Azadipyrromethene Complexes of d⁸ Metal Centers: Rhodium(I), Iridium(I), Palladium(II), and Platinum(II)

Azadipyrromethenes are blue pigments that chelate main-group and d-block Lewis acids. Reported here are azadipyrromethene complexes of d8 metal centers. The new compounds are prepared in salt metathesis reactions with chlorinated organometallic precursors. Sixteen new complexes are reported. The principal absorption features are an intense peak near 600 nm and transitions in the ultraviolet; all are characteristic of the azadipyrromethene chromophore. All compounds are dark solids that yield blue or blue-violet solutions. Ten complexes are crystallographically characterized. The structures uniformly show backbone strain, with a meso-nitrogen atom that dilates from pure sp2-hybridization. Structural comparisons are made to related dipyrromethene and tetra-azaporphyrin complexes. The electron-donating capacity of azadipyrromethene ligands is evaluated from CO stretching frequencies of three rhodium­(I) carbonyl complexes and from density-functional theory calculations. Frontier orbitals are confined to the azadipyrromethene ligand. HOMO–LUMO energy gaps are almost unperturbed from those of the free, anionic azadipyrromethene.氮杂二吡咯甲川（azadipyrromethenes）是一类蓝色色素，可与主族元素及d区路易斯酸发生螯合作用。本文报道了一系列d8金属中心的氮杂二吡咯甲川配合物。该类新型化合物通过氯化有机金属前驱体的盐复分解反应制备得到，共报道16种新型配合物。其主要吸收特征为600 nm附近的强吸收峰与紫外区电子跃迁，所有吸收均符合氮杂二吡咯甲川生色团的特征。所有目标化合物均为深色固体，其溶液呈蓝色或蓝紫色。其中10种配合物经晶体学表征，晶体结构均表现出骨架张力，其中介位氮原子偏离纯sp²杂化状态，发生键长扩张。本文还将该类配合物与相关二吡咯甲川及四氮杂卟啉配合物进行了结构对比。通过三种羰基铑(I)配合物的C≡O伸缩振动频率，以及密度泛函理论（density-functional theory, DFT）计算，评估了氮杂二吡咯甲川配体的给电子能力。前线轨道（Frontier orbitals）均局域于氮杂二吡咯甲川配体上。其最高占据分子轨道（Highest Occupied Molecular Orbital, HOMO）-最低未占据分子轨道（Lowest Unoccupied Molecular Orbital, LUMO）能隙与游离阴离子态氮杂二吡咯甲川的能隙几乎无明显扰动。