Base-free synthesis of benchtop stable Ru(III)-NHC complexes from RuCl 3 ·3H 2 O and their use as precursors for Ru(II)-NHC complexes.

A series of Ru(III)-NHC complexes, identified as [Ru III (PyNHC R )(Cl) 3 (H 2 O)] (1a-c), have been prepared, starting from RuCl 3 ·3H 2 O following a base-free route. The Lewis acidic Ru(III) centre operates via a halide-assisted, electrophilic C-H activation for carbene generation. The best results were obtained with azolium salts having the I - anion, while ligand precursors with Cl - , BF 4 - , and PF 6 - 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. Furthermore, these benchtop stable Ru(III)-NHC complexes were shown to be excellent metal precursors for the synthesis of new [Ru II (PyNHC R )(Cl) 2 (PPh 3 ) 2 ] (2a-c) and [Ru II (PyNHC R )(CNC Me )I]PF 6 (3a-c) complexes. All the complexes have been characterised using spectroscopic methods, and the 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.