Kinetic and Mechanistic Investigation of Metallacycle Ring Opening in an Ortho-Metalated Lutetium Aryl Complex

Reactivity involving metallacycle ring opening of ortho-metalated bis(phosphinimine)carbazolide complexes (LPh-κ3N,κ2CP-Ph)Lu(THF) (1a) and (LPipp-κ3N,κ2CP-Ph)Lu(THF) (1b); L = [1,8-(Ph2PNAr)2dmc]; Ar = Ph (LPh), p-isopropylphenyl (LPipp); dmc = 3,6-dimethylcarbazolide) is described. Reaction of 1a,b with bulky anilines (2,4,6-trimethylaniline, MesNH2; 2,4,6-triisopropylaniline, TripNH2) promoted metallacycle ring opening of two ortho-metalated P-phenyl groups to liberate the bis(anilide) products (LPh-κ3N)Lu(NHMes)2 (2) and (LPipp-κ3N)Lu(NHTrip)2 (3). Regardless of the quantity of TripNH2 or MesNH2 utilized, double ring opening always prevailed to afford the bis(anilide) product, rather than the mono(anilide). In contrast, reaction of complex 1b with the bulkier reagent 2,4,6-tri-tert-butylaniline (Mes*NH2) only caused metallacycle ring opening of one ortho-metalated P-phenyl group, affording the mono(anilide) complex (LPipp-κ3N,κCP-Ph)Lu(NHMes*) (4) exclusively. Complex 4 rapidly undergoes an intramolecular rearrangement whereby metalation of an N-aryl group promotes metallacycle ring opening of the ligated P-phenyl moiety to give (LPipp-κ3N,κCN-Pipp)Lu(NHMes*) (5) as the structural isomer. Through deuterium labeling and kinetic studies it was established that the thermal rearrangement of 4 does not proceed through an imido intermediate. Compounds 2, 3, and 5 were characterized by single-crystal X-ray diffraction studies.