US0075.24477B2

(12) United States Patent (10) Patent No.: US 7,524.477 B2 Spielvogel et al. (45) Date of Patent: Apr. 28, 2009

(54) METHOD OF PRODUCTION OF BH- 4,026,993 A 5, 1977 Ditter et al. AMMONUMI SALTS AND METHODS OF 4,115,520 A 9, 1978 Dunks et al. PRODUCTION OF BH, 4,115,521 A 9, 1978 Dunks et al. 4,153,672 A 5, 1979 Dunks et al. (75) Inventors: Bernard Spielvogel, Hubbards (CA); 4.338,289 A 7, 1982 Shore et al. Kevin Cook, Hammonds Plains (CA) 4,391.993 A 7/1983 Sayles (Continued) (73) Assignee: SemFouip Inc., N. Billerica, MA (US) FOREIGN PATENT DOCUMENTS (*) Notice: Subject to any disclaimer, the term of this WO WO-03/044837 A2 5, 2003 patent is extended or adjusted under 35 U.S.C. 154(b) by 451 days. (Continued) OTHER PUBLICATIONS (21) Appl. No.: 11/050,159 Mangeot et al., “(EtN)BoHo and (EtN)B12H12; synthesis from (22) Filed: Feb. 2, 2005 Et, NBH, separation and purification', Bulletin de la Socite Chimique de France (3), 385-9 (French) 1986 no month.* (65) Prior Publication Data (Continued) US 2005/O169828A1 Aug. 4, 2005 Primary Examiner Wayne Langel Related U.S. Application Data (74) Attorney, Agent, or Firm Peter F. Corless; Edwards Angell Palmer & Dodge LLP (60) Provisional application No. 60/541,322, filed on Feb. 2, 2004. (57) ABSTRACT (51) Int. Cl. The invention provides new methods for synthesis of BH, COIB 6/10 (2006.01) BioHo, BH, and B.H., salts, particularly alkylarn C07F 5/02 (2006.01) monium salts of B.H. BoHof, B.H., and BH-f. (52) U.S. Cl 423/294: 423/283: 564/8 More particularly, the invention provides methods of prepar ing tetraalkylamronium salts of BoHo, BioHo, B.H., (58) Field of Classification Search ...... 423/294, and B2H2 by pyrolysis of tetraalkylammonium borohy 423/283: 564/8 drides under controlled conditions. The invention addition See application file for complete search history. ally provides methods of preparing, in an atom efficient pro (56) References Cited cess, octadecaborane from the tetraalkylammonium salts of the invention. Preferred methods of the invention are suitable U.S. PATENT DOCUMENTS for preparation of isotopically enriched boranes, particularly 2,642.453 A 6/1953 Lippincott et al. isotopically enriched 'Bish, and 'Bish. 3,063,791 A 11, 1962 KollinitSchet al. 3,489,517 A 1/1970 Shore et al. 15 Claims, 1 Drawing Sheet

natural abundance or B(OH)3 Bloor B-11 enriched ROH

B(OR) NaH c NaAlH4 NaBH4 isolated or in situ RNX via Dunks process Route A Route B pyrolysis N. - > 80% yield from NaBH4 (RN);BioHoan < 30% yield from NaBH4 o with acid US 7,524.477 B2 Page 2

U.S. PATENT DOCUMENTS R. K. Hertz et al. "Quartenacy Ammonium and Phosphonium Heptahydrodiborates' Inorganic Syntheses, 1977, 17, 21, no month. 6,086,837 A 7/2000 Cowan et al. L.L. Ingram et al. “Mass Spectrum of n—Octadecaborane, n—BH' Spectroscopy. Letters, 1975, 8, 483, no month. FOREIGN PATENT DOCUMENTS A. Brandstrom et al. "An Improved Method for the Preparation of WO WO-2004/OO3973 A2 1, 2004 Solutions of Diborane” Tetrahedronbetters 1972, 31,3173-3176, no month. J.S. McAvoy et al. “The Preparation of n-BH via the Protonolysis OTHER PUBLICATIONS of the Tetradecahydroundecaborate Ion, BH-” Chemical Commu Y. Kawasaki et al. “Ultra-Shallow Junction Formation by BH Ion nications 1969, 1378-1379, no month. Implantation” Presented at: Ion Implantation Technology 2004, Oct. F.P. Olsen et al. “The Chemistry of n—BH and i —BH' 24-29, 2004, Taipe, Taiwan. Journal of the American Chemical Society 1968,90, 3946-3951, no L. Adams et al. “A New Synthetic Route to Boron-10 Enriched month. Pentaborane(9) from Boric Acid and its Conversion to anti M.F. Hawthorne et al. “The Preparation and Rearrangement of the 'BlsH,” Journal of the American Chemical Society 2002, 124, Three Isomeric BoHs' Ions” Journal of the American Chemical 7292-7293, no month. Society 1965, 87, 1893, no month. E.D. Jemmis et al. “Electronic Requirements for Macropolyhedral J. Plesek et al. “Chemistry of Boranes. VII. A New Synthesis of Boranes' Chemical Reviews 2002, 102, 93-144, no month. Borane BH; An Application of Three-Center Bonds Theory on E.D. Jemmis et al. “A Unifying Electron-Counting Rule for the Interpretation of Reaction Mechanisms' Coll. Czech. Chem. Macropolyhedral Boranes, Metallaboranes, and Metallocenes”,Jour Commun. 1967, 32, 1095-1103, no month. nal of the American Chemical Society, 2001, 123, 4313-4123, no M.F. Hawthorne et al. “Bis(triethylammonium) month. Decahydrodecaborate(2-) vol. IX, Inorganic Syntheses, Edited by S H. Mongeotet al. “(ET4N)2B10H10 et (ET4N)2B12H12: Synthese Young Tyree, Jr., McGraw-Hill Publishing Co., Inc., New York, New de EtANBH4. Separation et Purification' Bulletin De La Societe York (1967), 16-19, no month. Chimique De France 1986, 3,358-389, no month. E.L. Chamberland etal. “Chemistry of Boranes. XVIII. Oxidation of D.F. Gaines et al. "Preparation of n—Octadecaborane(22), in BH, BioHo' and Its Derivatives” Inorganic Chemistry 1964, 3, 1450 by Oxidative Fusion of Dodecahydrononaborane(1-) Clusters', no 1456, no month. date. P.G. Simpson et al. “Molecular, Crystal, and Valence Structures of A. Ouassas et al., Etude de la synthese des ions BHJ. Chem. Phys. 1963, 39, 26, no month. decahydrodecaborate(-2) B10H102- et dodecahydrodecaborate(-2) P.G. Simpson et al. “Molecular, Crystal, and Valence Structures of B12H122- Bulletin De La Societe Chimique De France 1984, 3, Iso-Bish,” J. Chem. Phys. 1963, 39, 2339, no month. 