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Synlett 2009(3): 477-481  
DOI: 10.1055/s-0028-1087542
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Hydroboration of Vinyl Arenes Using SiO2-Supported Rhodium Catalysts

Michael J. Geiera, Stephen J. Geiera, Christopher M. Vogelsa, François Bélandb, Stephen A. Westcott*a
a Department of Chemistry, Mount Allison University, Sackville, NB, E4L 1G8, Canada
Fax: +1(506)3642313; e-Mail: swestcott@mta.ca;
b Silicycle, 1200 St-Jean-Baptiste Avenue, Québec, PQ, G2E 5E8, Canada
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Publication History

Received 21 July 2008
Publication Date:
21 January 2009 (online)

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Abstract

The metal-catalyzed hydroboration of vinyl arenes using catecholborane (HBcat) and pinacolborane (HBpin) has been examined with SiO2-supported rhodium catalysts. Reactions with simple vinyl arenes (ArCH=CH2) and HBcat using Rh(acac)(coe)2 (coe = cyclooctene) gave selective formation of the corresponding branched isomers [ArCH(Bcat)Me]. Catalyst systems could be reused with no appreciable loss in activity or selectivity.

Key words

catalysis - heterogeneous - hydroborations - rhodium - silica support

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Si-DPP (R39030B) is available at SiliCycle (www.silicycle.com).

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Experimental Procedure
In a typical experiment, a THF (0.5 mL) solution of Rh(acac)(coe)2 (8 mg, 0.019 mmol) was added to a THF (2 mL) slurry of Si-DPP (60 mg, 0.056 mmol), and the mixture was stirred for 5 h. To this mixture was added a THF (0.5 mL) solution of 2-vinylnaphthalene (135 mg, 0.87 mmol) followed by a THF (0.5 mL) solution of HBcat (126 mg, 1.05 mmol). The reaction was allowed to proceed for 18 h at which point the mixture was filtered through a small plug of Celite before solvent was removed under vacuum. The residual oil was dissolved in C6D6 (1 mL) and analyzed by multinuclear NMR spectroscopy.5a,¹0 Confirmation of product formation was carried out using GC-MS on products derived from a basic, oxidative workup.
Selected NMR Spectroscopic Data 4-MeOC6H4CH(Bcat)Me (i; R = OMe; Bcat): ¹H NMR (270 MHz, C6D6): δ = 2.74 [q, J = 7.7 Hz, CH(Bcat)CH3], 1.48 [d, J = 7.7 Hz, CH(Bcat)CH 3].
4-MeOC6H4CH2CH2 (Bcat) (ii; R = OMe; Bcat): ¹H NMR (270 MHz, C6D6): δ = 2.79 [t, J = 7.9 Hz, CH 2CH2 (Bcat)], 1.42 [t, J = 7.9 Hz, CH2CH 2 (Bcat)].
4-MeOC6H4CH=CH(Bcat) (iii; R = OMe; Bcat): ¹H NMR (270 MHz, C6D6): δ = 7.82 [d, J = 18.3 Hz, CH=CH(Bcat)], 6.34 [d, J = 18.3 Hz, CH=CH(Bcat)].
4-MeOC6H4CH2CH(Bcat)2 (iv; R = OMe; Bcat): ¹H NMR (270 MHz, C6D6): δ = 3.36 [d, J = 8.2 Hz, CH 2CH(Bcat)2], 2.11 [t, J = 8.2 Hz, CH2CH(Bcat)2].
4-FC6H4CH(Bcat)Me (i; R = F; Bcat): ¹H NMR (270 MHz, C6D6): δ = 2.60 [q, J = 7.7 Hz, CH(Bcat)CH3), 1.36 [d, J = 7.7 Hz, CH(Bcat)CH 3].
4-FC6H4CH=CH(Bcat) (iii; R = F; Bcat): ¹H NMR (270 MHz, C6D6): δ = 7.62 [d, J = 18.3 Hz, CH=CH(Bcat)], 6.23 [d, J = 18.3 Hz, CH=CH(Bcat)].
4-FC6H4CH2CH(Bcat)2 (iv; R = F; Bcat): ¹H NMR (270 MHz, C6D6): δ = 3.22 [d, J = 8.2 Hz, CH 2CH(Bcat)2], 1.99 [t, J = 8.2 Hz, CH2CH(Bcat)2].

