Regioselective Coordination Research Articles

Regioselective Coordination toward Silver(I) Ions by Bis- and Tris(Tetra-Armed Cyclen)s via Differential Electron Density of Aromatic Side Arms.

Four types of bis- and tris(tetra-armed cyclen)s were prepared. 2MF is a bis(tetra-armed cyclen) with electron-rich side arms (three 4-methoxybenzyl groups) and electron-deficient side arms (three 3,5-difluorobenzyl groups), connected by a 4,4'-dimethyl-1,1'-biphenyl moiety. 3MFM is a tris(tetra-armed cyclen) with 4-methoxybenzyl and 3,5-difluorobenzyl groups introduced on both ends and the central cyclen, respectively. 4MFM is a V-shaped analogue of 3MFM. 3FMF is a tris(tetra-armed cyclen) where the aromatic side arms at both ends and the central cyclen of 3MFM are exchanged. The regioselective coordination of silver(I) ions by these ligands is reported. Initially, we added Ag+ ions to a compound (2MF) that consists of tetra-armed cyclen with 4-methoxybenzyl groups as an electron-donating substituent on the aromatic rings and 3,5-difluorobenzyl groups as an electron-withdrawing substituent. 1H NMR and 19F{1H} NMR spectroscopy exhibited that the cyclen with the 4-methoxybenzyl groups formed a complex with Ag+ ions first, followed by the cyclen with the 3,5-difluorobenzyl groups. Next, we employed a compound (3MFM) with three cyclen units, where the cyclen at each end was functionalized with three 4-methoxybenzyl groups, and the central cyclen was functionalized with two 3,5-difluorobenzyl groups. Upon adding Ag+ ions, we observed that the cyclen units at both ends formed complexes with Ag+ ions initially, followed by the central cyclen forming a complex with Ag+ ions. When we used 4MFM, which is a V-shaped compound, the Ag+-induced-1H NMR chemical shift changes are almost the same results as the 3MFM. Furthermore, we synthesized a compound (3FMF) by interchanging the substituents on the cyclen units at the ends and the center. Interestingly, the order of the complex formation was reversed in this compound. These results demonstrated that tuning the electron density on the aromatic side arms through substituents makes it possible to achieve regioselective coordination with Ag+ ions in bis- or tris(tetra-armed cyclen)s.

Improved Synthesis and Coordination Behavior of 1H-1,2,3-Triazole-4,5-dithiolates (tazdt2−) with NiII, PdII, PtII and CoIII

A new synthetic route to 1H-1,2,3-triazole-4,5-dithiols (tazdtH2) as ligands for the coordination of NiII, PdII, PtII and CoIII via the dithiolate unit is presented. Different N-protective groups were introduced with the corresponding azide via a click-like copper-catalyzed azide-alkyne [3 + 2] cycloaddition (CuAAC) and fully characterized by NMR spectroscopy. Possible isomers were isolated and an alternative synthetic route was investigated and discussed. After removal of the benzyl protective groups on sulfur by in situ-generated sodium naphthalide, complexes at the [(dppe)M] (M = Ni, Pd, Pt), [(PPh3)2Pt] and [(η5-C5H5)Co] moieties were prepared and structurally characterized by XRD analysis. In this process, the by-products 11 and 12 as monothiolate derivatives were isolated and structurally characterized as well. With regioselective coordination via the dithiolate unit, the electronic influence of different metals or protective groups at N was investigated and compared spectroscopically by means of UV/Vis spectroscopy and cyclic voltammetry. Complex [(η5-C5H5)Co(5c)] (10), is subject to a dimerization equilibrium, which was investigated by temperature-dependent NMR and UV/Vis spectroscopy (solution and solid-state). The thermodynamic parameters of the monomer/dimer equilibrium were derived.

Mimicking the Regulation Step of Fe-Monooxygenases: Allosteric Modulation of FeIV -Oxo Formation by Guest Binding in a Dinuclear ZnII -FeII Calix[6]arene-Based Funnel Complex.

