How does the tin(IV)-insertion to porphyrins proceed in water at ambient temperature?: Re-investigation by time dependent 1H NMR and detection of intermediates

Abstract Water soluble tin(IV)-porphyrins, trans -dihydroxy-5,10,15,20-tetra( N -methyl-4′-pyridiniumyl)porphyrinate tin (IV) (Sn(IV)TMPyP(OH) 2 ) was successfully synthesized in high yield (90%) through one-pot process in water at room temperature by treating the parent free base (H 2 TMPyP) with Sn(II)Cl 2 . Re-investigation by the detailed kinetic analysis of the time dependent 1 H NMR signals indicated that the tin(IV)-insertion reaction reversibly proceeded through three steps to start from free base dimer, [H 2 TMPyP] 2 , through Sn(II)TMPyP. New intermediate, an association complex between SnCl 2 and H 2 TMPyP, which should be a precursor of Sn(II)TMPyP, was clearly observed in UV–vis and 1 H NMR for the first time. Sn(II)TMPyP was also detected at around 500 nm in UV–vis spectroscopy, while it was silent against 1 H NMR, which was supported by DFT calculation to indicate that Sn(II)TMPyP has a paramagnetic nature through substantial population on triplet spin states. To explore possible one-pot process for other porphyrins, such as neutral tetra- meso -substituted-tolylporphyrin (TTP), tetra- meso -substituted-mesitylporphyrin (TMP), and anionic tetra- meso -substituted-carboxyphenylporphyrin (TCPP), the reactions in water, binary-phase system of water/dichloromethane, and methanol were examined. The anionic TCPP suffered the tin(IV)-insertion at ambient temperature only in methanol with good yield (90%).