Neutral and Cationic NCN Pincer Platinum(II) Complexes with 1,3-Bis(benzimidazol-2′-yl)benzene Ligands: Synthesis, Structures, and Their Photophysical Properties

Abstract

A series of neutral pincer Pt(II) chloride complexes 3–7 were first synthesized via the reaction of 1,3-bis(N-substituted benzimidazol-2′-yl) benzene (bzimb) ligands 2a–e with K2PtCl4 in refluxing HOAc. By treatment of complex 3 with KI and aromatic terminal alkynes in methanolic NaOH, the Pt(II) iodide complex 8 and Pt(II) acetylide complexes 9–11 were then obtained. Cationic Pt(II) complexes 12–15 were finally produced by the chloro-substitution reaction of complex 3 with AgOTf and several neutral N-donor ligands. With these new compounds in hand, various characterizations including elemental analysis, NMR, and IR were carried out to investigate their properties. On the basis of the X-ray single-crystal structure analysis of complexes 3–5, 8, 9, and 12, weak intermolecular interactions including π···π stacking and/or hydrogen bonds were found to be responsible for their assembly. After full investigation of the electronic absorption and photoluminescent properties of the Pt(II) complexes 3–15, time-dependent density functional theory (TD-DFT) calculations were carried out to elucidate the origins of the UV–vis absorptions. We were delighted to find that the luminescence quantum yields in degassed CH2Cl2 solution were around 0.13 in most cases and the emission lifetimes were in the microsecond range, indicating that these complexes could be used as bright phosphorescent materials with various potential applications in the future.

Synthesis and crystal structures of N-H, N-phenyl and N-benzyl-2-(4-hexyloxyphenyl)benzimidazoles

“…Although the crystal structures of more than a thousand 2-arylbenzimidazoles have been published so far (Cambridge Structural Database, version 5.42 updated to November 2020; Groom et al, 2016), fewer than 20 of them (including a few metal complexes) contain ethoxy groups or longer chains attached to the aryl ring (Geiger et al, 2017;Rahman et al, 2012;Wadhwa et al, 2016;Yeap et al, 2009;Ha, 2012;Wang, Sun et al, 2014). It is interesting to note that 5-(2-(p-chlorophenylbenzimidazol-1-yl-methyl)-4-(2-methylphenyl)-2,4-dihydro-[1,2,4]-triazole-3-thione is isostructural with compound 2 (Karayel et al, 2015).…”

Synthesis and structure of an arylselenenium(II) cation, [C34H41N4Se+]2[Hg(SeCN)4]2−, based on a 5-tert-butyl-1,3-bis(1-pentyl-1H-benzimidazol-2-yl)benzene scaffold

“…As far as the synthesis of transition metal complexes with the bis-benzimidazole group is concerned, there are several reports in the literature for platinum(II) pincer complexes with similar kinds of scaffolds. Some of these were investigated for their photoluminescence properties (Wang et al, 2014;Dorazco-Gonzá lez, 2014;Chan et al, 2016). Recently, we also reported some palladium(II) pincer complexes with a 1,3bis(N-substituted benzimidazol-2 0 -yl)benzene-based ligand.…”

Synthesis, Photophysical Properties and Catalytic Activity of Ƙ3-SCS Pincer Palladium (II) Complex of N,N'-Di-Tert-Butylbenzene-1,3-Dicarbothioamide Supported by DFT Analysis

“…render a significant influence on the type of complex formed and metal-ligand stoichiometry [4,6]. Extensive studies have been carried out on several pincer ligands with various combinations of C, N, S and P donors and related palladium/platinum complexes have been investigated for their photophysical and catalytic properties [7][8][9][10][11][12]. Amongst the well-known pincer complexes, the thioamide based ligands with SCS type are relatively less explored compared to the others [13,14].…”