WO2009058405A1 - Methods of preparing clusterboron - Google Patents

Abstract

The invention provides new methods for synthesis of ClusterBoron (B18H22). Preferred methods of the invention include in situ generation of the conjugate acid of B20H182- and degradation of the acid in solution to produce B18H22 in high yields and high purity. The invention further provides isotopically enriched boranes, particularly isotopically enriched 10B)18H22 and 11B18H22.

Description

METHODS OF PREPARING CLUSTERBORON

The present application claims the benefit of U.S. provisional application number 61/001682 filed November 2, 2007, which is incorporated by reference herein in its entirety.

BACKGROUND

1. Field of the Invention.

The invention provides methods for synthesizing Bi₈H₂₂ as a mixture of syn and anti isomers, commonly marketed as ClusterBoron. The invention further provides isotopically enriched Bi₈H₂₂ prepared by the aforementioned methods. In particular, the invention relates the preparation of natural abundance Bi₈H₂₂, ¹⁰B- enriched Bi₈H₂₂ and ^πB-enriched Bi₈H₂₂.

2. Background.

Large boron hydride compounds have become important feed stocks for boron doped P-type impurity regions in semiconductor manufacture. More particularly, high molecular weight boron hydride compounds, e.g., boron hydride compounds comprising at least a five (5) boron atom cluster, are preferred boron atom feed stocks for molecular boron implantation.

An important aspect of modern semiconductor technology is the continuous development of smaller and faster devices. This process is called scaling. Scaling is driven by continuous advances in lithographic process methods, allowing the definition of smaller and smaller features in the semiconductor substrate which contains the integrated circuits. A generally accepted scaling theory has been developed to guide chip manufacturers in the appropriate resize of all aspects of the semiconductor device design at the same time, i.e., at each technology or scaling node. The greatest impact of scaling on ion implantation processes is the scaling of junction depths, which requires increasingly shallow junctions as the device dimensions are decreased. This requirement for increasingly shallow junctions as integrated circuit technology scales translates into the following requirement: ion implantation energies must be reduced with each scaling step. The extremely shallow junctions called for by modern, sub-0.13 micron devices are termed "Ultra-Shallow Junctions" or USJs.

Methods of manufacturing boron doped P -type junctions have been hampered by difficulty in controlling the ion-implantation process using boron. The single boron atom, being light (MW =10.8), can penetrate too deeply into a silicon substrate and diffuse throughout the substrate lattice rapidly during annealing or other elevated temperature processes.

Boron clusters or cages, e.g., boranes have been investigated as a feed stock for delivering molecular boron species to a semiconductor substrate with reduced penetration. See PCT/US03/20197.

Large boron hydride compounds, that is boron compounds having between 5 and about 100 boron atoms are preferred for use in molecular ion implantation methods for delivering boron atoms to a semiconductor substrate. Typically, there may be isomers of the boron hydride compound that exist. That is, boron hydrides with the same number of boron and hydrogen atoms that possess different chemical properties, e.g. structural isomers or stereoisomers. In addition, two or more structurally related boron hydride compounds having the same number of boron atoms but different numbers of hydrogen atoms have been isolated for various sized boron clusters. For example, pentaborane(9) and pentaborane(l 1) have chemical formulas Of B₅H₉ and B₅Hn respectively. Such compounds are frequently classified as closo (B_nH_n), «/do(B_nH_n+2), arachno (B_nH_n+4), hypho (B_nH_n+6), conjuncto (B_nH_n+8), and the like. Thus, different boron hydride species, including isomers and compounds containing various amounts of hydrogen, are frequently known for boron hydrides having n boron atoms. Jemmis, et al. have provided a review of various macropolyhedral boranes and known compounds having n boron atoms and various amounts of hydrogen. ' ' ²

Mixtures of isomers and mixtures of n-boron atom containing boron hydrides are suitable for use in the implantation methods discussed. The molecular ions generated by the ionization process of boron hydride mixtures will have uniform and narrow weight distributions.

Current synthetic technologies for the preparation of large boron hydride molecules, e.g., boron hydride molecules with more than 12 boron atoms, are often plagued by complicated synthetic processes, low isolated yields, and/or inconsistent reproducibility.

