Pyrrole-based polyanions are versatile ligands for f block metals which have been proved capable of assembling large cluster structures and of substantially increasing the reactivity of their low-valent derivatives. This is especially evident in the chemistry of divalent samarium, where the utilization of tetraand dipyrrolyl anions leads to a larger extent of dinitrogen reduction through interaction with four metal centers. [1, 2] However, a complete breakage of the NΓN bond, as observed in transition-metal chemistry, [3] has not been observed in lanthanide chemistry, despite the possibility of assembling high-nuclearity low-valent clusters. [4] Trivalent and lower valence uranium complexes might be promising substrates for N 2 -activation purposes. For example, trisamide derivatives have recently provided the first two examples of dinitrogen fixation in actinide chemistry, [5] while the only existing complex of a formally divalent uranium amide displays a rare m,p coordination of toluene. [6] These studies suggest that a high level of reactivity may be expected for low-valent uranium compounds with N-donor-based ligands. In addition, the possibility of uranium exhibiting several oxidation states and of affording multielectron reductions makes its low-valent derivatives particularly desirable. Accordingly, a preliminary study has shown that a trivalent uranium tetrapyrrolide complex may perform different types of solvent fragmentation, CΓH bond oxidative addition, and ligand isomerization. [7] Herein, we describe the results of our attempts to prepare a highly reduced uranium complex, which results in a surprising variety of processes including dinitrogen cleavage, solvent deoxygenation, and polysilanol depolymerization.
The starting complex [(Et 8 -calix[4]tetrapyrrole)U-(dme)][K(dme)] (1, DME ΒΌ 1,2-dimethoxyethane) was synthesized by using the procedure previously reported for the preparation of the cyclohexyl congener [7] by the direct reaction of [UI 3 (dme) 2 ] with the tetrapotassium salt of the Et 8 -calix-[4]-tetrapyrrole ligand (Scheme 1). The crystalline compound, isolated upon cooling the solution in DME, was characterized by X-ray crystallography (see Supporting Information) and standard analytical techniques.