Abstract
AbstractThe cover picture shows various reactions of the carbene complex [Ru(η5‐C5Me5){κ2‐P,N‐PiPr2NHC5H4N}(=CHC6H5)]+ over a view of Cádiz (phoenician Gadir), one of the oldest european continuously inhabited cities. These processes illustrate its ambiphilic character. It reacts as a nucleophile with Br?nsted acids, yielding a complex with an η2‐benzyl ligand. There are some previously described examples of this coordination mode for early transition metal benzylidene complexes, but this represents the first example of a structural characterization in the case of ruthenium complexes. The electrophilic behaviour of [Ru(η5‐C5Me5){κ2‐P,N‐PiPr2NHC5H4N}(=CHC6H5)]+ has been shown by reaction with hydride, giving rise to an η1‐benzyl complex. Normally, NMR studies allow unambiguous characterization of the η1 coordination of a benzyl ligand. However, especially for late transition metal complexes, distinction between the usually disregarded η2 and the generally considered η3 mode is difficult. We propose, from this study, that the presence of an η2‐benzyl ligand in metal complexes should not be ruled out only on the basis of their NMR spectra. The carbene complex also reacts with other bases like KOtBu, KN(SiMe3)2 and PMe3. Details are discussed in the article by I. Macías‐Arce, M. C. Puerta and P. Valerga on p. 1767 ff.
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