Coordination and reactivity study of titanium phenoxo complexes containing a bulky bidentate imino-N-heterocyclic carbene ligand

The synthesis and structural characterisation of early transition metal complexes containing the aryl-substituted acyclic imino-N-heterocyclic carbene ligand are reported. X-ray crystallographic studies of titanium phenoxo complexes confirmed that the NHC ligand coordinates through the carbenoid carbon and the imine nitrogen atoms to form an octahedral complex. NMR spectroscopic analyses revealed restricted rotation about the aryl bonds. Attempts to prepare the corresponding titanium imido complex repeatedly led to decomposition products, presumably due to the enhanced reactivity of the imine group resulting in its cleavage from the C^Imine ligand scaffold. The catalytic activities of the phenoxo complexes towards ethylene polymerisation were assessed.

Graphical abstractTitanium phenoxo complexes containing a heteroditopic imino-N-heterocyclic carbene ligand were prepared. The effect of replacing two chloride ligands by the aryloxides on the performance of the complexes in polymerizing ethylene was studied.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Titanium phenoxide complexes containing a heteroditopic carbene were prepared. ► All complexes were structurally characterised. ► Restricted rotation of the aryl rings was observed in the catecholate complex. ► Upon coordination, the bidentate carbene became more reactive towards nucleophiles. ► All complexes were inactive in the polymerization of ethylene.