Gregory M. Ferrence

Controllable Formation of Heterotrimetallic Coordination Compounds: Systematically Incorporating Lanthanide and Alkali Metal Ions into the Manganese 12-Metallacrown-4 Framework

The inclusion of Ln(III) ions into the 12-MC-4 framework generates the first heterotrimetallic complexes of this molecular class. The controllable and deliberate preparations of these compounds are demonstrated through 12 crystal structures of the Ln(III)M(I)(OAc)4[12-MCMn(III)(N)shi-4](H2O)4·6DMF complex, where OAc(-) is acetate, shi(3-) is salicylhydroximate, and DMF is N,N-dimethylformamide. Compounds 1-12 have M(I) as Na(I), and Ln(III) can be Pr(III) (1), Nd(III) (2), Sm(III) (3), Eu(III) (4), Gd(III) (5), Tb(III) (6), Dy(III) (7), Ho(III) (8), Er(III) (9), Tm(III) (10), Yb(III) (11), and Y(III) (12). An example with M(I) = K(I) and Ln(III) = Dy(III) is also reported (Dy(III)K(OAc)4[12-MCMn(III)(N)shi-4](DMF)4·DMF (14)). When La(III), Ce(III), or Lu(III) is used as the Ln(III) ions to prepare the Ln(III)Na(I)(OAc)4[12-MCMn(III)(N)shi-4] complex, the compound Na2(OAc)2[12-MCMn(III)(N)shi-4](DMF)6·2DMF·1.60H2O (13) results. For compounds 1-12, the identity of the Ln(III) ion affects the 12-MCMn(III)(N)shi-4 framework as the largest Ln(III), Pr(III), causes an expansion of the 12-MCMn(III)(N)shi-4 framework as demonstrated by the largest metallacrown cavity radius (0.58 Å for 1 to 0.54 Å for 11), and the Pr(III) causes the 12-MCMn(III)(N)shi-4 framework to be the most domed structure as evident in the largest average angle about the axial coordination of the ring Mn(III) ions (103.95° for 1 to 101.69° for 11). For 14, the substitution of K(I) for Na(I) does not significantly affect the 12-MCMn(III)(N)shi-4 framework as many of the structural parameters such as the metallacrown cavity radius (0.56 Å) fall within the range of compounds 1-12. However, the use of the larger K(I) ion does cause the 12-MCMn(III)(N)shi-4 framework to become more planar as evident in a smaller average angle about the axial coordination of the ring Mn(III) ions (101.35°) compared to the analogous Dy(III)/Na(I) (7) complex (102.40°). In addition to broadening the range of structures available through the metallacrown analogy, these complexes allow for the mixing and matching of a diverse range of metals that might permit the fine-tuning of molecular properties where one day they may be exploited as magnetic materials or luminescent agents.

Synthesis and characterization of tetraphenyl-21,23-dideazaporphyrin: the best evidence yet that porphyrins really are the [18]annulenes of nature.

McMurry coupling of a pyrrole bisacrylaldehyde afforded a dipyrrolic macrocycle that is structurally midway between 1,10-diaza[18]annulene and the porphyrins. The diprotonated dication of this system retains porphyrin-like properties and provides insights into the nature of porphyrinoid aromaticity.

adj-Diazuliporphyrins, a new family of dicarbaporphyrinoids with unprecedented mesoionic characteristics.

A diazulenylmethane dialdehyde reacted with dipyrrylmethanes in the presence of HCl or HBr, followed by oxidation with FeCl(3), to give aromatic adj-diazuliporphyrins. The free base structures must exist as mesoionic species, although these porphyrinoids were isolated as salts of the monoprotonated macrocycles. Reaction with Pd(OAc)(2) gave an unprecedented zwitterionic palladium(II) complex that was characterized by X-ray crystallography.

[(Tpt-Bu, Me)Yb(μ-H)]2: a fecund precursor to a host of divalent, hydrotris(pyrazolyl)borate supported f-element complexes

Abstract We present an overview of recent work from our laboratories on the chemistry of the divalent lanthanide hydride [(Tp t -Bu,Me )Yb(μ-H)] 2 ( 1 ). The first section deals with the hydrotris(3- tert -butyl, 5-methyl-pyrazolyl)borate, (Tp t -Bu,Me ), ligated divalent lanthanide complexes leading up to the discovery of 1 . The remaining sections are centered on the divalent ytterbium hydride [(Tp t -Bu,Me )Yb(μ-H)] 2 ( 1 ), its preparation, molecular structure, NMR characteristics and reactivity. Three broad reactivity classes will be described, namely reactions with Lewis bases and Lewis acids, such as the perfluoroaryl boranes, σ-bond metathesis reactions generally involving acidic H X bonds, but also an example of C Si bond cleavage, and insertion chemistry, primarily involving alkynes. The molecular structures of several representative complexes have been determined by X-ray crystallography.

