Expanded Ligands Based upon Iron(II) Coordination Compounds of Asymmetrical Bis(terpyridine) Domains.

The synthesis and characterization of two tritopic ligands containing a 2,2':6',2″-terpyridine (tpy) metal binding domain and either a 3,2':6',3″- or a 4,2':6',4″-tpy domain are detailed. The synthetic routes to these ligands involved the [Pd(dppf)Cl2]-catalyzed coupling of a boronic ester-functionalized 2,2':6',2″-tpy with bromo-derivatives of 3,2':6',3″-tpy or 4,2':6',4″-tpy. The 2,2':6',2″-tpy domains of the tritopic ligands preferentially bind Fe2+ in reactions with iron(II) salts leading to the formation of two homoleptic iron(II) complexes containing two peripheral 3,2':6',3″-tpy or 4,2':6',4″-tpy metal-binding sites, respectively. These iron(II) complexes are potentially tetratopic ligands and represent expanded versions of tetra(pyridin-4-yl)pyrazine.

Adapting (4,4) Networks through Substituent Effects and Conformationally Flexible 3,2':6',3"-Terpyridines.

Coordination networks formed between Co(NCS)2 and 4'-substituted-[1,1'-biphenyl]-4-yl-3,2':6',3"-terpyridines in which the 4'-group is Me (1), H (2), F (3), Cl (4) or Br (5) are reported. [Co(1)2(NCS)2]n·4.5nCHCl3, [Co(2)2(NCS)2]n·4.3nCHCl3, [Co(3)2(NCS)2]n·4nCHCl3, [Co(4)2(NCS)2]n, and [Co(5)2(NCS)2]n·nCHCl3 are 2D-networks directed by 4-connecting cobalt nodes. Changes in the conformation of the 3,2':6',3"-tpy unit coupled with the different peripheral substituents lead to three structure types. In [Co(1)2(NCS)2]n·4.5nCHCl3, [Co(2)2(NCS)2]n·4.3nCHCl3, [Co(3)2(NCS)2]n·4nCHCl3, cone-like arrangements of [1,1'-biphenyl]-4-yl units pack through pyridine…arene π-stacking, whereas Cl…π interactions are dominant in the packing in [Co(4)2(NCS)2]n. The introduction of the Br substituent in ligand 5 switches off both face-to-face π-stacking and halogen…π-interactions, and the packing interactions are more subtly controlled. Assemblies with organic linkers 1-3 are structurally similar and the lattice accommodates CHCl3 molecules in distinct cavities; thermogravimetric analysis confirmed that half the solvent in [Co(3)2(NCS)2]n·4nCHCl3 can be reversibly removed.

Switching the Conformation of 3,2':6',3″-tpy Domains in 4'-(4-n-Alkyloxyphenyl)-3,2':6',3″-Terpyridines.

The preparation and characterization of 4'-(4-n-octyloxyphenyl)-3,2':6',3″-terpyridine (8) and 4'-(4-n-nonyloxyphenyl)-3,2':6',3″-terpyridine (9) are reported. The single crystal structures of 4'-(4-n-hexyloxyphenyl)-3,2':6',3″-terpyridine (6), 4'-(4-n-heptyloxyphenyl)-3,2':6',3″-terpyridine (7), and compounds 8 and 9 have been determined. The conformation of the 3,2':6',3″-tpy unit is trans,trans in 6 and 7, but switches to cis,trans in 8 and 9. This is associated with significant changes in the packing interactions with a more dominant role for van der Waals interactions between adjacent n-alkyloxy chains and C-Hmethylene... π interactions in 8 and 9. The solid-state structures of 6 and 7 with the n-hexyloxy and n-heptyloxy chains feature interwoven sheets of supramolecular assemblies of molecules, with pairs of n-alkyloxy chains threaded through cavities in an adjacent sheet.

Directing 2D-Coordination Networks: Combined Effects of a Conformationally Flexible 3,2':6',3″-Terpyridine and Chain Length Variation in 4'-(4-n-Alkyloxyphenyl) Substituents.

