Cyclometalated Platinum(II) Cyanometallates: Luminescent Blocks for Coordination Self-Assembly

Cyanido-bridged diplatinum(ii) complexes: ligand and solvent effect on aggregation and luminescence

The association of platinum(ii)-based luminophores, which is caused by metal⋯metal and π-π stacking interactions, has been actively exploited in supramolecular construction of photofunctional molecular materials. Herein, we describe a series of bimetallic complexes [{Pt(C^N^/*N)}2(CN)][BAr4F], containing cyanido-bridged cyclometalated Pt(ii) chromophore fragments (HC^N^N = 6-phenyl-2,2'-bipyridine, (benzyltriazolyl)-phenylpyridine, and pyrazolyl-phenylpyridine; HC^N*N = N-pentyl-6-phenyl-N-(pyridin-2-yl)pyridin-2-amine; ^/* denote five/six-membered metallocycles). These compounds are intensely phosphorescent at room temperature showing quantum yields up to 0.73 in solution and 0.62 in the solid state, which are generally higher than those of the mononuclear relatives [Pt(C^N^/*N)(CN)]. The complex cations bearing sterically unhindered -C^N^N ligands readily assemble in solution, reaching the tetrameric species [{Pt(C^N^N)}2(CN)]44+ as suggested by diffusion NMR spectroscopy. The size of the aggregates can be regulated by the concentration, temperature, and polarity of the solvent that allows to alter the emission from green to near-IR. In the solid state, the maximum of low-energy luminescence is shifted up to 912 nm. The results show that photophysical properties of discrete complexes and the intermolecular aggregation can be substantially enhanced by utilizing the rigid bimetallic units giving rise to novel dynamic light emitting Pt(ii) systems.

Luminescent Anionic Cyclometalated Organoplatinum (II) Complexes with Terminal and Bridging Cyanide Ligand: Structural and Photophysical Properties

We present the synthesis and characterization of two series of mononuclear heteroleptic anionic cycloplatinated(II) complexes featuring terminal cyanide ligand Q⁺[Pt(C^N)(p-MeC₆H₄)(CN)]^- [C^N = benzoquinolate (bzq), Q⁺ = K⁺ 1 and NBu₄⁺ 4; 2-phenylpyridinate (ppy), Q⁺ = K⁺ 2 and NBu₄⁺ 5 and 2-(2,4- difluorophenyl)pyridinate (dfppy), Q⁺ = K⁺ 3 and NBu₄⁺ 6] and a series of symmetrical binuclear complexes (NBu₄)[Pt₂(C^N)₂(p-MeC₆H₄)₂(μ-CN)] (C^N = bzq 7, ppy 8, dfppy 9). Compounds 5, 6, and 7-9 were further determined by single-crystal X-ray diffraction. There are no apparent intermolecular Pt···Pt interactions owing to the presence of bulky NBu₄⁺ counterion. Slow crystallization of K[Pt(ppy)(p-MeC₆H₄)(CN)] 2 in acetone/hexane evolves with formation of yellow crystals, which were identified by single-crystal X-ray diffraction methods as the salt complex {[Pt(ppy)(p-MeC₆H₄)(CN)]₂K₃(OCMe₂)₄(μ-OCMe₂)₂}[Pt(ppy)(p-MeC₆H₄)(μ-CN)Pt(ppy)(p-MeC₆H₄)]·2acetone (10), featuring the binuclear anionic unit 8^- neutralized by an hybrid inorganic-organometallic coordination polymer {[Pt(ppy)(p-MeC₆H₄)(CN)]₂K₃(OCMe₂)₄(μ-OCMe₂)₂}⁺. The photophysical properties of all compounds were recorded in powder, polystyrene film, and solution states with a quantum yield up to 21% for 9 in the solid state. All complexes displayed bright emission in rigid media, and for the interpretation of their absorption and emission properties, density functional theory (DFT) and time-dependent DFT calculations were applied.

The impact of cyclometalated and phosphine ligands on the luminescence properties of cycloplatinated(ii) complexes: photophysical and theoretical investigations

The effects of various C^N cyclometalated and phosphine ligands on the photophysical properties of cycloplatinated(ii) complexes were investigated experimentally and theoretically.

Fluorinated Cycloplatinated(II) Complexes Bearing Bisphosphine Ligands as Potent Anticancer Agents

A family of cationic cycloplatinated(II) complexes [Pt(dfppy)(P^P)]Cl, dfppy = 2-(2,4-difluorophenyl)pyridine, incorporating bisphosphine ligands, P^P = bis(diphenylphosphino)methane (1, dppm), 1,2-bis(diphenylphosphino)ethane (2, dppe) and 1,2-bis(diphenylphosphino)benzene (3, dppbz), was prepared. The complexes were characterized by means of several analytical and spectroscopic methods. These complexes displayed acceptable stability in the biological environments which was confirmed by NMR, HR ESI-MS and UV-vis techniques. The antiproliferative properties of these complexes were evaluated by National Cancer Institute (NCI) at National Institutes of Health (NIH) against 60 different human tumor cell lines such as leukemia, melanoma, lung, colon, brain, ovary, breast, prostate and kidney. These complexes showed higher cytotoxicity than cisplatin against a wide variety of cancer cell lines such as K-562 (leukemia), HOP-92 (lung), HCT-116 (colon), OVCAR-8 (ovarian), PC-3 (prostate), MDA-MB-468 (breast), and melanoma cancer cell lines. Complex 3 as the most potent compound in this study furnished an excellent anti-proliferative activity compared to the cisplatin against Hela, SKOV3, and MCF-7 cancer cell lines. The main mode of the interaction of 1-3 with DNA was also determined using molecular docking studies.

