Charge‐Transfer Effects on Arene Structure and Reactivity

Abstract

Arenes spontaneously form intermolecular 1:1 complexes with a wide variety of electrophiles, cations, acids, and oxidants that are all sufficiently electron-poor to be classified as electron acceptors. Spectral, structural, and thermodynamic properties of these donor/ acceptor associates are described within the context of the Mulliken charge-transfer (CT) formulation. The quantitative analyses of such CT complexes provide the mechanistic basis for understanding arene reactivity in different thermal and photochemical processes. 13.1 13.2 Mulliken's Quantitative Description of Intermolecular (Charge-Transfer) Complexes 437 a E o red in V vs. SCE, EA in eV, data from ref. [4]. b Singlet (s) and triplet (t) states.

A Uranium(II) Arene Complex That Acts as a Uranium(I) Synthon

“…The uranium−centroid distance of 2.602(2) Å is within the typical range for U(III) arenes. 31 Torsion angles for the bound arene, calculated by measuring the dihedral angle 19 formed by the C−C bonds on opposite sides of the arene, are relatively smallranging from 2.5(2)°t o 5.0(2)°suggesting that no significant reduced character is present in this moiety. U−O and U−N distances of 2.310(2) to 2.347(2) Å and 2.581(2) to 2.652(2) Å, respectively, for the amidates in 2 are similar to corresponding distances for κ 2 -O,N and κ 1 -O amidates in U(TDA) 4 and 1-crown.…”

“…Furthermore, the C1−C6 and C3− C4 bonds are slightly shortened relative to the remaining arene C−C bonds, which have torsion angles of 11.5(4)°and 15.5(4)°; these metrics are within the typical range for a monoreduced arene ligand. 19 In contrast, the other bound arene (C18−C23) adopts a planar geometry, with U−C distances of 2.706(6) to 2.763(6) Å and C−C bond lengths of 1.389 (7) to 1.440(6) Å. The torsion angles in this arene are minimal [0.9(4)°to 4.6(4)°], suggesting that this ligand possesses no significant reduced character in the solid state.…”

“…12−14 Such complexes are often formed via reductive binding of aromatic solvent molecules, 15−17 though in some cases intramolecular reduction of a pendant aromatic group on the ligand is observed. 18,19 However, bound arenes can introduce a challenge in assigning the oxidation state of organometallic complexes due to the numerous ways in which these moieties can interact with metal centers. Arenes are often treated as redox-neutral when assigning formal oxidation states, leading to reported examples such as [K[2.2.2]cryptand] 2 [Zr-(η 4 -C 10 H 8 ) 3 ] and [Na[2.2.2]cryptand][Ta(η 4 -C 10 H 8 ) 3 ], which are described as Zr(−2) and Ta(−1), respectively.…”

Chemistry at the interior atoms of polycyclic aromatic hydrocarbons

“…The formation of charge transfer complexes between PAHs and p-acids, such as tetracyanoethylene, for example, will not be considered here. 15 Likewise, transition metal p-complexes that involve interior carbon atoms of PAHs (e.g., Fig. 5) 16 lie outside the scope of this review.…”

“…The edge atoms of these carbon allotropes, however, do not bear hydrogen atoms. 15 Likewise, transition metal p-complexes that involve interior carbon atoms of PAHs (e.g., Fig. Readers interested in learning more about the functionalization reactions of these carbon materials are directed to the many reviews that have already been published on the subject.…”