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

The oxo- and catecholate-bridged U-IV/U(IV)Pacman complex [{(py)(UOUIV)-O-IV(mu-O2C6H4)(py)}(L-A)]A(L-A= a macrocyclic Pacman ligand; anthracenylene hinge between N-4-donor pockets, ethyl substituents onmeso-carbon atom of each N-4-donor pocket) featuring a bent U-IV-O-U(IV)oxo bridge readily reacts with small molecule substrates to undergo either oxo-atom functionalisation or substitution. ComplexAreacts with H2O or MeOH to afford [{(py)U-IV(mu-OH)(2)U-IV(mu-O2C6H4)(py)}(L-A)] (1) and [{(py)U-IV(mu-OH)(mu-OMe)U-IV(mu-O2C6H4)(py)}(L-A)] (2), respectively, in which the bridging oxo ligand inAis substituted for two bridging hydroxo ligands or one bridging hydroxo and one bridging methoxy ligand, respectively. Alternatively,Areacts with either 0.5 equiv. of S(8)or 4 equiv. of Se to provide [{(py)U-IV(mu-eta(2):eta(2)-E-2)U-IV(mu-O2C6H4)(py)}(L-A)] (E = S (3), Se (4)) respectively, in which the [E-2](2-)ion bridges the two U(IV)centres. To the best of our knowledge, complexAis the first example of either a d- or f-block bimetallic mu-oxo complex that activates elemental chalcogens. ComplexAalso reacts with XeF(2)or 2 equiv. of Me3SiCl to provide [{(py)U-IV(mu-X)(2)U-IV(mu-O2C6H4)(py)}(L-A)] (X = F (5), Cl (6)), in which the oxo ligand has been substituted for two bridging halido ligands. ReactingAwith either XeF(2)or Me3SiCl in the presence of O(Bcat)(2)at room temperature forms [{(py)U-IV(mu-X)(mu-OBcat)U-IV(mu-O2C6H4)(py)}(L-A)] (X = F (5A), Cl (6A)), which upon heating to 80 degrees C is converted to5and6, respectively. In order to probe the importance of the bent U-IV-O-U(IV)motif inAon the observed reactivity, the bis(boroxido)-U-IV/U(IV)complex, [{(py)(pinBO)(UOUIV)-O-IV(OBpin)(py)}(L-A)] (B), featuring a linear U-IV-O-U(IV)bond angle was treated with H2O and Me3SiCl. ComplexBreacts with two equiv. of either H2O or Me3SiCl to provide [{(py)(HOUOUOH)-O-IV-O-IV(py)}(L-A)] (7) and [{(py)(ClUOUCl)-O-IV-Cl-IV(py)}(L-A)] (8), respectively, in which reactions occur preferentially at the boroxido ligands, with the mu-oxo ligand unchanged. The formal U(IV)oxidation state is retained in all of the products1-8, and selective reactions at the bridging oxo ligand inAis facilitated by: (1) its highly nucleophilic character which is a result of a non-linear U-IV-O-U(IV)bond angle causing an increase in U-O bond covalency and localisation of the lone pairs of electrons on the mu-oxo group, and (2) the presence of the bridging catecholate ligand, which destabilises a linear oxo-bridging geometry and stabilises the resulting products.