Isolation of Ruthenium–Indolizine Complexes: Insight into the Metal-Induced Cycloisomerization of Propargylic Pyridines

Ruthenafuran Complexes Supported by the Bipyridine-Bis(diphenylphosphino)methane Ligand Set: Synthesis and Cytotoxicity Studies

Mononuclear and dinuclear Ru(II) complexes cis-[Ru(κ²-dppm)(bpy)Cl₂] (1), cis-[Ru(κ²-dppe)(bpy)Cl₂] (2) and [Ru₂(bpy)₂(μ-dpam)₂(μ-Cl)₂](Cl)₂ ([3](Cl)₂) were prepared from the reactions between cis(Cl), cis(S)-[Ru(bpy)(dmso-S)₂Cl₂] and diphosphine/diarsine ligands (bpy = 2,2′-bipyridine; dppm = 1,1-bis(diphenylphosphino)methane; dppe = 1,2-bis(diphenylphosphino)ethane; dpam = 1,1-bis(diphenylarsino)methane). While methoxy-substituted ruthenafuran [Ru(bpy)(κ²-dppe)(C^O)]⁺ ([7]⁺; C^O = anionic bidentate [C(OMe)CHC(Ph)O]⁻ chelate) was obtained as the only product in the reaction between 2 and phenyl ynone HC≡C(C=O)Ph in MeOH, replacing 2 with 1 led to the formation of both methoxy-substituted ruthenafuran [Ru(bpy)(κ²-dppm)(C^O)]⁺ ([4]⁺) and phosphonium-ring-fused bicyclic ruthenafuran [Ru(bpy)(P^C^O)Cl]⁺ ([5]⁺; P^C^O = neutral tridentate [(Ph)₂PCH₂P(Ph)₂CCHC(Ph)O] chelate). All of these aforementioned metallafuran complexes were derived from Ru(II)–vinylidene intermediates. The potential applications of these metallafuran complexes as anticancer agents were evaluated by in vitro cytotoxicity studies against cervical carcinoma (HeLa) cancer cell line. All the ruthenafuran complexes were found to be one order of magnitude more cytotoxic than cisplatin, which is one of the metal-based anticancer agents being widely used currently.

Iron(ii)-induced cycloisomerization of alkynes via"non-vinylidene" pathways for iron(ii)-indolizine and -indolizinone complexes

Reactions between pyridine-functionalized alkynes and an Fe(ii) precursor supported by 2,5,8-trithia[9](2,9)-1,10-phenanthrolinophane afforded the first Fe(ii)-indolizine and -indolizinone complexes. Structural analysis and theoretical calculations revealed the existence of unconventional "non-vinylidene" pathways and challenged the generality of vinylidene intermediacy in Fe(ii)-induced alkyne transformations.

Conventional and unconventional alkyne activations by Ru and Os for unprecedented dimetalated quinolizinium complexes

Two types of unexpected quinolizinium complexes were obtained from the reactions between pyridine-functionalized propargylic alcohol HC[triple bond, length as m-dash]CC(OH)(Ph)(CH₂(2-py)) (L1) and cis-[M(L^L)₂Cl₂] (M = Ru, Os; L^L = 1,1-bis(diphenylphosphino)methane (dppm), 2,2'-bipyridine (bpy)). Their molecular structures revealed that L1 can be activated by Ru and Os via the conventional "vinylidene-involving" or unconventional "non-vinylidene-involving" pathways.

Ruthenium-Induced Cyclization of Heteroatom-Functionalized Alkynes: Progress, Challenges and Perspectives

Metal-induced cyclization of functionalized alkynes represents one of the most general approaches to prepare organic heterocycles. Although Ru^II centers are well-established to promote alkyne to vinylidene rearrangements and many Ru^II -mediated alkyne cyclizations have been rationalized to be the results of post-vinylidene transformations, recent discoveries indicate that Ru^II centers can serve as electrophiles and induce alkyne cyclizations without vinylidene intermediacy. In this Minireview, an overview of the Ru^II -induced cyclization of heteroatom-functionalized alkynes in the last decade is provided, with an emphasis on the discoveries and validations of the unconventional "non-vinylidene-involving" pathways.

A New Tetradentate Mixed Aza-Thioether Macrocycle and Its Complexation Behavior towards Fe(II), Ni(II) and Cu(II) Ions

A new tetradentate mixed aza-thioether macrocyclic ligand 2,6-dithia[7](2,9)-1,10-phenanthrolinophane ([13]ane(phenN₂)S₂) was successfully synthesized. Reacting metal precursors [Fe(CH₃CN)₂(OTf)₂], Ni(ClO₄)₂·6H₂O, and Cu(ClO₄)₂·6H₂O with one equivalent of [13]ane(phenN₂)S₂ afforded [Fe([13]ane(phenN₂)S₂)(OTf)₂] (1), [Ni([13]ane(phenN₂)S₂)](ClO₄)₂ (2(ClO₄)₂), and [Cu([13]ane(phenN₂)S₂)(OH₂)](ClO₄)₂ (3(ClO₄)₂), respectively. The structures of [13]ane(phenN₂)S₂ and all of its metal complexes were investigated by X-ray crystallography. The [13]ane(phenN₂)S₂ was found to behave as a tetradentate ligand via its donor atoms N and S.

