Investigating the reactivity of a Lewis base-supported terminal uranium imido metallocene

Abstract

The Lewis base-supported terminal uranium imido metallocene, [η⁵-1,3-(Me₃Si)₂C₅H₃]₂UN(mesityl)(dmap) (2), is readily accessible from the reaction of [η⁵-1,3-(Me₃Si)₂C₅H₃]₂UMe₂ (1) with mesitylNH₂ in toluene in the presence of 4-dimethylaminopyridine (dmap). With compound 2 in hand, its reactivity towards small molecules was studied in detail. It reacts with terminal alkynes such as PhCCH to form the amido alkynyl complex [η⁵-1,3-(Me₃Si)₂C₅H₃]₂U[N(mesityl)CHCHPh](CCPh) (3) exclusively. In the reaction with thio-ketone Ph₂CS, CS₂, isothiocyanate PhNCS and ketone Ph₂CO, the initial [2 + 2] cycloaddition intermediates are too labile to be isolated, yielding [η⁵-1,3-(Me₃Si)₂C₅H₃]₂U(S₂CPh₂)(dmap) (4) or dimeric sulfido and oxido complexes {[η⁵-1,3-(Me₃Si)₂C₅H₃]₂U}₂(μ-E)₂ (E = S (5), O (6)), respectively. Moreover, complex 2 may also behave as a nucleophile in the reaction with bis(catecholato)diboron (B₂cat₂), yielding the amido catecholate complex [η⁵-1,3-(Me₃Si)₂C₅H₃]₂U[N(mesityl)B(BO₂C₆H₄)O(C₆H₄)O] (8). In addition, the imido moiety of 2 may also engage in deprotonation reactions as demonstrated by its reactivity with the carboxamide PhCONH(p-tolyl) and organic nitrile PhCH₂CN, obtaining the uranium(IV) bis-amidate complex [η⁵-1,3-(Me₃Si)₂C₅H₃]₂U[OC(Ph)N(p-tolyl)]₂ (7) and the uranium(IV) iminato amido complex [η⁵-1,3-(Me₃Si)₂C₅H₃]₂U[N(mesityl)C(CH₂Ph)NH](NCCHPh) (9), respectively. Furthermore, 2 may also participate in single- and two-electron transfer processes. It is singly oxidized by CuI, Ph₂S₂, Ph₂Se₂ and Ph₃CN₃, yielding the uranium(V) imido complexes [η⁵-1,3-(Me₃Si)₂C₅H₃]₂UN(mesityl)(X) (X = I (12), PhS (13), PhSe (14), and N₃ (17)), or doubly oxidized by organic azides (RN₃), forming the uranium(VI) bis-imido metallocenes [η⁵-1,3-(Me₃Si)₂C₅H₃]₂UN(mesityl)(NR) (R = p-tolyl (15), mesityl (16)), respectively. Nevertheless, the addition of 1,2-diphenylhydrazine PhNHNHPh to complex 2 results in deprotonation and ligand elimination processes, yielding the uranium(V) bis-imido complex [η⁵-1,3-(Me₃Si)₂C₅H₃]U[NPh]₂(dmap)₃ (11) in the presence of dmap.