• Keine Ergebnisse gefunden

Spectroelectrochemical investigations of the complexes showed the formation of a [(R- PyMA)Ni(Aryl)(Solv)]

N/A
N/A
Info
Herunterladen
Protected

Academic year: 2021

Aktie "Spectroelectrochemical investigations of the complexes showed the formation of a [(R- PyMA)Ni(Aryl)(Solv)]"

Copied!
1
0
0

Wird geladen.... (Jetzt Volltext ansehen)

Jetzt herunterladen ( 1 Seite )

Volltext

(1)

Abstract

The subject of the presented work is the synthesis of mononuclear square-planar [(R- PyMA)Ni(Aryl)X]-type organonickel complexes with N-(Pyridin-2-yl-methylene)aniline- ligands (R-PyMA) and the investigation of their structure, reactivity and electrochemistry.

Single crystal X-ray diffraction showed the crystallisation of the cis-isomer, in which the halide ligand (X) is located opposite to the pyridine part of the PyMA-ligand, to be favoured over the trans-isomer. Furthermore a shift of the cis-/trans-ratio towards the trans-isomer could be observed at low temperatures using variable temperature NMR-spectroscopy.

The electronic character of the R-PyMA ligands with various substituents was determined through DFT-calculations using a [Ir(allyl)(CO)(R-PyMA)]-type model complex. The assessment of the electronic properties reveals that the donor strength of the unsymmetric PyMA ligands lies between the values for the structurally similar ligands 2,2´bipyridine and N,N-bisphenyl-1,4-diazabutadiene. Additionally, the difference in Gibbs free energy ΔG between both isomers and the transition state for the isomerisation via the lowest energy pathway was determined. This transition state is a trigonal-planar arrangement, which is formed through decoordination of the halide ligand.

Spectroelectrochemical investigations of the complexes showed the formation of a [(R- PyMA)Ni(Aryl)(Solv)]

•

-radical species from all [(R-PyMA)Ni(Aryl)X]-type complexes upon reduction and cleavage of the halide ligand. The required reduction potentials for all complexes lie between –1.2 and –1.8 V (vs. ferrocene/ferrocenium) and shift to less negative potentials for electron-rich R-PyMA ligands. The cleavage of the halide ligand, which leads to catalytic activation of the complexes, can be promoted by variation of the halide ligand itself following the series F > Cl > Br > I, as well as by using less electron-rich aryl-ligands. The latter increases the tendency for the transmetallation reaction of two [(R-PyMA)Ni(Aryl)X]

complexes leading to the formation of [(R-PyMA)Ni(Aryl)

2

] bisaryl-complexes.

Further reduction of these species was proven to take place in dimers formed from two of the

R-PyMA)Ni(Aryl)(Solv)]

•

radical complexes.

Referenzen

Jetzt herunterladen ( PDF - 1 Seite - 208.58 KB )

ÄHNLICHE DOKUMENTE

Species formation: the driver of biodiversity

In this modern view, such adaptive “speciation attempts” are frequent, although they commonly fail in stable environments; after extrinsic habitat alterations and extinctions,

Formation of the Complexes [Fe(H2

Unusual in the first case is the total replacement of ligands of CpFe(CO) 2 Cl and in the second case the oxidation of Cr(0) to Cr(III) leading to the formation of complexes 3 and 4

of Ni

In the present paper, by taking into account SS, SOO, and OO interactions, the local structure and SH parame- ters of Ni 2+ ions in CsMgX 3 (X = Cl, Br, I) are inves- tigated, and

A New Simple Method for the Prepara- tion of Aryl Formates from Phenols

Firstly the formylating reagent triformamide ( 1b ) is generated from sodium diformamide ( 2 ) and methane- sulfonyl chloride in situ, which reacts with phenols 4a – f to give

A New Simple Method for the Prepara- tion of Aryl Formates from Phenols

In the present note we wish to report a new, even simpler method for the synthesis of aryl for- mates from phenols without isolating the formylating agent triformamide ( 1b )

Theoretical Investigations of the Defect Structure and the g Factors of a Tetragonal Ni

1.) The local distance ∆ Z , smaller than the host ∆ Z, can be illustrated by the modification of local struc- ture properties around the impurity Ni 3+ replacing the Ti 4+. Since

(M = Cr, Mo, W) On Complexes of the Type

While IR data indicate significant acceptor properties of the phosphane ligands, the X-ray structure analysis of 3c also allows the discussion of weak

Investigation of the structure of spliceosomal complexes from the yeast S. cerevisiae

In the human tri-snRNP structure, Sad1 is positioned at the interface between the U4/U6 and U5 snRNPs and potentially acts as a clamp which stabilizes the U4/U6 - U5 snRNP interaction