A heteroditopic ligand associated with a calix[6]arene scaffold bearing a tris(imidazole) coordinating site at its small rim and an amine/pyridine ligand at its large rim has been prepared, and its regioselective coordination to ZnII at the small rim and FeII in the amine/pyridine ligand has been achieved. The heterodinuclear complex obtained displays an overall cone conformation capped by the tris(imidazole)ZnII moiety and bears a non-heme FeII complex at its base. Each of the metal centers exhibits one labile position, allowing the coordination inside the cavity of a guest alkylamine at ZnII and the generation of reaction intermediates (FeIII (OOH) and FeIV O) at the large rim. A dependence between the chain length of the encapsulated alkylamine and the distribution of FeIII (OOH) intermediates and FeIII (OMe) is observed. In addition, it is shown that the generation of the FeIV O intermediate is enhanced by addition of the alkylamine guest. Hence, this supramolecular system gathers the three levels of reactivity control encountered in oxidoreductases: i) control of the FeII redox properties through its first coordination sphere, allowing us to generate high valent reactive species; ii) control of guest binding through a hydrophobic funnel that drives its alkyl chain next to the reactive iron complex, thus mimicking the binding pocket of natural systems; iii) guest-modulated reactivity of the FeII center towards oxidants.

1,4-Selective Polymerization of 1,3-Cyclohexadiene and Copolymerization with Styrene by Cationic Half-Sandwich Fluorenyl Rare Earth Metal Alkyl Catalysts

The regioselective coordination–insertion polymerization of 1,3-cyclohexadiene (CHD) and copolymerization with styrene (S) could be achieved by cationic half-sandwich fluorenyl rare earth metal alkyl catalysts generated by treating half-sandwich fluorenyl rare earth metal dialkyl complexes Flu′Ln(CH2SiMe3)2(THF)n (1–10) with an activator (such as [Ph3C][B(C6F5)4] (A), [PhNHMe2][B(C6F5)4] (B), or B(C6F5)3 (C)) and AliBu3. The homopolymerization of CHD afforded poly(CHD)s with complete 1,4 selectivity (1,4 selectivity up to 100%). The copolymerization of CHD with styrene gave new random CHD–S copolymers with CHD content ranging from 22 to 74 mol % containing 1,4-linked CHD–CHD, alternating CHD–S, and syndiotactic S–S sequences unavailable previously. The activity of the copolymerization and the comonomer compositions and sequences of the resulting CHD–S copolymers could be easily controlled by changing the substituted fluorenyl ligand, the metal center, the activator, the temperature, and the molar ratio of...

Targeting divalent metal cations with Re(I) tetrazolato complexes.

In order to exploit their potential as versatile luminescent sensors, four new Re(I)-tetrazolato complexes with the general formula fac-[Re(CO)3(diim)(L)], where diim is 2,2'-bipyridine (bipy) or 1,10-phenanthroline (phen) and L(-) is either the anion 5-(2'-pyridyl)tetrazolato (2-PTZ(-)) or 5-(2'-quinolyl)tetrazolato (2-QTZ(-)), were prepared and fully characterized. In all cases, the regioselective coordination of the Re(I) center through the N2 atom of the tetrazolato ring was observed. This particular feature ensures the availability of the diiminic (N^N) site that was systematically incorporated into the structure of the 2-PTZ(-) and 2-QTZ(-) ligands for further coordination with metal cations. Such a diimine-type coordination mode was preliminarily tested by using the mononuclear Re(I) complexes as N^N ligands for the preparation of two [(N^N)Cu(POP)] cationic species, where POP is the chelating diphosphine bis[2-(diphenylphosphino)phenyl]ether. The X-ray structures of the resulting Re(I)-Cu(I) dyads revealed that the Re(I) mononuclear complexes effectively behaved as chelating N^N ligands with respect to the [Cu(POP)](+) fragment, the coordination of which also resulted in significant modification of the Re(I)-centered luminescence. With these data in hand, the luminescent sensing abilities of the four new Re(I) tetrazolato complexes were screened with respect to divalent metal ions of toxicological and biological importance such as Zn(II), Cd(II) and Cu(II). The interaction of the Re(I) complexes with Zn(II) and Cd(II) was witnessed by the evident blue shift (Δλmax = 22-36 nm) of the emission maxima, which was also accompanied by a significant elongation of the emission lifetimes. On the contrary, the addition of the cupric ion caused substantial quenching of the radiative processes originating from the Re(I) luminophores.

