Organo-iridium compounds: synthesis, characterization and reactivity

Abstract

Today, few water-soluble organometallic compounds are known, and little research has been done in this area. Water-soluble organometallic complexes are of interest for two reactions. First, a water-soluble compound that could be developed as a catalyst eliminates the need for organic solvents and allows the catalyst to be easily recycled. Secondly, water-soluble compounds can be introduced into biological systems, and like the water-soluble complex cisplatin may show anticancer activity.

The compound, [lr(COD)(PMe3)3]CI (COD = 1,5-cyclooctadiene, Me = methyl), was synthesized and found to be water-soluble and fairly air-stable. Other water-soluble compounds, [lr(COD)(tripod)]CI, [lr(COD)(dmpe)]CI and [lrH(COD)(PMe3)3]CI2 [tripod = 1 ,1, 1-tris(diphenylphosphinomethyl)ethane, dmpe = (dimethylphosphino)ethane] were also synthesized by similar methods.

All of the water-soluble compounds prepared were characterized by nmr and/or x-ray crystallography. [lr(COD)(PMe3)3]CI was found to undergo intramolecular rearrangement in solution and have a square pyramidal structure, which is unique for five-coordinate organometallic compounds. lr(COD) (tripod)]CI was also fluxional in solution, but it had the trigonal bipyramidal structure, usually observed in five-coordinate compounds.

Several of the compounds synthesized were submitted to the National Cancer Institute for anticancer screening. Test results showed that the compounds exhibited some anticancer activity, but were non-selective towards a specific type of cancer. Nucleophilic addition reactions between [lr(COD)(PMe3)31CI and several nucleophiles were also studied.