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) mes(2)P-CH2CH2B(C6F5)(2) (3) reacts with phenyl(trimethylsilyl)acetylene by 1,1-carboboration to give the extended C-3-bridged FLP 6 featuring a substituted vinylborane subunit. The FLP 6 actively cleaves dihydrogen. The FLP 3 also undergoes a 1,1-carboboration reaction with diphenylphosphino(trimethylsilyl)acetylene to give the P/B/P FLP 11 that features a central unsaturated four-membered heterocyclic P/B FLP and a pendant CH2CH2-Pmes(2) functional group. Compound 11 reacts with nitric oxide (NO) by oxidation of the pendant Pmes(2) unit to the P(O)mes(2) phosphine oxide and N,N-addition of the P/B FLP unit to NO to yield the persistent P/B/PO FLPNO aminoxyl radical 14. This reaction is initiated by P(0)mes2 formation and opening of the central Ph2P center dot center dot center dot B(C6F5)(2) linkage triggered by the pendant CH2CH2 P(O)mes(2) group.