Synthesis, structure and spectroscopic study of Rh polypyridine complexes with phenylcyanamide derivative ligands

Several new Rh^III complexes, [Rh(tpy)(bpy)L](PF₆)₂ (tpy=2,2′:6′,2″-terpyridine, bpy=2,2′-bipyridine, and L=monoanions of phenylcyanamide(pcyd)), 4-methylphenylcyanamide (4-MePcyd), 2,4-dimethylphenylcyanamide (2,4-Me₂pcyd), 4-methoxyphenylcyanamide (4-MeOPcyd), 2-chlorophenylcyanamide (2-Clpcyd) and 2,5-dichlorophenylcyanamide (2,5-Cl₂pcyd) have been synthesized and characterized by elemental analysis, IR, ¹H NMR and electronic absorption spectroscopies. ORTEP drawing of [Rh(tpy)(bpy)(2,5-Cl₂pcyd)](PF₆)₂·1/2CH₃CN shows three pyridyl rings of the tpy ligand that are nearly coplanar, as are the two rings of bpy. The anionic cyanamide group is coordinated end-on by the nitrile nitrogen to the Rh^III. The Rh^III–NCN bond is bent, having an angle of 125.4°. This bent bond is largely determined by the σ-bonding interaction of a cyanamide non-bonding electron pair in a sp² hybrid orbital.     

Synthesis of dendritic bisphosphonates as bone targeting ligands

A dendritic bisphosphonate carrying three bisphosphonate (BP) units in close proximity was designed as a ligand to conjugate large therapeutic molecules for their bone selective delivery. The Bu₃P-catalyzed conjugate addition of nitromethane to vinylidene bisphosphonate was effective to construct a quaternary carbon center carrying BP units. Owing to multivalent interactions, the dendritic bisphosphonate showed considerable affinity for the bone mineral hydroxyapatite even in the presence of a competitor, demonstrating potential as a bone targeting ligand.     

Synthesis and structures of two mononuclear iron(ii) complexes derived from polypyridine ligands

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Synthesis and properties of novel ditopic polypyridine ligands bridged by one and two acetylenic bonds

Ethynyl substituted bipyridine chelates react with bromo or triflate functionalized bipyridine or terpyridine subunits, in the presence of catalytic amounts of Pd^o(PPh₃)₄ to yield, the new homo- and heteroditopic ethynyl bridge ligands 2a, 4a, 7a and 8. Self coupling of the ethynyl substituted bipyridine species in the presence of CuCl/TMEDA/O₂, yield the symmetric diethynyl bridge ligands 2b, 4b and 7b.     

Synthesis of new chiral thiazoline-containing ligands

New chiral ligands, including bi- and tridentate thiazoline derivatives, analogues of known oxazolines, have been synthesized by a general and convenient procedure, starting from dithioesters and commercial enantiopure 2-aminoalcohols. A preliminary test shows the ability of such ligands to act as asymmetric catalysts in Pd-catalyzed allylic substitution reaction.     

Synthesis,structure and spectroscopic study of Cu(II) polypyridine complexes with phenylcyanamide derivative ligands

Several new mononuclear copper(II) complexes, [Cu(phen)₂L]PF₆, where phen = 1,10-phenanthroline and L = monoanions of phenylcyanamide (pcyd), 2,5-dichlorophenylcyanamide (2,5-Cl₂pcyd), 2-dichlorophenylcyanamide (2-Clpcyd) and 4-methylphenylcyanamide (4-Mepcyd), have been prepared and characterized by elemental analysis, UV–Vis, IR and ¹H NMR spectroscopies and cyclic voltammetry. [Cu(phen)₂(2,5-Cl₂pcyd)]PF₆ crystallized with a molecule of acetone with empirical formula of C₃₁H₂₀N₆OF₆Cl₂PCu in a triclinic crystal system and space group P 1 with a = 9.2086(6) Å, b = 13.3117(9) Å, c = 15.5313(10) Å, α = 107.8210(10)°, β = 104.6180(10)°, γ = 104.1670(10)°, V = 1643.21(19) ų and Z = 2. The structure was refined using 7555 Mo-Kα reflections with I > 2σ(I) and R ₁ = 0.0276 and Rw = 0.0692. The results are consistent with a mostly σ bonding interaction between Cu(II) and cyanamide anion. The LMCT band intensity and electrochemical potentials are compared with ruthenium phenylcyanamide analogues.     

Tuning of ruthenium complex properties using pyrrole- and pyrrolidine-containing polypyridine ligands

The effect of pyrrole- and pyrrolidine-containing ligands (L) on the properties of heteroleptic [RuL2dcbpy]2+ complexes has been investigated. TiO2 electrodes modified with the new complexes exhibited extended absorption domains and high absorbances. Providing that a cobalt-based mediator was used for regeneration of the RuII state, good incident photon-to-current efficiency (near 80%) values were obtained in the pyrrole series.     

