A multitalented atom-transfer reagent

In chemistry, as in other art forms, a well-executed mash-up can be greater than the sum of its parts.

Researchers at the Technical University of Dortmund, led by Max Hansmann, combined the characteristic parts of two well-known reagents—a phosphorous ylide and a diazo compound—into a versatile new compound for transplanting carbon atoms into organic molecules (Science 2024, DOI: 10.1126/science.ado4564). “We very quickly saw that we can use it for different purposes depending on the starting material,” says Hansmann.

The molecule’s simple structure consists of a carbon atom flanked by a triphenylphosphine (PPh₃) on one side and dinitrogen on the other. Hansmann says the team’s initial motivation was simply to make the compound and explore its properties.

The researchers found that the diazophosphorous ylide was fairly straightforward to make by treating an already well-known carbodiphosphorane ylide compound (Ph₃P=C=PPh₃) with nitrous oxide (N₂O) to install the nitrogen piece.

The reagent can transfer different pieces of itself into other molecules to accomplish several types of reactions. With carbenes and other ligand-type structures, the CPPh₃portion undergoes ligand exchange to form novel ylide structures. The CN₂fragment can be used to create pyrazole rings by cycloaddition to alkenes. But what this reagent does especially well is appending its single carbon atom to carbonyl compounds to turn them into either cumulenes with three sequential double bonds or into alkynes—including strained internal alkynes that can be used in click reactions.

Organic chemist Guangbin Dong of the University of Chicago, who was not involved in the paper, called it “a remarkable work” in an email. In particular, he says, the ketone-to-cumulene transformation is “a really cool reaction” that may work better than other methods of making those compounds.

Hansmann says this work fits into the synthetic community’s growing interest in molecular editing—or methods for adding and deleting atoms from molecules’ carbon skeletons. “Carbon, obviously, is one of the most attractive atoms you want to transfer.”.