Treatment of Ti (NMe2) 4 with diphenylphosphinic amides Ph2P (O) (NHR) (R = Me, Ph) followed by reaction with tert-butylamine afforded dimeric complexes Ti (NtBu) κ2-Ph2P (O) (NR) μ2-Ph2P (O) (NR) 2 (R = Ph, 3; Me, 4), which were characterized crystallographically. Variable-temperature NMR studies demonstrated significant structural flexibility of both compounds in solution, and Eyring analysis suggests intramolecular conformational fluxionality of the eight-membered Ti2N2P2O2 metallacycles. While nonemissive in THF solution at room temperature, both complexes exhibit aggregation-induced emission upon the addition of hexane as a counter solvent. Solid-state photoluminescence bands occur with maxima at 648 and 632 nm for 3 and 4, respectively, with quantum yields of 4. 3% and 6. 3% and long-lived emission lifetimes (6. 8 and 3. 4 μs, respectively). Time-dependent density functional theory calculations reveal that the low-energy absorption features originate from mixed π (Ti=N) to π (P-phenyl) and π (Ti=N) to d (Ti) charge transfer transitions.
Lawler et al. (Tue,) studied this question.