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Free keywords:
low coordinate; manganese; N-heterocyclic carbene; complex; alkene complex
Abstract:
Low-coordinate zero-valent metal species are implicated as key intermediates in various transition-metal-catalyzed and -mediated reactions. However, knowledge on this type of metal species has been mainly restricted to the metals in groups 8–10, and that on the earlier transition-metal analogs is very limited. Herein, we report three-coordinate formal Mn(0) complexes [(NHC)Mn(η2:η2-dvtms)] (NHC = N-heterocyclic carbene, dvtms = divinyltetramethyldisiloxane). Spectroscopic and computational studies established that these formal Mn(0) complexes have an S = 3/2 ground-spin state and feature strong metal-to-alkene π backdonation. As a result of the high covalency of the metal-ligand bonding, these formal Mn(0) complexes are best described as resonance among a series of limiting canonical structures of Mn(0)-dvtms, Mn(II)-[dvtm]2–, and Mn(IV)-[dvtms]4–. These formal Mn(0) complexes can perform reductive coupling with unsaturated hydrocarbons and show diversified reactivity toward H2O, H2, CO, and I2, which hint at the synthetic utility of the three-coordinate formal Mn(0) species.
