Di(mesityl)cyclohexenylphosphine undergoes hydroboration with Piers' borane [HB(C6F5)2] to yield the cyclohexylene-anellated frustrated Lewis pair 5. This P/B pair splits H2 with the formation of the product 4 and adds to the CO double bond of phenyl isocyanate to yield 6. In the crystal, compound 5 features a puckered four-membered heterocyclic core structure with a long PB bond (av. 2.197(5) Å). The activation energy of the PB cleavage of the frustrated Lewis pair 5 was determined by dynamic 19F NMR spectroscopy at ΔG≠(298 K)=12.1±0.3 kcal mol−1.