Manganese carbonyls bearing tripodal polypyridine ligands as photoactive carbon monoxide-releasing molecules

The recently discovered cytoprotective action of CO has raised interest in exogenous CO-releasing materials (CORMs) such as metal carbonyls (CO complexes of transition metals). To achieve control on CO delivery with metal carbonyls, we synthesized and characterized three Mn(I) carbonyls, namely, [Mn(tpa)(CO)(3)]ClO(4) [1, where tpa = tris(2-pyridyl)amine], [Mn(dpa)(CO)(3)]Br [2, where dpa = N,N-bis(2-pyridylmethyl)amine], and [Mn(pqa)(CO)(3)]ClO(4) [3, where pqa = (2-pyridylmethyl)(2-quinolylmethyl)amine], by crystallography and various spectroscopic techniques. All three carbonyls are sensitive to light and release CO when illuminated with low-power UV (5-10 mW) and visible (λ > 350 nm, ~100 mW) light. The sensitivity of 1-3 to light has been assessed with respect to the number of pyridine groups in their ligand frames. When a pyridine ring is replaced with quinoline, extended conjugation in the ligand frame increases the absorptivity and makes the resulting carbonyl 3 more sensitive to visible light. These photosensitive CORMs (photoCORMs) have been employed to deliver CO to myoglobin under the control of light. The superior stability of 3 in aqueous media makes it a photoCORM suitable for inducing vasorelaxation in mouse aortic muscle rings.     

A new family of ruthenium(II) polypyridine complexes bearing 5-aryltetrazolate ligands as systems for electrochemiluminescent devices

A new family of mono- and dinuclear ruthenium polypyridyl complexes containing 5-aryltetrazolate ligands such as the deprotonated form of 4-(1H-tetrazol-5-yl)benzonitrile (4-TBNH) and bis(1H-tetrazol-5-yl)benzene (BTBH(2)) have been synthesized and thoroughly characterized. The reactivity of the mononuclear species toward different electrophiles such as H(+) and CH(3)(+) has been investigated, and the effects of the resulting regioselective electrophilic attacks on the electronic and structural properties of the tetrazolate ligand have been studied by NMR ((1)H, (13)C) spectroscopy and X-ray crystal structures. Absorption and emission spectroscopy, together with an electrochemical and UV-vis-NIR spectroelectrochemical investigation of the uncoordinated ligand and complexes, has been performed, highlighting a rather good luminescence efficiency and a poor bridge-mediated electronic communication between the metal centers of the dinuclear complexes. The electrogenerated chemiluminescence (ECL) of the dinuclear species has been explored, and for one of these, an exceptionally high ECL efficiency has been observed, comparable to that of [Ru(bpy)(3)](2+), which is considered a standard in ECL studies.     

Synthesis of new metallomesogens with enaminoketone chelating ligands

New liquid crystalline copper(II) enaminoketonates containing bridging ester groups were synthesized by hydrogenation of the heteroring in 3-(4-hydroxyphenyl)-5-pentylisoxazole to 1-amino-1-(4-hydroxyphenyl)oct-1-en-3-one, treatment of the latter with copper(II) acetate, and benzoylation of the coordination compound thus formed with 4-alkoxybenzoyl chlorides.     

Synthesis and complexation of two new phenylaminoglyoxime ligands

Two new soluble phenylaminoglyoxime ligands, 4-isopropylanilinephenylglyoxime (L¹H₂), 4-benzylpiperidinephenylglyoxime (L²H₂), were prepared by reacting 4-isopropylaniline and 4-benzylpiperidine with chlorophenylglyoxime. Mononuclear nickel(II), cobalt(II), copper(II), zinc(II), and cadmium(II) complexes with these ligands were synthesized. On the basis of the magnetic and spectral evidence a square-planar geometry for Ni(II) and Cu(II) complexes, a tedrahedral geometry for Cd(II) and Zn(II) complexes and octahedral geometry for Co(II) complexes are proposed. These compounds were elucidated by elemental analysis, IR, UV-Vis, and magnetic moments. The ligands were additionally characterized by ¹H NMR and ¹³C NMR spectra.     

Functional polypyridine ligands from copper-mediated room temperature coupling of 4-chloro-2-trimethylsilylpyridine

A range of functional polypyridine ligands (bipyridines and terpyridine) has been synthesized by copper-mediated oxidative homocoupling of 4-chloro-2-trimethylsilylpyridine or cross-coupling with functional bromopyridines. The reaction proceeded smoothly at room temperature.     

