Mervyn F. Hudson

Concerning meso-tetraphenylporphyrin purification

Treatment of crude meso-tetraphenylporphyrin with 2,3-dichloro-5,6-dicyanobenzoquinone affords a high recovery of ‘chlorin-free’meso-tetraphenylporphyrin (1), the excess of quinone and its transformation products being easily removed by adsorption on alumina. This new procedure is also applied to the purification of meso-tetraphenylporphyrin metal complexes.

Novel mercury(II) complexes of porphyrins

Abstract Treatment of octa-alkylporphyrins (e.g. 1–3 ) with mercury(II) acetate in methylene chloride and tetrahydrofuran affords novel complexes ( 4 ) containing two porphyrin rings layered between three Hg atoms. A new type of stereoisomerism in regularly substituted porphyrins (e.g. 1a , 2a ) is identified; it is observed by NMR spectroscopy and occurs because two forms of the complex ( 4 ) are possible, depending upon which faces of the porphyrin molecule are turned in towards the central Hg atom. The NMR spectra also indicate that in concentrated solution the double sandwich complexes ( 4 ) are stable towards disproportionation and recombination. On the basis of the inherent geometrical arrangements in the complex ( 4 ), an efficient NMR method for unambiguous identification of the four primary type isomers of the aetio- and copro-porphyrin series is described. In very dilute solution, or in mixtures containing nucleophilic solvents such as pyridine, methanol, dioxan, or tetrahydrofuran (in the absence of excess mercury(II) acetate), the double sandwich complexes (4) are destroyed to afford normal 1:1 metalloporphyrins.

Novel mercury(II) complexes of meso-tetraphenylporphyrin and N-methylporphyrins

Abstract Treatment of meso -tetraphenylporphyrin, H 2 TPP, with just over one equivalent of mercury(II) acetate in methylene chloride-THF gives mercury(II) meso -tetraphenylporphyrin, HgTPP. With excess of mercury(II) acetate, H 2 TPP and HgTPP afford a novel dimetallic mononuclear porphyrin, AcOHgTPPHgOAc. In contrast, HgTPP reacts with mercury(II) chloride to give the chloro-analogue, ClHgTPPHgCl, but there is no reaction between H 2 TPP and mercury(II) chloride. Demetallation of HgTPP in methylene chloride containing small amounts of hydrogen chloride proceeds via the dimetallic compound, ClHgTPPHgCl, to give free base HTPP. The reaction rate is dependent upon acid concentration suggesting that the rate determining step is protonation, but dilution causes no decrease in the rate; a mechanism which invokes the intermediacy of monohydrogen- meso -tetraphenylporphyrinatomercury(II) chloride, H(TPP)HgCl, in the formation of ClHgTPPHgCl and in its subsequent decomposition into H 2 TPP, is proposed. N-Methylporphyrins react with mercury(II) acetate in methylene chloride-tetrahydrofuran to give the corresponding N-methylporphyrinatomercury(II) acetates, Me(P)HgOAc.

Novel mercury(II) porphyrins: identification of poryphyrin primary ‘type-isomers’

N.m.r. spectroscopy of some novel mercury(II) porphyrins is used to differentiate between the individual aetio- and copro-porphyrin ‘type-isomers;’ the unusual ‘double-sandwich’ structure (1) is proposed for these chelates.

Bile pigment studies—III: Controlled oxidative degradation of 1,19(21,24h)-bilindiones (bilitrienes)

Treatment of the model 1,19(21,24H)-bilindione (1) with thallium(III) acetate in methanol gives the thallium(III) complex (11) which is unstable and in the presence of air and methanol is transformed into the 15,16-dimethoxy complex (12), characterised as the metal free derivative (13). When exposed to light, solutions of (12) are oxidised to afford, after work-up, the 14-formyl-1(15H)-tripyrrinone (4) and ethylmethylmaleimide (17). A general discussion of mechanistic implications is presented.

The nuclear magnetic resonance spectra of porphyrins. Part X. Carbon-13 nuclear magnetic resonance spectra of some meso-tetraarylporphyrins and their metal chelates

The 13C n.m.r. spectra of meso-tetraphenylporphyrin (TPP), the zinc(II), cadmium(II), bis[mercury(II) acetate], and various thallium(III) derivatives, and some related analogues are reported and assigned. In meso-tetra-(o-tolyl)-porphyrin and meso-tetra-(1-naphthyl)porphyrin only one species was observed. The introduction of zinc(II), cadmium(II), or bis[mercury(II) acetate] into the TPP nucleus does not significantly change the 13C shifts, but the thallium(II) derivative shows both extensive TI–13C couplings and non-equivalence of o-phenyl carbon atoms, the latter being due to the exoplanar position of the thallium atom. Specific TI–13C couplings to the o-phenyl carbon atoms are also observed.The phenomenon of slow protonation (TPP ⇄ TPPH22+) was identified and examined by using 13C and 1H n.m.r. spectroscopy, and the 13C shifts and assignments for the dication are reported. The large protonation shifts of TPP and high ΔG value for this process (ca. 16·3 kcal mol–1) are consistent with the further buckling of the macrocycle on protonation, due to decrease in the angle between the macrocycle and the phenyl rings. In contrast, the protonation shifts of meso-tetra-(o-tolyl)porphyrin are ‘normal’ owing to the additional steric requirements of the o-methyl groups. A hitherto unrecorded effect is the shift of the tetramethylsilane reference in trifluoroacetic acid compared with deuteriochloroform of 1·5 p.p.m. upfield with respect to other reference compounds.Identification of the coalescence temperature for the NH tautomerism in both the 13C and 1H spectra allows the kinetic parameters for this process to be determined (ΔG303ca. 12·3 kcal mol–1, ΔH ca. 9·2 kcal mol–1, and ΔS ca.–10 cal K–1 mol–1). These, and the isotope effect (KNH/KND) of ca. 12 (measured at one temperature to remove entropy of activation effects) are consistent with a two-step (rather than a concerted) process.