The synthesis and characterization of 4'-(4-n-propoxyphenyl)-3,2':6',3″-terpyridine is described. Five 2D-coordination networks have been isolated by crystal growth at room temperature from reactions of Co(NCS)2 with 4'-(4-n-alkyloxyphenyl)-3,2':6',3″-terpyridines in which the n-alkyl group is ethyl, n-propyl, n-butyl, n-pentyl and n-hexyl in ligands 2-6, respectively. The single-crystal structures of [{Co(2)2(NCS)2}.0.6CHCl3]n, [{Co(3)2(NCS)2}.4CHCl3.0.25H2O]n, [{Co(4)2(NCS)2}.4CHCl3]n, [Co2(5)4(NCS)4]n and [Co(6)2(NCS)2]n have been determined, and powder X-ray diffraction has demonstrated that the single-crystal structures are representative of the bulk materials. Each compound possesses a (4,4) net with Co centres as 4-connecting nodes. For the assemblies containing 2, 3 and 4, the (4,4) net comprises two geometrically different rhombuses, and the nets pack in an ABAB... arrangement with cone-like arrangements of n-alkyloxyphenyl groups being accommodated in a similar unit in an adjacent net. An increase in the n-alkyloxy chain length has two consequences: there is a change in the conformation of the 3,2':6',3″-tpy metal-binding domain, and the (4,4) net comprises identical rhombuses. Similarities and differences between the assemblies with ligands 2-6 and the previously reported [{Co(1)2(NCS)2}.3MeOH]n and [{Co(1)2(NCS)2}.2.2CHCl3]n in which 1 is 4'-(4-methoxyphenyl)-3,2':6',3″-terpyridine are discussed. The results demonstrate the effects of combining a variable chain length in the 4'-(4-n-alkyloxyphenyl) substituents of 3,2':6',3″-tpy and a conformationally flexible 3,2':6',3″-tpy metal-binding domain.

Anticancer Potential of Diiron Vinyliminium Complexes.

Although ferrocene derivatives have attracted considerable attention as possible anticancer agents, the medicinal potential of diiron complexes has remained largely unexplored. Herein, we describe the straightforward multigram-scale synthesis and the antiproliferative activity of a series of diiron cyclopentadienyl complexes containing bridging vinyliminium ligands. IC50 values in the low-to-mid micromolar range were determined against cisplatin sensitive and resistant human ovarian carcinoma (A2780 and A2780cisR) cell lines. Notable selectivity towards the cancerous cells lines compared to the non-tumoral human embryonic kidney (HEK-293) cell line was observed for selected compounds. The activity seems to be multimodal, involving reactive oxygen species (ROS) generation and, in some cases, a fragmentation process to afford monoiron derivatives. The large structural variability, amphiphilic character and good stability in aqueous media of the diiron vinyliminium complexes provide favorable properties compared to other widely studied classes of iron-based anticancer candidates.

Anticancer Potential of Diiron Vinyliminium Complexes.

Invited for the cover of this issue is the group of Fabio Marchetti at the Università di Pisa and Paul J. Dyson at Ecole Polytechnique Fédérale de Lausanne (EPFL). Read the full text of the article at 10.1002/chem.201902885.

Synthesis of Terpyridines: Simple Reactions-What Could Possibly Go Wrong?

The preparation of 24-functionalized 12,22:26,32-terpyridines (4'-functionalized 3,2:6',3''-terpyridines) by the reaction of three 4-alkoxybenzaldehydes with 3-acetylpyridine and ammonia was investigated; under identical reaction conditions, two (R = nC4H9, C2H5) gave the expected products whereas a third (R = nC3H7) gave only a cyclohexanol derivative derived from the condensation of three molecules of 3-acetylpyridine with two of 4-(n-propoxy)benzaldehyde. A comprehensive survey of ''unexpected'' products from reactions of ArCOCH3 derivatives with aromatic aldehydes is presented. Three different types of alternative product are identified.

Straight Versus Branched Chain Substituents in 4'-(Butoxyphenyl)-3,2':6',3″-terpyridines: Effects on (4,4) Coordination Network Assemblies.

