Anja Stammler

Spontaneous chiral resolution of a coordination polymer with distorted helical structure consisting of achiral building blocksDedicated to Professor Peter Jutzi on the occasion of his 65th birthday.

Reaction of achiral 2,5-diphenyl-3,4-di(3-pyridyl)cyclopenta-2,4-dien-1-one (2) with ZnCl2 and HgBr2, respectively, afforded the helically chiral coordination polymers [(2)ZnCl2]infinity and [(2)HgBr2]infinity, which show spontaneous chiral resolution, forming colonies of homochiral crystals.

C–F or C–H bond activation and C–C coupling reactions of fluorinated pyridines at rhodium: synthesis, structure and reactivity of a variety of tetrafluoropyridyl complexes

Reactions of [RhH(PEt3)3] (1) or [RhH(PEt3)4] (2) with pentafluoropyridine or 2,3,5,6-tetrafluoropyridine afford the activation product [Rh(4-C5NF4)(PEt3)3] (3). Treatment of 3 with CO, 13CO or CNtBu effects the formation of trans-[Rh(4-C5NF4)(CO)(PEt3)2] (4a), trans-[Rh(4-C5NF4)(13CO)(PEt3)2] (4b) and trans-[Rh(4-C5NF4)(CNtBu)(PEt3)2] (5). The rhodium(III) compounds trans-[RhI(CH3)(4-C5NF4)(PEt3)2] (6a) and trans-[RhI(13CH3)(4-C5NF4)(PEt3)2] (6b) are accessible on reaction of 3 with CH3I or 13CH3I. In the presence of CO or 13CO these complexes convert into trans-[RhI(CH3)(4-C5NF4)(CO)(PEt3)2] (7a), trans-[RhI(13CH3)(4-C5NF4)(CO)(PEt3)2] (7b) and trans-[RhI(13CH3)(4-C5NF4)(13CO)(PEt3)2] (7c). The trans arrangement of the carbonyl and methyl ligand in 7a-7c has been confirmed by the 13C-13C coupling constant in the 13C NMR spectrum of 7c. A reaction of 4a or 4b with CH3I or 13CH3I yields the acyl compounds trans-[RhI(COCH3)(4-C5NF4)(PEt3)2] (8a) and trans-[RhI(13CO13CH3)(4-C5NF4)(PEt3)2] (8b), respectively. Complex 8a slowly reacts with more CH3I to give [PEt3Me][Rh(I)2(COCH3)(4-C5NF4)(PEt3)](9). On heating a solution of 7a, the complex trans-[RhI(CO)(PEt3)2] (10) and the C-C coupled product 4-methyltetrafluoropyridine (11) have been obtained. Complex 8a also forms 10 at elevated temperatures in the presence of CO together with the new ketone 4-acetyltetrafluoropyridine (12). The structures of the complexes 3, 4a, 5, 6a, 8a and 9 have been determined by X-ray crystallography. 19F-1H HMQC NMR solution spectra of 6a and 8a reveal a close contact of the methyl groups in the phosphine to the methyl or acyl ligand bound at rhodium.

Exchange Interactions and Zero-Field Splittings in C3-Symmetric MnIII6FeIII: Using Molecular Recognition for the Construction of a Series of High Spin Complexes Based on the Triplesalen Ligand

