Organometallic Nickelamacrocycles of the Type [(R2R‘P)Ni(C2H4COO)]n: Synthesis and Self-Assembly to Form Different Molecular Architectures Tuned by the Phosphine

The reaction of succinic anhydride with a 1:2 mixture of (cod)2Ni and a monodentate
phosphine generates reactive monomeric nickelalactones, which undergo rapid aggregation
to form cyclic oligomers of the composition [(R2R‘P)Ni(C2H4COO)]n (R2R‘P = EtPh2P (2), Me3P
(4), (i-Pr)3P (5), Cy3P (6), Et3P (7)). The complexes were fully characterized by elemental
analyses (except 4), NMR and IR spectroscopy, and X-ray crystallography of single crystals.
Depending on the bulkiness of the phosphines, three types of nickelamacrocycles with
different ring size and different connectivity pattern of the monomeric units are formed.
The small Me3P stabilizes a cyclic tetramer (n = 4) in which the units are linked by Ni−O−Ni bonds. This bridge is stable in thf solution. The bulkiest phosphines stabilize another
type of cyclotetrameric architecture in 2, 5, and 6, in which the monomeric units are connected
by Ni−O−CO bridges. In contrast, 7, stabilized by the Et3P ligand, forms a hexacyclic
compound (n = 6) with Ni−O−CO bridges. The IR spectrum of 7 in thf shows two CO
valence frequencies, indicating that at least two species are present in which the carboxylate
group is differently coordinated (Ni−O and Ni−O−CO−Ni coordination).

琥珀酸酐与（cod）2Ni的1:2混合物以及一价磷烷的反应，生成了具有活性的单镍代乳酸酮，这些乳酸酮迅速聚合成由组成[(R2R‘P)Ni(C2H4COO)]n（R2R‘P = EtPh2P (2), Me3P (4), (i-Pr)3P (5), Cy3P (6), Et3P (7)）的环状寡聚物。这些配合物通过元素分析（除4号外）、核磁共振波谱、红外光谱以及单晶X射线衍射进行了全面表征。根据磷烷的体积大小，形成了三种不同环尺寸和单体单元连接模式的不同镍大环化合物。体积较小的Me3P稳定了环状四聚体（n = 4），其中单元通过Ni−O−Ni键相连。此桥在四氢呋喃溶液中稳定。体积较大的磷烷在2、5和6号中稳定了另一种环状四聚体结构，其中单体单元通过Ni−O−C=O桥相连。相比之下，由Et3P配体稳定的7号化合物形成了一个六元环化合物（n = 6），其通过Ni−O−C=O桥连接。7号化合物在四氢呋喃中的红外光谱显示了两个C=O价频，表明至少存在两种物种，其中羧酸基团以不同的方式配位（Ni−O和Ni−O−C=O−Ni配位）。