Synthesis of β-aryl substituted porphyrins by palladium-catalysed cross-coupling reactions

Abstract

Bromoporphyrins undergo Suzuki cross-coupling reactions with aryl boronic acids to give f3-arylporpyrins in high yields and X-ray analysis shows that H2TPP(Ph)4 2a (TPP = tetraphenylporphyrin) is centrosymmetric and possesses a hydrogen-bonded inner core.Substituents at the P-positions of porphyrins exert much larger steric and electronic effects on the porphyrin ring than substituents at meso aryl positions.' The P-substituents also induce the porphyrin ring into a non-planar conformation which may control the biological properties in tetrapyrrole systems like the P-450 and photosynthetic centres.

Impact of Distortion of Porphyrins on Axial Coordination in (Porphyrinato)zinc(II) Complexes with Aminopyridines as Axial Ligands

“…II complexes by adopting tetraphenylporphyrin (H 2 TPP), 2,3,5,10,12,13,15,20-octaphenylporphyrin (H 2 OPP), [12] and 2, 3,5,7,8,10,12,13,15,17,18,20-dodecaphenylporphyrin (H 2 DPP) [13] as porphyrin ligands showing different extents of distortion and aminopyridines as axial ligands. (Porphyrin)Zn II complexes can be useful probes to evaluate these effects, since Zn II is in a d 10 configuration without change of spin states, and the σ-donating ability of the pyrrole nitrogen atoms in the porphyrins directly reflects on the equilibrium of the axial ligation.…”

New Heck-Type Coupling Reactions of Natural Tetrapyrroles − Synthesis of Porphyrinoligomers Bridged by Divinyl- and Trivinylbenzene

“…This is particularly true for those possessing a substitution pattern related to that of the natural tetrapyrroles (e.g. hemato-or protoporphyrin [10] [11] ).In particular, palladium(0)-catalyzed coupling reactions have been shown to be very powerful in the functionalization and linking of porphyrins [3] [12] [13] [14] . Recent publications have described some impressive examples using this strategy, utilizing synthetic tetraphenyl-substituted porphyrin precursors which were linked by ethinyl and butadiinyl units to give up to pentameric units via Heck-type reactions [1] .…”

“…The development of new strategies in the synthesis of oligomeric porphyrins, especially those linked by CϪC bonds, has attracted considerable interest recently [1] [2] [3] [4] . This is due to the possibilities that it offers for gaining an insight into the mechanisms of photosynthesis [5] [6] [7] [8] , which demands the construction of large arrays of covalent linked porphyrins.…”

Transition Metal Catalysis in Porphyrin Modifications

“…[1] A short outline of the catalytic transformations of porphyrins should start from the application of the reactions of C-C bond formation. Suzuki coupling is well documented since 1994 when this reaction was first applied by Zhou for the exocyclic transformation of the porphyrin core, [2] porphyrin bearing halogen atoms [3] and borylated porphyrins [4] both find their applications in constructing new carbon-carbon bonds. The same is true for Sonogashira reaction which was first applied for the porphyrin modifications also in 1994, [5] and halogen-substituted porphyrins [6] as well as porphyrins with acetylene moieties [7] participate in the coupling.…”

“…[15] In 2001 amidation of β-bromoporphyrins using cyclic amides in the presence of Pd(dppf)Cl 2 /dppf was reported by Lier, [12] and in 2007 Zhang proposed an universal approach for the amidation of mono-and dibromoporphyrins and their metal complexes using Pd 2 (dba) 3 or Pd(OAc) 2 with Xantphos ligand. [16] Alkoxy-and aryloxylation reactions of mono-and di-meso-bromophenylporphyrins catalyzed by Pd(OAc) 2 or Pd 2 (dba) 3 with DPEphos or Xantphos were described in 2003 by same Zhang. [17] In 2007 he was also the first who reported on successful synthesis of β-substituted alkoxyand aryloxyporphyrins using Pd 2 (dba) 3 /DPEphos catalytic system and made chiral diporphyrin conjugates using catalytic C-O bond formation.…”