M. Senge, M. Vicente, Kevin R. Gerzevske
Dec 1, 1994
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0
Influential Citations
45
Citations
Journal
Inorganic Chemistry
Abstract
The low-valent titanium induced reductive coupling of metal(I1) 5-formyl-octaethylporphyrin (OEP) (2, 3) leads to the formation of ethene-bridged bisporphyrins. Structural studies on the main products of the coupling of Cu(I1) (2) and Ni(II) 5-formyl-OEP (3) revealed, surprisingly, the formation of the cis-isomers 1,2-bis[5-(2,3,7,8,12,13,17,18-octaethylporphyrinato)metal(II)]-cis-ethene (4, 5). This is in contrast to other reported reductive couplings of aldehydes and ketone which usually lead to the trans-product. The cis-isomer can undergo an acidcatalyzed isomerization to the trans-isomer (6,7) which is also formed as a side product in the coupling reaction. An explanation for the formation of the cis-ethene-bridged bisporphyrins may involve the strong aggregation tendencies of metalloporphyrins. These aggregation forces are evidenced in the crystal structures of the cisdimers which exhibit considerable overlap of the n-systems and have a cofacial macrocycle arrangement with almost coplanar macrocycles. Besides the strong intramolecular aggregation effects, intermolecular n-stacking was observed in the structures of the Cu(II) (4) and Ni(II) (5) cis-dimers, the nickel(I1) trans-isomer (7) and the related structure of bis[2-(3,7,8,12,13,17,18-heptaethylpophyrinato)nickel(II)]hydroxymethane (13) which is obtained by low valent titanium coupling of Ni(I1) 2-formyl-OEP (12). The synthesis of the cofacial cis-dimers is achieved in a single step from the corresponding formylporphyrins in high yields, thus presenting an improvement over other published procedures for synthesis of face-to-face bisporphyrins. Crystal data: 4, Mo Ka (A = 0.710 69 A) at 130 K, a = 19.208(7) A, b = 14.672(5) A, c = 24.170(7) A, p = 111.15(3)", V = 6352(4) A3, Z = 4, space group P21/n, R = 0.056; 5, Mo Ka (A = 0.710 69 A) at 130 K, a = 21.671(7) A, b = 14.079(5) A, c = 22.110(7) A, p = 108.86(2)", V = 6384(3) A3, Z = 4, space group P21/c, R = 0.064; 7, Cu Ka (A = 1.541 78 A) at 126 K, a = 11.163(3) A, b = 12.775(4) A, c = 14.554(3) A, a = 69.59(2)", ,l? = 81.15(2)", y = 73.21(2)", V = 1859(1) A3, Z = 1, space group P i , R = 0.072; 13, Mo Ka (A = 0.710 69 A) at 130 K, a = 40.31(2) A, b = 14.997(7) A, c = 21.954(11) A, p = 108.6(4)", V = 12579(10) A3, Z = 8, space group C2/c, R = 0.122.