Synthesis and Insertion Chemistry of a Cyclooctatetraenyl Uranium “Tuck-in” Metallocene, (η⁸-C₈H₈)(η⁵:η¹-C₅Me₄CH₂)U

Abstract

[(C5Me5)(C8H8)U(μ-OTf)]2, 1 (OTf = OSO2CF3), reacts with LiMe to form the metathesis product (C5Me5)(C8H8)UMe, 2, as well as the product of a methyl C−H activation, (C8H8)(C5Me4CH2)U, 3. Methane was observed in the 1H NMR spectrum of the reaction mixture, which is consistent with the metalation of a (C5Me5)− ligand by the uranium methyl group in 2. Complex 2 was identified in this reaction mixture by addition of iPrN═C═NiPr to form the previously reported (C5Me5)(C8H8)U[iPrNC(Me)NiPr-κ2N,N′], 4. The reactions of 1 with LiEt and LiCH2CMe3 similarly form mixtures at room temperature that contain 3 and compounds with 1H NMR spectra consistent with (C5Me5)(C8H8)UEt, 5, and (C5Me5)(C8H8)U(CH2CMe3), 6, respectively. Complexes 2, 5, and 6 convert to 3 after 24 h at 100 °C. Complex 3 can also be synthesized at 100 °C from (C5Me5)(C8H8)UPh, 7, and was characterized as the THF adduct of a “tuck-in” complex, (η8-C8H8)(η5:η1-C5Me4CH2)U(THF), 8, by X-ray crystallography. Complex 3 allowed the insertion chemistry of an isolable f element (η5:η1-C5Me4CH2)2− metallocene complex to be studied for the first time and provides access to new heteroleptic tethered metallocenes. iPrN═C═NiPr inserts into the U−C(η1-C5Me4CH2) bond of 3 to form the amidinate complex (C8H8)[C5Me4CH2C(NiPr)2]U, 9. tBuN≡C reacts in a series of steps through intermediates such as (C8H8)(C5Me4CH2C═NtBu)U, 10, and (C8H8)(C5Me4CH2C═NtBu)U(C≡NtBu) that leads to the isolation of the isocyanide double-insertion product, (η8-C8H8)[η5-C5Me4CH2C(═C═NtBu)NtBu-κN]U, 11.