Volume 86 Issue 45 | p. 37 | Concentrates
Issue Date: November 10, 2008

Carbon Dioxide Jumps In To Form New Ligand

CO2 displaces PPh2 groups in a strontium complex to create [N(CO2)3]3-, a previously unknown type of ligand
Department: Science & Technology
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The strontium complex Sr[N(PPh2)2]2(thf)3 absorbed 12 equivalents of CO2, forming an Sr6 complex with O2CN(PPh2)2 and [N(CO2)3]3- ligands (CO2-laden structure shown; Sr is green, P is pink, O is red, N is blue, and C is white). The [N(CO2)3]3- ligands are at the heart of the structure, as revealed in a close up of the complex's core.
Credit: Courtesy of Richard Kemp
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The strontium complex Sr[N(PPh2)2]2(thf)3 absorbed 12 equivalents of CO2, forming an Sr6 complex with O2CN(PPh2)2 and [N(CO2)3]3- ligands (CO2-laden structure shown; Sr is green, P is pink, O is red, N is blue, and C is white). The [N(CO2)3]3- ligands are at the heart of the structure, as revealed in a close up of the complex's core.
Credit: Courtesy of Richard Kemp

While studying how carbon dioxide reacts with certain types of main-group metal complexes, Diane A. Dickie, Marie V. Parkes, and Richard A. Kemp of the University of New Mexico, Albuquerque, discovered [N(CO2)3]3, a previously unknown type of ligand (Angew. Chem. Int. Ed., DOI: 10.1002/anie.200804218). Kemp's group is exploring potential methods for sequestering CO2 or using it as a feedstock to make value-added chemicals such as organic isocyanates and carbodiimides. When the researchers reacted CO2 with Sr[N(PPh2)2]2(thf)3, where Ph is phenyl and thf is tetrahydrofuran, an Sr6 complex formed and trapped 12 equivalents of CO2. Half of the CO2 inserted into Sr–N bonds to form six bridging phosphino carbamate ligands, O2CN(PPh2)2. But the researchers were surprised to find that the remaining CO2 displaced PPh2 groups to form two [N(CO2)3]3 ligands. After searching chemical databases, they concluded that they had a new ligand on their hands. The [N(CO2)3]3 ligand can be viewed as an anion derived from the hypothetical compound N(CO2H)3, Kemp notes. His group is now working to make this compound, possibly from known N(CO2R)3 esters, as a starting point for synthesizing [N(CO2)3]3–.

 
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