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

Zn-free μ-ethylidyne-μ-propylidyne complex, [(Cp*Ru) 2 (μ-CMe)(μ-CEt)] (2 b; Cp*=C 5 Me 5 ) was synthesized by the treatment of [(Cp*Ru) 2 (μ-CMe)(μ-CEt)(μ-ZnCl 2 )] (1 b) with ethylenediamine. Similarly, bis(μ-ethylidyne) complex [Cp*Ru(μ-CMe)] 2 (2 a) was synthesized from [Cp*RuCl 2 ] 2 . Although the bis(μ-alkylidyne) complexes 2 a, b adopted a coordinatively unsaturated 32electron configuration, these complexes were unreactive toward acetylene, ethylene, and H 2 . 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 Ru 2 C 2 core, viz. σand π-aromaticity. On the other hand, complexes 2 a and 2 b reacted with π-acidic CO to yield a μ-η 2 :η 2 -alkyne complex, [(Cp*Ru) 2 (μ-η 2 :η 2 -MeCCR)(μ-CO)] (6 a, R=Me; 6 b, R=Et) via CÀ C bond formation between the μalkylidyne ligands, along with RuÀ Ru bond formation. Dearomatization of the Ru 2 C 2 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.