Synthesis and structure of uranium(III) complexes with dihydrobis(pyrazolyl)borates

The synthesis of the novel uranium(III) complexes [UI2{H2B(3(t)Bu,5Me-pz)(2)}(THF)(2)] 1, [UI2{H2B(3(t)Bu,5Me-pz)(2)}(OPPh3)(2)] 2 (3(t)Bu,5Me-pz = 3-tert-butyl-5-methylpyrazolyl) and [U{Ph2B(pz)(2)}(3)] 3 are reported. The molecular structures have been determined by single crystal X-ray diffraction. In monomeric complexes 1 and 2 the U-III is seven-co-ordinated by the two pyrazolyl nitrogens, the two iodides and two oxygen atoms of the neutral ligands and by an agostic B-H ... U interaction. In monomeric 3 the uranium is six-co-ordinated by the nitrogen atoms of the chelating Ph2B(pz)(2) ligands which are arranged in a trigonal prismatic geometry around the uranium.