Synthesis and Characterization of an f‑Block Terminal Parent Imido [UNH] Complex: A Masked Uranium(IV) Nitride

Deprotonation of [U­(TrenTIPS)­(NH2)] (1) [TrenTIPS = N­(CH2CH2NSiPri3)3] with organoalkali metal reagents MR (M = Li, R = But; M = Na–Cs, R = CH2C6H5) afforded the imido-bridged dimers [{U­(TrenTIPS)­(μ-N­[H]­M)}2] [M = Li–Cs (2a–e)]. Treatment of 2c (M = K) with 2 equiv of 15-crown-5 ether (15C5) afforded the uranium terminal parent imido complex [U­(TrenTIPS)­(NH)]­[K­(15C5)2] (3c), which can also be viewed as a masked uranium­(IV) nitride. The uranium–imido linkage was found to be essentially linear, and theoretical calculations suggested σ2π4 polarized U–N multiple bonding. Attempts to oxidize 3c to afford the neutral uranium terminal parent imido complex [U­(TrenTIPS)­(NH)] (4) resulted in spontaneous disproportionation to give 1 and the uranium–nitride complex [U­(TrenTIPS)­(N)] (5); this reaction is a new way to prepare the terminal uranium–nitride linkage and was calculated to be exothermic by −3.25 kcal mol–1.