Substitution reactions of a water-soluble metalloporphyrin with azide and 1,1,3,3-tetramethyl-2-thiourea.
The substitution reactions of tetrakis-(4-N-methylpyridyl)porphinecobalt (III) (CoIIITMpyP) with azide and with 1,1,3,3-tetramethyl-2-thiourea (TMTU) have been studied as a function of pH at 25 degrees and an ionic strength of 0.5 M. The mechanistic pathway proposed for thiocyanate [1] and pyridine [2] is applicable to these ligands as well once allowance is made for two attacking forms of azide, N3- and HN3. A TMTU axial substituent has about the same influence on the rate of further ligand substitution as does SCN- and a much larger influence than does azide. Similar behavior between bound SCN- and bound TMTU is also shown in electron-transfer reactions with Ru(NH3)62+. Whereas both sulfur-containing ligands enhance the rate relative to the diaquo complex, the azide complex undergoes reduction an order of magnitude more slowly than does the diaquo complex.
D001386:Azides; D055598:Chemical Phenomena; D002621:Chemistry; D003035:Cobalt; D007700:Kinetics; D008024:Ligands; D008665:Metalloporphyrins; D010084:Oxidation-Reduction; D013816:Thermodynamics; D013890:Thiourea / Q000031:analogs & derivatives*
D001386:Azides; D008024:Ligands; D008665:Metalloporphyrins; D003035:Cobalt; D013890:Thiourea