The coordination and atom transfer chemistry of titanium porphyrin complexes

The preparation, characterization, and reactivity of a series of ({dollar}etasp2{dollar}-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 {dollar}etasp2{dollar}-alkyne complexes, (TTP)Ti({dollar}etasp2{dollar}-R-C{dollar}equiv{dollar}C-R{dollar}spprime{dollar}) (where R = R{dollar}spprime{dollar} = Me, Et, Ph; R = Me, R{dollar}spprime{dollar} = Et), are prepared by treatment of (TTP)TiCl{dollar}sb2{dollar} with LiAlH{dollar}sb4{dollar} in the presence of the alkyne. The structure of (OEP)Ti({dollar}etasp2{dollar}-Ph-C{dollar}equiv{dollar}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, {dollar}beta{dollar} = 136.622(7){dollar}spcirc{dollar}, V = 16784(9) A{dollar}sp3{dollar}, Z = 16, R = 0.060, R{dollar}sb{lcub}rm w{rcub}{dollar} =.062. These compounds undergo simple substitution to displace the alkyne and produce doubly substituted complexes. Where R = R{dollar}spprime{dollar} = Et or Me, the coordinated internal alkyne is displaced by a terminal alkyne, R{dollar}sp{lcub}primeprime{rcub}{dollar}-C{dollar}equiv{dollar}C-H (R{dollar}sp{lcub}primeprime{rcub}{dollar} = Ph, H). The structure of (TTP)Ti(4-picoline){dollar}sb2{dollar} 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, {dollar}alpha{dollar} = 92.18(2), {dollar}beta{dollar} = 98.10(2){dollar}spcirc{dollar}, {dollar}gamma{dollar} = 114.14(2){dollar}spcirc{dollar}, V = 1293.6(4) A, Z = 1, R =.0517, R{dollar}sb{lcub}rm w{rcub}{dollar} =.0542. The {dollar}etasp2{dollar}-alkynes undergo redox reaction with diazo reagents and phosphine chalcogenides. They also abstract a chalcogenide from (TTP)Ti({dollar}etasp2{dollar}-Ch{dollar}sb2{dollar}) 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{dollar}spcirc{dollar}C were determined to be 1.6 {dollar}pm{dollar} 0.4 and 2.4 {dollar}pm{dollar} 0.3 {dollar}times{dollar} 10{dollar}sp2{dollar} M{dollar}sp{lcub}-1{rcub}{dollar}s{dollar}sp{lcub}-1{rcub}{dollar}, 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{dollar}sb2{dollar} is treated with (OEP)Ti=O. The equilibrium constant was determined to be 47 {dollar}pm{dollar} 13 at 20{dollar}spcirc{dollar}C. The forward rate constant was found to be 5 {dollar}pm{dollar} 1 at 20{dollar}spcirc{dollar}C. Rate constants at various temperatures were determined to examine temperature dependence.