In our effort to discover novel selective and non-toxic agents effective against CRC, we synthesized a series of rhenium(I) tricarbonyl-based complexes with increased lipophilicity. Two of these novel compounds were discovered to possess remarkable anticancer, anti-angiogenic and antimetastatic activity in vivo (zebrafish-human HCT-116 xenograft model), being effective at very low doses (1-3 μM). At doses as high as 250 μM the complexes did not provoke toxicity issues encountered in clinical anticancer drugs (cardio-, hepato-, and myelotoxicity). In vivo assays showed that the two compounds exceed the anti-tumor and anti-angiogenic activity of clinical drugs cisplatin and sunitinib malate, and display a large therapeutic window.[1]

In another study, we reported a rhenium(II) dicarbonyl complex, which displayed better cytotoxicity against MCF-7 breast cancer cells than cisplatin.[2] We investigated later new synthetic routes to aerobically stable and substitutionally labile α-diimine rhenium(I) dicarbonyl complexes. The molecules were prepared in high yield from the cis–cis–trans-[Re(CO)₂(^tBu₂bpy)Br₂]⁻ anion ( where ^tBu₂bpy is 4,4′-di-tert-butyl-2,2′-bipyridine), which could be isolated from the one electron reduction of the corresponding 17-electron complex. Ligand substitution of Re(I) complexes proceeded via pentacoordinate intermediates capable of Berry pseudorotation. In addition to the cis–cis–trans-complexes, cis–cis–cis- (all cis) isomers were also formed. [Re(CO)₂(^tBu₂bpy)Br(L)] complexes may be considered as synthons for the preparation of a variety of new stable diamagnetic dicarbonyl rhenium cis-[Re(CO)₂]⁺ complexes, offering a convenient entry in the chemistry of the core.[3]