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.

将配合物[U(TrenTIPS)(NH₂)] (1) [其中TrenTIPS = N(CH₂CH₂NSiPri₃)₃]与有机碱金属试剂MR（M=Li，R=叔丁基(But)；M=Na~Cs，R=苄基(CH₂C₆H₅)）进行去质子化反应，可得到亚胺基桥联二聚体[{U(TrenTIPS)(μ-N[H]M)}₂] [对应M=Li~Cs的产物记为2a~2e]。将2c（M=K）与2当量的15-冠-5醚(15C5)反应，可制得铀端基母体亚胺基配合物[U(TrenTIPS)(NH)][K(15C5)₂] (3c)，该配合物亦可被视作掩蔽型四价铀氮化物。实验观测到铀-亚胺基键基本呈线性结构，理论计算结果表明其存在σ²π⁴极化的U-N多重键。尝试对3c进行氧化以制备中性铀端基母体亚胺基配合物[U(TrenTIPS)(NH)] (4)，但反应发生了自发歧化，生成原料1与铀氮化物配合物[U(TrenTIPS)(N)] (5)；该反应是制备端基铀-氮键的新方法，经计算其反应焓变为-3.25 kcal mol⁻¹（即放热3.25千卡每摩尔）。