Synthesis of Secondary, Tertiary and Quaternary 1,3,5-Triazapenta-1,3-dienes and Their CoII, ZnII, PdII, CuIIand BF2Coordination Compounds

Boron Complexes with Propiolamidinato Ligands: Synthesis, Structure, and Photophysical Properties

Two series of boron derivatives with propiolamidinato ligands, [BPh2{C(C≡CAr)(NR)2}] (Ar = Ph, p-MeOPh, p-FPh, p-Me2NPh, or phen; R = iPr or p-tolyl), were synthesized and structurally characterized. The corresponding propiolamidine (or propargylamidine) proligands have been obtained through sustainable methods. One is the catalytic hydroalkynylation of diisopropylcarbodiimide with different terminal alkynes, using simple ZnEt2 as a precatalyst. Alternatively, to obtain propiolamidines with aromatic groups on the nitrogen atoms, the formation of lithiated derivatives of terminal alkynes by reaction with n-BuLi in air and at room temperature, and subsequent addition to the di-p-tolylcarbodiimide, under the same conditions and using 2-MeTHF as a sustainable solvent, has been used for the first time. After reaction with BPh3, the corresponding boron amidinates were obtained, which are emissive in the solution state. The influence of the different substituents introduced into the ligands on the photophysical properties of the boron compounds has been studied. One of the obtained compounds can be used as a ratiometric fluorescent pH sensor in the acidic range.

Cyclic Palladium Formamidinate: Synthesis, Structure, Reactivity, and Application to Suzuki-Miyaura Cross-Coupling

The deprotonation of acyclic palladium amidine chloride (1) with potassium tert-butoxide in tetrahydrofuran results in palladium bis(formamidinate) (2). 2 undergoes a nucleophilic addition reaction with acetonitrile in the presence of PdCl₂ or Pd(OAc)₂ (OAc = acetate) to give dinuclear cyclic six-membered (triazapentadiene)palladium complexes (4a and 4b). These compounds are also prepared from cyclic six-membered (tap)PdCl₂ (5; tap = triazapentadiene) or formamidinium salts (6a-6c) with Pd(OAc)₂/NaOAc in acetonitrile, whereas the direct reaction of 2 with acetonitrile or acrylonitrile resulted in palladium black or an acyclic C-N-coupled product (3). A comparison of structure 4 from 2 suggests a possible intermediate dinuclear palladium complex whose structure was identified through theoretical calculations. Further, Suzuki-Miyaura cross-coupling reactions were carried out under different solvents notably in an ethanol/water medium at room temperature.

Ethylene-Bridged Hexadentate Bis(amidines) and Bis(amidinates) with Variable Binding Sites

Hexadentate bis(amidines) form versatile networks of hydrogen bonds both in solid state and solution, as revealed by X-ray crystallography, IR, and NMR spectroscopy. Moreover, the corresponding bis(amidinates) produce blue and green emissions in THF solution. Tethered tetradentate bis(amidines) have emerged in coordination chemistry, enantioselective catalysis, as building blocks for polyfunctional heterocycles, and in photoluminescent materials. The next generation of flexible bis(amidine)/bis(amidinate) platforms with up to six N-donor sites has now been established.

Synthesis and attempted reductions of bulky 1,3,5-triazapentadienyl groups 2 and 13 halide complexes

Three extremely bulky 1,3,5-triazapentadienes, ArNNNH (ArNNN = N{C(But)=N(Ar)}2; Ar = Mes (mesityl), Dep (2,6-diethylphenyl), or Dip (2,6-diisopropylphenyl)) have been prepared and structurally characterized. These are readily deprotonated, yielding a series of lithium and potassium triazapentadienyl complexes, one of which, (DipNNN)Li, has been structurally characterized. Similarly, three monomeric triazapentadienyl magnesium iodide complexes, (ArNNN)MgI(OEt2), and a dimeric calcium counterpart, {(MesNNN)Ca(THF)(μ-I)}2, have been prepared. Attempts to reduce the former gave homoleptic bis(triazapentadienyl) magnesium complexes, (ArNNN)2Mg (Ar = Mes or Dep) as the main products. One reaction also gave a very low yield of the magnesium(I) dimer, {(DepNNN)Mg–}2, which was structurally characterized. In related chemistry, two triazapentadienyl boron difluoride compounds, (ArNNN)BF2 (Ar = Mes or Dep), have been synthesized, and unsuccessful attempts have been made to reduce these to boron(I) heterocycles. For sake of comparison, attempts have been made to prepare a series of related amino-substituted β-diketiminato group 13 element(I) heterocycles. Although these were also not successful, several group 13 element(III) halide complexes incorporating this ligand class have been characterized.