X-Ray crystallographic and 13C nuclear magnetic resonance studies of 3,4,5,6-tetrahydro-2H-1,3,4-oxadiazin-2-ones derived from ephedrine and pseudoephedrine ☆

Abstract 3,4,5,6-Tetrahydro-2H-1,3,4-oxadiazin-2-ones derived from (1R,2S)-ephedrine and (1S,2S)-pseudoephedrine have been synthesized and their conformational properties have been examined. The ephedrine heterocycles 5–7a appear to favor one set of equilibrating conformers while the pseudoephedrine heterocycles 5–7b exist as multiple conformers at room temperature. The observed conformational behavior of these heterocycles is attributed to allylic strain and a gauche effect arising from the torsional energy barrier between the lone pair electrons of the N3- and N4-nitrogens.

Porphyrin on a half-shell! Synthesis and characterization of corannulenoporphyrins.

An efficient synthetic method for preparing corannulenoporphyrins is described. Nitrocorannulene was reacted with ethyl isocyanoacetate in the presence of a phosphazene base to generate the pivotal corannulenopyrrole intermediate. Following cleavage of the ethyl ester moiety with KOH in ethylene glycol at 180-190 degrees C, the heptacyclic system was reacted with acetoxymethylpyrroles under mildly acidic conditions to afford tripyrranes. The proton NMR spectra for these tripyrrolic intermediates suggest that they can take on helical geometries, but the conformations are dependent on the nature of the terminal ester groupings and may be altered by solvent interactions. Treatment of a di-tert-butyl ester tripyrrane with TFA cleaved the protective groups, and subsequent condensation with diformylpyrroles in TFA-CH(2)Cl(2), followed by oxidation with DDQ or ferric chloride, gave excellent yields of corannulenoporphyrins. Nickel(II), copper(II), and zinc complexes of this system were also prepared, and the nickel derivative was also further characterized by X-ray crystallography. The same synthetic strategy was also used to prepare a porphyrin with fused acenaphthylene and corannulene subunits. The fused bowl-shaped corannulene provides these porphyrins with a unique structural component that increases solubility by reducing pi-pi stacking interactions.

Preparation of furan and thiophene-derived fulvene dialdehydes: synthesis and structural characterization of a 22-oxa-21-carbaporphyrin and a related palladium(II) organometallic complex.

A series of fulvene monoaldehydes were prepared by reacting furan or thiophene carbaldehydes with an indene-derived enamine in the presence of di-n-butylboron triflate, but considerable difficulties were encountered in the preparation of fulvene dialdehydes needed for the synthesis of novel porphyrin analogues. These problems were overcome by reacting protected iodofulvenes with magnesium ate complexes at low temperatures, followed by addition of DMF and hydrolysis. The thiophene-containing fulvene gave good yields of the dialdehyde at -78 °C or -100 °C, but the furan system gave a major byproduct formally derived from valeraldehyde under the higher temperature conditions. This compound was fully characterized by NMR spectroscopy, mass spectrometry, and X-ray crystallography. However, this side reaction could be completely avoided at -100 °C, and the required furan-containing fulvene dialdehyde was isolated in 46% yield. The furan-derived dialdehyde reacted with a dipyrrylmethane in the presence of trifluoroacetic acid to give the 22-oxa-21-carbaporphyrin 19 in excellent yields (73-79%). However, the thiophene-containing fulvene dialdehyde failed to give any of the anticipated macrocyclic product. An unstable acyclic intermediate was isolated and partially characterized, but this species could not be induced to cyclize. Steric factors may play a role, but X-ray crystallography confirmed that the fulvene dialdehyde precursor does have the correct geometry to facilitate the formation of the porphyrinoid macrocycle. The new oxacarbaporphyrin was fully characterized and could easily be converted into the corresponding mono- and dicationic species. The second protonation involves addition onto the internal indene carbon and proton NMR spectroscopy for the sample in HCl-TFA demonstrates that it retains strongly diatropic characteristics. The free base oxacarbaporphyrin reacted with Pd(OAc)(2) in DMF to give the corresponding palladium(II) organometallic derivative 27. The proton NMR spectrum for this complex also shows the retention of a strong, albeit slightly reduced, diatropic ring current. The free base oxacarbaporphyrin and the palladium derivative were both structurally characterized by X-ray crystallography. The bond lengths for 19 and 27 were consistent with the presence of significant 18π-electron delocalization pathways.