Direct Base-Assisted C‒H Cyclonickelation of 6-Phenyl-2,2'-bipyridine

The organonickel complexes [Ni(Phbpy)X] (X = Br, OAc, CN) were obtained for the first time in a direct base-assisted arene C(sp²)-H cyclometalation reaction from the rather unreactive precursor materials NiX₂ and HPhbpy (6-phenyl-2,2'-bipyridine) or from the versatile precursor [Ni(HPhbpy)Br₂]₂. Different from previously necessary C‒Br oxidative addition at Ni(0), an extended scan of reaction conditions allowed quantitative access to the title compound from Ni(II) on synthetically useful timescales through base-assisted C‒H activation in nonpolar media at elevated temperature. Optimisation of the reaction conditions (various bases, solvents, methods) identified 1:2 mixtures of acetate and carbonate as unrivalled synergetic base pairs in the optimum protocol that holds promise as a readily usable and easily tuneable access to a wide range of direct nickelation products. While for the base-assisted C‒H metalation of the noble metals Ru, Ir, Rh, or Pd, this acetate/carbonate method has been established for a few years, our study represents the leap into the world of the base metals of the 3d series.

Intramolecular rearrangements guided by adaptive coordination-driven reactions toward highly luminescent polynuclear Cu(i) assemblies

Highly luminescent solid-state Cu₆, Au₂Cu₁₀ and Pt₄Cu₁₁ derivatives are obtained in one step reaction thanks to adaptive coordination-driven supramolecular chemistry using pre-assembled flexible Cu(i) precursors.

Chelating and Bridging Roles of 2-(2-Pyridyl)benzimidazole and Bis(diphenylphosphino)acetylene in Stabilizing a Cyclic Tetranuclear Platinum(II) Complex

The reaction of complex [Pt(Me)(DMSO)(pbz)], 1, (pbz = 2-(2-pyridyl)benzimidazolate) with [PtMe(Cl)(DMSO)₂], B, followed by addition of bis(diphenylphosphino)acetylene (dppac), gave the novel tetranuclear platinum complex [Pt₄Me₄(μ-dppac)₂(pbz)₂Cl₂], 2, bearing both the pbz and dppac ligands. In this structure, the pbz ligands are both chelating and bridging to stabilize the tetraplatinum framework. The tetranuclear Pt(II) complex was fully characterized by NMR spectroscopy, X-ray crystallography, and mass spectrometry, and its electronic structure was investigated and supported by DFT calculations.

Electronic Communication in Luminescent Dicyanorhenate-Bridged Homotrinuclear Rhenium(I) Complexes

A series of cyano-bridged homotrinuclear Re(I) complexes with the general formula of {[Re]'[Re][Re]'}⁺ {[Re]' = -[Re^I(CO)₂(LL)(X)]; [Re] = -[(NC)Re^I(CO)₂(phen)(CN)]-; LL = diimine, diphosphine, or two carbonyl ligands; X = triphenylphosphine or carbonyl ligand} and the corresponding mononuclear complex analogues were synthesized. The structures of most of the trinuclear Re(I) complexes have been determined by X-ray crystallography. The relative orientations of peripheral to central Re(I) units in these structures vary considerably. The photophysical properties of these trinuclear Re(I) complexes have been examined. Except for the trinuclear Re(I) complex with Br₂phen ligand, all the other triads display orange to red photoluminescence derived from the ³MLCT [dπ(Re) → π*(phen)] origin of the central Re(I) unit, suggestive of efficient energy transfer between the peripheral chromophores and the central unit. In addition to the efficient energy transfer processes between the Re(I) chromophores in these trinuclear complexes, the ability of the [NC-Re-CN] bridging ligands for electronic coupling between the rhenium metal centers is evidenced by ca. 0.2-0.3 V separation of the two rhenium metal-based oxidation potentials of the chemically equivalent peripheral units.

