Methods of synthesis of isotopically enriched borohydride and methods of synthesis of isotopically enriched boranes

1. A method of synthesizing an isotopically enriched metal borohydride, the method comprising the steps of:

(a) providing isotopically enriched boric acid;

(b) contacting the isotopically enriched boric acid with an alcohol under conditions conducive to formation of an isotopically enriched borate; and

(c) reducing the isotopically enriched borate with a metal aluminum hydride under conditions conducive to formation of isotopically enriched metal borohydride.

2. The method of claim 1 , wherein the isotopically enriched borate is a compound of Formula I:

[(RO) 2 B—O—] n —R ′

wherein

each occurrence of R is independently selected from the group consisting of linear or branched alkyl, cycloalkyl, cycloalkyl-alkyl, alkenyl, aryl, aralkyl, haloalkyl, and alkylether, or

two R groups taken in combination form α,ω-alkylene group or a 1,2-cylcoalkylene group each of which may be optionally substituted with one or more groups selected from the group consisting of alkyl, alkenyl, cycloalkyl, cycloalkyl-alkyl, aryl, aralkyl, and alkoxy;

n is 1 or 2; and

R′ is selected from the group consisting of alkyl, alkenyl, aryl, aralkyl, haloalkyl, and alkylether when n=1, or R′ is a α,ω-alkylene group or a 1,2-cylcoalkylene group each of which may be optionally substituted with one or more groups selected from the group consisting of alkyl, alkenyl, cycloalkyl, cycloalkyl-alkyl, aryl, aralkyl, and alkoxy when n=2.

3. The method of claim 1 , wherein the isotopically enriched borate is a compound of the formula, B(OR) 3 , wherein R is independently selected at each occurrence from the group consisting of linear or branched C 1-10 alkyl , phenyl, benzyl, C 3-8 cycloalkyl, C 3-8 cycloalkyl-C 1-10 alkyl, C 2-10 alkenyl, C 1-10 alkoxy, C 1-10 haloalkyl, and C 2-10 alkylether.

4. The method of claim 3 , wherein the isotopically enriched borate is a compound of the formula, B(OR) 3 , wherein each occurrence of R is the same and R is selected from the group consisting of linear or branched C 1-10 alkyl, phenyl, benzyl, C 3-8 cycloalkyl, C 3-8 cycloalkyl-C 1-10 alkyl, C 2-10 alkenyl, C 1-10 alkoxy, C 1-10 haloalkyl, and C 2-10 alkylether.

5. The method of claim 1 , wherein the isotopically enriched borate is a compound of Formula II:

wherein R 2 and R 3 are independently selected at each occurrence from the group consisting of hydrogen, linear or branched alkyl, cycloalkyl, cycloalkyl-alkyl, alkenyl, aryl, aralkyl, haloalkyl, and alkylether; and

p is an integer selected from 1-5.

6. The method of claim 5 , wherein the isotopically enriched borate is a compound of the formula:

wherein

q is 1 or 2; and

R x , R x , and R y are independently selected at each occurrence from the group consisting of hydrogen, linear and branched C 1-10 alkyl, C 1-10 alkoxy, and C 3-8 cycloalkyl, or R x and R y , taken in combination form a α,ω-alkylene group.

7. The method of claim 6 , wherein R x and R y are selected from the group consisting of hydrogen and linear or branched C 1-4 alkyl.

8. The method of claim 1 , wherein esterification step comprises contacting isotopically enriched boric acid with at least three equivalents of a linear or branched C 1-10 alkanol or at least one and a half (1.5) equivalents of a C 2-10 alkanediol.

9. The method of claim 8 , wherein the esterification step comprises contacting the isotopically enriched boric acid with at least three equivalents of a linear C 2-10 alkanol or at least one and a half (1.5) equivalents of a linear or branched 1,2-C 2-10 alkanediol.

10. The method of claim 9 , wherein the esterification step comprises contacting the isotopically enriched boric acid with about three equivalents of a linear C 2-10 alkanol or about one and a half (1.5) equivalents of a linear or branched 1,2-C 2-10 alkanediol.

11. The method of claim 1 , wherein water generated during the esterification step is removed from the reaction mixture.

12. The method of claim 1 , wherein the water is removed from the reaction mixture by distillation.

13. The method of claim 12 , wherein the water is removed as an azeotrope with a member selected from the group consisting of toluene, xylene, benzene, 1,2-dichloroethane, and mixtures thereof.

14. The method of claim 1 , wherein the esterification step is conducted at a temperature of above about 80° C.

15. The method of claim 1 , wherein the esterification step is conducted at a temperature of between about 95° C. and about 175° C.

16. The method of claim 1 , wherein the reduction step comprises contacting the borate with a mixture of a metal aluminum hydride and at least one solvent.

17. The method of claim 16 , wherein at least one solvent is selected from the group consisting of diethyl ether, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, 1,3-dioxane, methyl-tert-butyl ether, dimethoxyethane, diglyme, and mixtures thereof.

18. The method of claim 17 , wherein the mixture comprises at least one additional hydrocarbon solvent selected from the group consisting ofbenzene, cyclohexane, methylcyclohexane, toluene, xylenes, linear and branched C 5-10 alkanes, petroleum ethers, and mixtures thereof.

19. The method of claim 1 , wherein the metal aluminum hydride is selected from the group consisting of Group I and Group II metal Aluminum hydrides, and mixtures thereof.

20. The method of claim 19 , wherein the metal aluminum hydride is lithium aluminum hydride or sodium aluminum hydride.

21. A method of preparing isotopically enriched metal tetradecahydroundecaborate salt, the method comprising the steps of:

(a) providing isotopically enriched metal borohydride by carrying out the method of claim 1 ; and

(b) contacting a solution of the isotopically enriched metal borohydride with a compound of the formula, R—X or isotopically enriched BY 3 (ligand), under conditions conducive to the formation of a metal tetradecahydroundecaborate salt, wherein

R is alkyl, alkenyl, or aralkyl;

X is fluoro, chloro, bromo, iodo, alkylsulfonate, or arylsulfonate;

Y is fluoro, chloro, or bromo; and

the ligand of BY 3 (ligand) is absent, an ether, an amine, or a pyridine.

22. The method of claim 21 , wherein the metal borohydride and the compound of the formula, R—X are contacted at a temperature of between about 50° C. and about 200° C. or wherein the metal borohydride and the isotopically enriched compound of the formula, BY 3 (ligand) are contacted at a temperature of between about 50° C. and about 200° C.