Synthesis, antimicrobial activity, and catalytic activity of rhodium and iridium piano stool complexes: Teaching an old dog new tricks

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Virginia Tech


This dissertation describes the synthesis, antimicrobial properties, and catalytic activity of a variety of eta5-ligand rhodium and iridium complexes. CpRM(beta-diketonato)Cl (CpR = R-substituted tetramethylcyclopentadienyl ligand) complexes were found to have selective activity against Mycobacterium smegmatis, with activity highly dependent upon the substituents on the CpR ligand as well as on the beta-diketonato ligand. These complexes were synthesized in good yield from the reaction of the chloro bridged dimers ([CpRMCl2]2) with the desired beta-diketonato ligand under basic conditions. All complexes were fully characterized by 1H and 13C NMR. Twenty single crystal X-ray structures were solved.

The success of these syntheses led to investigation of another beta-diketonato ligand: 1,1,1,5,5,5-hexafluoroacetylacetonate (hfac). Though many metal complexes of this ligand are known, reaction with [CpMCl2]2 did not yield the desired CpM(hfac)Cl complexes. Instead, a variety of products were obtained, three of which were characterized crystallographically. The most interesting structure featured a non-coordinating trifluoroacetate (TFA) anion and a [CpIr]3Na1O4 cubane structure, which is an unprecedented and highly unusual arrangement for iridium. Attempts to synthesize this cluster rationally through reactions of [CpIrCl2]2 with TFA yielded instead a chloro bridged [CpIrCl(TFA)] dimer. Reaction of [CpMCl2]2 with 1,1,1-trifluoroacetylacetonate (tfac) yielded the expected CpM(tfac)Cl complex, indicating that the problem lies with using hfac as a ligand for CpM(III) complexes.

Finally, the indenyl effect was investigated for the oxidative annulation of 2-phenylimidazole with 1-phenyl-1-propyne catalyzed by a series of methyl-substituted [(indenyl)RhCl2] dimers. [(Ind*)RhCl2]2 was found to have significantly greater activity than [CpRhCl2]2 (100% vs. 51%). Two plausible catalytic cycles were proposed, one of which invokes a ring slip transition state. Though it is unclear if the "indenyl effect" is responsible for this differing activity, it is certainly apparent that using an indenyl ligand has a notable effect in this catalytic reaction. Cyclometalation was also investigated stoichiometrically for 2-phenyl-1H-imidazole and 1-phenylpyrazole and found to proceed readily for [(Ind)RhCl2]2. Additionally, the crystallographic structure of a Rh+ /Rh– ionic pair was solved. Ionic pairs such as this are rarely found in the literature.



rhodium, iridium, piano stool complex, antimicrobial agent, cluster, indenyl, indenyl effect, ring slip, catalysis, C-H activation, oxidative annulation