Structure and Conformation of Photosynthetic Pigments and Related Compounds 9 On the Structure and Macrocycle Conformation of Two Copper(II) Rhodochlorin Derivatives and Two Related Rhodoporphyrins

Crystal structure analyses of (rhodochlorinato-15-acetic trimethyl ester)copper(II) 3 and (3¹, 3²-didehydro-rhodochlorinato-15-formic acid trimethyl ester)copper(II) 4 reveal intriguing multiple macrocycle conformations of the metallochlorins in the crystal. The observed conformations range from almost planar macrocycles to distorted macrocycles with individual atoms being displaced up to 0.72 Å from the mean plane. The nonplanar macrocycles show a S₄-ruffled macrocycie distortion with significant distortions for the meso-carbons and tilting of the Cb- Cb axes. A comparison with the related free base porphyrins rhodoporphyrin-15- acetic acid trimethyl ester 5 and rhodoporphyrin dimethyl ester 6 shows that the conformational distortion is due to the mixing of metal and substituent effects, hydroporphyrin character, and packing forces. Crystal data: 3, monoclinic, P2₁, a = 12.096(4) Å, b - 14.307(4) Å, c = 22.343(9) Å , β = 104.94(4)°, Z = 4 (2 indep. mol.), R = 0.069 for 8141 reflections with I > 2.0σ(I); 4, triclinic, P 1, a = 10.528(3) Å . b - 10.646(4) Å, c = 34.026(13) Å, α = 89.81(4)°, β = 88.72(3)°, γ = 60.38(2)°, Z = 4 (4 indep. mol.). R = 0.073 for 9446 reflections with I > 2.5σ(I); 5, triclinic, P 1̄, a = 9.591(2) Å, b = 12.959(4) Å, c = 13.453(4) Å, α = 105.86(2)°, β = 92.67(2)°, γ = 96.12(2)°, Z = 2, R = 0.060 for 4990 reflections with I > 2.5 σ(I); 6, triclinic, P 1̄, a = 8.908(4) Å, b = 12.895(5) Å, c = 13.482(6) Å , α = 102.74(3)°, β = 90.38(4)°, γ = 91.84(3)°, Z = 2, R = 0.089 for 3369 reflections with I > 2.0σ(I).