Abstract
Supported palladium catalysts were evaluated for the synthesis of 2-(aryl)vinylphosphonate by Heck coupling. The optimised reaction conditions (1.3
mol% [Pd(NH
3)
4]/NaY, DMF, K
2CO
3, 110–140
°C) were applied to the reaction of diethyl vinylphosphonate with a range of aryl bromides giving good to high isolated yields. Interestingly, with activated aryl bromides the palladium loading could be lowered to only 0.25
mol%. A Pd/SiO
2 catalyst, while highly active with aryl iodides (i.e. 0.15
mol%), was found to be inappropriate when engaging aryl bromides due to lack of activation through
in situ reduction.
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▶ Direct Heck coupling reaction of the diethyl vinylphosphonate with aryl or heteroaryl halides. ▶ Synthesis of diethyl 2-(aryl)vinylphosphonate using solid [Pd]/NaY catalyst at low loading. ▶ Detailed study of a Pd/SiO2 catalyst by XPS, XRD and TEM: on the origin – and absence – of cross-coupling reaction using aryl iodides or bromides with diethyl vinylphosphonate.
The synthesis of diethyl 2-(aryl)vinylphosphonate through direct Heck coupling reaction of the diethyl vinylphosphonate with aryl or heteroaryl halides catalysed by solid materials ([Pd(NH
3)
4]/NaY, Pd/C, PdO/SiO
2) is reported. After optimising the reaction conditions (1.3
mol% [Pd(NH
3)
4]/NaY, DMF, K
2CO
3, 110–140
°C), various aryl and heteroaryl halides were engaged in this reaction leading in all cases good to high yields. Interestingly, when using activated aryl bromides the palladium loading could be lowered to only 0.25
mol%. While highly active when coupling aryl iodides (i.e. only 0.15
mol% required), the PdO/SiO
2 catalyst was found to be inactive when considering aryl bromides. Deep study of this catalytic material revealed that in the case of aryl bromides, absence of
in situ reduction of the catalyst precursor prevents the cross-coupling reaction with this latter material.