Cyclometallated Platinum(II) Complexes with a Phenylpropene-derived π/σ-Chelator and N-heterocyclic Carbenes

A series of heteroleptic platinum(II) complexes of the general formula [PtX(iPrEug)(NHC)] (2-7) bearing the organometallic π/σ chelator iPrEug (isopropyl eugenoxyacetate), varying halido and NHCs ligands derived from imidazole, benzimidazole and triazole have been prepared and fully characterized by elemental analyses, ESI mass spectrometry, IR and NMR spectroscopies. Complexes 3 and 5-7 were also characterized by single-crystal X-ray diffraction. The air-stable complexes are rare examples of platinum(II) compounds containing three different types of carbon donors, i.e. aryl, carbene and olefin. Unsymmetrical NHCs lead to rotameric pairs of 4 and 5 exhibiting different NMR spectroscopic features. Spectroscopic studies also revealed that the introduction of a NHC leads to a weakening of the metal-olefin bond and strengthening of the metal-aryl bond. Backbone and thus electronic variations among the NHCs on the other hand show little influence on the bonding of the iPrEug chelator.

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