Synthesis and structural characterization of unprecedented bis-asymmetric heteroscorpionate U(III) complexes:: [U{κ3-H2B(pztBu,Me)(pzMe,tBu)}2I] and [U{κ3 -H2B(pztBu,Me)( pzMe2)}2I]

[UI3(THF)(4)] reacts at room temperature with 2 equiv of KBp(tBu,Me), in toluene, yielding [U{kappa(3)-H(mu-H)B(pZt(Bu,Me))-(pz(Me,tBu))}(2)I] (1). This unprecedented complex, stabilized by two asymmetric heteroscorpionate ligands, is formed due to an isomerization process promoted in situ by the metal center. To find a general method for preparing this type of compound, we synthesized the novel asymmetric K[H2B(pz(tBu,Me))(pz(Me2))], and by a straightforward salt metathesis with [UI3(THF)(4)] the novel bis-asymmetric complex [U{kappa(3)-H(mu-H)B(pz(tBu,Me)) (pz(Me2))}(2)I] (2) was isolated and characterized in the solid state and in solution. As indicated by X-ray crystallographic analysis, the U(III) in 1 and 2 is seven-coordinated by two tridentate asymmetric dihydrobis(pyrazoly)borates and by an iodide. In both cases, the coordination geometry around the metal is very distorted, the pentagonal bipyramid being the one which better describes the arrangement of the atoms around the U(III). An approximate C-2 axis can be defined in the solid state, and is maintained in solution as indicated by the H-1 NMR spectrum of 1 and 2. In the course of attempting to crystallize some of the compounds, monocrystals of the dimer [U{kappa(3)-Bp(tBu,Me)}(Hpz(tBu,Me))I(mu-I)](2) (3) were isolated. In this compound each U(III) atom is seven-coordinated by one kappa(3)-Bp(tBu,Me), by one terminal and by two bridging iodide ligands, and by a monodentate Hpz(tBu,Me), exhibiting a distorted 4:3 tetragonal base-trigonal geometry.