Cyclopentadienyl Ligand Effects on Enthalpies of Protonation of the Ru−Ru Bond in Cp‘2Ru2(CO)4Complexes
- 1 December 1997
- journal article
- research article
- Published by American Chemical Society (ACS) in Inorganic Chemistry
- Vol. 36 (26) , 6000-6008
- https://doi.org/10.1021/ic970181e
Abstract
Basicities of a series of Cp‘2Ru2(CO)4 complexes were established by measuring the heats evolved (ΔHMHM) when the complexes were protonated by CF3SO3H in 1,2-dichloroethane at 25.0 °C. Spectroscopic studies show that the protonation occurs at the metal−metal bond to form [Cp‘2Ru2(CO)4(μ-H)]+CF3SO3-, in which all of the CO ligands are terminal. The basicities (−ΔHMHM) increase with the Cp‘2 ligands in the following order: (C5Me4CF3)2 < (C9H7)2 < C5H4C5H4 < C5H4CH2CH2C5H4 < (C5H5)2 < (C5Me5)2 < C5H4CH2C5H4. This trend can be understood in part by considering that more strongly donating Cp‘ ligands increase the basicity of the Ru−Ru bond. Another important factor is the CO-bridging or nonbridging form of each Cp‘2Ru2(CO)4 complex. A dimer with bridging CO groups is significantly less basic than another dimer with only terminal CO groups although the donor abilities of their Cp‘ ligands are nearly equal. The Ru−Ru bond in Cp2Ru2(CO)4 is substantially more basic than the Ru in the related mononuclear CpRu(CO)2H. Molecular structures of [Cp2Ru2(CO)4(μ-H)]+CF3SO3-, [(C5H4CH2C5H4)Ru2(CO)4(μ-H)]+CF3SO3-, and (C5H4CH2CH2C5H4)Ru2(CO)4 as determined by X-ray diffraction studies are also presented.Keywords
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