1-336-389, no month. A.R. Pitochelli et al. “The Preparation of a New Boron Hydride BH'Journal of the American Chemical Society 1962, 84, 3218, N.N. Greenwood et al. Chemistry of the Elements, Chapter 6, But no month. terworth-Heinemann, Oxford, UK (1984), no month. A. Kaczmarczyk et al. “Reactions of BioHo Ion” Proceedings of D. H. Gibson et al. “Reductions of Metal Carbonyls by Quaternary the National Academy of Sciences of the United States of America Ammonium Borohydrides' Journal of Ogranometallic Chemistry 1962, 48,729-733, no month. 1981, 218, 325-336, no month. M.F. Hawthorne et al. “The Reactions of Bis-Acetonitrile G. B. Dunks et al. “Simplified Synthesis of B10H14 from NaBH4 via Decaborane with Amines”,Journal of the American Chemical Society the B11H14-Ion” Inorganic Chemistry 1981, 20, 1962-1697, no 1959, 81, 5519, no month. month. H. Steinberget al. "Preparation and Rate of Hydrolysis of Boric Acid W. E. Hill et al. "From Sodium Borohydride to 1,2-dicarba-closo Esters' Industrial and Engineering Chemistry, 1957, 49, 174, no dodecabomes” in Boron Chemistry 1979, 33-39, no month. month. G. B. Dunks et al. “A One-Step Synthesis of B11H14-from NaBH4” Inorganic Chemistry 1978, 17, 1514-1516, no month. * cited by examiner U.S. Patent Apr. 28, 2009 US 7,524.477 B2

natural abundance Or B(OH)3 B-10 or B-11 enriched ROH

B(OR) NaH O NaAlH4 NaBH4 isolated or in situ RNX via Dunks process Route A Route B RNBH4 B10H4 pyrolysis N. - > 80% yield from NaBH4 (RAN)2B10H10 < 30% yield from NaBH4 oxidize

(RAN)2B20H18

contact with acid

RNX H2B20H 18 XH2O US 7,524,477 B2 1. 2 METHOD OF PRODUCTION OF BH A typical molecular ion beam of BH contains ions of a AMMONUMI SALTS AND METHODS OF wide range of masses due to loss of a varying number of PRODUCTION OF BH, hydrogens from the molecularion as well as the varying mass due to the two naturally occurring isotopes. Because mass CROSS-REFERENCE TO RELATED selection is possible in an implanter device used in semicon APPLICATION(S) ductor manufacture, use of isotopically enriched boron in BH can greatly reduce the spread of masses, thereby This application claims priority from U.S. Provisional providing an increased beam current of the desired implan Patent Application 60/541.322 which was filed on Feb. 2, tation species. Thus, B-11 and B-10 isotopically-enriched 2004, which is incorporated by reference. 10 BH is also of great interest. BH can be prepared by the oxidation of alkylammo FIELD OF THE INVENTION nium salts of the BioHo dianion. Preparation of this dianion can be accomplished in high yield from decaborane (M. F. The invention provides methods for synthesizing borane Hawthorne and A. R. Pitochelli J. Am. Chem. Soc. 81, 5519, compounds comprising pyrolysis of ammonium borohydride 15 1959.). However decaborane is toxic, expensive and difficult compounds under controlled thermal conditions. The inven to prepare by reported synthetic procedures (see, U.S. Pat. tion further provides isotopically enriched boron compounds No. 4,115,521, issued to Dunks et al.). More particularly, the prepared by the aforementioned methods. In certain aspects, Dunks method of synthesis of decaborane employs costly the invention relates to methods of preparing BH, includ Solvents and reagents, time consuming reaction conditions, ing "B- and 'B-enriched Bish, and methods of preparing and often laborious work up procedures. Thus, the overall salts of BoHo, BioHo, B, Ha, and B12H12. yield for the preparation of salts of the BoHo dianion start ing from Sodium borohydride and proceeding through BACKGROUND OF THE INVENTION decaborane is typically below 30%. Preparation of B-10 and B-11 enriched salts of the BoHo Large boron hydride compounds have become important 25 dianion, and preparation of large boronhydrides from salts of feed stocks for boron doped P-type impurity regions in semi the BioHo dianion (such as BH), via enriched decabo conductor manufacture. More particularly, high molecular rane is a particularly expensive process in part because Sub weight boron hydride compounds, e.g., boron hydride com stantial quantities of preparation of B-10 or B-11 enriched pounds comprising at least a five (5) boron atom cluster, are from sodium borohydride is diverted to byproducts instead of preferred boron atom feed stocks for boron atom implanta 30 incorporation into the enriched decaborane and enriched tion. BioHo dianion. An important aspect of modern semiconductor technology International patent application WO 03/044837, (Applied is the continuous development of Smaller and faster devices. Materials, Inc, Santa Clara Calif.) recites methods of ion This process is called Scaling. Scaling is driven by continuous implantation in which an isotopically enriched boron com advances in lithographic process methods, allowing the defi 35 pounds including 'B enriched compounds are ionized and nition of Smaller and Smaller features in the semiconductor then implanted into a substrate. The 837 publication recites Substrate which contains the integrated circuits. A generally the preparation of the iosotopically enriched boranes by the accepted Scaling theory has been developed to guide chip method recited in U.S. Pat. No. 6,086,837 (Cowan, et al.), manufacturers in the appropriate resize of all aspects of the which methods are reported to be the current industrial pro semiconductor device design at the same time, i.e., at each 40 cess for the preparation of boranes isotopically enriched in technology or scaling node. The greatest impact of scaling on B or B. ion implantation processes is the scaling of junction depths, Cowan (U.S. Pat. No. 6,086,837) recites a method of pre which requires increasingly shallow junctions as the device paring B-10 enriched decaborane starting with B-10 enriched dimensions are decreased. This requirement for increasingly boric acid. The Cowan preparation of either B-10 or B-11 shallow junctions