Pseudocryptand-Type [3]Pseudorotaxane and “Hook-Ring” Polypseudo[2]catenane Based on a Bis(<i>m</i>-phenylene)-32-crown-10 Derivative and Bisparaquat Derivatives

The first pseudocryptand-type supramolecular [3]pseudorotaxane was designed and prepared via the self-assembly of a bispicolinate BMP32C10 derivative and a bisparaquat. The complexation behavior was cooperative. In addition, the complex comprised of the BMP32C10 derivative and a cyclic bisparaquat demonstrated strong binding; interestingly, a poly[2]pseudocatenane structure was formed in the solid state for the first time

TCNE Dimer Dianion Coordination Complexes, [Mn(TPA)(TCNE)]₂[μ₂-(TCNE)₂] and [Mn(TPA)(μ₄-C₄(CN)₈)_0.5]·ClO₄, TPA = tris(2-Pyridylmethyl)amine: Synthesis, Structure and Magnetic Properties

The structures and magnetic properties of two products that result from the reactions of [Mn(TPA)(CH3CN)2](ClO4)2, TPA = tris(2-pyridylmethyl)amine and potassium tetracyanoethylenide, KTCNE, are reported. [Mn(TPA)(TCNE)]2[μ2-(TCNE)2] (1) and [Mn(TPA)(μ4-C4(CN)8)0.5]·ClO4 (2) are obtained by using two different ratios of the initial reactants. Each was intended to possess two or more cis-TCNE radical anions (TCNE•/-) as ligands. 1 is a dinuclear species that crystallizes in the triclinic system in the space group P1̄, with a = 10.4432(17), b = 12.2726(16), and c = 13.708(2) Å; α = 88.505(12), β = 75.560(14), and γ = 87.077(12)°; V = 1698.9(4) Å3; and Z = 1 and features two metal centers each with three nearly orthogonal TCNE•/- ligands. However, the three TCNE•/- ligands are all dimerized via the formation of four-center, two-electron bonds:  two bridge the two Mn(II) centers, and a third TCNE•/- ligand forms an intermolecular bond to another equivalent TCNE•/-. 2 crystallizes in the tetragonal system in the space group P42212, with a = 17.170(3), b = 17.170(3), and c = 17.1837(6) Å; V = 5065.9(13) Å3; and Z = 8. It consists of a ribbon-like coordination polymer containing the previously observed but still relatively rare octacyanobutyl dianion. The [C4(CN)8]2- anion is derived from the dimerization of two TCNE radical anions via the formation of a new σ bond, and each anion bridges four Mn(II) centers. Both 1 and 2 display magnetic behavior consistent with only weak antiferromagnetic coupling between the high-spin d5 Mn(II) in which the TCNE•/- are rendered diamagnetic through dimerization

Facile Supramolecular Engineering of Porphyrin cis Tautomers: The Case of β‑Octabromo-<i>meso</i>-tetraarylporphyrins

A porphyrin cis tautomer, where the two central NH protons are on adjacent pyrrole rings, has long been invoked as an intermediate in porphyrin tautomerism. Only recently, however, has such a species been isolated and structurally characterized. Thus, single-crystal X-ray structure determinations of two highly saddled free-base porphyrins, β-heptakis­(trifluoromethyl)-meso-tetrakis­(p-fluorophenyl)­porphyrin, H2[(CF3)7TFPP], and β-octaiodo-5,10,15,20-tetrakis­(4′-trifluoromethylphenyl)­porphyrin, H2[I8TCF3PP], unambiguously revealed cis tautomeric structures, each stabilized as a termolecular complex with a pair of ROH (R = CH3 or H) molecules that form hydrogen-bonded N–H···O–H···N straps connecting the central NH groups with the antipodal unprotonated nitrogens. The unusual substitution patterns of these two porphyrins, however, have left open the question how readily such supramolecular assemblies might be engineered, which prompted us to examine the much more synthetically accessible β-octabromo-meso-tetraphenylporphyrins. Herein, single-crystal X-ray structures were obtained for two such compounds, 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis­(4′-trifluoromethylphenyl)­porphyrin, H2[Br8TCF3PP], and 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis­(4′-fluorophenyl)­porphyrin, H2[Br8TFPP], and although the central hydrogens could not all be located unambiguously, the electron density could be convincingly modeled as porphyrin cis tautomers, existing in each case as a bis-methanol adduct. In addition, a perusal of the Cambridge Structural Database suggests that there may well be additional examples of porphyrin cis tautomers that have not been recognized as such. We are therefore increasingly confident that porphyrin cis tautomers are readily accessible via supramolecular engineering, involving the simple stratagem of crystallizing a strongly saddled porphyrin from a solvent system containing an amphiprotic species such as water or an alcohol

Structural Characterization of OC₃OPor Capped Porphyrins: H₂(OC₃OPor), Fe(OC₃OPor)(Cl), Fe(OC₃OPor)(CO)(1-MeIm), and Fe(OC₃OPor)(CO)(1,2-Me₂Im)

