Magnetic and Structural Studies of Vanadium Arene Complexes

The temperature dependence of the solid-state magnetic susceptibility for the paramagnetic V(I) complexes trans-(CpV)2(μ-η6:η6-C6H6) (1) and CpV(η6-C6H6) (2) has been investigated. Complex 1 obeys the Curie−Weiss law over the temperature range 10−300 K with μeff = 4.81 μB and ϑ = −18.8 K. The high-temperature moment is consistent with the presence of a total of four unpaired electrons derived from two low-spin V(I) d4 metal centers in an S = 2 configuration. However, at ca. 9 K the magnetic susceptibility displays a broad maximum. This magnetic behavior may be modeled over the full temperature range (4−300 K) using the Heisenberg intracluster magnetic exchange expression for an S1 = S2 = 1 system with g = 2.37, ϑ = −12.3 K, and J = −2.64 cm-1. Complex 2 obeys the Curie−Weiss law over the temperature range 5−300 K, with μeff = 2.86 μB and ϑ = −5.0 K. The X-ray structure of 2 (P21/a, a = 10.7842(4) Å, b = 7.8233(4) Å, c = 11.2017(5) Å, β = 113.830(2)° at 150 K, Z = 4) has been determined. Crystals of 2 undergo a reversible phase transition to a new monoclinic cell with a‘ ≈ (a + c)/2, b‘ ≈ b, c‘ ≈ (c − a)/2 over the temperature range 290−270 K

Lanthanide Borohydride Complexes Supported by Diaminobis(phenoxide) Ligands for the Polymerization of ε-Caprolactone and l- and <i>r</i><i>ac</i>-Lactide

Reaction of Na2O2NN‘ [H2O2NN‘ = (2-C5H4N)CH2N{2-HO-3,5-C6H2tBu2}2] with M(BH4)3(THF)3 afforded the dimeric, rare-earth borohydride compounds [M(O2NN‘)(μ-BH4)(THF)n]2 [M = YIII, n = 0.5 (1-Y); M = NdIII, n = 1 (1-Nd); M = SmIII, n = 0 (1-Sm)]. For comparison the chloride analogues [M(O2NN‘)(μ-Cl)(THF)n]2 (2-M; M = LaIII or SmIII, n = 0; M = NdIII, n = 1) and the corresponding pyridine adducts [M(O2NN‘)(μ-X)(py)]2 [X = BH4 (3-M) or Cl (4-M); M = LaIII, NdIII, or SmIII] were prepared and structurally characterized for 4-La. Compounds 1-M initiated the ring-opening polymerization of ε-caprolactone. The best molecular weight control (suppression of chain transfer) for all three monomers was found for the samarium system 1-Sm. The most effective heterotactic enrichment (Pr) in the polymerization of rac-lactide was found for 1-Y (Pr = 87%). Compound 1-Nd catalyzed the block copolymerization of ε-caprolactone and l- and rac-lactide provided that ε-caprolactone was added first. Attempted block polymerization by the addition of l-lactide first, or random copolymerization of a ca. 1:1 mixture of ε-caprolactone and l-lactide, gave only a poly(l-lactide) homopolymer

Lanthanide Borohydride Complexes Supported by Diaminobis(phenoxide) Ligands for the Polymerization of ε-Caprolactone and l- and <i>r</i><i>ac</i>-Lactide

Reaction of Na2O2NN‘ [H2O2NN‘ = (2-C5H4N)CH2N{2-HO-3,5-C6H2tBu2}2] with M(BH4)3(THF)3 afforded the dimeric, rare-earth borohydride compounds [M(O2NN‘)(μ-BH4)(THF)n]2 [M = YIII, n = 0.5 (1-Y); M = NdIII, n = 1 (1-Nd); M = SmIII, n = 0 (1-Sm)]. For comparison the chloride analogues [M(O2NN‘)(μ-Cl)(THF)n]2 (2-M; M = LaIII or SmIII, n = 0; M = NdIII, n = 1) and the corresponding pyridine adducts [M(O2NN‘)(μ-X)(py)]2 [X = BH4 (3-M) or Cl (4-M); M = LaIII, NdIII, or SmIII] were prepared and structurally characterized for 4-La. Compounds 1-M initiated the ring-opening polymerization of ε-caprolactone. The best molecular weight control (suppression of chain transfer) for all three monomers was found for the samarium system 1-Sm. The most effective heterotactic enrichment (Pr) in the polymerization of rac-lactide was found for 1-Y (Pr = 87%). Compound 1-Nd catalyzed the block copolymerization of ε-caprolactone and l- and rac-lactide provided that ε-caprolactone was added first. Attempted block polymerization by the addition of l-lactide first, or random copolymerization of a ca. 1:1 mixture of ε-caprolactone and l-lactide, gave only a poly(l-lactide) homopolymer

