Dimeric aggregates of five-coordinated methyl(phthalocyaninato)Rh(III):: 1H NMR evidence for staggered and slipped cofacial dimers

The H-1 NMR spectra of the five-coordinated rhodium phthalocyanine complex Me(RPc)Rh(III) (1, RPc = dianion of 1,4,8,11,15,18,22,25-octa-n-pentylphthalocyanine) in toluene indicate that it exists as a discrete monomer at low concentrations. The complex forms a dimer aggregate reversibly in the concentration range of 2.6-10.2 mM at -90 < T < 22 degreesC. The dimerization constants at -60, -80, and -90 degreesC are 2.0 x 10(2), 5.7 x 10(2), and 1.0 x 10(3) M-1, respectively. In chloroform, aggregation of the complex occurs at similar to0.3 mM, reflecting the lower solvating power of chloroform for this complex. The H-1 NMR spectra of the chloroform solutions indicate that at concentrations greater than 1.0 mM, two discrete dimers in the ratio of 87:13 are reversibly formed. The H-1 NMR spectra of the major isomer, 2a, suggest that it is the 45 degrees -staggered cofacial dimer, a dimer with a D-4d symmetry. The H-1 NMR spectra of the minor isomer, 2b, suggest that it is a slipped cofacial dimer with a C-2h symmetry, which is formed by slipping a (RPc)Rh plane of the eclipsed dimer (a D-4h dimer) along a line connecting two opposing meso nitrogens of (RPc)Rh. Interestingly, the solution conformation of 2b is similar to that of the basic stacking unit found in the crystal structure of 1. Published in 2001 by John Wiley & Sons, Ltd.