as integrated circuit technology scales 45 enriched boron hydrides begins with boric acid and involves translates into the following requirement: ion implantation a multitude of synthetic and purification steps. More particu energies must be reduced with each scaling step. The larly, the Cowan process for conversion of boric acid into an extremely shallow junctions called for by modern, sub-0.13 alkali metal borohydride involves numerous time consuming micron devices are termed “Ultra-Shallow Junctions' or steps and results in a relatively low yield of valuable B-10 USJS. 50 enriched borohydride which must then be subjected to further Methods of manufacturing boron doped P-type junctions reactions to obtain final product. have been hampered by difficulty in the ion-implantation Thus, the Cowan method starts with the preparation of process using boron. The boron atom, being light (average B-10 methylborate from boric acid and methanol using an atomic weight of 10.8), can penetrate more deeply into a azeotropic distillation method. The methylborate is separated silicon substrate and diffuse throughout the substrate lattice 55 from remaining methanol by freeze recrystallization by rapidly during annealing or other elevated temperature pro means of three one step procedures to produce an 80% yield CCSSCS. of trimethylborate. The trimethylborate is then added to a Boron clusters or cages, e.g., boranes have been investi suspension of sodium hydride in mineral oil at 220°C.-250° gated as a feed stock for deliveringboronto a semiconductor C. and heated for 12 hrs. For safety, a metal reflux condenser substrate with reduced penetration. For example, as recited in 60 is required. Isolation of the formed borohydride requires spe commonly assigned International Patent Application PCT/ cial attention. First, the excess sodium hydride is destroyed by US03/20197 filed Jun. 26, 2003, boronions may be implanted pouring the mineral oil mixture into a mixture of ice and into a substrate by ionizing boron hydride molecules of the water, a rather exothermic process evolving gaseous hydro formula B.H., (where 100>nd5 and msn+8) and an ion gen. Then the aqueous borohydride is separated from the Source for use in said implantation methods. Certain preferred 65 mineral oil by decantation or use of separatory funnel. The compounds for use in the boron ion implantation methods aqueous borohydride must be purged of methanol by either included decaborane (BoH) and octadecaborane (BiH). heating to 60° C. and purged with a nitrogen stream or by US 7,524,477 B2 3 4 removal under reduced pressure. The resulting aqueous solu borohydride and pyrolysis of the alkylammonium borohy tion is comprised of sodium hydroxide and the B-10 enriched dride to generate an alkylammonium salt of BioHo. The borohydride. Carbon dioxide gas is bubbled through the solu methods of the invention are suitable for use in preparing tion converting the sodium hydroxide to Sodium carbonate. naturally abundant, B-10 enriched and B-11 enriched alky The resulting slurry is then extracted with n-propylamine and lammonium salts of the BioHo dianion. the n-propylamine evaporated to yield final product. The In one aspect, the invention provides a method of preparing solubilty of sodium borohydride in n-propylamine is limited an alkylammonium salt of BioHo dianion, the method com and appreciable volumes of the volatile solvent are needed. prising the steps of: Typical yields of 45-65% are obtained. A total often time (a) contacting a boric acid and a primary, secondary, or consuming steps are required to prepare isotopically enriched 10 tertiary alcohol under conditions conducive to formation sodium borohydride by the procedure recited in Cowan. of aborate ester; Several literature documents recite conflicting synthetic (b) reducing the borate ester with NaAlH4 or NaH to form reports regarding the preparation of salts of the BioHo NaBH; and anion from tetralkylammonium borohydride salts. The litera (c) contacting NaBH with an alkylammonium salt of the ture recites conducting the pyrolysis in a variety of reactors, in 15 formula, RNX, where R is a linear or branched alkyl the presence or absence of a solvent, and under a variety of group or an aralkyl group under conditions conducive to reaction conditions. See, for example, (1) W. E. Hill et al. formation of either in situ or after isolation of RNBH; “Boron Chemistry 4. Pergamon Press, Oxford 1979, p 33: and (2) Mongeotetal Bull. Soc. Chim. Fr. 385, 1986; and (3) U.S. (d) pyrolysis of solid RNBR at about 185°C. to forman Pat. Nos. 4,150,057 and 4.391.993, issued to Sayles. The ammonium salt of BioHo. published procedures do not provide the means for industri In another aspect, the invention provides methods of pre ally significant production of the BioHo anion, predictable paring B.H., the method comprising the steps of: and consistent conversion to product are not taught, and puri (a) contacting boric acid with a primary, secondary, or fication techniques are inadequate for the intended use. tertiary alcohol under conditions conducive to borate Several reports have recited processes for the preparation 25 ester formation; of naturally abundant tetraalkylammonium borohydride (b) reducing the borate ester with a metal hydride or metal compounds from sodium borohydride. However, the litera hydride salt to afford a metal borohydride; ture methods are not suitable for preparation of isotopically (c) contacting the metal borohydride with a salt of the enriched ammonium borohydrides, in part because, a Sub formula RNX, wherein R is a hydrocarbon group and X stantial amount of the borohydride is sacrificed during cation 30 is an anion to afford RNBH; exchange. For example, Gibson and Shore separately recite (d) heating solid R.NBH at a temperature sufficient to contacting two equivalents of sodium borohydride with a selectively form a salt of the BioHo anion during mixture of tetraethylammonium hydroxide and sodium pyrolysis; hydroxide in methanol to generate one equivalent of tetra ethylammonium borohydride, which may be contaminated 35 (e) contacting the salt of the BioHo anion with an oxi with sodium hydroxide (D. Gibson et al., J. Organornet. dant under conditions conducive to formation of a salt of Chem, 218, 325, 1981; and S. Shore et al., Inorg. Synth. 