Diphosphination of Electron Poor Alkenes

Studies of the reactions between an unsymmetrically substituted 1,1-diaminodiphosphine and electron poor alkenes revealed that, in contrast to the regioselective 1,2-addition of the P−P bond to α,β-unsaturated esters and nitriles with terminal double bonds, ethyl(vinyl)ketone reacted via 1,4-addition and α,β-unsaturated esters or ketones with internal double bonds failed to react at all, presumably owing to the deactivating influence of the alkyl groups. Reaction of 1 with maleic N-phenylimide proceeded stereoselectively under cis-addition but diesters of maleic and fumaric acid gave mixtures of diastereomeric 1,2-bisphosphines. The addition products were characterized by 31P NMR before being converted into palladium complexes that were isolated and comprehensively characterized by spectroscopic data and in most cases by X-ray diffraction studies. Monitoring the reactions of 1 with maleic and fumaric diesters by NMR revealed that both E/Z-isomerization of alkene starting materials and epimerization of stereogenic centers in 1,2-bisphosphines take place and allow isolation from the mixtures of diastereomeric ligands of complexes featuring a uniform stereochemistry of the C2 backbone

Diphosphination of Electron Poor Alkenes

Studies of the reactions between an unsymmetrically substituted 1,1-diaminodiphosphine and electron poor alkenes revealed that, in contrast to the regioselective 1,2-addition of the P−P bond to α,β-unsaturated esters and nitriles with terminal double bonds, ethyl(vinyl)ketone reacted via 1,4-addition and α,β-unsaturated esters or ketones with internal double bonds failed to react at all, presumably owing to the deactivating influence of the alkyl groups. Reaction of 1 with maleic N-phenylimide proceeded stereoselectively under cis-addition but diesters of maleic and fumaric acid gave mixtures of diastereomeric 1,2-bisphosphines. The addition products were characterized by 31P NMR before being converted into palladium complexes that were isolated and comprehensively characterized by spectroscopic data and in most cases by X-ray diffraction studies. Monitoring the reactions of 1 with maleic and fumaric diesters by NMR revealed that both E/Z-isomerization of alkene starting materials and epimerization of stereogenic centers in 1,2-bisphosphines take place and allow isolation from the mixtures of diastereomeric ligands of complexes featuring a uniform stereochemistry of the C2 backbone

Diphosphination of Electron Poor Alkenes

Studies of the reactions between an unsymmetrically substituted 1,1-diaminodiphosphine and electron poor alkenes revealed that, in contrast to the regioselective 1,2-addition of the P−P bond to α,β-unsaturated esters and nitriles with terminal double bonds, ethyl(vinyl)ketone reacted via 1,4-addition and α,β-unsaturated esters or ketones with internal double bonds failed to react at all, presumably owing to the deactivating influence of the alkyl groups. Reaction of 1 with maleic N-phenylimide proceeded stereoselectively under cis-addition but diesters of maleic and fumaric acid gave mixtures of diastereomeric 1,2-bisphosphines. The addition products were characterized by 31P NMR before being converted into palladium complexes that were isolated and comprehensively characterized by spectroscopic data and in most cases by X-ray diffraction studies. Monitoring the reactions of 1 with maleic and fumaric diesters by NMR revealed that both E/Z-isomerization of alkene starting materials and epimerization of stereogenic centers in 1,2-bisphosphines take place and allow isolation from the mixtures of diastereomeric ligands of complexes featuring a uniform stereochemistry of the C2 backbone

Rare-Earth Metal(III) Oxide Selenides M₄O₄Se[Se₂] (M = La, Ce, Pr, Nd, Sm) with Discrete Diselenide Units: Crystal Structures, Magnetic Frustration, and Other Properties

