Chemistry

A Late Triple

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Science  19 Jun 2009:
Vol. 324, Issue 5934, pp. 1493
DOI: 10.1126/science.324_1493b
CREDIT: SCHÖFFEL ET AL., ANGEW. CHEM. INT. ED. 48, 4734 (2009)

Transition metals with comparatively few valence electrons, such as titanium and chromium, tend to form multiple bonds with carbon, oxygen, and nitrogen (N) atoms fairly easily. In contrast, late metals such as iridium (Ir) and platinum engage more rarely in this mode of bonding, an observation that has been justified by repulsive interactions between the ligand's lone pairs and residual d orbital electrons at the metal center. Schöffel et al. show that mild heating of an azide-substituted Ir complex in the solid state leads efficiently to N2 loss and resultant formation of a stable Ir-N triple bond. The compound was characterized crystallographically, and the observed bond length, coupled with indepth theoretical analysis, supports a formal bond order between 2 and 3. Reaction with hydrogen led to very clean direct reduction at nitrogen, forming an Ir amide complex that was also structurally characterized by x-ray diffraction. An isotopic labeling study confirmed H2 as the proton source.

Angew. Chem. Int. Ed. 48, 4734 (2009).

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