The Effect of the Equatorial Environment on Oxo‐Group Silylation of the Uranyl Dication: A Computational Study

Abstract

We thank the Insitut Universitaire de France, CALMIP, CCRT, and CINES for their grant of computing time; CNRS, UPS, and CEA for financial support of this work; and the EPSRC and the University of Edinburgh for funding. Supporting information:Supporting information for this article is available online at http://dx.doi.org/10.1002/chem.200902991 Cartesian coordinates of the optimised structures are included. Keywords:density functional calculations;equatorial ligands;macrocycles;silylation;uranium Synopsis:A DFT study of the silylation of the U-O bond in a macrocyclic uranyl complex demonstrates the importance of the presence, but not the identity, of the equatorial ligands upon the silylation of the uranyl U-O bond, and the influence of the oxo-potassium interaction at the opposing oxo group. Page 1 of 21 AbstractA theoretical investigation of the reductive oxo-group silylation reaction of the uranyl dication held in a Pacman macrocylic environment has been carried out. The effect of the modeling of the Pacman ligand on the reaction profiles is found to be important, with the dipotassiation of a single oxo group identified as a key component in promoting the reaction between the SiX and uranium-oxo bonds. This reductive silylation reaction is also proposed to occur in an aqueous environment but was found not to operate on bare ions; in this latter case, substitution of a ligand in the equatorial plane was the most likely reaction. These results demonstrate the importance of the presence but not the identity of the equatorial ligands upon the silylation of the uranyl UO bond.

Oxo Ligand Substitution in a Cationic Uranyl Complex: Synergistic Interaction of an Electrophile and a Reductant

“…The average U-O OTf distance (av. U-O = 2.39 Å) is similar to other U(IV)-O OTf distances, [20][21][22] but is slightly longer than those observed in the structurally related complex, U IV (OTf) 4 (DME) 2 (av. U-O = 2.28 Å), 23 which is probably a result of the steric bulk of the dppmo ligands.…”

“…[2][3][4][5][6][7] For example, Arnold and co-workers demonstrated that sequential reaction of U VI O 2 (THF)(H 2 L) (L = polypyrrolic macrocycle) with KN(SiMe 3 ) 2 and FeI 2 resulted in formation of the U(V) silyloxide, [U V O(OSiMe 3 )(THF)Fe 2 I 2 L]. 7 Similarly, our research group has demonstrated that reaction of U VI O 2 ( Ar acnac) 2 ( Ar acnac = ArNC(Ph)CHC(Ph)O, Ar = 3,5-t Bu 2 C 6 H 3 ), 8 with a mixture of B(C 6 F 5 ) 3 and HSiR 3 (R = Ph, Et), 9,10 or with Ph 3 SiOTf alone, 11 results in formation of the reductive silylation products, U V (OSiR 3 )(OB{C 6 11 respectively.…”

“…In contrast to these oxo functionalization reactions, examples of complete oxo substitution remain rare. For instance, Ephritikhine and co-workers reported that reaction of U VI O 2 I 2 with Me 3 SiX (X = Cl, Br, I) in MeCN resulted in formation of U IV X 4 (MeCN) 4 . 12 In this example, the uranyl oxo ligand is likely converted into Me 3 SiOSiMe 3 .…”

Strongly coupled binuclear uranium–oxo complexes from uranyl oxo rearrangement and reductive silylation

“…The low yields of 2 and lack of obvious reducing agent in the synthetic procedure led us to investigate reactions at lower temperatures ( Figure 5). It is clear from these investigations that two competing reactions occur, one at lower temperature that involves metallation of the uranyl oxo, and one at 44,45 While a detailed evaluation of the mechanism of formation of 2 is ongoing, the observations described above suggest that two competing, reductive pathways occur that involve either U-N or N-Si bond homolysis (for a speculative mechanism see Figure SI. 19).…”

Reductive silylation of a uranyl dibenzoylmethanate complex: an example of controlled uranyl oxo ligand cleavage

“…[13][14][15][16][17][18][19] Reductive silylation was rst demonstrated by Arnold and co-workers, who showed that a strongly donating macrocyclic ligand promoted the reductive silylation of UO 2 (THF)(H 2 L) (L ¼ 'Pacman' polypyrrolic macrocycle) to produce the U(V) silyloxide, [UO(OSi-Me 3 )(THF)Fe 2 I 2 L]. 13,14,20,21 Subsequently, our research group reported the reductive silylation of the b-ketoiminate complex, UO 2 ( Ar acnac) 2 ( Ar acnac ¼ ArNC(Ph)CHC(Ph)O; Ar ¼ 3,5-t Bu 2 C 6 H 3 ) using a combination of B(C 6 F 5 ) 3 and HSiR 3 (R ¼ Ph, Et) to generate U(OSiPh 3 )(OB{C 6 F 5 } 3 )( Ar acnac) 2 22 and [U(OSiEt 3 ) 2 ( Ar acnac) 2 ][HB(C 6 F 5 ) 3 ]. 23 In our original report we argued that the strong electron donating ability of the b-ketoiminate ligand, Ar acnac, 22 activated the uranyl oxo groups toward functionalization.…”