AbstractTetrahydro(cyclopenta)quinolines are synthesized by combining the reduction of nitroanilines with a Povarov reaction in a three‐component one‐pot approach.

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The three-component reaction between a nitrobenzene, an aldehyde, and a dienophile in the presence of iron powder as a reductant and montmorillonite K10 as a catalyst in aqueous citric acid delivers the products of an aza-Diels-Alder (Povarov) reaction with high endo-selectivity and yields up to 99%.

Reactions of silylamides [Ln{N(SiHMe2)2}3(thf)2] with sterically crowded terphenylamine DmpNH2 (Dmp = 2,6-Mes2C6H3 with Mes = 2,4,6-Me3C6H2) afforded via a template reaction the formation of a new tridentate ligand, and derived complexes of composition [LnN{SiMe2N(Dmp)}2] (Ln = Ce, Pr) were obtained. Usage of the even more bulky amine Ar*NH2 (Ar* = 2,6-Trip2C6H3 with Trip = 2,4,6-iPr3C6H2) yielded the free protonated ligand NH{SiMe2NH(Ar*)}2.

Bridged metal complexes [{Cu(tmpa)}2(μ-L(1)-2H)](ClO4)2 (1), [{Cu(tmpa)}2(μ-L(2)-2H)](ClO4)2 (2), [{Cu(tmpa)}2(μ-L(3)-2H)](BPh4)2 (3), and [{Cu(tmpa)}2(μ-L(4)-2H)](ClO4)2 (4) (tmpa = tris(2-pyridylmethyl)amine, L(1) = chloranilic acid, L(2) = 2,5-dihydroxy-1,4-benzoquinone, L(3) = (2,5-di-[2-(methoxy)-anilino]-1,4-benzoquinone, L(4) = azophenine) were synthesized from copper(II) salts, tmpa, and the bridging quinonoid ligands in the presence of a base. X-ray structural characterization of the complexes showed a distorted octahedral environment around the copper(II) centers for the complexes 1-3, the donors being the nitrogen atoms of tmpa, and the nitrogen or oxygen donors of the bridging quinones. In contrast, the copper(II) centers in 4 display a distorted square-pyramidal coordination, where one of the pyridine arms of each tmpa remains uncoordinated. Bond-length analyses within the bridging ligand exhibit localization of the double bonds inside the bridge for 1-3. In contrast, complete delocalization of double bonds within the bridging ligand is observed for 4. Temperature-dependent magnetic susceptibility measurements on the complexes reveal an antiferromagnetic coupling between the copper(II) ions. The strength of antiferromagnetic coupling was observed to depend on the energy of the HOMO of the bridging quinone ligands, with exchange coupling constants J in the range between -23.2 and -0.6 cm(-1) and the strength of antiferromagnetic coupling of 4 > 3 > 2 > 1. Broken-symmetry density functional theory calculations (DFT) revealed that the orientation of magnetic orbitals in 1 and 2 is different than that in 3 and 4, and this results in two different exchange pathways. These results demonstrate how bridge-mediated spin-spin coupling in quinone-bridged metal complexes can be strongly tuned by a rational design of the bridging ligand employing the [O] for [NR] isoelectronic analogy.

