Insights Into Metal−π Arene Interactions of the Highly Lewis Acidic Rh₂⁴⁺ Core with a Broad Set of π-Ligands: From Ethylene to Corannulene and C₆₀-Fullerene

Abstract

The first systematic theoretical investigation of interactions of the Lewis acidic Rh(II) centers with a number of pi-ligands having isolated unsaturated carboncarbon bonds (acetylene and ethylene) or delocalized pi-systems with planar (benzene, naphthalene, acenaphthylene, and pyrene) or curved surfaces (corannulene and the C(3)-hemifullerene), including the C(60)-fullerene, has been undertaken. The effect of size, geometry, site specificity, and curvature of pi-ligands on their interaction energy with Rh(II) has been examined. The geometric and electronic structures of pi-adducts have been modeled at the DFT level of theory by using the hybrid Perdew-Burke-Ernzerhof parameter free exchange-correlation functional (PBE0). The nature of Rh(II)-pi interactions was found to be similar in all products with the bonding energy ranging from 14.59 kcal/mol in the benzene adduct to 50.13 kcal/mol in the fullerene complex. Importantly, the quantitative evaluation of two bonding components, namely, ligand-to-metal and metal-to-ligand contributions, allowed us to rationalize the observed trends in pi-binding affinity of the selected ligands as well as in stability of the resulting products. These trends deduced from DFT calculations are important for considering the synthetic feasibility of novel pi-complexes in these systems.

A Strain‐Releasing Trap for Highly Reactive Electrophiles: Structural Characterization of Bowl‐Shaped Arenium Carbocations

“…[14] It should also open practical routes for utilizing C À C covalentbond-forming reactions for target derivatization of p-bowl surfaces. Moreover, this work illustrates that the strain energy stored within the curved nonplanar structures can be used to trap reactive intermediates, such as a CH 3 + cation. We can anticipate the potential application of these reactions as a useful tool for the structural characterization of a variety of elusive chemical species.…”

“…The 1 H NMR spectra of cations 1-3 demonstrate the significantly high-field-shifted resonance signals for the CH x Cl 3Àx groups (0.12 ppm, 2.08 ppm, and 4.01 ppm for 1, 2, and 3, respectively) compared to those of CH 3 (Table 2). These values compare well with those found in the 13 C NMR spectra of C 70 -CHCl 2 + (198 ppm, in CF 3 SO 3 H) [6b] and in the protonated form of C 60 (182 ppm, 1,2-C 6 H 4 Cl 2 ).…”

“…The formation of these cations is attributed to the abstraction of a chloride ion from the corresponding halogenated reagent followed by electrophilic attack of the in situ generated CH x Cl 3Àx + cations at the hub C atom of C 20 H 10 . Although DFT calculations showed that the energy difference between electrophilic attacks at the hub and rim at the curved corannulene surface is small, especially when compared with the noticeably larger values for planar polyarenes, [3] only two examples of C À C bond formation at the bowl interior have been reported. Firstly, reaction of dichlorocarbene with C 20 H 10 led to the product of the [1+2] addition to the spoke C=C bond via a zwitterionic intermediate.…”

“…Herein, we report the successful isolation of bulk crystalline products and the first X-ray crystallographic characterization of a family of nonplanar arenium carbocations C 20 H 10 R + (R = CH 3 , CH 2 Cl, CHCl 2 , and CCl 3 ), obtained by electrophilic attack at the interior surface of corannulene (Scheme 1).…”

Functionalized Corannulene Carbocations: A Structural Overview

“…The electrophilic attack on corannulene occurs at the hub carbon atom, which has the highest occupied molecular orbital with the largest atomic coefficient 28a. 44 With more stable carbocations, such as the tert ‐butyl cation, the initial electrophilic attack, which occurs at the interior site, is reversible and is followed by migration of the alkyl group to a methine position on the rim to generate an arenium ion. Fast deprotonation through extrusion of a proton affords a rearomatized corannulene with the perimeter derivatization.…”