Redox-active tripodal aminetris (aryloxide) complexes of titanium (IV)

D Lionetti, AJ Medvecz, V Ugrinova… - Inorganic …, 2010 - ACS Publications
D Lionetti, AJ Medvecz, V Ugrinova, M Quiroz-Guzman, BC Noll, SN Brown
Inorganic chemistry, 2010ACS Publications
New sterically encumbered tripodal aminetris (aryloxide) ligands N (CH2C6H2-3-t Bu-5-X-2-
OH) 3 (t Bu, XLH3) with relatively electron-rich phenols are prepared by Mannich
condensation (X= OCH3) or by a reductive amination/Hartwig− Buchwald amination
sequence on the benzyl-protected bromosalicylaldehyde (X= N [C6H4-p-OCH3] 2), followed
by debenzylation using Pearlman's catalyst (Pd (OH) 2/C). The analogous dianisylamino-
substituted compound lacking the tert-butyl group ortho to the phenol (H, An2NLH3) is also …
New sterically encumbered tripodal aminetris(aryloxide) ligands N(CH2C6H2-3-tBu-5-X-2-OH)3 (tBu,XLH3) with relatively electron-rich phenols are prepared by Mannich condensation (X = OCH3) or by a reductive amination/Hartwig−Buchwald amination sequence on the benzyl-protected bromosalicylaldehyde (X = N[C6H4-p-OCH3]2), followed by debenzylation using Pearlman’s catalyst (Pd(OH)2/C). The analogous dianisylamino-substituted compound lacking the tert-butyl group ortho to the phenol (H,An2NLH3) is also readily prepared. The ligands are metalated by titanium(IV) tert-butoxide to form the five-coordinate alkoxides LTi(OtBu). Treatment of the tert-butoxides with aqueous HCl yields the five-coordinate chlorides LTiCl, and with acetylacetone gives the six-coordinate diketonates LTi(acac). The diketonate complexes tBu,XLTi(acac) show reversible ligand-based oxidations with first oxidation potentials of +0.57, +0.33, and −0.09 V (vs ferrocene/ferrocenium) for X = tBu, MeO, and An2N, respectively. Both dianisylamine-substituted complexes R,An2NLTi(acac) (R = tBu, H) show similar electrochemistry, with three one-electron oxidations closely spaced at ∼0 V and three oxidations due to removal of a second electron from each diarylaminoaryloxide arm at ∼ + 0.75 V. The new electron-rich tripodal ligands therefore have the capacity to release multiple electrons at unusually low potentials for aryloxide groups.
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