Titanium Carboxylate Complexes through CO₂ Capture

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–Cexo 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.