Uranium Hydridoborates: Synthesis, Magnetism, and X-ray/Neutron Diffraction Structures

Abstract

While uranium hydridoborate complexes containing the [BH4](-) moiety have been well-known in the literature for many years, species with functionalized borate centers remained considerably rare. We were now able to prepare several uranium hydridoborates (1-4) with amino-substituted borate moieties with high selectivity by smooth reaction of [Cp*2UMe2] (Cp* = C5Me5) and [Cp'2UMe2] (Cp' = 1,2,4-tBu3C5H2) with the aminoborane H2BN(SiMe3)2. A combination of nuclear magnetic resonance spectroscopy, deuteration experiments, magnetic SQUID measurements, and X-ray/neutron diffraction studies was used to verify the anticipated molecular structures and oxidation states of 1-4 and helped to establish a linear tridentate coordination mode of the borate anions.

Chelating Borohydrides for Lanthanides and Actinides: Structures, Mechanochemistry, and Case Studies with Phosphinodiboranates

“…As a result, Ln(BH 3 R) 3 complexes have large voids in the coordination sphere that yield numerous intermolecular B−H−M bridging coordination modes, 3 which dramatically attenuates their volatility. 2,22,38 This problem can be circumvented to some extent by adding neutral Lewis bases to fill voids in the coordination sphere and form complexes that can be dissolved in organic solvents. 2,4,22,39−41 The same is true for trivalent An(BH 4 ) 3 complexes, 42,43 which are often formed by borohydride-induced reduction.…”

“…In contrast to tetravalent actinides (An 4+ ), trivalent lanthanide complexes with BH 4 – yield nonvolatile Ln­(BH 4 ) 3 because the ligands are too small to saturate the larger coordination sphere of Ln 3+ . ,, Trivalent Ln 3+ ions are not only larger but they also require fewer ligands to offset the lower charge on the metal than do tetravalent An 4+ ions. As a result, Ln­(BH 3 R) 3 complexes have large voids in the coordination sphere that yield numerous intermolecular B–H–M bridging coordination modes, which dramatically attenuates their volatility. ,, This problem can be circumvented to some extent by adding neutral Lewis bases to fill voids in the coordination sphere and form complexes that can be dissolved in organic solvents. ,,,− The same is true for trivalent An­(BH 4 ) 3 complexes, , which are often formed by borohydride-induced reduction. U­(BH 4 ) 4 can be reduced to U­(BH 4 ) 3 by heating or photolysis, ,− and Np­(BH 4 ) 4 and Pu­(BH 4 ) 4 are even more thermally unstable with respect to reduction, decomposing readily at room temperature to what is presumed to be Np­(BH 4 ) 3 and Pu­(BH 4 ) 3 …”

Structural, Electrochemical, and Magnetic Studies of Bulky Uranium(III) and Uranium(IV) Metallocenes

“…The organometallic chemistry of uranium prominently features complexes containing substituted or unsubstituted cyclopentadienyl ligands, Cp R . − In particular, uranium metallocenes featuring the (Cp R ) 2 U moiety have supported a large variety of intriguingand often quite reactivestructural motifs, such as uranium–ligand multiple bonds, − a uranium–aluminum interaction, uranium­(V) complexes, − cationic uranium­(III) species, , and uranium hydrides. − In the past few years, bulky [Cp R ] − ligands have also enabled the synthesis of base-free dysprosium­(III) metallocenium cation salts [(Cp R ) 2 Dy]­[B­(C 6 F 5 ) 4 ], which, incredibly, function as single-molecule magnets with magnetic blocking temperatures near and exceeding 77 K, higher than any previously reported systems. − This synthetic strategy was also very recently extended to the preparation of the uranium­(III) metallocenium complex [(Cp iPr5 ) 2 U]­[B­(C 6 F 5 ) 4 ] (Cp iPr5 = penta­(isopropyl)­cyclopentadienyl), which was also found to exhibit slow magnetic relaxation in the presence of an applied magnetic field …”

Catalytic Dehydrogenation of Dimethylamine Borane by Highly Active Thorium and Uranium Metallocene Complexes

“…20−22 In addition, Braunschweig and co-workers reacted (C 5 Me 5 ) 2 UMe 2 and (1,2,4-t Bu 3 -C 5 H 2 ) 2 UMe 2 with the amino borane (Me 3 Si) 2 N BH 2 to prepare (C 5 Me 5 ) 2 U[H 3 BN(SiMe 3 ) 2 ] 2 and (1,2,4-t Bu 3 -C 5 H 2 ) 2 U[H 3 BN(SiMe 3 ) 2 ], respectively. 23 We have been interested in developing routes that avoid the use of H 2 gas to thorium(IV), uranium(IV), and uranium(III) hydrides to expand and better understand their chemistry. 24,25 During our studies, we discovered that the actinide dimethyl complexes (C 5 Me 5 ) 2 AnMe 2 (An = Th (1), U (2)) and hydride complexes, [(C 5 Me 5 ) 2 An(H)(μ-H)] 2 (An = Th (3), U (4)) and [(C 5 Me 5 ) 2 UH] 2 (5; see Figure 1), catalyze the dehydrogenation of dimethylamine borane (Me 2 NH•BH 3 , 6) with metrics comparable to those previously reported for highly active Rh and Ru catalysts.…”