Xanthene-Bridged Cofacial Bisporphyrins

The synthesis and characterization of cofacial bisporphyrins juxtaposed by xanthene-bridged pillars are presented.
The one-pot preparation of the xanthene dialdehyde avoids the lengthy bridge synthesis accompanying other
cofacial porphyrin systems, thus allowing for the facile preparation of homobimetallic zinc (10), copper (11), and
nickel (12) complexes. The cofacial orientation of the two porphyrin macrocycles was confirmed by X-ray
crystallography. Structural data are provided for bisporphyrins 10−12:  10 (C79H82N8OZn2), triclinic, space group
P1̄, a = 11.2671(2) Å, b = 14.9809(2) Å, c = 20.4852(2) Å, α = 101.6680(10)°, β = 100.8890(10)°, γ =
101.8060(10)°, Z = 2; 11 (C79H82N8OCu2), triclinic, space group P1̄, a = 11.21410(10) Å, b = 14.9539(5) Å, c
= 20.6915(7) Å, α = 101.810(2)°, β = 101.044(2)°, γ = 101.722(2)°, Z = 2; 12 (C79H82N8ONi2), monoclinic,
space group C2/c, a = 24.1671(4) Å, b = 10.669 Å, c = 50.5080(9) Å, β = 99.553(2)°, Z = 8. Exciton interactions
between the porphyrin rings are apparent in electronic spectra, consistent with the cofacial superstructure. The
combination of structural and spectroscopic data provides a basis for the design of additional metal derivatives
for the activation of dioxygen and other small molecules.