CHIRAL TRANSITION METAL COMPLEXES: SYNTHESIS, CHARACTERIZATION, APPLICATIONS.

The main target of this thesis was the investigation of different
aspects of the chirality at the metal centre. In particular we studied
stereo-specific synthesis of octahedral transition metallic complexes
or their resolution in enantiomeric pure form, in order to evaluate
the influence of the chirality at the metal centre in different fields
such as: catalysis, emission or interaction with chiral environment.
The use of chiral-at-metal complexes in catalysis is somewhat less
common than that of other chiral organometallic architectures. Via
stereospecific reaction, we were able to obtain ruthenium(II) complexes
of general formula [Ru(NN)(PP)Cl2] in optically pure form,
where NN was a chiral diamine and PP was a chelating or two
mono phosphines. These complexes, after the activation into the hydride
species, were active catalysts for the reduction of ketones via
asymmetric transfer hydrogenation. We observed that, in complexes
where two chiral ligands were simultaneously present, the third chirality
that located at the metal centre was prevalent in the definition
of the configuration of the products.
In order to introduce the planar chirality, we synthesised different
complexes of the types [h6-arene-Ru(NN)Cl], however in the most
cases intractable complex mixture of stereoisomers were obtained.
This results prompted us to explore different techniques able to describe
complex mixtures of complexes with several type of chirality
involved.
VCD in tandem with DFT calculation is powerful technique for
the determination of the absolute configuration and conformational
analysis; despite new results concerning transition metal complexes
are coming out, their application in the study of metallorganic compounds
are not common. The strength of IR and VCD spectroscopy
lies in the fact that the spectra of a chiral molecule contain sufficient
stereochemical details to be consistent with only a single absolute
configuration and an unique solution-state conformation, or distribution
of conformations, of the molecule; moreover compared with
ECD the DFT calculation is more reliable.
For our purpose we selected three common motifs in organometallic
chemistry never investigated by VCD spectroscopy. We decided to investigate the carbon monoxide as the first chromophore;
carbon monoxide is one on the most common ligand for
transition metal complexes; the carbonyl complexes found application
as catalysts, precatalysts or stoichiometric reagents in many different
reactions. Therefore we synthesised and resolved a series of
of heteroleptic ruthenium (II) cyclopentadienyl complexes.
The second chromophore was a metal-hydride, which has important
role in catalytic reduction. We were able to synthesis one
Ru(II) hydride complex as single enantiomer that was completely
and whose metal chirality was highlighted by VCD.
The third class of compounds was the cyclometallated iridium(III)
complexes that due to their photophysical properties have been extensively
studied in the last years, founding application in several
fields. Here the chromophore was constituted by two orthometalled
phenylpyridine coordinated at the metal in helical shape.
In this latter case, our interest was also adressed to study the photophysical
properties of the different diastereomers and in order to
verify if the emission could be influenced by the diastereomeric nature
of the complexes. In spite of that in solution no differences were
highlighted, we found that the different packing of the enantiomers
and stereoisomers produces aggregates with different emitting properties.
By VCD spectrometry integrated with DFT calculation we were
able to identify the characteristic features of the different stereogenic
centre present in the co