Structure and Dynamic Features of an Intramolecular Frustrated Lewis Pair

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 H-2 with the formation of the product 4 and adds to the C=O double bond of phenyl isocyanate to yield 6. In the crystal, compound 5 features a puckered four-membered heterocyclic core structure with a long P B bond (ay. 2.197(5) angstrom). The activation energy of the P B cleavage of the frustrated Lewis pair 5 was determined by dynamic F-19 NMR spectroscopy at Delta G(not equal) (298 K) = 12.1 +/- 0.3 kcal mol(-1).