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

Mixed alkylamido lutetium complexes, LiPrLu(CH2SiMe3)(NHCPh3) (7CPh3) and LiPrLu(CH2SiMe3)(NHDipp) (7Dipp) (LiPr = 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 LiPrLu(CH2SiMe3)2 (6). Unlike complexes supported by the related pincer ligand LPh (LPh = 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 LiPrLu(NHCPh3)2 (8CPh3) and LiPrLu(NHDipp)2 (8Dipp), respectively, as well as 0.5 equivalents of LiPrLu(CH2SiMe3)2, which decomposed in the presence of DMAP. Incorporation of internal Lewis bases was accomplished by replacing the N-aryl substituents in LiPr with 4,6-dimethylpyrimidine groups (LPm, 11). The correspondng dialkyl lutetium complex LPmLu(CH2SiMe3)2 (12) was prepared, from which loss of SiMe4 occured over a period of hours in benzene-d6 solution.