Soft interactions with hard Lewis acids: generation of mono- and dicationic alkaline-earth metal arene-complexes by direct oxidation

Abstract

The alkaline earths like it hard and soft! By employing a radical cationic ligand-forming oxidising agent we gained access to unprecedented mono and dicationic arene complexes of calcium, strontium and barium.

A Highly Lewis Acidic Strontium ansa‐Arene Complex for Lewis Acid Catalysis and Isobutylene Polymerization

“… [19, 22] Moreover, both aromatic rings adopt an η 6 ‐coordination with Sr−C distances ranging from 2.945(3)–3.117(3) Å. These values coincide with previously reported distances for the strontium HMB complex [19] …”

“…In the molecular structure, the metal cation is in addition to the DXE ligand coordinated by two κ 2 ‐bound o ‐DFB molecules with Sr−F distances between 2.534(2) Å and 2.669(2) Å (Figure 2). [19, 22] Moreover, both aromatic rings adopt an η 6 ‐coordination with Sr−C distances ranging from 2.945(3)–3.117(3) Å. These values coincide with previously reported distances for the strontium HMB complex [19] …”

“…These values coincide with previously reported distances for the strontium HMB complex. [19] The cation-arene interaction was analyzed by means of the quantum theory of atom in molecules (QTAIM). The calculated electronic charge densities 1 and Laplacians of the electron density D1 are summarized along with results of QTAIM and natural bond orbital (NBO) population analyses in Figure 3 a.…”

A Highly Lewis Acidic Strontium ansa‐Arene Complex for Lewis Acid Catalysis and Isobutylene Polymerization

“…In analogy to QTAIM studies on known Ae arene complexes, [16, 19] the partial positive charge on the arene ligand indicates a ligand‐to‐metal bonding. Computed electron densities at the cage and bond critical points (CCP & BCP) match ρ values obtained for the strontium HMB complex 3 2+ [19] . This implies an interaction energy per arene moiety of DXE comparable to HMB.…”

Stack by Stack: From the Free Cyclopentadienylgermanium Cation Via Heterobimetallic Main‐Group Sandwiches to Main‐Group Sandwich Coordination Polymers

“…The cationic group 2 arene complexes of Harder and Hill and co‐workers represent one example [36] . Our recently developed dicationic complexes [M(HMB)] 2+ (M=Ca, Sr) as o ‐difluorobenzene ( o DFB) solvates can be directly compared with the corresponding Cp* − complexes [37] . However, the arene/Cp ( * )− structural relationships are most evident when comparing neutral group 13 Cp* − complexes with the cationic arene complexes, for example, [Ga(η 5 ‐Cp*)] versus [Ga(η 6 ‐HMB)] + .…”