SYNTHESIS AND CHARACTERIZATION OF LITHIUM, SODIUM, AND POTASSIUM PORPHYRIN COMPLEXES - X-RAY CRYSTAL-STRUCTURES OF LI2(C6H12O2)2TMPP, NA2(THF)4OEP, AND K2(PYRIDINE)4OEP

Reaction of free-base porphyrins (H2Por = octaethylporphyrin (OEP), meso-tetraphenylporphyrin (TPP), meso-tetra-p-tolylporphyrin (TTP), meso-tetrakis)4-tert-butylphenyl)porphyrin (TBPP), meso-tetrakis(3,4,5-tri-methoxyphenyl)porphyrin (TMPP)) with 2 equiv of MN(SiMe3)2 (M = Li, Na, K) in THF or dimethoxyethane (DME) yields dimetal salts of empirical formula M2(THF)4Por and M2(DME)2Por, respectively. The lithium derivatives crystallize from donor solvents in the form of 1:1 salts [Li(solv)n] [Li(Por)] (solv = THF, n = 4; solv = DME, diacetone alcohol, n = 2). The crystallography determined structure of the TMPP derivative crystallized from acetone consists of a [Li(TMPP)]- anion and a [Li(diacetone alcohol)2]+ counterion. Li-7 NMR spectroscopy and conductivity measurements suggest these ionic structures are retained in polar solvents; however, in relatively nonpolar solvents symmetrical ion-paired structures are observed. For the larger sodium ion, X-ray crystallography shows two Na(THF)2 moieties symmetrically bound to all four nitrogens, one on each face of the porphyrin ring. The structure of the pyridine complex K2(pyr)4(OEP) has also been determined; it is similar to the sodium salt but shows the solvent molecules positioned perpendicular to the porphyrin ring, presumably to maximize pi-interactions between neighboring molecules in the crystal. X-ray data are as follows: Li2(C6H12O2)2 (TMPP): P1BAR with a = 12.420(2) angstrom, b = 12.965(2) angstrom, c = 13.998(2) angstrom, alpha = 66.29(2)degrees, beta = 60.21(2)degrees, gamma = 77.00(2)degrees, V = 1790 angstrom3, d(calc) = 1.23 g cm-3, and Z = 1. Na2-(THF)4(OEP): P1BAR with a = 9.801(3) angstrom, b = 11.598(3) angstrom, c = 12.106(2) angstrom, alpha = 96.81(2)degrees, beta = 106.67(2)degrees, gamma = 107.52(2)degrees, V = 1225 angstrom3, d(calc) = 1.18 g cm-3, and Z = 1. K2(pyr)4(OEP): P1BAR with a = 10.102(4) angstrom, b = 13.974(5) angstrom, c = 19.029(4) angstrom, alpha = 89.88(2)degrees, beta = 76.78(2)degrees, gamma = 72.90(2)degrees, V = 2493 angstrom3, d(calc) = 1.24 g cm-3, and Z = 2.