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

The oxo- and catecholate-bridged U/U Pacman complex [{(py)UOU(μ-OCH)(py)}(L)] (L = a macrocyclic "Pacman" ligand; anthracenylene hinge between N-donor pockets, ethyl substituents on -carbon atom of each N-donor pocket) featuring a bent U-O-U oxo bridge readily reacts with small molecule substrates to undergo either oxo-atom functionalisation or substitution. Complex reacts with HO or MeOH to afford [{(py)U(μ-OH)U(μ-OCH)(py)}(L)] () and [{(py)U(μ-OH)(μ-OMe)U(μ-OCH)(py)}(L)] (), respectively, in which the bridging oxo ligand in is substituted for two bridging hydroxo ligands or one bridging hydroxo and one bridging methoxy ligand, respectively. Alternatively, reacts with either 0.5 equiv. of S or 4 equiv. of Se to provide [{(py)U(μ-η:η-E)U(μ-OCH)(py)}(L)] (E = S (), Se ()) respectively, in which the [E] ion bridges the two U centres. To the best of our knowledge, complex is the first example of either a d- or f-block bimetallic μ-oxo complex that activates elemental chalcogens. Complex also reacts with XeF or 2 equiv. of MeSiCl to provide [{(py)U(μ-X)U(μ-OCH)(py)}(L)] (X = F (), Cl ()), in which the oxo ligand has been substituted for two bridging halido ligands. Reacting with either XeF or MeSiCl in the presence of O(Bcat) at room temperature forms [{(py)U(μ-X)(μ-OBcat)U(μ-OCH)(py)}(L)] (X = F (), Cl ()), which upon heating to 80 °C is converted to and , respectively. In order to probe the importance of the bent U-O-U motif in on the observed reactivity, the bis(boroxido)-U/U complex, [{(py)(pinBO)UOU(OBpin)(py)}(L)] (), featuring a linear U-O-U bond angle was treated with HO and MeSiCl. Complex reacts with two equiv. of either HO or MeSiCl to provide [{(py)HOUOUOH(py)}(L)] () and [{(py)ClUOUCl(py)}(L)] (), respectively, in which reactions occur preferentially at the boroxido ligands, with the μ-oxo ligand unchanged. The formal U oxidation state is retained in all of the products , and selective reactions at the bridging oxo ligand in is facilitated by: (1) its highly nucleophilic character which is a result of a non-linear U-O-U 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.