The rare-earth metal(III) oxide selenides of the formula La4O4Se[Se2], Ce4O4Se[Se2], Pr4O4Se[Se2], Nd4O4Se[Se2], and Sm4O4Se[Se2] were synthesized from a mixture of the elements with selenium dioxide as the oxygen source at 750 °C. Single crystal X-ray diffraction was used to determine their crystal structures. The isostructural compounds M4O4Se[Se2] (M = La, Ce, Pr, Nd, Sm) crystallize in the orthorhombic space group Amm2 with cell dimensions a = 857.94(7), b = 409.44(4), c = 1316.49(8) pm for M = La; a = 851.37(6), b = 404.82(3), c = 1296.83(9) pm for M = Ce; a = 849.92(6), b = 402.78(3), c = 1292.57(9) pm for M = Pr; a = 845.68(4), b = 398.83(2), c = 1282.45(7) pm for M = Nd; and a = 840.08(5), b = 394.04(3), c = 1263.83(6) pm for M = Sm (Z = 2). In their crystal structures, Se2− anions as well as [Se−Se]2− dumbbells interconnect {[M4O4]4+}∞2 layers. These layers are composed of three crystallographically different, distorted [OM4]10+ tetrahedra, which are linked via four common edges. The compounds exhibit strong Raman active modes at around 215 cm−1, which can be assigned to the Se−Se stretching vibration. Optical band gaps for La4O4Se[Se2], Ce4O4Se[Se2], Pr4O4Se[Se2], Nd4O4Se[Se2], and Sm4O4Se[Se2] were derived from diffuse reflectance spectra. The energy values at which absorption takes place are typical for semiconducting materials. For the compounds M4O4Se[Se2] (M = La, Pr, Nd, Sm) the fundamental band gaps, caused by transitions from the valence band to the conduction band (VB−CB), lie around 1.9 eV, while for M = Ce an absorption edge occurs at around 1.7 eV, which can be assigned to f-d transitions of Ce3+. Magnetic susceptibility measurements of Ce4O4Se[Se2] and Nd4O4Se[Se2] show Curie−Weiss behavior above 150 K with derived experimental magnetic moments of 2.5 µB/Ce and 3.7 µB/Nd and Weiss constants of θp = −64.9 K and θp = −27.8 K for the cerium and neodymium compounds, respectively. Down to 1.8 K no long-range magnetic ordering could be detected. Thus, the large negative values for θp indicate the presence of strong magnetic frustration within the compounds, which is due to the geometric arrangement of the magnetic sublattice in form of [OM4]10+ tetrahedra

Rare-Earth Metal(III) Oxide Selenides M₄O₄Se[Se₂] (M = La, Ce, Pr, Nd, Sm) with Discrete Diselenide Units: Crystal Structures, Magnetic Frustration, and Other Properties

The rare-earth metal(III) oxide selenides of the formula La4O4Se[Se2], Ce4O4Se[Se2], Pr4O4Se[Se2], Nd4O4Se[Se2], and Sm4O4Se[Se2] were synthesized from a mixture of the elements with selenium dioxide as the oxygen source at 750 °C. Single crystal X-ray diffraction was used to determine their crystal structures. The isostructural compounds M4O4Se[Se2] (M = La, Ce, Pr, Nd, Sm) crystallize in the orthorhombic space group Amm2 with cell dimensions a = 857.94(7), b = 409.44(4), c = 1316.49(8) pm for M = La; a = 851.37(6), b = 404.82(3), c = 1296.83(9) pm for M = Ce; a = 849.92(6), b = 402.78(3), c = 1292.57(9) pm for M = Pr; a = 845.68(4), b = 398.83(2), c = 1282.45(7) pm for M = Nd; and a = 840.08(5), b = 394.04(3), c = 1263.83(6) pm for M = Sm (Z = 2). In their crystal structures, Se2− anions as well as [Se−Se]2− dumbbells interconnect {[M4O4]4+}∞2 layers. These layers are composed of three crystallographically different, distorted [OM4]10+ tetrahedra, which are linked via four common edges. The compounds exhibit strong Raman active modes at around 215 cm−1, which can be assigned to the Se−Se stretching vibration. Optical band gaps for La4O4Se[Se2], Ce4O4Se[Se2], Pr4O4Se[Se2], Nd4O4Se[Se2], and Sm4O4Se[Se2] were derived from diffuse reflectance spectra. The energy values at which absorption takes place are typical for semiconducting materials. For the compounds M4O4Se[Se2] (M = La, Pr, Nd, Sm) the fundamental band gaps, caused by transitions from the valence band to the conduction band (VB−CB), lie around 1.9 eV, while for M = Ce an absorption edge occurs at around 1.7 eV, which can be assigned to f-d transitions of Ce3+. Magnetic susceptibility measurements of Ce4O4Se[Se2] and Nd4O4Se[Se2] show Curie−Weiss behavior above 150 K with derived experimental magnetic moments of 2.5 µB/Ce and 3.7 µB/Nd and Weiss constants of θp = −64.9 K and θp = −27.8 K for the cerium and neodymium compounds, respectively. Down to 1.8 K no long-range magnetic ordering could be detected. Thus, the large negative values for θp indicate the presence of strong magnetic frustration within the compounds, which is due to the geometric arrangement of the magnetic sublattice in form of [OM4]10+ tetrahedra

Reversible Intramolecular Single-Electron Oxidative Addition Involving a Hemilabile Noninnocent Ligand

Using the noninnocent ligand Q [= 4,6-di-tert-butyl-(2-methylthiophenylimino)-o-benzoquinone] with a thioether group as potential coordination function, it has been possible to substantiate a single-electron transfer induced oxidative addition within the complex [IrCp*Q]0/+ (Cp* = C5Me5) via structural characterization (catecholato → semiquinonato transition coupled with reversible S→Ir coordination), via cyclic voltammetry, EPR, and DFT (semiquinone formulation with about 8% Ir participation). The intramolecular rearrangement of the 16-electron precursor [IrCp*Q] triggered by electron removal illuminates the complementary activities of the substrate binding metal and the electron-buffering ligand as was recently employed by Ringenberg et al. in dihydrogen activation (Organometallics 2010, 29, 1956)

