Base-free synthesis of air- and moisture-stable Ru(III)-NHC complexes, [RuIII(PyNHCR)(Cl)3(H2O)] as precursors for Ru(II)-NHC complexes

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.