This thesis describes the synthesis, characterisation and reactivity of new
manganese and rhenium(I) NHC complexes, which have been investigated both
thermally and photochemically and the results contrasted with existing
phosphine analogues in the literature.
Cp’Mn(CO)2(NHC) (NHC = IEt2Me2 1, IMes 2, IiPr2Me2 3 and IPr 4) were
synthesised and investigated by TRIR spectroscopy. Loss of CO was observed
after 355 nm irradiation to form agostically stabilised intermediates, which
reformed the parent species by recombination with CO on the nanosecond
timescale. Loss of NHC was not observed, in contrast to Cp’Mn(CO)2(PPh3)
which lost both CO and PPh3 upon photolysis.
[Re(NHC)(Bpy)(CO)3]BAr4F (NHC = IEt2Me2 5, IMes 6) were synthesised and
investigated by TRIR spectroscopy and UV/Vis absorption and emission
spectrometry. Inclusion of an NHC altered the excited state manifold of the
complexes, favouring population of the 3MLCT over the 3IL excited state. The
lowest energy excited state for both 5 and 6 proved to be a 3MLCT excited state
at 298 and 77 K. In contrast, [Re(PPh3)(Bpy)(CO)3]BAr4F exhibited 3MLCT at
298 K, but 3IL at 77 K.
A series of complexes, M(NHC)(CO)4X and M(NHC)2(CO)3X (M = Re, X = Cl; M
= Mn, X = Br) formed upon reaction of the corresponding M(CO)5X species and
free NHC. The substitution pattern was dictated by the steric bulk of the NHC.
Generation of the corresponding cations by halide abstraction was investigated.
M(NHC)2(CO)3X was found to form agostic stabilised species upon halide
abstraction by NaBAr4F in CH2Cl2. Under the same conditions, Re(IPr)(CO)4Cl
was found to form the dichloromethane complex,
[Re(IPr)(CO)4(η1-CH2Cl2)]BAr4F. In C6H5F solution under an atmosphere of
dihydrogen, the CH2Cl2 ligand could be displaced by H2 to form the dihydrogen
|Date of Award||26 Oct 2011|
|Supervisor||Michael Whittlesey (Supervisor)|
- N-heterocyclic carbenes