Molecular Orbital Insights of Transition Metal-Stabilized Carbocations

Abstract

Transition metal-stabilized carbocations are characterized by synthetically valuable interactions, yet, to date there are no comprehensive reports of the many bonding modes that can exist between a metal and carbocation. This review summarizes developments in these complexes to provide a clear picture of their properties and reactivities. In order to strategically exploit them, we propose this summary of the different bonding modes for transition metal-carbocation complexes. These models will help chemists understand the orbital interactions involved in these compounds so that they can approach their synthetic goals most effectively. Multiple transition metals and carbocations will be discussed.

Synthesis and crystal structures of 2-(ferrocenylcarbonyl)benzoic acid and 3-ferrocenylphthalide

“…1), similar to the reduction of aryl ketones reported by Zhang and co-workers (Zhang et al, 2007). Upon acidification during reaction workup, alcohol 1 0 0 0 undergoes solvolysis to give the carbocation, which is electronically stabilized by the ferrocenyl group (Goodman et al, 2019). The nucleophilic attack of the carboxylic O atom leads to the formation of the cyclic lactone, 2.…”

Stabilized Carbenium Ions as Latent, Z‐type Ligands

“…In other words, a carbenium ion should be a more potent σ‐acceptor ligand, leading to a greater enhancement in the hardness and Lewis acidity of the metal atom. Carbenium ions, which have already received interest as ligands for transition metals, may also present a higher chemical resilience, in particular to oxidative conditions. With a view to capitalize on these attributes, we thus decided to reengage in carbenium chemistry and explore the synthesis and properties of carbenium‐based analogues of known L/Z ambiphilic boron‐containing ligands (Figure C) .…”

Ligand-enforced intimacy between a gold cation and a carbenium ion: impact on stability and reactivity

“…21 The carbenium ion of these phosphines, which we refer to as -cationic phosphines, lacks a direct connection to the phosphorus atom, the electronic attributes of which remain, consequently, largely unaffected. Instead, the carbenium ion is positioned to act as a Z-type ligand, [28][29][30][31][32] capable of interacting directly with the metal center through a M→C + interaction [33][34][35] as in complexes of type E[M]. 36 Interactions are also possible between the carbenium unit and metal-bound anionic ligands, as evoked by Gianetti for complexes of type F. 37 Because such -cationic phosphines are prone to phosphonium ion formation via "coordination" of the phosphorus atom to the carbenium center, 38 we have developed a strategy that provides direct access to the gold complexes [1-AuCl] + and [2-AuCl] + (Figure 1).…”

“… 21 In these phosphines, which we refer to as γ-cationic phosphines, the carbenium ion and the phosphorus atom lack a direct connection and are thus partly insulated from one another. However, the carbenium ion is positioned to act as a Z-type ligand, 28–32 capable of interacting directly with the metal center through a M → C + interaction 33–35 as in complexes of type E [M] . 36 Interactions are also possible between the carbenium unit and metal-bound anionic ligands, as evoked by Gianetti for complexes of type F .…”