Fig. 1: Design and synthesis of an air- and moisture-stable ruthenium(II) precatalyst.
From: An air- and moisture-stable ruthenium precatalyst for diverse reactivity
a, Selection of ruthenium(II) precatalysts typically used for application, discovery and synthetic method development within C–H functionalization chemistry. Broadly available air-stable precatalysts such as 1 and 2 exhibit poor levels of reactivity under mild reaction conditions and have high barriers that must be overcome to form active catalysts. Preactivated complexes such as 4 and 5 are highly reactive and operate under mild conditions but are extremely air sensitive. The air-stable complex [(tBuCN)5Ru(H2O)](BF4)2 (3) provides an alternative that has broad reactivity without the need for harsh reaction conditions. b, Left: synthesis of complex 3 by zinc reduction of ruthenium(III) trichloride and chloride-to-tetrafluoroborate metathesis. Right: X-ray crystal structure of 3 with 50% probability thermal ellipsoids; BF4 counterions are omitted for clarity. Color coding: lilac, Ru; red, O; blue, N; grey, C. Ligand exchange rate constants for [Ru(H2O)6]2+ and [Ru(NCMe)6]2+ are given in ref. 15. c, Air-stability test of solid complex 3, 4 and 5 over 72 h. d, NMR study of stoichiometric arene C(sp2)–H bond activation under mild reaction conditions using 3 to give biscyclometallated species 7—a key species required for reactivity with halide nucleophiles. Yield was determined by 19F NMR using 1,4-difluorobenzene as an internal standard. r.t., room temperature.