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Selected NMR Spectroscopic Data
4-MeOC6H4CH(Bpin)Me (i; R = OMe; Bpin): ¹H NMR (270 MHz, C6D6): δ = 2.56 [q, J = 7.7 Hz, CH(Bpin)CH3], 1.50 [d, J = 7.7 Hz, CH(Bpin)CH 3].
4-MeOC6H4CH2CH2(Bpin) (ii; R = OMe; Bpin): ¹H NMR (270 MHz, C6D6): δ = 2.87 [t, J = 7.9 Hz, CH 2CH2 (Bpin)], 1.12 [t, J = 7.9 Hz, CH2CH 2(Bpin)].
4-MeOC6H4CH=CH(Bpin) (iii; R = OMe; Bpin): ¹H NMR (270 MHz, C6D6): δ = 7.80 [d, J = 18.3 Hz, CH=CH(Bpin)], 6.40 [d, J = 18.3 Hz, CH=CH(Bpin)].
4-FC6H4CH(Bpin)Me (i; R = F; Bpin): ¹H NMR (270 MHz, C6D6): δ = 2.45 [q, J = 7.7 Hz, CH(Bpin)CH3], 1.38 [d, J = 7.7 Hz, CH(Bpin)CH 3].
4-FC6H4CH2CH2(Bpin) (ii; R = F; Bpin): ¹H NMR (270 MHz, C6D6): δ = 2.70 [t, J = 8.1 Hz, CH 2CH2 (Bpin)], 1.12 [t, J = 8.1 Hz, CH2CH 2(Bpin)].
4-FC6H4CH=CH(Bpin) (iii; R = F; Bpin): ¹H NMR (270 MHz, C6D6): δ = 7.60 [d, J = 18.5 Hz, CH=CH(Bpin)], 6.27 [d, J = 18.5 Hz, CH=CH(Bpin)].
4-FC6H4CH2CH(Bpin)2 (iv; R = F; Bpin): ¹H NMR (270 MHz, C6D6): δ = 3.11 [d, J = 8.2 Hz, CH 2CH(Bpin)2], 1.50 [t, J = 8.2 Hz, CH2CH(Bpin)2].
PhCH(Bpin)Me (i; R = H; Bpin): ¹H NMR (270 MHz, C6D6): δ = 2.51 [q, J = 7.4 Hz, CH(Bpin)CH3], 1.42 [d, J = 7.4 Hz, CH(Bpin)CH 3].
PhCH2CH2(Bpin) (ii; R = H; Bpin): ¹H NMR (270 MHz, C6D6): δ = 2.80 [t, J = 8.0 Hz, CH 2CH2 (Bpin)], 1.03 [t, J = 8.0 Hz, CH2CH 2 (Bpin)].
PhCH=CH(Bpin) (iii; R = H; Bpin): ¹H NMR (270 MHz, C6D6): δ =7.70 [d, J = 18.5 Hz, CH=CH(Bpin)], 6.40 [d, J = 18.5 Hz, CH=CH(Bpin)].
PhCH2CH(Bpin)2 (iv; R = H; Bpin): ¹H NMR (270 MHz, C6D6): δ = 3.20 [d, J = 8.0 Hz, CH 2CH(Bpin)2], 1.30 [t, J = 8.0 Hz, CH2CH(Bpin)2].

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Selected NMR Spectroscopic Data
2,4,6-Me3C6H2CH(Bcat)Me (v): ¹H NMR (270 MHz, C6D6): δ = 2.90 [q, J = 7.7 Hz, CH(Bcat)CH3], 1.42 [d, J = 7.7 Hz, CH(Bcat)CH 3].
2,4,6-Me3C6H2CH2CH2(Bcat) (vi): ¹H NMR (270 MHz, C6D6): δ = 2.81 [t, J = 7.9 Hz, CH 2CH2 (Bcat)], 1.31 [t, J = 7.9 Hz, CH2CH 2 (Bcat)].
2,4,6-Me3C6H2CH=CH(Bcat) (vii): ¹H NMR (270 MHz, C6D6): δ = 7.90 [d, J = 18.3 Hz, CH=CH(Bcat)], 6.10 [d, J = 18.3 Hz, CH=CH(Bcat)].
2,4,6-Me3C6H2CH2CH(Bcat)2 (viii): ¹H NMR (270 MHz, C6D6): δ = 3.41 [d, J = 8.2 Hz, CH 2CH(Bcat)2], 2.11 [t, J = 8.2 Hz, CH2CH(Bcat)2].