General Synthesis of Trialkyl- and Dialkylarylsilylboranes: Versatile Silicon Nucleophiles in Organic Synthesis

Compared
to carbon-based nucleophiles, the number of silicon-based
nucleophiles that is currently available remains limited, which significantly
hampers the structural diversity of synthetically accessible silicon-based
molecules. Given the high synthetic utility and ease of handling of
carbon-based boron nucleophiles, silicon-based boron nucleophiles,
i.e., silylboranes, have attracted considerable interest in recent
years as nucleophilic silylation reagents that are activated by transition-metal
catalysts or bases. However, the range of practically accessible silylboranes
remains limited. In particular, the preparation of sterically hindered
and functionalized silylboranes remains a significant challenge. Here,
we report the use of rhodium and platinum catalysts for the direct
borylation of hydrosilanes with bis­(pinacolato)­diboron, which allows
the synthesis of new trialkylsilylboranes that bear bulky alkyl groups
and functional groups as well as new di­alkyl­aryl­silyl­boranes
that are difficult to synthesize via conventional methods using alkali
metals. We further demonstrate that these compounds can be used as
silicon nucleophiles in organic transformations, which significantly
expands the scope of synthetically accessible organosilicon compounds
compared to previously reported methods. Thus, the present study can
be expected to inspire the development of efficient methods for novel
silicon-containing bioactive molecules and organic materials with
desirable properties. We also report the first 11B­{1H} and 29Si­{1H} NMR spectroscopic evidence
for the formation of i-Pr3SiLi generated
by the reaction of i-Pr3Si–B­(pin)
with MeLi.