From Bent to Linear Uranium Metallocenes:  Influence of Counterion, Solvent, and Metal Ion Oxidation State

Abstract

Reactions of Cp*2UCl2 with a slight excess of Me3SiI or Me3SiOTf in acetonitrile provide convenient routes to Cp*2UI2 (1) or Cp*2U(OTf)2 (2) (Cp* = η-C5Me5; OTf = OSO2CF3), which were isolated with excellent yields. Crystals of the bent metallocenes Cp*2UI2(NCR) (R = Me (3), tBu (4)) have been obtained by addition of excess RCN to a toluene solution of 1. The triflate analogue Cp*2U(OTf)2(NCMe) (5) contains monodentate OTf ligands. Treatment of Cp*2UMe2 with 2 equiv of HNEt3BPh4 in acetonitrile led to the immediate formation of [Cp*2U(NCMe)5][BPh4]2 (6). The 1H NMR spectra of 1 and 2 in acetonitrile are similar to that of 6, indicating the presence of the dicationic species [Cp*2U(NCMe)5][X]2 [X = I (7), OTf (8)] in this solvent. Compounds 6−8 are the first linear metallocenes of an f-element and exhibit an unprecedented structure with auxiliary donor ligands in the equatorial plane parallel to the cyclopentadienyl rings. When treated with Me3SiOTf, the uranium(III) species Cp*2UCl2Na(thf)2 did not afford the trivalent complex Cp*2U(OTf) (9) but gave crystals of the dimeric uranium(IV) “ate” compound [Cp*2U(OTf)3Na(thf)2]2·2(CH2)4O (10·2(CH2)4O). The first organouranium(III) triflate, 9, was isolated in 90% yield from the reaction of U(OTf)3 with 2 equiv of KCp* in thf. Dissolution of Cp*2UI(py) in acetonitrile gave the adduct Cp*2UI(NCMe)2 (11), which, like its cerium analogue, adopts a bent sandwich structure in its crystalline form. The 1H NMR spectra of 11 and Cp*2U(OTf)(NCMe)2 are similar in benzene and acetonitrile, suggesting that the trivalent linear metallocene [Cp*2U(NCMe)5][X] (X = I or OTf) is not present in pure acetonitrile. These observations are confirmed by the addition of 3 equiv or excess MeCN to a solution of [Cp*2U(thf)2][BPh4] in thf, which afforded the stable [Cp*2U(NCMe)3][BPh4] as the sole product.

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.…”

Expanding the Chemistry of Actinide Metallocene Bromides. Synthesis, Properties and Molecular Structures of the Tetravalent and Trivalent Uranium Bromide Complexes: (C5Me4R)2UBr2, (C5Me4R)2U(O-2,6-iPr2C6H3)(Br), and [K(THF)][(C5Me4R)2UBr2] (R = Me, Et)

“…To the best of our knowledge, this is the first time that compounds 33 and 34 have been fully characterized. The 1 H Nuclear Magnetic Resonance (NMR) spectrum of 33 in benzene-d6 shows a singlet at 15.70 ppm, which is intermediate in value compared to (C5Me5)2UCl2 (13.5 ppm) [3] and (C5Me5)2UI2 (17.9 ppm) [28][29][30]; while that of complex 34 shows four singlets corresponding to the three inequivalent methyl groups (25.1, 15.6 and 13.1 ppm) and the methylene group (0.31 ppm) of the C5Me4Et ligand. The 1 H NMR shifts of 34 are also downfield compared to the analogous (C5Me4Et)2UCl2 (22.9, 13.8 and −2.8 ppm, respectively) and (C5Me4Et)2U(CH3)2 (14.1, 5.6, 5.1 and −4.3 ppm, respectively) [31].…”

“…The K-Br bond lengths of 41 (3.1684 (14) [26] and [UBr3(DME)2]2 (U-Br = 2.898(2), 2.887(2), 3.016(2) and 3.098(2) Å) [40] and are longer than those of 33 (U-Br = 2.7578(5) Å) and 34 (U-Br = 2.7609(4) and 2.7607(4) Å). In addition, the U-C Cent bond distances of 41 (2.495 (7) [29,[67][68][69][70][71][72][73][74][75][76][77][78][79][80][81].…”

“…Complex (C 5 Me 5 ) 3 UBr (22) is thermally unstable and leads to isolation of (C 5 Me 5 ) 2 UBr (28), from which (C 5 Me 5 ) 2 UBr(THF) (29) can be formed [20].…”

“…(26), t Bu (27)), respectively [7,[23][24][25]. Complex (C5Me5)3UBr (22) is thermally unstable and leads to isolation of (C5Me5)2UBr (28), from which (C5Me5)2UBr(THF) (29) can be formed [20]. Finally, [1,3- …”