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

Ruthenium allyl carbene complexes of the type [RuCp(=C(R)-(eta(3)-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 eta(3)-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 C-4-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 eta(4)-butadiene complexes. In these, one R of PR3 is sigma-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 C-4-unit features eta(3)-allyl moiety and the metal center is eta(2)-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.