Homo- and Hetero-Oligonuclear Complexes of Platinum Group Metals (PGM) Coordinated by Imine Schiff Base Ligands

Abstract

Chemistry of Schiff base (SB) ligands began in 1864 due to the discovery made by Hugo Schiff (Schiff, H., Justus Liebigs Ann. der Chemie 1864, 131 (1), 118–119). However, there is still a vivid interest in coordination compounds based on imine ligands. The aim of this paper is to review the most recent concepts on construction of homo- and hetero-oligonuclear Schiff base coordination compounds narrowed down to the less frequently considered complexes of platinum group metals (PGM). The combination of SB and PGM in oligonuclear entities has several advantages over mononuclear or polynuclear species. Such complexes usually exhibit better electroluminescent, magnetic and/or catalytic properties than mononuclear ones due to intermetallic interactions and frequently have better solubility than polymers. Various construction strategies of oligodentate imine ligands for coordination of PGM are surveyed including simple imine ligands, non-innocent 1,2-diimines, chelating imine systems with additional N/O/S atoms, classic N2O2-compartmental Schiff bases and their modifications resulting in acyclic fused ligands, macrocycles such as calixsalens, metallohelical structures, nano-sized molecular wheels and hybrid materials incorporating mesoionic species. Co-crystallization and formation of metallophilic interactions to extend the mononuclear entities up to oligonuclear coordination species are also discussed.

Transition metal(II) complexes featuring push-pull dianionic Schiff base ligands: synthesis, crystal structure, electrochemical, and NLO studies

“…They are characterized by an imine group (>C=N-), which exhibits strong bands in infrared spectroscopy [4]. Schiff bases that usually coordinate to a metal center through the imine nitrogen atom, have been widely used as ligands in coordination chemistry [5][6][7][8]. This is due to their facile synthesis, structural flexibility, easily tunable electronic properties, associated with their diverse applications in various branches of science [9].…”

A Review on the Advancements in the Field of Metal Complexes with Schiff Bases as Antiproliferative Agents

“…In this case, the oxygen and nitrogen atoms on the sulfisoxazole ring, the oxygen atom of sulfonyl groups and oxygen and nitrogen atoms attached to the benzene ring are thought to be involved in the hydrogen bonds' formation. Ismail et al (2021) [49] studied several complexes in which the N 1 ,N 2 -bis(furan-2-ylmethylene)-4-methylbenzene-1,2-diamine (L) is complexed with several metals, namely Ag(I), Cr(III), Fe(III), Co(II), Cu(II) and Cd(II) (13)(14)(15)(16)(17)(18), and studied their cytotoxicity against the HepG2 cell lines. The IC 50 values were 12.9 µg/mL, 14.8 µg/mL, 7.31 µg/mL, 8.53 µg/mL, 17.1 µg/mL and 1.95 µg/mL, respectively.…”

“…Schiff bases, as well as diarylureas [8][9][10], have been defined as "privileged" ligands in organic synthesis, thanks to their affordability, easy synthesis and different biological activities and ability to form complexes with almost all metals [11][12][13]. Actually, they may form complexes with transition metals, platinum group metals (PGM) [14], lanthanides [15,16], and actinides [17,18] and many of them have been extensively described in the literature [19,20]. Metal complexes bearing in the structure a Schiff base are known for their numerous applications and biological activities including antimicrobial [21], antioxidant [22], antitumor [23], antinflammatory [24], and ureases inhibitors [25], and occupy a central role in the development of coordination chemistry [26][27][28].…”

Decoding Directing Groups and Their Pivotal Role in C−H Activation

“…Imines are one of the most applied organic functional groups, mainly identified by the presence of the C=N bond, [143] being present in several ligands [144][145][146][147][148] and bioactive compounds. [149,150] They can be synthesized from condensation between an amine and an aldehyde or ketone, [151] and they are usually unstable since they can be easily hydrolyzed to their original carbonyl form, either in a basic or acid environment.…”