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

Abstract

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.