Accessing Low-Valent Titanium CCC-NHC Complexes: Toward Nitrogen Fixation

Abstract

The dramatic expansion of the earth’s population can be directly correlated with the Haber–Bosch process for nitrogen fixation becoming widely available after World War II. The ready availability of artificial fertilizer derived thereof dramatically improved food supplies world-wide. Recently, artificial nitrogen fixation surpassed the natural process. The Haber–Bosch process is extremely energy and green-house gas intensive due to its high-temperature and H2 demands. Many low valent Ti(II) complexes of N2 are known. We report herein a preliminary investigation of the low-valent chemistry of Ti with the CCC-NHC ligand architecture. These CCC-NHC pincer Ti(IV) complexes are readily reduced with KC8 or Mg powder. Preliminary results indicate very different reactivity patterns with alkynes and phosphines for this ligand architecture versus prior ligands. Successful reduction to an intact low-valent (CCC-NHC)Ti complex was confirmed by re-oxidation with PhICl2.

Keywords

• <b>Keywords</b>: titanium
• CCC-NHC pincer ligand
• <i>N</i>-heterocyclic carbene
• reduction
• oxidation
• carbene