Bridgehead substituted scorpionates providing helically chiral complexes
View/ Open
Date
29/06/2013Author
Bell, Nicola Louise
Metadata
Abstract
Tripodal borate ligands, including Tp and Tm, are some of the most
widely used in organometallic chemistry and were originally prepared, as
anions, from the reaction of the relevant heterocycle with an alkali metal
borohydride. However, an alternate route, allowing access to zwitterionic,
charge-neutral, scorpionates was recently developed within the Bailey group
using tris(dimethylamino)borane as the boron source.
This thesis describes the expansion of the borane synthetic route to create
new, charge-neutral, zwitterionic, tris(methimazolyl)borate (ZTm) ligands
containing B-N, B-O and B-C coordinate bonds. Unusual reactivity with
isonitrile donors is also presented which has allowed access to boron
substituted anionic Tm ligands from the charge-neutral starting material,
(HNMe2)ZTm. Attempts to control the helical chirality of ZTm complexes, by
using chiral imidazoline donors on the central boron are also described.
The borane synthetic route has allowed access to the novel ligand ZThp,
the first example of a tripod based on 2-hydroxypyridine ligand arms. As
with Tm, this ligand exhibits helical chirality upon complexation and
demonstrates how individual atom hybridisation within the ligand arms
affects the helicity and thus the chirality of flexible scorpionate ligands.
Coordination studies of both zwitterionic and boron-substituted anionic
Tm ligands have shown a tendency for the formation of ‘sandwich’
complexes of the form L2M with some metal precursors, whilst the formation
of the corresponding ‘half-sandwich’ complexes of these ligands with
ruthenium and rhodium was found to be disfavoured.