Maji Somnath, Sarkar Biprajit, Patra Srikanta, Fiedler Jan, Mobin Shaikh M, Puranik Vedavati G, Kaim Wolfgang, Lahiri Goutam Kumar
Department of Chemistry, Indian Institute of Technology-Bombay, Powai, Mumbai-400076, India.
Inorg Chem. 2006 Feb 6;45(3):1316-25. doi: 10.1021/ic051532p.
Reaction of 3,6-diaryl-1,2,4,5-tetrazines (aryl = R = phenyl, 2-furyl or 2-thienyl) with 2 equiv of Ru(acac)2(CH3CN)2 results in reductive tetrazine ring opening to yield diruthenium complexes [(acac)2Ru(III)(dih-R(2-))Ru(III)(acac)2] bridged by the new 1,2-diiminohydrazido(2-) (dih-R(2-) = HNC(R)NNC(R)NH(2-)) ligands. rac/meso diastereoisomers could be detected and separated for the compounds with R = phenyl and 2-thienyl, all species are diamagnetic and were characterized by 1H NMR spectroscopy. Crystal structure determination of the meso isomers with R = phenyl and 2-thienyl confirmed the 1,2-diiminohydrazido formulation through long N-N (approximately 1.40 A) and short C=N(H) bonds (approximately 1.31 A), implying two bridged ruthenium(III) centers at about 4.765 A distance with strong antiferromagnetic coupling. The complexes undergo two reversible and well-separated one-electron reduction and oxidation processes, respectively. EPR Spectroscopy of the paramagnetic intermediates with comproportionation constants K(c) > 10(12) and UV-vis-NIR spectroelectrochemistry were used to identify the accessible redox states as [(acac)2Ru(II)(dih-R(2-))Ru(II)(acac)2]2-, [(acac)2Ru(II)(dih-R(-))Ru(II)(acac)2]-, [(acac)2Ru(III)(dih-R(2-))Ru(III)(acac)2], [(acac)2Ru(III)(dih-R(-))Ru(III)(acac)2]+, and [(acac)2Ru(III)(dih-R)Ru(III)(acac)2]2+. While the UV-vis-NIR spectroscopic response of (acac)2Ru(dih-R)Ru(acac)2 is very similar to that of (bpy)2Ru(adc-R)Ru(bpy)2, adc-R(2-) = 1,2-diacylhydrazido(2-), the EPR result indicating ligand-centered spin for [(acac)2Ru(II)(dih-R(*-))Ru(II)(acac)2]- despite deceptive NIR absorptions around 1400 nm reveals distinct differences in the electronic structures.
3,6-二芳基-1,2,4,5-四嗪（芳基 = R = 苯基、2-呋喃基或2-噻吩基）与2当量的Ru(acac)2(CH3CN)2反应，导致四嗪环发生还原开环，生成由新型1,2-二亚氨基肼基(2-)（dih-R(2-) = HNC(R)NNC(R)NH(2-)）配体桥连的二钌配合物[(acac)2Ru(III)(dih-R(2-))Ru(III)(acac)2]。对于R = 苯基和2-噻吩基的化合物，可以检测并分离出rac/内消旋非对映异构体，所有物种均为抗磁性，通过1H NMR光谱进行了表征。R = 苯基和2-噻吩基的内消旋异构体的晶体结构测定通过长的N-N键（约1.40 Å）和短的C=N(H)键（约1.31 Å）证实了1,2-二亚氨基肼基的结构，这意味着两个桥连的钌(III)中心距离约为4.765 Å，具有强反铁磁耦合。这些配合物分别经历两个可逆且分离良好的单电子还原和氧化过程。使用歧化常数K(c) > 10(12)的顺磁性中间体的EPR光谱和紫外可见近红外光谱电化学来确定可及的氧化还原态为[(acac)2Ru(II)(dih-R(2-))Ru(II)(acac)2]2-、[(acac)2Ru(II)(dih-R(-))Ru(II)(acac)2]-、[(acac)2Ru(III)(dih-R(2-))Ru(III)(acac)2]、[(acac)2Ru(III)(dih-R(-))Ru(III)(acac)2]+和[(acac)2Ru(III)(dih-R)Ru(III)(acac)2]2+。虽然(acac)2Ru(dih-R)Ru(acac)2的紫外可见近红外光谱响应与(bpy)2Ru(adc-R)Ru(bpy)2非常相似，adc-R(2-) = 1,2-二酰肼基(2-)，但EPR结果表明，尽管在1400 nm附近有欺骗性的近红外吸收，但[(acac)2Ru(II)(dih-R(*-))Ru(II)(acac)2]-的自旋以配体为中心，这揭示了电子结构上的明显差异。