Although there are several synthetic routes reported in the literature for the preparation Of Bi₈H₂₂ as a mixture of isomers, they are lengthy, often result in notably low yields, are unreliable and have safety issues associated with the synthesis.

It thus would be desirable to have new methods for preparation Of Bi₈H₂₂.

SUMMARY

We have now discovered new methods for the preparation of octadecaborane, B₁₈H₂₂. The invention is particularly useful for facile synthesis and purification of large quantities Of B]₈H₂₂. The present invention also relates to isotopically-enriched Bi₈H₂₂. Whereas, by definition, enriched means the modification of the boron isotopes natural abundance. Depending on source natural abundance of the ¹⁰B isotope ranges from 19.10 % to 20.31 % and natural abundance of the ^{1 1}B isotope ranges from 80.90 % to 79.69 %.

A typical Bj₈H₂₂ molecular ion beam contains a wide range of ion masses due to a varying number of hydrogen losses from the molecular ion as well as the varying mass due to the two naturally occurring isotopes. As mass selection is possible in an implanter device used in semiconductor manufacture, use of isotopically enriched boron in Bi₈H₂₂ can greatly reduce the spread of masses, thereby providing an increased beam current of the desired implantation species. Thus, B and B isotopically-enriched Bj₈H₂₂ is also of great interest.

In one aspect, the invention provides methods for synthesizing octadecaborane

(Bi₈H₂₂), which methods suitably comprise: (a) contacting the borane anion Bi₀HiO^2" with an oxidizing agent to produce B₂₀Hi₈ ^2"; and (b) contacting the borane anion B₂₀Hi₈ ^2" with acid to produce H₂B₂₀Hi₈*xH₂O.

In a further aspect, the invention provides methods for synthesizing octadecaborane (Bi₈H₂₂), which methods suitably comprise (a)contacting the borane anion Bi₀Hi₀ ^2" with an oxidizing agent to produce B₂₀Hi₈ ^2"; (b) contacting the borane anion B₂₀Hi₈ ^2" with acid to produce H₂B₂₀Hi₈»xH₂O; and (c) separating insoluble byproducts from the reaction mixture.

In certain aspects the invention provides synthesizing Bi₈H₂₂ by methods comprising the steps of:

(a) contacting the borane anion B _I0Hi₀ ^2" in solvent with an oxidizing cage- coupling agent to produce B₂₀Hi₈ ^2" in situ; (b) washing of the B₂₀Hi₈ ^2" such as to remove byproducts

(c) contacting the borane anion B₂₀H]₈ ^2" in solvent and water with acid, preferably a molar excess thereof, to produce H₂B₂₀H i₈»xH₂O in situ;

(d) removing water from the reaction vessel, preferably in the presence of a Bj₈H₂₂ solubilizing solvent that remains essentially chemically inert in the system; (e) separating insoluble byproducts from the reaction mixture through (i) filtration and/or (ii) concentration of reaction solvent, dissolution Of Bj₈H₂₂ into aliphatic solvent and filtration of byproducts; (f) isolation of B ₁₈H₂₂ such as through removal of solvent.

Preferred methods of the invention are suitable to prepare isotopically pure

Bi₈H₂₂ and mixtures of structural isomers Of Bi₈H₂₂. That is, the method of the invention, provide Bi₈H₂₂ capable of generating a suitable molecular ion beam for ion implantation and high purity Bi₈H₂₂ for use in other applications.

In some aspects of the invention, a solution Of Bi₀Hi₀ ^2" is reacted in solution with an oxidant in a cage-coupling oxidation to form B₂₀Hi₈ ^2". Preferred oxidants form stable species on reduction that do not significantly react with the B₂₀Hi₈ produced. Possible oxidizing agents include inorganic metal reagents or organic oxidants with a standard reduction potential of E⁰ > 0 V. These may include Sn(IV), Fe(III), Cu(II), Mn(VII), Ag(I), Mn(IV), Cr(VI), Cl₂, Br₂, Hg(I), Hg(II), Au(III), Ce(IV), Pb(IV), Co(III), F₂, 1₂, O₃, hydrogen peroxide, organic peroxides, or organometallic compounds. Preferred solvents are mixtures in which the Bi₀HiO^2" salt is soluble but not destroyed and B₂₀H i₈ ^2" salt is insoluble but not destroyed. These solvents may include water, alcohols, nitriles, ethers, sulfones, and the like.

