NDLI: C–H functionalization: thoroughly tuning ligands at a metal ion, a chemist can greatly enhance catalyst's activity and selectivity

Content Provider	World Health Organization (WHO)-Global Index Medicus
Author	Shul'pin, Georgiy B.
Description	Author Affiliation: Shul'pin GB ( Semenov Institute of Chemical Physics, Russian Academy of Sciences, ul. Kosygina 4, Moscow 119991, Russia. Shulpin@chph.ras.ru gbsh@mail.ru.)
Abstract	This brief essay consists of a few “exciting stories” devoted to relations within a metal-complex catalyst between a metal ion and a coordinated ligand. When, as in the case of a human couple, the rapport of the partners is cordial and a love cements these relations, a chemist finds an ideal married couple, in other words he obtains a catalyst of choice which allows him to functionalize C–H bonds very efficiently and selectively. Examples of such lucky marriages in the catalytic world of ions and ligands are discussed here. Activity of the catalyst is characterized by turnover number (TON) or turnover frequency (TOF) as well as by yield of a target product. Introducing a chelating N,N- or N,O-ligand to the catalyst molecule (this can be an iron or manganese derivative) sharply enhances its activity. However, the activity of vanadium derivatives (with additionally added to the solution pyrazinecarboxylic acid, PCA) as well as of various osmium complexes does not dramatically depend on the nature of ligands surrounding metal ions. Complexes of these metals are very efficient catalysts in oxidations with $H_{2}O_{2}.$ Osmium derivatives are record-holders exhibiting extremely high TONs whereas vanadium complexes are on the second position. Finally, elegant examples of alkane functionalization on the ions of non-transition metals (aluminium, gallium etc.) are described when one ligand within the metal complex (namely, hydroperoxyl ligand $HOO^{−})$ helps other ligand of this complex $(H_{2}O_{2}$ molecule coordinated to the metal) to disintegrate into two species, generating very reactive hydroxyl radical. Hydrogen peroxide molecule, even ligated to the metal ion, is perfectly stable without the assistance of the neighboring $HOO^{−}$ ligand. This ligand can be easily oxidized donating an electron to its partner ligand $(H_{2}O_{2}).$ In an analogous case, when the central ion in the catalyst is a transition metal, this ion changing its oxidation state can donate an electron to the coordinated $H_{2}O_{2}$ fragment. This provokes the O–O bond rupture in the hydrogen peroxide molecule as is assumed for the role of $Fe^{2+}$ ions in the Fenton system.
ISSN	14779226
Issue Number	36
Journal	Dalton Trans.
Volume Number	42
e-ISSN	13645447
Language	English
Publisher	Royal Society of Chemistry
Publisher Date	2013-09-28
Publisher Place	Great Britain (UK)
Access Restriction	Subscribed
Subject Keyword	Chemistry
Content Type	Text
Resource Type	Article
Subject	Inorganic Chemistry

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