Synthesis of an adj-dicarbaporphyrin and the formation of an unprecedented tripalladium sandwich complex.

An adj-dicarbaporphyrin was prepared by carrying out a base-catalyzed MacDonald reaction between bis(3-indenyl)methane and a dipyrrylmethane dialdehyde. The porphyrinoid system exhibited highly diatropic characteristics, and the proton NMR spectrum gave resonances at -5.74 and -6.24 ppm for the internal NH and CH protons, respectively. The UV-vis spectrum was also porphyrin-like, giving a Soret band at 455 nm and a series of Q bands at longer wavelengths. Addition of trifluoroacetic acid gave a C-protonated monocation, and at higher acid concentrations a dicationic species was observed. Addition of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) afforded a monodeprotonated porphyrinoid anion. All of these species retained highly diatropic characteristics. Density functional theory calculations showed that a nonplanar tautomer with four internal hydrogens was favored, in agreement with the spectroscopic data. Nucleus-independent chemical shift calculations also confirmed the aromatic characteristics of the free-base, cationic, and anionic structures. The dicarbaporphyrin reacted with palladium(II) acetate in refluxing acetonitrile to give an unusual tripalladium sandwich complex consisting of two dianionic palladium(II) dicarbaporphyrin units surrounding a palladium(IV) cation with unique η(5) interactions involving meso-carbon atoms.

Synthesis of a series of aromatic benziporphyrins and heteroanalogues via tripyrrane-like intermediates derived from resorcinol and 2-methylresorcinol.

Tripyrrane analogues were prepared by reacting resorcinol or 2-methylresorcinol with 2 equiv of an acetoxymethylpyrrole in the presence of p-toluenesulfonic acid and calcium chloride. Following removal of the benzyl ester protective groups, the resorcinol-derived benzitripyrrane was reacted with a pyrrole dialdehyde to give an aromatic hydroxyoxybenziporphyrin. However, furan and thiophene dialdehydes gave highly insoluble products that could not be fully characterized. The methylresorcinol-derived tripyrrane analogue reacted with pyrrole, furan, thiophene, and selenophene dialdehydes to give unstable porphyrinoids that were further oxidized with [bis(trifluoroacetoxy)iodo]benzene to give stable benziporphyrin derivatives. These oxidized benziporphyrins showed strongly diatropic properties by proton NMR spectroscopy where the differences in chemical shifts (Δδ) were >18 ppm in some cases. The selenophene-derived system was further characterized by X-ray crystallography, and these results showed that one of the pyrrole subunits in this crowded structure was tilted by 21° relative to the mean macrocyclic plane. The tripyrrolic system reacted with silver(I) acetate to give the corresponding silver(III) organometallic complex. Regioselective alkylation with methyl or ethyl iodide and potassium carbonate gave diastereomeric mixtures of N-alkyl derivatives, and the N-ethyl substitution products showed highly diastereotopic characteristics.

Synthesis of benziporphyrins and heterobenziporphyrins and an assessment of the diatropic characteristics of the protonated species.

Benzitripyrranes were prepared by reacting diphenyl-substituted benzenedicarbinols with excess pyrrole in the presence of BF3·Et2O. These dipyrrolic compounds underwent acid-catalyzed condensations with a pyrrole dialdehyde to afford good yields of diphenylbenziporphyrins, and further reaction with palladium(II) acetate gave stable organometallic derivatives. The X-ray crystal structure of a palladium(II) benziporphyrin showed that the system deviates significantly from planarity. Although the benzitripyrranes failed to give stable macrocyclic products with furan or thiophene dialdehydes, they afforded tetraphenyl heterobenziporphyrins upon reaction with diphenyl-substituted furan- or thiophenedicarbinols and BF3·Et2O. Benziporphyrins and their heteroanalogues showed no indication of a diamagnetic ring current by proton NMR spectroscopy, but addition of TFA gave rise to the formation of weakly diatropic dications.