Boratriazines: inducing luminescence through boron incorporation into a terpy-type framework

The synthesis and physicochemical properties of pyridyl and pyrimidyl functionalized 1,3,5,2-triazaborinines are reported, along with the Lewis acid–base adduct pyrimidine-2-carboximidamide trifluoroborane, which forms as a side product in the reaction with the pyrimidyl substituents.

1,3,5-Triazapentadienes by Nucleophilic Addition to 1,3- and 1,4-Dinitriles-Sterically Constrained Examples by Incorporation into Cyclic Peripheries: Synthesis, Aggregation, and Photophysical Properties

1,3,5-Triazapentadienes usually show U- or twisted S-shaped conformations along the N-C-N-C-N skeleton due to dominating n/π* interactions. If, however, the 1,3,5-triazapentadiene unit is part of a ring, its W conformation might be restricted to the plane. Here, we describe the synthesis of 13 new 1,3,5-triazapentadienes 10-12, which are sterically restrained by incorporation into six- or seven-membered ring systems, by addition of a lithiated primary amine or hydrazine 5 to a dinitrile 7, 8, or 9 with the two cyano groups in 1,3 or 1,4 distance. These novel compounds show very strong tendency for aggregation due to hydrogen bonding, especially to form homodimers as seen from X-ray data in the solid state. Additional hydrogen bonding generates also linear chains in the crystal. Several of the new compounds show fluorescence in solution. Quantum chemical DFT calculations were used for evaluation of the dimerization energies and for interpretation of the photophysical properties.

Fluorinated triazapentadienyl ligand supported ethyl zinc(ii) complexes: reaction with dioxygen and catalytic applications in the Tishchenko reaction

Ethyl zinc complexes [N{(C3F7)C(Dipp)N}2]ZnEt, [N{(C3F7)C(Cy)N}2]ZnEt, [N{(CF3)C(2,4,6-Br3C6H2)N}2]ZnEt and [N{(C3F7)C(2,6-Cl2C6H3)N}2]ZnEt have been synthesized from the corresponding 1,3,5-triazapentadiene and diethyl zinc. X-ray data show that [N{(C3F7)C(Dipp)N}2]ZnEt has a distorted trigonal planar geometry at the zinc center. The triazapentadienyl ligand binds to zinc in a κ(2)-mode. The zinc-ethyl bonds of [N{(C3F7)C(Dipp)N}2]ZnEt, [N{(C3F7)C(Cy)N}2]ZnEt, [N{(CF3)C(2,4,6-Br3C6H2)N}2]ZnEt and [N{(C3F7)C(2,6-Cl2C6H3)N}2]ZnEt readily undergo oxygen insertion upon exposure to dry air to produce the corresponding zinc-ethoxy or zinc-ethylperoxy compounds. The ethoxy zinc adducts {[N{(CF3)C(2,4,6-Br3C6H2)N}2]ZnOEt}2 and {[N{(C3F7)C(2,6-Cl2C6H3)N}2]ZnOEt}2 as well as the ethylperoxy zinc adduct {[N{(C3F7)C(Cy)N}2]ZnOOEt}2 have been isolated and fully characterized by several methods including X-ray crystallography. They feature dinuclear structures with four-coordinate zinc sites and bridging-ethoxy or -ethylperoxy groups. The ethyl zinc complexes catalyze the Tishchenko reaction of benzaldehyde under solventless conditions affording benzyl benzoate. The reaction of ethyl zinc complexes with dioxygen and their catalytic behaviour in the Tishchenko reaction are affected by the electronic and steric factors of the triazapentadienyl ligand. {[N{(C3F7)C(Cy)N}2]ZnOOEt}2 is an excellent reagent for the epoxidation of trans-chalcone.

Nickel(ii)-2-amino-4-alkoxy-1,3,5-triazapentadienate complexes as catalysts for Heck and Henry reactions

Nickel(ii)-triazapentadienate complexes are synthesized and found to act as catalysts in the Heck and Henry reactions.

