The 'Indenyl Effect' in iridium(I) olefin complexe

The complexes CpIr($etasp2$-C$sb8$H$sb{14}$)CO and ($etasp5$-C$sb9$H$sb7$)Ir($etasp2$-C$sb8$H$sb{14}$)CO were prepared in high yield from (($etasp2$-C$sb8$H$sb{14}$)$sb2$Ir(CO)Cl) $sb2$ and thallium cyclopentadienide or potassium indenide, respectively. The stereoisomers of CpIr($etasp2$-C$sb8$H$sb{14}$)CO, ($etasp5$-C$sb9$H$sb7$)Ir($etasp2$-C$sb8$H$sb{14}$)CO, and ($etasp5$-C$sb9$H$sb7$)Ir($etasp2$-C$sb8$H$sb{14}$)$sb2$, were characterized by two-dimensional NMR techniques. Due to the "Indenyl Effect," ($etasp5$-C$sb9$H$sb7$)Ir($etasp2$-C$sb8$H$sb{14}$)CO was more reactive than CpIr($etasp2$-C$sb8$H$sb{14}$)CO toward Lewis bases. The labile cyclooctene ring of ($etasp5$-C$sb9$H$sb7$)Ir($etasp2$-C$sb8$H$sb{14}$)CO was readily replaced under mild conditions by other two electron donors such as triphenylphosphine, carbon monoxide, ethylene, or phenylacetylene; CpIr($etasp2$-C$sb8$H$sb{14}$)CO was not reactive under identical or more severe conditions. The complex ($etasp5$-C$sb9$H$sb7$)Ir($etasp2$-C$sb8$H$sb{14}$)CO readily oxidatively added C-Br and Si-H bonds, again under mild conditions, and was found to be an active and robust catalyst for the hydrogenation and hydrosilylation of alkenes and alkynes. The reaction of CO with ($etasp5$-C$sb9$H$sb7$)Ir(CO)$sb2$ resulted in the formation of the $etasp1$-slipped indenyl ring of ($etasp1$-C$sb9$H$sb7$)Ir(CO)$sb3$.;For CpIr($etasp2$-C$sb2$H$sb4$)L and ($etasp5$-C$sb9$H$sb7$)Ir($etasp2$-C$sb2$H$sb4$)L, where L = ethylene or CO, the barrier to ethylene rotation about the iridium-ethylene bond axis was determined by lineshape fitting of variable-temperature $sp1$H NMR spectra. The free energies of activation were found to be 5-6 kcal/mole less for the indenyl complexes than for the corresponding cyclopentadienyl complexes (14 and 20 kcal/mole, respectively). This lowering of the barrier to ethylene rotation is an attribute of the "Indenyl Effect.".;Some related projects included the following. Attempted preparation of CpIr($etasp2$-C$sb8$H$sb{14}$)$sb2$ resulted in an unexpected but useful synthesis of the cyclopentadiene complex CpIr($etasp4$-C$sb5$H$sb6$). The proton and carbon resonances of the series of complexes CpM($etasp4$-C$sb5$H$sb6$), where M = Co, Rh, or Ir, were compared. Protonation studies of CpIr($etasp2$-C$sb8$H$sb{12}$) and ($etasp5$-C$sb9$H$sb7$)Ir($etasp2$-C$sb8$H$sb{12}$) allowed us to examine $etasp5$ to $etasp6$ haptotropic indenyl ring shifts. Synthetic routes to a metal cyclopentaphenanthrene complex Cp*Ru($etasp5$-C$sb{15}$H$sb9$), were explored.