Frustrated Lewis Pair Modification by 1,1-Carboboration: Disclosure of a Phosphine Oxide Triggered Nitrogen Monoxide Addition to an Intramolecular P/B Frustrated Lewis Pair

The vicinal frustrated Lewis pair (FLP) mes₂P–CH₂CH₂–B­(C₆F₅)₂ (<b>3</b>) reacts with phenyl­(trimethylsilyl)­acetylene by 1,1-carboboration to give the extended C₃-bridged FLP <b>6</b> featuring a substituted vinylborane subunit. The FLP <b>6</b> actively cleaves dihydrogen. The FLP <b>3</b> also undergoes a 1,1-carboboration reaction with diphenylphosphino­(trimethylsilyl)­acetylene to give the P/B/P FLP <b>11</b> that features a central unsaturated four-membered heterocyclic P/B FLP and a pendant CH₂CH₂–Pmes₂ functional group. Compound <b>11</b> reacts with nitric oxide (NO) by oxidation of the pendant Pmes₂ unit to the P­(O)­mes₂ phosphine oxide and N,N-addition of the P/B FLP unit to NO to yield the persistent P/B/PO FLPNO aminoxyl radical <b>14</b>. This reaction is initiated by P­(O)­mes₂ formation and opening of the central Ph₂P···B­(C₆F₅)₂ linkage triggered by the pendant CH₂CH₂–P­(O)­mes₂ group