Synthesis and Characterization of Tetrahedral and Square Planar Bis(iminopyrrolyl) Complexes of Cobalt(II)

A series of 2-iminopyrrole ligand precursors with increasing bulkiness [HNC4H3C(R)N-2,6-R‘2C6H3] (R = R‘ =
H, 1a; R = Me, R‘= H, 1b; R = H, R‘ = Me, 1c; R = R‘ = Me, 1d; R = H, R‘ = iPr, 1e; R = Me, R‘ = iPr,
1f) were synthesized and deprotonated with NaH to give the corresponding iminopyrrolyl sodium salts 2a−f. A set
of homoleptic bis-ligand Co(II) complexes of the type [Co(κ2N,N‘-NC4H3C(R)N-2,6-R‘2C6H3)2] (R = R‘= H, 3a;
R = Me, R‘= H, 3b; R = H, R‘ = Me, 3c; R = R‘ = Me, 3d; R = H, R‘ = iPr, 3e; R = Me, R‘ = iPr, 3f) was
prepared by reaction of CoCl2 with the corresponding iminopyrrolyl sodium salts 2a−f. The new complexes were
characterized by elemental analysis, magnetic susceptibility measurements, in powder and in solution, UV/vis/NIR,
and, in some cases, X-ray crystallography. According to X-ray diffraction and magnetic measurements, the Co
complexes 3a−e proved to be tetrahedral, which is the preferred geometry for Co(II) compounds. However, a
square planar geometry is observed in the case of 3f, as determined by several characterization techniques. In this
case, DFT calculations suggest the square planar geometry is slightly more stable than the tetrahedral one probably
due to a combination of steric and electronic reasons.

一系列位阻逐渐增大的2-亚胺吡咯配体前驱体[HNC4H3C(R)N-2,6-R′2C6H3]（其中R=R′=H时记为1a；R=Me、R′=H时记为1b；R=H、R′=Me时记为1c；R=R′=Me时记为1d；R=H、R′=iPr时记为1e；R=Me、R′=iPr时记为1f）被成功合成，并经氢化钠（NaH）去质子化，得到对应的亚胺吡咯基钠盐2a~2f。通过二氯化钴（CoCl₂）与上述亚胺吡咯基钠盐2a~2f的反应，制备得到一系列通式为[Co(κ²N,N′-NC4H3C(R)N-2,6-R′2C6H3)2]的同配体双配体二价钴（Co(II)）配合物（其中R=R′=H时记为3a；R=Me、R′=H时记为3b；R=H、R′=Me时记为3c；R=R′=Me时记为3d；R=H、R′=iPr时记为3e；R=Me、R′=iPr时记为3f）。研究团队对上述新型配合物开展了元素分析、粉末及溶液态磁化率测试、紫外-可见-近红外（UV/vis/NIR）光谱表征，部分配合物还通过X射线单晶衍射（X-ray crystallography）进行了结构表征。基于X射线衍射与磁化率测试结果，配合物3a~3e均为四面体构型，这与二价钴化合物的优势配位几何一致；而配合物3f则呈现平面正方形构型，该结论通过多种表征技术得以证实。密度泛函理论（DFT）计算表明，此体系中平面正方形构型相较于四面体构型略具热力学稳定性，这可能源于位阻效应与电子效应的共同作用。