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Title: Mechanistic and kinetic studies on aryl and alkyl amination reaction catalysed by palladium n-heterocyclic carbene complexes
Author: Esposito, Oriana
ISNI:       0000 0001 3449 3817
Awarding Body: University of Sussex
Current Institution: University of Sussex
Date of Award: 2008
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Several studies have been carried out to establish the sequence of intermediates in the catalytic cycle for amination of aryl halides. I ,2 The mechanism suggested by Cloke and Caddick group for the catalytic amination of aryl chloride employing [Pd(NRC)2l as precatalyst (NRC = ·N-heterocyclic carbene), proposed a neutral, 12-electrons mono-ligated Pd(NHC) species as the active intermediate.3 The isolation of a series of (ItBu)2Pd(R-aryl)chloride complexes (ltBu = 1,3-di-tert-butylimidazol-2-ylidene) allowed for kinetic studies hence leading to a mechanistic understanding of the I oxidative addition step, confirming that it occurs by a dissociative mechanism. The subsequent step in the amination catalytic cycle, namely, the dissociation of a carbene and coordination of an amine was investigated and the results are presented in this thesis, and an array of (ItBu)Pd(amine)(R-aryl)chloride complexes were isolated and fully characterized. Kinetic studies were undertaken in order to identify the rate determinig step of the transamination reaction. Moreover, the electronic properties of the para-substituents (R) on the aryl groups of the (ItBu)2Pd(R-aryl)chloride complexes were found not only to influence the rate of the oxidative addition reaction, but also to affect the carbene displacement by the amines. Parallel research based on the understanding of the mechanism of oxidative addition of alkyl halides to the Pd(NHC)2 species have been undertaken, and the synthesis of (ItBu)Pd(neopentyl)chloride (trans isomer) and (IPr)Pd(neopentyl)chloride (cis isomer) (IPr = 1,3-Bis(2,6-Diisopropylphenyl)imidazol-2-ylidene) were. accomplished. Reactivity of these· two complexes was tested toward amines, revealing the significant influence ofN-substituents on the stability of the resulting compounds, and highlighting a possible barrier concerning the achievement of a Pd-catalysed alkyl amination reaction. The oxidative addition of (trimethylsilyl)methyl iodide to Pd(ItBu)z complex was investigated for comparison to the oxidative addition reactions of alkyl halides to the same palladium complex. The unexpected resultant complex, Pd(CHzltBu)zlz, was subjected to DFT study by Dr. Hazari to confirm the zwitterionic nature of the ligand. Kinetic study was conducted on the oxidative addition of TMSI to Pd(ItBu)z to reveal the occurrence of pre-dissociation of one ligand before the addition ofTMSI to yield the [(ItBu)Pd(TMS)(J.t-I)]z.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available