Versatile New <i>C</i>₃-Symmetric Tripodal Tetraphosphine Ligands; Structural Flexibility to Stabilize Cu^I and Rh^I Species and Tune Their Reactivity

The high-yielding synthesis and detailed characterization of two well-defined, linkage isomeric tripodal, tetradentate all-phosphorus ligands 1−3 is described. Coordination to CuI resulted in formation of complexes 4−6, for which the molecular structures indicate overall tridentate coordination to the copper atom in the solid state, with one dangling peripheral phosphine. The solution studies suggest fast exchange between the three phosphine side-arms. For these new CuI complexes, preliminary catalytic activity in the cyclopropanation of styrene with ethyldiazoacetate (EDA) is disclosed. The anticipated well-defined tetradentate coordination in a C3-symmetric fashion was achieved with RhI and IrI, leading to the overall five-coordinated complexes 7−12. Complex 11 has the norbornadiene (nbd) ligand coordinated in an unprecedented monodentate 2,3-η2 mode to Rh. Furthermore, unexpected but very interesting redox-chemistry and reactivity was displayed by the Rh(Cl)-complexes 7 and 8. Oxidation resulted in the formation of stable RhII metalloradicals [7]PF6 and [8]PF6 that were characterized by X-ray crystallography, magnetic susceptibility measurements, cyclic voltammetry, and electron paramagnetic resonance (EPR) spectroscopy. Subsequent redox-reactivity of these metalloradicals toward molecular hydrogen is described, resulting in the formation of RhIII hydride compounds.本文报道了两种结构明确、键合异构的三脚架型四齿全膦配体1−3的高产率合成与详细表征。将其与一价铜（CuI）配位得到配合物4−6，单晶分子结构显示，固态下该类配合物的铜原子均为三齿配位，且带有一个悬空的外围膦配体。溶液相研究表明，三个膦侧臂之间存在快速交换过程。针对这些新型一价铜配合物，本文还公开了其在苯乙烯与重氮乙酸乙酯（ethyldiazoacetate, EDA）的环丙烷化反应中的初步催化活性。通过与一价铑（RhI）和一价铱（IrI）配位，成功实现了预期的C3对称模式下的四齿配位，得到整体为五配位的配合物7−12。其中配合物11的降冰片二烯（norbornadiene, nbd）配体以前所未有的单齿2,3-η2配位模式与铑结合。此外，含氯一价铑配合物7和8展现出意外但极具研究价值的氧化还原化学与反应活性：氧化后生成稳定的铑(II)金属自由基[7]PF6和[8]PF6，通过X射线晶体衍射、磁化率测试、循环伏安法以及电子顺磁共振（electron paramagnetic resonance, EPR）波谱对其进行了表征。本文还报道了这些金属自由基与分子氢后续的氧化还原反应活性，该反应生成了铑(III)氢化物类化合物。