The work described in this thesis is primarily focused on the synthesis and characterisation of two-coordinate zerovalent palladium complexes bearing an N-heterocyclic carbene ligand. These complexes have been assessed as pre-catalysts for coupling reactions in particular ami nation reactions involving the generation of a C-N bond. Chapter 1 presents the synthesis of complexes r, r bearing the ligand [CNCBu)(CH)2NCBu)]. An alternative synthesis for [Pd{CNCBu)(CH)2NCBu)h] 1 is reported involving reaction of [{Pd(T)3-C4H7)Clhl with sodium dimethyl malonate and carbene. Reaction of 1 with iodobenzene led to formation of a Pd(II) speCies, r , [Pd{CNCBu)(CHhNCBu)h(C6Hs)I] 2. An intermediate in the synthesis of 1, r [Pd(T)3-C4H7){CNCBu)(CHhNCBu)h(C6Hs)C] 3, has been isolated and fully characterised. Two r , mixed carbene phosphine complexes, [Pd{CNCBu)(CHhNCBu)}{P(o-tolylh}] 4 and r , [Pd{CNCBu)(CHhNCBu)} {PCY3} 1 S, have also been synthesised. Complexes 1,4 and S have been assessed as a pre-catalysts for ami nation couplings with limited success. Chapter 3 presents the r , synthesis of two complexes bearing the ligand [CN(Me)(CMe)2N(Me)]. Metal vapour synthesis was r , used to synthesise [Pd{CN(Me)(CMehN(Me)h] 6 and the diiodide complex r , [Pd{CN(Me)(CMehN(Me)hI2] 7 was also prepared. Complexes 6 and 7 were shown to have no activity as pre-catalysts in amination couplings. Chapter 4 presents the synthesis of complexes r· ~. bearing the ligand [CN(2,6-'Pr2-C6H3)(CH2hN(2,6-'PrrC6H3)]. The methodology used to synthesise r. ~. 1 was applied to the synthesis of [Pd{CN(2,6-'Pr2-C6H3)(CH2hN(2,6-'PrrC6H3)h] 8. Substitution of a phosphine ligand In [Pd {P(o-tolylh hl by carbene led to formation of r. ~. [Pd{CN(2,6-'PrrC6H3)(CH2hN(2,6-'PrrC6H3)}{P(o-tolyl)3}] 9. Complexes 8 and 9 were successfully employed as pre-catalysts for amination couplings. 4-Chlorotoluene was shown to couple to a variety of primary and secondary amines including cyclic, acyclic and aryl substituted as well as an imine. The same proceedure was also used to couple chloropyridines with morpho line Reactions were typically conducted with 2 mol% pre-catalyst and KOtBu base in dioxane at 100 °C and were found to be complete after 0.5-5 h. The isolated yields of product obtained were typically r· ~. above 95%. Reaction of 1 with [CN(2,6-'Pr2-C6H3)(CH2hN(2,6-'Pr2-C6H3)] led to formation of r \ r. ~. [Pd{CN(,Bu)(CH)2N(,Bu)} {CN(2,6-'Pr2-C6H3)(CH2hN(2,6-'Pr2-C6H3)}] 10. Complex 10 was found to be less active as a pre-catalyst for amination couplings than either 8 or 9. A copper carbene r. ~. complex [Cu {CN(2,6-'Pr2-C6H3)(CH2)2N(2,6-'Pr2-C6H3)} I] 11 was also synthesised and shown to facilitate the coupling of 4-iodotoluene with morpholine to give the coupled product in a 38% yield. Chapter 5 presents the results of some ligand substitution reactions. Complexes 1 and 8 were reacted with phosphines to give mixed carbene phosphine complexes 4, S and 9. The results obtained showed that phosphines can displace carbenes despite the strength of metal carbene bonds
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:395012 |
| Date | January 2001 |
| Creators | Titcomb, Lisa Rae |
| Publisher | University of Sussex |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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