The coordination and atom transfer chemistry of titanium porphyrin complexes

Hays, James
Journal Title
Journal ISSN
Volume Title
Source URI
Research Projects
Organizational Units
Organizational Unit
Journal Issue

The preparation, characterization, and reactivity of a series of ([eta][superscript]2-alkyne)(meso-tetratolylporphyrinato)titanium(II) complexes are described. Also described are intermetal oxygen atom transfer reactions involving titanium(IV) and titanium(III) porphyrin complexes. The [eta][superscript]2-alkyne complexes, (TTP)Ti([eta][superscript]2-R-C≡C-R[superscript]') (where R = R[superscript]' = Me, Et, Ph; R = Me, R[superscript]' = Et), are prepared by treatment of (TTP)TiCl[subscript]2 with LiAlH[subscript]4 in the presence of the alkyne. The structure of (OEP)Ti([eta][superscript]2-Ph-C≡C-Ph) (OEP = octaethylporphryin) was determined by a single-crystal X-ray diffraction. The complex crystallizes in a monoclinic space group C2/c with a = 49.369(7) A, b = 13.734(9) A, c = 36.042(4) A, [beta] = 136.622(7)°, V = 16784(9) A[superscript]3, Z = 16, R = 0.060, R[subscript] w =.062. These compounds undergo simple substitution to displace the alkyne and produce doubly substituted complexes. Where R = R[superscript]' = Et or Me, the coordinated internal alkyne is displaced by a terminal alkyne, R[superscript]''-C≡C-H (R[superscript]'' = Ph, H). The structure of (TTP)Ti(4-picoline)[subscript]2 was determined by single-crystal X-ray diffraction. The complex crystallizes in the triclinic space group P1 with a = 9.764(2) A, b = 10.899(2) A, c = 13.530(2) A, [alpha] = 92.18(2), [beta] = 98.10(2)°, [gamma] = 114.14(2)°, V = 1293.6(4) A, Z = 1, R =.0517, R[subscript] w =.0542. The [eta][superscript]2-alkynes undergo redox reaction with diazo reagents and phosphine chalcogenides. They also abstract a chalcogenide from (TTP)Ti([eta][superscript]2-Ch[subscript]2) where Ch = O, S, Se;Treatment of (TTP)Ti=O with (OEP)Ti-Cl yields intermetal O/Cl exchange. This is formally a one electron redox process mediated by oxygen atom transfer. The equilibrium and forward rate constants at 20°C were determined to be 1.6 ± 0.4 and 2.4 ± 0.3 x 10[superscript]2 M[superscript]-1s[superscript]-1, respectively. Studies were performed to determine temperature, axial ligand, and solvent dependencies. Also, a zero-electron redox process mediated by atom transfer is observed when (TTP)TiCl[subscript]2 is treated with (OEP)Ti=O. The equilibrium constant was determined to be 47 ± 13 at 20°C. The forward rate constant was found to be 5 ± 1 at 20°C. Rate constants at various temperatures were determined to examine temperature dependence.

Chemistry, Inorganic chemistry