C−C Bond Formation between the μ‐Alkylidyne Ligands in a Diruthenium Bis(μ‐alkylidyne) Complex; σ‐ and π‐Aromaticity of the Ru2C2 Core

Abstract

AbstractZn‐free μ‐ethylidyne‐μ‐propylidyne complex, [(Cp*Ru)2(μ‐CMe)(μ‐CEt)] (2 b; Cp*=C5Me5) was synthesized by the treatment of [(Cp*Ru)2(μ‐CMe)(μ‐CEt)(μ‐ZnCl2)] (1 b) with ethylenediamine. Similarly, bis(μ‐ethylidyne) complex [Cp*Ru(μ‐CMe)]2 (2 a) was synthesized from [Cp*RuCl2]2. Although the bis(μ‐alkylidyne) complexes 2 a, b adopted a coordinatively unsaturated 32‐electron configuration, these complexes were unreactive toward acetylene, ethylene, and H2. Adaptive natural density partitioning (AdNDP) analysis suggested that the enhanced stability of 2 a and 2 b was due to the dual aromaticity of the planar Ru2C2 core, viz. σ‐ and π‐aromaticity. On the other hand, complexes 2 a and 2 b reacted with π‐acidic CO to yield a μ‐η2:η2‐alkyne complex, [(Cp*Ru)2(μ‐η2:η2‐MeCCR)(μ‐CO)] (6 a, R=Me; 6 b, R=Et) via C−C bond formation between the μ‐alkylidyne ligands, along with Ru−Ru bond formation. Dearomatization of the Ru2C2 core is crucial for this transformation. Complex 6 a further reacted with CO in the presence of methanol to yield [Cp*Ru(CO)(μ‐CO)]2 (7) by liberating 2‐butyne.