YF[MoO₄] and YCl[MoO₄]: Two Halide Derivatives of Yttrium <i>ortho</i>-Oxomolybdate: Syntheses, Structures, and Luminescence Properties

The halide derivatives of yttrium ortho-oxomolybdate YX[MoO4] (X = F, Cl) both crystallize in the monoclinic system with four formula units per unit cell. YF[MoO4] exhibits a primitive cell setting (space group P21/c; a = 519.62(2) pm, b = 1225.14(7) pm, c = 663.30(3) pm, β = 112.851(4)°), whereas the lattice of YCl[MoO4] shows face-centering (space group C2/m; a = 1019.02(5) pm, b = 720.67(4) pm, c = 681.50(3) pm, β = 107.130(4)°). The two compounds each contain crystallographically unique Y3+ cations, which are found to have a coordination environment of six oxide and two halide anions. In the case of YF[MoO4], the coordination environment is seen as square antiprisms, and for YCl[MoO4], trigon-dodecahedra are found. The discrete tetrahedral [MoO4]2− units of the fluoride derivative are exclusively bound by six terminal Y3+ cations, while those of the chloride compound show a 5-fold coordination around the tetrahedra with one edge-bridging and four terminal Y3+ cations. The halide anions in each compound exhibit a coordination number of two, building up isolated planar rhombus-shaped units according to [Y2F2]4+ in YF[MoO4] and [Y2Cl2]4+ in YCl[MoO4], respectively. Both compounds were synthesized at high temperatures using Y2O3, MoO3, and the corresponding yttrium trihalide in a molar ratio of 1:3:1. Single crystals of both are insensitive to moist air and are found to be coarse shaped and colorless with optical band gaps situated in the near UV around 3.78 eV for the fluoride and 3.82 eV for the chloride derivative. Furthermore, YF[MoO4] seems to be a suitable material for doping to obtain luminescent materials because the Eu3+-doped compound shows an intense red luminescence, which has been spectroscopically investigated

Reversible Intramolecular Single-Electron Oxidative Addition Involving a Hemilabile Noninnocent Ligand

Using the noninnocent ligand Q [= 4,6-di-tert-butyl-(2-methylthiophenylimino)-o-benzoquinone] with a thioether group as potential coordination function, it has been possible to substantiate a single-electron transfer induced oxidative addition within the complex [IrCp*Q]0/+ (Cp* = C5Me5) via structural characterization (catecholato → semiquinonato transition coupled with reversible S→Ir coordination), via cyclic voltammetry, EPR, and DFT (semiquinone formulation with about 8% Ir participation). The intramolecular rearrangement of the 16-electron precursor [IrCp*Q] triggered by electron removal illuminates the complementary activities of the substrate binding metal and the electron-buffering ligand as was recently employed by Ringenberg et al. in dihydrogen activation (Organometallics 2010, 29, 1956)

The Laccase-Catalyzed Domino Reaction between Catechols and Heterocyclic 1,3-Dicarbonyls and the Unambiguous Structure Elucidation of the Products by NMR Spectroscopy and X-ray Crystal Structure Analysis

The laccase-catalyzed reaction between catechols and heterocyclic 1,3-dicarbonyls (pyridinones, quinolinones, thiocoumarins) using aerial oxygen as the oxidant delivers benzofuropyridinones, benzofuroquinolinones, and thiocoumestans in a simple fashion, highly regioselectively with yields ranging from 55 to 98%. With barbituric acid derivatives the exclusive formation of dispiropyrimidinone derivatives takes place. The unambiguous and complete structure elucidation of all reaction products has been achieved by means of NMR spectroscopic methods (HSQMBC and band-selective HMBC) as well as by X-ray crystal structure analysis

Reversible Intramolecular Single-Electron Oxidative Addition Involving a Hemilabile Noninnocent Ligand

Using the noninnocent ligand Q [= 4,6-di-tert-butyl-(2-methylthiophenylimino)-o-benzoquinone] with a thioether group as potential coordination function, it has been possible to substantiate a single-electron transfer induced oxidative addition within the complex [IrCp*Q]0/+ (Cp* = C5Me5) via structural characterization (catecholato → semiquinonato transition coupled with reversible S→Ir coordination), via cyclic voltammetry, EPR, and DFT (semiquinone formulation with about 8% Ir participation). The intramolecular rearrangement of the 16-electron precursor [IrCp*Q] triggered by electron removal illuminates the complementary activities of the substrate binding metal and the electron-buffering ligand as was recently employed by Ringenberg et al. in dihydrogen activation (Organometallics 2010, 29, 1956)