The compounds 2-[2-(trifluoromethyl)-anilino]-5-hydroxy-1,4-benzoquinone (L(1)), 2,5-di-[2-(trifluoromethyl)-anilino]-1,4-benzoquinone (L(2)), 2-[2-(methylthio)-anilino]-5-hydroxy-1,4-benzoquinone (L(3)), and 2,5-di-[2-(methylthio)-anilino]-1,4-benzoquinone (L(4)) were prepared in high yields by reacting 2,5-dihydroxy-1,4-benzoquinone with the corresponding amines in a one-pot synthesis in refluxing acetic acid. This straightforward and "green" synthesis delivers biologically relevant asymmetric p-quinones such as L(1) and L(3) in a rare, simple, one-step process. The proposed synthetic route is general and can be applied to generate a variety of such molecules with different substituents on the nitrogen atoms. Structural characterization of L(2) and L(4) shows electron delocalization across the "upper" and "lower" parts of the molecule, thus showing the importance of charge separated species in the proper description of such molecules. Reactions of these ligands with [Cl(η(6)-Cym)Ru(μ-Cl)(2)Ru(η(6)-Cym)Cl] (Cym = p-Cymene = 1-isopropyl-4-methyl-benzene) in the presence of a base result in the formation of complexes [{Cl(η(6)-Cym)Ru}(2)(μ-L(-2H)(1))] (1), [{Cl(η(6)-Cym)Ru}(2)(μ-L(-2H)(2))] (2), [{Cl(η(6)-Cym)Ru}(2)(μ-L(-2H)(3))] (3), and [{Cl(η(6)-Cym)Ru}(2)(μ-L(-2H)(4))] (4). Structural characterization of 2 and 4 shows a rare syn-coordination of the chloride atoms. The SMe groups in 3 and 4 are not coordinated to the ruthenium center, and the bridging ligands thus function in a bis-bidentate form. Abstraction of the chloride atoms in these complexes with AgClO(4) in CH(3)CN results in the expected formation of solvent substituted complexes [{(CH(3)CN)(η(6)-Cym)Ru}(2)(μ-L(-2H)(1))][ClO(4)](2) (5[ClO(4)](2)) and [{(CH(3)CN)(η(6)-Cym)Ru}(2)(μ-L(-2H)(2))][ClO(4)](2) (6[ClO(4)](2)) with the ligands where there are no additional donor atoms on the nitrogen substituents. The same chloride abstraction reaction in the cases of 3 and 4 leads to an unprecedented substituent induced release of the Cym ligand, resulting in complexes of the form [(CH(3)CN)(η(6)-Cym)Ru(μ-L(-2H)(3))Ru(CH(3)CN)(3)][ClO(4)](2) (7[ClO(4)](2)) and [{(CH(3)CN)(3)Ru}(2)(μ-L(-2H)(4))][ClO(4)](2) (8[ClO(4)](2)), where the SMe groups are now coordinated to the metal center. In the case of complex 3, which contains an asymmetric bridging ligand, Cym release is observed only at the side that contains an additional SMe donor, thus proving the necessity of such donor substituents for the observed reactivity. The increase in Lewis acidity at the ruthenium center on chloride abstraction is made responsible for SMe coordination and the rigidity of the ligand systems, and their concomitant failure to coordinate in a "fac" manner as is required for a piano stool configuration results in the eventual Cym release. The bridging ligand which then coordinates in a bis-meridional fashion in 8[ClO(4)](2) results in a bis-pincer type of coordination. These observations were validated by a structural analysis of 8[ClO(4)](2). The results show the potential hemilabile character of ligands such as L(3) and L(4). Electrochemical and spectroscopic investigations are reported on 8[ClO(4)](2), and substitution reactions of the CH(3)CN molecules are presented to show the use of 8[ClO(4)](2) as a versatile precursor for other reactions.

We demonstrate the use of a Cu(I) catalyzed "Click" reaction in the synthesis of novel ligands for spin crossover complexes. The reaction between azides and alkynes was used to synthesize the reported tripodal ligand tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine, TBTA, and the new ligands tris[(1-cyclohexyl-1H-1,2,3-triazol-4-yl)methyl]amine, TCTA, and tris[(1-n-butyl-1H-1,2,3-triazol-4-yl)methyl]amine, TBuTA. Reactions of TBTA with Co(ClO(4))(2) lead to complexes of the form [Co(TBTA)(CH(3)CN)(3)](ClO(4))(2), 1, and [Co(TBTA)(2)](ClO(4))(2), 2, where complex formation can be controlled by the metal/ligand ratio and the complexes 1 and 2 can be chemically and reversibly switched from one form to another in solution resulting in coordination ambivalence. The benzyl substituents of TBTA in 2 show intramolecular C-H-π T-stacking that generates a chemical pressure to stabilize the low spin (LS) state at lower temperatures. The structural parameters of 2 are consistent with a Jahn-Teller active LS Co(II) (elongation) ion showing four short and two long bonds. 2 shows spin-crossover (SCO) behavior in the solid state and in solution with a high T(0) close to room temperature which is driven by the T-stacking. 1 remains high spin (HS) between 2 and 400 K. Reversible chemical switching is observed between 1 and 2 at room temperature, with an accompanying change in the spin state from HS to LS. The importance of the intramolecular T-stacking in driving the SCO behavior is proven by comparison with two analogous compounds that lack an aromatic substituent and remain HS down to very low temperatures.

