The synthesis of the bulky 1-(1-arylimino-2,2-dimethylpropyl)-3-(aryl)imidazolium salt from the corresponding imidazole and the activated imidoyl chloride is presented. The absence of acidic protons adjacent to the iminic carbon allowed for the first isolation of an imino-N-heterocyclic carbene of this ligand class. The free carbene was isolated, structurally characterised, and coordinated to titanium, zirconium, hafnium and chromium. The resulting metal halide complexes were fully characterised and were tested at room temperature and atmospheric pressure for their activity as ethylene polymerisation catalysts. The Zr(IV) complex was found to be the most active with a productivity of 140 kg PE mol M(-1) h(-1).

The first aryl-substituted imino-N-heterocyclic ligand precursor was prepared and structurally characterised, along with the corresponding silver(i) and copper(i) chloride complexes. An unusual T-shape coordination mode for the copper centre was observed.

Two different heteroditopic bis(aryl)-substituted imino-N-heterocyclic carbene ligands were coordinated to nickel using new copper carbene dimers as transmetalating agents. The oxidative addition of an imidazolium salt precursor with Ni(COD) 2 led to the unexpected bis(carbene)NiCl 2 complex, presumably through a putative nickel hydride intermediate. All new complexes were isolated in good yield and were structurally characterized. The size of the iminic carbon substituent was found to have a profound impact on the bond angles and bond lengths about the metal center. All nickel complexes were tested for ethylene polymerization activity at standard temperature and pressure and were found to be inactive.

Gold(I) complexes of 1-[1-(2,6-dimethylphenylimino)alkyl]-3-(mesityl)imidazol-2-ylidene (C^Imine(R)), 1,3-dimesitylimidazol-2-ylidene (IMes) and of the corresponding thione derivatives (S^Imine(R) and IMesS) were prepared and structurally characterised. The solid-state structure of the C^Imine(R) and S^Imine(R) gold(I) complexes showed monodentate coordination of the ligand and a dangling imine group that could bind reversibly to the metal centre to stabilise otherwise unstable catalytic intermediates. Interestingly, reaction of C^Imine(tBu) with [AuCl(SMe(2))] led to the formation of [(C^Imine(tBu))AuCl], which rearranges upon crystallisation into the unusual complex cation [(C^Imine(tBu))(2)Au](+), with AuCl(2)(-) as the counterion. The activity of the gold complexes in the hydroamination of phenylacetylene with substituted anilines was tested and compared to control catalyst systems. The best catalytic performance was obtained with [(C^Imine(tBu))AuCl], with the exclusive formation of the Markovnikov addition product in excellent yield (>95 %) regardless of the substituents on aniline.

The synthesis and isolation of N-imidazol-2ylidene-N′-p-tolylureate and thioureate proligands is described. Titanium(IV), nickel(II), and palladium(II) complexes containing one or two equivalents of the ligand were prepared by transmetalation of the ureate or thioureate salts. The X-ray structure of titanium complexes corroborated our prediction based on spectroscopic data and showed the ureate binds in a bidentate fashion through the oxygen and nitrogen atoms of the isocyanate building block, leaving the imidazol-2-imine fragment uncoordinated. Carbon−nitrogen bond lengths indicate substantial electron delocalization from the imidazole ring to the ureate group. In contrast, the ligand adopts a different coordination mode and binds to nickel and palladium through the N imidazol-2-ylidene and N p-tolyl atoms. Surprisingly, despite the softer nature of sulfur, coordination of the thioureate was exclusively through the sulfur and nitrogen atoms of the isothiocyanate building block with all three metals studied. All complexes were tested for ethylene polymerization at ambient conditions using methylaluminoxane as cocatalyst. Titanium(IV) complexes were found to be the most active, with activities up to 60 kg PE mol −1 catalyst h −1 .