- Atom transfer reactions of (TTP)Ti(n2-3-hexyne): Synthesis and molecular structure of trans-(TTP)Ti[OP(Oct)3]2
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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.
- Thorman,Young Jr.,Boyd,Guzei,Woo
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p. 499 - 506
(2008/10/08)
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- Synthesis, characterization, substitution, and atom-transfer reactions of (n2-alkyne)(tetratolylporphyrinato)titanium(II). X-ray structure of trans-bis(4-picoline)(tetratolylporphyrinato)titanium(II)
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A general preparative method for (tetratolylporphyrinato)titanium(II) η2-acetylene complexes, (TTP)Ti(η2-RC≡CR′), (R = R′ = CH3, CH2CH3, C6H5; R = CH3, R′ = CH2CH3) is described. Displacement of 2-butyne from (TTP)Ti(η2-MeG≡CMe) with terminal acetylenes allows the preparation of (TTP)Ti(η2-HC≡CH) and (TTP)Ti(η2-PnC≡CH). The π complexes undergo simple substitution reactions with pyridine (py) and 4-picoline (pic) to afford the bis(ligand) complexes trans-(TTP)Ti(py)2 and trans-(TTP)Ti(pic)2. The structure of the bis(picoline) complex, C66H56N4Ti, was determined by single-crystal X-ray diffraction (triclinic, P1, a = 9.764(2) A?, b = 10.899(2) A?, c = 13.530(2) A?, α = 92.18(2)?, β = 98.10(2)°, γ = 114.14(2)°, V = 1293.6(4) A?3, Z = 1, R = 5.2%, and Rw 5.4%). Crystallographic symmetry requires that the Ti atom resides in the center of the 24 atom porphyrin plane. The Ti-Npic distance is 2.223(3) A?, and the average Ti-Npyrrole distance is 2.047(8) A?. The two picoline ligands are coplanar, and the dihedral angle formed by the plane of the picoline rings and the Ti-N1 vector is 43°. When (η2-PhC≡CPh)Ti(TTP) is treated with di-p-tolyldiazomethane, a diazo adduct (TTP)Ti=NN=C(C6H4CH3)2 is formed. Atom transfer occurs when (η2-PhC≡CPh)Ti(TTP) is treated with X=PPh3 (X = S, Se), resulting in a two-electron oxidized product, (TTP)Ti=X, PPh3, and free PhC≡CPh. Treatment of (TTP)Ti(η2-PhC≡CPh) with elemental sulfur or selenium produces the perchalcogenido complexes (TTP)Ti(S2) and (TTP)Ti(Se2). The chalcogenide ligand complexes (TTP)Ti=S and (TTP)Ti=Se were also electrochemically characterized for comparison with related derivatives of (P)Ti(S2) and (P)Ti(Se2). Each compound undergoes two reversible one-electron reductions which are located at E1/2 = -1.07 ± 0.01 and 1.47 ± 0.01 V in CH2Cl2 containing 0.1 M tetra-n-butylammonium perchlorate. They also undergo two oxidations, the first of which is irreversible, consistent with an electrode reaction involving the axial ligand rather than the porphyrin macrocycle. A comparison of potentials for oxidation of (TTP)Ti=X and (TPP)Ti (η2-X2) indicates a stronger titanium-chalcogen bond in the case of the terminal selenide and sulfide derivatives as compared to the metal-chalcogen bond in the η2-X2 complexes.
- Woo, L. Keith,Hays, J. Alan,Young Jr., Victor G.,Day, Catherine L.,Caron, Cecile,D'Souza, Francis,Kadish, Karl M.
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p. 4186 - 4192
(2008/10/08)
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