Titanium(IV) and zirconium(IV) sulfato complexes containing the Kläui tripodal ligand: Molecular models of sulfated metal oxide surfaces

Treatment of titanyl sulfate in about 60 nM sulfuric acid with NaL, (LOEt= [(η5-C5H5)Co-{(P(O)(OEt)2}3]-) afforded the μ-sulfato complex [(LOEtOEtTi)2(μ-O)2(μ-SO4)] (2). In more concentrated sulfuric acid (> 1 M), the same reaction yielded the di-μ-sulfato complex [(LOEtTi)2(μ-O)(μ-SO4)2] (3). Reaction of 2 with HOTf (OTf = triflate, CF3SO3) gave the tris-(triflato) complex [LOEtTi(OTf)3] (4), whereas treatment of 2 with Ag(OTf) in CH2Cl2afforded the sulfato-capped trinuclear complex [{(LOEt)3Ti3(μ-O)3}(μ3-SO4){Ag(OTf)}][OTf] (5), in which the Ag(OTf) moiety binds to a μ-oxo group in the Ti3(μ-O)3core. Reaction of 2 in H2O with Ba(NO3)2afforded the tetranuclear complex (LOEt)4Ti4(μ-O)6(6). Treatment of 2 with [{Rh(cod)Cl}2] (cod = 1,5-cyclooctadiene), [Re(CO)5Cl], and [Ru(tBu2-bpy)(PPh3)2Cl2] (tBu2bpy = 4,4′-dl-tert-butyl-2,2′-dipyridyl) in the presence of Ag(OTf) afforded the heterometallic complexes [(LOEt)2Ti2(O)2(SO4){Rh- (cod)}2][OTf]2(7), [(LOEt)2Ti(O)2-(SO4){Re(CO)3}][OTf] (8), and [{(LOEt)2Ti2(μ-O)}(μ3-SO4)(μ-O)2{Ru-(PPh3)(tBu2bpy)}] [OTf]2(9), respectively. Complex 9 is paramagnetic with a measured magnetic moment of about 2.4 μB. Treatment of zirconyl nitrate with NaLOEtin 3.5 M sulfuric acid afforded [(LOEt)2Zr(NO3)][LOEtZr(SO4)-(NO3)] (10). Reaction of ZrCl4in 1.8 M sulfuric acid with NaLOEtin the presence Na2SO4gave the μ-sulfato-bridged complex [LOEtZr(SO4)(H2O)]2(μ-SO4) (11). Treatment of 11 with triflic acid afforded [(LOEt)2Zr][OTf]2(12), whereas reaction of 11 with Ag(OTf) afforded a mixture of 12 and trinuclear [{LOEtZr(SO4)(H2O)}3(μ3-SO4)][OTf] (13). The ZrIVtriflato complex [LOEtZr-(OTf)3] (14) was prepared by reaction of LOEtZrF3with Me3SiOTf. Complexes 4 and 14 can catalyze the Diels-Alder reaction of 1,3-cyclohexadiene with acrolein in good selectivity. Complexes 2-5, 9-11, and 13 have been characterized by X-ray crystallography.