New Benzylpotassium Reagents and Their Utility for the Synthesis of Homoleptic Uranium(IV) Benzyl Derivatives

Abstract

A new family of benzylpotassium reagents, KBn′(1-Bn′) (Bn′ = p-i PrBn, p-t BuBn, p-NMe 2 Bn, p-SMeBn, m-OMeBn, o-OMeBn, 2-picolyl), was synthesized using a modified literature procedure and characterized by multinuclear NMR spectroscopy. Combining four equivalents of 1-Bn′ with UCl 4 at low temperature in THF afforded the homoleptic uranium(IV) derivatives 2-Bn′ (2-p-i Pr, 2-p-t Bu, 2-p-NMe 2 , 2-p-SMe, 2-o-Picolyl, 2-m-OMe, 2-o-OMe). In addition to 1 H NMR spectroscopic characterization, structural studies of five of these organouranium compounds (2-p-i Pr, 2-p-t Bu, 2-o-Picolyl, 2-m-OMe, 2-o-OMe) were performed, showing that in many cases the benzyl groups are coordinated in an η 4 -fashion, lending stability to these otherwise low-coordinate molecules. In the cases of U(o-OMeBn) 4 (2-o-OMe) and U(2-picolyl) 4 (2-o-Picolyl), heteroatom coordination to the uranium center is observed.

Homoleptic Aryl Complexes of Uranium (IV)

“…Originally proposed for applications in isotope separation and enrichment over 70 years ago, homoleptic organometallic complexes of uranium with simple alkyl or aryl ligands are of significant research interest for insight into electronic structure and bonding in uranium organometallic chemistry. Despite the significant challenges inherent in their isolation and characterization due to their severe air and thermal sensitivities, the past 30 years have seen seminal contributions in the synthesis and characterization of homoleptic uranium‐alkyl complexes from Sattelberger, Hayton, and Bart . Unfortunately, corresponding advances in the isolation and characterization of homoleptic uranium‐aryl complexes have been exceedingly more rare despite decades of research.…”

The Exceptional Diversity of Homoleptic Uranium–Methyl Complexes

“…When compared with the homoleptic uranium–benzyl derivatized complexes, the homoleptic uranium–methyl complex does not benefit from additional stabilizing effects (i.e. interaction with the ipso carbon of the benzyl substituents), other than the use of the cation complexant TMEDA (Figure ) . In our iron work, additives such as N ‐methyl‐2‐pyrrolidone (NMP) also displayed a similar role as cation complexant .…”

“…This represented the first successful synthesis of homoleptic uranium–aryl complexes without the advantageous use of sterically bulky aryl ligands for kinetic stabilization. Prior to this report, homoleptic uranium–alkyl and ‐aryl complexes were made isolable by introducing large steric bulk to the corresponding alkyl or aryl substituents …”

13C NMR Shifts as an Indicator of U–C Bond Covalency in Uranium(VI) Acetylide Complexes: An Experimental and Computational Study

“…1,2 Since that time, a number of uranium(IV) alkyl complexes have been synthesized, supported by substituted cyclopentadienyl, [3][4][5][6] amide, [7][8][9][10] alkoxide, 11 phosphine, 12,13 and homoleptic ligand frameworks. [14][15][16][17] However, uranium alkyl complexes in the oxidation states III, 18,19 V, 20 and VI 10,20,21 remain relatively scarce. Among the known organometallic uranium complexes are a number of uranium(IV) acetylide complexes.…”