Formation, structural characterization, and reactions of a unique cyclotrimeric vicinal Lewis pair containing (C6F5)2P-Lewis base and (C6F5) BH-Lewis acid components

The synthesis of the new vicinal frustrated Lewis pair 5 containing (C6F5)(2)P-Lewis base and (C6F5)BH-Lewis acid functionality is described. It forms a unique cyclotrimer (5)(3) which was structurally characterized by X-ray crystallography and high-resolution solid-state NMR spectroscopy. The relevant NMR Hamiltonian parameters (B-11 and P-31 chemical shielding tensors, B-11 quadrupotar coupling tensors, and (31)p-B-11 spin-spin coupling constants) indicate significant intramotecular covalent B...P interactions, consistent with results from density functional theory (DFT) calculations. In addition, the B-11/P-31 and P-31/P-31 three-spin geometries are accurately reproduced by suitable high-resolution hetero- and homonuclear dipolar NMR experiments. As predicted from the bonding character portrayed by the solid-state NMR results, the cyclotrimer (5)(3) possesses only moderate catalytic activity. However, it undergoes an addition reaction with pyridine and hydroboration reactions with benzaldehyde and tert-butylacetylene. The products of the hydroboration reactions form stable adducts with pyridine.