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1. Engendering reactivity at group 5-heteroatom multiple bonds via π-loading

   https://doi.org/10.1039/D2SC02706B  

   Fostvedt, Jade I.; Mendoza, Jocelyne; Lopez-Flores, Sacy; Alcantar, Diego; Bergman, Robert G.; Arnold, John (July 2022, Chemical Science)

   In this Perspective, we discuss the strategy of π-loading, i.e. , coordination of two or more strongly π-donating ligands to a single metal center, as it applies to promoting reactivity at group 5 transition metal-imido groups. When multiple π-donor ligands compete to interact with the same symmetrically-available metal d π orbitals, the energy of the imido-based frontier molecular orbitals increases, leading to amplified imido-based reactivity. This strategy is of particular relevance to group 5 metals, as mono(imido) complexes of these metals tend to be inert at the imido group. Electronic structure studies of group 5 bis(imido) complexes are presented, and examples of catalytically and stoichiometrically active group 5 bis(imido) and chalcogenido–imido complexes are reviewed. These examples are intended to encourage future work exploring π-loaded bis(imido) systems of the group 5 triad. 

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2. π-Hydrogen Bonding Probes the Reactivity of Aromatic Compounds: Nitration of Substituted Benzenes

   https://doi.org/10.1021/acs.jpca.8b12508  

   Galabov, Boris; Koleva, Gergana; Hadjieva, Boriana; Schaefer, Henry F. (January 2019, The Journal of Physical Chemistry A)
3. Placing gold on a π ⁺ -surface: ligand design and impact on reactivity

   https://doi.org/10.1039/D2SC05574K  

   Liu, Wei-Chun; Gabbaï, François P. (January 2023, Chemical Science)

   We describe a novel gold chloride complex supported by an ambiphilic phosphine/xanthylium ligand in which the AuCl moiety interacts with the π + surface of the xanthylium unit as indicated by structural studies. Energy decomposition analyses carried out on a model system indicates the prevalence of non-covalent interactions in which the electrostatic and dispersion terms cumulatively dominate. The presence of these AuCl–π + interactions correlates with the high catalytic activity of this complex in the cyclisation of 2-(phenylethynyl)phenylboronic acid, N -propargyl- t -butylamide, and 2-allyl-2-(2-propynyl)malonate. Comparison with the significantly less active acridinium and the 9-oxa-10-boraanthracene analogues reinforces this conclusion. 

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4. Isolation and reactivity of a gold( i ) hydroxytrifluoroborate complex stabilized by anion-π ⁺ interactions

   https://doi.org/10.1039/D1CC04105C  

   Zhou, Jiliang; Litle, Elishua D.; Gabbaï, François P. (October 2021, Chemical Communications)

   A 9,9-dimethylxanthene-based ligand substituted at the 4- and 5-positions by a phosphine and a xanthylium unit, respectively, has been prepared and converted into an AuCl complex, the structure of which reveals an intramolecular Au–Cl⋯π + interaction. This new ligand platform was also found to support the formation of an unprecedented hydroxytrifluoroborate derivative featuring a “hard/soft” mismatched Au– μ (OH)–BF 3 motif. Despite its surprising stability, this gold hydroxytrifluoroborate complex is a remarkably potent carbophilic catalyst which readily activates alkynes, without activator. 

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5. Tuning of Metal Complex Electronics and Reactivity by Remote Lewis Acid Binding to π-Coordinated Pyridine Diphosphine Ligands

   https://doi.org/10.1021/acs.organomet.5b00562  

   Horak, Kyle T.; VanderVelde, David G.; Agapie, Theodor (August 2015, Organometallics)