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

Abstract

The behavior of the cationic alkynylphosphine complex [Rh(η 5-Cp*;)a(PPh2C≅CPh) 2](CF3SC3) (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{KP:η5-C5Me4-(CH 2CPh≈CHPPh2)}Cl(PPh2C≅CPh)](CF 3SO3) (2), and the symmetrical 1,2 -dihydroalkylated derivative [Rh{K2PP'.η5-C5Me 3-1,2-(CH2CPh≈CHPPh2)2}C1] (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-Cpast;)Cl(PPh2C≅CPh) 2](CF3SO3) (1) with Na2CO 3 evolves with the formation of the new asymmetrical 1,2-and 1,3-dihydroactivated isomers [Rh{K2PP'η5-1,2-(PPh 2CH2CPh≈CH)C5Me3(CH 2CPh≈CHPPh2)}Cl](CF3SO3) (3, X-ray) and [Rh{K2PP': η5-1,3-(PPh2CH 2CPh≈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. © 2009 American Chemical Society.