Synthesis, Photophysical and Electrochemical Investigation of Dinuclear Tetrazolato-Bridged Rhenium Complexes

Starting from anionic tetrazole-based ligands, namely, 5-(4′-cyanophenyl)tetrazolate and 5-(4′-pyridyl)tetrazolate, mononuclear and dinuclear complexes of fac-[Re(CO)3(phen)]+ (phen = 1,10-phenanthroline) were prepared and characterized. For the mononuclear complexes, regioselective coordination of the metal fragments on the negatively charged tetrazolato ring is exclusively obtained. Coordination to the benzonitrile and pyridine groups was achieved by previous alkylation of the tetrazole ring. Dinuclear complexes were obtained by treatment of the corresponding mononuclear tetrazole-bound complexes with fac-[Re(CO)3(phen)(THF)]+. The second rhenium fragment coordinated either to the pyridine ring or, in the case of the benzonitrile ligand, to the tetrazole ring. The electrochemical properties were probed in an imidazolium ionic liquid, highlighting reduction processes centered on the phen ligand and oxidation processes localized on the metal. The photophysical properties of the complexes are characterized by phosphorescent emission from triplet metal-to-ligand charge transfer excited states, with trends in the lifetime and quantum yield in qualitative agreement with the energy gap law. The two dinuclear complexes show almost superimposable emission profiles: in the 5-(4′-cyanophenyl)tetrazolate-bridged complex, the two metal fragments coordinated to the tetrazole are equivalent and share a positive charge of +1. On the other hand, the photophysical properties of the 5-(4′-pyridyl)tetrazolate-bridged dinuclear complex suggest energy transfer between the two metal centers.

Synthesis and Characterization of NH-triazole-Bound Rhodium(I) Complexes: Substituted-Group-Controlled Regioselective Coordination

4,5-Disubstituted NH-1,2,3-triazoles (TRIA) were used to coordinate with Rh(I) metal cation, forming a new class of triazole-bridged [Rh(COD)(TRIA)]2 complexes in near-quantitative yields. X-ray cr...

Site-selective ligand substitution in CoRu(CO)7(μ-PPh2) using (Z)-Ph2PCH=CHPPh2 and reactivity of DMAD with CoRu(CO)5[(Z)-Ph2PCH=CHPPh2](μ-PPh2). X-ray structures of CoRu(CO)5[(Z)-Ph2PCH=CHPPh2](μ-PPh2) and CoRu(CO)3(μ-CO)[(Z)-Ph2PCH=CHPPh2] [μ, η3-Ph2PC(CO2Me)C(CO2Me)

The heterometallic complex CoRu(CO)7(μ-PPh2) (1) reacts with the diphosphine ligand (Z)-Ph2PCH=CHPPh2 under both thermolysis and Me3NO activation to furnish CoRu(CO)5[(Z)-Ph2PCH=CHPPh2](μ-PPh2) (2) in good yield. Treatment of 2 with dimethyl acetylenedicarboxylate (DMAD) at elevated temperature leads to the formal insertion of the DMAD ligand into the Co–phosphido bond and formation of the metallocyclic compound CoRu(CO)3(μ-CO)[(Z)-Ph2PCH=CHPPh2][μ,η3-Ph2PC(CO2Me)C(CO2Me)] (3) that contains a 5e− alkenylphosphine moiety. These new CoRu compounds have been isolated by chromatography and fully characterized in solution by IR and NMR (1H and 31P) spectroscopies, and the solid-state structures of both 2 and 3 have been determined by X-ray diffraction analysis. CoRu(CO)5[(Z)-Ph2PCH=CHPPh2](μ-PPh2) crystallizes in the monoclinic space group P21/n, a = 11.493(8), b = 20.24(1), c = 17.04(1) A, β = 91.03(1)°, V = 3964(5) A3, Z = 4, Dcalc = 1.477 Mg/m3; R = 0.0475, Rw = 0.1054 for 5120 observed reflections with I > 2σ (I). CoRu(CO)3(μ-CO)(Z)-Ph2PCH=CHPPh2][μ,η3-Ph2PC(CO2Me)C(CO2Me)], as the CH2Cl2 solvate, crystallizes in monoclinic space group P21/c, a = 17.0307(9) A, b = 11.2124(6) A, c = 24.083(1) A, β = 97.755(1)°, V = 4556.8(4) A3, Z = 4, Dcalc = 1.579 Mg/m3; R = 0.0379, Rw = 0.0609 for 10774 observed reflections with I > 2σ(I). The regioselective coordination of the (Z)-Ph2PCH=CHPPh2 ligand to the two equatorial sites of the ruthenium center in 2 and the presence of the metallocyclic alkenylphosphine ligand in 3 are confirmed by the structural studies. The regiochemistry found in the coordination of (Z)-Ph2PCH=CHPPh2 to 1 is contrasted with the related diphosphine ligands bma and bpcd, while the DMAD insertion reactivity with 2 is discussed relative to alkyne reactions reported for the parent compound CoRu(CO)7(μ-PPh2).

