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

Treatment of titanyl sulfate in about 60 mM sulfuric acid with NaLOEt (L-OEt(-) = [(eta(5)-C5H5)Co{P(O)(OEt)(2)}(3)](-)) afforded the mu-sulfato complex [(LOEtTi)(2)(mu-O)(2)(mu-SO4)] (2). In more concentrated sulfuric acid (>1 M), the same reaction yielded the di-mu-sulfato complex [(LOEtTi)(2)(mu-O)(mu- 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 CH2Cl2 afforded the sulfato-capped trinuclear complex [{(L-OEt)(3)Ti-3(mu- O)(3)}(mu(3)-SO4){Ag(OTf)}][OTf] (5), in which the Ag(OTf) moiety binds to a mu-oxo group in the T-3(mu-O)(3) core. Reaction of 2 in H2O with Ba(NO3)(2) afforded the tetranuclear complex (L-OEt)(4)Ti-4(mu-O)(6) (6). Treatment of 2 with [{Rh(cod)Cl}(2)] (cod = 1,5-cyclooctadiene), [Re(CO)(5)Cl], and [Ru(tBu(2)bpy)(PPh3)(2)Cl-2] (tBu(2)bpy=4,4'-di-tertbutyl-2,2'-dipyridyl) in the presence of Ag(OTf) afforded the heterometallic complexes [(L-OEt)(2)Ti-2(O)(2)(SO4) {Rh(cod)}(2)][OTf](2) (7), [(L-OEt)(2)Ti(O)(2)- (SO4){Re(CO)(3)}][OTf] (8), and [{(L-OEt)(2)Ti-2(mu-O)} mu(3) - SO4) (mu-O)(2){Ru(PPh3)(tBu(2)bpy)}][OTf](2) (9), respectively. Complex 9 is paramagnetic with a measured magnetic moment of about 2.4 mu(B). Treatment of zirconyl nitrate with NaLOEt in 3.5 M sulfuric acid afforded [(L-OEt)(2)Zr(NO3)][LOEtZr(SO4) (NO3)] (10). Reaction of ZrCl4 in 1.8 M sulfuric acid with NaLOEt in the presence Na2SO4 gave the R-sulfato-bridged complex [LOEtZr(SO4)(H2O)](2)(mu-SO4) (11). Treatment of 11 with triflic acid afforded [(LOEt)(2)Zr][OTf](2) (12), whereas reaction of 11 with Ag(OTf) afforded a mixture of 12 and trinuclear [{LOEtZr(SO4)(H2O)}(3)(mu-SO4)][OTf] (13). The Zr-IV triflato complex [LOEtZr(OTf)(3)] (14) was prepared by reaction of LOEtZrF3 with 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