Collins reagent is the complex of chromium(VI) oxide with pyridine in dichloromethane.

According to X-ray crystallography, the complex is 5-coordinate with mutually trans pyridine ligands.

[3] In terms of history, the complex was first produced by Sisler et al.[4] Collins reagent is especially useful for oxidations of acid sensitive compounds.

Primary and secondary alcohols are oxidized respectively to aldehydes and ketones in yields of 87-98%.

The application of this reagent to oxidations was discovered by G. I. Poos, G. E. Arth, R. E. Beyler and L.H.