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 [ i Pr 2 TACN-(B)-N t Bu] (B = (CH 2 ) 2, L1; SiMe 2, L2 ) are described. For Y, these were obtained by reaction of Y(CH 2 SiMe 3 ) 2 (THF) 2 with H L, whereas for La in situ peralkylation of LaBr 3 (THF) 4 preceded reaction with H L . In C 6 D 5 Br solvent, reaction of L MR 2 with [PhNMe 2 H][B(C 6 F 5 ) 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 [ L YR(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 SiMe 4, followed by loss of propene. Thus decomposition is likely to involve initial cyclometalation of a ligand i Pr group, followed by propene extrusion. Decomposition of [ L2 LaR(THF) x ] + in THF solution yields the dinuclear dication {[ t BuN(Me 2 Si)N(C 2 H 4 ) 2 N(C 2 H 4 )N i Pr] 2 La 2 (THF) 2 } 2+, which was structurally characterized. Kinetic data of the decomposition suggest that the process involves initial THF dissociation.