Investigation of Streamlined Syntheses of Porphyrins Bearing Distinct Meso Substituents

Abstract

The use of porphyrins in fundamental studies and diverse applications requires facile access to ample quantities of material in pure form. The existing conditions for the condensation of a dipyrromethane plus a dipyrromethane-dicarbinol employ 2.5 mM reactants and afford ∼30% yields with no detectable scrambling. Large-scale syntheses require condensation and oxidation conditions that function at higher concentrations. Thirty-one acids (plus additives) have been examined for reactions at 25 mM reactants using the synthesis of a trans-A 2 B 2 -porphyrin as a model. The porphyrin was formed in ∼20% yield upon condensation in CH 2 Cl 2 at room temperature using ( 1) Sc(OTf) 3 (3.2 mM) + 2,6-di-tert-butylpyridine (32 mM), or (2) Zn(OTf) 2 (10 mM). Nine porphyrins were prepared in this manner in yields of 15-22% with no detectable scrambling, whereas three other porphyrins afforded low levels of scrambling and/or lower yields (8-14%). Conditions for the oxidation also have been investigated. The reaction of 5-mesityldipyrromethane and the dicarbinol derived from 1-(4methoxybenzoyl)-9-(4-methylbenzoyl)-5-phenyldipyrromethane (18 mmol each in 720 mL of CH 2 Cl 2 ; 25 mM) with catalysis by Sc(OTf) 3 /2,6-di-tert-butylpyridine and aerobic oxidation [(t-Bu 4 FePc) 2 O and DDQ, 2.5 mol % each with a stream of O 2 ] afforded 2.88 g (22.8% yield) of the corresponding ABCD-porphyrin. The present synthesis (25 mM), at 4.5-times larger scale than the largest prior analogous synthesis (2.5 mM reactants with stoichiometric use of DDQ), afforded 4.0 times as much porphyrin on a molar basis while employing about one-half the amount of solvent and < 1 / 25 the amount of DDQ. A three-step one-flask process also was developed that employs (i) condensation at 25 mM reactants, (ii) aerobic oxidation, and (iii) metal insertion to afford the metalloporphyrin [Mg(II), Ni-(II), Cu(II), Zn(II), Pd(II)] in a streamlined manner. Taken together, the various improvements facilitate gram-scale syntheses of diverse porphyrins.

Nonlinear Optical Properties of Porphyrins

“…Recent advances in synthetic porphyrin chemistry, especially for asymmetrically substituted porphyrins have rekindled interest in very simple meso substituted push-pull porphyrins. [64,164] Thus, contemporary work continues to study push-pull porphyrins, primarily those that possess a strong intramolecular dipole moment, and divulges into novel types of porphyrin-like macrocycles, especially those with extended p-conjugation systems.…”

Electrophilic Activation of Aldehydes “On Water”: A Facile Route to Dipyrromethanes

“…[1] Lindsey and co-workers reported a practical and high yielding synthesis of porphyrins [2] by tetramerization of monopyrrole derivatives. An alternative and valuable synthesis of porphyrins can be obtained by the condensation of two dipyrromethane moieties ( Figure 1).…”

Effects of Linker Torsional Constraints on the Rate of Ground-State Hole Transfer in Porphyrin Dyads

“…Here, the same porphyrins were prepared in a rational manner by coupling dipyrromethane-dicarbinol (1-OH) and a dipyrromethane (2a−d) respectively, using a literature procedure. 28 The procedure entailed reaction in CH 2 Cl 2 containing Sc(OTf) 3 (2.8 mM) and 2,6-di-tertbutylpyridine (2,6-DTBP) (28 mM) at room temperature followed by oxidation with DDQ. The putative dipyrromethane-dicarbinol (1-OH) was obtained by the reduction of diacyldipyrromethane−tin complex 1 using NaBH 4 (Scheme 1).…”