Lewis Acid-Directed Reactions of Quinones with Styrenyl Systems: The Case of 2-Methoxy-3-methyl-1,4-benzoquinone

Reactions of 2-methoxy-3-methyl-1,4-benzoquinone with various (E)-1-propenylbenzenes promoted by 1 equiv of Ti(IV), as a 1:1 mixture of TiCl4−Ti(O-i-Pr)4, produce rel-(1S,6R,7R,8R)-8-aryl-4,7-dimethyl-3-methoxybicyclo[4.2.0]oct-3-ene-2,5-diones 3 and trans-2-aryl-3,7-dimethyl-6-methoxy-2,3-dihydro-5-benzofuranols 5 as the major products. Reactions promoted by 2 equiv of Ti(IV) as a 1:1 mixture of TiCl4−Ti(O-i-Pr)4 or 1 equiv of either TiCl4, SnCl4, or BF3·OEt2 give regioisomeric rel-(1R,6S,7R,8R)-7-aryl-4,8-dimethyl-3-methoxybicyclo[4.2.0]oct-3-ene-2,5-diones (4) and/or trans-2-aryl-3,6-dimethyl-7-methoxy-2,3-dihydro-5-benzofuranols (6). A mechanism involving regioselective coordination of the various Lewis acids to the quinone is used to explain the formation of the products. These reactions demonstrate the effective regiocontrol exerted over the reactions by the nature of the Lewis acid promoters. Cyclobutanes 3 and 4 cleanly undergo rearrangement to the corresponding benzofuranols 5 and 6 on treatment with protic acid. In contrast, reactions of 2-methoxy-1,4-benzoquinone promoted by either BF3·OEt2 or Ti(IV), as 1 equiv or excess amounts of TiCl4 or 1:1 TiCl4−Ti(O-i-Pr)4, all afford the same regioisomeric products, i.e., rel-(1S,6R,7R,8R)-8-aryl-7-methyl-3-methoxybicyclo[4.2.0]oct-3-ene-2,5-dione 25 and/or trans-2-aryl-3-methyl-6-methoxy-2,3-dihydro-5-benzofuranol 27.

Quantum-chemical interpretation of regioselective coordination in the series of 2-aminoazole?metal complexes

Relative thermodynamic stabilities and competitive bonding (regioselective coordination) of Pearson acids MCl2 (hard BeCl2, intermediate ZnCl2, and soft HgCl2) with aminohetero-cycles L (2-aminooxazole, 2-aminothiazole, and 2-aminoimidazole) have been calculated by the quantum-chemical MNDO method. It follows from the results of the calculation that in tetrahedral MCl2·2L complexes the coordination bond is formed by the endocyclic pyridine-type nitrogen atom independent of the type of ligands.

Synthesis of 1-phenyl-and 5-phenyl-3-(vinylthio)-1,2,4-triazoles and their proton NMR spectra transformed by complexation

1. New vinyl monomers were synthesized from 1-and 5-phenyl-substituted 1,2,4-triazole-3-thione. 2. According to the proton NMR spectra with additions of Mn (II) and Gd (III) paramagnetic broadening compounds, it was determined that in a CDCl3 solution these monomers are able to enter into regioselective coordination with transition and rare-earth metal ions primarily by means of the N4 nitrogen atom.