17. BoHis: 21, 1977). Due to the stoichometric loss of boron, these (f) contacting the BHis salt in its free form, as a slurry processes are not suitable for preparation of B-10 or B-11 in at least one non-aqueous solvent, as an aqueous solu enriched tetraalkylammonium borohydride salts. 40 tion, or as a solution in at least one non-aqueous solvent Brändström et al recites methods of synthesis of tetralky with an acid under conditions conducive to the forma lammonium borohydride compounds containing 12 or more tion of a conjugate acid of the BoHis salt; carbon atoms from tetraalkylammonium hydrogen Sulfate (g) removing Volatile components of the solution compris and a 10% excess of sodium borohydride (Brändström et al ing the conjugate acid of the BoHis salt under condi Tet. Lett. 31, 3173, 1972). Notwithstanding the quantitative 45 tions conducive to the degradation of at least a portion of conversion to the desired production solution, Applicants the conjugate acid of the BoHis salt; attempts to isolate the product tetralkylammonium borohy (h) extracting the residue with hexanes or other suitable dride from Solution were plagued by unsatisfactory isolated hydrocarbon solvents in which boric acid byproduct is yields and development of viscous “oils” that were difficult to insoluble; crystallize and purify following the recited procedure. 50 (i) repeating steps (g) and (h) until no further B.H. is It would be desirable to have a reproducible, atom-effi produced; cient, high-yielding process for preparing high-purity salts of (i) contacting the residues with solvent to dissolve any the BioHo dianion from borohydride precursors. More BoHis containing salts: particularly, it would be desirable to have methods of prepar (k) repeating steps (f)-() at least once; and ing high purity natural abundant, B-10 enriched, or B-11 55 (1) concentrating the combined hydrocarbon Solutions to enriched salts of BioHo, which methods have a reduced afford B.H. number of synthetic procedures. In another aspect, the invention provides methods of pre paring 'B-enriched Bish, the method comprising the steps SUMMARY OF THE INVENTION of: 60 (a) contacting boric acid with a primary, secondary, or We have discovered a new method of synthesis of alkylam tertiary alcohol under conditions conducive to borate monium salts of the BioHo dianion. More particularly, we ester formation; have discovered an atom efficient, high yield method of syn (b) reducing the borate ester with a metal hydride or metal thesis of alkylammonium salts of BioHo, which methods hydride salt to afford a metal borohydride; do not include formation of decaborane as an intermediate. 65 (c) contacting the metal borohydride with a salt of the The methods of the invention generally comprise the prepa formula RNX, wherein R is a hydrocarbon group and X ration of a tetraalkylammonium borohydride from sodium is an anion to afford RNBH; US 7,524.477 B2 5 6 (d) heating solid RNBH at a temperature sufficient to The FIGURE is a flow chart of a synthetic method of selectively form a salt of the BioHo anion during preparing Bishby a method of the present invention (Route pyrolysis; A) and a method of preparing Bish, using the Dunks pro (e) contacting the salt of the BioHo anion with an oxi cess to prepare (NR)BoHo (Route B). dant underconditions conducive to formation of a salt of 5 BoHis: DETAILED DESCRIPTION OF THE INVENTION (f) contacting the BoHis salt in its free form, as a slurry in at least one non-aqueous solvent, as an aqueous solu Remarkably, we have discovered new methods for the tion, or as a solution in at least one non-aqueous solvent preparation of ammonium salts of anionic boron hydrides with an acid under conditions conducive to the forma 10 having between 9 and 12 boron atoms from various ammo tion of a conjugate acid of the BHis salt; nium borohydrides. We have also discovered new methods of (g) removing Volatile components of the solution compris preparing boronhydrides, including Bish, and related large ing the conjugate acid of the BoHis salt under condi boronhydride compounds, which can be useful as feed stocks tions conducive to the degradation of at least a portion of for methods of implanting boron atoms in a substrate by the conjugate acid of the BoHis salt; 15 molecular ion implantation. (h) extracting the residue with hexanes or other suitable Now referring to the FIGURE, certain preferred methods hydrocarbon solvents in which boric acid byproduct is of synthesizing Bish provided by the invention are insoluble; depicted in Route A. In contrast, the synthetic procedure of (i) repeating steps (g) and (h) until no further Bsh is Route B refers to certain methods of making B.H. using the produced; Dunks procedure to make ammonium decaborane salts. (j) contacting the residues with solvent to dissolve any Enriched tetraalkylammonium borohydride salts can be Bo His containing salts: obtained by the preparation of enriched sodium borohydride (k) repeating steps (f)-(j) at least