Recent advances in stable main group element radicals: preparation and characterization

Radical species are significant in modern chemistry. Their unique chemical bonding and novel physicochemical properties play significant roles not only in fundamental chemistry, but also in materials science. Main group element radicals are usually transient due to their high reactivity. Highly stable radicals are often stabilized by π-delocalization, sterically demanding ligands, carbenes and weakly coordinating anions in recent years. This review presents the recent advances in the synthesis, characterization, reactivity and physical properties of isolable main group element radicals.

Broad Spectrum Functional Activity of Structurally Related Monoanionic Au(III) Bis(Dithiolene) Complexes

The biological properties of sixteen structurally related monoanionic gold (III) bis(dithiolene/diselenolene) complexes were evaluated. The complexes differ in the nature of the heteroatom connected to the gold atom (AuS for dithiolene, AuSe for diselenolene), the substituent on the nitrogen atom of the thiazoline ring (Me, Et, Pr, iPr and Bu), the nature of the exocyclic atom or group of atoms (O, S, Se, C(CN)₂) and the counter-ion (Ph₄P⁺ or Et₄N⁺). The anticancer and antimicrobial activities of all the complexes were investigated, while the anti-HIV activity was evaluated only for selected complexes. Most complexes showed relevant anticancer activities against Cisplatin-sensitive and Cisplatin-resistant ovarian cancer cells A2780 and OVCAR8, respectively. After 48 h of incubation, the IC₅₀ values ranged from 0.1–8 µM (A2780) and 0.8–29 µM (OVCAR8). The complexes with the Ph₄P⁺ ([P]) counter-ion are in general more active than their Et₄N⁺ ([N]) analogues, presenting IC₅₀ values in the same order of magnitude or even lower than Auranofin. Studies in the zebrafish embryo model further showed that, despite their marked anticancer effect, the complexes with [P] counter-ion exhibited low in vivo toxicity. In general, the exocyclic exchange of sulfur by oxygen or ylidenemalononitrile (C(CN)₂) enhanced the compounds toxicity. Most complexes containing the [P] counter ion exhibited exceptional antiplasmodial activity against the Plasmodium berghei parasite liver stages, with submicromolar IC₅₀ values ranging from 400–700 nM. In contrast, antibacterial/fungi activities were highest for most complexes with the [N] counter-ion. Auranofin and two selected complexes [P][AuSBu(=S)] and [P][AuSEt(=S)] did not present anti-HIV activity in TZM-bl cells. Mechanistic studies for selected complexes support the idea that thioredoxin reductase, but not DNA, is a possible target for some of these complexes. The complexes [P] [AuSBu(=S)], [P] [AuSEt(=S)], [P] [AuSEt(=Se)] and [P] [AuSeiPr(=S)] displayed a strong quenching of the fluorescence intensity of human serum albumin (HSA), which indicates a strong interaction with this protein. Overall, the results highlight the promising biological activities of these complexes, warranting their further evaluation as future drug candidates with clinical applicability.

Diselenolene proligands: reactivity and comparison with their dithiolene congeners

Selenophene and diselenine were synthesized from diselenolene proligands.

Halogen and chalcogen-bonding interactions in sulphur-rich π-electron acceptors

Sulphur and iodine heteroatoms on the acceptor skeleton induce chalcogen⋯chalcogen and halogen-bonding interactions.

Charge-transfer complexes of sulfur-rich acceptors derived from birhodanines

The title acceptors form charge-transfer complexes with mixed stacks, whose transistors are affected by the S–S interaction between the acceptors.

Diaminomaleonitrile as a versatile building block for the synthesis of 4,4′-biimidazolidinylidenes and 4,4′-bithiazolidinylidenes

Ring closure reactions of diaminomaleonitrile (DAMN) with electrophilic aryl isocyanates and aryl isothiocyanates lead to the formation of the target 5,5′-diimino-1,1′-diaryl-4,4′-biimidazolidinylidene-2,2′-diones 2a,b and 2,2′-diarylimino-4,4′-bithiazolidinylidenes 4a–e, respectively. The protocol provides a new strategy for the synthesis of a wide range of alkenes with two electron-donating and two withdrawing substituents of DAMN in moderate to good yields.

Bithiazolidinylidene polymers: synthesis and electronic interactions with transition metal dichalcogenides

We describe the synthesis of electron acceptors consisting of bithiazolidinylidene (BT) derivatives incorporated into solution processible polymers. Novel BT-containing polymers displayed p-doping behavior when in contact with the n-type transition metal dichalcogenide (TMDC) MoS2. A work function (WF) increase of MoS2, resulting from contact with BT polymers, was measured by Kelvin probe force microscopy (KPFM), representing the first example of polymer p-doping of MoS2, which is beneficial for advancing the design of electronically tailored TMDCs.

Chiral 1,2-dithiine as a sulfur rich electron acceptor

Both enantiomers of a 1,2-dithiine containing two 1-phenylethyl groups of the same chirality were selectively synthesized and electrochemically and spectro-electrochemically characterized.