A Crystalline Monomeric Phosphaborene.

We report the synthesis of the monomeric phosphaborene ArP═B(TMP) () (Ar = 2,6-bis(triisopropylphenyl)-3,5-diisopropylphenyl) containing 2-coordinate phosphorus and boron centers. Compound has a PB bond length of 1.741(3) Å, the shortest reported to date. Computational examination of the bonding in reveals, in addition to the σ bond, the presence of a single classical π bond and a large Wiberg bond index of 1.9707, consistent with double bond, and not triple bond, character. The chemistry of is marked by its low reactivity, which is rationalized by examination of the frontier molecular orbitals and steric considerations.