A series of Ru(III)-NHC complexes, identified as [RuIII(PyNHCR)(Cl)3(H2O)] (1a-c), have been prepared, starting from RuCl3·3H2O following a base-free route. The Lewis acidic Ru(III) centre operates via a halide-assisted, electrophilic C-H...

The effect of contact ion pairs and comparison of the three halide ions on the C-H activation during the synthesis of Ru(III)-NHC complexes 1a and 1b have been investigated. DFT modeling of two pathways for the formation of Ru(III)-NHC complexes, viz. halide coordination pathway and ion-pair pathway, reveals the effect of ion pairing. The ion-pair path is preferred for azolium salts with Cl- and I-, whereas with Br-, the reaction follows the halide coordination route leading to the mixed halide complex. The higher activation barrier for the reaction with Cl- ions can be explained in terms of greater stabilization of the intermediates, compared to the transition states, due to halide coordination or hydrogen bonding with Cl- ions. Furthermore, the successful synthesis of 1b from the reaction of RuCl3·3H2O and the corresponding imidazolium salt precursor with Cl- in dioxane at 100 °C validates the conclusions of the DFT studies.

A series of Ru(III)-NHC complexes, identified as [RuIII(PyNHCR)(Cl)3(H2O)] (1a-c), have been prepared, starting from RuCl3·3H2O following a base-free route. The Lewis acidic Ru(III) centre operates via a halide-assisted, electrophilic C-H activation for carbene generation. Best results were obtained with azolium salts having I- anion while ligand precursors with Cl-, BF4-, and PF6- gave no complex formation and those with Br- gave a product with mixed halides. The structurally simple, air and moisture-stable complexes represent rare examples of paramagnetic Ru(III)-NHC complexes. Further, these benchtop stable Ru(III)-NHC complexes were shown to be excellent metal precursors for the synthesis of new [RuII(PyNHCR)(Cl)2(PPh3)2] (2a-c) and [RuII(PyNHCR)(CNCMe)I]PF6 (3a-c) complexes. All the complexes have been characterised using spectroscopic methods, and structures of 1a, 1b, 2c and 3a have been determined using the single-crystal X-ray diffraction technique. This work allows easy access to new Ru-NHC complexes for the study of new properties and novel applications.

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A series of Ru(III)-PyNHC complexes, identified as [RuIII(PyNHCR)(Cl)3(H2O)] (1ac), have been prepared following a base-free route. The structurally simple, air and moisture stable complexes represent rare examples of Ru(III)-NHC complexes. Further, these benchtop stable Ru(III)-PyNHC complexes were shown to be excellent metal precursors for the synthesis of new [RuII(PyNHCR)(Cl)2(PPh3)2] (2a-c) and [RuII(PyNHCR)(CNCMe)I]PF6 (3a-c) pincer complexes. All the complexes have been characterised using spectroscopic methods, and structures of 1a, 1b, 2c and 3a have been determined using the single-crystal X-ray diffraction technique.