Organic chemistry of binuclear metal centres. Part 6. µ-Vinylidene and µ-ethylidyne diruthenium complexes: crystal structures of cis-[Ru2(CO)2(µ-CO)(µ-CCH2)(η-C5H5)2] and cis-[Ru2(CO)2(µ-CO)(µ-CMe)(η-C5H5)2][BF4]
Abstract
The dimetallacycles [Ru2(CO)(µ-CO){µ-C(O)C2HR}(η-C5H5)2](R = H or Ph) isomerise in boiling toluene to the µ-vinylidene complexes [Ru2(CO)2(µ-CO)(µ-CCHR)(η-C5H5)2], shown by a deuterium-labelling experiment to involve an intramolecular hydrogen shift. Protonation of the µ-C![[double bond, length half m-dash]](https://www.rsc.org/images/entities/char_e006.gif)
CH2 complex with HBF4·OEt2 gives the µ-ethylidyne species [Ru2(CO)2(µ-CO)(µ-CMe)(η-C5H5)2][BF4], which deprotonates readily when treated with water, triethylamine, or methyl-lithium; with NaBH4 the cation is attacked by hydride to produce the µ-ethylidyne complex [Ru2(CO)2(µ-CO)(µ-CHMe)(η-C5H5)2]. Successive addition of methyl-lithium and HBF4·OEt2 to [Ru2(CO)4(η-C5H5)2] also yields the complex [Ru2(CO)2(µ-CO)(µ-CMe)(η-C5H5)2][BF4], whose subsequent conversion to [Ru2(CO)2(µ-CO)(µ-CCH2)(η-C5H5)2] or [Ru2(CO)2(µ-CO)(µ-CHMe)(η-C5H5)2] provides an excellent route to these complexes. Similar successive addition of phenyl-lithium, HBF4·OEt2, and NaBH4 to [Ru2(CO)4(η-C5H5)2] gives [Ru2(CO)2(µ-CO)(µ-CHPh)(η-C5H5)2] in high yield. The molecular structures of cis-[Ru2(CO)2(µ-CO)(µ-CCH2)(η-C5H5)2] and cis-[Ru2(CO)2(µ-CO)(µ-CMe)(η-C5H5)2][BF4] have been determined by X-ray diffraction studies. Crystals of both compounds are monoclinic, space group P21/n with Z= 4 and unit-cell dimensions a= 8.620(6), b= 15.712(9), c= 10.844(8)Å, β= 92.57(4)° and a= 9.121(2), b= 9.724(3), c= 20.666(6)Å, β= 106.42(3)° respectively. The structures were solved by heavy-atom methods and refined by least squares to give final residuals R of 0.051 and 0.026 for 2 503 and 3 044 unique, observed, diffractometer data respectively. Both cis-[Ru2(CO)2(µ-CO)(µ-CCH2)(η-C5H5)2] and cis-[Ru2(CO)2(µ-CO)(µ-CMe)(η-C5H5)2]+ show approximate Cs symmetry in the solid state, with Ru–Ru single bond distances of 2.696(1) and 2.714(1)Å respectively. In both cases each ruthenium atom is co-ordinated by terminal carbonyl and η-cyclopentadienyl ligands in addition to bridging carbonyl and hydrocarbon (vinylidene and ethylidyne) groups. The geometry and orientation of the bridging vinylidene ligand is consistent with a C–C bond order of two [C–C 1.326(11)Å] and contact carbon bonding to the Ru2 fragment via donor and acceptor interactions of σ and π symmetry in the Ru2C plane. The µ-ethylidyne ligand in cis-[Ru2(CO)2(µ-CO)(µ-CMe)(η-C5H5)2][BF4] shows average Ru–C distances shorter than those of the η-vinylidene ligand in cis-[Ru2(CO)2(µ-CO)(µ-CCH2)(η-C5H5)2][1.937(4)vs. 2.030(7)Å], and has a longer C–C distance [1.462(6)Å] consonant with a C(sp)-C(sp3) single bond. These geometric features, and the reactivity of the cationic µ-ethylidyne complex towards nucleophiles, are explained in terms of a simple molecular orbital model.
Please wait while we load your content...