once; and through the following steps: (1) concentrating the combined hydrocarbon solutions to (a) B-11 or B-10 enriched boric acid is converted to an afford Bish. 25 organic ester which can be prepared from a wide variety of In another aspect, the invention provides methods of pre alcohols, glycols, and phenols. See, for example Steinberg paring "B-enriched Bish22, the method comprising the steps and Hunter, J. of Industrial and Engineering Chemistry, Vol of: 49, 174-181. Generally, selection of alcohol, glycol, or phe (a) Contacting a boric acid and a primary, secondary, or nol is made on the basis of cost and availability of the esteri tertiary alcohol under conditions conducive to borate 30 fying agent and ease of preparation. Certain non-limiting ester formation; examples of suitable alcohols and glycols include n-butanol (b) reducing the borate ester with a metal hydride or metal and 2-methyl-2,4-pentanediol. Typically glycols generate a hydride salt to afford a metal borohydride: tri(glycolate)bisborate structure in high yield, e.g., tri(2-me (c) contacting the metal borohydride with a salt of the thyl-2,4-pentanediolate)bisborate can be prepared in essen formula RNX, wherein R is a hydrocarbon group and X 35 tially quantitative yield. is an anion to afford RNBH; (b) The borate ester is reduced directly to B-11 or B-10 (d) heating solid RNBH at a temperature sufficient to enriched alkali metal borohydride using alkali metal hydrides selectively form a salt of the BioHo anion during such as sodium aluminum hydride. Preferable is the use of pyrolysis; sodium aluminum hydride in tetrahydrofuran (THF) and/or (e) contacting the salt of the BioHo anion with an oxi 40 diethylether which may further comprise toluene as a cosol dant underconditions conducive to formation of a salt of Vent. Addition of toluene as a co-solvent may be desirable in BoHis: certain embodiments, in part because the use of toluene (f) contacting the Bo His salt in its free form, as a slurry reduces the risks associated with the use of ethereal solvents. in at least one non-aqueous solvent, as an aqueous solu (c) The B-11 or B-10 enriched metal borohydride salts tion, or as a solution in at least one non-aqueous solvent 45 prepared in step (b) are of sufficient purity to proceed with the with an acid under conditions conducive to the forma production of enriched tetraalkylammonium borohydride. tion of a conjugate acid of the BHis salt; Tetraalkylammonium borohydride salts (RN' BH) are (g) removing Volatile components of the solution compris prepared by contacting sodium borohydride with one or more ing the conjugate acid of the BHis salt under condi molar equivalents of a tetralkylammonium salt such as tions conducive to the degradation of at least a portion of 50 tetralkylammonium hydrogensulfate, or the like, in an aque the conjugate acid of the BHis salt; ous or alcohol solution. Sodium hydroxide or the like is then (h) extracting the residue with hexanes or other suitable added to the reaction mixture to generate a basic reaction hydrocarbon solvents in which boric acid byproduct is mixture. When an aqueous reaction medium is used, the insoluble; aqueous solution is extracted with methylene chloride in a (i) repeating steps (g) and (h) until no further BFI is 55 biphasic extraction. Alternatively, when an alcohol solvent is produced; used, the alcohol is evaporated and the residue extracted with (j) contacting the residues with solvent to dissolve any methylene chloride. After drying, the methylene chloride BoHis containing salts; Solution is concentrated to afford a viscous solution. Addition (k) repeating steps (f)-(j) at least once; and of diethylether to the concentrated methylene chloride solu (l) concentrating the combined hydrocarbon solutions to 60 tion results in precipitation of the borohydride salt in high afford Bish yield. Alternatively, when the methylene chloride can be Other aspects of the invention are discussed infra. removed completely and the crude solid recrystallized from ethyl acetate albeit in lower isolated yield. BRIEF DESCRIPTION OF THE DRAWINGS The invention provides methods of production of tetraalky 65 lammonium salts of the BioHo dianion by pyrolysis of at We first briefly describe the drawings of the preferred least one tetraalkylammonium borohydride. Certain pre embodiment of the invention. ferred pyrolytic methods of the invention are scalable for US 7,524,477 B2 7 8 large scale synthesis of tetraalkylammonium salts of BoHis salts. The BoHis salts are then contacted with an BioHo. The pyrolysis reaction can be performed using the acid exchange resin and the free acid decomposed to produce solid tetraalkylammonium borohydride or as a slurry of the BH by the following method: tetraalkylammonium borohydride in a hydrocarbon solvent (a) providing a salt of (BoHs); having a boiling point of at least 100° C. Certain preferred 5 (b) contacting the (BoHs) salt in its free form, as a hydrocarbon solvents include alkane solvents having slurry in at least one non-aqueous solvent, as an aqueous between 8 and 18 carbon atoms. Solution, or as a solution in at least one non-aqueous solvent Pyrolysis reactions of the invention are preferably con with an acid under conditions conducive to the formation of a ducted in a reaction apparatus that has ports to allow the conjugate acid of the (BHs) salt; vessel to be evacuated and/or to allow for introduction of an 10 (c) removing Volatile components of the Solution compris inert atmosphere (e.g., nitrogen, argon, or the like). In addi ing the conjugate acid of the (BoHs) salt under conditions tion, preferred pyrolysis reaction apparatus comprise