Synthesis, Characterization, Substitution, and Atom-Transfer Reactions of (η2-Alkyne)(tetratolylporphyrinato)titanium(II). X-ray Structure of trans-Bis(4-picoiine)(tetratolylporphyrinato)titanium(II)

L. Keith Woo, J. Alan Hays, Victor G. Young, Catherine L. Day, Cecile Caron, Francis D'Souza, Karl M. Kadish

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Abstract

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-MeCCMe) with terminal acetylenes allows the preparation of (TTP)Ti(η2-HCCH) and (TTP)Ti(η2-PhC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, P1̅, a = 9.764(2) Å, b = 10.899(2) Å, c = 13.530(2) Å, α = 92.18(2)°, β = 98.10(2)°, γ = 114.14(2)°, V= 1293.6(4) Å3, 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) Å, and the average Ti-Npyrrole distance is 2.047(8) Å. 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 PhCsCPh. 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 CH2C12 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.

Original languageEnglish (US)
Pages (from-to)4186-4192
Number of pages7
JournalInorganic Chemistry
Volume32
Issue number20
DOIs
StatePublished - Jan 1 1993

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