Synthesis and characterization of an f-block terminal parent imido [U=NH] complex: A masked uranium(IV) nitride

Deprotonation of [U(TrenTIPS)(NH2)] (1) [Tren TIPS = N(CH2CH2NSiPri 3)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 σ 2π4 polarized U-N multiple bonding. Attempts to oxidize 3c to afford the neutral uranium terminal parent imido complex [U(Tren TIPS)(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. © 2014 American Chemical Society.