SYNTHESIS, CHARACTERIZATION, SUBSTITUTION, AND ATOM-TRANSFER REACTIONS OF (ETA-2-ALKYNE)(TETRATOLYLPORPHYRINATO)TITANIUM(II) - X-RAY STRUCTURE OF IS(4-PICOLINE)(TETRATOLYLPORPHYRINATO)TITANIUM(II)

A general preparative method for (tetratolylporphyrinato)titanium(II) eta2-acetylene complexes, (TTP)Ti(eta2-RC=CR'), (R = R' = CH3, CH2CH3, C6H5; R = CH3, R' = CH2CH3) is described. Displacement of 2-butyne fr om (TTP)Ti(eta2-MeC=CMe) with terminal acetylenes allows the preparati on of (TTP)Ti(eta2-HC=CH) and (TTP)Ti(eta2-PhC=CH). The pi complexes u ndergo simple substitution reactions with pyridine (py) and 4-picoline (pic) to afford the bis(ligand) complexes trans-(TTP)Ti(PY)2 and tran s-(TTP)Ti(PiC)2. The structure of the bis(picoline) complex, C66H56N4T i, was determined by single-crystal X-ray diffraction (triclinic, P1BA R, a - 9.764(2) angstrom, b = 10.899(2) angstrom, c = 13.530(2) angstr om, alpha = 92.18(2)-degrees, beta = 98.10(2)-degrees, gamma = 114.14( 2)-degrees, V = 1293.6(4) angstrom3, Z = 1, R = 5.2%, and R, = 5.4%). Crystallographic symmetry requires that the Ti atom resides in the cen ter of the 24 atom porphyrin plane. The Ti-N(pic) distance is 2.223(3) angstrom, and the average Ti-N(pyrrole) distance is 2.047(8) angstrom . 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 ( eta2-PhC=CPh)Ti(TTP) is treated with di-p-tolyldiazomethane, a diazo a dduct (TTP)Ti=NN=C(C6H4CH3)2 is formed. Atom transfer occurs when (eta 2-PhC=CPh)Ti(TTP) is treated with X=PPh3 (X = S, Se), resulting in a t wo-electron oxidized product, (TTP)Ti=X, PPh3, and free PhC=CPh. Treat ment of (TTP)Ti(eta2-PhC=CPh) with elemental sulfur or selenium produc es the perchalcogenido complexes (TTP)Ti(S2) and (TTP)Ti(Se2). The cha lcogenide ligand complexes (TTP)Ti=S and (TTP)Ti=Se were also electroc hemically characterized for comparison with related derivatives of (P) Ti(S2) and (P)Ti(Se2). Each compound undergoes two reversible one-elec tron 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 rath er than the porphyrin macrocycle. A comparison of potentials for oxida tion of (TTP)Ti=X and (TPP)Ti(eta2-X2) indicates a stronger titanium-c halcogen bond in the case of the terminal selenide and sulfide derivat ives as compared to the metal-chalcogen bond in the eta2-X2 complexes.