Reactions of RuCp and RuCp* Allyl Carbene Complexes: Products Derived from Activation of Phenyl, Cyclohexyl, and Methyl C−H Bonds in PPh₃, PCy₃, and Cp* Ligands

Abstract

Ruthenium allyl carbene complexes of the type [RuCp(C(R)-(η3-CHC(R)CHPR‘3))]PF6 (R, R‘ = aryl, alkyl substituents) are characterized by two reaction modes. (i) They behave as masked coordinatively unsaturated complexes and react readily with the donor ligands PR3 and P(OR)3 to give η3-butadienyl complexes. This is not a simple nucleophilic addition at the metal center but involves changes in both the bonding mode and the stereochemistry of the allyl carbene C4-chain. The incoming nucleophile induces C−H bond activation effecting formally a 1,4 hydrogen shift. (ii) They are capable of activating C−H bonds of aryl and alkyl groups in the bulky tertiary phosphine ligands PPh3 and PCy3 to give novel η4-butadiene complexes. In these, one R of PR3 is σ-bonded to the metal center. A divergent rearrangement results if the allyl carbene complex derives from parent acetylene (instead of a terminal alkyne). In this case the C4-unit features a η3-allyl moiety and the metal center is η2-coordinated to an arene ring of the PPh3 substituent. Finally, RuCp* allyl carbene complexes have been prepared for the first time. They are reactive entities and react slowly with cleavage of one of the ring methyl C−H bonds of the Cp* ligand to give tetramethylfulvene-type complexes.