The pincer ligand PPh(2-HSC 6 H 4 ) 2 reacts with GaCl 3 in the presence of triethylamine to yield the anionic gallium complex 4)] were obtained by reaction of PPh(2-HSC 6 H 4 ) 2 with trialkyl gallium compounds (GaMe 3 , Ga t Bu 3 ). Compound 4 is light-sensitive and decomposes in daylight or under UV irradiation. Three decomposition products could be isolated: tetranuclear hydrido-bridged mixed-valent gallium(II)-gallium(III) complex [Ga III {PPh(2-SC 6 H 4 )-k 2 S,P-m-(2-SC 6 H 4 )-kS 0 } 2 ] 2 (m 3 -H) 2 Ga II 2 (Ga-Ga) (5), gallium(II) complex [Ga{PPh(2-SC 6 H 4 ) 2 -k 3 S,S 0 ,P}] 2 (Ga-Ga) (6), and sulfido-bridged dinuclear complex [Ga{PPh(2-SC 6 H 4 ) 2 -k 3 S,S 0 ,P}] 2 (m-S) (7). The molecular structures of 2-7 are described.

In cancer therapy the platinum-based drugs are used frequently with a good clinical outcome, but besides unwanted side effects which occur, the tumour cells subjected to treatment are prone to develop tolerance or even multidrug resistance (MDR). Metal compounds with a central atom other than platinum are efficient in targeting the chemoresistant cells, therefore the biological outcome of two recently synthesized gallium phosphinoarylbisthiolato complexes was studied, having the formula [X][Ga{PPh(2-SC6H4)2-κ(3)S,S',P}{PPh(2-SC6H4)2-κ(2)S,S'}] where [X] is either the NEt3H (1) or PPh4 (2) cation. Compounds 1 and 2 display in vitro cytotoxicity against both platinum-sensitive and platinum-resistant cell lines (A2780 and A2780cis). Morphological and ultrastructural evidence points toward their capacity to impair tumour cells survival. This behaviour is based on malignant cells capacity to selectively intake gallium, and to bind to the cellular DNA. They are able to cause massive DNA damage in treated cancer cells, focusing on 7-methylguanine and 8-oxoguanine sites and oxidizing the pyrimidine bases; this leads to early apoptosis of a significant percent of treated cells. The intrinsic and extrinsic apoptotic pathways are influenced through the modulation of gene expression following the treatment with complexes 1 and 2, which accompanies the negative regulation of P-glycoprotein 1 (Pgp-1), an important cellular ABC-type transporter from the multidrug resistance (MDR) family. The studied Ga(III) compounds demonstrated the capacity to counteract the chemoresistance mechanisms in the tumours defiant to standard drug action. Compound 2 shows a good anticancer potential and it could represent an alternative to platinum-based drugs especially in the situation of standard treatment failure.

P(2‐SHC6H4)3 (PS3H3) reacts with GaMe3 (1:1) to give GaMe{P(2‐SC6H4)2(2‐SHC6H4)‐κ3S,S′,P} (1), which could be deprotonated with NEt3 to give [NEt3H][GaMe{P(2‐SC6H4)3‐κ3S,S′,P}] (2). The 1:2 reaction of E(2‐SHC6H4)3 [E = P (PS3H3), As (AsS3H3)] with GaMe3 gave the dinuclear complexes GaMe{E(2‐SC6H4)2(2‐S{GaMe2(THF)}C6H4)‐κ3S,S′,E} [E = P (3), As (4)]. Serendipitous hydrolysis of 4 resulted in small amounts of the hexanuclear gallium hydroxide complex cyclo‐{GaMe(μ‐OH)}6{As(2‐SC6H4)3‐κS,S′,S′′}2 (5). Complexes 1–4 were fully characterized, complexes 2–5 also by X‐ray crystallography.