and the like) of at most 18 carbons, and R'' is a divalent hydrocarbon group of at most 18 carbons.

Many of the compounds of the invention are obtained by reacting the dodecahydrododecaborate (2~), i.e., the B1212 salt or acid, with an electrophilic reagent. Substituents introduced by this process into the anion are called hereinafter "electrophilic groups." Compounds of Formula 1 obtained by a process of electrophilic attack form a second preferred class of products of the invention. In this preferred group of compounds of Formula 1, X is defined as a monovalent group which is capable of bonding to carbon of a benzene nucleus by reaction of benzene or a substituted benzene with an electrophilic reagent.

An electrophilic group is a group which is deficient in electrons and which has a point of low electron density. Electrophilic groups and reagents which are employed to effect substitution of such groups for hydrogen on carbon of a benzene nucleus are described in conventional textbooks, of which the following are examples:

Remick, "Electronic Interpretations of Organic Chemistry," pp. 89-110, Wiley (1943). Ingold, "Structure and Mechanism in Organic Chemistry," pp. 198-200, 269-304 (especially pp. 202, 211), Cornell University Press (1953).

Fuson, "Advanced Organic Chemistry," chap. 1, Wiley (1953).

Wheland, "Advanced Organic Chemistry," 2nd ed., p. 83, Wiley (1949). Examples of electrophilic groups or substituents, represented by X in Formula 1, which are included in this preferred group are as follows: halogens (F, Cl, Br, I), hydrocarbon (-R'), carboxyl

where Y is F, Cl, Br, I), cyano (-CN), trihalomethyl (—CCl3,-CF3, etc.), acyl

nitro (NO2), nitroso (-NO), azo (-N-N-R'), sulfo (-SO,H), sulfonyl (-SOR'), hydrocarbonoxy (OR'), hydrocarbonmercapto (-SR'), and mercuric acetyl

(-HgO (CH3)
HgOCCH1)

R', where used in the above substituents is a monovalent organic group which is preferably a hydrocarbon group (alkyl, cycloalkyl, alkenyl, cycloalkenyl, aryl, alkaryl, aralkyl) of at most 18 carbons.

The number of substituents which can be present on the dodecahydrododecarborate(2-) anion is not less than 1 or more than 12. Thus, the anion (B12H12-yXy)-2, in the generic formula M2(B12H12-yXy)b, can range from (B12H11X)-2 through successively decreasing hydrogen content to (B12X12)-2. Examples of the new compounds of the invention, illustrated by formulas, are as follows:

[(C2H5)4N]2B12H11OH, [(C2H3)2NH2]2B12H10(OH)2

HgB12H10(OH)2, (H2O)2B12HCOOH. [(CH3)2NNH3)2B12H10Cl,
CaB1H8C14, Na¿B12H10(CH3)2, K2B1¿H¡¡C2H5, Nа2B12H,(C3H:);

The invention includes within its scope compounds with two or more X groups which are unlike, e.g.,

and the like.

[(CH3)4P]2B 2C14F,(SC4H9)2(OCH)2

The new compounds are usually solid products which are salt-like in character. Many of the compounds dissolve in water. The color of the compounds is dependent on the nature of the M group and of the electrophilic group bonded to boron. For example, the cupric ammonium salts are bright blue, alkali metal salts are are usually white.

Most of the compounds are stable and usually can be handled in a conventional manner. Thus, compounds having halogen, alkyl or acyl substituents are stable and they can be kept in storage for prolonged periods in ordinary containers. However, the precautions usually followed in handling new compositions should be employed.

The scope of the monovalent groups encompassed by X in generic Formula 1 for the compounds of the invention can be understood more clearly by describing methods for obtaining the compounds.

The ionic charge of -2 on the boron-containing anion, which was discussed previously, refers to a charge which is inherent in the boron-hydrogen cage structure. The value of the ionic charge is independently of and does not take into consideration any ionic charge which may reside in the X substituents by virtue of ionizable functional groups. The ions which are formed by ionizable substituents are considered to be part of the X groups and are included within the scope of these groups. For example, carboxyl, sulfo, amino, thiol and like substituents will function as groups which possess acidic or basic properties which are independent of the boron cage structure.

Preparation of compounds

Electrophilic substitution.—In this method, which involves the direct substitution of hydrogen, two reactants are employed which are defined as follows: (a) a boron-containing compound of the general formula M,(BH12H12) b, wherein M, a and b have the meanings given earlier in generic Formula 1 for the novel compounds.

(b) a reagent capable of introducing an electrophilic group into a benzene nucleus by replacement of hydrogen bonded to a carbon of said nucleus. This second reactant is referred to as an electrophilic reagent.

The characteristics of each group of reactants are discussed in more detail in the following paragraphs.

