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 mM sulfuric acid with NaL O E t (L O E t - = [η 5 -C 5 H 5 )Co-{P(O)(OEt) 2 } 3 ] - ) afforded the μ-sulfato complex [(L O E t Tι) 2 (μ-O) 2 (μ-SO 4 )] (2). In more concentrated sulfuric acid (> 1M), the same reaction yielded the di-μ-sulfato complex [(L O E t Ti) 2 (μ-O)(μ-SO 4 ) 2 ] (3). Reaction of 2 with HOTf (OTf=triflate, CF 3 SO 3 ) gave the tris-(triflato) complex [L O E t Ti(OTf) 3 ] (4), whereas treatment of 2 with Ag(OTf) in CH 2 Cl 2 afforded the sulfato-capped trinuclear complex [{(L O E t ) 3 Ti 3 (μ-O) 3 }(μ 3 -SO 4 ){Ag(OTf)}][OTf] (5), in which the Ag(OTf) moiety binds to a μ-oxo group in the Ti 3 (μ-O) 3 core. Reaction of 2 in H 2 O with Ba(NO 3 ) 2 afforded the tetranuclear complex (L O E t ) 4 Ti 4 (μ-O) 6 (6). Treatment of 2 with [{Rh(cod)Cl} 2 ] (cod=1,5-cyclooctadiene), [Re(CO) 5 Cl], and [Ru(tBu 2 -bpy)(PPh 3 ) 2 Cl 2 ] (tBu 2 bpy=4,4'-di-tert-butyl-2,2'-dipyridyl) in the presence of Ag(OTf) afforded the heterometallic complexes [(L O E t ) 2 Ti 2 (O) 2 (SO 4 ){Rh-(cod)} 2 ][OTf] 2 (7), [(L O E t ) 2 Ti(O) 2 -(SO 4 ){Re(CO) 3 }][OTf] (8), and [{(L O E t ) 2 Ti 2 (μ-O)}(μ 3 -SO 4 )(μ-O) 2 {Ru-(PPh 3 )(tBu 2 bpy)}][OTf] 2 (9), respectively. Complex 9 is paramagnetic with a measured magnetic moment of about 2.4 μ B . Treatment of zirconyl nitrate with NaL O E t in 3.5 M sulfuric acid afforded [(L O E t ) 2 Zr(NO 3 )][L O E t Zr(SO 4 )-(NO 3 )] (10). Reaction of ZrCl 4 in 1.8M sulfuric acid with NaL O E t in the presence Na 2 SO 4 gave the μ-sulfato-bridged complex [L O E t Zr(SO 4 )(H 2 O)] 2 (μSO 4 ) (11). Treatment of 11 with triflic acid afforded [(L O E t ) 2 Zr][OTf] 2 (12), whereas reaction of 11 with Ag(OTf) afforded a mixture of 12 and trinuclear [{L O E t Zr(SO 4 )(H 2 O)} 3 (μ 3 -SO 4 )][OTf] (13). The Zr I V triflato complex [L O E t Zr-(OTf) 3 ] (14) was prepared by reaction of L O E t ZrF 3 with Me 3 SiOTf. 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.