Emergence of comparable covalency in isostructural cerium(iv)- and uranium(iv)-carbon multiple bonds.
Emergence of comparable covalency in isostructural cerium(iv)- and uranium(iv)-carbon multiple bonds.
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DOI：
10.1039/c6sc00278a
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发表时间：
2016-05-01
期刊：
影响因子：
8.4
通讯作者：
Liddle ST
中科院分区：
文献类型：
--
作者：
Gregson M;Lu E;Tuna F;McInnes EJL;Hennig C;Scheinost AC;McMaster J;Lewis W;Blake AJ;Kerridge A;Liddle ST
与预期相反，铈（IV）-碳多重键相互作用中的共价性基本上与铀（IV）类似物一样共价。我们报告了在同结构卡宾配合物[M（BIPMTMS）（ODipp）2] [M = Ce（1），U（2），Th（3）; BIPMTMS = C（PPh 2NSiMe 3）2; Dipp = C6 H3 - 2，6-iPr 2]中铈-和铀-碳多重键的可比共价水平，而对于M = Th，MC键相互作用更离子化。通过单晶X射线衍射、核磁共振、红外光谱、电子顺磁共振、XANES光谱和超导量子干涉仪等手段，证实配合物1-3为真正的金属配合物。为了避免基于轨道的理论分析方法的不足，我们通过分析RASSCF和CASSCF导出的密度来探索1- 3的成键，该密度明确地处理轨道能量近简并和重叠对共价的贡献。对于这些络合物，发现铈（IV）和铀（IV）具有类似的共价水平，而钍（IV）被发现更具有离子性，并且在所采用的所有计算方法中独立地发现了这种趋势。计算确定的这些Ce → U > Th体系的共价性趋势也在1-3与MCl 4盐的实验交换反应中重现，其中1和2不与ThCl 4交换，但3与MCl 4（M = Ce，U）交换，1和2分别与UCl 4和CeCl 4反应以建立平衡。因此，这项研究提供了补充的理论和实验证据，对比公认的描述，一般镧系元素-配体键合在非零氧化态配合物是压倒性的离子，但铀是共价键。
Against expectations the covalency in a cerium(iv)–carbon multiple bond interaction is essentially as covalent as the uranium(iv) analogue. We report comparable levels of covalency in cerium– and uranium–carbon multiple bonds in the iso-structural carbene complexes [M(BIPMTMS)(ODipp)2] [M = Ce (1), U (2), Th (3); BIPMTMS = C(PPh2NSiMe3)2; Dipp = C6H3-2,6-iPr2] whereas for M = Th the MC bond interaction is much more ionic. On the basis of single crystal X-ray diffraction, NMR, IR, EPR, and XANES spectroscopies, and SQUID magnetometry complexes 1–3 are confirmed formally as bona fide metal(iv) complexes. In order to avoid the deficiencies of orbital-based theoretical analysis approaches we probed the bonding of 1–3via analysis of RASSCF- and CASSCF-derived densities that explicitly treats the orbital energy near-degeneracy and overlap contributions to covalency. For these complexes similar levels of covalency are found for cerium(iv) and uranium(iv), whereas thorium(iv) is found to be more ionic, and this trend is independently found in all computational methods employed. The computationally determined trends in covalency of these systems of Ce ∼ U > Th are also reproduced in experimental exchange reactions of 1–3 with MCl4 salts where 1 and 2 do not exchange with ThCl4, but 3 does exchange with MCl4 (M = Ce, U) and 1 and 2 react with UCl4 and CeCl4, respectively, to establish equilibria. This study therefore provides complementary theoretical and experimental evidence that contrasts to the accepted description that generally lanthanide–ligand bonding in non-zero oxidation state complexes is overwhelmingly ionic but that of uranium is more covalent.
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