The compounds [(dppf)Cu(L)](BF4) (1[BF4]) [dppf = 1,1′-bis(diphenylphosphanylferrocene), L = N-(2-methyl-5,8-dioxo-5,8-dihydroquinolin-7-yl)acetamide] and [(acac)2Ru(L)] (2) (acac = acetylacetonato) were prepared from the reactions of [Cu(dppf)(CH3CN)2](BF4) or [Ru(acac)2(CH3CN)2], respectively with L. Structural characterization of 1[BF4] shows a distorted tetrahedral coordinated copper center. Both complexes show one-electron reversible oxidation as well as reduction processes in their cyclic voltammogram. The first oxidation process of 1[BF4] leads to absorptions at around 900 nm in the UV/Vis/NIR spectrum and results in an EPR silent species up to 110 K thus indicating a dppf-centered oxidation. The reduction processes of 1[BF4] show features in the UV/Vis/NIR, IR as well as EPR spectrum that are compatible with L-centered redox processes. In contrast to this, the ruthenium complex 2 shows metal-centered spin in both the one-electron oxidized as well as reduced forms. These results show that the copper center does not participate in the redox processes in 1[BF4] whereas the ruthenium center participates strongly in the electron-transfer processes in 2. Results obtained from electrochemistry as well as from UV/Vis/NIR, IR, and EPR spectroelectrochemistry are invoked to show the noninnocent nature of L in these complexes as well as the more relative importance of metal–L covalency in 2 as compared to 1[BF4].

The zerovalent metal in [Mo(CO)(4)(bmiq)] binds the two imidazole-N-imine donors of 2,3-bis(1-methylimidazol-2-yl)quinoxaline (bmiq), resulting in a seven-membered chelate ring coordinated in cis configuration. DFT calculations confirm the preference for a seven-membered vs five-membered ring chelation alternative as well as the experimental structural parameters. The complex is reversibly reduced in CH2Cl2 at -2.08 V and reversibly oxidized at -0.14 V vs ferrocenium/ferrrocene. The facilitated oxidation to a stable cation is attributed to the donor effect from the imidazole rings. In agreement with the DFT-calculated characteristics of the HOMO and LUMO, the in situ EPR studies at a Pt electrode reveal a Mo-I signature for the cation (g(1) = 1.967, g(2) = 1.944, g(3) = 1.906; A(iso)((95,97) MO) = 50 G) and a quinoxaline radical-type EPR spectrum with dominant N-14 coupling (2 N) of 6.0 G for the anion. IR spectroelectrochemistry confirms these assignments, showing small (Delta nu <= 20 cm(-1)) low-energy shifts of carbonyl stretching bands on reduction but significantly larger high-energy shifts (Delta nu = 77-142 cm(-1)) after oxidation. The neutral compound with a weak, broad MLCT absorption band at 500 nm is photolabile in solution. The unusual stability of both the anion and the cation is attributed to the spatial and electronic separation of the sites for electron loss (at the metal) and for electron uptake (at the uncoordinated quinoxaline ring).

Reduction of an unsymmetrically substituted α-diimine followed by condensation with PCl3 yielded a P-chloro-N-aryl-N′-alkyl diazaphospholene which was further converted into an unsymmetrical diazaphospholium triflate by reaction with trimethylsilyl triflate. Reaction of tetramers of N-H- or N-alkyl-benzo-1,3,2-diazaphospholes with methyl triflate or triflic acid led in one step to triflate salts of unsymmetrically substituted benzo-1,3,2-diazaphospholium cations. Determination of the crystal structures of two of these derivatives by single-crystal X-ray diffraction studies revealed that individual cations and anions in the crystal lattice interact via specific electrostatic, π-stacking, or van-der-Waals type interactions to form supramolecular assemblies. Thermoanalytical measurements disclosed that benzo-diazaphospholium triflates with medium length alkyl chains melt below 100°C and exhibit a strong tendency to form supercooled liquids.

