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Abstract:
Dehydrohalogenation of secondary diarylphosphine ruthenium complexes in the presence of benzonitrile yields stable, isolable nitrile adducts of the formula [Ru(η5-indenyl)(PAr2)(NCPh)(PPh3)], in which the terminal phosphido ligand is pyramidal at P and contains a stereochemically active lone pair. Unlike the analogous carbonyl adducts [Ru(η5-indenyl)(PAr2)(CO)(PPh3)], these benzonitrile complexes behave as masked sources of the highly reactive planar phosphido complexes [Ru(η5-indenyl)(PAr2)(PPh3)], which contain a Ru═PAr2 π bond. This is illustrated by the addition (or cycloaddition) reactions of the benzonitrile adducts with dihydrogen, methyl iodide, and 1-hexene, as well as their thermal decomposition via orthometalation of the PPh3 ligand. Enthalpies of CO vs NCPh dissociation from the [Ru(η5-indenyl)(PR2)(PPh3)] fragments (R = alkyl, aryl) have been calculated, as has the trajectory of addition of H2 to the model planar phosphido complex [Ru(η5-indenyl)(PMe2)(PMe3)]. The latter study shows the intermediacy of an η2-H2 adduct, [Ru(η5-indenyl)(PAr2)(η2-H2)(PPh3)], in the formation of [RuH(η5-indenyl)(HPMe2)(PMe3)], a further indication of the importance of the variable binding modes of the terminal phosphido ligand in this system.