Dipyrrolylquinoxaline difluoroborates with intense red solid-state fluorescence

Dipyrrolylquinoxalines and their BF₂ complexes were synthesized and characterized by their X-ray structural analysis, optical and electrochemical properties. These dyes exhibit strong broad absorption in the visible region and intensely tunable solid-state fluorescence.

Cyclic six-membered palladium complexes derived from palladium mediated C–N coupling of organonitrile and formamidine

Synthesis and structural characterizations of neutral, cationic and anionic six-membered palladium complexes obtained through palladium mediated C–N bond coupling between organonitrile and formamidinium salt are reported.

Photophysical and electrochemical properties of a novel 4f–3d heterometallic porphyrin

A 4f-3d heterometallic porphyrin, [ TbCo ( TPPS ) H 3 O ]n (1) ( H 2 TPPS = tetra (4- sulfonatophenyl ) porphyrin ), has been synthesized via a hydrothermal reaction and structurally characterized by single crystal X-ray diffraction analysis. The structure of 1 consists of [ TbCo ( TPPS ) H 3 O ]n molecules. The Tb 3+ ions are coordinated by eight oxygen atoms from eight sulfonic groups, yielding a distorted square anti-prism geometry. Compound 1 is characterized by a three-dimensional (3-D) porous open framework that is thermally stable up to 350°C. Compound 1 displays a fluorescent emission band in the ultraviolet region and its fluorescence lifetime is 1.14 ms. A slow scan CV curve of compound 1 reveals one reversible wave with E1/2 being equal to -0.78 V, which is close to the value -0.74 V of DPV diagram.

Facile synthesis of highly fluorescent BF2 complexes bearing isoindolin-1-one ligand

A new class of isoindolin-1-one based BF₂ complexes containing pyridine or benzothiazole groups has been prepared from a “one-pot” reaction.

Varied reactions of [M(L)]3 with HgCl2, FeBr2, CeCl3, AgOTf; ligand transfer, nucleophilic attack with recombination and/or fragmentation [M = Li or Na; L = N(SiMe3){C(H)N}3SiMe3]

The crystalline compounds [Hg{N(R)C(H)NR}(2)] (1), [Fe(L)(2)](2) (2), [Ce(L)(2)Cl](2) (3), [(AlMe(2))(3){(N(R)C(H)NC(H)N)(2)C(H)NC(H)NR}] (4), and [Ag(8)Na{(N(R)C(H)N)(2)(C(H)N)(4)R}(3)] (5) were obtained from [Li(L)](3) (A) (for 1) or [Na(L)](3) (B) and HgCl(2), FeBr(2), CeCl(3), Al(Cl)Me(2), and AgOTf, respectively [L = N(R){C(H)N}(3)R; R = SiMe(3)]. Compounds 1, 2, 3, and 5 were prepared in tetrahydrofuran (THF) at 20 degrees C; for 4, it was C(6)H(14) at -78 degrees C. NMR data for 1 showed only a single SiMe(3) environment for 1, implicating a fast exchange process. Single crystal X-ray data showed dinuclear structures for 2 and 3. Each ligand [L](-) in crystalline 2 was bound to each of the two Fe atoms in a kappa(1)- or kappa(2)-fashion, respectively, with one NSiMe(3) group of the former unattached; this was consistent with VT (1)H NMR spectral data indicative of fast exchange (at 313 K) between axial kappa(1)- and equatorial kappa(2)-N,N'-coordination to Fe. The magnetic moment for 2 in C(6)H(6) was appropriate for high-spin octahedral Fe(II). The ligands [L](-) in crystalline 3 are arranged in a helical fashion. The NMR spectra of 4 in C(6)D(5)CD(3) showed that there is an equilibrium between two asymmetric structures; minor co-products were 4', assigned as a symmetrical isomer of 4, and N(R)C(H)NR(2). The anion of 5 is proposed to be identical to that of 4'. Routes to the ligands of 1, 4, 4', and 5 are suggested; the key feature is that the ligand [L](-), unless tethered in an appropriate metal-containing matrix (as in A, B, 2, or 3), is labile because of SiMe(3) mobility, fragmentation, and/or recombination.