Gently Excising Nitrogen

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Science  12 Oct 2007:
Vol. 318, Issue 5848, pp. 171
DOI: 10.1126/science.318.5848.171b

Removal of nitrogen from heterocyclic aromatic components of crude petroleum is performed at enormous scale through high-temperature catalytic hydrogenolysis, with the aim of minimizing generation of nitrogen oxides during combustion. However, the mechanistic details of this process are only loosely understood, and there has been little headway in finding well-characterized homogeneous systems that excise aromatic nitrogen directly. Fout et al. have now discovered that a titanium carbene complex cleanly and selectively swaps its carbon for the nitrogen in pyridine on treatment with trimethylsilyl chloride. The homogeneous reaction proceeds at 65°C to yield a substituted benzene and Ti imido complex as products. The authors propose a mechanism of electrocyclic rearrangements initiated by N-silylation; substituting a protic acid for the silyl reagent failed to drive the swap. The titanium reagent is recoverable by alkylation after donation of its imido group to high-valent molybdenum, which leads to an easily separable insoluble Mo nitride species. — JSY

J. Am. Chem. Soc. 129, 10.1021/ja075326n (2007).

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