Dimethylcyclobutadiene

AvdL

Confinement of 1,3-dimethylcyclobutadiene in a crystalline matrix Y.-M. Legrand, A. van der Lee, M. Barboiu Institut Européen des Membranes Montpellier France

Dimethylcyclobutadiene

AvdL

Cyclobutadiene

Cyclobutadiene’s extremely unstable structure

Unstability I

strained 90 degrees angles

I

anti-aromatic character ?

I

lifetime several seconds

can be stabilized by the formation of metal complexes dimerizes and transforms to cyclooctatetraene

Dimethylcyclobutadiene

AvdL

Cram’s hemicarcerand container

The hemicarcerand molecular container

Dimethylcyclobutadiene Doing better than Cram

Cyclobutadiene in the solid sate

Cram succeeded in stabilizing cyclobutadiene in a hemicarcerand container, but only in solution !

Looking for alternatives I

change the molecular container

I

change the stable molecular precursor

I

fine-tune the photolysis procedures

Dimethylcyclobutadiene

AvdL

Host and guest structures

4,6-dimethyl-α-pyrone

Dimethylcyclobutadiene

AvdL

Host and guest structures

4,6-dimethyl-α-pyrone within calixarene

Dimethylcyclobutadiene

AvdL

Experimental procedure

The experiments φ UV

T = 175 K t = 10 min λ = 320 − 500 nm

φκωθ X-ray

T = 175 K t = 18 hr λ = 0.0709 nm

Dimethylcyclobutadiene

AvdL

Photolysis of dimethyl-α-pyrone

Modeling disorder

∆F (1.5σ) before photolysis

∆F (1.5σ) after photolysis

Dimethylcyclobutadiene

AvdL

Photolysis of dimethyl-α-pyrone First irradiation

First UV irradiated state

50% occupation probability

50% occupation probability

Dimethylcyclobutadiene

AvdL

Photolysis of dimethyl-α-pyrone Second irradiation

Second UV irradiated state

77% occupation probability Dewar-β-lactone valence isomer

23% occupation probability