Introducing the Staudinger phosphazene reaction to porphyrin chemistry

Abstract

The syntheses, characterizations and transformations of three tetraphenylporphyrins derived from methoxymethylated benzaldehyde 3 are described. Benzaldehyde 3 reacted with pyrrole under Lewis acid catalysis to give dipyrromethane 4 which was used as precursor in porphyrin syntheses. Porphyrins 6, αα-7 and αβ-7 were obtained using conditions for sterically encumbered benzaldehydes, with αα-7 and αβ-7 being atropisomers. The methoxymethyl groups of 6, αα-7 and αβ-7 were transformed into bromomethyl substituents (porphyrins 8, αα-9 and αβ-9) which were easily modified by nucleophilic reaction with the azide anion. Porphyrin azide 10 was subjected to a Staudinger phosphazene formation with triphenylphosphine. Subsequent reaction of the porphyrin phosphazene 12 with carboxylic acids gave acetamide 13, benzamide 14, and ferrocene carboxamide 15, respectively. Kornblum oxidation of monobromomethyl porphyrin 8 gave the formyl derivative 16.

A p‐Quinodimethane‐Bridged Porphyrin Dimer

“…To this end, the dialdehyde‐linked porphyrin dimer 13 was first prepared as a key intermediate. To synthesize dimer 13 , we first tried to reduce the terephthalate‐bridged porphyrin dimer 7 a or 7 b with lithium aluminum hydride and then oxidize the resulting diols with pyridinium chlorochromate 20. However, the overall yields from these two steps were lower than 5 % because of significant decomposition of the porphyrin.…”

“…To synthesize dimer 13, we first tried to reduce the tere-A C H T U N G T R E N N U N G phthalate-bridged porphyrin dimer 7 a or 7 b with lithium aluminum hydride and then oxidize the resulting diols with pyridinium chlorochromate. [20] However, the overall yields from these two steps were lower than 5 % because of significant decomposition of the porphyrin. We next tried Suzuki coupling reaction between 5 and 2,5-dibromoterephthalaldehyde, [21] but again the yield of 13 was lower than 5 % due to significant deboronation of 5.…”

Novel Synthetic Cycloketo‐Tetraphenylporphyrins

“…All systems bearing exocyclic ketone moieties show strong shifts of the half‐wave potentials to positive potentials in the cathodic region compared with a non‐annelated reference system 10 , that is, 5 4 ,10 4 ,15 4 ,20 4 ‐tetra‐ tert ‐butyl‐5 2 ‐methoxymethyl‐5 6 ‐methyl‐5,10,15,20‐tetraphenylporphyrin 9. In Figure 1, the half‐wave potentials for reference compound 10 , which is the direct precursor of 3a ,9 are displayed as dashed lines. The exact potential values are given in Table 1.…”

“…As a consequence, a suitable system should have low symmetry, an exocyclic ketone moiety connecting a meso substituent with the proximate β‐pyrrolic position on the macrocycle and a preserved porphyrin structure without the formation of a partially reduced system to grant higher stability. We chose our recently developed monofunctionalized porphyrin building block,9 being easily accessible and also easily converted into the target 2a which fulfils the above‐mentioned criteria. For comparative studies we furthermore chose two reference systems: one simpler model bearing the same exocycle, 2b , and a model with a six‐membered exocycle, 2c (Scheme ), in analogy to systems already reported by Callot and co‐workers 10…”

Novel cycloketo tetraphenylporphyrins: spectroscopic study of structure-properties relationships

“…31,32 These were metallated with zinc(II) quantitatively (Zn(OAc) 2 , CH 2 Cl 2 /MeOH) in order to ease the substitution reaction with KCN in polyethylene glycol 400 (PEG400). The central metal thereby coordinated the cyanide ion and guaranteed high yield conversions.…”