Kinetic study and UV–Vis spectra of 1:2 complexation of free base para-substituted meso-tetraphenylporphyrins with trimethylsilyl chloride
✍ Scribed by Afsaneh Safavi; Zarangiz Movahedi; Daryoush Mohajer; Hamid Abdollahi
- Publisher
- John Wiley and Sons
- Year
- 2007
- Tongue
- English
- Weight
- 194 KB
- Volume
- 39
- Category
- Article
- ISSN
- 0538-8066
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✦ Synopsis
Abstract
The UV–Vis spectra for 1:2 complexation of four different para‐substituted meso‐tetraphenylporphyrin (H~2~t(4‐X)pp) and meso‐tetraphenylporphyrins (H~2~tpp) with trimethylsilyl chloride (TMSC) displayed large and different redshifts (28–32.4 nm) of Soret and (15–41.7 nm) Q~(0‐0)~ bands, whereas 1:2 complexation of the less flexible tetramesitylporphyrin (H~2~tmp) with TMSC led to rather small redshift (24.8 nm) of the Soret band and blueshift (−7.4 nm) of the Q~(0‐0)~ band. The varying spectral behavior for the porphyrins complexation seems to essentially reflect the different extent of π‐interactions between the meso‐aryl groups and the presumably saddled porphyrin macrocycle, through their relative coplanarity. The observed order of the rate constants for the complexation of various para‐substituted porphyrins, H~2~t(4‐OCH~3~)pp (9.27 ± 0.03) × 10^−3^ > H~2~t(4‐CH~3~)pp (6.68 ± 0.05) × 10^−3^ > H~2~tpp (3.2 ± 0.05) × 10^−3^ > H~2~t(4‐Cl)pp (8.36 ± 0.06) × 10^−4^, clearly demonstrated a higher reaction rate for the porphyrins containing para‐substituents with stronger electron donor ability. The calculated order for porphyrins (0.9 ± 0.1) and for TMSC (1.0 ± 0.1) suggests rate = K[Por][TMSC] for the complexation. Attempts were made to explain the absence of spectral evidence for the presence of an intermediate 1:1 (TMSC) Por adduct in terms of its high reactivity and/or relative instability. © 2007 Wiley Periodicals, Inc. 39: 231–235, 2007