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

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.