Coordination Complexes of Bismuth Triflates with Tetrahydrofuran and Diphosphine Ligands

The reaction of CH3OSO2CF3 (MeOTf) with BiBr3 in tetrahydrofuran (THF) yields (THF)2BiBr2(OTf) (1), which is converted to (dmpe)­BiBr2(OTf) (2Br) upon displacement of the THF ligands with bis­(dimethylphosphino)­ethane (dmpe). The chloride derivatives (dmpe)­BiCl2(OTf) (2Cl) and (dmpe)­BiCl­(OTf)2 (3) are obtained from the reaction of BiCl3 and dmpe with 1 and 2 equiv of Me3SiOSO2CF3 (TMSOTf), respectively. The complexes readily decompose in solution to give elemental bismuth and a mixture of products. The solid-state structures reveal dimeric units bridged by both triflate O–S–O interactions and weak Bi–X–Bi interactions (X = Cl, Br). Comparison of the solid-state structures illustrates that both cis and trans configurations of halides are possible in complexes of the form L2BiX2(OTf), depending upon the denticity of the ligand. The experimentally observed configurations are consistent with minima calculated at the MP2 level for the triflate-free cations in the gas phase. Examination of the MP2-calculated electronic structure of 3 reveals the presence of low-lying π-type orbitals that may result in Z-type ligand activity. However, the attempted coordination of 3 with the electron-rich metal center in K2PdCl4, via metal-to-ligand back-donation, leads instead to halide abstraction, giving [(dmpe)2Pd]­[(CH3CN)2Bi2Cl6(OTf)2] (8). The anion in 8 consists of two octahedral bismuth environments bridged along one edge by two triflate anions. The results illustrate new coordination chemistry for bismuth.三氟甲磺酸甲酯（methyl triflate, MeOTf）与三溴化铋（BiBr3）在四氢呋喃（tetrahydrofuran, THF）中反应，得到配合物(THF)₂BiBr₂(OTf)（1），其中OTf为三氟甲磺酰基（triflate）；将该配合物中的四氢呋喃配体替换为双(二甲基膦基)乙烷（bis(dimethylphosphino)ethane, dmpe），即可转化为(dmpe)BiBr₂(OTf)（2Br）。氯代衍生物(dmpe)BiCl₂(OTf)（2Cl）与(dmpe)BiCl(OTf)₂（3）可分别通过三氯化铋（BiCl3）、双(二甲基膦基)乙烷与1当量、2当量的三甲基硅基三氟甲磺酸盐（trimethylsilyl triflate, TMSOTf）反应制得。上述配合物在溶液中易发生分解，生成单质铋与多种产物的混合物。固态结构表征显示，配合物中存在由三氟甲磺酰基的O–S–O桥联作用与弱Bi–X–Bi相互作用（X=Cl、Br）共同稳定的二聚单元。对固态结构的对比分析表明，在L₂BiX₂(OTf)型配合物中，卤离子可采取顺式（cis）与反式（trans）两种构型，具体取决于配体的齿合度。实验观测到的构型与气相中无三氟甲磺酰基阳离子的二阶莫勒-普莱塞特微扰理论（Møller-Plesset perturbation theory of the second order, MP2）水平计算得到的能量极小值相符。对配合物3的MP2计算电子结构进行分析后发现，其存在低能级π型轨道，这可能使其具备Z型配体活性。然而，尝试通过金属到配体的反馈配位作用，使配合物3与K₂PdCl4中的富电子金属中心配位时，却发生了卤离子攫取反应，生成产物[(dmpe)₂Pd][(CH3CN)₂Bi₂Cl6(OTf)₂]（8）。产物8中的阴离子由两个八面体配位铋单元构成，两个单元通过一条边上的两个三氟甲磺酰基阴离子桥联。本研究结果揭示了铋的新型配位化学。