Base-Controlled Directed Synthesis of Metal–Methyleneimidazoline (MIz) and Metal–Mesoionic Carbene (MIC) Compounds KaurMandeep PatraKamaless Din ReshiNoor U BeraJitendra K. 2019 Reactions of a host of metal precursors with pyridyl­(benzamide)-functionalized C<sup>2</sup>-methyl-protected imidazolium salts [L<sup>1</sup>H<sub>2</sub>]I and [L<sup>2</sup>H]I afforded the metal–methyleneimidazoline (MIz) compounds [Ru­(L<sup>1</sup>-κ<i>C</i><sup>1</sup>)­(<i>p</i>-cymene)]I (<b>1</b>), [Mn­(L<sup>1</sup>-κ<i>C</i><sup>1</sup>)­(CO)<sub>3</sub>] (<b>2</b>), [Ru­(L<sup>2</sup>-κ<i>C</i><sup>1</sup>)­(<i>p</i>-cymene)­Cl]­PF<sub>6</sub> <b>(3</b>), and [Ir­(L<sup>2</sup>-κ<i>C</i><sup>1</sup>)­(Cp*)­Cl]­PF<sub>6</sub> (<b>4</b>) in the presence of different external bases, such as LiHMDS, Na<sub>2</sub>CO<sub>3</sub>, <sup><i>t</i></sup>BuOK, and NaH. However, the use of NaOAc led to the selective formation of the metal–mesoionic carbene (MIC) compounds [Ru­(L<sup>2</sup>-κ<i>C</i><sup>5</sup>)­(<i>p</i>-cymene)­Cl]­PF<sub>6</sub> (<b>5</b>), [Ir­(L<sup>2</sup>-κ<i>C</i><sup>5</sup>)­(Cp*)­Cl]­PF<sub>6</sub> (<b>6</b>), [Ir<sub>2</sub>(L<sup>1</sup>-κ<i>C</i><sup><i>5</i></sup>)­(Cp*)<sub>2</sub>I]­PF<sub>6</sub> (<b>8</b>), and the ortho-metalated compound [Ir­(L<sup>1</sup>)­(Cp*)­I] (<b>7</b>). All compounds have been characterized by spectroscopic techniques and X-ray crystallography. Being more acidic, the C<sup>2</sup>-methyl is readily deprotonated by the external base to give the metal–MIz products. A metal-bound acetate, in contrast, interacts selectively with the imidazolium C<sup>5</sup>–H and drives the reaction toward the metal–MIC formation. DFT calculations support a concerted metalation–deprotonation pathway for selective C–H activation and metalation.