Tetraphenylcyclopentadienone

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Tetraphenylcyclopentadienone

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Tetraphenylcyclopentadienone is an organic compound with the formula Template:Chem2. 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.

Structure

The C₅O core of the molecule is planar and conjugated, but the bonds have a definite alternating single- and double-bond nature. The C2–C3 and C4–C5 distances are 1.35 Å, while the C1–C2, C3–C4, C5–C1 are closer to single bonds with distances near 1.50 Å. 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.

Synthesis

Tetraphenylcyclopentadienone can be synthesized by a double aldol condensation involving benzil and dibenzyl ketone in the presence of a basic catalyst.

File:Synthesis of tetraphenylcyclopentadienone.png

Reactions

The central ring can serve as a diene in Diels–Alder 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.

File:Hexaphenylbenzene synthesis from tetraphenylcyclopentadienone.svg

Similarly, pentaphenylpyridine derivatives may be prepared via a Diels–Alder reaction between tetraphenylcyclopentadienone and benzonitrile.

Tetraphenylcyclopentadienone can provide an effective alternative to DDQ in aromatization of porphyrins:

File:Aromatization with cyclone.tif

Ligand in organometallic chemistry

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The Shvo catalyst is a ruthenium complex of tetraphenylcyclopentadienone

Tetraarylcyclopentadienones are a well studied class of ligands in organometallic chemistry. The Shvo catalyst, useful for certain hydrogenations, is derived from tetraphenylcyclopentadienone.