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

Article abstract of DOI:10.1021/om020094g

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 tetramethyl-fulvene-type complexes.