Redox-Active Tripodal Aminetris(aryloxide) Complexes of Titanium(IV)

New sterically encumbered tripodal aminetris(aryloxide) ligands N(CH2C6H2-3-Bu-t-5-X-2-OH)(3) ((LH3)-L-tBu,X) 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 ((LH3)-L-H,An2N) is also readily prepared. The ligands are metalated by titanium(IV) tert-butoxide to form the five-coordinate alkoxides LTi((OBu)-Bu-t). 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 (LTi)-L-tBu,X(acac) show reversible ligand-based oxidations with first oxidation potentials of +0.57, +0.33, and 0.09 V (vs ferrocene/ferrocenium) for X=Bu-t, MeO, and An(2)N, respectively. Both dianisylamine-substituted complexes (LTi)-L-R.An2N(acac) (R=Bu-t, 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 similar to + 0.75 V. The new electron-rich tripodal ligands therefore have the capacity to release multiple electrons at unusually low potentials for aryloxide groups.