Isolation of a C3-metalated indolizine complex and a phosphonium ring-fused bicyclic metallafuran from the osmium-induced transformation of pyridine-tethered alkynes

The first C3-metalated indolizine complex was prepared from the reaction between cis-[Os(dppm)2Cl2] (dppm = 1,1-bis(diphenylphosphino)methane) and propargylic pyridine, HC[triple bond, length as m-dash]CC(OH)(2-py)2. A phosphonium ring-fused bicyclic osmafuran complex was also prepared from the reaction between cis-[Os(dppm)2Cl2] and pyridyl ynone, HC[triple bond, length as m-dash]C(C[double bond, length as m-dash]O)(2-py). The formation of these two products revealed the intermediacy of metal-vinylidene species regarding [Os(dppm)2Cl]+-mediated alkyne transformations. Comparison of the d6 transition-metal precursors employed to activate HC[triple bond, length as m-dash]CC(OH)(2-py)2 suggests that precursors with higher π-basicity favor the vinylidene-involving pathway.

Synthesis and study of Au(iii)-indolizine derivatives: turn-on luminescence by photo-induced controlled release

The photo- and structural properties of a series of Au(iii) indolizine complexes were determined. Controlled release of halogenated indolizine derivatives from the corresponding Au(iii) complexes was achieved by photoinduced C-X bond formation, which provided turn-on luminescence with an increase in emission intensity of up to 67 times.

Ruthenium–indolizinone complexes as a new class of metalated heterocyclic compounds: insight into unconventional alkyne activation pathways, revelation of unexpected electronic properties and exploration of medicinal application

The first examples of metal–indolizinone complexes prepared by Ru-assisted activation of pyridine-tethered alkynes exhibit moderate cytotoxicity against several human cancer cell lines.

Catalytic σ-activation of carbon–carbon triple bonds: reactions of propargylic alcohols and alkynes

A variety of organic transformations have been developed based on conceptually novel catalytic σ-activation of CC bonds of alkynes.

Versatile Coordination Mode of a New Pyridine-Based Ditopic Ligand with Transition Metals: From Regular Pyridine to Alkyne and Alkenyl Bindings and Indolizinium Formation

The new BPMPB ligand, namely, bis[1-bis(2-pyridylmethyl),1 (pyridyl)]butyne, can be very easily obtained as a side product in the known reaction of picolyl chloride and sodium acetylide (which major product is the known terminal alkyne-substituted tripod). This symmetrical ligand contains two identical coordination sites with two methylenepyridines and one pyridyl group on each side, linked by an alkyne function providing a semirigid segment. Together with the molecular structure of the ligand which is reported, we describe the preparation of complexes with Fe(II)Cl2, Co(II)Cl2, Ni(II)Cl2, Cu(I)Cl, and Zn(II)Cl2 salts. All complexes have been characterized by X-ray diffraction studies as well as by standard spectroscopic techniques. The striking point in this work is the diversity of the structures that are obtained. Co(II) and Zn(II) provide isostructural dinuclear complexes in which both coordination sites are occupied within a tetrahedral symmetry. The Cu(I) complex is also a dinuclear compound, but in that case, the copper atom is coordinated to the alkyne moiety, two pyridines, and a bridging chloride. The (13)C NMR spectrum of the copper complex confirms that the metal center is coordinated to the alkyne in solution. The coordination of Ni(II) results in the formation of a mononuclear complex in which a pyridine has fused with the alkyne moiety to generate an indolizinium group; the structure of the corresponding alkenyl complex is reported. Finally, the addition of FeCl2 to the ligand results in the formation of a mononuclear complex with a free, noncoordinated indolizinium. The sequence developed in the present work illustrates the possibility for the metal centers to adopt various coordination modes which may be relevant to the conversion of an alkyne and a pyridyl unit into indolizinium.

Luminescent ruthenium(II) complex bearing bipyridine and N-heterocyclic carbene-based C∧N∧C pincer ligand for live-cell imaging of endocytosis

Luminescent ruthenium(II)-cyanide complex with N-heterocyclic carbene pincer ligand C(∧)N(∧)C = 2,6-bis(1-butylimidazol-2-ylidene)pyridine and 2,2'-bipyridine (bpy) shows minimal cytotoxicity to both human breast carcinoma cell (MCF-7) and human retinal pigmented epithelium cell (RPE) in a wide range of concentration (0.1-500 μM), and can be used for the luminescent imaging of endocytosis of the complex in these cells.

Hyperbranched polyester nanorods with pyrrolo[2,1-a]isoquinoline end groups for fluorescent recognition of Fe3+

Novel hyperbranched polyester nanorods HBPE-CICA₆ and HBPE-CICA₂ were obtained and used to establish a highly sensitive fluorescent sensor for Fe³⁺ ions.

Silver-catalyzed cyclization of 2-pyridyl alkynyl carbinols with isocyanides: divergent synthesis of indolizines and pyrroles

Divergent syntheses of indolizines and 2,4-disubstituted pyrroles by the silver-catalyzed cyclization of 2-pyridyl alkynyl carbinols with isocyanides are reported.