a vent conducive to the degradation of at least a portion of the port to transfer gaseous byproducts to an appropriate Scrub conjugate acid of the (BoHs) salt; ber. (d) extracting the residue with hexanes or other suitable Careful regulation of the temperature of the reaction mix- 15 hydrocarbon solvents in which boric acid byproduct is ture during pyrolysis improves control of the composition and insoluble; purity of the product mixture. Thus, preferred reactors permit (e) repeating steps (c) and (d) until no further BFI is precise temperature control. More preferably, the apparatus produced comprises a thermowell or the like to take precise internal (f) contacting the residues with acetonitrile to dissolve any temperature readings, an external furnace or otherheat Source 20 Bo His containing salts, that delivers even heating to the reaction, a method of cooling (g) repeating steps (b)-(f) at least once; and the reaction mixture that prohibits overheating while maxi (h) concentrating the combined hydrocarbon Solutions to mizing temperature control, and a temperature control unit afford B.H. that can maintain a temperature program containing multiple In certain preferred methods of preparing octadecaborane “ramp' and “soak” events. Pyrolysis of a tetraalkylammo- 25 (e.g., BH) provided by the invention, the boric acid is nium borohydride in this reaction vessel provided good to isotopically enriched. That is, the boric acid is B-10 enriched highyields of tetraalkylammonium salts of BioHo, BoHo, boric acid or B-11 enriched boric acid. BH, and B.H., by regulating the temperature profile In certain other preferred methods of preparing octade of the reaction vessel during pyrolysis. caborane (e.g., BH) provided by the invention, the step of The reaction apparatus further permits incorporation of 30 preparing RNBH comprises contacting about equal molar additional reagents (such as trialkylamine borane adducts) amounts of sodium borohydride and RNX. In certain pre and/or solvents in order to achieve the optimum production of ferred methods, the sodium borohydride is isotopically a specified boron hydride anion (e.g., BioHo, B.H., enriched. That is, the sodium borohydride is B-10 enriched BH, and B.H.). Yields up to 90% for BioHo, or sodium borohydride or B-11 enriched sodium borohydride. BH have been obtained by the methods of the invention. 35 In certain other preferred methods, the sodium borohydride is From NaBH, the overall yield for tetraalkylammonium salts prepared and used in situ. One, non-limiting method of pre of BioHo can be greater than 80%, which is substantially paring Sodium borohydride contemplated for use in the greater than yields obtained by synthetic procedures using instant method comprises contacting the borate ester and decaborane as an intermediate (i.e., by the Dunks process NaAlH4 in an ethereal solvent at a temperature of from about which provides overall yields of less than 30%). 40 65° C. to about 135° C. Preferred ethereal solvents comprise In certain preferred methods of preparing salts of tetrahydrofuran, diethyl ether, or mixtures of tetrahydrofuran BioHo, B.H. B. H. and/or B.H., the RNBH is and toluene. dissolved, Suspended or mixed with a solvent having a boiling In certain other preferred methods of preparing octade point of at least about 100° C. Certain preferred solvents caborane (e.g., BH) provided by the invention, the non include Cs-Cs alkanes or mixtures of Cs-Csalkanes, more 45 aqueous solvent is a nitrile, alcohol, ether or combination particularly, preferred solvents include n-dodecane and mix thereof. Certain particularly preferred non-aqueous solvents tures of, by volume, about 50-70% n-decane and about include acetonitrile or ethanol. 50-30% n-dodecane. In certain other preferred methods of preparing octade In certain other preferred methods of preparing salts of caborane (e.g., BH) provided by the invention, the extrac BioHo, BoHo, BiH, and/or B12H12, a mixture of 50 tion hydrocarbon is a C-C alkane, Cs-Co cycloalkane, RNBH and a trialkylamine borane adduct is pyrolyzed. benzene, or alkylated benzene. Particularly preferred extrac Preferably the molar ratio of the ammonium borohydride and tion hydrocarbons are selected from hexanes, cyclohexane, trialkylamine borane is between about 1:3 to about 3:1 where benzene, toluene or Xylene. an equimolar ratio of ammonium borohydride and trialky The following non-limiting examples are illustrative of the lamine borane are particularly preferred. In certain preferred 55 invention. All documents mentioned herein are incorporated methods in which isotopically enriched salts of BioHo, herein by reference. BoHo, BH and/or B.H. are desirable, the RNBH and/or the trialkylamine borane adduct is isotopically EXAMPLE 1. enriched in either 'B or ''B. The tetraalkylammonium salts provided by the pyrolytic 60 Preparation of 'B Tributylborate methods of the invention, including salts of the BioHo, BoHo, BiH, and B2H2 anions, are suitable for use as A one-neck 500 mL round bottom flask having a Dean starting materials in the synthesis of a variety of large boron Stark receiver and reflux condensor attached thereto was hydride compounds having more than about 12 boronatoms. charged with "B-boric acid (40 g), n-butanol (200g), and For example, oxidation of tetraalkylammonium salts of 65 toluene (about 100 mL). The mixture was heated to reflux and BioHo in aqueous solution using an appropriate oxidants water was removed from the mixture by distillation of a such as iron(III) trichloride results in the formation of toluene-water azeotrope. After removing the Dean-Stark US 7,524,477 B2 10 receiver, the product mixture was fractionally distilled. 