Phosphato, Chromato, and Perrhenato Complexes of Titanium(IV) and Zirconium(IV) Containing Klaui's Tripodal Ligand

Treatment of titanyl sulfate in dilute sulfuric acid with 1 equiv of NaL OEt (L OEt - = [(η 5 -C 5 H 5 )Co{P(O)(OEt) 2 } 3 ] - ) in the presence of Na 3 PO 4 and Na 4 P 2 O 7 led to isolation of [(L OEt Ti) 3 (μ-O) 3 (μ 3 -PO 4 )] (1) and [(L OEt Ti) 2 (μ-O)(μ-P 2 O 7 )] (2), respectively. The structure of 1 consists of a Ti 3 O 3 core capped by a μ 3 -phosphato group. In 2, the [P 2 O 7 ] 4- ligands binds to the two Ti's in a μ:η 2 ,η 2 fashion. Treatment of titanyl sulfate in dilute sulfuric acid with NaL OEt and 1.5 equiv of Na 2 Cr 2 O 7 gave [(L OEt Ti) 2 (μ-CrO 4 ) 3 ] (3) that contains two L OEt Ti 3+ fragments bridged by three μ-CrO 4 2- -O,O' ligands. Complex 3 can act as a 6-electron oxidant and oxidize benzyl alcohol to give ca. 3 equiv of benzaldehyde. Treatment of [L OEt Ti(OTf) 3 ] (OTf- = triflate) with [n-Bu 4 N][ReO 4 ] afforded [{L OEt Ti(ReO 4 ) 2 } 2 (μ-O)] (4). Treatment of [L OEt MF 3 ] (M = Ti and Zr) with 3 equiv of [ReO 3 (OSiMe 3 )] afforded [L OEt Ti(ReO 4 ) 3 ] (5) and [L OEt Zr(ReO 4 ) 3 (H 2 O)] (6), respectively. Treatment of [L OEt MF 3 ] with 2 equiv of [ReO 3 (OSiMe 3 )] afforded [L OEt Ti-(ReO 4 ) 2 F] (7) and [{L OEt Zr(ReO 4 ) 2 } 2 (μ-F)2] (8), respectively, which reacted with Me 3 SiOTf to give [L OEt M(ReO 4 ) 2 -(OTf)] (M = Ti (9), Zr (10)). Hydrolysis of [L OEt Zr(OTf) 3 ] (11) with Na 2 WO 4 ·xH 2 O and wet CH 2 Cl 2 afforded the hydroxo-bridged complexes [{L OEt Zr(H 2 O)} 3 (μ-OH) 3 (μ 3 -P)][OTf] 4 (12) and [{L OEt Zr(H20) 2 } 2 (μ-OH)2][OTf]4 (13), respectively. The solid-state structures of 1-3, 6, and 11-13 have been established by X-ray crystallography. The L OEt Ti IV complexes can catalyze oxidation of methyl p-tolyl sulfide with tert-butyl hydroperoxide. The bimetallic Ti/ Re complexes 5 and 9 were found to be more active catalysts for the sulfide oxidation than other Ti(IV) complexes presumably because Re alkylperoxo species are involved as the reactive intermediates.