The reaction of the tris(tetradentate) triplesalen ligand H6talen(t-Bu2), which provides three salen-like coordination environments bridged in a meta-phenylene arrangement by a phloroglucinol backbone, with Mn(II) salts under aerobic conditions affords, in situ, the trinuclear Mn(III) triplesalen complexes [(talen(t-Bu2)){Mn(III)(solv)n}3]3+. These can be used as molecular building blocks in the reaction with [Fe(CN)6]3- as a hexaconnector to form the heptanuclear complex [{(talen(t-Bu2)){Mn(III)(solv)n}3}2{Fe(III)(CN)6}]3+ ([Mn(III)6Fe(III)]3+). The regular ligand folding observed in the trinuclear triplesalen complexes preorganizes the three metal ions for the reaction of three facially coordinated nitrogen atoms of a hexacyanometallate and provides a driving force for the formation of the heptanuclear complexes [M(t)6M(c)]n+ (M(t), terminal metal ion of the triplesalen building block; M(c), central metal ion of the hexacyanometallate) by molecular recognition, as has already been demonstrated for the single-molecule magnet [Mn(III)6Cr(III)]3+. [{(talen(t-Bu2))(Mn(III)(MeOH))3}2{Fe(III)(CN)6}][Fe(III)(CN)6] (1) was characterized by single-crystal X-ray diffraction, FTIR, ESI- and MALDI-TOF-MS, Mössbauer spectroscopy, and magnetic measurements. The molecular structure of [Mn(III)6Fe(III)]3+ is overall identical to that of [Mn(III)6Cr(III)]3+ but exhibits a different ligand folding of the Mn(III) salen subunits with a helical distortion. The Mössbauer spectra demonstrate a stronger distortion from octahedral symmetry for the central [Fe(CN)6]3- in comparison to the ionic [Fe(CN)6]3-. At low temperatures in zero magnetic fields, the Mössbauer spectra show magnetic splittings indicative of slow relaxation of the magnetization on the Mössbauer time scale. Variable-temperature-variable-field and mu(eff) versus T magnetic data have been analyzed in detail by full-matrix diagonalization of the appropriate spin-Hamiltonian, consisting of isotropic exchange, zero-field splitting, and Zeeman interaction taking into account the relative orientation of the D tensors. Satisfactory reproduction of the experimental data has been obtained for parameters sets J(Mn-Mn) = -(0.85 +/- 0.15) cm(-1), J(Fe-Mn) = +(0.70 +/- 0.30) cm(-1), and D(Mn) = -(3.0 +/- 0.7) cm(-1). Comparing these values to those of [Mn(III)6Cr(III)]3+ provides insight into why [Mn(III)6Fe(III)]3+ is not a single-molecule magnet.

Trinuclear Fragments as Nucleation Centres: New Polyoxoalkoxyvanadates by (Induced) Self‐Assembly

The presence of pentaerythritol (C(CH2OH)(4)) in an aqueous vanadate solution leads-depending on the pH value and other specific reaction conditions-to the formation of (CN3H6)(4)Na-2 [(H4V6P4O30)-P-IV{(CH2)(3)-CCH2OH2]. 14H(2)O (1), Na-6[(H4V6P4O30)-P-IV{(CH2)(3)CCH2OH}(2)]. 18 H2O (2), (NH4)(7)[(H7V12V7O50)-V-IV-O-V (CH2)(3)CCH2OH]. 11.5 H2O . (3), (CN3H6)(4)[(V3V4O19F)-V-IV-O-V(CH2)(3)CCH2OH] . 5.25 H2O (4), Na-6[(V10V2O30F2)-V-IV-O-V{(CH2)(3)CCH2OH}(2)]. 22- H2O (5) or (CN3H6)(4)[(V2V8O28F2)-V-IV-O-V-{(CH2)(3)CCH2OH}(2)] . 4 H2O (6). The corresponding anions contain as basic structural elements trinuclear {V3O13} or {V3O12F} units, which are stabilized by the organic substituent acting as a tripod ligand. It can be assumed in principle that these units act as nucleation centres during the formation processes of the cluster anions. In this context it is remarkable that the trinuclear units can even occur in a quasi-isolated state, as in the anions of 1 and 4, The compounds were characterized by IR, UV/Vis/NIR and EPR spectroscopy as well as by magnetochemical investigations and single-crystal X-ray structure determinations. Susceptibility data are especially useful for identifying the trinuclear units as well as the nature of their magnetic coupling with the rest of the structure.

