Phosphato, Chromato, and Perrhenato Complexes of Titanium(IV) and Zirconium(IV) Containing Kläui's Tripodal Ligand
dataset
posted on 2006-01-09, 00:00 authored by Yi, Qian-Feng Zhang, Tony C. H. Lam, Eddie Y. Y. Chan, Ian D. Williams, Wa-Hung LeungTreatment of titanyl sulfate in dilute sulfuric acid with 1 equiv of NaL<sub>OEt</sub> (L<sub>OEt</sub><sup>-</sup> = [(η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>)Co{P(O)(OEt)<sub>2</sub>}<sub>3</sub>]<sup>-</sup>) in
the presence of Na<sub>3</sub>PO<sub>4</sub> and Na<sub>4</sub>P<sub>2</sub>O<sub>7</sub> led to isolation of [(L<sub>OEt</sub>Ti)<sub>3</sub>(μ-O)<sub>3</sub>(μ<sub>3</sub><sub>-</sub>PO<sub>4</sub>)] (<b>1</b>) and [(L<sub>OEt</sub>Ti)<sub>2</sub>(μ-O)(μ-P<sub>2</sub>O<sub>7</sub>)]
(<b>2</b>), respectively. The structure of <b>1</b> consists of a Ti<sub>3</sub>O<sub>3</sub> core capped by a μ<sub>3</sub>-phosphato group. In <b>2</b>, the [P<sub>2</sub>O<sub>7</sub>]<sup>4-</sup>
ligands binds to the two Ti's in a μ:η<sup>2</sup>,η<sup>2</sup> fashion. Treatment of titanyl sulfate in dilute sulfuric acid with NaL<sub>OEt</sub>
and 1.5 equiv of Na<sub>2</sub>Cr<sub>2</sub>O<sub>7</sub> gave [(L<sub>OEt</sub>Ti)<sub>2</sub>(μ-CrO<sub>4</sub>)<sub>3</sub>] (<b>3</b>) that contains two L<sub>OEt</sub>Ti<sup>3+</sup> fragments bridged by three
μ-CrO<sub>4</sub><sup>2-</sup>-<i>O</i>,<i>O</i>‘ ligands. Complex <b>3</b> can act as a 6-electron oxidant and oxidize benzyl alcohol to give ca. 3 equiv
of benzaldehyde. Treatment of [L<sub>OEt</sub>Ti(OTf)<sub>3</sub>] (OTf<sup>-</sup> = triflate) with [<i>n</i>-Bu<sub>4</sub>N][ReO<sub>4</sub>] afforded [{L<sub>OEt</sub>Ti(ReO<sub>4</sub>)<sub>2</sub>}<sub>2</sub>(μ-O)]
(<b>4</b>). Treatment of [L<sub>OEt</sub>MF<sub>3</sub>] (M = Ti and Zr) with 3 equiv of [ReO<sub>3</sub>(OSiMe<sub>3</sub>)] afforded [L<sub>OEt</sub>Ti(ReO<sub>4</sub>)<sub>3</sub>] (<b>5</b>) and
[L<sub>OEt</sub>Zr(ReO<sub>4</sub>)<sub>3</sub>(H<sub>2</sub>O)] (<b>6</b>), respectively. Treatment of [L<sub>OEt</sub>MF<sub>3</sub>] with 2 equiv of [ReO<sub>3</sub>(OSiMe<sub>3</sub>)] afforded [L<sub>OEt</sub>Ti(ReO<sub>4</sub>)<sub>2</sub>F] (<b>7</b>) and [{L<sub>OEt</sub>Zr(ReO<sub>4</sub>)<sub>2</sub>}<sub>2</sub>(μ-F)<sub>2</sub>] (<b>8</b>), respectively, which reacted with Me<sub>3</sub>SiOTf to give [L<sub>OEt</sub>M(ReO<sub>4</sub>)<sub>2</sub>(OTf)] (M = Ti (<b>9</b>), Zr (<b>10</b>)). Hydrolysis of [L<sub>OEt</sub>Zr(OTf)<sub>3</sub>] (<b>11</b>) with Na<sub>2</sub>WO<sub>4</sub>·<i>x</i>H<sub>2</sub>O and wet CH<sub>2</sub>Cl<sub>2</sub> afforded the
hydroxo-bridged complexes [{L<sub>OEt</sub>Zr(H<sub>2</sub>O)}<sub>3</sub>(μ-OH)<sub>3</sub>(μ<sub>3</sub>-O)][OTf]<sub>4</sub> (<b>12</b>) and [{L<sub>OEt</sub>Zr(H<sub>2</sub>O)<sub>2</sub>}<sub>2</sub>(μ-OH)<sub>2</sub>][OTf]<sub>4</sub> (<b>13</b>),
respectively. The solid-state structures of <b>1</b><b>−</b><b>3</b>, <b>6</b>, and <b>11</b><b>−</b><b>13</b> have been established by X-ray crystallography. The
L<sub>OEt</sub>Ti<sup>IV</sup> complexes can catalyze oxidation of methyl <i>p</i>-tolyl sulfide with <i>tert</i>-butyl hydroperoxide. The bimetallic
Ti/ Re complexes <b>5</b> and <b>9</b> 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.
