Direct synthesis of palladium porphyrins from acyldipyrromethanes.
[reaction: see text] Palladium porphyrins are valuable photosensitizers and luminescent agents in biology and materials chemistry. New methodology is described wherein a 1-acyldipyrromethane is converted into the palladium chelate of a trans-A(2)B(2) porphyrin via a one-flask reaction. The reaction entails self-condensation of the 1-acyldipyrromethane in refluxing ethanol containing KOH (5-10 mol equiv) and Pd(CH(3)CN)(2)Cl(2) (0.6 mol equiv) exposed to air. This direct route to palladium porphyrins is more expedient than the four steps of the traditional synthesis: (1) reduction of the 1-acyldipyrromethane; (2) acid-catalyzed condensation; (3) oxidation of the porphyrinogen intermediate; and (4) metal insertion. The new synthesis requires neither acid nor DDQ and formally entails only a 2e(-) + 2H(+) oxidation overall versus the traditional multistep synthesis which requires a 2e(-) + 2H(+) reduction per each 1-acyldipyrromethane (4e(-) + 4H(+) overall) followed by a 6e(-) + 6H(+) oxidation. The analogous reaction of a 1,9-diacyldipyrromethane and a dipyrromethane also gives the palladium porphyrin. Seven palladium porphyrins have been prepared in yields of 25-57%. The direct route also can be used with Cu(OAc)(2).H(2)O to give the copper porphyrin albeit in low yield. In summary, this methodology readily affords palladium porphyrins directly from acyldipyrromethanes.
Sharada
Duddu S
DS
Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, USA.
Muresan
Ana Z
AZ
Muthukumaran
Kannan
K
Lindsey
Jonathan S
JS
D002384:Catalysis; D007202:Indicators and Reagents; D049408:Luminescent Agents / Q000138:chemical synthesis*; D008665:Metalloporphyrins / Q000138:chemical synthesis*; D008697:Methane / Q000031:analogs & derivatives* / Q000737:chemistry*; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010165:Palladium / Q000737:chemistry*; D011758:Pyrroles / Q000737:chemistry*
D007202:Indicators and Reagents; D049408:Luminescent Agents; D008665:Metalloporphyrins; D011758:Pyrroles; D010165:Palladium; D008697:Methane