The Bi₈H₂₂ precursor H₂B₂₀H ig»xH₂O is produced in situ by contacting the

B₂₀H)₈ ^2" salt with acid in a chemically inert solvent and water. Preferred acids have a pKa < 2.0 and should not be destructive to any reaction starting materials, intermediates or B]₈H₂₂. These may include mineral acids such as sulfuric acid, nitric acid, phosphoric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid as well as organic acids such as sulfonic acids, halogenated acetic acids, and oxalic acids.

Bi₈H₂₂ is formed from H₂B₂₀Hi₈^xH₂O with the simultaneous or subsequent removal of water from the system. Although not wishing to be bound by theory, conditions conducive to removal of water from the hydrated hydronium ion salt, H₂B₂₀H]₈*xH₂O (where x is a positive real number), are also suitable to induce partial hydronium ion degradation. Typically, preferred degradation conditions include the use of Dean Stark trap, moisture traps, moisture scavengers or contacting the hydrated hydronium salt with one or more drying agents. Drying agents may include, but are not limited to molecular sieves, phosphorus pentoxide, alumina, silica, silicates and the like, or a combination thereof. Reaction solvents should not cause degradation or show significant reactivity to Bi₈H₂₂ or any starting materials or intermediates produced during the course of the reaction. These may include, but are not limited to aromatic and arene solvents, alkane solvents, ethers, sulfones, esters, and the like. Reaction temperatures to promote water removal from the system range from 0 ⁰C to about 250 ⁰C.

In a preferred aspect, the invention provides for the synthesis of Bi₈H₂₂ by methods comprising the steps of:

(a) contacting an ammonium salt Of Bi₀Hi₀ ^2" in acidic water (pH < 2.0) with FeCl₃ at reflux to produce B₂₀H)₈ ^2";

(b) washing of the B₂₀H)₈ ^2" with water such as to remove byproducts; (c) contacting the borane anion B₂₀H )₈ ^2" in toluene and water with 5-40 molar equivalents ofp-toluenesulfonic acid to produce H₂B₂₀Hi ₈*xH₂O in situ;

(d) removing water from the reaction vessel such as in the presence of a hot toluene (90 °C to 120 °C) and through the use of a Dean Stark moisture trap;

(e) separating insoluble byproducts from the reaction mixture through filtration; (f) removal or concentration of toluene to leave crude Bj₈H₂₂ that is contaminated with boric acid and borates;

(g) dissolution of crude Bi₈H₂₂ into hexanes and filtration of insolubles;

(h) removal of hexanes to isolate B)₈H₂₂.

In yet another preferred aspect, the invention provides for the synthesis of

B 18h22 by methods comprising the steps of:

(c) contacting the borane anion B₂₀H)₈ ^2" in toluene and water with 5-40 molar equivalents of/?-toluenesulfonic acid to produce H₂B₂₀H ig»xH₂O in situ;

(d) removing water from the reaction vessel such a sin the presence of a hot toluene (90 °C to 120 ⁰C) such as through the use of a Dean Stark moisture trap;

(e) separating insoluble byproducts from the reaction mixture through filtration;

(f) removal or concentration of toluene to leave crude B)₈H₂₂ that is contaminated with boric acid and borates;

(g) dissolution of crude B)₈H₂₂ into hexanes and filtration of insolubles; (h) removal of hexanes to isolate B)₈H₂₂. Preferred methods of the invention are suitable to provide Bi₈H₂₂ capable of generating a suitable molecular ion beam for ion implantation and high purity Bi₈H₂₂ for use in other applications.

The methods of synthesis, which provide Bi₈H₂₂ in high isolated yield (>50%) and with few synthetic procedures, are suitable for use in preparing isotopically enriched Bi₈H₂₂, e.g., the isotopic concentration of ¹⁰B or 1 IB is greater than natural abundance. Preparation of isotopically enriched, ¹⁰B or ¹¹B, Bj₈H₂₂ is practical using the invention synthesis methods due to the limited number of synthetic steps, mass efficiency, and high overall synthetic yield (>65 % from B₂₀Hi₈ ^2").