The sterically encumbered OC3OPor system consists of a 1,2,4,5-substituted benzene cap with five-atom arms of the type −O(CH2)3O− linking the benzene cap to the ortho positions of 5,10,15,20-tetraphenylporphyrin. The structures of the following compounds have been determined by single-crystal X-ray diffraction methods:  H2(OC3OPor) (1), Fe(OC3OPor)(Cl) (2), Fe(OC3OPor)(CO)(1-MeIm) (3), and Fe(OC3OPor)(CO)(1,2-Me2Im) (4). Structures 1−3 pack as one crystallographically independent porphyrin with solvate molecules, whereas structure 4 packs with half of a crystallographically independent porphyrin molecule and a solvate molecule. In compound 2 the Cl ligand is bound to the Fe center on the unprotected side of the porphyrin. In 3 and 4, which represent R-state (relaxed) and T-state (tense) models for hemoglobin, respectively, CO is bound underneath the cap and either 1-MeIm (3) or 1,2-Me2Im (4) is bound to the sixth coordination site, opposite the CO and outside the cap. The bulkier 1,2-Me2Im in 4 forces the Fe atom 0.10 Å out of the mean nitrogen plane toward the 1,2-Me2Im ligand. In 3, where the base is less bulky, the Fe atom lies 0.06 Å out of the plane toward the CO ligand. The cap-to-porphyrin distance increases approximately 0.8 Å to accommodate CO, from 4.74 and 4.65 Å in 1 and 2, respectively, to 5.55 and 5.59 Å in 3 and 4, respectively. The Fe−C−O angle is 173.9(7)° in 3 and is constrained by symmetry to be 180° in 4

Facile Supramolecular Engineering of Porphyrin cis Tautomers: The Case of β‑Octabromo-<i>meso</i>-tetraarylporphyrins

A porphyrin cis tautomer, where the two central NH protons are on adjacent pyrrole rings, has long been invoked as an intermediate in porphyrin tautomerism. Only recently, however, has such a species been isolated and structurally characterized. Thus, single-crystal X-ray structure determinations of two highly saddled free-base porphyrins, β-heptakis­(trifluoromethyl)-meso-tetrakis­(p-fluorophenyl)­porphyrin, H2[(CF3)7TFPP], and β-octaiodo-5,10,15,20-tetrakis­(4′-trifluoromethylphenyl)­porphyrin, H2[I8TCF3PP], unambiguously revealed cis tautomeric structures, each stabilized as a termolecular complex with a pair of ROH (R = CH3 or H) molecules that form hydrogen-bonded N–H···O–H···N straps connecting the central NH groups with the antipodal unprotonated nitrogens. The unusual substitution patterns of these two porphyrins, however, have left open the question how readily such supramolecular assemblies might be engineered, which prompted us to examine the much more synthetically accessible β-octabromo-meso-tetraphenylporphyrins. Herein, single-crystal X-ray structures were obtained for two such compounds, 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis­(4′-trifluoromethylphenyl)­porphyrin, H2[Br8TCF3PP], and 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis­(4′-fluorophenyl)­porphyrin, H2[Br8TFPP], and although the central hydrogens could not all be located unambiguously, the electron density could be convincingly modeled as porphyrin cis tautomers, existing in each case as a bis-methanol adduct. In addition, a perusal of the Cambridge Structural Database suggests that there may well be additional examples of porphyrin cis tautomers that have not been recognized as such. We are therefore increasingly confident that porphyrin cis tautomers are readily accessible via supramolecular engineering, involving the simple stratagem of crystallizing a strongly saddled porphyrin from a solvent system containing an amphiprotic species such as water or an alcohol

TCNE Dimer Dianion Coordination Complexes, [Mn(TPA)(TCNE)]₂[μ₂-(TCNE)₂] and [Mn(TPA)(μ₄-C₄(CN)₈)_0.5]·ClO₄, TPA = tris(2-Pyridylmethyl)amine: Synthesis, Structure and Magnetic Properties

The structures and magnetic properties of two products that result from the reactions of [Mn(TPA)(CH3CN)2](ClO4)2, TPA = tris(2-pyridylmethyl)amine and potassium tetracyanoethylenide, KTCNE, are reported. [Mn(TPA)(TCNE)]2[μ2-(TCNE)2] (1) and [Mn(TPA)(μ4-C4(CN)8)0.5]·ClO4 (2) are obtained by using two different ratios of the initial reactants. Each was intended to possess two or more cis-TCNE radical anions (TCNE•/-) as ligands. 1 is a dinuclear species that crystallizes in the triclinic system in the space group P1̄, with a = 10.4432(17), b = 12.2726(16), and c = 13.708(2) Å; α = 88.505(12), β = 75.560(14), and γ = 87.077(12)°; V = 1698.9(4) Å3; and Z = 1 and features two metal centers each with three nearly orthogonal TCNE•/- ligands. However, the three TCNE•/- ligands are all dimerized via the formation of four-center, two-electron bonds:  two bridge the two Mn(II) centers, and a third TCNE•/- ligand forms an intermolecular bond to another equivalent TCNE•/-. 2 crystallizes in the tetragonal system in the space group P42212, with a = 17.170(3), b = 17.170(3), and c = 17.1837(6) Å; V = 5065.9(13) Å3; and Z = 8. It consists of a ribbon-like coordination polymer containing the previously observed but still relatively rare octacyanobutyl dianion. The [C4(CN)8]2- anion is derived from the dimerization of two TCNE radical anions via the formation of a new σ bond, and each anion bridges four Mn(II) centers. Both 1 and 2 display magnetic behavior consistent with only weak antiferromagnetic coupling between the high-spin d5 Mn(II) in which the TCNE•/- are rendered diamagnetic through dimerization

