Efficient Pd(0)-Catalyzed Hydrosilylation of Alkynes with Triorganosilanes

Abstract

An electron-rich Pd(0) complex, a Pd₂(dba)₃·CHCl₃-tricyclohexylphosphine combination catalyzes highly efficient hydrosilylation of alkynes at room temperature with Ph₃SiH or Ph₂MeSiH without solvents. The regioselectivity of this process is higher than that with the conventional Pt(0)-catalyzed hydrosilyl­ation.

Key words

hydrosilylation - palladium - phosphine - alkyne - alkene

References

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10

Experimental Procedure: The reaction of dodec-1-en-11-yne with Ph₃SiH is representative. In a 30 mL round-bottomed flask, Pd₂(dba)₃·CHCl₃ (5.2 mg, 0.005 mmol) and tricyclohexylphosphine (5.6 mg, 0.02 mmol) were placed under argon atmosphere, and dodec-1-en-11-yne (0.26 mL, 1.2 mmol) was introduced via a syringe. The mixture was stirred well for 10 min to make it homogeneous. To the mixture, triphenylsilane (260 mg, 1.0 mmol) was added at room temperature. Triphenylsilane was soon dissolved and the mixture became homogeneous. After 1 h, the reaction mixture was submitted on silica gel purification to provide (E)-1-triphenylsilyl-dodeca-1,11-diene (369 mg, 0.87 mmol) in 87% yield along with a minor amount of 2-triphenylsilyl-dodeca-1,11-diene (3%).

11

None of alkenylsilanes were obtained with triethylsilane.

13

Experimental Procedure for Aqueous Reaction: In a round-bottomed flask, Pd₂(dba)₃·CHCl₃ (5.2 mg, 0.005 mmol), tris(2,4,6-trimethoxyphenyl)phosphine (10.7 mg, 0.02 mmol), and 1-octyne (0.30 mL, 2.0 mmol) were mixed well. To the mixture, distilled water (5 mL, non-degassed) was introduced and the mixture was stirred vigorously (1500 rpm) for 5 min. Triphenylsilane (260 mg, 1.0 mmol) was then added, and the heterogeneous mixture was stirred vigorously for 6 h. Extractive workup and purification provided (E)-1-triphenylsilyl-1-octene (256 mg, 0.69 mmol) along with 2-triphenylsilyl-1-octene (13%).

14

An addition of a small amount of water (0.1 mL) to the neat reaction did not enhance the reactivity. Therefore, the amount of water is essential.