Formation of Trivalent U–C, U–N, and U–S Bonds and Their Reactivity toward Carbon Dioxide and Acetone

A family of uranium(III) complexes of the form Tp*₂UX (Tp* = hydrotris(3,5-dimethylpyrazolyl)borate, X = CCPh (2-CCPh), CCSiMe₃ (3-CCSiMe₃), NHPh (4-NHPh), NHCH₂Ph (5-NHCH₂Ph), SPh (6-SPh)) have been synthesized in quantitative yields by protonation of the benzyl group Tp*₂U(CH₂Ph) (1-CH₂Ph) with organic precursors. Full characterization of these complexes, which contain newly formed uranium–carbon, uranium–nitrogen, and uranium–sulfur bonds, was performed using ¹H NMR and IR spectroscopies. These data along with the structural parameters of the uranium acetylide (2-CCPh) and uranium thiolate (6-SPh) species are reported. Treating the trivalent uranium acetylides and amides with 1 atm of carbon dioxide results in its insertion into the uranium–element bond to form the corresponding carboxylate or carbamate moiety in quantitative isolable yields. Reversible insertion of carbon dioxide (1 atm) into the uranium–sulfur bond of Tp*₂U(SPh) (6-SPh) was also noted. The new family of CO₂-inserted uranium(III) derivatives Tp*₂UO₂CX (X = CCPh (7-O₂CCCPh), CCSiMe₃ (8-O₂CCCSiMe₃), NHPh (9-O₂CNHPh), NHCH₂Ph (10-O₂CNHCH₂Ph), SPh (11-O₂CSPh)) has been characterized spectroscopically and, in the case of 7-O₂CCCPh, crystallographically. The newly formed U–O bonds were cleaved by addition of trimethylsilyl halides, generating the monohalide derivative. Attempts to insert acetone into the uranium–carbon bonds of 1-CH₂Ph and 2-CCPh or the uranium–nitrogen bond in 4-NHPh resulted exclusively in protonation of the benzyl ligand and isomerization to form a rare enolate complex Tp*₂U(OC(CH₃)CH₂) (12-OC(CH₃)CH₂). This complex has been fully characterized by ¹H NMR and infrared spectroscopies as well as X-ray crystallography.