'B reflux and maintained at reflux for several hours. Upon cool tributylborate was obtained as a fraction boiling at 226-228 ing, crude solid 'Benriched sodium borohydride was filtered C. under ambient pressure (195g, 87% isolated yield). under a positive pressure of argon atmosphere, the Solid was washed with dry toluene to remove aluminum butoxide EXAMPLE 2 byproducts, and the toluene removed by filtration under a positive pressure argon atmosphere. The toluene wash and Preparation of ''B Enriched Tributylborate filtration process is repeated as necessary to remove residual aluminum butoxide byproducts. Yield: 55.5 g, 1.46 mole, Starting with ''B enriched boric acid, 'B tributylborate 93.1%. The only boron species observed by ''B NMR spec was prepared according to the procedure recited in Example 10 troscopy is the resonance corresponding to 'BH (a 1:4:6:4:1 1. quintet centered at -37 ppm). If necessary, ''B enriched Na'BH can be further purified by recrystallization from EXAMPLE 3 diglyme or by extraction with liquid ammonia. The resulting products retain the isotopic purity of the starting 'Benriched Preparation of 'B Enriched 15 'B(OH), and 'B enriched tributylborate. This preparation tris(2-methyl-2,4-pentanediolate)diborate has been Successfully scaled up to multi-kilogram quantities without loss of product quality. A mixture of "B enriched boric acid, 2-methyl-2,4-pen tanediol, and toluene were combined in a 1:1.5:1 molar ratio EXAMPLE 7 in a reactor having a Dean-Stark Receiver and a condenser attached thereto. The reaction mixture was heated to reflux Preparation of Tetraethylammonium Borohydride and water generated by the condensation reaction was removed as a toluene-water azeotrope. The mixture was NaBH (261.4 g. 6.9 moles) is weighed into a 4 L erlen heated until the three molar equivalents of water had been meyer flask and dissolved into 2.3 L of the prepared basic collected in the Dean-Stark trap. The reaction mixture com 25 methanol solution. 600 mL of the basic methanol is used to prises the product 'B Enriched tris(2-methyl-2,4-pen dissolve Et NBr (1452.5 g. 6.9 moles) in a 2 L Erlenmeyer tanediolate)diborate in essentially quantitative yield and tolu flask. To this solution is added anhydrous MgSO (158.4g, ene. The mixture may be contacted directly with metal 1.3 moles). With rapid stirring the Et NBr solution is slowly aluminum hydride in the next step of the metal borohydride added to the NaBH solution to produce an immediate white synthesis. Alternatively, the "B Enriched tris(2-methyl-2,4- 30 precipitate of NaBr. The solution is stirred for 3 hours at room pentanediolate)diborate may be purified by toluene removal temperature. Any remaining solid is removed by vacuum under a reduced pressure atmosphere. filtration and the filtrate is collected and the methanol removed to give a white solid. After removing any remaining methanol under vacuum, the solid is extracted with CHC1. OH OH 35 (2x1.7 L). The CHCl extracts are combined, dried over 2B(OH)3 + 3 - htt - MgSO and filtered. The filtrate is collected and the CH-Cl -6H2O removed on a rotary evaporator until most of the CHCl is removed and white crystalline solid begins to form. CHC1. recovered in the receiving bulb is saved for future use. Dieth 40 ylether (1.4 L) is added to the CHCl solution to precipitate EtNBH as a white microcrystalline powder. After cooling to 0° C. the Et NBH is isolated by filtration and dried under vacuum. Yield: 910.2g, 6.3 moles, 90.9%. The preparation is successfully used in the synthesis of 'B or "B-enriched 45 product. EXAMPLE 4 EXAMPLE 8 Preparation of ''B Enriched tris(2-methyl-2,4-pentanediolate)diborate Preparation of Tetraethylammonium 50 Decahydrodecaborate 'B Enriched tris(2-methyl-2,4-pentanediolate)diborate was prepared by the method of Example 3 wherein 'B EtNBH (1000.0 g. 6.9 moles) is weighed into a beaker enriched boric acid was used in place of "B boric acid. and then transferred into a 5 L 3-necked round bottom flask using a powder funnel. The flask is set into a 5 L heating EXAMPLE 5 55 mantle. A 60:40 mixture of n-decane:n-dodecane (2.5 L) is added to the flask through a funnel. The center neck of the Preparation of ''B Enriched Sodium Borohydride flask is equipped with a Trubore.C. glass bearing and glass stir rod with 24mmx130 mm blade. The stir rod is inserted into A five liter 3-neck flask equipped with an overhead stirrer the chuck of an overhead mixer. To one side neck is added a and a reflux condenser was charged with anhydrous tetrahy 60 Claisen thermometer adapter fitted with a thermometer and a drofuran (1 L) and anhydrous diethyl ether (700 mL) under an stopcock with valve used as an argon inlet. To the third neck argon atmosphere. Sodium aluminum hydride (105 g, ca 86% is added a condenser equipped with a tubing adapter. The purity, 1.77 mole) was added to the reaction flask and a pres tubing adapter is attached to two isopropanol bubblers. To the sure equalized addition funnel was charged with "'Benriched inlet is attached an argon hose and the entire apparatus is tributylborate (427 mL, 1.57 mole) which was prepared in 65 thoroughly purged with argon. After the purge the argon inlet Example 2. The borate was added dropwise to a stirred reac valve is shut and the reaction mixture heated to reflux (185° tion mixture and the reaction mixture was gradually heated to C.) with stirring. The reflux is maintained for 16 hours. After US 7,524,477 B2 11 12 16 h the heating mantle is turned off mixture cooled under (c) preparing RNBH from NaBH and RNX either in argon and the white precipitate is vacuum filtered. Any situ or after