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The Nature of the UC Double Bond: Pushing the Stability of High-Oxidation-State Uranium Carbenes to the Limit.

著者 Cooper OJ , Mills DP , McMaster J , Tuna F , McInnes EJ , Lewis W , Blake AJ , Liddle ST
Chemistry.2013 Apr 4 ; ():.
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School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD (UK).

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Treatment of [K(BIPM(Mes) H)] (BIPM(Mes) ={C(PPh2 NMes)2 }(2-) ; Mes=C6 H2 -2,4,6-Me3 ) with [UCl4 (thf)3 ] (1 equiv) afforded [U(BIPM(Mes) H)(Cl)3 (thf)] (1), which generated [U(BIPM(Mes) )(Cl)2 (thf)2 ] (2), following treatment with benzyl potassium. Attempts to oxidise 2 resulted in intractable mixtures, ligand scrambling to give [U(BIPM(Mes) )2 ] or the formation of [U(BIPM(Mes) H)(O)2 (Cl)(thf)] (3). The complex [U(BIPM(Dipp) )(μ-Cl)4 (Li)2 (OEt2 )(tmeda)] (4) (BIPM(Dipp) ={C(PPh2 NDipp)2 }(2-) ; Dipp=C6 H3 -2,6-iPr2 ; tmeda=N,N,N',N'-tetramethylethylenediamine) was prepared from [Li2 (BIPM(Dipp) )(tmeda)] and [UCl4 (thf)3 ] and, following reflux in toluene, could be isolated as [U(BIPM(Dipp) )(Cl)2 (thf)2 ] (5). Treatment of 4 with iodine (0.5 equiv) afforded [U(BIPM(Dipp) )(Cl)2 (μ-Cl)2 (Li)(thf)2 ] (6). Complex 6 resists oxidation, and treating 4 or 5 with N-oxides gives [{U(BIPM(Dipp) H)(O)2 - (μ-Cl)2 Li(tmeda)] (7) and [{U(BIPM(Dipp) H)(O)2 (μ-Cl)}2 ] (8). Treatment of 4 with tBuOLi (3 equiv) and I2 (1 equiv) gives [U(BIPM(Dipp) )(OtBu)3 (I)] (9), which represents an exceptionally rare example of a crystallographically authenticated uranium(VI)-carbon σ bond. Although 9 appears sterically saturated, it decomposes over time to give [U(BIPM(Dipp) )(OtBu)3 ]. Complex 4 reacts with PhCOtBu and Ph2 CO to form [U(BIPM(Dipp) )(μ-Cl)4 (Li)2 (tmeda)(OCPhtBu)] (10) and [U(BIPM(Dipp) )(Cl)(μ-Cl)2 (Li)(tmeda)(OCPh2 )] (11). In contrast, complex 5 does not react with PhCOtBu and Ph2 CO, which we attribute to steric blocking. However, complexes 5 and 6 react with PhCHO to afford (DippNPPh2 )2 CC(H)Ph (12). Complex 9 does not react with PhCOtBu, Ph2 CO or PhCHO; this is attributed to steric blocking. Theoretical calculations have enabled a qualitative bracketing of the extent of covalency in early-metal carbenes as a function of metal, oxidation state and the number of phosphanyl substituents, revealing modest covalent contributions to UC double bonds.
PMID: 23559370 [PubMed - as supplied by publisher]
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