Titanium Carboxylate Complexes through CO2 Capture

Abstract

Addition of gaseous CO₂ to solutions of bis(π-η⁵:σ-η¹-pentafulvene)titanium complexes results in the selective insertion reaction of one equivalent of O═C═O into one of the two frustrated Ti–C_exo bonds under mild conditions. The formation of κ¹O- and κ²O,O-carboxylate titanium complexes is observed and characterized by single crystal X-ray analysis, NMR and IR spectroscopy. The nature of Ti–O interactions is established by computational studies. The reactivity of the remaining pentafulvene ligand is demonstrated in reactions with H-acidic and multiple-bond-containing substrates. The reactions with etheric HCl results in the selective formation of Ti–Cl complexes by protonation of the second pentafulvene moiety, disregarding the carboxylate ligand. The formed chlorido complexes are used in follow-up reactions with methyllithium, resulting in the methylation of the complexes via salt metathesis reactions, and reduction of the chloride complexes with sodium amalgam results in the formation of dimeric κ¹O-μ-O/bridged-carboxylate Ti^(III) complexes.