Ring Strain-Promoted Activation of Pyridines by a Saturated BSi₂ Cycle

Ring strain is a well-established strategy to increase reactivity. Employing an elusive saturated BSi₂ ring motif, we here exploit the size mismatch between boron and silicon to this end. The reaction of disilenide Tip₂Si = SiTipLi with BH₃·SMe₂ selectively affords the lithium salt of anionic boratadisilirane c-SiTip₂SiHTipBH₂ ^- (Tip = 2,4,6-triisopropylphenyl), which according to DFT calculations on the parent system BSi₂H₆ ^- is much more strained than isoelectronic analogues such as cyclopropane (C₃H₆), boratirane (BC₂H₆ ^-), and cyclotrisilane (Si₃H₆). Indeed, it spontaneously and selectively activates a range of pyridine derivatives: pyridine itself undergoes ortho-CH activation under dearomatization of a second equivalent; 2 equivalents of para-dimethylaminopyridine (DMAP) are C─C-coupled in ortho- and meta-position; and pentafluoropyridine (PFP) is CF-activated in para-position.