Mobile Metal-Metal Bonds: Studies on Mixed Valence Ir3 and Ir4 Clusters
Mobile Metal-Metal Bonds: Studies on Mixed Valence Ir3 and Ir4 Clusters
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DOI：
10.1021/ja00090a030
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发表时间：
1994-06
影响因子：
15
通讯作者：
Anne Venturelli;T. Rauchfuss
中科院分区：
文献类型：
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作者：
Anne Venturelli;T. Rauchfuss
用(C5Me~)IrCl2与(Me_3Si)_2反应生成阳离子簇合物(CsMes)41R4S4)2+(112+)和(C5Me5)31R3S~(2+)2+。对四Ir簇合物(112+)的结晶学表征表明，它是由互穿的Ir4和S4四面体组成的立方体模体。由于2.764(1)A的单一IrIv-1rIv键接触，Ir4核的理想四面体对称性发生了扭曲，四个IrIv-Ir11接触在3.5A几乎相等，而Ir11…Irll距离为3.683(1)A。变温1H核磁共振研究表明，(112+)是流动的，结合温度为13oC(400 MHz)，对应的AG*=57kJ/m o l。这一动态过程归因于Ir*v/IrIII内部自交换引起的金属-金属键的迁移。循环伏安研究表明，(112+)在-218 mV和-487 mV处与Ag/AgCl发生可逆单电子还原。钴对(1)~(2+)有化学还原作用，而中性团簇则能被HCl/02重新氧化。在固体(2)中，2+具有三方双锥结构的Ir3S2核，平均Ir-Ir接触数为2.82 8，Ira距离为2.28 A。循环伏安研究表明，该化合物在-712 mV和-993 mV处经历了两次单电子还原。钴还原(2)2+得到中性(21°)的深蓝色晶体。(21°)的变温核磁共振谱表现出动力学行为，在60oC(400 MHz)处发生聚合，对应于AG*=kJ/mol。这些结构动力学表明，IR3三角形三个边之间的非成键Ir-Ir相互作用发生了迁移。
The dicationic clusters ((CsMes)41r4S4)2+ ( (112+) and ((C5Me5)31r3S~)2+ were prepared by treatment of ( (C5Me~)IrCl2)2 with (Me3Si)zS followed by ion exchange chromatography. Crystallographic characterization of the tetrairidium cluster ( 112+ reveals a cubane motif consisting of interpenetrated Ir4 and S4 tetrahedra. The Ir4 core is distorted from idealized tetrahedral symmetry by virtue of a single IrIv-1rIv bonding contact of 2.764(1) A. The four IrIv-Irlll contacts are nearly equivalent at 3.5 A, while the Irlll...Irlll distance is 3.683( 1) A. Variable-temperature 1H NMR studies indicate that (112+ is fluxional with a coalescence temperature of 13 OC (400 MHz), corresponding to AG* = 57 kJ/mol. This dynamic process is attributed to migration of the metal-metal bond arising from internal Ir*v/IrIII self-exchange. Cyclic voltammetry studies of ( 112+ reveal a pair of reversible one-electron reductions at -21 8 and -487 mV vs Ag/AgCl. Chemical reduction of (1)2+ was effected with cobaltocene while the neutral cluster could be reoxidized with HC1/02. In the solid state (2)2+ features a trigonal-bipyramidal Ir3S2 core with average Ir-Ir contacts of 2.82 8, and Ira distances of 2.28 A. Cyclic voltammetry studies indicate that this closo dication undergoes two single electron reductions at -712 and -993 mV. Cobaltocene reduction of (2)2+ afforded dark blue crystals of neutral (21°. Variable-temperature lH NMR spectra of (21° reveal dynamic behavior, with coalescence at 60 OC (400 MHz), corresponding to AG* = 64 kJ/mol. These structural dynamics suggest migration of the nonbonding Ir-Ir interaction among the three edges of the Ir3 triangle.