Selective meso-monobromination of 5,15-diarylporphyrins via organopalladium porphyrins

Abstract

ABSTRACT:The selective meso-monobromination of 5,15-diarylporphyrins is difficult to achieve and extensive chromatography is required to obtain pure products. A sequence of (i) dibromination, (ii) selective monoinsertion of [Pd(dppe)] [dppe = 1,2-bis(diphenylphosphino)ethane] and (iii) hydrodepalladation using methanolic base affords pure monobromoporphyrins in typically ≥60% overall yield without isolation of the organopalladium porphyrin. Monobromo derivatives of even highly lipophilic 5,15-diarylporphyrins are thus readily available without tedious, expensive and environmentally undesirable chromatography.

Bromination of porphyrins (Review)

“…The authors of [77] proposed their own version of the solution to the production of monobrominated porphyrins. While observing the complexity and difficulty of the chromatographic separation of mono-and dibrominated porphyrins they proposed to obtain dibromodiarylporphyrins by known methods [16] and then to substitute one of the bromine atoms by the complex of palladium with 1,2-bis(diphenylphosphine)ethane and hydrodepalladize the obtained compound with a solution of alkali in methanol.…”

A new type of chiral porphyrin: Organopalladium porphyrins with chiral chelating diphosphine ligands

“…The suite of new chiral derivatives 2-4 was prepared according to the methods we have used previously for achiral diphosphine ligands, namely oxidative addition of meso-bromoporphyrin (1) to Pd(0) diphosphine precursors [21,22,27]. The latter were prepared in situ by reaction of the diphosphine ligand with Pd 2 dba 3 (dba = dibenzylideneacetone) in hot toluene under argon atmosphere (Scheme 2).…”

“…The Pd porphyrins decompose on the TLC plates, forming NiDPP, so the formation of the Pd species cannot be followed directly by TLC [27]. The diphos complexes 4a,b precipitated from hot toluene within 15 min, while the other two ligands yielded complexes that were soluble in toluene.…”

“…We have prepared numerous examples in which we varied the lateral aryl substituents (Ar = phenyl, p-tolyl, 3,5-di-tert-butylphenyl) on the 10,20 porphyrin carbons, the centrally coordinated metal ion (M = 2H, MnCl, Co, Ni, Zn, InCl), the neutral ligands (L 2 = monodentate aryl or alkyl phosphines, chelating diphosphine, chelating diamine), and the external ligand (X = Br, Cl, NO 3 , CF 3 SO 3 , pyridines, pyridyl porphyrins). Syntheses, spectra, crystal structures, electrochemistry and uses as synthetic intermediates have been described [21][22][23][24][25][26][27][28]. For chelating diphosphines, only the Pd(II) complexes have been prepared [21,22,27], while for monodentate phosphines and chelating diamines, both Pd(II) and Pt(II) systems are known [23][24][25].…”

“…Syntheses, spectra, crystal structures, electrochemistry and uses as synthetic intermediates have been described [21][22][23][24][25][26][27][28]. For chelating diphosphines, only the Pd(II) complexes have been prepared [21,22,27], while for monodentate phosphines and chelating diamines, both Pd(II) and Pt(II) systems are known [23][24][25]. Palladium catalysis has recently been used to prepare chiral 5,15-disubstituted derivatives of diarylporphyrins, but the ligands on the palladium were not themselves chiral [29].…”