Combining two different redox-active organometallic moieties, we prepared the compounds [(Cym)-RuCl(dpf)](PF6), with Cym = p-cymene = 1-isopropyl-4-methylbenzene, and the diphosphinoferrocenes (dpf) 1,1'-bis(diphenylphosphino)ferrocene (dppf; complex 3), 1,1'-bis(diisopropylphosphino)ferrocene (dippf; complex 4), and 1,1'-bis(diethylphosphino)ferrocene (depf; complex 5) as well as the structurally characterized hydride complex [(C5Me5)RuH(dippf)] (2). In contrast to the case for 2, with an approximately staggered ferrocene conformation, the chloride complexes 3-5 exhibit a syn-periplanar ferrocene arrangement, due to a Cl center dot center dot center dot H(C5H4) interaction in the solid and in solution. The related new compounds [(Cym)RuH(dppf)](PF6) (6) and trinuclear (mu-dpf)[(Cym)RuCl2)](2) (7-9) were also obtained and identified by H-1 and P-31 NMR spectroscopy. The redox behavior of 2-6 and of the known [(C5Me5)RuH(dppf)] (1) was investigated using cyclic voltammetry, spectroelectrochemistry in the UV/vis/near-IR and ER regions, and, in part, by EPR. The first oxidation of the areneruthenium compounds 3-6 occurs reversibly at the ferrocene site, while the reduction proceeds via an ECE two-electron pattern under chloride dissociation. These results are compared to those obtained for the pentamethylcyclopentadienide/hydride complexes 1 and 2, which demonstrate unambiguously the ruthenium center as the site of the first electron loss. The different results for the two kinds of heterodimetallic d(5)/d(6) mixed-valent intermediates, (FeRuIII)-Ru-II for 1(+) and 2(+) and Fe-III Ru-II for 3(+) -6(+), are discussed with respect to the possible uses of such heterodinuclear systems in H-2 conversion catalysis.

Reaction of Ru(bpy)(2)Cl-2 center dot 2 H2O with 1,2-bis(trifluoroacetyl)hydrazine H-2(adc-CF3) under basic conditions yields the dinuclear [(mu-adc-CF3){Ru(bpy)(2)}(2)](2+) ion which was isolated and crystallized for structure determination in the meso diastereoisomer form as the bis(hexafluorophosphate). The Ru center dot center dot center dot Ru distance was determined at 5.029(1) angstrom, and the N-N bond length at 1.463(5) angstrom reveals a hydrazido(2-) form of the bridge, implying unchanged +II metal oxidation states. Besides bpy-based reduction, the cyclic voltammetric analysis revealed two oxidation waves with a (3+) intermediate. Spectroelectrochemistry demonstrated that this intermediate [(mu-adc-CF3){Ru(bpy)(2)}(2)](3+) with a comproportionation constant of K-c = 10(8.8) and an absorption at 1680 nm (epsilon=9900 M-1 cm(-1)) is a mixed-valent species as evident most convincingly from the EPR parameters at g(1)=2.239, g(2)=2.065, g(3)=1.891 (g(av)=2.101, Delta g=g(1) - g(3)=0.348). (C) 2010 Elsevier B.V. All rights reserved.

Reactions of N,N'-di-n-butyl-2-amino-5-alcoholate-1,4-benzoquinonemonoiminium L-1, or N,N'-diisopropyl-2-amino-5-alcoholate-1,4-benzoquinonemonoiminium L-2 with [{(dppf)Cu}(2)(mu-Cl)(2)] (dppf = 1,1'-bis(diphenylphosphino)ferrocene) or [{(dispf)Cu}(2)(mu-Cl)(2)] (dispf = 1,1'-bis(diisopropylphosphino)ferrocene) led to the formation of the heterodinuclear complexes [(dppf)(CuL-H1)] (2), [(dppf)(CuL-H2)] (3), [(dispf)(CuL-H1)] (4), and [(dispf)(CuL-H2)] (5). The crystal structure of L-2 was determined by X-ray diffraction and shows that the molecule exists in a 6 pi + 6 pi zwitterionic form, with two chemically connected but electronically nonconjugated pi-subunits. The crystal structures of complexes 2-4 show a distorted tetrahedral coordination environment for the Cu(I) center and a more localized pi-system for the ligands. Cyclic voltammetry on the ligands and complexes indicates various redox processes. The first oxidation of the complexes leads to an electron paramagnetic resonance supported formulation where the ligand radical is bound to Cu(I). UV-visible spectroscopy of the ligands and the complexes is also reported and discussed.

The reactions of 1,1-diamino-2,2-diphenyl-substituted diphosphines featuring various degrees of P-P bond polarization with different alkynes were investigated. All diphosphines reacted with alkynes carrying one or two electron withdrawing carboxylic ester moieties under cleavage of the P-P bond and stereospecific phosphinyl-phosphination at the triple bond to give unsymmetrical ethane-1,2- bisphosphines. Several of the products were further converted into chelate complexes upon reaction with group-10 metal dihalides. All isolated compounds were characterized by analytical and spectroscopic data, and several of the new ligands and complexes by single-crystal X-ray diffraction studies. Graphical Abstract Activation of Polarized Phosphorus–Phosphorus Bonds by Alkynes: Rational Synthesis of Unsymmetrical 1,2-Bisphosphine Ligands and Their Complexes