Other aspects of the invention are disclosed infra.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows schematically a preferred process of the invention;

Figure 2 shows use of a reaction set-up according to a preferred process of the invention.

DETAILED DESCRIPTION

In one preferred aspect, the present includes methods of synthesizing octadecaborane (Bi₈H₂₂), comprising:

(a) contacting the borane anion B _I0Hi₀ ^2' preferably in solvent with an oxidizing agent (preferably, an oxidizing cage-coupling agent) to produce B₂₀Hi₈ ^2" preferably in situ;

(b) optionally washing the B₂₀Hi₈ ^2" to remove byproducts;

(c) contacting the borane anion B₂₀Hi₈ ^2" preferably in solvent (e.g. is water, alcohols, nitriles, ethers, sulfones, arenes, aliphatic hydrocarbons, and combinations thereof) and water with acid (preferably a molar excess of acid, with suitable acids including organic and inorganic acids having a pKa of less than about 2 e.g. p-toluene sulfonic acid) to produce H₂B₂₀Hi₈»xH₂O preferably in situ;

(d) optionally removing water from the reaction vessel in the presence of a Bi₈H₂₂ solubilizing solvent that remains essentially chemically inert in the system; (e) separating insoluble byproducts from the reaction mixture preferably through (i) filtration and/or (ii) concentration of reaction solvent, dissolution Of B₁₈H₂₂ into aliphatic solvent (e.g. alkanes, ethers, or a combination thereof) and filtration of byproducts; and (f) preferably isolation of Bi₈H₂₂ such as through solvent removal.

In the above method, the oxidizing agent preferably has a standard reduction potential of E⁰ > 0 V. More particularly, the oxidizing agent suitably may be an inorganic salt with standard reduction potential of E⁰ > 0 V. The oxidizing agent also may be an iron(III) salt. The oxidizing agent suitably may be an organometallic compound with a standard reduction potential of E⁰ > 0 V. The oxidizing agent also suitably may be an organic oxidant with a standard reduction potential of E⁰ > 0 V. Preferred oxidizing agents include iron(IIl) salts.

Suitable solvents in step (c) of the above method include wherein the solvent is a mixture of aqueous and non-aqueous solvents, and suitable non-aqueous solvents may be suitably selected from the group consisting of alcohols, nitriles, ethers, arenes, aliphatic hydrocarbons and combinations thereof, more preferably hexanes, toluene, xylenes or a combination thereof, and suitably wherein the non-aqueous solvent comprises between about 1 % and about 99% by volume of the total solvent component, suitably with the solvent component comprising between about 1% and 99% water by volume based on total volume of the solvent component.

In another preferred aspect, methods are provided to synthesize octadecaborane (Bi₈H₂₂), the methods comprising:

(a) contacting the borane anion B₂₀H)₈ ^2' preferably in solvent and water with acid (preferably a molar excess, , with suitable acids including organic and inorganic acids having a pKa of less than about 2 e.g. p-toluene sulfonic acid) to produce H₂B₂₀H)₈*xH₂O preferably in situ; (b) preferably removing water from the reaction vessel in the presence of a B]₈H₂₂ solubilizing solvent that remains essentially chemically inert in the system; (c) preferably separating insoluble byproducts from the reaction mixture such as through (i) filtration and/or (ii) concentration of reaction solvent, dissolution of Bi₈H₂₂ into aliphatic solvent (e.g. alkanes, ethers, or a combination thereof) and filtration of byproducts; and (d) preferably isolating Bi₈H₂₂ such as through removal of solvent.

In the above methods, the Bi₀Hi₀ ^2" salt may be suitably an alkyl ammonium salt with a cation formula of [NR¹R²R³R⁴]*, wherein

R¹, R², and R³ are independently selected from the group consisting of hydrogen, Ci_-20alkyl, C_6-i₀aryl, C_7-ioaralkyl, or any two of R¹, R², or R³ taken in combination form a heterocyclic ring; and

R⁴ is selected from hydrogen, Ci_-20alkyl, or C_6-ioaryl;

In the above methods, the B₂₀Hi₈ ^2" salt may be suitably an alkyl ammonium salt with a cation formula of [NR¹R²R³R⁴J⁺, wherein

R¹, R , and R³ are independently selected from the group consisting of hydrogen, Ci_-20alkyl, C_6-i₀aryl, C_7-i₀aralkyl, or any two of R , R , or R taken in combination form a heterocyclic ring; and

R⁴ is selected from hydrogen, Ci_-20alkyl, or C_6-i₀aryl;

In the above methods, the B₂₀Hi₈ ^2" salt may be suitably an inorganic salt.

