Darensbourg Donald J, Wildeson Jacob R, Lewis Samuel J, Yarbrough Jason C
Department of Chemistry, Texas A&M University, College Station, Texas 77843, USA.
J Am Chem Soc. 2002 Jun 19;124(24):7075-83. doi: 10.1021/ja020184c.
The reaction of CdN(SiMe(3))(2) with 2 equiv of the corresponding phenol in toluene has led to the isolation of Cd(O-2,6-R(2)C(6)H(3))(2) derivatives, where R represents the sterically bulky (t)Bu and Ph substituents. The dimeric nature of these complexes in the solid state has been established via X-ray crystallography, i.e., trigonal geometry around cadmium is observed in 1 (R = (t)Bu) where the two cadmium centers are bridged by two phenoxides with each metal containing a terminal phenoxide. Complex 2 (R = Ph) contains an additional interaction of the metal centers with carbon atoms of the aromatic substituents on the phenoxide ligands. These dimeric structures are maintained in weakly coordinating solvents as revealed by (113)Cd NMR in d(2)-methylene chloride, which displays (111)Cd-(113)Cd coupling. Nevertheless, because of the excessive steric requirements of these phenoxide ligands, these dimers are easily disrupted in solution by weak donor ligands such as epoxides. Three bisepoxide adducts have been isolated as crystalline solids and characterized by X-ray crystallography. As previously observed in other Cd(O-2,6-(t)Bu(2)C(6)H(3))(2) x L(2) complexes, these epoxide adducts adopt a crystallographically imposed square-planar geometry about the cadmium centers, with the exception of the exo-2,3-epoxynorbornane derivative, which displays a distorted tetrahedral geometry. Temperature-dependent (113)Cd NMR studies have established that there is little difference in the binding abilities of these epoxides with either complex 1 or complex 2. Importantly, it is concluded from these studies that the lack of reactivity of alpha-pinene oxide and exo-2,3-epoxynorbornane toward copolymerization reactions with carbon dioxide, in the presence of zinc bisphenoxide catalysts, is not due to differences in epoxide metal binding. This is further affirmed by the isolation and crystallographic characterization of the very stable Zn(O-2,6-(t)Bu(2)C(6)H(3))(2) x (exo-2,3-epoxynorbornane)(2) derivative.
在甲苯中，CdN(SiMe(3))(2)与2当量的相应苯酚反应，分离得到了[Cd(O-2,6-R(2)C(6)H(3))(2)]衍生物，其中R代表空间位阻较大的(t)Bu和Ph取代基。通过X射线晶体学确定了这些配合物在固态下的二聚性质，即在1（R = (t)Bu）中观察到镉周围的三角几何构型，其中两个镉中心由两个酚盐桥连，每个金属含有一个末端酚盐。配合物2（R = Ph）中金属中心与酚盐配体上芳基取代基的碳原子存在额外的相互作用。如在d(2)-二氯甲烷中的(113)Cd NMR所示，这些二聚结构在弱配位溶剂中得以保持，显示出(111)Cd-(113)Cd耦合。然而，由于这些酚盐配体的空间位阻过大，这些二聚体在溶液中很容易被弱供体配体如环氧化物破坏。已分离出三种双环氧化物加合物作为晶体固体，并通过X射线晶体学进行了表征。如之前在其他Cd(O-2,6-(t)Bu(2)C(6)H(3))(2)·L(2)配合物中观察到的那样，这些环氧化物加合物在镉中心周围呈现出晶体学强制的平面正方形几何构型，但外-2,3-环氧降冰片烷衍生物除外，它呈现出扭曲的四面体几何构型。温度依赖的(113)Cd NMR研究表明，这些环氧化物与配合物1或配合物2的结合能力几乎没有差异。重要的是，从这些研究中得出结论，在双酚锌催化剂存在下，α-蒎烯氧化物和外-2,3-环氧降冰片烷对与二氧化碳的共聚反应缺乏反应性，并非由于环氧化物与金属结合的差异。非常稳定的Zn(O-2,6-(t)Bu(2)C(6)H(3))(2)·(外-2,3-环氧降冰片烷)(2)衍生物的分离和晶体学表征进一步证实了这一点。
