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Paramagnetic (Alkene)Rh and (Alkene)Ir Complexes: Metal or Ligand Radicals?

Authors

  • Bas de Bruin,

    1. University of Amsterdam, Van't Hoff Institute for Molecular Chemistry (HIMS), Department of Homogeneous and Supramolecular Catalysis, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands, Fax: +31-20-525-6422
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  • Dennis G. H. Hetterscheid

    1. Radboud University Nijmegen, Institute for Molecules and Materials (IMM), Toernooiveld 1, 6525 ED Nijmegen, The Netherlands
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  • Dedicated to Professor Karl Wieghardt on occasion of his 65th birthday

Abstract

In this review a detailed overview is given of the (electronic) structure and reactivity of open-shell (paramagnetic) alkene rhodium and iridium complexes Mx(alkene) (M = Rh, Ir; x = 0, +II). In most cases these species are highly reactive, but some notable exceptions of stable species for which not much reactivity has been described are also included (section 2). Understanding the electronic structure of the reactive nitrogen-ligand-based [MII(por)(alkene)] and [MII(alkene)(N-ligand)]2+ species (section 3) is complicated by a substantial spin distribution over the metal and the alkene ligand. This dual-mode metallo-radical and ligand radical behavior is reflected by their high and diverse reactivity. Metallo-radical character is demonstrated by a variety of metal-to-radical coupling reactions with a series of other radicals, as well as metal-based allylic hydrogen atom abstractions from MII(α-alkene) species. On the other hand, (donor induced) ligand radical character is crucial in a variety of M–C and C–C radical coupling reactions, C–O bond formation by oxygenation of MII(alkene) species and alkene “insertions” into (por)M–H bonds. The review concludes with some speculations about possible roles of paramagnetic M(olefin) (M = Rh, Ir) species in catalytic olefin oxygenation and carbene transfer reactions.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

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