Probing the 5f Orbital Contribution to the Bonding in a U(V) Ketimide Complex

Reaction of UCl4 with 5 equiv of Li­(NCtBuPh) generates the homoleptic U­(IV) ketimide complex [Li­(THF)2]­[U­(NCtBuPh)5] (1) in 71% yield. Similarly, reaction of UCl4 with 5 equiv of Li­(NCtBu2) affords [Li­(THF)]­[U­(NCtBu2)5] (2) in 67% yield. Oxidation of 2 with 0.5 equiv of I2 results in the formation of the neutral U­(V) complex U­(NCtBu2)5 (3). In contrast, oxidation of 1 with 0.5 equiv of I2, followed by addition of 1 equiv of Li­(NCtBuPh), generates the octahedral U­(V) ketimide complex [Li]­[U­(NCtBuPh)6] (4) in 68% yield. Complex 4 can be further oxidized to the U­(VI) ketimide complex U­(NCtBuPh)6 (5). Complexes 1–5 were characterized by X-ray crystallography, while SQUID magnetometry, EPR spectroscopy, and UV–vis–NIR spectroscopy measurements were also preformed on complex 4. Using this data, the crystal field splitting parameters of the f orbitals were determined, allowing us to estimate the amount of f orbital participation in the bonding of 4.

将四氯化铀(UCl₄)与5当量的N-叔丁基-N-苯基酮亚胺锂反应，以71%的产率得到均配型四价铀酮亚胺络合物[Li(四氢呋喃(THF))₂][U(N=CtBuPh)₅]（记为1）。类似地，四氯化铀(UCl₄)与5当量的N,N-二叔丁基酮亚胺锂反应，以67%的产率得到[Li(THF)][U(N=CtBu₂)₅]（记为2）。使用0.5当量的碘(I₂)氧化络合物2，可得到中性五价铀酮亚胺络合物U(N=CtBu₂)₅（记为3）。与之相反，先用0.5当量的碘氧化络合物1，再加入1当量的N-叔丁基-N-苯基酮亚胺锂，最终以68%的产率得到八面体型五价铀酮亚胺络合物[Li][U(N=CtBuPh)₆]（记为4）。络合物4可进一步被氧化为六价铀酮亚胺络合物U(N=CtBuPh)₆（记为5）。络合物1至5均通过X射线晶体衍射(X-ray crystallography)完成表征；针对络合物4，还额外开展了超导量子干涉仪磁测量(SQUID magnetometry)、电子顺磁共振波谱(EPR spectroscopy)以及紫外-可见-近红外光谱(UV–vis–NIR spectroscopy)测试。基于上述实验数据，我们确定了f轨道的晶体场分裂参数，借此估算出络合物4成键过程中f轨道的参与程度。