Suitable solvents in step (a) of the above method include wherein the solvent is a mixture of aqueous and non-aqueous solvents, and suitable non-aqueous solvents may be suitably selected from the group consisting of alcohols, nitriles, ethers, arenes, aliphatic hydrocarbons and combinations thereof, more preferably hexanes, toluene, xylenes or a combination thereof, and suitably wherein the non-aqueous solvent comprises between about 1% and about 99% by volume of the total solvent component, suitably with the solvent component comprising between about 1 % and 99% water by volume based on total volume of the solvent component. In the above methods, water may be removed from the reaction mixture by a variety of methods including e.g. through the use of moisture traps, moisture scavengers, or more drying agents such as molecular sieves, phosphorus pentoxide, alumina, silica, silicates and the like, or a combination thereof. A Dean-Stark trap can be preferred such as illustrated in Figure 2..

In another aspect, a method of synthesizing octadecaborane (Bi₈H₂₂) is provided, the method comprising:

(a) contacting an ammonium salt OfBi₀Hi₀ ^" in acidic water (pH < 2.0) with FeCl₃ at reflux to produce B₂₀Hj₈ ^2";

(b) washing of the B₂₀Hi₈ ^2" with water to remove byproducts;

(c) contacting the borane anion B₂₀Hi₈ ^2" in toluene and water with 5-40 molar equivalents ofp-toluenesulfonic acid to produce H₂B₂₀H i₈*xH₂O in situ;

(d) removing water from the reaction vessel in the presence of a hot toluene (90 °C to 120 °C) through the use of a Dean Stark moisture trap (see Figure 3);

(e) separating insoluble byproducts from the reaction mixture through filtration;

(f) removal or concentration of toluene to leave crude Bi₈H₂₂ that is contaminated with boric acid and borates;

(g) dissolution of crude Bi₈H₂₂ into hexanes and filtration of insolubles; (h) removal of hexanes to isolate Bi₈H₂₂

In a further aspect, a method of synthesizing octadecaborane (Bi₈H₂₂) is provided, the method comprising:

(a) contacting the borane anion B₂₀Hi₈ ^2' in toluene and water with 5-40 molar equivalents of/?-toluenesulfonic acid to produce H₂B₂₀Hi₈^xH₂O in situ;

(b) removing water from the reaction vessel in the presence of a hot toluene (90 °C to 120 °C) through the use of a Dean Stark moisture trap (see Figure 3);

(c) separating insoluble byproducts from the reaction mixture through filtration;

(d) removal or concentration of toluene to leave crude Bi₈H₂₂ that is contaminated with boric acid and borates;

(e) dissolution of crude Bj₈H₂₂ into hexanes and filtration of insolubles;

(f) removal of hexanes to isolate B 1₈H₂₂ In methods of the invention wherein the isotopic concentration of ¹⁰B atoms suitably may be greater than the natural abundance, e.g. wherein at least about 50% of the boron atoms present in the product Bi₈H₂₂ are ¹⁰B, or wherein at least about 80% of the boron atoms present in the product Bi₈H₂₂ are ¹⁰B, or wherein at least about 90% of the boron atoms present in the product B)₈H₂₂ are ¹⁰B, or wherein at least about 95% of the boron atoms present in the product Bi₈H₂₂ are ¹⁰B, or wherein at least about 99% of the boron atoms present in the product Bi₈H₂₂ are ¹⁰B.

In the methods of the invention, the isotopic concentration of ¹¹B atoms suitably may be greater than the natural abundance, e.g. wherein at least about 90% of the boron atoms present in the product Bi₈H₂₂ are ¹¹B, or wherein at least about 95% of the boron atoms present in the product Bi₈H₂₂ are ' ¹B, or wherein at least about 99% of the boron atoms present in the product Bj₈H₂₂ are ¹¹B.

Figure 1 of the drawings also depicts a specifically preferred method of the invention.

