An Analysis of the Link between Customers' Intention to Recommend a Firm and the Lifetime Value of its Customers

An Analysis of the Link between Customers' Intention to Recommend a Firm and the Lifetime Value of its Customer

Convenient Synthetic Route to Palladium Complexes of Unconventional N‑Heterocyclic Carbenes Derived from Pyridazine and Phthalazine

Several Pd­(II) complexes with unconventional pyridazine- and phthalazine-derived carbene ligands were synthesized via direct oxidative addition of Cl derivatives of the alkylated diazine heterocycles to Pd(0) species. The alkylated ligand precursors are readily prepared from commercial starting materials, and oxidative addition is regioselective. DFT calculations confirm that the thermodynamically favored products are formed. Four complexes (1–4) have been fully characterized, including by X-ray crystallography. Attractive intramolecular π–π stacking between the electron-poor N-alkylated diazine heterocycles and adjacent phenyl groups of the PPh3 coligands is revealed by the solid-state structures

An Analysis of the Link between Customers' Intention to Recommend a Firm and the Lifetime Value of its Customers

An Analysis of the Link between Customers' Intention to Recommend a Firm and the Lifetime Value of its Customer

Convenient Synthetic Route to Palladium Complexes of Unconventional N‑Heterocyclic Carbenes Derived from Pyridazine and Phthalazine

Several Pd­(II) complexes with unconventional pyridazine- and phthalazine-derived carbene ligands were synthesized via direct oxidative addition of Cl derivatives of the alkylated diazine heterocycles to Pd(0) species. The alkylated ligand precursors are readily prepared from commercial starting materials, and oxidative addition is regioselective. DFT calculations confirm that the thermodynamically favored products are formed. Four complexes (<b>1</b>–<b>4</b>) have been fully characterized, including by X-ray crystallography. Attractive intramolecular π–π stacking between the electron-poor N-alkylated diazine heterocycles and adjacent phenyl groups of the PPh₃ coligands is revealed by the solid-state structures

Gold(I), Gold(III), and Heterometallic Gold(I)–Silver(I) and Gold(I)–Copper(I) Complexes of a Pyridazine-Bridged NHC/Pyrazole Hybrid Ligand and Their Initial Application in Catalysis

The pyridazine-bridged NHC/pyrazole ligand L (HL = 3-[3-(2,4,6-trimethylphenyl)-3<i>H</i>-imidazolium-1-yl]-6-(3,5-dimethylpyrazol-1-yl)-pyridazine) that provides an organometallic and a classical N-donor compartment is shown to serve as a versatile scaffold for a variety of homo- and heterometallic gold­(I) carbene complexes. Complexes [LAuX] (<b>1</b>^<b>Cl</b>, X = Cl; <b>1</b>^<b>Br</b>, X = Br), [L₂Au]­(PF₆) (<b>2</b>), [L₂AuAg]­(BF₄)­(PF₆) (<b>3</b>), [L₂AuAg₃(MeCN)₆]­(BF₄)₄ (<b>5</b>), and [L₂AuCu]­(OTf)_0.75(PF₆)_1.25 (<b>6</b>) have been characterized by X-ray crystallography. In all cases Au­(I) binds to the NHC site while the additional Ag­(I) in <b>3</b> or Cu­(I) in <b>6</b> is accommodated in the pyrazole-derived site. Both <b>3</b> and <b>6</b> form two-stranded helical structures; racemization of the <i>P</i> and <i>M</i> enantiomers is much more facile in the Ag­(I) case <b>3</b> but has a barrier of around 65 kJ/mol in the Cu­(I) case <b>6</b>, which is rationalized on the basis of the different coordination chemistry preferences of these two metal ions. <b>3</b> may bind two further Ag­(I) ions to the central pyridazine N, giving <b>5</b>. Treatment of <b>1</b>^<b>Br</b> with Br₂ leads to bromination at the pyrazole C⁴ of the ligand backbone, yielding [L^BrAuBr] (<b>8</b>). In contrast, <b>1</b>^<b>Cl</b> could be successfully oxidized to the Au­(III) complex [LAuCl₃] (<b>7</b>) using PhICl₂; both <b>7</b> and the gold­(I) complex <b>8</b> have been characterized crystallographically. Preliminary screening shows that <b>7</b>, in combination with AgBF₄, is a good catalyst for the etherification of 1-indanol with a variety of alcohol substrates and shows significantly higher activity than the gold­(I) catalyst <b>1</b>^<b>Cl</b>

Gold(I), Gold(III), and Heterometallic Gold(I)–Silver(I) and Gold(I)–Copper(I) Complexes of a Pyridazine-Bridged NHC/Pyrazole Hybrid Ligand and Their Initial Application in Catalysis

