65496-72-2Relevant articles and documents
Activation barriers to meso-aryl group rotation in titanyl tetraaryltetrapyrroles. An investigation of the out-of-plane flexibility of hydroporphyrins
Stolzenberg, Alan M.,Haymond, G. Scott
, p. 300 - 308 (2002)
The free-base and titanyl (TiIVO) complexes of meso-tetratolyl- and meso-tetra(3,5-xylyl)hydroporphyrins were synthesized and characterized. Metalation of the hydroporphyrins with titanium was achieved by reaction of the lithium salts of the hydroporphyrin with TiCl4. Other methods used to metalate porphyrins with titanium required harsher reaction conditions and led to substantial oxidative dehydrogenation of the macrocycle when applied to hydroporphyrins. The titanyl group differentiates the two faces of the macrocycle and consequently the two sides of the meso-aryl groups, which are tilted nearly perpendicular to the macrocycle plane. The 1H NMR signals for the nonequivalent ortho protons and nonequivalent meta protons averaged on the NMR time scale at elevated temperatures due to aryl group rotation. Activation barriers for aryl group rotation in the para-substituted and meta-disubstituted titanyl hydroporphyrin complexes and in related titanyl porphyrin complexes were determined from variable-temperature NMR spectra and ranged from 15.6 to 18.4 kcal/mol. In chlorin compounds, barriers for rotation of aryl groups located between a pyrrole and a pyrroline (reduced) ring are greater than those of aryl groups located between two pyrrole rings. Comparisons of barriers in complexes with different macrocycle saturation levels show that the increased barriers for aryl groups adjacent to pyrroline rings cannot be attributed solely to the increased steric bulk of the pyrroline β-CH2 group relative to the pyrrole β-CH group. Variations in flexibility and electronic environments at meso carbons in the hydroporphyrins may also contribute. Rotation barriers for metadisubstituted aryl groups, which are higher than those for para-substituted aryl groups, increase with the size and mass of the substituent.
Atom transfer reactions of (TTP)Ti(n2-3-hexyne): Synthesis and molecular structure of trans-(TTP)Ti[OP(Oct)3]2
Thorman,Young Jr.,Boyd,Guzei,Woo
, p. 499 - 506 (2008/10/08)
Atom and group transfer reactions were found to occur between heterocumulenes and (TTP)Ti(n2-3-hexyne), 1 (TTP = meso-5,10,15,20-tetra-p-toly]porphyrinato dianion). The imido derivatives (TTP)Ti=NR (R = ′Pr, 2; ′Bu, 3) were produced upon treatment of complex 1 with ′PrN=C=N′Pr, ′PrNCO, or ′BuNCO. Reactions between complex 1 and CS2, ′BuNCS, or ′BuNCSe afforded the chalcogenido complexes, (TTP)Ti=Ch (Ch = Se, 4; S, 5). Treatment of complex 1 with 2 equiv of PEt3 yielded the bis(phosphine) complex, (TTP)Ti(PEt3)2, 6. Although (TTP)Ti(n2-3-hexyne) readily abstracts oxygen from epoxides and sulfoxides, the reaction between 1 and O=P(Oct)3 did not result in oxygen atom transfer. Instead, the paramagnetic titanium(II) derivative (TTP)-Ti[O=P(Oct)3]2, 7, was formed. The molecular structure of complex 7 was determined by single-crystal X-ray diffraction: Ti-O distance 2.080(2) A and Ti-O-P angle of 138.43(10)°. Estimates of Ti=O, Ti=S, Ti=Se, and Ti=NR bond strengths are discussed.
Halogenated oxo- and peroxotitanium porphyrinates as sensitizers for the photooxygenation of olefinic compounds
Esser, Peter E.,Driessen-Hoelscher, Birgit,Keim, Wilhelm
, p. 13 - 24 (2008/10/09)
A series of porphines, oxotitanium(IV) and peroxotitanium(IV) porphyrinates were tested as photosensitizers of the singlet oxygen ene reaction with cyclohexene and cis-cyclooctene. The relative order of activity is: H2(P) ≥ O=Ti(P) ≥ Ti(O2)P. Best stability is obtained for porphines or porphyrinate complexes with fluorine substituents. Oxotitanium(IV) porphyrinates are active in the decomposition of allylic hydroperoxides. The (photo)catalytic epoxidation occurs less readily than the thermal reaction at 82°C. Attempts of photocatalytic hydrogen peroxide activations lead to fast destruction of O=Ti(P).
