elevated temperatures of 100 °C, starts with H–Bpin activation which subsequently generates Li[BH4], so that the mechanism eventually turns into “hidden borohydride catalysis”. Ph(H)CNPh, Ph2CO, Ph2CCH2, and iPrNCNiPr undergo hydroboration already at room temperature. Here, the active hydroboration catalyst is the [4 + 2] cycloadduct between the respective substrate and Li2[DBA-Me2]: in the key step
9,10-dimethyl-9,10-dihydro-9,10-diboraanthrancene 的碱
金属盐 (M 2 [
DBA-Me 2 ]; M + = Li + , Na + , K + ) 激活 H–B 键THF 中的
频那醇硼烷 (HBpin) 已经在室温下。对于M + = Na + , K + ,形成加成产物M 2 [ 4 ],其中包含一个新的H–B和一个新的B–Bpin键;对于 M + = Li +,H −离子瞬间从
DBA-Me 2单元转移到另一个等效的 HBpin 以提供 Li[ 5]. 尽管 Li[ 5 ] 通常被认为是中性
DBA-Me 2的 [Bpin ]加合物,但它会向 Li[SiPh 3 ] 提供一个 [Bpin] +阳离子,生成甲
硅烷基
硼烷 Ph 3 Si–Bpin;带有芳香中心 B 2 C 4环的Li 2 [
DBA-Me 2 ]作为离去基团。此外,Li 2 [
DBA-Me