Efficient Synthesis of Diborylalkenes from Alkenes and Diboron by a New PSiP-Pincer Palladium-Catalyzed Dehydrogenative Borylation
作者:Jun Takaya、Naohiro Kirai、Nobuharu Iwasawa
DOI:10.1021/ja205186k
日期:2011.8.24
as 1,1-, trans-1,2-, and cyclic 1,2-diborylalkenes from alkenes and diboron was achieved for the first time. Selective preparation of di- and monoborylalkenes was also realized by the appropriate choice of reaction conditions. The reaction was found to proceed via a new mechanism of dehydrogenative borylation through a monoborylpalladium complex bearing an anionic PSiP-pincer ligand as a key intermediate
首次实现了以烯烃和二硼为原料高效合成1,1-、反式-1,2-和环状1,2-二硼基烯烃等多种二硼基烯烃。Selective preparation of di- and monoborylalkenes was also realized by the appropriate choice of reaction conditions. 发现该反应通过一种新的脱氢硼化机制进行,以带有阴离子PSiP-钳状配体的单硼基钯配合物为关键中间体,实现了有效的硼化而不牺牲烯烃的硼氢化或氢化。
PSiP-Pincer Type Palladium-Catalyzed Dehydrogenative Borylation of Alkenes and 1,3-Dienes
Dehydrogenative borylation of alkenes and 1,3-dienes was realized by carrying out the reaction in the presence of bis(pinacolato)diboron (B2pin2) and a catalytic amount of PSiP-pincer palladium complex. This protocol has the following notable features. 1) Monoanionic nature of the PSiP-pincer ligand prevents the formation of boryl(hydrido)- or dihydridopalladium species, enabling synthesis of various vinyl- or dienylboronic esters in good yield from a 1:1 mixture of B2pin2 and alkenes or 1,3-dienes without forming hydroboration or hydrogenation products. 2) Due to the strong trans influence of the silicon atom, PSiP-pincer palladium complex showed high activity toward migratory insertion. 3) Suppression of these side-reactions and the high reactivity of the PSiP-pincer palladium complex enabled an efficient, successive dehydrogenative borylation to give 1,1- or 1,2-diborylated products depending on the kind of substituent on alkenes by using more than 2 equivalents of B2pin2. Mechanistic study revealed that PSiP-pincer borylpalladium complex was generated from hydridopalladium complex and B2pin2, and this complex underwent alkene insertion followed by β-hydride elimination to give alkenylboronic ester with regeneration of the hydridopalladium complex.