The pyridazine-bridged NHC/pyrazole ligand L (HL = 3-[3-(2,4,6-trimethylphenyl)-3<i>H</i>-imidazolium-1-yl]-6-(3,5-dimethylpyrazol-1-yl)-pyridazine) that provides an organometallic and a classical N-donor compartment is shown to serve as a versatile scaffold for a variety of homo- and heterometallic gold­(I) carbene complexes. Complexes [LAuX] (<b>1</b>^<b>Cl</b>, X = Cl; <b>1</b>^<b>Br</b>, X = Br), [L₂Au]­(PF₆) (<b>2</b>), [L₂AuAg]­(BF₄)­(PF₆) (<b>3</b>), [L₂AuAg₃(MeCN)₆]­(BF₄)₄ (<b>5</b>), and [L₂AuCu]­(OTf)_0.75(PF₆)_1.25 (<b>6</b>) have been characterized by X-ray crystallography. In all cases Au­(I) binds to the NHC site while the additional Ag­(I) in <b>3</b> or Cu­(I) in <b>6</b> is accommodated in the pyrazole-derived site. Both <b>3</b> and <b>6</b> form two-stranded helical structures; racemization of the <i>P</i> and <i>M</i> enantiomers is much more facile in the Ag­(I) case <b>3</b> but has a barrier of around 65 kJ/mol in the Cu­(I) case <b>6</b>, which is rationalized on the basis of the different coordination chemistry preferences of these two metal ions. <b>3</b> may bind two further Ag­(I) ions to the central pyridazine N, giving <b>5</b>. Treatment of <b>1</b>^<b>Br</b> with Br₂ leads to bromination at the pyrazole C⁴ of the ligand backbone, yielding [L^BrAuBr] (<b>8</b>). In contrast, <b>1</b>^<b>Cl</b> could be successfully oxidized to the Au­(III) complex [LAuCl₃] (<b>7</b>) using PhICl₂; both <b>7</b> and the gold­(I) complex <b>8</b> have been characterized crystallographically. Preliminary screening shows that <b>7</b>, in combination with AgBF₄, is a good catalyst for the etherification of 1-indanol with a variety of alcohol substrates and shows significantly higher activity than the gold­(I) catalyst <b>1</b>^<b>Cl</b>

Synthesis and Characterization of Di- and Tetracarbene Iron(II) Complexes with Chelating N-Heterocyclic Carbene Ligands and Their Application in Aryl Grignard–Alkyl Halide Cross-Coupling

A series of new and known bis­(imidazolium) chloride and bromide salts bridged by either a methylene group (1–8, 10a,b) or an ethylene group (9a,b) and bearing different N substituents (Me, Et, Bn, tBu, Mes) have been reacted with [Fe­{N­(SiMe3)2}2]2 to yield the four-coordinate iron­(II) complexes [LFeX2] (11–20; X = Cl, Br; L = chelating bis­(imidazolylidene) ligand). Molecular structures of six of these complexes have been characterized by X-ray crystallography, and selected examples have been characterized by 1H NMR and UV–vis spectroscopy, cyclic voltammetry, Mössbauer spectroscopy, and SQUID magnetometry. In all cases the iron­(II) is found in a distorted-tetrahedral environment; it is in the high-spin state and shows large quadrupole splittings in the range 3.67–4.03 mm·s–1 (δ = 0.73–0.81 mm·s–1). Subtleties of the metric parameters depend on the bridging unit between the two imidazolylidene groups, the peripheral N substituents, and the coligand (Cl or Br). In case of rather small (Me, Et) or flexible (Bn) N substituents the dicarbene species [LFeX2] are formed together with ferrous tetracarbene complexes [L2FeX2] (21–23), which are difficult to separate and could not be isolated in pure form. When the latter are dissolved in MeCN in the presence of residual [FeBr2(solv)x], however, they transform into the ionic complexes [L2Fe­(MeCN)2]­[FeBr4] (24–26), which have been characterized by single-crystal X-ray diffraction. They feature low-spin iron­(II) (Mössbauer parameters δ ≈ 0.15 mm s–1, ΔEQ ≈ 1.36 mm s–1) and distorted-octahedral structures with the two MeCN ligands in a cis configuration. Selected examples of the new dicarbene complexes [LFeX2] have been tested as catalysts for the standard cross-coupling reaction between p-tolylmagnesium bromide and bromo- or chlorocyclohexane. They show moderate activity that appears to be generally lower than for related complexes with two monodentate NHC ligands, but the activities clearly depend on the peripheral N substituents and the linker between the two imidazolylidene groups; the best results are obtained for complex 19, which features a long ethylene bridge and bulky Mes substituents, and hence the most shielded metal center

