Base-Controlled Directed Synthesis of Metal–Methyleneimidazoline (MIz) and Metal–Mesoionic Carbene (MIC) Compounds
dataset
posted on 2019-12-13, 13:38 authored by Mandeep Kaur, Kamaless Patra, Noor U Din Reshi, Jitendra K. BeraReactions 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.