Structural Characterization of OC₃OPor Capped Porphyrins: H₂(OC₃OPor), Fe(OC₃OPor)(Cl), Fe(OC₃OPor)(CO)(1-MeIm), and Fe(OC₃OPor)(CO)(1,2-Me₂Im)

The sterically encumbered OC3OPor system consists of a 1,2,4,5-substituted benzene cap with five-atom arms of the type −O(CH2)3O− linking the benzene cap to the ortho positions of 5,10,15,20-tetraphenylporphyrin. The structures of the following compounds have been determined by single-crystal X-ray diffraction methods:  H2(OC3OPor) (1), Fe(OC3OPor)(Cl) (2), Fe(OC3OPor)(CO)(1-MeIm) (3), and Fe(OC3OPor)(CO)(1,2-Me2Im) (4). Structures 1−3 pack as one crystallographically independent porphyrin with solvate molecules, whereas structure 4 packs with half of a crystallographically independent porphyrin molecule and a solvate molecule. In compound 2 the Cl ligand is bound to the Fe center on the unprotected side of the porphyrin. In 3 and 4, which represent R-state (relaxed) and T-state (tense) models for hemoglobin, respectively, CO is bound underneath the cap and either 1-MeIm (3) or 1,2-Me2Im (4) is bound to the sixth coordination site, opposite the CO and outside the cap. The bulkier 1,2-Me2Im in 4 forces the Fe atom 0.10 Å out of the mean nitrogen plane toward the 1,2-Me2Im ligand. In 3, where the base is less bulky, the Fe atom lies 0.06 Å out of the plane toward the CO ligand. The cap-to-porphyrin distance increases approximately 0.8 Å to accommodate CO, from 4.74 and 4.65 Å in 1 and 2, respectively, to 5.55 and 5.59 Å in 3 and 4, respectively. The Fe−C−O angle is 173.9(7)° in 3 and is constrained by symmetry to be 180° in 4

Exploring the Formation of Copper–Ruthenium Bimetallic Complexes in Olefin Metathesis

Copper(I) halides are often added to olefin metathesis reactions to inhibit catalyst degradation, control product isomerization, enhance catalyst activation, or facilitate catalyst dimerization. In each of these examples, the copper salt is presumed to operate as an independent species separate from the ruthenium center. We have discovered, however, that certain copper salts can form complexes with the ruthenium catalyst itself, forming heterobimetallic copper–ruthenium olefin metathesis catalysts. We confirmed the formation of two complexes through single-crystal X-ray crystallography and NMR spectroscopy. The crystal structure revealed the presence of a four-membered ring containing ruthenium, carbon, copper, and chlorine or bromine. The heterobimetallic catalyst displayed higher latency and lower activity in ring-opening metathesis polymerization (ROMP) of norbornene compared to analogous monometallic catalysts. For example, norbornene polymerization catalyzed by the monometallic complex reached 80% conversion after 4 h but only 12% conversion when catalyzed by the heterobimetallic copper–ruthenium complex under the same conditions. Conversion increased to 63% when the temperature increased to 50 °C for 1 h, indicating that the bimetallic complex retains activity but requires a higher temperature to activate. The formation of these copper–ruthenium bimetallic complexes suggests the possibility of multimetallic olefin metathesis catalysts, potentially with different activity and properties than their traditional monometallic counterparts

Pseudocryptand-Type [3]Pseudorotaxane and “Hook-Ring” Polypseudo[2]catenane Based on a Bis(<i>m</i>-phenylene)-32-crown-10 Derivative and Bisparaquat Derivatives

The first pseudocryptand-type supramolecular [3]pseudorotaxane was designed and prepared via the self-assembly of a bispicolinate BMP32C10 derivative and a bisparaquat. The complexation behavior was cooperative. In addition, the complex comprised of the BMP32C10 derivative and a cyclic bisparaquat demonstrated strong binding; interestingly, a poly[2]pseudocatenane structure was formed in the solid state for the first time

Pseudocryptand-Type [3]Pseudorotaxane and “Hook-Ring” Polypseudo[2]catenane Based on a Bis(<i>m</i>-phenylene)-32-crown-10 Derivative and Bisparaquat Derivatives

The first pseudocryptand-type supramolecular [3]pseudorotaxane was designed and prepared via the self-assembly of a bispicolinate BMP32C10 derivative and a bisparaquat. The complexation behavior was cooperative. In addition, the complex comprised of the BMP32C10 derivative and a cyclic bisparaquat demonstrated strong binding; interestingly, a poly[2]pseudocatenane structure was formed in the solid state for the first time