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Facile Single or Double C−H Bond Activation on a Cp* Ligand Promoted by the Presence of Alkynylphosphine Ligands

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posted on 12.01.2009, 00:00 authored by María Bernechea, Jesús R. Berenguer, Elena Lalinde, Javier Torroba
The behavior of the cationic alkynylphosphine complex [Rh(η5-Cp*)Cl(PPh2CCPh)2](CF3SO3) (1) under thermal or basic conditions is described. Complex 1 rearranges thermally (toluene, reflux) to generate a solution from which a mixture formed by 1, the monohydroalkylated derivative [Rh{κP:η5-C5Me4(CH2CPhCHPPh2)}Cl(PPh2CCPh)](CF3SO3) (2), and the symmetrical 1,2 -dihydroalkylated derivative [Rh{κ2PP′:η5-C5Me3-1,2-(CH2CPhCHPPh2)2}Cl](CF3SO3) (3′) (∼30:60:10, respectively) can be isolated. From this mixture, compounds 1 and 2 cocrystallize together, giving rise to a solid solution, as has been confirmed by X-ray crystallography. In contrast, treatment of [Rh(η5-Cp*)Cl(PPh2CCPh)2](CF3SO3) (1) with Na2CO3 evolves with the formation of the new asymmetrical 1,2- and 1,3-dihydroactivated isomers [Rh{κ2PP′:η5-1,2-(PPh2CH2CPhCH)C5Me3(CH2CPhCHPPh2)}Cl](CF3SO3) (3, X-ray) and [Rh{κ2PP′:η5-1,3-(PPh2CH2CPhCH)C5Me3(CH2CPhCHPPh2)}Cl](CF3SO3) (4), generated by the occurrence of a simultaneous 1,2- or 1,3-double C−H bond addition to the triple bonds, together with an additional isomerization process. A detailed study of this reaction (reflux or room temperature) provides evidence that these asymmetrical deactivated complexes (3, 4) are generated by initial formation of the corresponding symmetrical 1,2- and 1,3-dihydroalkylated species 3′ and 4′, respectively.

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