The boron-containing reactant, M.(B12H12) b, is a dibasic acid or a salt of a dibasic acid which has, as a characterizing group, a divalent anion, (B12H12-2). This anion will be referred to as the "dodecahydrododecaborate (2) anion" or, for simplicity, as "dodecahydrodecaborate (2-)."

At this point, it should be noted that the novelty of the compounds of the invention is such that no officially approved system of nomenclature has yet been established. The name "dodecahydrododecaborate (2-) "follows the lines recommended for naming other boron compounds and its use here permits the logical naming of a derivative of the (B12H12)-2 anion as a substituted "dodecaborate (2-)".

Dodecahydrododecaborate (-2) is an unusual species of divalent anion which has remarkable and unexpected chemical properties. In many respects it shows much greater chemical stability than any previous reported boron hydrides, whether neutral or bearing a charge. For example, the anion is inert to sodium methoxide in refluxing methanol and it does not hydrolyze in water. The anion forms salts with basic materials, e.g., amines and metals, and from these salts there can be obtained a strongly acidic hydronium compound by treatment with an ion exchange resin. Solutions of silver nitrate are not reduced by aqueous solutions containing the B12H12-2 anion, a behavior which is in marked contrast to the behavior of other boron hydrides. The stability of the B12H12-2 anion to strong bases, strong acids, and oxidizing agents is unique for boron hydride structures.

It is surprising, in view of the chemical stability described above, to find that the dodecahydrododecaborate (2-) anion undergoes a wide range of substitution reactions in a manner which resembles the behavior of a carbocyclic aromatic compound, e.g., benzene or naphthalene. More specifically, the hydrogens bonded to boron in the B12H122 group are replaceable by substituents which can also replace hydrogen bonded to nuclear carbon in benzene or a substituted benzene such as toluene. This behavior of the dodecahydrododecaborate (2-) anion is particularly surprising in view of the completely inorganic composition of the anion. It is the previously unknown "aromatic character" of the dodecahydrododecaborate (2-) anion which forms the basis of the present invention leading to a broad range of novel substituted dodecaborates (2−).

It is evident from the above description of the chemistry of the dodecahydrododecaborate (2-) anion that the second reactant, i.e., the electrophilic reagent, employed in preparing the novel compounds is a reagent which can effect a substitution reaction in a benzene nucleus. These reagents, in view of the extensive work which has been done on substitution reactions in the benzene nucleus, form a well-known group of compounds.

Electrophilic reagents which are broadly operable in the process are reagents which will effect direct substitution of hydrogen bonded to carbon of a benzene

nucleus, i.e., the hydrogen is replaced by a group derived from the electrophilic reagent. Electrophilic reagents are compounds which react by acquiring electrons or acquiring a share in electrons which previously belonged to a foreign molecule (see Ingold, vide supra, p. 201). Examples of electrophilic reagents which are within the scope of the above definition and which are operable in the process of the invention are given below, together with the substituent group which in the process is bonded to boron in the final product.

In the above groups, R' is a monovalent organic radical, preferably hydrocarbon of at most 18 carbons, which can be alkyl, alkyenl, cycloalkyl, cycloalkenyl, aryl, alkaryl, aralkyl, and the like.

In the reactions employing some of the above electrophilic reagents, a catalyst may be used, e.g., aluminium trichloride, boron trifluoride and polyphosphoric acid. These catalysts are employed in the same manner as in the well-known procedures in organic chemistry. In some cases the boron compounds themselves function as catalysts, e.g., in alkylation of (H3O)2B12H12.

The electrophilic reagents employed in the process are materials which are usually readily available of which are obtained by conventional methods.

It is evident from the above discussion that a wide range of processes is available for the preparation of compounds of the invention. These processes are illustrated more fully in the examples which are given later in the discussion of the invention. Processes which are employed to introduce one or more X groups on the boron cage are not necessarily identical with the processes employed to introduce the X groups on a benzene nucleus. Consideration must be given to differences in reactivity or in reaction mechanism between a completely inorganic system, as represented by the B2H122 anion and an organic aromatic system represented by the benzene ring.

It is further noted that in the preparation of compounds of the invention by methods discussed earlier the substituent which ultimately is bonded to boron in the final product is not necessarily the substituent which would be obtained with a process employing a conventional carbocyclic aromatic reactant. To illustrate, reaction of formaldehyde with a dodecahydrododecaborate (2-) yields a compound of Formula 1 in which X is-OCH, instead of-CH2OH which might be obtained. Variations of this nature from conventional results are, as mentioned earlier, not unexpected in view of the completely inorganic character of the dodecahydrododecaborate(2−) anion. Such variations do not change the view of the basic aromatic character of the boron sphere or cage in the dodecaborate anion. Differences in preparative procedures or variations in the types of substituents which may be obtained do not change in any way the common characteristics or property of all the X groups, i.e., the property of bonding to a nuclear carbon of a benzene ring.