This thesis describes the reactivity of different heavier alkaline earth catalysts
[M{X(SiMe3)2}2(THF)n]m (M = Ca, Sr, Ba; X = N, CH; n= 0, 2; m= 1, 2) in the
intermolecular hydroamination of styrene derivatives. The scope of these reactions with
respect to the substrate was determined and detailed kinetic studies to establish rate law and
temperature dependence of the hydroamination reactions reported were conducted. Overall, it
was found that [Ca{N(SiMe3)2}2]2 is favoured enthalpically (Ca: ΔH‡ = 51 kJ∙mol-1, Sr:
ΔH‡ = 71 kJ∙mol-1) however the corresponding strontium bis(amide) proved a significantly
better catalyst, likely due to a favourably high entropy of activation value (Ca: ΔS‡ =
-168 J/mol-1
·K-1, Sr: ΔS‡ = -92 J∙mol-1∙K-1). Large kinetic isotope effects of 4.1 and 7.9 at
55 °C for the intermolecular hydroamination of styrene with piperidine mediated by
[Ca{N(SiMe3)2}2]2 and [Sr{N(SiMe3)2}2]2, respectively, suggest a rate-determining alkene
insertion into the M-N bond with immediate or concerted protonolysis. The methodology used
in these hydroamination reactions was extended to simple dienes, diphenylacetylene and an
activated enyne.
The catalyst initiation of the metal bis(amides) with piperidine was shown to be reversible and
the equilibrium constant solvent dependent. Novel calcium and strontium dialkyl complexes
[M{CH(SiMe3)2}2(THF)2] (M= Ca, Sr) were used to overcome the problem of catalyst
initiation and showed a different solvent dependence. An enhanced reactivity was found for
the dialkyl complexes compared to the metal bis(amides). This increased reactivity allowed
the application in new reactions such as the C-F activation of fluorobenzenes.
Furthermore, the use of these catalytic systems was successfully extended to intramolecular
hydroalkoxylation reactions of alkynyl alcohols in the formation of five- and six-membered
enol ethers. In this case, [Ba{N(SiMe3)2}2]2 displayed significant reactivity although the
“catalyst of choice” for these reactions proved to be strongly dependent on substrate
substitution pattern. Through detailed kinetic studies the catalyst, substrate and temperature
dependence of the cyclisation reaction were established and an unusual rate law with inverse
substrate dependence proposed.