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Physical Chemistry

Platinum Oxo Complex Isolated

Compound is stable without electron-withdrawing ligands

by Bethany Halford
October 27, 2008 | A version of this story appeared in Volume 86, Issue 43

Elusive Species
A platinum oxo complex without electron withdrawing groups (C is black, Pt is pink, P is orange, O is red,and N is blue).
A platinum oxo complex without electron withdrawing groups (C is black, Pt is pink, P is orange, O is red,and N is blue).

AN ISRAELI TEAM reports preparing an elusive late-transition-metal oxo complex, in which platinum is doubly bonded to oxygen, without the use of electron-withdrawing ligands to stabilize the electron-rich metal (Nature 2008, 455, 1093). Such complexes have been proposed as intermediates in certain enzymes, catalytic transformations, and industrial oxidation reactions, and the new compound could shed light on how these systems work.

Transition-metal oxo complexes are characterized by a multiple bond between oxygen and the metal. Late transition metals, such as platinum, silver, and gold, are packed with d electrons, making their oxo complexes so reactive that it wasn't until the 1990s that one was isolated. Until now, all late-transition-metal oxo complexes with d-electron-rich metals, such as platinum, have used electron-withdrawing ligands to stabilize the molecule.

By reacting a pincer complex of platinum with dioxirane, David Milstein and coworkers at Weizmann Institute of Science were able to generate a platinum oxo complex that's stable at room temperature, even though it contains no electron-withdrawing ligands. Milstein's group couldn't obtain a crystal structure of the complex, but they verified the structure through exhaustive analytical, computational, and reactive analyses.

Milstein's findings "go a long way to substantiating the previous reports of platinum, palladium, and gold oxo complexes," Emory University chemistry professor Craig L. Hill notes in a commentary that accompanies the report. "This, in turn, makes it hard to argue that late-transition-metal oxo complexes don't exist, as might reasonably have been argued before on the basis of conventional wisdom about modes of bonding. On the contrary, it seems that they might be fairly widespread. They can certainly now be regarded as realistic candidates for intermediates in many important catalytic reactions that involve oxygen."


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