The invention now being generally described, it will be more readily understood by reference to the following examples, which are included merely for purposes of illustration of certain aspects and embodiments of the present invention, and are not intended to limit the invention.

Example 1 Re-crystallized but not dried (HNEt₃)₂B₂₀H i₈*xH₂O prepared from

(HNEt₃)₂BioH,o (100.0 g, 0.31 mol) and^-C₇H₄SO₃H»H₂O (265.4 g, 1.40 mol) are weighed into a 1 L two-necked round bottomed flask. Toluene (1 L) and water (1 13 mL) are added to the flask the Dean Stark apparatus is assembled as in Figure 3 and the trap filled with toluene. After purging with argon for 45 minutes, the solution is brought to reflux with rapid stirring. Following the removal of most of the water from the reaction, hydrogen evolution significantly increases and precipitate begins to form. When hydrogen evolution ceases, the reaction is cooled and insolubles filtered away. The toluene layer is separated from any oils present, washed with water (3 x 200 mL), dried over MgSO₄ and concentrated to dryness to give a light yellow powder. The powder is extracted with 1 L of hexanes and any insolubles are removed by filtration. The hexane solution is removed to leave white to off-white Bi₈H₂₂ (16.8 g, 50.6 %).

Example 2

Re-crystallized but not dried (HNEt₃)₂' ¹B₂₀H₁₈^xH₂O prepared from (HNEt₃)₂' ¹Bi₀Hi₀ (5.00 g, 15.4 mmol) andp-C₇H₄SO₃H»H₂O (14.32 g, 75.3 mmol) are weighed into a 1 L two-necked round bottomed flask. Toluene (150 L) and water (30 mL) are added to the flask the Dean Stark apparatus is assembled as in Figure 3 and the trap filled with toluene. After purging with argon for 45 minutes, the solution is brought to reflux with rapid stirring. Following the removal of most of the water from the reaction, hydrogen evolution significantly increases and precipitate begins to form. When hydrogen evolution ceases, the reaction is cooled and insolubles filtered away. The toluene layer is separated from any oils present, washed with water (3 x 100 mL), dried over MgSO₄ and concentrated to dryness to give a light yellow powder. The powder is extracted with 250 mL of hexanes and any insolubles are removed by filtration. The hexane solution is removed to leave white to off-white ¹¹Bi₈H₂₂ (0.85 g, 50.1 %). ¹¹B enrichment was determined to be that of the starting material (> 98.6 % ¹¹B isotopic enrichment).

The invention has been described in detail with reference to preferred embodiments thereof. However, it will be appreciated that those skilled in the art, upon consideration of the disclosure, may make modifications and improvements within the spirit and scope of the invention.

References:

1. Jemmis, E. D.; Balakrishnarajan, M. M.; Pancharatna, P. D., Electronic Requirements for Macropolyhedral Boranes. Chem. Rev. 2002, 102, 93-144.

2. Jemmis, E. D.; Balakrishnarajan, M. M.; Pancharatna, P. D., A unifying Electron-Counting Rule for Macropolyhedral Boranes, metallaboranes, and Metallocenes. J. Amer. Chem. Soc. 2001, 123, 4313-4323. 3. Pitochelli, A. R.; Hawthorne, M. F., The Preparation of a New Boron Hydride B₁₈H₂₂. J. Amer. Chem. Soc. 1962, 84, 3218.

4. Hawthorne, M. F.; Pilling, R. L.; Stokely, P. F., The preparation and rearrangement of the three isomeric B₂₀Hi₈ ^4" ions. J. Am. Chem. Soc. 1965, 87, 1893- 1899.

5. Olsen, F. P.; Vasavada, R. C; Hawthorne, M. F., The chemistry of n-B)₈H₂₂ and i-Bi₈H₂₂. J. Am. Chem. Soc. 1968, 90, (15), 3946-3951.

6. Chamberland, E. L.; Muetterties, E. L., Chemistry of Boranes. XVIII. Oxidation Of Bi₀Hi₀ ^"2 and its derivatives. Inorg. Chem. 1964, 3, 1450-1456.

All of the patents and publications cited herein are hereby incorporated by reference in their entirety.

Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the following claims.

