Reversible C−H activation, facile C−B/B−H metathesis and apparent hydroboration catalysis by a dimethylxanthene‐based frustrated Lewis pair

A dimethylxanthene‐based phosphine/borane frustrated Lewis pair (FLP) is shown to effect reversible Candminus;H activation, cleaving phenylacetylene, PhCCH, to give an equilibrium mixture of the free FLP and phosphonium acetylide in CD2Cl2andnbsp;solution at room temperature. This system also reacts with Bandminus;H bonds although in a different fashion: reactions with HBpin and HBcat proceed via Candminus;B/Bandminus;H metathesis, leading to replacement of the ‐B(C6F5)2andnbsp;Lewis acid component by ‐Bpin/‐Bcat, and transfer of HB(C6F5)2andnbsp;to the phosphine Lewis base. This transformation underpins the ability of the FLP to catalyze the hydroboration of alkynes by HBpin: the active species is derived from the HB(C6F5)2fragment generated in this exchange process.