Highly Congested Donor–Acceptor P–B Compound: Synthesis and Properties of a BMes2- and a PPh2‑Functionalized 1,8-Naphthalene

A PPh2- and BMes2-functionalized (Mes = mesityl) 1,8-naphthalene molecule (1) has been synthesized and fully characterized. Compound 1 is a highly congested molecule with a P–B dative bond. NMR studies support that the P–B bond in 1 is persistent in solution. Compound 1 is thermally and photochemically stable. It is highly fluxional in solution. The only reactivity it displays is its reactions with halogen molecules (PhI·Cl2 and I2), leading to the isolation of a hydrolyzed product 2, in which an oxygen atom is inserted between the P and B atom. The crystal structures of 1 and 2 have been determined by single-crystal X-ray diffraction analyses. A DFT computational study established that the open form of 1 has a P–B separation distance of 3.00 Å, much longer than the closed one (2.23 Å). Furthermore, a computational study showed that the energy difference between the two forms is very small, ∼1 kcal/mol, which can be attributed to the highly congested nature of the molecule.