Half-Sandwich Titanium(IV) Complexes with Klaui's Tripod Ligand

Abstract

Treatment of [Ti(O-i-Pr)2Cl2] with NaLOEt (LOEt- = [CpCo{P(O)(OEt)2}3]-, Cp = η5-C5H5) afforded [LOEtTi(O-i-Pr)2Cl] that reacted with HCl in ether to give [LOEtTiCl3] (1). The average Ti−O and Ti−Cl distances in 1 are 1.975 and 2.293 Å, respectively. Reaction of titanyl sulfate with NaLOEt in water followed by addition of HBF4 afforded [LOEtTiF3] (2), the Ti−O and Ti−F distances of which are 2.020(2) and 1.792(2) Å, respectively. The Zr(IV) analogue [LOEtZrF3] (3) was prepared similarly from zirconyl nitrate, NaLOet, and HBF4 in water. The Zr−O and average Zr−F distances in 3 are 2.139(2) and 1.938(2) Å, respectively. Treatment of 1 with tetrachlorocatechol (H2Cl4cat) afforded [LOEtTi(Cl4cat)Cl] (4). The average Ti−O(P), Ti−O(C), and Ti−Cl distances in 4 are 1.972, 1.926, and 2.334 Å, respectively. Hydrolysis of 4 in the presence of Et3N yielded the μ-oxo dimer [(LOEt)2Ti2(Cl4cat)2(μ-O)] (5). The average Ti−O(P), Ti−O(C), and Ti−O(Ti) distances in 5 are 2.027, 1.926, and 1.7977(9) Å. Treatment of 1 with 1,1‘-binaphthol (BINOLH2) in the presence of Et3N afforded [(LOEt)2Ti2(μ-O)2(μ-BINOL)]·2BINOLH2 (6·2BINOLH2). Complex 1 is capable of catalyzing ring opening of epoxides with Me3SiN3 under solvent-free conditions presumably via a Ti−azide intermediate.