Method for preparing bis-(silylalkyl)carbonate esters
Carbonate esters of Formula (I): (R 1 )(R 2 )(R 3 )Si—R 4 —O—C(═O)—O—R 4 —Si(R 1 )(R 2 )(R 3 ) are prepared by reaction of a silyl-substituted alcohol of Formula (II): (R 1 )(R 2 )(R 3 )Si—R 4 —OH with an activated carbonyl compound of Formula (III): C(═O)Z 2 in the presence of a catalyst (e.g., an bicyclic amidine, a bicyclic guanidine, or a phosphazene) in an aprotic solvent. In Formulas (I) and (II) each of R 1 and R 2 independently is alkyl; R 3 is alkyl or —X 1 —Si(R 5 )(R 6 )(R 7 ); X 1 is O or alkylene; R 4 is alkylene; and each R 5 , R 6 , and R 7 independently is alkyl. In Formula (III), Z is 1-N-imidazolyl or 1-N-succinimidyl. In some embodiments, the catalyst used in the methods described herein comprises at least one base selected from the group consisting of a bicyclic amidine and a bicyclic guanidine. The reaction proceeds readily under both bulk and continuous flow reactor conditions.
1. A method of preparing a bis-(silylalkyl)carbonate of Formula (I):
(R 1 )(R 2 )(R 3 )Si—R 4 —O—C(═O)—O—R 4 —Si(R 1 )(R 2 )(R 3 ); the method comprising the sequential steps of:
(a) contacting at least about two molar equivalents of silyl-substituted alcohol of Formula (II): (R 1 )(R 2 )(R 3 )Si—R 4 —OH with about 1 molar equivalent of an activated carbonyl compound of Formula (III): C(═O)Z 2 in the presence of a catalyst in an aprotic solvent; and
(b) isolating the bis-(silylalkyl)carbonate of Formula (I) from the solvent;
wherein:
the catalyst comprises at least one material selected from the group consisting of a bicyclic amidine base, a bicyclic guanidine base, and a phosphazene base;
each of R 1 and R 2 independently is alkyl;
R 3 is alkyl or —X 1 —Si(R 5 )(R 6 )(R 7 );
X 1 is O or alkylene;
R 4 is alkylene;
each of R 5 , R 6 , and R 7 independently is alkyl; and
Z is 1-N-imidazolyl or 1-N-succinimidyl.
2. The method of claim 1 , wherein each of R 1 and R 2 independently is C 1 to C 6 alkyl.
3. The method of claim 1 , wherein each of R 1 R 2 , and R 3 is methyl.
4. The method of claim 1 , wherein R 4 is —CH 2 —.
5. The method of claim 2 , wherein R 3 is methyl.
6. The method of claim 2 , wherein R 3 is —X 1 —Si(R 5 )(R 6 )(R 7 ) and each of R 5 , R 6 , and R 7 independently is C 1 to C 6 alkyl.
7. The method of claim 6 , wherein each of R 5 , R 6 , and R 7 is methyl.
8. The method of claim 6 , wherein X 1 is C 1 to C 6 alkylene.
9. The method of claim 6 , wherein X 1 is —CH 2 —.
10. The method of claim 1 , wherein Z is 1-N-imidazolyl.
11. The method of claim 1 , wherein the catalyst comprises:
(a) a bicyclic amidine base selected from the group consisting of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), and 1,5-diazabicyclo[4.4.0]dec-5-ene (DBD);
(b) a bicyclic guanidine base selected from the group consisting of 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), 7-methyl-1,5,7-triazabicyclo-[4.4.0]dec-5-ene (MTBD), 7-ethyl-1,5,7-triazabicyclo-[4.4.0]dec-5-ene (ETBD), and 7-isopropyl-1,5,7-triazabicyclo-[4.4.0]dec-5-ene (ITBD); or
(c) a combination of (a) and (b).
12. The method of claim 1 , wherein the catalyst comprises at least one base selected from the group consisting of TBD and DBU.
13. The method of claim 1 , wherein the aprotic solvent comprises at least one solvent selected from the group consisting of an ether, a nitrile, an ester, and organic carbonate ester, an amide, a ketone, a sulfone, a sulfoxide, a hydrocarbon, and a halogenated hydrocarbon.
14. The method of claim 1 , wherein the aprotic solvent comprises acetonitrile.
15. The method of claim 1 , wherein each of each of R 1 , R 2 , and R 3 is methyl; R 4 is —CH 2 —; and Z is 1-N-imidazolyl.
16. The method of claim 13 , wherein the solvent comprises acetonitrile; and the catalyst comprises DBU or TBD.
17. The method of claim 1 , wherein the contacting step (a) is performed at a temperature in the range of about 0 to about 180° C.
18. The method of claim 1 , wherein the contacting step (a) is performed over a time period in the range of about 1 hour to about 24 hours.
19. The method of claim 1 , wherein the contacting step is performed in a heated continuous flow reactor at a temperature in the range of about 20 to about 180° C. with a residence time within the heated continuous flow reactor in the range of about 0.1 to about 8 minutes.
20. The method of claim 1 , wherein the compound of Formula (II) is present in the aprotic solvent at a concentration of about 0.1 to about 6 M, and the activated carbonyl compound is present in the aprotic solvent at a concentration of about 0.1 to about 2 M.
21. The method of claim 1 , wherein the catalyst is present in the aprotic solvent at a concentration of about 0.5 to about 25 mol % relative to the concentration of the compound of Formula (II).