Process for synthesis of dialkoxyorganoboranes
The invention relates to a process for the synthesis of dialkoxyorganoboranes, in particular to a process for the synthesis of dialkoxyorganoboranes by an ester exchange reaction. Moreover, the invention relates to a process for the synthesis of organo-oxazaborolidine catalysts (organo-CBS) and of trialkylboroxins. Furthermore, the invention relates to methods of using dialkoxyorganoboranes for the preparation of organo-CBS catalysts and in Suzuki-type coupling reactions.
1. A process for the preparation of a dialkoxyorganoborane (3) of the formula R 1 —B(OR 2 ) 2 , comprising the step of reacting a triorganoboroxin (1) of the formula (R 1 —BO) 3 and a trialkylborate (2) of the formula B(OR 2 ) 3 ,
wherein
R 1 is C 1 -C 20 alkyl, C 3 -C 10 cycloalkyl, C 6 -C 14 aryl, C 7 -C 24 aralkyl, C 7 -C 24 alkaryl, C 2 -C 20 alkenyl, C 5 -C 15 cycloalkenyl, C 2 -C 20 alkynyl, CH 2 SiMe 3 , substituted C 1 -C 20 -alkyl
and
R 2 is C 1 -C 20 alkyl,
or two R 2 groups in compounds (2) or (3) together with the —BO 2 — moiety form a cyclic structure of the formula
with the divalent group R 3 selected from the group of consisting of —CH 2 CH 2 —, —CH(CH 3 )CH 2 —, —CH 2 CH 2 CH 2 —, —CH(CH 3 )CH(CH 3 )—, —CH(CH 2 CH 3 )CH 2 —, —C(CH 3 ) 2 C(CH 3 ) 2 —, —CH 2 C(CH 3 ) 2 CH 2 —, —(CH 2 ) 6 —, ortho-C 6 H 4 or ortho-C 6 H 3 alkyl.
2. The process of claim 1 , wherein the dialkoxyorganoborane (3) is separated from the reaction mixture by distillation.
3. The process of claim 1 , wherein R 1 is methyl, ethyl, n-propyl, isopropyl or n-butyl and R 2 is isopropyl or n-butyl.
4. The process of claim 1 , wherein the reaction is carried out in the presence of at least one non-coordinating solvent.
5. The process of claim 4 , wherein the solvent is tetrahydrofurane (THF), diethylether, tert.-butylmethylether, hexane, pentane, toluene or benzene.
6. The process of claim 1 , wherein the mole ratio of the triorganoboroxin (1) to the trialkylborate (2) is in the range of approximately 1:2 to 1:4.
7. The process of claim 1 , wherein the reaction is carried out at a temperature from −20° C. to +120° C.
8. A process for the preparation of a dialkoxymethylborane (3a) of the formula H 3 C—B(OR 2 ) 2 , comprising the steps of
a) reacting diborane with carbon monoxide in a solvent to form the trimethylboroxin 1a of the formula (H 3 C—BO) 3 ,
b) reacting the trimethylboroxin (1a) with a trialkylborate (2) of the formula B(OR 2 ) 3 , and
c) separating the dialkoxymethylborane (3a) from the reaction mixture by distillation,
wherein R 2 is C 1 -C 20 alkyl
or two R 2 groups in compounds (2) or (3a) together with the —BO 2 — moiety form a cyclic structure of the formula
with the divalent group R 3 selected from the group of consisting of —CH 2 CH 2 —, —CH(CH 3 )CH 2 —, —CH 2 CH 2 CH 2 —, —CH(CH 3 )CH(CH 3 )—, —CH(CH 2 CH 3 )CH 2 —, —C(CH 3 ) 2 C(CH 3 ) 2 —, —CH 2 C(CH 3 ) 2 CH 2 —, —(CH 2 ) 6 —, ortho-C 6 H 4 or ortho-C 6 H 3 alkyl.