Reactivity Studies on the Lewis Base-Supported Terminal Uranium Imido Metallocene [η<sup>5</sup>-1,3-(Me<sub>3</sub>C)<sub>2</sub>C<sub>5</sub>H<sub>3</sub>]<sub>2</sub>U═N(<i>p</i>-tolyl)(dmap)
Tongyu Li, Yi Heng, Dongwei Wang, Guofu Zi, Marc D. Walter
Abstract
Addition of p-tolylNH2 to a toluene solution of [η5-1,3-(Me3C)2C5H3]2UMe2 (1) in the presence of 4-dimethylaminopyridine (dmap) yields the Lewis base-supported terminal uranium imido metallocene, [η5-1,3-(Me3C)2C5H3]2U═N(p-tolyl)(dmap) (2), concomitant with methane release. Complex 2 undergoes a [2 + 2] cycloaddition with internal alkynes such as PhC≡CMe to form [η5-1,3-(Me3C)2C5H3]2U[N(p-tolyl)C(Me)═C(Ph)] (3) exclusively. Formal [2 + 2] cycloadditions also initiate the reactions of complex 2 with ketones, thio-ketones, CS2, isothiocyanates, and seleno-ketones, but these [2 + 2] cycloaddion products are too unstable to be isolated, yielding dimeric oxido, sulfido, and selenido complexes, respectively. In the reaction with esters, carbodiimides, acyl nitriles, chlorosilanes, and bis(catecholato)diboron (B2cat2), uranium(IV) alkoxido amidate, guanidato, amidinato cyanido, amido chloride, and amido catecholate complexes are formed, respectively, indicating that this imido moiety may also act as a nucleophile. Moreover, the imido moiety in complex 2 may also engage in deprotonation reactions, as shown by its reactivity with the carboxamide PhCONH(p-tolyl), the organic nitriles PhCH2CN, Ph2CHCN, PhCN, and 1,4-(CH2)4(CN)2 to yield the uranium(IV) bis-amidate [η5-1,3-(Me3C)2C5H3]2U[OC(Ph)N(p-tolyl)]2 (8), the uranium(IV) iminato amido complexes [η5-1,3-(Me3C)2C5H3]2U[N(p-tolyl)═C(CH2Ph)NH](N═C═CHPh) (11), [η5-1,3-(Me3C)2C5H3]2U[N(p-tolyl)═C(CHPh2)NH](N═C═CPh2) (12), and [η5-1-{N═C(Ph)N═C(Ph)}-2,4-(Me3C)2C5H2][η5-1,3-(Me3C)2C5H3]U[N(p-tolyl)═C(Ph)NH] (15), and the dimeric uranium(IV) imido {[η5-1,3-(Me3C)2C5H3]2U═N(C5H6)CN}2 (13), respectively. Furthermore, 2 may also be doubly oxidized with organic azides (RN3), forming the uranium(VI) bis-imido metallocenes [η5-1,3-(Me3C)2C5H3]2U═N(p-tolyl)(═NR) (R = p-tolyl (19), mesityl (20)). Nevertheless, addition of Ph2S2 or Ph2Se2 to complex 2 results in ligand redistribution processes, yielding the uranium(VI) bis-imido complexes U[═N(p-tolyl)]2(SPh)2(dmap)2 (21) and [η5-1,3-(Me3C)2C5H3]U[═N(p-tolyl)]2(SePh)(dmap)2 (22) in low yield, respectively.