The preparation and characterization of the isomers rac-4'-(4-butan-2-yloxyphenyl)-3,2':6',3″-terpyridine (rac-2), 4'-(2-methylpropoxyphenyl)-3,2':6',3″-terpyridine (3) and 4'-(tert-butoxyphenyl)-3,2':6',3″-terpyridine (4) are reported. The compounds react with Co(NCS)2 under conditions of crystal growth at room temperature to give single crystals of [{Co(rac-2)2(NCS)2}·CHCl3]n, [Co(3)2(NCS)2]n and [{Co(4)2(NCS)2}·CHCl3]n which possess (4,4) networks, with the Co centers acting as 4-connecting nodes. Powder X-ray diffraction (PXRD) was used to confirm that the crystals chosen for single crystal X-ray diffraction were representative of the bulk samples. The detailed structures of the three networks have been compared with that of the previously reported [{Co(1)2(NCS)2}·4CHCl3]n in which 1 is 4'-(butoxyphenyl)-3,2':6',3″-terpyridine. Whereas the switch from 1 with the straight-chain butoxy substituent to rac-2, 3 and 4 with branched chains causes significant structural perturbation, changes in the spatial properties of the branched substituents are accommodated with subtle conformational changes in the 3,2':6',3″-tpy domain.

Single and Double-Stranded 1D-Coordination Polymers with 4'-(4-Alkyloxyphenyl)-3,2':6',3"-terpyridines and {Cu2(µ-OAc)4} or {Cu4(µ3-OH)2(µ-OAc)2(µ3-OAc)2(AcO-κO)2} Motifs.

Five coordination polymers formed from combinations of copper(II) acetate and 4'-(4-alkyloxyphenyl)-3,2':6',3''-terpyridines with methoxy (1), n-butoxy (2), n-pentyloxy (3) and n-heptyloxy (4) substituents are reported. Reaction of 1 with Cu(OAc)2∙H2O leads to the 1D-polymer [Cu2(µ-OAc)4(1)]n in which {Cu2(-OAc)4} paddle-wheel units are connected by ligands 1, or [{Cu4(µ3-OH)2(µ-OAc)2(µ3-OAc)2(AcO-κO)2(1)2}.2MeOH]n in which centrosymmetric tetranuclear clusters link pairs of ligands 1 to give a double-stranded 1D-polymer. Layering solutions of Cu(OAc)2∙H2O (in MeOH) over 2, 3 or 4 (in CHCl3) leads to the assembly of the 1D-polymers [2{Cu2(µ-OAc)4(2)}.1.25MeOH]n, [Cu2(µ-OAc)4(3)]n and [{Cu2(µ-OAc)4(4)}.0.2CHCl3]n. In all compounds, the 3,2':6',3''-tpy unit coordinates only through the outer pyridine rings, but the conformation of the 3,2':6',3''-tpy responds to changes in the length of the alkyloxy tails leading to changes in the conformation of the polymer backbone and in the packing of the chains in the crystal lattice in the chains featuring {Cu2(-OAc)4} paddle-wheel linkers.

Competition in Coordination Assemblies: 1D-Coordination Polymer or 2D-Nets Based on Co(NCS)2 and 4'-(4-methoxyphenyl)-3,2':6',3″-terpyridine.

The synthesis and characterization of 4'-(4-methoxyphenyl)-3,2':6',3″-terpyridine (2) (IUPAC PIN 24-(4-methoxyphenyl)-12,22:26,32-terpyridine) are described, and its coordination behaviour with cobalt(II) thiocyanate has been investigated. In a series of experiments, crystals were grown at room temperature by layering a MeOH solution of Co(NCS)2 over a CHCl3 solution of 2 using 1:1, 1:2 or 2:1 molar ratios of metal salt-to-ligand. Crystals harvested within 2-3 weeks proved to be the 1D-coordination polymer [Co(2)(NCS)2(MeOH)2]n and powder X-ray diffraction (PXRD) confirmed that the crystals selected for single-crystal X-ray diffraction were representative of the bulk samples. Longer crystallization times with a Co(NCS)2 to 2 molar ratio of 1:1 yielded crystals of [Co(2)(NCS)2(MeOH)2]n (1D-chain) and the pseudopolymorphs [{Co(2)2(NCS)2}·3MeOH]n and [{Co(2)2(NCS)2}·2.2CHCl3]n ((4,4)-nets), each type of crystal originating from a different zone in the crystallization tube. PXRD for this last experiment confirmed that the dominant product in the bulk sample was the 1D-coordination polymer.

Correction: Rocco, D.; et al. Competition in Coordination Assemblies: 1D-Coordination Polymer or 2D-Nets Based on Co(NCS)2 and 4'-(4-methoxy)-3,2':6',3″-terpyridine. Polymers 2019, 11, 1224; doi:10.3390/polym11071224.

We wish to make the following corrections to our published paper [...].