Claims

What is claimed is:

1. A method of synthesizing octadecaborane (Bi₈H₂₂), the method comprising:

(a) Cc⁽ontacting the borane anion Bi₀Hi_O ^2" with an oxidizing agent to produce

B₂₀Hi₈ ^2"; and

(b) contacting the borane anion B₂₀Hi₈ 2-^" with acid to produce H₂B₂₀H i₈»xH₂O.

2. A method of synthesizing octadecaborane (B_]8H₂₂), the method comprising:

(a) contacting the borane anion Bi₀Hi₀ ^2" with an oxidizing agent to produce B₂₀Hi₈ ;

(b) contacting the borane anion B₂₀Hi₈ ^2" with acid to produce H₂B₂₀H i₈*xH₂O; and

(c) separating insoluble byproducts from the reaction mixture.

3. The method of claim 1 or 2 wherein the oxidizing agent is a oxidizing cage- coupling agent.

4. The method of claim 1 or 2 further comprising after step (b) removing water from the reaction vessel in the presence of a Bi₈H₂₂ solubilizing solvent that remains essentially chemically inert in the system;

5. The method of claim 1 or 2 wherein in step (c) byproducts can be separated through (i) filtration and/or (ii) concentration of reaction solvent, dissolution of B)₈H₂₂ into aliphatic solvent and filtration of byproducts.

6. The method of claim 1 or 2 wherein after step (c) B)₈H₂₂ is isolated.

7. The method of claim 6 wherein Bi₈H₂₂ is isolated through solvent removal.

8. A method of synthesizing octadecaborane (B)₈H₂₂), the method comprising: (a) contacting the borane anion B₂₀Hi₈ ^2" with acid to produce H₂B₂₀Hi₈^xH₂O; (b) removing water from the reaction vessel in the presence of a Bj₈H₂₂ solubilizing solvent that remains essentially chemically inert in the system; and

(c) separating insoluble byproducts from the reaction mixture through (i) filtration and/or (ii) concentration of reaction solvent, dissolution Of Bj₈H₂₂ into aliphatic solvent and filtration of byproducts.

9. The method of claim 8 wherein Bj₈H₂₂ is isolated through removal of solvent.

10. The method of claim 1, 2 or 8 wherein the BioHio^2" salt is an alkyl ammonium salt with a cation formula of [NR¹ R²R³R⁴J⁺, wherein

R¹, R², and R³ are independently selected from the group consisting of hydrogen, Ci_-20alkyl, C_ό-ioaryl, C_7-ioaralkyl, or any two of R¹, R², or R³ taken in combination form a heterocyclic ring; and

R⁴ is selected from hydrogen,

or C_ό-ioaryl;

11. The method of claims 1 , 2 or 8 wherein the B₂₀Hi₈ ^2" salt is an alkyl ammonium salt with a cation formula of [NR¹R²R³R⁴]*, wherein

R¹, R², and R³ are independently selected from the group consisting of hydrogen, Cj.₂oalkyl, Cn-ioaryl, C_7-i₀aralkyl, or any two of R¹, R², or R³ taken in combination form a heterocyclic ring; and

R⁴ is selected from hydrogen, Cj_-2oalkyl, or C_δ-ioaryl;

12. The method of claim 1, 2 or 8 wherein the B₂₀Hj₈ ^2" salt is an inorganic salt.

13. The method of claim 1 or 2 wherein the oxidizing agent has a standard reduction potential of E⁰ > 0 V.

14. The method of claim 1 or 2 wherein the oxidizing agent is an inorganic salt with standard reduction potential of E⁰ > 0 V.

15. The method of claim 1 or 2 wherein the oxidizing agent is an iron(III) salt.

- 15 -

16. The method of claim 1 or 2 wherein the oxidizing agent is an organometallic compound with a standard reduction potential of E⁰ > 0 V.

17. The method of claim 1 or 2 wherein the oxidizing agent is an organic oxidant with a standard reduction potential of E⁰ > 0 V.

18. The method of claims 1, 2 or 8 wherein the acid is an organic acid having a pKa of less than about 2.

19. The method of claims 1 , 2 or 8 wherein the acid is an inorganic acid having a pKa of less than about 2.

20. The method of claims 1, 2 or 8 wherein the acid is/j-toluenesulfonic acid.

21. The method of claims 4 or 8 wherein the solvent comprise a mixture of one or more aqueous solvents and one or more non-aqueous solvents.

