The eighteen new μ-alkylidene ruthenium complexes
5a–r and
5t are very easily and cleanly obtained along the diazoalkane or the hydrazone routes that involve treatment of the dinuclear, metal-metal doubly bonded precursor compound [(η
5-C
5H
5)Ru(μ-NO)]
2 (
3) either with the diazoalkanes oxidizing agent (e.g., MnO
2), with the respective hydrazones. Similarly, sulfur dioxide adds cleanly to the RuRu double bond of
3, thus giving the complex (μ-SO
2)[(η
5-C
5H
5)Ru(NO)]
2 (
5s). Regardless of the nature of the carbene bridge ligands, the dimetallacyclopropanes exhibit, in contrast to their iron analogues, exclusively terminal nitrosyl ligands.
cis/trans-Isomerism with predominating amounts of the
trans-isomers is observed for the derivatives that display unsymmetrically substituted carbene bridges.Treatment of the μ-methylene- and μ-ethylidene complexes (μ-CH
2)[(η
5-C
5H
5)Ru(NO)]
2 (
5a) and (μ-CHCH
3)[(η
5-C tetrafluoroboric acid or trifluoromethanesulfonic acid in diethyl ether yields, at ambient temperature, quantitatively the ionic complexes
6a,b and
7a,b, respectively, which were shown by
1H NMR spectroscopy to contain metal-metal bridging hydrogen functionalities. The reaction of hydrogen bromide with
5a under the same conditions gives the neutral bromo(methyl) complex
6d. This latter compound results from the isolable ionic intermediate of composition [(μ-CH
2)(μ-H){(η
5C
5H
5)Ru(NO)}
2]
+Br
? (
6c), which reaction stems from the nucleophilicity of the halide ion present in
6c.
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