Coordinatively- and electronically-unsaturated square planar cobalt(iii) complexes of a pyridine dianionic pincer ligand.

A series of low-valent Co(iii) square planar complexes supported by a dianionic pincer ligand bis(arylamido)pyridine ([NNN]2-) was synthesized, including the first structurally characterized square planar hydroxide complex ([NNN]Co(OH), 4) of a 3d transition metal in the +3 oxidation state. The magnetic properties of the Co(iii) complexes were highly dependent on the charge of the complex and on the coordination environment of the metal. The diamagnetic cationic complex {[NNN]Co(py)}BF4 (2) can be converted to neutral paramagnetic complexes [NNN]Co(OR) (R = Ph 3a, iPr 3b, and H 4) by a simple substitution of the ancillary pyridine ligand in 2. The double bond character between the metal and the anilido nitrogen was evident from short Co-N2,3 bond lengths in the solid-state structures, and further supported by density functional theory calculations. Complex 2 showed well-behaved redox processes at -0.93 and +0.70 V assigned to CoII/III and [NNN]2-/1- redox couples, respectively. In contrast, both complexes 3a and 4 showed some irreversibility in redox processes on either cobalt or ligands.

Formation of a dicationic ruthenium benzyl complex by halide abstraction from a Grubbs-type second-generation benzylidene.

A ruthenium benzylidene complex with a neutral bidentate N-heterocyclic carbene was prepared and evaluated in ring-closing metathesis of diallyl substrates. Reaction with AgPF6 to generate a four-coordinate complex produced an unexpected dicationic ruthenium benzyl degradation product through nucleophilic attack of the NHC ligand on the benzylidene carbon.

N-heterocyclic carbenes and imidazole-2-thiones as ligands for the gold(I)-catalysed hydroamination of phenylacetylene.

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.

Titanium(IV) imido complexes of imine imidazol-2-imine ligands.

Free imine imidazol-2-imine ligands with two different substitution patterns have been isolated for the first time and they were found to exist as an equilibrium mixture of geometric and mesomeric isomers. The relative ratios of these isomers are dependent on both the nature of the substituents and of the solvent. The synthesis of the titanium(IV) alkyl and arylimido complexes of these ligands was unexpectedly found to be very selective and was successfully achieved only with the lesser sterically-demanding 2,4,6-trimethylphenyl derivative IMesN^Imine 2a. The solid-state structure of the alkylimido complex further confirms the zwitterionic character of the ligand. The isolated titanium imido complexes were found to be active catalysts for the polymerisation of ethylene.

New stable aryl-substituted acyclic imino-N-heterocyclic carbene: synthesis, characterisation and coordination to early transition metals.

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).

Coordination study of a new class of imine imidazol-2-imine ligands to titanium(IV) and palladium(II).

A new family of ligand precursors, N-(1-(2,6-dimethylphenylimino)ethyl)-1,3-bis(aryl)imidazol-2-imine hydrochloride, wherein aryl = 2,4,6-trimethylphenyl (3a) and 2,6-diisopropylphenyl (3b), was prepared and structurally characterised. Deprotonation of the salts yields molecules with delocalised pi-electrons, leading to zwitterionic mesomeric structures. Titanium(IV) (4a,b) and palladium(II) (5a,b) complexes were isolated and also structurally characterised. Two different coordination modes were observed where the ligand is either coordinated in a bidentate fashion as expected, or in a monodentate fashion through the more basic aryliminic nitrogen atom.

First aryl-substituted acyclic imino-N-heterocyclic carbene ligand precursor: synthesis, characterisation and coordination with silver(I) and copper(I).

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.