1226976-99-3Relevant academic research and scientific papers
Redox-active tripodal aminetris(aryloxide) complexes of titanium(IV)
Lionetti, Davide,Medvecz, Andrew J.,Ugrinova, Vesela,Quiroz-Guzman, Mauricio,Noll, Bruce C.,Brown, Seth N.
experimental part, p. 4687 - 4697 (2010/08/13)
New sterically encumbered tripodal aminetris(aryloxide) ligands N(CH 2C6H2-3-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,An2NLH 3) is also readily prepared. The ligands are metalated by titanium(IV) tert-butoxide to form the five-coordinate alkoxides LTi(O tBu). 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.
