Periodic Reporting for period 1 - LWIMT (Main group chemistry, inorganic polymers, catalysis, silicon- and phosphorus-based polymers)
Periodo di rendicontazione: 2016-03-01 al 2018-02-28
The project is important for society because with the new catalytic route there are no wasteful byproducts and the process also does not involve the use of toxic and expensive transition metals like most current catalytic processes. The new route to silylphosphines provides a prototype example of how main group substrates can be converted into useful products.
The overall long term objective is to harness main group substrates based on abundant elements such as silicon and phosphorus as precursors to a wide variety of useful products, both molecular and polymeric.
Furthermore, the skills learned during the project enabled Dr. Wu to return to his homeland, China, with a faculty position in Lanzhou institute of Chemical Physics and to obtain a prestigious “1000 talents” award.
Remarkably, we found that by using PhCN as the H2-acceptor (absorb the H2 release during the reaction) we could obtain silylphosphane in 99% yield within 20 min at 25°C. This is a dramatic acceleration effect and allowed the reaction to be performed with only 1 mol% catalyst loading and still gave 99% yield at 25°C, further-more, with even 0.5 mol% catalyst loading at 50 °C the re-action was essentially complete in 3 h with 99% yield.
We also explore the possibility of using PhCN free system for the heterodehyrodcoupling of phosphines (R1R2PH) with hydrosilanes (R1'R2'R3'SiH). We first examined the reaction between PhPH2 and Et3SiH in the presence of catalytic amounts of various Lewis acids ([Ph3C][B(C6F5)4], AgNO3, Zn(OAc)2), carbene (IMes) or combinations of B(C6F5)3 with different bulky Lewis bases. We found that B(C6F5)3 alone gave superior results and produced mono-silylation product and bis-silylation product. It is worth noting that no reaction took place with-out the addition of B(C6F5)3 even at 130 °C. Further experiments showed that this reaction was sensitive to temperature: at 80 °C after 16 h only 50% of PhPH2 was consumed albeit with 100% selectivity to mono-silyphosphanes. The reaction conditions were optimized with 10 mol% B(C6F5)3, at 100 °C for 16 h in benzene to give 95% conversion of PhPH2 and 98% selectivity for mono-silyphosphanes.