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

Abstract

Reactivity involving metallacycle ring opening of ortho-metalated bis(phosphinimine)carbazolide complexes ( L Ph -κ 3 N,κ 2 C P-Ph )Lu(THF) ( 1a ) and ( L Pipp -κ 3 N,κ 2 C P-Ph )Lu(THF) ( 1b ); L = [1,8-(Ph 2 P═NAr) 2 dmc]; Ar = Ph ( L Ph ), p -isopropylphenyl ( L Pipp ); dmc = 3,6-dimethylcarbazolide) is described. Reaction of 1a, b with bulky anilines (2,4,6-trimethylaniline, MesNH 2; 2,4,6-triisopropylaniline, TripNH 2 ) promoted metallacycle ring opening of two ortho-metalated P-phenyl groups to liberate the bis(anilide) products ( L Ph -κ 3 N )Lu(NHMes) 2 ( 2 ) and ( L Pipp -κ 3 N )Lu(NHTrip) 2 ( 3 ). Regardless of the quantity of TripNH 2 or MesNH 2 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*NH 2 ) only caused metallacycle ring opening of one ortho-metalated P-phenyl group, affording the mono(anilide) complex ( L Pipp -κ 3 N,κ C P-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 ( L Pipp -κ 3 N,κ C N-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.