Preparation of stannyl complexes of ruthenium and osmium stabilised by polypyridine and phosphite ligands

Trichlorostannyl complexes [M(SnCl3)(bpy)2P]BPh4 [M = Ru, P = P(OEt)(3), 1a PPh(OEt)2 1b; M = Os, P = P(OEt)3 2; bpy = 2,2'-bipyridine] were prepared by allowing chloro complexes [MCl(bpy)2P]BPh4 to react with SnCl2 in 1,2-dichloroethane. Bis(trichlorostannyl) compounds Ru(SnCl3)2(N-N)P2 [N-N = bpy, P = P(OEt)3 3a, PPh(OEt)2 3b; N-N = 1,10-phenanthroline (phen), P = P(OEt)3 4] were also prepared by reacting [RuCl(N-N)P3]BPh4 precursors with SnCl2.2H2O in ethanol. Treatment of both mono- 1a, 2 and bis 3a trichlorostannyl complexes with NaBH4 afforded mono- and bis(trihydridestannyl) derivatives [M(SnH3)(bpy)2P]BPh4 5, 6 and Ru(SnH3)2(bpy)P2 7[P = P(OEt)3], respectively. Treatment of 1a, 2 with MgBrMe gave the trimethylstannyl complexes [M(SnMe3)(bpy)2P]BPh4 8, 9 and treatment of 3a afforded the bis(stannyl) Ru(SnClMe2)2(bpy)P2 10 derivative. Alkynylstannyl complexes [M{Sn(C triple bond CR)3}(bpy)2P]BPh4 11-13 and Ru[Sn(C triple bond CR)3]2(N-N)P2 14-17(R = p-tolyl, Bu t; N-N = bpy, phen) were also prepared by allowing trichlorostannyl compounds 1-4 to react with Li+[RC triple bond C]* in thf. The complexes were characterised spectroscopically and by the X-ray crystal structure determination of [Ru(SnMe3)(bpy)2{P(OEt)3}]BPh4 derivative.     

New polypyridine ligands functionalized with redox-active Fe(II) organometallic fragments

We report in this Communication the isolation and characterization, including structure determinations, of 2,2',6',2"-terpyridine (2) and 2,2'-bipyridine (3) ligands bearing two redox-active "(eta2-dppe)(eta5-C5Me5)FeC[triple bond]C-" moieties grafted to the 5 and 5" positions of terpy or to the 5 and 5' positions of bipy. These "metalloligands" have been complexed with Ru(II) and Mo(0), providing new heterotrinuclear complexes displaying intense absorptions around 700 and 600 nm, respectively, for the Fe2Ru/terpy and Fe2Mo/bipy species. In both cases, the Fe(II)/Fe(III) oxidation potentials of the free ligands became more positive by more than 50 mV upon complexation.     

Synthesis of new polydentate tweezers ligands of amido-amine type

A series of new tweezers amido-amine ligands containing pyrrole, bipyrrole, and dipyrrolylmethane fragments were synthesized by reaction of 2-thioxothiazolidin-3-yl derivatives of α-pyrrolecarboxylic acids {5-[1-(5-carboxy-3-methyl-4-phenyl-1H-pyrrol-2-yl)-1-methylethyl]-4-methyl-3-phenyl-1H-pyrrole-2-carboxylic acid, 5-[(5-carboxy-3-methyl-4-phenyl-1H-pyrrol-2-yl)phenylmethyl]-4-methyl-3-phenyl-1H-pyrrole-2-carboxylic acid, 5-(5-carboxy-3-methyl-4-phenyl-1H-pyrrol-2-yl)-4-methyl-3-phenyl-1H-pyrrole-2-carboxylic acid, and 3,4-dimethyl-pyrrole-2,5-dicarboxylic acid} with o-phenylenediamine. All compounds obtained were characterized by elemental analysis, NMR and mass spectra.     

Synthesis of precursors to new tripodal phosphine oxide ligands

Russian Journal of General Chemistry - A number of precursors of new tripodal ligands was obtained by hydroxyethylation of the starting tris(2-hydroxyphenyl)phosphine oxide, followed by conversion...     

Organoerbium compounds containing dendritic ligands

The reactions of Er[N(SiMe₃)₂]₃ with phenylethynyl dendrons of the first and second generations gave complexes of erbium with dendritic ligands, Er[C≡CC₆H₃(C≡CPh)₂-3,5]₃ and Er{C≡CC₆H₃[C≡CC₆H₃(C≡CPh)₂-3,5]₂-3,5}₃.     

Synthesis of new macromolecular, functionalized carboxylic-acid-PEG-DHLA surface ligands

An efficient method for the synthesis of new macromolecular surface ligands for quantum dots functionalization has been developed. The new ligands contain a dihydrolipoic acid unit which is connected to either a mono- or a diacid terminal function by a PEG chain.     

Synthesis of new chelating ligands containing two pyrazole fragments

7-[Pyrazol-3(5)-yl]4,5,6,7-tetrahydro-1H-indazole and 6-[pyrazol-3(5)-yl]-1,4,5,6-tetrahydrocyclopenta[c]pyrazole, potential chelating ligands, were synthesized by condensation of 2-acetylcyclohexanone and 2-acetylcyclopentanone difluoroboron complexes with dimethylformamide dimethyl acetal followed by cyclization with hydrazine hydrate.