Trinuclear C3-Symmetric Extension of Jacobsen’s Catalyst: Synthesis, Characterization, and Catalytic Properties of a Chiral Trinuclear MnIII Triplesalen Complex

The synthesis of a chiral version of a triplesalen ligand has been performed in two steps starting from 2,4,6-triacetyl-1,3,5-trihydroxybenzene (1). Reaction with excess trans-(1R,2R)-1,2-cyclohexanediamine and trans-(1S,2S)-1,2-cyclohexanediamine provided the chiral triplesalen half units 2,4,6-tris[1-((1R,2R)-2-aminocyclohexylimino)ethyl]-1,3,5-trihydroxybenzene (2(RR)) and 2,4,6-tris[1-((1S,2S)-2-aminocyclohexylimino)ethyl]-1,3,5-trihydroxybenzene (2(SS)), respectively. The two enantiomeric pure triplesalen ligands H(6)chand(RR) and H(6)chand(SS) were obtained by reaction of the triplesalen half units with 3,5-di-tert-butylsalicylaldehyde. Reaction with MnCl(2) x 2 H(2)O under basic aerobic conditions afforded the chiral trinuclear triplesalen complexes 3(RR) and 3(SS). Single-crystal X-ray diffraction studies on both enantiomers showed the presence of the two ionization isomers [(chand){Mn(III)Cl(MeOH)}(3)] and [(chand){Mn(III)(MeOH)(2)}(3)]Cl(3) in the solid state, resulting in the formulation of 3 (either 3(RR) or 3(SS)) as [(chand){Mn(III)Cl(MeOH)}(3)][(chand){Mn(III)(MeOH)(2)}(3)]Cl(3). The crystal structures exhibit chiral hydrophobic channels of approximately 8 A diameter decorated with tert-butyl groups. These form left-handed helices in the 3(RR) enantiomer and right-handed helices in the 3(SS) enantiomer. Magnetic measurements are in accord with weak exchange interactions between the Mn(III) S(i) = 2 ions and strong local magnetic anisotropy as has been found in other trinuclear Mn(III)(3) triplesalen complexes. As a proof-of principal, we have investigated the catalytic ability of the two enantiomers in the enantioselective epoxidation of unfunctionalized olefins. The chiral trinuclear Mn(III)(3) triplesalen acts under non-optimized conditions as a catalyst with relatively good yields and moderate enantiomeric excess.

Synthesis, structure and reactivity of fluorovinyl nickel complexes: formation of a phosphonioethenyl complexDedicated to Professor Dieter Naumann on the occasion of his 60th birthday.

Treatment of [Ni(COD)2] with trifluoroiodoethene or 1,1-dibromodifluoroethene in the presence of PEt3 effects the formation of the complexes trans-[NiI(CFCF2)(PEt3)2] (1) and trans-[NiBr(CBrCF2)(PEt3)2] (2), respectively. Reaction of 1 with NaBAr′4 and acetonitrile gives trans-[Ni(CFCF2)(NCMe)(PEt3)2]BAr′4 (4) [Ar′ = 3,5-C6H3(CF3)2]. Treatment of 1 with NaBAr′4 in the presence of CO yields the cationic complex trans-[Ni(CFCF2)(CO)(PEt3)2]BAr′4 (5), which is only stable in a CH2Cl2 solution. The reaction of 1 with NaBAr′4 and tBuNC affords the compound trans-[Ni(CFCF2)(CNtBu)(PEt3)2]BAr′4 (6). On treatment with NaBAr′4 and PEt3 complex 6 can be converted into the dicationic phosphonioethenyl compound trans-[Ni{CFCF(PEt3)}(CNtBu)(PEt3)2][BAr′4]2 (7). The structures of complexes 2 and 7 have been determined by X-ray crystallography. The phosphonioethenyl ligand in 7 is bound at nickel with a Ni–C distance of 1.893(5) A. The CC and the CF–P bond lengths are 1.309(6) A and 1.794(5) A, respectively.

Probing the radialene-character in triplesalophen ligands by spectroscopic and structural analysis.

