Trifonov Alexander A, Mahrova Tatyana V, Luconi Lapo, Giambastiani Giuliano, Lyubov Dmitry M, Cherkasov Anton V, Sorace Lorenzo, Louyriac Elisa, Maron Laurent, Lyssenko Konstantin A
G. A. Razuvaev Institute of Organometallic Chemistry of Russian Academy of Sciences, Tropinina str. 49, 603950 Nizhny Novgorod, GSP-445, Russia.
Istituto di ChimicadeiCompostiOrganometallici (ICCOM - CNR), Via Madonna del Piano 10, 50019, Sesto Fiorentino, Italy.
Dalton Trans. 2018 Jan 30;47(5):1566-1576. doi: 10.1039/c7dt04299j.
A systematic study of reactions between CpYb(THF) (Cp = η-CMe, 1) and iminopyridine ligands (IPy = 2,6-PrCHN[double bond, length as m-dash]CH(CHN-R), R = H (2a), 6-CHO (2b), 6-CHS (2c), 6-CH (2d)) featuring similar electron accepting properties but variable denticity and steric demand, has provided a new example of steric control on the redox chemistry of ytterbocenes. The reaction of the unsubstituted IPy 2a with 1, either in THF or toluene, gives rise to the paramagnetic species CpYb(IPy)˙ (3a) as a result of a formal one-electron oxidation of the Yb ion along with IPy reduction to a radical-anionic state. The reactions of 1 with substituted iminopyridines 2b-d, bearing aryl or hetero-aryl dangling arms on the 6 position of the pyridine ring occur in a non-coordinating solvent (toluene) only and afford coordination compounds of a formally divalent ytterbium ion, coordinated by neutral IPy ligands CpYb(IPy) (3b-d). The X-ray diffraction studies revealed that 2a-c act as bidentate ligands; while the radical-anionic IPy in 3a chelates the Yb ion with both nitrogens, neutral IPy ligands in 3b and 3c participate in the metal coordination sphere through the pyridine nitrogen and O or S atoms from the furan or thiophene moieties, respectively. Finally, in complex 3d the neutral IPy ligand formally adopts a monodentate coordination mode. However, an agostic interaction between the Yb ion and an ortho C-H bond of the phenyl ring has been detected. Imino-nitrogens in 3b-d are not involved in the metal coordination. Variable temperature magnetic measurements on 3a are consistent with a multiconfigurational ground state of the Yb ion and suggest that the largest contribution arises from the 4f-radical configuration. For complexes 3b and 3c the data of magnetic measurements are indicative of a Yb-closed shell ligand electronic distribution. Complex 3d is characterized by a complex magnetic behavior which does not allow for an unambiguous estimation of its electronic structure. The results are rationalized using DFT and CSSCF calculations. Unlike diazabutadiene analogues, 3a does not undergo a solvent mediated metal-ligand electron transfer and remains paramagnetic in THF solution. On the other hand, complexes 3b-d readily react with THF to afford 1 and free IPy 2b-d.
对CpYb(THF)（Cp = η-CMe，1）与亚氨基吡啶配体（IPy = 2,6-PrCHN[双键，长度为m破折号]CH(CHN-R)，R = H (2a)，6-CHO (2b)，6-CHS (2c)，6-CH (2d)）之间反应的系统研究提供了一个关于茂镱氧化还原化学中空间控制的新例子，这些亚氨基吡啶配体具有相似的吸电子性质，但齿合度和空间需求不同。未取代的IPy 2a与1在四氢呋喃（THF）或甲苯中反应，由于Yb离子发生形式上的单电子氧化以及IPy还原为自由基阴离子态，生成顺磁性物种CpYb(IPy)˙ (3a)。1与在吡啶环6位带有芳基或杂芳基悬垂臂的取代亚氨基吡啶2b - d之间的反应仅在非配位溶剂（甲苯）中发生，并得到由中性IPy配体配位的形式上二价镱离子的配位化合物CpYb(IPy) (3b - d)。X射线衍射研究表明，2a - c作为双齿配体；虽然3a中的自由基阴离子IPy通过两个氮原子螯合Yb离子，但3b和3c中的中性IPy配体分别通过吡啶氮原子以及呋喃或噻吩部分的O或S原子参与金属配位球。最后，在配合物3d中，中性IPy配体形式上采用单齿配位模式。然而，已检测到Yb离子与苯环邻位C - H键之间存在agostic相互作用。3b - d中的亚氨基氮原子不参与金属配位。对3a进行的变温磁性测量与Yb离子的多组态基态一致，并表明最大贡献来自4f - 自由基构型。对于配合物3b和3c，磁性测量数据表明其具有Yb闭壳层配体电子分布。配合物3d的特征是具有复杂的磁性行为，这使得无法明确估计其电子结构。使用密度泛函理论（DFT）和完全活性空间自洽场（CSSCF）计算对结果进行了合理化解释。与二氮杂丁二烯类似物不同，3a不会发生溶剂介导的金属 - 配体电子转移，并且在THF溶液中保持顺磁性。另一方面，配合物3b - d很容易与THF反应生成1和游离的IPy 2b - d。
