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Chemistry, Ames Laboratory

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Inorganic Chemistry





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A general preparative method for (tetratolylporphyrinato)titanium{II) 77 2-acetylene complexes, (TTP)Ti(712. RC==CR'), (R = R' = CH3, CH2CH3, C6Hs; R = CH3, R' = CH2CH3) is described. Displacement of 2-butyne from (TTP)Ti(772-MeC==CMe) with terminal acetylenes allows the preparation of (TTP)Ti(77 2-HC==CH) and (TTP)Ti(77 2-PhC==CH). The 11' complexes undergo simple substitution reactions with pyridine (py) and 4-picoline (pic) to afford the bis(ligand) complexes trans-(TTP)Ti(pyh and trans-(TTP)Ti(pich The structure of the bis(picoline) complex, C66Hs6N 4 Ti, was determined by single-crystal X-ray diffraction ( triclinic, PI, a = 9. 764(2) A, b = 10.899(2) A, c = 13.530(2) A, a= 92.18(2)', p = 98.10(2) 0 , 'Y = 114.14(2) 0 , V= 1293.6(4) A3, 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-N pic distance is 2.223(3) A, and the average Ti-Npyrrole distance is 2.047(8) A. The two pi co line ligands are coplanar, and the dihedral angle formed by the plane of the picoline rings and the Ti-N 1 vector is 43°. When (71 2-PhC==CPh)Ti(TTP) is treated with di-p-tolyldiazomethane, a diazo adduct (TTP)Ti=NN=C(C6H 4CH3h is formed. Atom transfer occurs when (71 2-PhC==CPh)Ti(TTP) is treated with X=PPh 3 (X = S, Se), resulting in a two-electron oxidized product, (TTP)Ti=X, PPh3, and free PhC==CPh. Treatment of {TTP)Ti{772-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 £1;2 = -1.07 :I: 0.01 and 1.47 :I: 0.01 V in CH2Ch 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(77 2-X2) indicates a stronger titaniurn-chalcogen bond in the case of the terminal selenide and sulfide derivatives as compared to the metal--chalcogen bond in the 77 2-X2 complexes.


Reprinted (adapted) with permission from Inorganic Chemistry 32 (1993): 4186, doi:10.1021/ic00072a007. Copyright 1993 American Chemical Society.

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