Charge-Delocalized κ²<i>C</i>,<i>N</i>‑NHC-Amine Complexes of Rhodium, Iridium, and Ruthenium

The development of a novel set of complexes bearing an NHC-amine ligand (CNHC-NH2) is described. M­(cod) complexes (M = Ir, Rh) and a Ru complex have been synthesized in which three different coordination modes of the ligand were established: monodentate, neutral bidentate, and anionic bidentate. The anionic bidentate coordination mode of the anionic CNHC-NH– ligand arises from deprotonation of the amine moiety of the neutral CNHC-NH2 ligand. Ligand deprotonation proved to be reversible for the Rh and Ir complexes, as was shown by subsequent treatment of the complexes with base and acid. The structural parameters of these differently coordinated ligands were examined, and it was shown that the conjugation of the aniline ring plays a major role in determining the ligand properties. Structural parameters derived from DFT calculations confirm delocalization of the anionic charge over the ligand framework, as is clear from a comparison of the (hypothetical) neutral bidentate complexes [M­(cod)­(κ2C,N-{CNHC-NH2})]+ with those of the (synthesized) monoanionic complexes [M­(cod)­(κ2C,N-{CNHC-NH})] (M = Rh, Ir). A similar trend in the structure and bond lengths of the aniline rings was found in the solid-state structure of the novel dimeric complex [(Ru­(κ2C,N-{CNHC-NH})­(κ2C,N-{CNHC-NH2})­Cl)2(μ-Cl)]­(PF6). The octahedral d5 ruthenium­(III) centers in this complex both contain a neutral bidentate CNHC-NH2 ligand as well as an anionic bidentate CNHC-NH– ligand. Quite remarkably, the complex is diamagnetic, arising from antiferromagnetic coupling of the two low-spin ruthenium­(III) centers over the chloride linker. DFT calculations indeed confirm that the open-shell singlet electronic structure is most stable.本文报道了一类新型含氮杂环卡宾-胺配体（NHC-amine ligand）CNHC-NH2的配合物的研发工作。成功合成了M(cod)型配合物（M=铱(Ir)、铑(Rh)）以及一种钌(Ru)配合物，该配体在其中存在三种不同的配位模式：单齿配位、中性双齿配位与阴离子双齿配位。 阴离子型CNHC-NH–配体的阴离子双齿配位模式，源于中性CNHC-NH2配体的胺基质子脱除。实验证实，铑与铱配合物的配体脱质子过程具有可逆性，通过后续用碱与酸处理该类配合物即可验证这一点。 研究人员对上述不同配位模式的配体结构参数进行了系统考察，结果表明苯胺环的共轭效应对配体性质具有决定性影响。通过密度泛函理论（DFT）计算得到的结构参数证实，阴离子电荷在配体骨架上存在离域现象：对比假想的中性双齿配合物[M(cod)(κ2C,N-{CNHC-NH2})]+与已合成的单阴离子配合物[M(cod)(κ2C,N-{CNHC-NH})]（M=Rh、Ir）的结构，即可清晰观察到这一特征。 在新型二聚配合物[(Ru(κ2C,N-{CNHC-NH})(κ2C,N-{CNHC-NH2})Cl)2(μ-Cl)](PF6)的固态结构中，同样观测到了苯胺环结构与键长的相似变化趋势。该配合物中的八面体d5构型钌(III)中心，同时结合了一个中性双齿CNHC-NH2配体与一个阴离子双齿CNHC-NH–配体。值得注意的是，该配合物呈现反磁性，这源于两个低自旋钌(III)中心通过氯桥联配体发生的反铁磁耦合作用。密度泛函理论（DFT）计算同样证实，开壳层单重态电子结构为该体系的最稳定构型。