Stepwise Preparation of meso‐Tetraphenyl‐ and meso‐Tetrakis(4‐trifluoromethylphenyl)bacteriodilactones and their Zinc(II) and Palladium(II) Complexes

Abstract

While the direct, one-step conversion of meso-tetrakis(pentafluorophenyl)porphyrin to its corresponding bacteriodilactone is well established, no such reaction has been achieved for meso-tetraphenyl or meso-tetrakis(4-trifluoromethylphenyl)porphyrin. Thus, we describe two stepwise oxidation approaches of these porphyrins toward the corresponding bacteriodilactones, as mixtures of two inseparable regioisomers. As [ ‡] Oxazolochlorins. 475shown by 1 H NMR spectroscopy, the ratio of the two isomers is oxidant-dependent. Their Zn II and Pd II complexes were formed by metal ion insertion into the free bases. Some of the free base dilactones and their metal complexes were also characterized crystallographically, demonstrating the planarity of the macrocycle. This report makes these intriguing porphyrinoids synthetically accessible for further study. Full Paperlactone analogues of the carbaporphyrins, [20] subporphyrin, [21] dithiaporphyrin, [22] and hydroporphyrins. [19,23] Since their discovery in 1984, [24] a number of oxidative pathways were described that generated porpholactones from various ( -substituted) porphyrins and chlorins. [2c,3,4,17a,25] In fact, porpholactones appear to be a common -and frequently adventitious -product when the -positions of meso-arylporphyrins are being manipulated under oxidizing conditions. [4,24,25c,26] This is remarkable in as much as there is no known precedent for the formation of porpholactones in nature as part of the degradation pathways of the naturally occurring -alkyl-porphyrins and -chlorins. [27] Among the synthesis pathways toward porpholactones, the direct, one-step oxidation of a non-activated porphyrin is an attractive option. [25a,25b,25d,28] It is possible to oxidize meso-tetraphenylporphyrin 2a directly to the corresponding porpholactone 1a, [25a] but surprisingly, the direct oxidation pathway was most practical only for meso-tetrakis(pentafluorophenyl)porphyrin 2c. [25a,25d] However, the drawback of using porphyrin 2c is that the one-step reactions also readily generate higher oxidation products. Thus, method dependent, up to all Scheme 1. Stepwise syntheses of the bacteriodilactones 3 and their metal complexes 3M.

Oxazolochlorins 21. Most Efficient Access to meso-Tetraphenyl- and meso-Tetrakis(pentafluorophenyl)porpholactones, and Their Zinc(II) and Platinum(II) Complexes

“…Moreover, closely related porphyrins of utility can be derived, like the thionolactones used as hypochlorite sensors [ 18 ], the porpholactone reduction products porpholactols [ 4 , 55 , 56 , 57 ] useful as photosensitizers [ 58 ] or hydrogen evolution catalysts [ 28 ], as well as chlorolactones and chlorolactams [ 59 , 60 ], porpholactams [ 59 , 60 ], and imidazoloporphyrins [ 60 ], even if alternative synthetic pathways for the latter porphyrinoid were developed that circumvent the intermediate porpholactone [ 61 ]. The method described also allow direct access to the meso -pentafluorophenyl-substituted porphodilactone isomers of broad utility [ 17 ], though longer but more rational syntheses might be desirable when more than 10 −5 mol quantities are desired of either the fluorinated or non-fluorinated series [ 17 , 62 ].…”

Lanthanide porphyrinoids as molecular theranostics

“…89 Porphodilactone is a porphyrinoid product in which two 3,4-pyrrolic CQC bonds are replaced by two lactone moieties with cis-or trans-carbonyl groups. [159][160][161] To date, Zhang and co-workers have reported that the resulting configurational difference may be used to tune photophysical properties, 162 affect the self-assembly morphology, 163 modulate the extent of aromaticity, 164 and modify the efficacy of photon upconversion. 165 In the case of Zhang and co-worker's porphodilactone, regioisomerism modulated the T 1 energy state of cis/trans-F 20 TPPDL, in loose analogy to ChI b, d, and f (Fig.…”

Crystal structure of cis-7,8-dihydroxy-5,10,15,20-tetraphenylchlorin and its zinc(II)–ethylenediamine complex

“…Importantly, chlorin diols 2 Ar M are the starting materials for the generation of a wide range of planar and non-planar chlorin analogues (so-called pyrrole-modified porphyrins) (Bru ¨ckner, 2016;Sharma et al, 2017;Hewage et al, 2019;Bru ¨ckner et al, 2020;Luciano et al, 2020;Wu et al, 2020), whereby the parent chlorin diols 2 Ph H 2 and 2 Ph Zn generally serve as spectroscopic benchmarks. Since the conformation of a porphyrinic macrocycle greatly influences its electronic structure, the structural characterization of the benchmark compounds 2 Ph H 2 and 2 Ph Zn is important.…”