title: Redox-active tripodal aminetris(aryloxide) complexes of titanium(IV).
abstract: New sterically encumbered tripodal aminetris(aryloxide) ligands N(CH(2)C(6)H(2)-3-(t)Bu-5-X-2-OH)(3) ((tBu,X)LH(3)) with relatively electron-rich phenols are prepared by Mannich condensation (X = OCH(3)) or by a reductive amination/Hartwig-Buchwald amination sequence on the benzyl-protected bromosalicylaldehyde (X = N[C(6)H(4)-p-OCH(3)](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,An(2)N)LH(3)) is also readily prepared. The ligands are metalated by titanium(IV) tert-butoxide to form the five-coordinate alkoxides LTi(O(t)Bu). 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,X)LTi(acac) show reversible ligand-based oxidations with first oxidation potentials of +0.57, +0.33, and -0.09 V (vs ferrocene/ferrocenium) for X = (t)Bu, MeO, and An(2)N, respectively. Both dianisylamine-substituted complexes (R,An(2)N)LTi(acac) (R = (t)Bu, H) show similar electrochemistry, with three one-electron oxidations closely spaced at approximately 0 V and three oxidations due to removal of a second electron from each diarylaminoaryloxide arm at approximately + 0.75 V. The new electron-rich tripodal ligands therefore have the capacity to release multiple electrons at unusually low potentials for aryloxide groups.
authors.affiliation: Department of Chemistry and Biochemistry, 251 Nieuwland Science Hall, University of Notre Dame, Notre Dame, Indiana 46556-5670, USA.
authors.forename: Davide
authors.initials: D
authors.lastname: Lionetti
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Medvecz
authors.forename: Vesela
authors.initials: V
authors.lastname: Ugrinova
authors.forename: Mauricio
authors.initials: M
authors.lastname: Quiroz-Guzman
authors.forename: Bruce C
authors.initials: BC
authors.lastname: Noll
authors.forename: Seth N
authors.initials: SN
authors.lastname: Brown