Formation and hydrolysis of gas‐phase [UO₂(R)]⁺: R═CH₃, CH₂CH₃, CH═CH₂, and C₆H₅

Abstract

The goals of the present study were (a) to create positively charged organo-uranyl complexes with general formula [UO 2 (R)] + (eg, R═CH 3 and CH 2 CH 3 ) by decarboxylation of [UO 2 (O 2 C─R)] + precursors and (b) to identify the pathways by which the complexes, if formed, dissociate by collisional activation or otherwise react when exposed to gas-phase H 2 O. Collision-induced dissociation (CID) of both [UO 2 (O 2 C─CH 3 )] + and [UO 2 (O 2 C─CH 2 CH 3 )] + causes H + transfer and elimination of a ketene to leave [UO 2 (OH)] + . However, CID of the alkoxides [UO 2 (OCH 2 CH 3 )] + and [UO 2 (OCH 2 CH 2 CH 3 )] + produced [UO 2 (CH 3 )] + and [UO 2 (CH 2 CH 3 )] + , respectively. Isolation of [UO 2 (CH 3 )] + and [UO 2 (CH 2 CH 3 )] + for reaction with H 2 O caused formation of [UO 2 (H 2 O)] + by elimination of ·CH 3 and ·CH 2 CH 3 : Hydrolysis was not observed. CID of the acrylate and benzoate versions of the complexes, [UO 2 (O 2 C─CH═CH 2 )] + and [UO 2 (O 2 C─C 6 H 5 )] + , caused decarboxylation to leave [UO 2 (CH═CH 2 )] + and [UO 2 (C 6 H 5 )] + , respectively. These organometallic species do react with H 2 O to produce [UO 2 (OH)] + , and loss of the respective radicals to leave [UO 2 (H 2 O)] + was not detected. Density functional theory calculations suggest that formation of [UO 2 (OH)] + , rather than the hydrated U V O 2 + , cation is energetically favored regardless of the precursor ion. However, for the [UO 2 (CH 3 )] + and [UO 2 (CH 2 CH 3 )] + precursors, the transition state energy for proton transfer to generate [UO 2 (OH)] + and the associated neutral alkanes is higher than the path involving direct elimination of the organic neutral to form [UO 2 (H 2 O)] + . The situation is reversed for the [UO 2 (CH═CH 2 )] + and [UO 2 (C 6 H 5 )] + precursors: The transition state for proton transfer is lower than the energy required for creation of [UO 2 (H 2 O)] + by elimination of CH═CH 2 or C 6 H 5 radical.

Organolanthanide Complexes Containing Ln–CH3 σ-bonds: Unexpectedly Similar Hydrolysis Rates for Trivalent and Tetravalent Organocerium

“…This was demonstrated by van Stipdonk et al, who noted that UO 2 2+ acetates fragment differently depending on the polarity of the complex: ketene elimination to form cationic UO 2 OH + or neutral ligand elimination to form an anionic UO 2 + acetate. 78,81 Because of the disparate cationic and anionic reactivity observed in the gas-phase, future studies that probe hydrolysis rates experimentally in [Ln III (CH 3 )-(Cl) 3 ] − and computationally in the cationic complexes of [Ln III (CH 3 )(CH 3 CO 2 )] + and [Ln III (CH 3 )(Cl)] + are encouraged.…”

“…75,77,78,81,83 While reduction and decarboxylation are competitive for [Yb III (CH 3 CO 2 ) 4 ] − , reduction outcompetes decarboxylation for [Eu III (CH 3 CO 2 ) 4 ] − , and we are unable to isolate the trivalent organoeuropium complex. However, [Eu III (OH)-(CH 3 CO 2 ) 3 ] − is observable as a minor product, which could result either from an extremely fast hydrolysis with k hyd ′(EuIII ) > 2000 s −1 [unlikely in view of the other much slower k hyd ′(Ln III )] or via a ketene (CH 2 CO) elimination as a direct fragmentation product.…”

Ion‐molecule reactions of mass‐selected ions

“…Recent studies have reduced the levels of background H 2 O by employing a 2‐D linear ion trap, revealing reactions not seen with the previous instrument. After collisional activation under lower pressures of H 2 O, the [U VI O 2 (ClO 4 )] + ion forms the [U VI O 2 (Cl)] + ion, which will react over time with background H 2 O to form the familiar [U VI O 2 (OH)] + ion(Tatosian et al, 2019). This indicated that the original study observed a two‐step reaction, obscured by the high background levels of H 2 O in the 3‐D ion trap.…”

“…Many oxygen‐containing organic ligands were studied by the van Stipdonk group. The uranyl propiolate ion, [UO 2 (O 2 C‐C = CH)] + , was subject to two rounds of CID, resulting in decarboxylation and the elimination of CO to yield the [OUCH] + ion (Tatosian et al, 2019). The product is a uranium‐methylidyne ion with a U ≡ C triple bond which reacts readily with O 2 upon collisional activation to form the UO 2 + ion.…”

“…The product is a uranium‐methylidyne ion with a U ≡ C triple bond which reacts readily with O 2 upon collisional activation to form the UO 2 + ion. The formation and hydrolysis of several complexes were studied to create [UO 2 (R)] + ions where R ═ CH 3 and CH 2 CH 3 (Tatosian et al, 2019). Fragmentation of alkoxides [UO 2 (OCH 2 CH 3 )] + and [UO 2 (OCH 2 CH 2 CH 3 )] + resulted in the successful formation of the [UO 2 (CH 3 )] + and [UO 2 (CH 2 CH 3 )] + ion, which reacted with water to eliminate the alkyl groups and form the [UO 2 (H 2 O)] + ion.…”