Cd(II), Zn(II), and Pd(II) Complexes of an Isoindoline Pincer Ligand: Consequences of Steric Crowding

The sterically crowded isoindoline pincer ligand, 6‘-MeLH, prepared by condensation of 4-methyl-2-aminopyridine
and phthalonitrile, exhibits very different reaction chemistry with Cd2+, Zn2+, and Pd2+. Three different ligand
coordination modes are reported, each dependent upon choice of metal ion. This isoindoline binds to Cd2+ as a
charge-neutral, zwitterionic, bidentate ligand using imine and pyridine nitrogen atoms to form the eight-coordinate
fluxional complex, Cd(6‘-MeLH)2(NO3)2. In the presence of Zn2+, however, loss of a pyridine arm occurs through
solvolysis and tetrahedrally coordinated complexes are formed with coordination of pyrrole and pyridine nitrogen
atoms. Reaction with Pd2+ produces the highly distorted, square planar complex Pd(6‘-MeL)Cl in which a deprotonated
isoindoline anion coordinates as a tridentate pyridinium NNC pincer ligand.

由4-甲基-2-氨基吡啶与邻苯二甲腈经缩合反应制备得到的空间位阻较大的异吲哚啉钳形配体6'-MeLH，与Cd²+、Zn²+及Pd²+展现出截然不同的反应化学行为。本研究报道了三种不同的配体配位模式，其配位形式完全取决于所选用的金属离子。该异吲哚啉配体以电荷中性的两性离子双齿配体形式与Cd²+结合，通过亚胺氮原子与吡啶氮原子配位，形成八配位流变配合物Cd(6'-MeLH)₂(NO₃)₂。当体系中存在Zn²+时，配体的吡啶臂会通过溶剂解反应脱除，最终形成由吡咯氮原子与吡啶氮原子参与配位的四面体配位配合物。与Pd²+反应则生成高度畸变的平面正方形配合物Pd(6'-MeL)Cl，其中去质子化的异吲哚啉阴离子作为三齿吡啶鎓NNC钳形配体进行配位。