Structurally characterized 2-methylselenomethyl-1H-benzimidazole (msbi) is shown to form complexes in 2:1 ratio with copper(II). Whereas the central cation [Cu(msbi)(2)Cl](+) = 1(+) in [Cu(msbi)(2)Cl]Cl center dot 2MeOH crystallizes in an approximately mixed square-pyramidal/trigonal-bipyramidal structure (tau = 0.52) with the second and third row atoms chlorine and selenium in the equatorial plane, the related [Cu(msbi)(2)(MeOH)](BF4)(2) = [2](BF4)(2) exhibits a closer to square-pyramidal arrangement with tau = 0.36 for that complex dication 2(2+). In both cases, the Cu-N bonds are short at about 1.94 angstrom, whereas the Cu-Se distances vary between 2.62 angstrom for 1(+) and ca. 2.54 angstrom for 2(2+). Slight differences between the Jahn-Teller influenced species 1(+) and 2(2+) are also apparent from absorption and EPR spectra. Since copper(I) complexes of msbi suitable for crystal structure analysis could not be obtained, the related 1-methyl-2-phenylselenomethyl-1H-benzimidazole (mpsbi) was prepared and used to obtain [Cu(mpsbi)(2)](X) = [3](X)(X = BF4 or PF6). The copper(I) ion in the corresponding cation 3(+) shows a DFT-reproduced distorted tetrahedral configuration with an N-Cu-I-N angle at 146.7(3)degrees, less straightened than the ca. 170 degrees in similar Cu-I complexes with thioether-1H-benzimidazole ligands. A copper(I) compound [Cu(psbi)(2)][Cu(psbi)(psbi-H+)](PF6) = [4][4'](PF6) with another related ligand, 2-phenylselenomethyl-1H-benzimidazole (psbi), was crystallized in partially benzimidazole-deprotonated acetonitrile solvate form, showing short Cu-N bonds of 1.898(5) angstrom, an N-Cu-I-N angle of 157.5(3)degrees, a Se center dot center dot center dot Se interaction at 3.6237(3) angstrom, and a very small Se-Cu-Se angle of 78.23(4)degrees. The different responses resulting from thioether and selenoether coordination to copper in the complexes at hand are being discussed.

Isoelectronic benzo-1,3,2-diazaphospholium cations and benzo-1,3,2-diazaphospholide anions were prepared from the same phosphazane precursor; both species display according to computational studies similar aromaticity as the neutral benzo-1,3,2-diazaphosphole but are chemically more stable due to their ionic nature.

Because of their similar cationic radii, potassium and thallium(I) compounds are usually regarded as closely related. Homologous molecular species containing either K+ or Tl+ are very rare, however, We have synthesized potassium and thallium salts MEAr* [M, E = K, S (2a); K, Se (2b); Tl, S (3a); Tl, Se (3b); Ar* = 2,6-Trip(2)C(6)H(3), Trip = 2,4,6-iPr(3)C(6)H(2)] derived from terphenyl-substituted thio- and selenophenols. In the solid-state structures of dimeric 2a, 2b, 3a, and 3b additional metal-eta(n)-pi-arene interactions to the flanking arms of the terphenyl substituents of different hapticity 11 are observed. Remarkably, the homologous potassium and thallium complexes 2b and 3b crystallize in isomorphous cells. For 2a, 3a, and model complexes of the composition METph (Tph = C6H4-2-Trip) the nature of the M-E and M center dot center dot center dot C(arene) bonding was studied by density functional theory calculations. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451. Weinheim, Germany, 2008)

The heterodinuclear compound [(PhenQ)Cu(dppf)](BF4), PhenQ = 9,10-phenanthrenequinone and dppf = 1,1'-bis(diphenylphosphino)ferrocene, was identified structurally and spectroscopically (NMR, IR, UV-vis) as a copper(I) complex of a completely unreduced ortho-quinone. Crystallographic and DFT calculation results suggest that this stabilization of a hitherto elusive arrangement is partially owed to intramolecular pi/pi interactions phenyl/PhenQ. Intermolecular PhenQ/PhenQ pi stacking is also observed in the crystal. According to DFT calculations, the pi interactions are responsible for the considerably distorted coordination geometry at CuI with one short and one longer Cu-O and Cu-P bond, respectively, and with bond angles at copper ranging from 99 degrees to 133 degrees. Electrochemical reduction proceeds reversibly at low temperatures to yield an EPR spectroscopically characterized semiquinone-copper(I) species.