Kinetics and Thermodynamics of Intra- and Intermoiecular Rearrangement in Binaphthoiate Complexes of Titanium(IV)

Timothy J. Boyle, Denise L. Barnes, Joseph A. Heppert, Luis Morales, Fusao Takusagawa

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3,3′-Disubstituted-1,1′-bi-2-naphthols (H2R2BINO where R = Me or SiMe2-t-Bu) react with Ti(O-i-Pr)4 to produce molecules of empirical formula [(R2BINO)Ti(O-i-Pr)2]n. Analytical methods including NMR spectroscopy, molecular weight cryoscopy, and X-ray crystallography were used to identify the (t-BuMe2Si)2BINO-substituted complex as a monomer and the Me2BINO-substituted complex as a dimer. This dinuclear complex possesses a highly distorted edge-fused trigonal-bipyramidal structure, whose 1,3-Ti2O2 core is bridged by two naphthoxide units. There is a distinct thermodynamic preference for the incorporation of ligands of like chirality into the dimer. A second set of complexes having empirical formula (R2BINO)Ti2(O-i-Pr)6 (R = Me, SiMe2-t-Bu) are accessible through either the reaction of 2 equiv of Ti(O-i-Pr)4 with H2R2BINO or a reaction between [(R2BINO)Ti(O-i-Pr)2]n and Ti(O-i-Pr)4. The (Me2BINO)Ti2(O-i-Pr)6 complex possesses C1 symmetry at the low-temperature limit, implying that the molecule adopts an edge-fused trigonal-bipyramidal structure bridged by one naphthoxide and one isopropoxide ligand. At higher temperatures, a fluxional process, (Δ G‡240 = 10.8 kcal/mol) generates time-averaged C2 symmetry consistent with the rupture of the isopropoxide bridge to produce a binaphthoiate ligand bound to two “Ti(O-i-Pr)3” units. {(t-BuMe2Si)2BINO}Ti2(O-i-Pr)6 adopts this C2-symmetric structure in both solution and the solid state. Both the (Me2BINO)Ti2(O-i-Pr)6 and {(t-BuMe2Si)2BINO}Ti2(O-i-Pr)6 complexes display temperature-dependent equilibria in solution between Ti(O-i-Pr)4 and either [(Me2BINO)Ti(O-i-Pr)2]2 or {(t-BuMe2Si)2BINO}Ti(O-i-Pr)2, respectively. The thermodynamic characteristics of these equilibria follow: Me2BINO, ΔH° = -12.5 ± 0.6 kcal/mol, ΔS° = 38 ± 2 eu; (t-BuMe2Si)2BINO, ΔH° = -12.0 ± 0.8 kcal/mol, ΔS° = -44 ± 4 eu. The (Me2BINO)Ti2(O-i-Pr)6 complex also engages in an independent intermolecular exchange processes in which a “Ti(O-i-Pr)4” unit is exchanged with free Ti(O-t-Pr)4 in solution (ΔH‡ = 14.1 ± 0.9 kcal/mol, ΔS‡ = -2 ± 2 eu). When compared with the previously observed fluxional process in (Me2BINO)Ti2(O-t-Pr)6, this observation demonstrates that polynuclear titanium complexes can engage in distinct intramolecular and intermolecular exchange processes. Crystal data for {(t-BuMe2Si)2BINO)Ti(O-i-Pr)2 at 113 K: a = 10.866 (3) Å, b = 15.572 (4) Å, c = 23.059 (4) Å, β = 93.76 (2)°, Z = 4, Dcalc = 1.152, space group P21/c, R(F) = 0.037, Rw(F) = 0.051 for 3861 reflections. Crystal data for [(Me2BINO)Ti(O-i-Pr)2]2 at 106 K: a = 17.728 (3) Å,b= 11.079 (4) Å, c = 26.232 (4) Å, β = 101.00 (3)°, Z-4,Dcalc = 1.257, space group P21/c, R(F) = 0.069, Rw(F) = 0.077 for 3231 reflections. Crystal data for {(t-BuMe2Si)2BINO)Ti2(O-i-Pr)6 at 113 K: a = 14.444 (2) Å,b = 18.676 (3) Å, c = 20.788 (4) Å, β = 98.76 (2)°, Z = 4, = 1.143, space group C2/c, R(F) = 0.059, Rw(F) = 0.091 for 2860 reflections.

Original languageEnglish
Pages (from-to)1112-1126
Number of pages15
Issue number3
StatePublished - Mar 1 1992


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