The triplesalen ligand system based on three salen-like coordination environments bridged by a common phloroglucinol ring has been designed and successfully applied for the rational synthesis of single-molecule magnets from two trinuclear triplesalen complexes and one hexacyanometallate by supramolecular recognition. In order to optimize this system with respect to magnetic anisotropy, the triplesalophen ligand system has been identified, which should allow for the synthesis of nonanuclear complexes composed of two trinuclear triple-salophen complexes and three connecting units. Herein, the convergent synthesis of the triplesalophen ligand system is described, which differs fom the divergent strategy for the triplesalen ligand system. The molecular and elecrtronic structures of the triplesalophen ligands H(6)baron(R) (R = Me, Cl, Br) have been established by single-crystal X-ray diffraction, NMR, FTIR, and UV-vis spectroscopies. These complementary methods allowed the assignment of the central compartment not to be in the O-protonated tautomer but in the N-protonated tautomer with the prevalence of a keto-enamine resonance description, which resembles a heteroradialene. Furthermore, the comparison with the mononucleating unsymmetrical salophen reference ligand H(2)carl(Cl) and with compounds from the literature provides unique signatures for the appearance of the heteroradialene motif not only in NMR spectra and structural parameters but also in IR and UV-vis spectra. These signatures form the basis for the interpretation and understanding of the electronic structures of transition metal complexes with the triplesalophen ligand system.

Environmental Influence on the Single-Molecule Magnet Behavior of [MnIII6CrIII]3+: Molecular Symmetry versus Solid-State Effects

The structural, spectroscopic, and magnetic properties of a series of [Mn(III)(6)Cr(III)](3+) (= [{(talen(t-Bu(2)))Mn(III)(3)}(2){Cr(III)(CN)(6)}](3+)) compounds have been investigated by single-crystal X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and electronic absorption spectroscopy, elemental analysis, electro spray ionization-mass spectrometry (ESI-MS) and matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS), cyclic voltammetry, AC and DC magnetic measurements, as well as theoretical analysis. The crystal structures obtained with [Cr(III)(CN)(6)](3-) as a counterion exhibit (quasi-)one-dimensional (1D) chains formed by hydrogen-bonded (1) or covalently linked (2) trications and trianions. The rod-shaped anion lactate enforces a rod packing of the [Mn(III)(6)Cr(III)](3+) complexes in the highly symmetric space group R3[overline] (3) with a collinear arrangement of the molecular S(6) axes. Incorporation of the spherical anion BPh(4)(-) leads to less-symmetric crystal structures (4-6) with noncollinear orientations of the [Mn(III)(6)Cr(III)](3+) complexes, as evidenced by the angle between the approximate molecular C(3) axes taking no specific values in the range of 2°-69°. AC magnetic measurements on freshly isolated crystals (1a and 3a-6a), air-dried crystals (3b-6b), and vacuum-dried powder samples (3c-6c) indicate single-molecule magnet (SMM) behavior for all samples with U(eff) values up to 28 K. The DC magnetic data are analyzed by a full-matrix diagonalization of the appropriate spin-Hamiltonian including isotropic exchange, zero-field splitting, and Zeeman interaction, taking into account the relative orientation of the D-tensors. Simulations for 3a-6a and 3c-6c indicate a weak antiferromagnetic exchange between the Mn(III) ions in the trinuclear subunits (J(Mn-Mn) = -0.70 to -0.85 cm(-1), Ĥ(ex) = -2∑(i<j )J(ij)Ŝ(i)·Ŝ(j)) that is overcome by the stronger antiferromagnetic interaction via the Cr-C≡N-Mn pathway (J(Cr-Mn) = -3.00 to -5.00 cm(-1)), leading to an overall ferrimagnetic coupling scheme with an S(t) = (21)/(2) spin ground state. The differences in U(eff), J(Mn-Mn), and J(Cr-Mn) for the investigated samples are rationalized in terms of subtle variations in the molecular and crystal structures. In particular, a magnetostructural correlation between the Mn-N(C≡N) bond length and the J(Cr-Mn) exchange coupling is inferred from the magnetic measurements and corroborated by DFT calculations. The results of this detailed study on [Mn(III)(6)Cr(III)](3+) allow the formulation of some key recipes for a rational improvement of the SMM behavior.

