Cationic Group 3 Alkyl Complexes with Isopropyl-Substituted Triazacyclononane-amide Ligands: Synthesis, Structure, and Thermal Decomposition Processes

Yttrium and lanthanum dialkyl complexes with the isopropyl-substituted triazacyclononane-amide
monoanionic ligands [iPr2TACN-(B)-NtBu] (B = (CH2)2, L1; SiMe2, L2) are described. For Y, these
were obtained by reaction of Y(CH2SiMe3)2(THF)2 with HL, whereas for La in situ peralkylation of
LaBr3(THF)4 preceded reaction with HL. In C6D5Br solvent, reaction of LMR2 with [PhNMe2H][B(C6F5)4]
results in rapid decomposition involving loss of propene from the ligand. This decomposition is prevented
(Y) or retarded (La) in THF solvent. For yttrium, salts of the cations [LYR(THF)]+ were isolated and
structurally characterized. ES-MS of these cations revealed facile desolvation. At increased nozzle voltages,
fragmentation is observed with initial loss of SiMe4, followed by loss of propene. Thus decomposition
is likely to involve initial cyclometalation of a ligand iPr group, followed by propene extrusion.
Decomposition of [L2LaR(THF)x]+ in THF solution yields the dinuclear dication {[tBuN(Me2Si)N(C2H4)2N(C2H4)NiPr]2La2(THF)2}2+, which was structurally characterized. Kinetic data of the decomposition suggest that the process involves initial THF dissociation.