A UV-vis spectroscopic study of 1:2 adduct formation of some free-base meso-tetraaryl- and meso-tetraalkylporphyrins with PhSnCl3 and (CH3)2SnCl2.
Molecular complexation of meso-tetraalkylporphyrins (with primary alkyl residues) (alkylpor), para-substituted meso-tetraphenylporphyrins (para=H, CH(3), Cl, OCH(3), NO(2)) (arylpor) and meso-teramesitylporphyrin (H(2)tmp) with PhSnCl(3) (A(I)) and (CH(3))(2)SnCl(2) (A(II)) led to the red shift of the Soret bands. Comparison of the Soret bands of A(I) (or A(II))(2)arylpor with those of (A(I) or A(II))(2)alkylpor shows a red shift of ca. 10-20nm for the formers with respect to the latters. According to the very similar saddled porphyrin core reported for the dications of H(2)tpp and H(2)t(n-Pr)p with CF(3)COOH, it may be concluded that in addition to the Q(0,0) bands the Soret bands may be also affected by the pi-donation of meso-aryl substituents to the porphyrin aromatic system. An overlap between one of the e(1g) orbital of phenyl groups and the a(1u) orbital of porphyrin core is suggested to explain the observed red shifts in the case of pi-donor para-substituents. Very similar red shift of the Soret bands of (A(I) or A(II))(2)H(2)t(4-OMe)pp and (A(I) or A(II))(2)H(2)t(4-NO(2))pp with respect to that of (A(I) or A(II))(2)H(2)t(n-Pr)p, in spite of the pi-electron withdrawing effects of para-NO(2) groups, seems to be resulted in by the pi-interaction of LUMOs of (4-NO(2))phenyl substituent with e(g) orbital of porphyrin core; this interaction would lead to the stabilization of e(g) orbital and the observed red shift of the Soret band. However, due to the distribution of electron densities of the a(2u) orbital on meso-positions, as well as the central nitrogens, the Q(0,0) bands are more strongly affected by the pi-donation of meso-aryl groups to the porphyrin core.
Mohajer
Daryoush
D
Shiraz University, Department of Chemistry, 71454 Shiraz, Iran.
Sakhtemanian
Elham
E
Rayati
Saeed
S
Zakavi
Saeed
S
D009682:Magnetic Resonance Spectroscopy; D008665:Metalloporphyrins / Q000737:chemistry*; D008958:Models, Molecular; D009947:Organotin Compounds / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D017186:Titrimetry
D008665:Metalloporphyrins; D009947:Organotin Compounds; C529623:dichlorodimethylstannane; C529622:trichlorophenylstannane