Dual Function of β‐Hydroxy Dithiocinnamic Esters: RAFT Agent and Ligand for Metal Complexation

Abstract

The reversible addition‐fragmentation chain‐transfer (RAFT) process has become a versatile tool for the preparation of defined polymers tolerating a large variety of functional groups. Several dithioesters, trithiocarbonates, xanthates, or dithiocarbamates have been developed as effective chain transfer agents (CTAs), but only a few examples have been reported, where the resulting end groups are directly considered for a secondary use besides controlling the polymerization. Herein, it is demonstrated that β‐hydroxy dithiocinnamic esters represent a hitherto overlooked class of materials, which are originally designed for the complexation of transition metals but may as well act as reversible CTAs. Modified with a suitable leaving group (R‐group), these vinyl conjugated dithioesters indeed provide reasonable control over the polymerization of acrylates, acrylamides, or styrene via the RAFT process. Kinetic studies reveal linear evolutions of molar mass with conversion, while different substituents on the aromatic unit has only a minor influence. Block extensions prove the livingness of the polymer chains, although extended polymerization times may lead to side reactions. The resulting dithiocinnamic ester end groups are still able to form complexes with platinum, which verifies that the structural integrity of the end group is maintained. These findings open a versatile new route to tailor‐made polymer‐bound metal complexes.

Novel Homoleptic and Heteroleptic Pt(II) β‐oxodithiocinnamic ester Complexes: Synthesis, Characterization, Interactions with 9‐methylguanine and Antiproliferative Activity

“…The methyl groups of the coordinated dimethyl sulfoxide (DMSO) in [Pt(L1–L9)(DMSO)Cl] complexes were observed at δ 3.60 ppm as a singlet accompanied by platinum satellites 3 J Pt‐H ≈22 Hz in the 1 H NMR spectra and δ 46 ppm with platinum–carbon coupling 2 J Pt‐C ≈50 Hz in the 13 C{1H} NMR spectra, respectively. Compared to the free DMSO, there is observed a downfield shift by 1.1 and 6 ppm in both 1 H and 13 C{1H} NMR spectra, respectively, which also confirm the formation of a mono‐chelate complex with S‐coordinated DMSO ligand which is in accordance with previously described Pt‐DMSO complexes [13–16,35–39,42–46] . 195 Pt NMR spectra for the bis‐chelate complexes [Pt(L1–L9) 2 ] as well as the mono‐chelate complexes [Pt(L1–L9)(DMS)Cl] and [Pt(L1–L9)(DMSO)Cl] were obtained.…”

“…All compounds were characterized by NMR spectroscopy, mass spectrometry and elemental analysis. The chemical shifts in 1 H NMR and 13 C{1H} NMR spectra for ligands HL1‐HL9 are generally in good agreement with previously reported values [8–17,35–39] . In the 1 H NMR spectra, HL1‐HL9 display a single resonance signal in the range of δ 14.49–15.17 ppm belonging to the hydroxyl group (−OH) proton, which is not observed in the complexes [Pt(L1–L9) 2 ], [Pt(L1–L9)(DMS)Cl], and [Pt(L1–L9)(DMSO)Cl].…”

“…The chemical shifts in 1 H NMR and 13 C{1H} NMR spectra for ligands HL1-HL9 are generally in good agreement with previously reported values. [8][9][10][11][12][13][14][15][16][17][35][36][37][38][39] In the 1 H NMR spectra, HL1-HL9 display a single resonance signal in the range of δ 14.49-15.17 ppm belonging to the hydroxyl group (À OH) proton, which is not observed in the complexes [Pt(L1-L9) 2 ], [Pt(L1-L9)(DMS)Cl], and [Pt(L1-L9)(DMSO)Cl]. The methine proton (=CHÀ ) found at δ 6.66-7.44 ppm and δ 6.76-7.32 ppm for the ligands and complexes, respectively, is virtually unchanged.…”

“…Compared to the free DMSO, there is observed a downfield shift by 1.1 and 6 ppm in both 1 H and 13 C{1H} NMR spectra, respectively, which also confirm the formation of a mono-chelate complex with Scoordinated DMSO ligand which is in accordance with previously described Pt-DMSO complexes. [13][14][15][16][35][36][37][38][39][42][43][44][45][46] 195 Pt NMR spectra for the bis-chelate complexes [Pt(L1-L9) 2 ] as well as the mono-chelate complexes [Pt(L1-L9)(DMS)Cl] and [Pt(L1-L9)(DMSO)Cl] were obtained. The signals appeared in the range of (À 2267 to À 2350 ppm) and (À 2879 to À 3079 ppm), for the bis-chelate and mono-chelate complexes, respectively, which is in good agreement with the previously reported values.…”

Synthetic Approaches towards Peptide‐Conjugates of Pt(II) Compounds with an (O,S) Chelating Moiety

“…In this respect, their aromatic and aliphatic subunits have been modified to a reasonable extent, enabling e. g. the production of defined polymer materials. [2] Incorporation of functional groups that would allow for the formation of metal complexes as bioconjugates has to date not been reported, but represents a desirable aim. Such bioconjugates could improve e. g. the compounds' selectivity towards certain biological targets through specific receptor targeting.…”