Benzeneruthenium(II) chloride dimer
[CAS# 37366-09-9]

Identification

• Classification: Organic raw materials >> Organometallic compound >> Organic ruthenium
• Name: Benzeneruthenium(II) chloride dimer
• Synonyms: Bis[(benzene)dichlororuthenium]
• Molecular Formula: C₁₂H₁₂Cl₄Ru₂
• Molecular Weight: 500.18
• CAS Registry Number: 37366-09-9
• EC Number: 626-792-3
• SMILES: C1=CC=CC=C1.C1=CC=CC=C1.Cl[Ru]Cl.Cl[Ru]Cl

Safety Data

• Hazard Symbols: GHS07 Warning
• Risk Statements: H315-H319-H335
• Safety Statements: P261-P264-P264+P265-P271-P280-P302+P352-P304+P340-P305+P351+P338-P319-P321-P332+P317-P337+P317-P362+P364-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Skin irritation	Skin Irrit.	2	H315
Eye irritation	Eye Irrit.	2	H319
Specific target organ toxicity - single exposure	STOT SE	3	H335
Chronic hazardous to the aquatic environment	Aquatic Chronic	4	H413
Acute toxicity	Acute Tox.	4	H312
Acute toxicity	Acute Tox.	4	H332
Acute toxicity	Acute Tox.	4	H302

Discovery and Applications

Benzeneruthenium(II) chloride dimer is an organometallic compound consisting of two ruthenium(II) centers each coordinated to a benzene ligand and bridged by two chloride ligands. The general formula of the compound is [(C₆H₆)RuCl₂]₂, where each ruthenium atom is in the +2 oxidation state and bonded to an η⁶-benzene ring and two chloride ligands, one of which forms a bridge between the metal centers.

This compound is part of a broader class of arene–ruthenium complexes, in which the η⁶-coordinated arene provides electron density to the metal center via delocalized π-interactions. In benzeneruthenium(II) chloride dimer, the benzene ligand is firmly η⁶-bound to the ruthenium atom, creating a stable sandwich-like structure. The dimeric nature of the complex, with two bridging chlorides, is common among Group 8 arene-metal halide dimers, and this feature imparts both stability and reactivity suitable for further functionalization.

Benzeneruthenium(II) chloride dimer is typically synthesized by reacting ruthenium trichloride hydrate (RuCl₃·xH₂O) with benzene in the presence of a reducing agent such as ethanol or zinc under reflux conditions. This reduction leads to formation of the Ru(II) species, and the η⁶-benzene ligand binds to the metal center while chlorides coordinate to complete the octahedral coordination environment. The resulting product precipitates as an air-stable red or reddish-brown crystalline solid.

The compound serves as a valuable precursor in organometallic and coordination chemistry, especially for the preparation of monomeric [Ru(arene)(L)₂Cl]⁺-type complexes, where L represents monodentate or bidentate ligands such as phosphines, N-heterocyclic carbenes, or nitrogen-containing ligands. Ligand substitution reactions on the chloride and/or arene ligands enable the synthesis of a wide variety of ruthenium complexes with tailored electronic and steric properties.

Benzeneruthenium(II) chloride dimer has been used extensively in the development of catalytic systems. Its applications include homogeneous catalysis for hydrogenation, oxidation, and transfer hydrogenation reactions. The arene ligand's ability to stabilize low oxidation state ruthenium is crucial in such transformations. Furthermore, its role in C–H activation and asymmetric catalysis has been actively explored in both academic and industrial settings.

This dimer is also of interest in medicinal chemistry, particularly in the design of organoruthenium compounds with anticancer properties. Some derivatives of arene-ruthenium complexes have shown cytotoxic activity and are under investigation for their potential in chemotherapy. The stable yet labile coordination environment of the benzene–ruthenium core makes it a suitable scaffold for further functionalization with bioactive ligands or delivery vectors.

In terms of handling and stability, benzeneruthenium(II) chloride dimer is relatively stable in air and moisture under ambient conditions but should be stored in a dry environment to avoid hydrolysis. It is soluble in organic solvents such as dichloromethane, chloroform, acetone, and ethanol, facilitating its use in a wide range of laboratory procedures.

Characterization of the compound is commonly performed using spectroscopic methods. Nuclear magnetic resonance (NMR) spectroscopy confirms the presence of the coordinated benzene ring and the metal center. Infrared (IR) spectroscopy reveals characteristic metal–chloride stretching bands, while single-crystal X-ray diffraction provides detailed structural information, confirming the dimeric structure and coordination geometry.

In summary, benzeneruthenium(II) chloride dimer is a versatile and well-established organoruthenium compound that serves as a crucial intermediate in the synthesis of a wide range of organometallic complexes. Its applications span catalysis, materials science, and medicinal chemistry, underlining its significance in modern coordination chemistry.

References

2016. A prolific catalyst for dehydrogenation of neat formic acid. Nature Communications, 7.
DOI: 10.1038/ncomms11308

2014. Ruthenium-Catalyzed Hydrogen Generation from Alcohols and Formic Acid, Including Ru-Pincer-Type Complexes. Topics in Organometallic Chemistry.
DOI: 10.1007/3418_2014_84

2012. Me-BIPAM for the Synthesis of Optically Active 3-Aryl-3-hydroxy-2-oxindoles by Ruthenium-catalyzed Addition of Arylboronic Acids to Isatins. Chemistry - An Asian Journal, 7(7).
DOI: 10.1002/asia.201200481