New Pt→M (M = Ag or Tl) complexes based on anionic cyclometalated Pt(ii) complexes

Anionic cyclometalated complexes (NBu₄)[Pt(CNC)X] (X = Cl (1), CN (2), or S-2py (pyridine-2-thiolate) (3); -CNC- = 2,6-di(phen-2-ide)-pyridine) have been used as precursors in the synthesis of heteropolynuclear Pt-Ag or Pt-Tl complexes containing donor-acceptor metal-metal bonds. Their reaction with AgClO₄ or [Ag(OClO₃)(PPh₃)] produces complexes in which the nuclearity and structure seem to be determined by the ability of the ligand X to form bridges between the metals. Thus, the characteristic linear bridging of the cyano ligand leads to the formation of an octanuclear [{Pt(CNC)(μ-CN)}₄Ag₄] (4) or tetranuclear [{Pt(CNC)(μ-CN)}₂{Ag(PPh₃)}₂] (6) complex, with CN bridges between different "Pt-Ag" units. However, the S-2py ligand can act as a bridge between Pt and Ag of the same "Pt-Ag" unit, giving rise to the complex [{Pt(CNC)(S-2py)}₂Ag₂]·CH₂Cl₂ (5). On the other hand, the reaction of 1-3 with TlPF₆ yields the complexes [PtTl(CNC)Cl] (7), [PtTl(CNC)(CN)] (8), and (NBu₄)[{Pt(CNC)(S-2py)}₂Tl] (9), while with [Tl(S-2py)], [PtTl(CNC)(S-2py)] (10) is obtained. The structures of all these Pt-Tl complexes show great variation, with several geometric arrangements which sometime co-exist in the same crystal structure: discrete Pt-Tl, Pt-Tl-Pt and Pt-Tl-Pt-Tl units, as well as infinite Pt-Tl-Pt-Tl chains. This variability could be due to the lability of the Pt-Tl bonds and the ability of the thallium center to establish secondary interactions with donor atoms or aromatic π electron density from neighboring moieties.

Cyanoferrocenes as redox-active metalloligands for coordination-driven self-assembly

Ferrocene-based Lewis bases have found utility as metalloligands in a wide variety of applications. The coordination chemistry of cyanoferrocenes however, is underexplored. Herein, we describe a new synthetic protocol for the generation of cyanoferrocenes. The coordination chemistry of these metalloligands to [Cu(NCMe)4][PF6], [(PPh3)2Cu(NCMe)2][PF6] and [(dppf)Cu(NCMe)2][PF6] salts has been explored, providing crystallographic evidence of cluster and polymeric forms of 1,1'- and 1,2-dicyanoferrocene complexes. The stability of the complexes and ligand dissociation were found to be strongly solvent-dependent.

Adaptive Coordination-Driven Supramolecular Syntheses toward New Polymetallic Cu(I) Luminescent Assemblies

A thermally activated delayed fluorescence (TADF) tetrametallic Cu(I) metallacycle A behaves as a conformationally adaptive preorganized precursor to afford, through straightforward and rational coordination-driven supramolecular processes, a variety of room-temperature solid-state luminescent polymetallic assemblies. Reacting various cyano-based building blocks with A, a homometallic Cu(I) 1D-helical coordination polymer C and Cu₈M discrete circular heterobimetallic assemblies D_M (M = Ni, Pd, Pt) are obtained. Their luminescence behaviors are studied, revealing notably the crucial impact of the spin-orbit coupling offered by the central M metal center on the photophysical properties of the heterobimetallic D_M derivatives.

Improvement of the Photophysical Performance of Platinum-Cyclometalated Complexes in Halogen-Bonded Adducts

Three groups of luminescent platinum complexes [Pt(C^N)(L)(Y)] [C^N=benzothienyl-pyridine (1), bezofuryl-pyridine (2), phenyl-pyridine (3); L/Y=DMSO/Cl (a), PPh₃ /Cl (b), PPh₃ /CN (c)] have been probed as halogen-bond (XB) acceptors towards iodofluorobenzenes (IC₆ F₅ and I₂ C₆ F₄ ). Compounds 1 a and 2 a (L/Y=DMSO/Cl) afford the adducts 1 a⋅⋅⋅I₂ C₆ F₄ and 2 a⋅⋅⋅I₂ C₆ F₄ , which feature I⋅⋅⋅S_btpy /I⋅⋅⋅π_btpy and I⋅⋅⋅O_DMSO /I⋅⋅⋅Cl short contacts, respectively. The phosphane-cyanide derivatives 1 c and 2 c (L/Y=PPh₃ /CN) co-crystallise with both IC₆ F₅ and I₂ C₆ F₄ . None of the phpy-based species 3 a-3 c participated in XB interactions. Although the native complexes are rather poor luminophores in the solid state (Φ_em =0.023-0.089), the adducts exhibit an up to 10-fold increase of the intensity with a minor alteration of the emission energy. The observed gain in the quantum efficiency is mainly attributed to the joint influence of non-covalent interactions (halogen/hydrogen bonding, π-π stacking), which govern the crystal-packing mode and diminish the radiationless pathways for the T₁ →S₀ transition by providing a rigid environment around the chromophore.

A H-shaped heterometallic Sn4Au4 system with guest-tuneable multicolour and selective luminescence sensing properties

A H-shaped heterometallic Sn₄Au₄ system displays guest-dependent optical properties and its stimuli-responsive methylred-rich crystals are sensitive towards pH variations.