Contracted and Expanded <i>meso</i>-Alkynyl Porphyrinoids: from Triphyrin to Hexaphyrin

The boron trifluoride-catalyzed Rothemund condensation of triisopropylsilyl (TIPS) propynal 1 with 3,4-diethylpyrrole in dichloromethane, followed by oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) generates a mixture of products, including [15]triphyrin(1.1.3) H3, corrole H34, porphyrin H22, [24]pentaphyrin(1.1.1.1.1) H45, [28]hexaphyrin(1.1.1.1.1.1) H46, and two linear tripyrromethenes H27 and H28. We report the spectroscopic characteristics of these unusual chromophores, together with the crystal structures of triphyrin H3 (and its zinc complex ZnCl3), porphyrin H22 (and its metal complexes Zn2, Ni2 and Pt2), hexaphyrin H46, and tripyrromethene nickel(II) complex Ni7. When the condensation is catalyzed with trifluoroacetic acid, rather than boron trifluoride, the triphyrin H3 become the main product (26% yield). This novel macrocycle is linked with a TIPS-substituted exocyclic double bond. This CC bond makes an η2-interaction with the zinc center in ZnCl3 with C−Zn distances of 2.863 and 3.025 Å. The porphyrin H22 is severely ruffled, and its absorption spectrum is red-shifted and broadened compared with the analogous compound without ethyl substituents. The hexaphyrin H46 adopts a figure-of-eight conformation with virtual C2 symmetry in the solid state and C2 symmetry in solution on the NMR time scale. Oxidation with DDQ appears to convert this nonaromatic [28]hexaphyrin into an aromatic [26]hexaphyrin with a strongly red-shifted absorption spectrum, but the oxidized macrocyle is too unstable to isolate

A Mono-Diazenide Complex from Perrhenate: Toward a New Core for Rhenium Radiopharmaceuticals

A new method for the synthesis of low to intermediate oxidation state rhenium complexes containing a bifunctional ligand has been developed. Reaction of [ReO4]- with substituted phenylhydrazines and triphenylphosphine in acetonitrile in the presence of HCl allows the isolation of [ReCl2(NNC6H4-4-R)(NCCH3)(PPh3)2] (where R = OCH3, Cl, or CO2CH3). The substituted hydrazine acts as both a reductant and source of a monodentate diazenide ligand. The compounds have all been characterized in the solid state by X-ray crystallography and in the solution state by NMR, electrospray mass spectrometry, and HPLC. Cyclic voltammetry measurements show that the mono-diazenide complexes undergo a reversible oxidation

Contracted and Expanded <i>meso</i>-Alkynyl Porphyrinoids: from Triphyrin to Hexaphyrin

The boron trifluoride-catalyzed Rothemund condensation of triisopropylsilyl (TIPS) propynal 1 with 3,4-diethylpyrrole in dichloromethane, followed by oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) generates a mixture of products, including [15]triphyrin(1.1.3) H3, corrole H34, porphyrin H22, [24]pentaphyrin(1.1.1.1.1) H45, [28]hexaphyrin(1.1.1.1.1.1) H46, and two linear tripyrromethenes H27 and H28. We report the spectroscopic characteristics of these unusual chromophores, together with the crystal structures of triphyrin H3 (and its zinc complex ZnCl3), porphyrin H22 (and its metal complexes Zn2, Ni2 and Pt2), hexaphyrin H46, and tripyrromethene nickel(II) complex Ni7. When the condensation is catalyzed with trifluoroacetic acid, rather than boron trifluoride, the triphyrin H3 become the main product (26% yield). This novel macrocycle is linked with a TIPS-substituted exocyclic double bond. This CC bond makes an η2-interaction with the zinc center in ZnCl3 with C−Zn distances of 2.863 and 3.025 Å. The porphyrin H22 is severely ruffled, and its absorption spectrum is red-shifted and broadened compared with the analogous compound without ethyl substituents. The hexaphyrin H46 adopts a figure-of-eight conformation with virtual C2 symmetry in the solid state and C2 symmetry in solution on the NMR time scale. Oxidation with DDQ appears to convert this nonaromatic [28]hexaphyrin into an aromatic [26]hexaphyrin with a strongly red-shifted absorption spectrum, but the oxidized macrocyle is too unstable to isolate

