The catalytic generation of a stannylium-ion-like tin electrophile by heterolytic cleavage of the Sn-H bond in hydrostannanes at the Ru-S bond of Ohki-Tatsumi complexes is reported. Reacting these activated hydrostannanes with terminal acetylenes does not lead to hydrostannylation of the C-C triple bond but to dehydrogenative stannylation of the alkyne terminus. The scope of this rare direct C(sp)-H bond stannylation with hydrostannanes is broad, and a mechanism involving a β-tin-stabilized vinyl cation likely having a bridged structure is presented.
A metal-free method for the anti-addition of n-Bu3SnH across
terminal and internal alkynes,
including related α,β-unsaturated carboxyl compounds,
is reported. The reaction is initiated by the trityl salt [Ph3C]+[B(C6F5)4]− and proceeds through β-tin-stabilized vinyl
cations. Their reduction by hydride transfer from n-Bu3SnH explains the high Z-selectivity
in the formation of the vinyl stannanes.
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