Mondal Arpan, Price Christopher G T, Tang Jinkui, Layfield Richard A
Department of Chemistry, School of Life Sciences, University of Sussex, Brighton BN1 9QJ, U.K.
State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, P.R. China.
J Am Chem Soc. 2023 Sep 13;145(36):20121-20131. doi: 10.1021/jacs.3c07600. Epub 2023 Sep 1.
High-yield syntheses of the lanthanide dinitrogen complexes [(CpM)(μ-1,2-N)] (, M = Gd, Tb, Dy; Cp = 1,2,4-CBuH), in which the [N] ligands solely adopt the rare end-on or 1,2-bridging mode, are reported. The bulk of the -butyl substituents and the smaller radii of gadolinium, terbium, and dysprosium preclude formation of the side-on dinitrogen bonding mode on steric grounds. Elongation of the nitrogen-nitrogen bond relative to N is observed in , and their Raman spectra show a major absorption consistent with N═N double bonds. Computational analysis of identifies that the local symmetry of the metallocene units lifts the degeneracy of two 5d orbitals, leading to differing overlap with the π* orbitals of [N], a consequence of which is that the dinitrogen ligand occupies a singlet ground state. Magnetic measurements reveal antiferromagnetic exchange in and single-molecule magnet (SMM) behavior in . Ab initio calculations show that the magnetic easy axis in the ground doublets of and align with the {M-N═N-M} connectivity, in contrast to the usual scenario in dysprosium metallocene SMMs, where the axis passes through the cyclopentadienyl ligands. The [N] ligands in allow these compounds to be regarded as two-electron reducing agents, serving as synthons for divalent gadolinium, terbium, and dysprosium. Proof of principle for this concept is obtained in the reactions of with 2,2'-bipyridyl (bipy) to give [CpM(κ-bipy)] (, M = Gd, Tb, Dy), in which the lanthanide is ligated by a bipy radical anion, with strong metal-ligand direct exchange coupling.
报道了镧系双氮配合物[(CpM)(μ-1,2-N)]（M = Gd、Tb、Dy；Cp = 1,2,4-CBuH）的高产率合成方法，其中[N]配体仅采用罕见的端基或1,2-桥连模式。大量的叔丁基取代基以及钆、铽和镝的较小半径基于空间位阻原因阻止了侧基双氮键合模式的形成。在[具体配合物]中观察到相对于N₂的氮-氮键伸长，并且它们的拉曼光谱显示出与N═N双键一致的主要吸收峰。对[具体配合物]的计算分析表明，茂金属单元的局部对称性消除了两个5d轨道的简并性，导致与[N₂]的π*轨道有不同的重叠，其结果是双氮配体占据单重基态。磁性测量揭示了[具体配合物]中的反铁磁交换以及[具体配合物]中的单分子磁体（SMM）行为。从头算计算表明，[具体配合物]和[具体配合物]基态双重态中的磁易轴与{M-N═N-M}连接性对齐，这与镝茂金属SMM中的通常情况相反，在后者中该轴穿过环戊二烯基配体。[具体配合物]中的[N₂]配体使这些化合物可被视为双电子还原剂，作为二价钆、铽和镝的合成子。在[具体配合物]与2,2'-联吡啶（bipy）反应生成[CpM(κ-bipy)]（M = Gd、Tb、Dy）的过程中获得了这一概念的原理证明，其中镧系元素由联吡啶自由基阴离子配位，具有强的金属-配体直接交换耦合。
