University of Sussex
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Palladium N-neterocyclic carbene complexes as catalysts for C-N, C-Si and C-S bond formations

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posted on 2023-06-08, 15:12 authored by Deborah Elizabeth Roberts
This work is foremost a study of various palladium-bearing N-heterocyclic carbenes complexes and their catalytic potential to form C-N bonds. Both alkyl amination and aryl amination are considered. Further elucidation on the mechanism of such catalytic activity is investigated. The viability of alkyl amination using palladium complexes bearing the ligands, ITMe, 1,2,3,4- tetramethylimidazol-2-ylidene, and ICy, 1,3- bis-cyclohexylimidazol-2-ylidene, as catalysts, is investigated. This includes the synthesis of [Pd(ITMe)(neopentyl)Cl]2,[Pd(ITMe)2(neopentyl)Cl], [Pd(ITMe)(neopentyl)(tbutylamine)Cl], [Pd(ITMe)(neopentyl)(hexylamine)Cl], with successful elimination of the alkyl-amination reaction product in low yield from the latter complex. [Pd(ICy)(neopentyl)Cl]2, [Pd(ICy)2(neopentyl)Cl] are also isolated. Unsuccessful attempts were made to vary the electronic properties of the complexes by replacing the amine with a hydrazine. Work was also done on indirect alkylation using tBuLi which led to a new method for synthesis of [Pd(ItBu)2] and novel complex, [Pd(ItBu)Cl3. ItBuH] (ItBu = 1,3- bis-tertbutylimidazol-2-ylidene). Aryl amination catalysed by complexes of palladium bearing the ligand, ITMe, is considered. This includes an improved synthesis of [Pd(ITMe)2] and synthesis of [Pd(ITMe)2(anisole)Cl]. Unsuccessful attempts at the elucidation of the mechanism of [Pd(ITMe)2(anisole)] formation led to the unexpected formation of [Pd(ITMe)2(SiMe3)(Si(SiMe3)3)] and [Pd(ITMe)2(SiMe3)2]. Aryl amination with using [Pd(ITMe)2(SiMe3)2] led to two aryl amination products, 4-ortho-methoxyphenyl morpholine as well as the expected para isomer. The use of complexes [Pd(ItBu)2] and [Pd(SIPr)2] (SIPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) in C-S bond formation was explored. Addition of mesityl magnesium bromide to Pd(1,5-COD)Cl2 led to addition of mesityl substrate across 1,5-COD double bond and the addition of ITMe formed the Heck cycle intermediate [Pd(8-mesityl-1,4,5-?3 – C8H12)X2] (X=Cl, Br). Addition of 4-tolyl magnesium chloride resulting in the formation of Pd(ItBu)2(tolyl)Cl via an indirect route.


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University of Sussex

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