School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, United States.
Department of Chemistry, The University of Akron, Akron, Ohio 44325-3601, United States.
Inorg Chem. 2023 Feb 6;62(5):2304-2316. doi: 10.1021/acs.inorgchem.2c04056. Epub 2023 Jan 20.
The development of high-valent transuranic chemistry requires robust methodologies to access and fully characterize reactive species. We have recently demonstrated that the reducing nature of imidophosphorane ligands supports the two-electron oxidation of U to U and established the use of this ligand to evaluate the inverse-trans-influence (ITI) in actinide metal-ligand multiple bond (MLMB) complexes. To extend this methodology and analysis to transuranic complexes, new small-scale synthetic strategies and lower-symmetry ligand derivatives are necessary to improve crystallinity and reduce crystallographic disorder. To this end, the synthesis of two new imidophosphorane ligands, [N═PBu(pip)] () and [N═PBu(pyrr)] () (pip = piperidinyl; pyrr = pyrrolidinyl), is presented, which break pseudo- axes in the tetravalent complexes, and . The reaction of these complexes with two-electron oxygen-atom-transfer reagents (NO, trimethylamine -oxide (TMAO) and 2,3:5,6-dibenzo-7-azabicyclo[2.2.1]hepta-2,5-diene (dbabhNO)) yields the U mono-oxo complexes and . This methodology is optimized for direct translation to transuranic elements. Of the two ligands, the framework is most suitable for facilitating detailed bonding analysis and assessment of the ITI. Theoretical evaluation of the U-(NPC) bonding confirms a substantial difference between axially and equatorially bonded N atoms, revealing markedly more covalent U-N interactions. The U 6d + 5f combined contribution for U-N is nearly double that of U-N, accounting for ITI shortening and increased bond order of the axial bond. Two distinct N-atom hybridizations in the pyrrolidine/piperidine rings are noted across the complexes, with approximate sp and sp configurations describing the slightly shorter P-N and slightly longer P-N bonds, respectively. In all complexes, the ligands feature more planar N atoms than , in accordance with a higher electron-donating capacity of the former.
高价锕系元素化学的发展需要强大的方法来获取和全面表征反应性物种。我们最近证明，亚膦酰胺配体的还原性质支持 U 到 U 的两电子氧化，并建立了该配体的使用来评估锕系金属-配体多重键（MLMB）络合物中的逆反式影响（ITI）。为了将这种方法和分析扩展到锕系元素络合物，需要新的小规模合成策略和低对称配体衍生物来提高结晶度并减少晶体结构无序。为此，合成了两种新的亚膦酰胺配体[N═PBu(pip)]（）和[N═PBu(pyrr)]（）（pip = 哌啶基；pyrr = 吡咯烷基），打破了四价配合物[和]中的伪轴。这些配合物与两电子氧原子转移试剂（NO、三甲胺 -氧化物（TMAO）和 2,3:5,6-二苯并-7-氮杂双环[2.2.1]庚-2,5-二烯（dbabhNO））反应生成 U 单加氧配合物[和]。这种方法经过优化，可直接转化为锕系元素。在这两种配体中，[N═PBu(pip)] 的框架最适合于促进详细的成键分析和评估 ITI。对 U-(NPC)键合的理论评估证实了轴向和赤道键合的 N 原子之间存在显著差异，表明 U-N 相互作用具有明显的共价性。U 6d + 5f 对 U-N 的综合贡献几乎是 U-N 的两倍，这解释了 ITI 缩短和轴向键的键序增加。在整个配合物中，注意到在吡咯烷/哌啶环中的两个不同的 N 原子杂化，分别用近似 sp 和 sp 构型描述稍短的 P-N 和稍长的 P-N 键。在所有配合物中，[N═PBu(pip)] 的配体特征是 N 原子比[N═PBu(pyrr)] 的更平面，这与前者更高的电子供体能力一致。