22. The method of claim 21 wherein the non-aqueous solvent is selected from the group consisting of alcohols, nitriles, ethers, arenes, aliphatic hydrocarbons and combinations thereof.

23. The method of claim 21 wherein the non-aqueous solvent comprises hexanes, toluene, xylenes or a combination thereof.

24. The method of claim 21 wherein the non-aqueous solvent comprises between about 1% and about 99% by volume of the total solvent component.

25. The method of claim 21 wherein the solvent comprises between about 1% and 99% water by volume of the total solvent component.

- 16 -

26. The method of claim 1, 2 or 8 wherein water is removed through the use of moisture traps, moisture scavengers, or more drying agents such as molecular sieves, phosphorus pentoxide, alumina, silica, silicates and the like, or a combination thereof,

27. The method of claim 1 , 2 or 8 wherein water is removed through the use of a Dean-Stark trap.

28. The method of claim 1 , 2 or 8 wherein the reaction temperature is between about 0 ⁰C and about 200 ⁰C.

29. The method of claim 1, 2 or 8 wherein the reaction temperature is between about 50 ⁰C and about 150 ⁰C.

30. The method of claim 1, 2 or 8 wherein the dissolution solvent is selected from the group consisting of alkanes, ethers, or a combination thereof.

31. The method of claim 30 wherein the dissolution solvent is hexanes.

32. A method of synthesizing octadecaborane (B_{I 8}H₂₂), the method comprising: (a) contacting an ammonium salt of BioHio^2" in acidic water (pH < 2.0) with FeCl₃ to produce B₂oHi₈ ^2';

(c) contacting the borane anion B₂₀Hi₈ ^2" with acid to produce H₂B₂₀Hi₈^xH₂O in situ;

(d) removing water from the reaction vessel;

(e) separating insoluble byproducts from the reaction mixture;

(f) optional solvent removal to provide crude B]₈H₂₂ that is contaminated with boric acid and borates;

(g) dissolution of crude B ₁₈H₂₂ into hexanes and filtration of insolubles.

33. The method of claim 32 comprising removal of solvent to isolate Bi₈H₂₂.

34. A method of synthesizing octadecaborane (B) ₈H₂₂), the method comprising:

- 17 - (a) contacting the borane anion B₂oHi₈ ^2" in toluene and water with 5-40 molar equivalents ofp-toluenesulfonic acid to produce H₂B₂₀Hi ₈*xH₂O in situ;

(b) removing water from the reaction vessel in the presence of a hot toluene (90 °C to 120 °C) through the use of a Dean Stark moisture trap (see Figure 3);

(c) separating insoluble byproducts from the reaction mixture through filtration;

(d) removal or concentration of toluene to leave crude Bi₈H₂₂ that is contaminated with boric acid and borates;

(e) dissolution of crude Bi₈H₂₂ into hexanes and filtration of insolubles;

(f) removal of hexanes to isolate Bi₈H₂₂

35. The method of any one of claims 1 through 34 wherein the isotopic concentration of ¹⁰B atoms is greater than the natural abundance.

36. The method of claim 35 wherein at least about 50% of the boron atoms present in the product Bi₈H₂₂ are ¹⁰B.

37. The method of claim 35 wherein at least about 80% of the boron atoms present in the product Bi₈H₂₂ are ¹⁰B.

38. The method of claim 35 wherein at least about 90% of the boron atoms present in the product Bj₈H₂₂ are ¹⁰B.

39. The method of claim 35 wherein at least about 95% of the boron atoms present in the product Bi₈H₂₂ are ' B.

40. The method of claim 35 wherein at least about 99% of the boron atoms present in the product B₁₈H₂₂ are ¹⁰B.

41. The method of any one of claims 1 through 35 wherein the isotopic concentration of ' ¹B atoms is greater than the natural abundance.

42. The method of claim 41 wherein at least about 90% of the boron atoms present in the product Bi₈H₂₂ are ¹¹B.

43. The method of claim 41 wherein at least about 95% of the boron atoms present in the product Bi₈H₂₂ are ^{1 1}B.

44. The method of claim 41 wherein at least about 99% of the boron atoms present in the product B]₈H₂₂ are ' ¹B.