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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >Dinuclear iridium and rhodium complexes with bridging arylimidazolide-N-3,C-2 ligands: synthetic, structural, reactivity, electrochemical and spectroscopic studies
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Dinuclear iridium and rhodium complexes with bridging arylimidazolide-N-3,C-2 ligands: synthetic, structural, reactivity, electrochemical and spectroscopic studies

机译：具有桥联芳酰亚胺-N-3，C-2配体的双核铱和铑配合物：合成，结构，反应性，电化学和光谱研究

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摘要

Deprotonation of 1-arylimidazoles (aryl = mesityl (Mes), 2,6-diisopropylphenyl (Dipp)), with n-butyl lithium afforded the corresponding derivatives (1-aryl-1H-imidazol-2-yl) lithium (1a, Ar = Mes; 1b, Ar = Dipp) in good yield. Reaction of 1a with 0.5 equiv. of [Ir(cod)(mu-Cl)](2) yielded two geometrical isomers of a doubly C-2, N-3-bridged dinuclear complex [Ir(cod){mu-C3H2N2(Mes)-kappa C-2,kappa N-3}](2) (3), 3(H-H), a head-to-head (H-H) isomer of C-S symmetry, and 3(H-T), the thermodynamically preferred head-to-tail (H-T) isomer of C-2 symmetry. The metallated carbon of the 4 electron donor anionic bridging ligands has some carbene character, reminiscent of the situation in N-metallated protic NHC complexes. Displacement of cod ligands from 3(H-H) and 3(H-T) afforded the tetracarbonyl complexes [Ir(CO)(2){mu-C3H2N2(Mes)-kappa C-2,kappa N-3}](2) 4(H-H) and 4(H-T), respectively. The reaction with PMe3, which gave only one complex, [Ir(CO)(PMe3){mu-C3H2N2( Mes)-kappa C-2,kappa N-3}](2) (5), demonstrates that the isomerization of the central core Ir[mu-C3H2N2(Mes)-kappa C-2,kappa N-3] 2Ir from H-H to H-T on going from 4(H-H) to 5 is readily triggered by phosphine substitution under mild conditions. Oxidative-addition of MeI to 5 afforded the formally metal-metal bonded d(7)-d(7) complex [Ir-2(CO)(2)(PMe3)(2)(Me)I{mu-C3H2N2(Mes)-kappa C-2,kappa N-3}(2)] (6). The blue [Ir(C2H4)(2){mu-C3H2N2(Mes)-kappa C-2,kappa N-3}](2) (7) and purple [Rh(C2H4)(2){mu-C3H2N2(Dipp)-kappa C-2,kappa N-3}](2) (9) tetraethylene complexes were also obtained with only a H-T arrangement of the bridging ligands. Although only modestly efficient in alkane dehydrogenation, complex 7 was found to be a more active pre-catalyst than 3(H-T), 4(H-T) and 5, probably because of the favorable lability of the ethylene ligands. From cyclic voltammetry, exhaustive coulometry and spectroelectrochemistry studies, it was concluded that 3(H-T) undergoes a metal-based one electron oxidation to generate the mixed-valent Ir(I)/Ir(II) system. The energy of the intervalence band for the orange dirhodium complex [Rh(cod){mu-C3H2N2(Mes)-kappa C-2,kappa N-3}](2) (8) is shifted toward lower energies in comparison with 3(H-T), reflecting the decrease of the energy with the intermetallic distance. It was concluded from the EPR study that the Ir and Rh centres contribute substantially to the experimental magnetic anisotropy and thus to the singly occupied molecular orbital (SOMO) in the mixed-valent Ir(I)/Ir(II) and Rh(I)/Rh(II) systems. The molecular structures of 3(H-H), 3(H-T), 8 and 9 have been determined by X-ray diffraction.
机译：用正丁基锂对1-芳基咪唑（芳基=甲磺酰基（Mes），2,6-二异丙基苯基（Dipp））进行质子化反应，得到相应的衍生物（1-芳基-1H-咪唑-2-基）锂（1a，Ar = Mes; 1b，Ar = Dipp），收率良好。 1a与0.5当量的反应[Ir（cod）（mu-Cl）]（2）的合成产生了两个C-2，N-3-桥联双核络合物[Ir（cod）{mu-C3H2N2（Mes）-kappa C-2 ，kappa N-3}]（2）（3），3（HH）（CS对称的头对头（HH）异构体）和3（HT）（热力学上优选的头对尾（HT）） C-2对称性的异构体。 4个电子给体阴离子桥联配体的金属化碳具有一定的卡宾特性，让人联想到N-金属化质子NHC配合物的情况。从3（HH）和3（HT）置换cod配体得到四羰基配合物[Ir（CO）（2）{mu-C3H2N2（Mes）-kappa C-2，kappa N-3}]（2）4（ HH）和4（HT）。与PMe3的反应仅产生一种络合物[Ir（CO）（PMe3）{mu-C3H2N2（Mes）-kappa C-2，kappa N-3}]（2）（5），证明了在温和条件下，磷化氢很容易触发从4HH到5HH到HT的中心核Ir [mu-C3H2N2（Mes）-κC-2，κN-3] 2Ir。将MeI氧化加成5可得到形式上呈金属-金属键的d（7）-d（7）络合物[Ir-2（CO）（2）（PMe3）（2）（Me）I {mu-C3H2N2（Mes ）-κC-2，κN-3}（2）]（6）。蓝色的[Ir（C2H4）（2）{mu-C3H2N2（Mes）-kappa C-2，kappa N-3}]（2）（7）和紫色的[Rh（C2H4）（2）{mu-C3H2N2（还获得了仅具有桥联配体的HT排列的Dipp）-κC-2，κN-3}]（2）（9）四亚乙基配合物。尽管在烷烃脱氢中仅适度有效，但发现配合物7是比3（H-T），4（H-T）和5更具活性的预催化剂，这可能是由于乙烯配体的不稳定性所致。从循环伏安法，详尽的库仑法和光谱电化学研究中得出的结论是，3（H-T）经历了基于金属的单电子氧化，以生成混合价Ir（I）/ Ir（II）系统。橙ho络合物[Rh（cod）{mu-C3H2N2（Mes）-kappa C-2，kappa N-3}]（2）的间隔带的能量与3相比移向较低的能量（HT），反映了随着金属间距离能量的减少。从EPR研究得出的结论是，Ir和Rh中心在很大程度上影响了实验的磁各向异性，从而对混合价Ir（I）/ Ir（II）和Rh（I）中的单分子轨道（SOMO）产生了影响/ Rh（II）系统。通过X射线衍射确定了3（H-H），3（H-T），8和9的分子结构。

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