6-Methoxy-5-phosphaphenanthrene: a molecule with an unreactive P=C double bond.

A multi-step synthesis of the title compound has been devised. In spite of its P=C double bond, the compound does not react at 100 °C with methanol and 2,3-dimethyl-1,3-butadiene. DFT calculations indicate a planar core, a long P=C double bond at 1.725 Å and a high-lying LUMO. Complexation can force the methoxy substituent to rotate out of the plane, thus restoring partly the double bond character of the P=C bond.