Ferrocenophanes are ferrocene derivatives in which the cyclopentadienyl ligands are connected by one or more bridging groups. Silicon-bridged [1]ferrocenophanes, for example, can serve as strained monomers to give poly(ferrocenylsilanes) via ring-opening polymerization. Sila[1]ferrocenophanes are readily accessible via salt-metathesis reactions between the corresponding dilithioferrocene derivative and a silicon dichloride of the type RR’SiCl₂. In contrast, less is known about ruthenocenophanes, and no examples of a silicon-bridged [1]ruthenocenophane had been known so far.

Jens Müller, University of Saskatchewan, Saskatoon, Canada, and colleagues have synthesized the first sila[1]ruthenocenophanes (pictured). The team used a heterogeneous reaction mixture, in which dichlorodimethylsilane (Me₂SiCl₂) was slowly added to a suspension of 1,1′-dilithioruthenocene·tmeda (tmeda = tetramethylethylenediamine) in a mixture of heptane and dibutyl ether at 85 °C. They obtained an isolated yield of 1 % of crystalline sila[1]ruthenocenophane. Improved yields were observed for an ⁱPr-substituted sila[1]ruthenocenophane, which was synthesized in 10 % isolated yield.

The team investigated the difference between these difficult-to-access sila[1]ruthenocenophanes and sila[1]ferrocenophanes, which can be obtained in high isolated yields. They propose that the cyclopentadienyl units in the ruthenocene derivatives basically react independently from each other, which leads to the formation of unwanted disubstituted products. In the corresponding ferrocene derivatives, the reactivity of the second lithiated cyclopentadienyl ring in a key intermediate is significantly reduced, promoting the formation of the desired bridged products. According to the researchers, sila[1]ruthenocenophanes could be useful monomers, if the problem of low yields were to be resolved.

• Sila[1]ruthenocenophanes: Long Sought‐After Family Members,
  Satavisha Bhattacharya, Ahmadreza Nezamzadeh, Jianfeng Zhu, Jens Müller,
  Chem. Eur. J. 2023.
  https://doi.org/10.1002/chem.202300121