Base-Controlled Directed Synthesis of Metal–Methyleneimidazoline (MIz) and Metal–Mesoionic Carbene (MIC) Compounds

Reactions of a host of metal precursors with pyridyl­(benzamide)-functionalized
C2-methyl-protected imidazolium salts [L1H2]I and [L2H]I afforded the metal–methyleneimidazoline
(MIz) compounds [Ru­(L1-κC1)­(p-cymene)]I (1), [Mn­(L1-κC1)­(CO)3] (2), [Ru­(L2-κC1)­(p-cymene)­Cl]­PF6 (3), and [Ir­(L2-κC1)­(Cp*)­Cl]­PF6 (4) in the presence of different external bases, such
as LiHMDS, Na2CO3, tBuOK, and NaH. However, the use of NaOAc led to the selective formation
of the metal–mesoionic carbene (MIC) compounds [Ru­(L2-κC5)­(p-cymene)­Cl]­PF6 (5), [Ir­(L2-κC5)­(Cp*)­Cl]­PF6 (6), [Ir2(L1-κC5)­(Cp*)2I]­PF6 (8), and the ortho-metalated
compound [Ir­(L1)­(Cp*)­I] (7). All compounds
have been characterized by spectroscopic techniques and X-ray crystallography.
Being more acidic, the C2-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 C5–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.

金属前驱体与吡啶基-(苯甲酰胺)功能化的C2甲基保护的咪唑盐[L1H2]I和[L2H]I在不同外部碱，如LiHMDS、Na2CO3、tBuOK和NaH的存在下，反应生成了金属-亚甲基咪唑(MIz)化合物[Ru-(L1-κC1)-(对甲苯基)]I(1)、[Mn-(L1-κC1)-(CO)3](2)、[Ru-(L2-κC1)-(对甲苯基)-Cl]PF6(3)和[Ir-(L2-κC1)-(Cp*)-Cl]PF6(4)。然而，NaOAc的使用则导致了金属-中离子碳烯(MIC)化合物[Ru-(L2-κC5)-(对甲苯基)-Cl]PF6(5)、[Ir-(L2-κC5)-(Cp*)-Cl]PF6(6)、[Ir2(L1-κC5)-(Cp*)2I]PF6(8)以及邻位金属化化合物[Ir-(L1)-(Cp*)-I](7)的选择性形成。所有化合物均已通过光谱技术和X射线晶体学进行了表征。由于C2甲基具有更高的酸性，它容易在外部碱的作用下去质子化，从而生成金属-亚甲基咪唑产物。相比之下，金属结合的乙酸盐则选择性地与咪唑的C5-H相互作用，驱动反应向金属-中离子碳烯形成方向进行。密度泛函理论(DFT)计算支持了一种协同的金属化-去质子化途径，该途径对选择性C-H活化及金属化至关重要。