Molecular and Electronic Structures of Dinuclear Iron Complexes Incorporating Strongly Electron-Donating Ligands: Implications for the Generation of the One- and Two-Electron Oxidized Forms

The ligands (L(t-Bu(2)))(2-), (L(Me(2)))(2-), and (L(Cl(2)))(2-) have been employed for the synthesis of the dinuclear Fe(III) complexes [L(t-Bu(2))Fe(μ-O)FeL(t-Bu(2))], [L(Me(2))Fe(μ-O)FeL(Me(2))], and [L(Cl(2))Fe(μ-O)FeL(Cl(2))]. The strongly electron-donating groups (tert-amines and phenolates) were chosen to increase the electron density at the coordinated ferric ions and thus to facilitate the oxidation of the complexes, with the possibility of fine-tuning the electronic structures by variation of the remote substituents. Molecular structures established in the solid (by single-crystal X-ray diffraction) and in solution (by X-ray absorption spectroscopy) show that the Fe ions are five-coordinate in a square-pyramidal coordination environment with the ligand adopting a trans-conformation. Spectroscopic and magnetic characterization establishes the highly covalent nature of the Fe(III)-O(oxo) and Fe(III)-O(Ph) bonds. The variations in the donor capabilities of the phenolates (due to changes in the remote substituents) are compensated for by a flexible electron donation of the Fe(III)-O(oxo) bonding. Spectroelectrochemical characterization demonstrates that [L(t-Bu(2))Fe(μ-O)FeL(t-Bu(2))] can be oxidized reversibly at +0.27 and +0.44 V versus Fc(+)/Fc, whereas [L(Me(2))Fe(μ-O)FeL(Me(2))] and [L(Cl(2))Fe(μ-O)FeL(Cl(2))] exhibit irreversible oxidations at +0.29 and +0.87 V versus Fc(+)/Fc, respectively. UV-vis, electron paramagnetic resonance (EPR), X-ray absorption spectroscopy (XAS), and Mössbauer spectroscopy show that the successive oxidations of [L(t-Bu(2))Fe(μ-O)FeL(t-Bu(2))] are ligand-centered leading to the monophenoxyl radical complex [(•)L(t-Bu(2))Fe(III)(μ-O)Fe(III)L(t-Bu(2))](+) (with the oxidation primarily localized on one-half of the molecule) and the diphenoxyl radical complex [(•)L(t-Bu(2))Fe(III)(μ-O)Fe(III•)L(t-Bu(2))](2+). Both products are unstable in solution and decay by cleavage of an Fe(III)-O(oxo) bond. The two-electron oxidized species is more stable because of two equally strong Fe(III)-O(oxo) bonds, whereas in the singly oxidized species the Fe(III)-O(oxo) bond of the non-oxidized half is weakened. The decay of the monocation results in the formation of [L(t-Bu(2))Fe(III)](+) and [L(t-Bu(2))Fe(IV)=O], while the decay of the dication yields [(•)L(t-Bu(2))Fe(III)](2+) and [L(t-Bu(2))Fe(IV)=O]. Follow-up reactions of the oxidized fragments with the counteranion of the oxidant, [SbCl(6)](-), leads to the formation of [Fe(III)Cl(4)](-).

Formation of a “less stable” polyanion directed and protected by electrophilic internal surface functionalities of a capsule in growth: [{Mo6O19}2−⊂{MoVI72FeIII30O252(ac)20(H2O)92}]4−

The spherical capsule skeleton of the host-guest system [{Mo6O19}2- subset {Mo(VI)72Fe(III)30O252(CH3COO)20(H2O)92}]4- 1a--built up by 12 {(Mo(VI))Mo(VI)5} type pentagonal units linked by 30 Fe(III) centers which span the unique icosahedral Archimedean solid, the icosidodecahedron--can now be constructed deliberately and with a simpler composition than before from an acidified aqueous molybdate solution containing the mentioned (virtual) pentagonal units; the encapsulated hexamolybdate--normally not formed in water--is built up in an unprecedented way concomitant with capsule growth, while being directed by the corresponding internal electrophilic surface functionalities.