Department of Chemistry, Jahangirnagar University, Dhaka 1342, Bangladesh.
Institut für Anorganische Chemie und Strukturchemie, Universität Düsseldorf, Universitätsstr. 1, D-40225 Düsseldorf, Germany.
Molecules. 2022 Dec 25;28(1):172. doi: 10.3390/molecules28010172.
Condensation of 2-hydroxybenzaldehyde (salicylaldehyde) or 2-hydroxy-1-naphthaldehyde with 2-ethylaniline yields the Schiff base compound of ()-2-(((2-ethylphenyl)imino)methyl)phenol (HL) or ()-1-(((2-ethylphenyl)imino)methyl)naphthalen-2-ol (HL), which in turn react with the dinuclear complex of [Rh(η-cod)(µ-OCCH)] (cod = cycloocta-1,5-diene) to afford the mononuclear (η-cod){()-2-(((2-ethylphenyl)imino)methyl)phenolato-κN,O}rhodium(I), [Rh(η-cod)(L)] () or (η-cod){()-1-(((2-ethylphenyl)imino)methyl)naphthalen-2-olato-κN,O}rhodium(I), [Rh(η-cod)(L)] () (L or L = deprotonated Schiff base ligand). The X-ray structure determination revealed that the HL exists in the solid state not as the usual (imine)N···H-O(phenol) form (enolamine form) but as the zwitterionic (imine)N-H···O(phenol) form (ketoamine form). H NMR spectra for HL in different solvents demonstrated the existence of keto-enol tautomerism (i.e., keto ⇆ enol equilibrium) in solution. The structure for and showed that the deprotonated Schiff base ligand coordinates to the Rh(η-cod)-fragment as a six-membered N^O-chelate around the rhodium atom with a close-to-square-planar geometry. Two symmetry-independent molecules (with Rh1 and Rh2) were found in the asymmetric unit in in a structure with Z' = 2. The supramolecular packing in HL was organized by π-π and C-H···π contacts, while only two recognized C-H···π contacts were revealed in and . Remarkably, there were reciprocal or pairwise C-H···π contacts between a pair of each of the symmetry-independent molecules in . This pairwise C-H contact to the Rh-N^O chelate (metalloaromatic) ring may be a reason for the two symmetry-independent molecules in . Differential scanning calorimetry (DSC) analyses revealed an irreversible phase transformation from the crystalline-solid to the isotropic-liquid phase and subsequently confirmed the thermal stability of the compounds. Absorption spectra in solution were explained by excited state properties from DFT/TD-DFT calculations.
2-羟基苯甲醛（水杨醛）或 2-羟基-1-萘醛与 2-乙基苯胺缩合得到（）-2-（（2-乙基苯基）亚氨基）甲基）苯酚（HL）或（）-1-（（2-乙基苯基）亚氨基）甲基）萘-2-醇（HL）的席夫碱化合物，后者反过来与双核配合物[Rh（η-cod）（µ-OCCH）]（cod = 环辛-1,5-二烯）反应，得到单核（η-cod）{（）-2-（（2-乙基苯基）亚氨基）甲基）苯并呋喃）），[Rh（η-cod）（L）]（）或（η-cod）{（）-1-（（2-乙基苯基）亚氨基）甲基）萘-2-醇ato-κN，O}铑（I），[Rh（η-cod）（L）]（）（L 或 L = 去质子化的席夫碱配体）。X 射线结构测定表明，HL 在固态中不是通常的（亚胺）N···H-O（苯酚）形式（烯醇胺形式），而是两性离子（亚胺）N-H···O（苯酚）形式（酮胺形式）。HL 在不同溶剂中的 1H NMR 谱表明，在溶液中存在酮-烯醇互变异构（即酮 ⇆ 烯醇平衡）。和 的结构表明，去质子化的席夫碱配体作为六元 N^O-螯合配体围绕铑原子配位，具有近乎正方形平面的几何形状。在不对称单元中发现了两个对称独立的分子（具有 Rh1 和 Rh2），在结构中具有 Z'=2。HL 的超分子堆积由π-π 和 C-H···π 接触组织，而在 中仅揭示了两个公认的 C-H···π 接触。值得注意的是，在每个对称独立分子之间存在一对相互或成对的 C-H···π 接触。这种对称独立分子之间的对 C-H···π 接触到 Rh-N^O 螯合（金属芳香）环可能是中的两个对称独立分子的原因。差示扫描量热法（DSC）分析表明，从结晶固态到各向同性液态的不可逆相转变，随后证实了化合物的热稳定性。溶液中的吸收光谱通过 DFT/TD-DFT 计算解释了激发态性质。
