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Issue 27, 2020
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Selective oxo ligand functionalisation and substitution reactivity in an oxo/catecholate-bridged UIV/UIV Pacman complex

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Abstract

The oxo- and catecholate-bridged UIV/UIV Pacman complex [{(py)UIVOUIV(μ-O2C6H4)(py)}(LA)] A (LA = a macrocyclic “Pacman” ligand; anthracenylene hinge between N4-donor pockets, ethyl substituents on meso-carbon atom of each N4-donor pocket) featuring a bent UIV–O–UIV oxo bridge readily reacts with small molecule substrates to undergo either oxo-atom functionalisation or substitution. Complex A reacts with H2O or MeOH to afford [{(py)UIV(μ-OH)2UIV(μ-O2C6H4)(py)}(LA)] (1) and [{(py)UIV(μ-OH)(μ-OMe)UIV(μ-O2C6H4)(py)}(LA)] (2), respectively, in which the bridging oxo ligand in A is substituted for two bridging hydroxo ligands or one bridging hydroxo and one bridging methoxy ligand, respectively. Alternatively, A reacts with either 0.5 equiv. of S8 or 4 equiv. of Se to provide [{(py)UIV(μ-η22-E2)UIV(μ-O2C6H4)(py)}(LA)] (E = S (3), Se (4)) respectively, in which the [E2]2− ion bridges the two UIV centres. To the best of our knowledge, complex A is the first example of either a d- or f-block bimetallic μ-oxo complex that activates elemental chalcogens. Complex A also reacts with XeF2 or 2 equiv. of Me3SiCl to provide [{(py)UIV(μ-X)2UIV(μ-O2C6H4)(py)}(LA)] (X = F (5), Cl (6)), in which the oxo ligand has been substituted for two bridging halido ligands. Reacting A with either XeF2 or Me3SiCl in the presence of O(Bcat)2 at room temperature forms [{(py)UIV(μ-X)(μ-OBcat)UIV(μ-O2C6H4)(py)}(LA)] (X = F (5A), Cl (6A)), which upon heating to 80 °C is converted to 5 and 6, respectively. In order to probe the importance of the bent UIV–O–UIV motif in A on the observed reactivity, the bis(boroxido)-UIV/UIV complex, [{(py)(pinBO)UIVOUIV(OBpin)(py)}(LA)] (B), featuring a linear UIV–O–UIV bond angle was treated with H2O and Me3SiCl. Complex B reacts with two equiv. of either H2O or Me3SiCl to provide [{(py)HOUIVOUIVOH(py)}(LA)] (7) and [{(py)ClUIVOUIVCl(py)}(LA)] (8), respectively, in which reactions occur preferentially at the boroxido ligands, with the μ-oxo ligand unchanged. The formal UIV oxidation state is retained in all of the products 1–8, and selective reactions at the bridging oxo ligand in A is facilitated by: (1) its highly nucleophilic character which is a result of a non-linear UIV–O–UIV bond angle causing an increase in U–O bond covalency and localisation of the lone pairs of electrons on the μ-oxo group, and (2) the presence of the bridging catecholate ligand, which destabilises a linear oxo-bridging geometry and stabilises the resulting products.

Graphical abstract: Selective oxo ligand functionalisation and substitution reactivity in an oxo/catecholate-bridged UIV/UIV Pacman complex

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Supplementary files

Article information


Submitted
23 Apr 2020
Accepted
11 Jun 2020
First published
12 Jun 2020

This article is Open Access
All publication charges for this article have been paid for by the Royal Society of Chemistry

Chem. Sci., 2020,11, 7144-7157
Article type
Edge Article

Selective oxo ligand functionalisation and substitution reactivity in an oxo/catecholate-bridged UIV/UIV Pacman complex

B. E. Cowie, I. Douair, L. Maron, J. B. Love and P. L. Arnold, Chem. Sci., 2020, 11, 7144
DOI: 10.1039/D0SC02297G

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