isolation of NaBH wherein R is a hydro remaining reaction solvent in the crude Solid is removed carbon and X is an anion; through washing with hexanes. The crude solid is dissolved (d) pyrolysis of solid R.NBH at about 185°C. to form into acetonitrile (1 l), the solution heated to 40° C. and air BioHo: bubbled through for 30 minutes. The solution is cooled and (e) oxidation of BioHo to give Bo His any precipitate is filtered off. Acetonitrile is removed and the (f) contacting a solution of BoHis with acidic cation residue recrystallised from a water-isopropanol mixture. exchange resin; (g) decomposing the resultant acid to give BH; Yield of (EtN).B.H. 124.9 g, 0.33 moles, 48.1%. (h) extracting the residue with solvent in which boric acid 10 byproduct is insoluble; EXAMPLE 9 (i) repeating steps (g) and (h) until no further B.H. is produced; Preparation of Octadecaborane (i) contacting the residues with solvent to dissolve any BoHis containing salts and excluding boric acid (NEt).BoHs (10.8 g. 21.8 mmol) was dissolved into a 15 byproduct; solution comprising 40 mL of acetonitrile and 5 mL of water and then stirred over 54.0 g of acidic exchange resin for 24 (k) repeating steps with (f)-() at least once; and hours. The resin was filtered off and washed thoroughly with (1) concentrating the combined hydrocarbon Solutions to acetonitrile. The filtrate and washings were combined and afford B.H. concentrated to a yellow oil. The oil was placed under vacuum 2. The method of claim 1, wherein the boric acid is B-10 until a hard solid formed (-5 days) and then extracted with enriched boric acid. 100 mL of hexanes. Removal of hexanes left pale yellow 3. The method of claim 1, wherein the boric acid is B-11 BH (2.0 g, 0.92 mmol). The residue left over from the enriched boric acid. hexane extraction was exposed to vacuum and extracted a 4. The method of claim 1, wherein the step of preparing second time to remove more BH. Total yield: 2.8 g. 12.9 RNBH comprises contacting about equal molar amounts of 25 sodium borohydride and RNX. mmol, 59.2%. 5. The method of claim 4, wherein the sodium borohydride is B-10 enriched sodium borohydride. EXAMPLE 10 6. The method of claim 4, wherein the sodium borohydride is B-11 enriched sodium borohydride. Preparation of 'B-enriched Octadecaborane 7. The method of claim 4, wherein the sodium borohydride 30 prepared in step (b) is used in situ. 'B enriched (NEth).BoHs (17.4g, 35.2 mmol) was 8. The method of claim 1, wherein the step of preparing dissolved into 50 mL of acetonitrile and 5 mL of HO. The NaBH comprises contacting the borate ester and NaAIH in Solution was placed on a column containing 500 g of acidic an ethereal solvent at a temperature of from about 65° C. to exchange resin and allowed to sit for 18 hours. The solution about 135° C. was eluted from the column and the resin rinsed thoroughly 35 9. The method of claim8, wherein the borate ester is a B-10 with acetonitrile. The eluant and washings were combined enriched borate ester. and passed through a second column over 2 hours. Acetoni 10. The method of claim8, wherein the borate esteris B-11 trile was removed to form a thick slurry containing yellow enriched borate ester. crystals of HBoHis XH2O. The slurry was exposed to 11. The method of claim 8, wherein the ethereal solvent is vacuum over 10 days to produce a yellow solid. To the solid 40 tetrahydrofuran. was added 100 mL of H2O and 100 mL of hexanes and the 12. The method of claim 8, wherein the ethereal solvent mixture was stirred for 3 hours. The hexane layer was sepa further comprises toluene as a co-solvent. rated from the water layer, dried over KCO and filtered. 13. The method of claim 11, wherein the ethereal solvent After removal of hexanes 'B enriched Bish, was left as a further comprises toluene as a co-solvent. pale yellow powder (3.5g, 16.1 mmol, 45.9%). ''B enrich 14. A method of preparing BH from boric acid, com ment was determined to be that of the starting boric acid 45 prising: (>98.6% 'B isotopic enrichment). (a) preparation of borate ester from boric acid and an alco The invention has been described in detail with reference to hol; preferred embodiments thereof. However, it will be appreci (b) reducing the borate ester to form NaBH; ated that those skilled in the art, upon consideration of the (c) preparing RNBH from NaBH and RNX, wherein R disclosure, may make modifications and improvements 50 is a hydrocarbon and X is an anion; within the spirit and scope of the invention. (d) pyrolysis of solid R.NBH to form BioHo: All of the patents and publications cited herein are hereby (e) oxidation of BioHo to give BoHis: incorporated by reference. (f) contacting a solution of Bo His with acidic cation Those skilled in the art will recognize, or be able to ascer exchange resin; tain using no more than routine experimentation, many 55 (g) decomposing the resultant acid to give BH; equivalents to the specific embodiments of the invention (h) extracting the residue with solvent in which boric acid described herein. Such equivalents are intended to be encom byproduct is insoluble; passed by the following claims. (i) repeating steps (g) and (h) until Substantially no further Bs22 is produced; What is claimed is: 60 (i) contacting the residues with solvent to dissolve any 1. A method of preparing BH from boric acid compris BoHis containing salts and excluding boric acid ing the steps of byproduct. (a) preparation of borate ester from boric acid and a pri mary, secondary, or tertiary alcohol; 15. The method of claim 14, wherein steps with (f)-(j) are (b) reducing the borate ester with NaAIH or NaH to form repeated at least once. NaBH; k k k k k