Fakultät Chemie, Technische Unversität Dortmund, Otto-Hahn-Strasse 6, 44221 Dortmund, Germany.
Chemistry. 2011 Apr 4;17(15):4195-204. doi: 10.1002/chem.201002722. Epub 2011 Mar 8.
Pyrimidine (pym) ligands with their two endocyclic N-donor atoms provide 120° angles for molecular constructs, which, with the 90° angle metal fragments cis-a(2)M(II) (M=Pt, Pd; a=NH(3) or a(2)=diamine), form cyclic complexes known as metallacalix[n]arenes (with n=3, 4, 6, 8, …). The number of possible isomers of these species depends on the symmetry of the pym ligand. Although highly symmetrical (C(2v)) pym ligands form a single linkage isomer for any n and can adopt different conformations (e.g., cone, partial cone, 1,3-alternate, and 1,2-alternate in the case of n=4), low-symmetry pym ligands (C(s)) can produce a higher number of linkage isomers (e.g., four in the case of n=4) and a large number of different conformers. In the absence of any self-sorting bias, the number of possible species derived from a self-assembly process between cis-a(2)M(II) and a C(s)-symmetrical pym ligand can thus be very high. By using the C(s)-symmetric pym nucleobase cytosine, we have demonstrated that the number of feasible isomers for n=4 can be reduced to one by applying preformed building blocks such as cis-a(2)M(cytosine-N3)(2) or cis-[a(2)M(cytosinate-N1)(2)] (for the latter, see the accompanying paper: A. Khutia, P. J. Sanz Miguel, B. Lippert, Chem. Eur. J. 2011, 17, DOI: 10.1002/chem.2010002723) and treating them with additional cis-a(2)M(II) . Moreover, intramolecular hydrogen-bonding interactions between the O2 and N4H(2) sites of the cytosine ligands reduce the number of possible rotamers to one. This approach of the "directed" assembly of a defined metallacalix[4]arene is demonstrated.
嘧啶（pym）配体具有两个内环 N-供体原子，可为分子结构提供 120°角，与顺式-a(2)M(II)（M=Pt、Pd；a=NH(3)或 a(2)=二胺）的 90°角金属片段一起，形成称为金属杯芳烃（n=3、4、6、8、...）的环状配合物。这些物种的可能异构体的数量取决于 pym 配体的对称性。尽管高度对称（C(2v)）的 pym 配体为任何 n 形成单一连接异构体，并可采用不同构象（例如，n=4 时为锥形、部分锥形、1,3-交替和 1,2-交替），低对称 pym 配体（C(s)）可以产生更多的连接异构体（例如，n=4 时为四个）和大量不同的构象体。在没有任何自分类偏差的情况下，通过顺式-a(2)M(II)和 C(s)对称的 pym 配体之间的自组装过程衍生的可能物种的数量可能非常高。通过使用 C(s)对称的 pym 碱基胞嘧啶，我们已经证明，通过应用预先形成的构建块，如顺式-a(2)M(胞嘧啶-N3)(2)或顺式-[a(2)M(胞苷-N1)(2)]（对于后者，见伴随的论文：A. Khutia、P. J. Sanz Miguel、B. Lippert，Chem. Eur. J. 2011, 17, DOI: 10.1002/chem.2010002723）并对其进行额外的顺式-a(2)M(II)处理，n=4 的可行异构体的数量可以减少到一个。这种“定向”组装特定金属杯芳烃的方法得到了证明。
