“A new synthetic route to the electron-deficient ligand tris(3,4,5-tribromopyrazol-1-yl)phosphine oxide”

The anionic tris(pyrazolyl)borates, or scorpionates, have proven to be extremely useful ligands. Neutral tris(pyrazolyl)methane ligands, however, are difficult to prepare and require numerous purification steps for a number of substitution patterns. We have previously outlined two different routes for accessing neutral tris(pyrazolyl) ligands. We describe here an adaptation of the previously published procedures for the synthesis of the electron-poor ligand tris(3,4,5-tribromopyrazol-1-yl)phosphine oxide, C9Br9N6OP. Similar electron-deficient ligands have been proven to unlock unique chemistry for the anionic scorpionates. The title perbrominated tris(pyrazolyl)phosphine oxide displays a network of halogen bonds in the solid state. All the bonds in the pyrazole ring are rather similar to the reported borate analogues, which makes this molecule promising as a ligand for applications where very electron-poor metal complexes are required.</jats:p

C-H Bond Addition across a Transient Uranium-Nitrido Moiety and Formation of a Parent Uranium Imido Complex

Uranium complexes in the +3 and +4 oxidation states were prepared using the anionic PN- (PN- = (N-(2-(diisopropylphosphino) -4-methylphenyl)-2,4,6-trimethylanilide) ligand framework. New complexes include the halide starting materials, (PN)(2)(UI)-I-III (1) and (PN)(2)(UCl2)-Cl-IV (2), which both yield (PN)(2)U-IV(N-3)(2) (3) by reaction with NaN3. Compound 3 was reduced with potassium graphite to produce a putative, transient uranium-nitrido moiety that underwent an intramolecular C-H activation to form a rare example of a parent imido complex, [K(THF)(3)][(PN)U-IV(= NH)[(Pr2P)-Pr-i(C6H3Me)N(C6H2Me2CH2)]] (4). Calculated reaction energy profiles strongly suggest that a C-H insertion becomes unfavorable when a reductant is present, offering a distinctively different reaction pathway than previously observed for other uranium nitride complexes. © 2018 American Chemical Societ