Tetraphenylcyclopentadienone is an organic compound with the formula . It is classified as a cyclic dienone. It is a dark purple to black crystalline solid that is soluble in organic solvents. It is an easily made building block for many organic and organometallic compounds.
The C<sub>5</sub>O core of the molecule is planar and conjugated, but the bonds have a definite alternating single- and double-bond nature. The C2âÂÂC3 and C4âÂÂC5 distances are 1.35 à, while the C1âÂÂC2, C3âÂÂC4, C5âÂÂC1 are closer to single bonds with distances near 1.50 à. The phenyl groups of tetraphenylcyclopentadienone adopt a "propeller" shape in its 3D conformation. The four phenyl rings are rotated out of the plane of the central ring because of steric repulsion with each other.
Unlike the parent compound cyclopentadienone, which rapidly dimerizes, the tetraphenyl derivative is isolable at room temperature.
Tetraphenylcyclopentadienone can be synthesized by a double aldol condensation involving benzil and dibenzyl ketone in the presence of a basic catalyst.
The central ring can serve as a diene in DielsâÂÂAlder reactions with various dienophiles. For example, reaction with benzyne leads to 1,2,3,4-tetraphenylnaphthalene and reaction with diphenylacetylene leads to hexaphenylbenzene. In this way, it is a precursor to graphene-like molecules, such as coronene.
Similarly, pentaphenylpyridine derivatives may be prepared via a DielsâÂÂAlder reaction between tetraphenylcyclopentadienone and benzonitrile.
Tetraphenylcyclopentadienone can provide an effective alternative to DDQ in aromatization of porphyrins:
Tetraarylcyclopentadienones are a well studied class of ligands in organometallic chemistry. The Shvo catalyst, useful for certain hydrogenations, is derived from tetraphenylcyclopentadienone.