| Abstract
| - Reactions of Cp*2UCl2 with a slight excess of Me3SiI or Me3SiOTf in acetonitrile provide convenientroutes to Cp*2UI2 (1) or Cp*2U(OTf)2 (2) (Cp* = η-C5Me5; OTf = OSO2CF3), which were isolated withexcellent yields. Crystals of the bent metallocenes Cp*2UI2(NCR) (R = Me (3), tBu (4)) have beenobtained 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 inacetonitrile led to the immediate formation of [Cp*2U(NCMe)5][BPh4]2 (6). The 1H NMR spectra of 1and 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 ofan f-element and exhibit an unprecedented structure with auxiliary donor ligands in the equatorial planeparallel 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. Dissolutionof 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 theaddition of 3 equiv or excess MeCN to a solution of [Cp*2U(thf)2][BPh4] in thf, which afforded thestable [Cp*2U(NCMe)3][BPh4] as the sole product.
- The easily prepared precursors Cp*2UX2 (X = I, OSO2CF3) were transformed into the bent Lewis base adducts Cp*2UX2(NCMe) or the dication [Cp*2U(NCMe)5]2+, the first linear metallocene of an f-element. Such bent to linear transformation was not observed with the corresponding uranium(III) complexes.
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