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Title:The 'Indenyl Effect' in iridium(I) olefin complexes
Author(s):Szajek, Lawrence Philip
Doctoral Committee Chair(s):Shapley, John R.
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Chemistry, Inorganic
Abstract:The complexes CpIr($\eta\sp2$-C$\sb8$H$\sb{14}$)CO and ($\eta\sp5$-C$\sb9$H$\sb7$)Ir($\eta\sp2$-C$\sb8$H$\sb{14}$)CO were prepared in high yield from (($\eta\sp2$-C$\sb8$H$\sb{14}$)$\sb2$Ir(CO)Cl) $\sb2$ and thallium cyclopentadienide or potassium indenide, respectively. The stereoisomers of CpIr($\eta\sp2$-C$\sb8$H$\sb{14}$)CO, ($\eta\sp5$-C$\sb9$H$\sb7$)Ir($\eta\sp2$-C$\sb8$H$\sb{14}$)CO, and ($\eta\sp5$-C$\sb9$H$\sb7$)Ir($\eta\sp2$-C$\sb8$H$\sb{14}$)$\sb2$, were characterized by two-dimensional NMR techniques. Due to the "Indenyl Effect," ($\eta\sp5$-C$\sb9$H$\sb7$)Ir($\eta\sp2$-C$\sb8$H$\sb{14}$)CO was more reactive than CpIr($\eta\sp2$-C$\sb8$H$\sb{14}$)CO toward Lewis bases. The labile cyclooctene ring of ($\eta\sp5$-C$\sb9$H$\sb7$)Ir($\eta\sp2$-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($\eta\sp2$-C$\sb8$H$\sb{14}$)CO was not reactive under identical or more severe conditions. The complex ($\eta\sp5$-C$\sb9$H$\sb7$)Ir($\eta\sp2$-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 ($\eta\sp5$-C$\sb9$H$\sb7$)Ir(CO)$\sb2$ resulted in the formation of the $\eta\sp1$-slipped indenyl ring of ($\eta\sp1$-C$\sb9$H$\sb7$)Ir(CO)$\sb3$.
For CpIr($\eta\sp2$-C$\sb2$H$\sb4$)L and ($\eta\sp5$-C$\sb9$H$\sb7$)Ir($\eta\sp2$-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($\eta\sp2$-C$\sb8$H$\sb{14}$)$\sb2$ resulted in an unexpected but useful synthesis of the cyclopentadiene complex CpIr($\eta\sp4$-C$\sb5$H$\sb6$). The proton and carbon resonances of the series of complexes CpM($\eta\sp4$-C$\sb5$H$\sb6$), where M = Co, Rh, or Ir, were compared. Protonation studies of CpIr($\eta\sp2$-C$\sb8$H$\sb{12}$) and ($\eta\sp5$-C$\sb9$H$\sb7$)Ir($\eta\sp2$-C$\sb8$H$\sb{12}$) allowed us to examine $\eta\sp5$ to $\eta\sp6$ haptotropic indenyl ring shifts. Synthetic routes to a metal cyclopentaphenanthrene complex Cp*Ru($\eta\sp5$-C$\sb{15}$H$\sb9$), were explored.
Issue Date:1991
Rights Information:Copyright 1991 Szajek, Lawrence Philip
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9211007
OCLC Identifier:(UMI)AAI9211007

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