Crowning of Coinage Metal Pyrazolates: Double-Decker Homo- and Heteronuclear Complexes with Synergic Emissive Properties

A new pyrazole ligand with flexible thioether chelate arms was synthesized and was used to obtain an unprecedented class of hexanuclear coinage metal complexes of general formula [MM′L]₃Y₃ (M, M′ = Cu, Ag, Au; Y = OTf, BF₄). Three of them were characterized by X-ray crystallography, namely, homometallic [Ag₂L]₃(OTf)₃ and [Ag₂L]₃(BF₄)₃ as well as heterometallic [CuAgL]₃(OTf)₃, revealing that the classical [M­(μ-pz)]₃ core is crowned by a second deck of S-bound M′ ions. Depending on the solvent, these oligonuclear systems undergo rapid dynamics and show cation–anion aggregation in solution, which has been investigated by DOSY and temperature dependent NMR spectroscopy. Preliminary luminescence data for selected hexametallic [MM′L]₃Y₃ complexes show that the combination of ligand-directed intramolecular and supramolecular d¹⁰ metal ion interactions in the solid state gives rise to synergic emissive properties that allow for a selective addressing of different emission wavelengths

Crowning of Coinage Metal Pyrazolates: Double-Decker Homo- and Heteronuclear Complexes with Synergic Emissive Properties

A new pyrazole ligand with flexible thioether chelate arms was synthesized and was used to obtain an unprecedented class of hexanuclear coinage metal complexes of general formula [MM′L]₃Y₃ (M, M′ = Cu, Ag, Au; Y = OTf, BF₄). Three of them were characterized by X-ray crystallography, namely, homometallic [Ag₂L]₃(OTf)₃ and [Ag₂L]₃(BF₄)₃ as well as heterometallic [CuAgL]₃(OTf)₃, revealing that the classical [M­(μ-pz)]₃ core is crowned by a second deck of S-bound M′ ions. Depending on the solvent, these oligonuclear systems undergo rapid dynamics and show cation–anion aggregation in solution, which has been investigated by DOSY and temperature dependent NMR spectroscopy. Preliminary luminescence data for selected hexametallic [MM′L]₃Y₃ complexes show that the combination of ligand-directed intramolecular and supramolecular d¹⁰ metal ion interactions in the solid state gives rise to synergic emissive properties that allow for a selective addressing of different emission wavelengths

Synthesis and Characterization of Di- and Tetracarbene Iron(II) Complexes with Chelating N-Heterocyclic Carbene Ligands and Their Application in Aryl Grignard–Alkyl Halide Cross-Coupling

A series of new and known bis­(imidazolium) chloride and bromide salts bridged by either a methylene group (1–8, 10a,b) or an ethylene group (9a,b) and bearing different N substituents (Me, Et, Bn, tBu, Mes) have been reacted with [Fe­{N­(SiMe3)2}2]2 to yield the four-coordinate iron­(II) complexes [LFeX2] (11–20; X = Cl, Br; L = chelating bis­(imidazolylidene) ligand). Molecular structures of six of these complexes have been characterized by X-ray crystallography, and selected examples have been characterized by 1H NMR and UV–vis spectroscopy, cyclic voltammetry, Mössbauer spectroscopy, and SQUID magnetometry. In all cases the iron­(II) is found in a distorted-tetrahedral environment; it is in the high-spin state and shows large quadrupole splittings in the range 3.67–4.03 mm·s–1 (δ = 0.73–0.81 mm·s–1). Subtleties of the metric parameters depend on the bridging unit between the two imidazolylidene groups, the peripheral N substituents, and the coligand (Cl or Br). In case of rather small (Me, Et) or flexible (Bn) N substituents the dicarbene species [LFeX2] are formed together with ferrous tetracarbene complexes [L2FeX2] (21–23), which are difficult to separate and could not be isolated in pure form. When the latter are dissolved in MeCN in the presence of residual [FeBr2(solv)x], however, they transform into the ionic complexes [L2Fe­(MeCN)2]­[FeBr4] (24–26), which have been characterized by single-crystal X-ray diffraction. They feature low-spin iron­(II) (Mössbauer parameters δ ≈ 0.15 mm s–1, ΔEQ ≈ 1.36 mm s–1) and distorted-octahedral structures with the two MeCN ligands in a cis configuration. Selected examples of the new dicarbene complexes [LFeX2] have been tested as catalysts for the standard cross-coupling reaction between p-tolylmagnesium bromide and bromo- or chlorocyclohexane. They show moderate activity that appears to be generally lower than for related complexes with two monodentate NHC ligands, but the activities clearly depend on the peripheral N substituents and the linker between the two imidazolylidene groups; the best results are obtained for complex 19, which features a long ethylene bridge and bulky Mes substituents, and hence the most shielded metal center