Ylide ligands as building blocks for bioactive group 11 metal complexes

Abstract

The reactivity of the phosphonium salt (cyanomethyl)triphenylphosphonium chloride and the ylide (triphenylphosphonio)cyanomethanide towards Group 11 metal complexes is described. Mononuclear neutral gold(I) and gold(III) complexes of the type [AuX{CH(CN)PPh3 }] or [AuX3 {CH(CN)PPh3 }] and cationic derivatives such as [AuL{CH(CN)PPh3 }]X have been prepared. Surprisingly, the cationic gold species could only be prepared with ligands with a large steric hindrance, such as bulky NHCs or the JohnPhos phosphine, in contrast to silver and copper derivatives, which have dimeric structures through the coordination of the metal to the cyano group of the ylide of a second complex. Bis(ylide) metal complexes have also been synthesised in which a different structure is observed for the gold complexes compared with the copper and silver complexes. Although gold forms mononuclear species, the silver complex presents a two-dimensional polymeric structure as a result of further coordination of the silver centre to the nitrogen atoms of cyano groups of further silver complexes. These complexes possess two chiral centres; the gold compound was obtained as a mixture of diastereoisomers, whereas the copper and silver derivatives afford only one diastereoisomer. These compounds were screened for their in vitro cytotoxic activity against the human lung carcinoma cell line (A549). The IC50 values reveal an excellent cytotoxic activity for these metal complexes compared with cisplatin.