Supervisors info:
Χ. Μητσοπούλου Καθηγήτρια (επιβλέπουσα),Μ. Πιτσικάλης Αναπλ. Καθηγητής , Π. Παρασκευοπούλου Λέκτορας
Summary:
The present work studies the catalytic reactivity of a new family of tripodal
CoII complexes towards controlled radical polymerization (CRP) reactions.
These complexes bear trianionic triphenylamido-amine ligands with a variety of
pendant arms (aryl, acyl, alkyl), and feature a distorted trigonal-pyramidal
geometry. In two cases, the presence of acetonitrile adds a fifth moiety to the
coordination sphere.
Electrochemical data establish that all aryl- and alkyl-armed ligands give rise
to reversible or semi-reversible CoII/CoIII couples, with redox potentials
ranging by as much as 575 mV. On the other hand, the electron-withdrawing
acyl-armed ligands demonstrate irreversible features, exhibiting anodic waves
at positive voltages, for which ligand participation cannot be excluded.
The catalytic reactivity of these complexes towards the CRP of styrene (St) and
methyl methacrylate (MMA) has been studied in various solvents. In toluene,
compounds 2 and 4-6, give high yields of polymers (60-90%), whereas 3 and 7
provide lower yields (12-16% for PS and 30-45% for PMMA). In THF, higher yields
and better control of the polymerization of St (complexes 3 and 7) and MMA (2
and 7) are observed. The steric factor seems to play an essential role, since
CoII compounds that feature a less hindered fifth coordination site show the
highest reactivity and better control over polymerization. The polymers
obtained are predominately syndiotactic, with a few exceptions that exhibit
unusually high ratios of isotactic triads. Interestingly, in many cases, the
polymers obtained feature bimodal distributions, while the molecular weight
distributions are not very broad (1.40-2.00), and this strongly indicates that
two parallel mechanisms may be in operation.
Keywords:
Cobalt complexes, Trisamidoamine ligands, Electrochemistry, Controlled radical polymerization, Atom-transfer reactions
