AZABORINE COMPOUNDS AS HYDROGEN STORAGE SUBSTRATES
Selected 1,2-azaborine compounds exhibit utility as hydrogen storage substrates, and are useful as components of hydrogen storage devices.
1 . A method of hydrogen storage, comprising
a) providing an azaborine substrate having the formula
wherein R 1 is halogen, alkyl having 1-6 carbons, aryl having 1-6 carbons, heteroaryl having 1-6 carbons, acyl having 1-6 carbons, alkenyl having 1-6 carbons, alkynyl having 1-6 carbons, sulfonyl, —OR 7 , —SR 7 , or Si(R 8 ) 3 where each R 7 is independently hydrogen, alkyl having 1-6 carbons, acyl having 1-6 carbons, alkenyl having 1-6 carbons, tert-butyloxycarbonyl, or sulfonyl; each R 8 is independently alkyl having 1-6 carbons, aryl having 1-6 carbons, alkoxy having 1-6 carbons, acyl having 1-6 carbons, alkenyl having 1-6 carbons, or tert-butyloxycarbonyl;
R 2 is hydrogen, halogen, acyl having 1-6 carbons, amide, amine, —CN, —OR 7 , —SR 7 , alkyl having 1-6 carbons, alkenyl having 1-6 carbons, alkynyl having 1-6 carbons, or R 2 is an aromatic heterocycle; or R 1 and R 2 taken in combination form a fused 5- or 6-membered ring that optionally incorporates one or more heteroatoms, and that is itself optionally further substituted by alkyl having 1-6 carbons, aryl having 1-6 carbons, acyl having 1-6 carbons, tert-butyloxycarbonyl, or Si(R 8 ) 3 ;
R 3 -R 6 are independently hydrogen, halogen, alkyl having 1-6 carbons, acyl having 1-6 carbons, amide, amine, —CN, —OR 7 , —SR 7 , alkenyl having 1-6 carbons, alkynyl having 1-6 carbons, aryl having 1-6 carbons, or heteroaryl having 1-6 carbons;
b) hydrogenating the azaborine substrate with at least one formal equivalent of dihydrogen.
2 . The method of claim 1 , wherein hydrogenating the azaborine substrate includes hydrogenating the azaborine substrate with three formal equivalents of dihydrogen.
3 . The method of claim 2 , wherein the hydrogenated azaborine substrate has the formula
4 . The method of claim 1 , further comprising releasing one or more equivalents of dihydrogen from the hydrogenated azaborine substrate.
5 . The method of claim 1 , wherein hydrogenating the azaborine substrate includes reducing at least one multiple bond in the azaborine substrate.
6 . The method of claim 5 wherein hydrogenating the azaborine substrate occurs in the presence of a hydrogenation catalyst.
7 . The method of claim 1 , wherein hydrogenating the azaborine substrate includes reducing the azaborine substrate with a source of hydride.
8 . The method of claim 7 wherein the hydride adds to the boron atom of the azaborine substrate.
9 . The method of claim 1 , wherein hydrogenating the azaborine substrate includes protonating the ring nitrogen atom of the azaborine substrate.
10 . The method of claim 1 , wherein hydrogenating the azaborine substrate includes:
a) reducing at least one multiple bond in the azaborine substrate to yield a saturated intermediate;
b) reducing the saturated intermediate with a source of hydride; and
c) protonating the ring nitrogen atom of the azaborine substrate.
11 . The method of claim 1 , wherein providing the azaborine substrate includes providing a substrate wherein R 3 -R 6 are hydrogen.
12 . The method of claim 1 , wherein providing the azaborine substrate includes providing a substrate wherein R 1 and R 2 are hydrogen or lower alkyl.
13 . The method of claim 1 , wherein providing the azaborine substrate includes providing a substrate having the formula
wherein R 1 is H or tert-butyl.
14 . A hydrogen storage system, comprising:
an azaborine substrate having the formula
wherein R 1 is halogen, alkyl having 1-6 carbons, aryl having 1-6 carbons, heteroaryl having 1-6 carbons, acyl having 1-6 carbons, alkenyl having 1-6 carbons, alkynyl having 1-6 carbons, sulfonyl, —OR 7 , —SR 7 , or Si(R 8 ) 3 where each R 7 is independently hydrogen, alkyl having 1-6 carbons, acyl having 1-6 carbons, alkenyl having 1-6 carbons, tert-butyloxycarbonyl, or sulfonyl; each R 8 is independently alkyl having 1-6 carbons, aryl having 1-6 carbons, alkoxy having 1-6 carbons, acyl having 1-6 carbons, alkenyl having 1-6 carbons, or tert-butyloxycarbonyl;
R 2 is hydrogen, halogen, acyl having 1-6 carbons, amide, amine, —CN, —OR 7 , —SR 7 , alkyl having 1-6 carbons, alkenyl having 1-6 carbons, alkynyl having 1-6 carbons, or R 2 is an aromatic heterocycle; or R 1 and R 2 taken in combination form a fused 5- or 6-membered ring that optionally incorporates one or more heteroatoms, and that is itself optionally further substituted by alkyl having 1-6 carbons, aryl having 1-6 carbons, acyl having 1-6 carbons, tert-butyloxycarbonyl, or Si(R 8 ) 3 ;
R 3 -R 6 are independently hydrogen, halogen, alkyl having 1-6 carbons, acyl having 1-6 carbons, amide, amine, —CN, —OR 7 , —SR 7 , alkenyl having 1-6 carbons, alkynyl having 1-6 carbons, aryl having 1-6 carbons, or heteroaryl having 1-6 carbons.
15 . The hydrogen storage system of claim 14 , wherein the azaborine substrate is present in the storage system in a liquid phase.
16 . The hydrogen storage system of claim 14 , wherein the hydrogen storage system is incorporated into a portable power cell, or installed in conjunction with a hydrogen-burning engine.
17 . The hydrogen storage system of claim 14 , further comprising apparatus for hydrogenating the azaborine substrate.
18 . The hydrogen storage system of claim 14 , further comprising apparatus for recovering dihydrogen from a hydrogenated azaborine substrate.