Kumari Maya, Bera Sudip Kumar, Lahiri Goutam Kumar
Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai-400076, India.
Dalton Trans. 2021 Jul 21;50(28):9891-9903. doi: 10.1039/d1dt01488a.
The article deals with the sensitive electronic forms in accessible redox states of structurally and spectroscopically authenticated deprotonated 1,2-bis((1H-pyrrol-2-yl)methylene)hydrazine (H2LR, R = H) or 1,2-bis((3,5-dimethyl-1H-pyrrol-2-yl)methylene)hydrazine (H2LR, R = Me), a BODIPY analogue bridged diruthenium complex as a function of varying ancillary ligands. It involved rac-(acac)2RuIII(μ-LR 2-)RuIII(acac)21a, R = H; 1b, R = Me (S = 1, acac = acetylacetonate), rac-(bpy)2RuII(μ-L2-)RuII(bpy)22 22 (S = 0, bpy = 2,2'-bipyridine) and diastereomeric (pap)2RuII(μ-L2-)RuII(pap)22meso-3a2/rac-3b2 (S = 0, pap = phenylazopyridine). The crystal structure established the linkage of the conjugated -C5[double bond, length as m-dash]N2-N3[double bond, length as m-dash]C6- central unit with the two terminal deprotonated pyrrole units of coordinated L2-. The bridging L2- in 1a, 1b, 22, 3b2 and 3a2 was slightly twisted and planar with torsional angles of 41.54°, 42.91°, 37.38°, 35.33° and 0°, respectively, with regard to the central N2-N3 bond. The extent of twisting of the bridge followed an inverse relationship with the RuRu separation: 4.935/4.934 Å 1a/1b < 5.141 Å 22 < 5.201 Å 3b2 < 5.351 Å 3a2. This is also attributed to the intermolecular ππ/CHπ interactions between the nearby aromatic rings of L and bpy or pap in 22 or 32, respectively. The multiple redox steps of the complexes varied appreciably based on the σ-donating (acac) and π-acidic (bpy, pap) characteristics of the ancillary ligands. Experimental (structure, EPR) and theoretical (DFT) evaluation pertaining to the electronic forms of 1n, 2n and 3n demonstrated the preferential involvement of L based frontier orbitals in electron transfer processes even in combination with the redox facile ruthenium ion. This in turn highlighted its redox non-innocent feature as in the case of well-documented metal coordinated quinonoid, formazanate, diimine (bpy), azo (pap) and β-diketiminate functions.
本文研究了结构和光谱鉴定的去质子化1,2-双((1H-吡咯-2-基)亚甲基)肼(H2LR, R = H)或1,2-双((3,5-二甲基-1H-吡咯-2-基)亚甲基)肼(H2LR, R = Me)（一种BODIPY类似物桥连的二钌配合物）处于可及氧化还原态的敏感电子形式，该形式是辅助配体变化的函数。研究涉及rac-(acac)2RuIII(μ-LR 2-)RuIII(acac)2 1a, R = H; 1b, R = Me（S = 1，acac = 乙酰丙酮），rac-(bpy)2RuII(μ-L2-)RuII(bpy)22 22（S = 0，bpy = 2,2'-联吡啶）以及非对映体(pap)2RuII(μ-L2-)RuII(pap)22 meso-3a2/rac-3b2（S = 0，pap = 苯基偶氮吡啶）。晶体结构确定了共轭-C5[双键，长度为中虚线]N2-N3[双键，长度为中虚线]C6-中心单元与配位L2-的两个末端去质子化吡咯单元的连接。1a、1b、22、3b2和3a2中的桥连L2-相对于中心N2-N3键略有扭曲且呈平面状，扭转角分别为41.54°、42.91°、37.38°、35.33°和0°。桥连的扭曲程度与RuRu间距呈反比关系：4.935/4.934 Å 1a/1b < 5.141 Å 22 < 5.201 Å 3b2 < 5.351 Å 3a2。这也归因于22或32中L与bpy或pap的附近芳香环之间分别存在的分子间ππ/CHπ相互作用。配合物的多个氧化还原步骤根据辅助配体的σ供体（acac）和π酸性（bpy、pap）特征有明显变化。关于1n、2n和3n电子形式的实验（结构、电子顺磁共振）和理论（密度泛函理论）评估表明，即使与氧化还原易变的钌离子结合，基于L的前沿轨道在电子转移过程中也优先参与。这反过来突出了其氧化还原非惰性特征，如同在充分记录的金属配位醌类、甲臜类、二亚胺（bpy）、偶氮（pap）和β-二酮亚胺功能的情况一样。
