Alkylamido lutetium complexes as prospective lutetium imido precursors: synthesis, characterization and ligand design

Mixed alkylamido lutetium complexes, L^iPrLu(CH₂SiMe₃)(NHCPh₃) (7CPh3) and L^iPrLu(CH₂SiMe₃)(NHDipp) (7Dipp) (L^iPr = 2,5-[ⁱPr₂P = N(4-ⁱPrC₆H₄)]₂C₄H₂N^-), were synthesized by addition of a bulky primary amine, NH₂R (R = CPh₃, Dipp) (Dipp = 2,6-ⁱPr₂C₆H₃) to the dialkyl complex L^iPrLu(CH₂SiMe₃)₂ (6). Unlike complexes supported by the related pincer ligand L^Ph (L^Ph = 2,5-[Ph₂P = N(4-ⁱPrC₆H₄)]₂C₄H₂N^-) these species proved resistant to C-H cyclometalative processes. Attempts to access lutetium imdes via addition of 4-dimethylaminopyridine (DMAP) to 7CPh3 and 7Dipp promoted disproportionation, affording 0.5 equivalents of the corresponding bisamide complexes L^iPrLu(NHCPh₃)₂ (8CPh3) and L^iPrLu(NHDipp)₂ (8Dipp), respectively, as well as 0.5 equivalents of L^iPrLu(CH₂SiMe₃)₂, which decomposed in the presence of DMAP. Incorporation of internal Lewis bases was accomplished by replacing the N-aryl substituents in L^iPr with 4,6-dimethylpyrimidine groups (L^Pm, 11). The correspondng dialkyl lutetium complex L^PmLu(CH₂SiMe₃)₂ (12) was prepared, from which loss of SiMe₄ occured over a period of hours in benzene-d₆ solution.