A Mono-Diazenide Complex from Perrhenate: Toward a New Core for Rhenium Radiopharmaceuticals

A new method for the synthesis of low to intermediate oxidation state rhenium complexes containing a bifunctional ligand has been developed. Reaction of [ReO4]- with substituted phenylhydrazines and triphenylphosphine in acetonitrile in the presence of HCl allows the isolation of [ReCl2(NNC6H4-4-R)(NCCH3)(PPh3)2] (where R = OCH3, Cl, or CO2CH3). The substituted hydrazine acts as both a reductant and source of a monodentate diazenide ligand. The compounds have all been characterized in the solid state by X-ray crystallography and in the solution state by NMR, electrospray mass spectrometry, and HPLC. Cyclic voltammetry measurements show that the mono-diazenide complexes undergo a reversible oxidation

Bending, Twisting, and Breaking CuCN Chains to Produce Framework Materials: The Reactions of CuCN with Alkali-Metal Halides^†

The reactions of the low-temperature polymorph of copper(I) cyanide (LT-CuCN) with concentrated aqueous alkali-metal halide solutions have been investigated. At room temperature, KX (X = Br and I) and CsX (X = Cl, Br, and I) produce the addition products K[Cu2(CN)2Br]·H2O (I), K3[Cu6(CN)6I3]·2H2O (II), Cs[Cu3(CN)3Cl] (III), Cs[Cu3(CN)3Br] (IV), and Cs2[Cu4(CN)4I2]·H2O (V), with 3-D frameworks in which the −(CuCN)− chains present in CuCN persist. No reaction occurs, however, with NaX (X = Cl, Br, I) or KCl. The addition compounds, I−V, reconvert to CuCN when washed. Both low- and high-temperature polymorphs of CuCN (LT- and HT-CuCN) are produced, except in the case of Cs[Cu3(CN)3Cl] (III), which converts only to LT-CuCN. Heating similar AX−CuCN reaction mixtures under hydrothermal conditions at 453 K for 1 day produces single crystals of I−V suitable for structure determination. Under these more forcing conditions, reactions also occur with NaX (X = Cl, Br, I) and KCl. NaBr and KCl cause some conversion of LT-CuCN into HT-CuCN, while NaCl and NaI, respectively, react to form the mixed-valence Cu(I)/Cu(II) compounds [CuII(OH2)4][CuI4(CN)6], a known phase, and [CuII(OH2)4][CuI4(CN)4I2] (VI), a 3-D framework, which contains infinite −(CuCN)− chains. After 3 days of heating under hydrothermal conditions, the reaction between KI and CuCN produces [CuII(OH2)4][CuI2(CN)I2]2 (VII), in which the CuCN chains are broken into single Cu−CN−Cu units, which in turn are linked into chains via iodine atoms and then into layers via long Cu−C and Cu−Cu interactions

Copper Complexes of Thiosemicarbazone−Pyridylhydrazine (THYNIC) Hybrid Ligands: A New Versatile Potential Bifunctional Chelator for Copper Radiopharmaceuticals

Two new thiosemicarbazone−pyridylhydrazine (THYNIC) hybrid ligands have been synthesized. Copper(II) and copper(I) complexes of the ligands have been prepared and characterized by X-ray crystallography. Cyclic voltammetry measurements show that the copper(II) complexes undergo quasi-reversible reductions at biologically accessible potentials. One of the ligands, bearing a pendant carboxylate arm, has been conjugated to N-α-(tert-butoxycarbonyl)-l-lysine

Synthesis and Characterization of a Bimetallic Boratabenzene Cobalt Complex

Reaction of 1,4-(BBr2)2C6H4 with cobaltocene gives a bimetallic cobalt complex with cyclopentadienyl and boratabenzene ligands. Oxidation allows the dicationic dicobalt(III) complex to be isolated; the bis(hexafluorophosphate) salt has been structurally characterized. Variable-temperature magnetic susceptibility measurements on the neutral dicobalt(II) complex showed substantial deviation from the Curie−Weiss law; a fit to the Bleaney−Bowers equation for a singlet ground state and a triplet excited state gave an exchange interaction of J = ca. −28 cm-1. Electrochemical studies, as well as near-infrared data on the mixed-valence species, suggest that the interaction between the metal centers is weak