Rhodium(I)-Catalyzed Synthesis of Aryltriethoxysilanes from Arenediazonium Tosylate Salts with Triethoxysilane

Abstract

An efficient method for the preparation of aryltriethoxy­silanes from arenediazonium tosylate salts has been developed, which expands the substrates of rhodium-catalyzed silylation from iodides, bromides, and triflates to diazonium salts. A new method for hydrodediazoniation has also been explored.

Key words

silylation - diazo compounds - aryltriethoxysilane - rhodium catalyst - arenes

References and Notes

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23

Typical Method for the Preparation of Arenediazonium Tosylate Salts
To a solution of methyl 4-aminobenzoate (1.0 mmol) in THF (5 mL) and AcOH (5 mL) was added PTSA˙H₂O (1.1 mmol). Immediately, pale solids were precipitated. About 8 mL of AcOH was added until the solution turned clear again. The solution was then cooled to -10 ˚C, and then t-BuONO (1.5 mmol) was added dropwise to the reaction. The mixture was stirred for 30 min and then warmed to r.t. for another 30 min. The clear solution was poured into Et₂O (100 mL), and the diazonium tosylate salt was precipitated. After careful filtration, the product was collected to give a yield of 91%.
4-Methoxycarbonylbenzenediazonium Tosylate
IR (neat): 3566, 3483, 3101, 2311, 1723, 1438, 1302, 1195, 1122, 1036, 1009, 865, 817, 763, 684, 568, 525 cm^-¹. ^¹H NMR (400 MHz, DMSO-d ₆): δ = 2.27 (s, 3 H), 3.95 (s, 3 H), 7.09 (d, 2 H, J = 8.0 Hz), 7.46 (d, 2 H, J = 8.0 Hz), 8.39-8.43 (m, 2 H), 8.78-8.80 (m, 2 H) ppm. ^¹³C NMR (100 MHz, DMSO-d ₆): δ = 20.86, 51.68, 115.41, 120.34, 125.59, 128.24, 131.47, 138.03, 145.30, 162.04, 166.13 ppm. MS (ESI): m/z = 163 [M⁺], 162.9.

24

Typical Procedure for the Silylation
Toluenediazonium tosylate salt (280 mg, 1.0 mmol, and Bu₄NI (369 mg, 1.0 mmol) were placed in a 25 mL of three-necked flask which was capped with septum rubbers. The flask was evacuated and backfilled with argon, and then charged with DMF (4 mL), Et₃N (3.0 mmol), and chloro(1,5-cyclooctadiene) rhodium(I) dimer (5 mol%, 0.05 mmol). The reaction mixture was stirred for 2 h at r.t. Triethoxysilane (2.0 mmol) was added by a syringe through the septum rubber. The reaction mixture was then stirred at 80-100 ˚C. After the reaction, the mixture was diluted with Et₂O, washed three times with H₂O to remove DMF, and dried over Na₂SO₄. The solvent was removed under reduced pressure, and the residue was purified by Kugelrohr distillation or silica gel column to give the desired
4-tolyltriethoxysilane 223 mg, yield 89%.
IR (neat): 2975, 2926, 2887, 1656, 1630, 1444, 1391, 1295, 1167, 1127, 1103, 1080, 959, 781, 712, 505 cm^-¹. ^¹H NMR (400 MHz, CDCl₃): δ = 1.30 (t, 9 H, J = 7.2 Hz), 2.38 (s, 3 H), 3.91 (q, 6 H, J = 7.2 Hz), 7.23 (d, 2 H, J = 8.0 Hz), 7.63 (d, 2 H, J = 8.0 Hz) ppm. ^¹³C NMR (100 MHz, CDCl₃): δ = 17.86, 21.20, 58.33, 127.81, 128.38, 134.59, 139.91 ppm. MS (EI): m/z = 254 [M⁺], 254, 209, 195, 181, 162, 147, 139, 119, 91, 45.

32

General Procedure for the Hydrodediazoniation
To a solution of arenediazonium tetrafluoroborate (1.0 mmol) in anhyd DMF (2 mL), was added catalytic amount (0.0005 mmol) of chloro(1,5-cyclooctadiene) rhodium(I) dimer at r.t. Then triethoxysilane (1 equiv, 164 mg, 1.0 mmol) was added to the solution in one portion. Lots of gas escaped rapidly and the yellow-color reaction mixture turned into dark and green. The reaction was allowed to stir at r.t. for 30 min. After no nitrogen bumbled, the mixture was extracted with Et₂O and washed many times with H₂O to remove the DMF as much as possible. The crude product was purified with silica gel column or identified by GC-MS to obtain the required arene with yields from 85-95%.