Marc Drouin

Fine tuning of the photophysical properties of cofacial diporphyrins via the use of different spacers

The crystal and molecular structures of two unmetallated diporphyrin species using the biphenylene and dibenzofuran spacers, H4(DPB) and H4(DPO), respectively (DPB 4 − =1,8-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]biphenylene; DPO 4 − =4,6-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]dibenzofuran), are reported. These data are compared to their literature metallated analogs, stressing on the properties related to the flexibility of the ligands, ··· and M···M interactions. In addition, the lowest energy fluorescence properties of these non-phosphorescent diporphyrin compounds as well as three other related species, H4(DPA), H4(DPX), and H4(DPS) (DPA 4 − = 1,8-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]anthracene; DPX 4 − =4,5-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]-9,9-dimethylxanthene; DPS 4− =4,6-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]dibenzothiophene), have been examined both at room temperature in 2-MeTHF in the presence of Ar, air and O2, and at 77 K. In all cases, the fluorescence arises from the 1 Q(*), and the photophysical data at 77 and 298 K under Ar atmosphere correlate readily with the molecular geometry of these pincer ligands, where the non-radiative rate constants increase as the interplanar distances decrease. In the presence of dioxygen in solution, both the fluorescence lifetimes and quantum yields decrease as expected for quenching, with the second-order rate constants for bimolecular deactivation (kQ) ranging from 0.9 × 10 10 to 1.7 × 10 10 s − 1 M − 1 . The H4(DPB) compound exhibits the lowest kQ indicating lesser ability for O2 to interact with the interior of the diporphyrin cavity.

Transannular Diels-Alder model studies on the total synthesis of chatancin. The furanophane approach. Part 2 [1]: Macrocyclization and Diels-Alder reaction

Abstract Title investigation of three generations of model substrates targeting chatancin is presented. An unfunctionalized furan affords a reversible transannular Diels-Alder reaction producing only the two TAC -frameworks where the expected one is the kinetic product. A furan 3-COOMe functionalization allows the selective formation of the expected isomer which is still favored even in the presence of a quasi-axial isopropyl group on the furanophane.

X-ray structures and luminescence properties of Co(II) and Co(III) complexes of cofacial diporphyrins

The crystal structures of two face-to-face diporphyrin compounds based upon the DPA ligand (1,8-bis(5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethyl-porphyrinyl))anthracene), i.e. H4(DPA) and (DPA)Co2 are reported. The structural data are compared to that of other bimetallic DPA systems, and diporphyrinic Co complexes. In addition, the luminescence properties of (OEP)Co (OEP = 2,3,7,8,12,13,17,18-octaethylporphyrin), H2(DPA)Co, H2(DPA)(CoIm)O2, (DPA)Co2, (DPA)(CoIm)2O2 are reported, where Im is 1-t-butyl-5-phenyl imidazole. Contrary to previous literature reports, the Co(II) species are found to be weakly luminescent, where fluorescence is detected for both the mono- and diporphyrinic systems, and is assigned to emissions arising from the lowest 1Q(ππ*) states, while phosphorescence is detected at 77 K only for the monoporphyrin species, (OEP)Co. On the other hand, the Co(III) complexes are not luminescent.

Solid-state structure determination and solution-state NMR characterization of the (2R,4R)/(2S,4S)- and (2R,4S)/(2S,4R)-diastereomers of the agricultural fungicide propiconazole, the (2R,4S)/(2S,4R)-symmetrical triazole constitutional isomer, and a ditriazole analogue

Single-crystal X-ray diffraction analysis was used to determine the structure of a racemic diastereomer of the agricultural fungicide propiconazole [1-(2-(2,4-dichlorophenyl)-4-n-propyl-1,3-dioxolane-2-yl-methyl)-1-H-1,2,4-triazole] and of two by-products (a symmetrical 1,3,4-triazole racemic-constitutional isomer and a propiconazole ditriazole analogue). All three crystalline racemic-diastereomers had (2R,4S)/(2S,4R)-stereochemistry in which then-propyl group was observed in atrans-to-phenyl disposition. Propiconazole (2R,4S)/(2S,4R)-diastereomer gives crystals belonging to the monoclinic space group P21,/a, and, at 293 K,a=8.1192(3),b=18.9769(6),c=10.7137(4) å,Β=99.765(3)ℴ,V=1626.8(1) å3, Z=4,R(F)=0.060, andRw(F)=0.058. The constitutional isomer by-product (2R,4S)/(2S,4R)-1-(2-(2,4-dichlorophenyl)-4-n-pro-pyl-1,3-dioxolane-2-yl-methyl)-1-H-1,3,4-triazole gives crystals belonging to the monoclinic space group P21/n, and, at 293 K,a=11.1763(6),b=10.7716(4),c=14.5804(8) å,Β=107.445(4)ℴ,V=1674.6(1) å3, Z=4,R(F)=0.043, andRw(F)=0.043. The ditriazole byproduct (2R,4S)/(2S,4R)-1-(2-(2-chloro-4-(1,2,4-triazole-1-yl)phenyl)-4-n-propyl-1,3-dioxolane-2-yl-methyl)-1-H-1,2,4-triazole gives crystals belonging to the triclinic space groupP¯ 1, and, at 193 K,a=5.3329(8),b=8.3738(7),c=20.240(2) å, α=84.213(6)ℴ,Β=87.20(1)ℴ,γ=86.23(1)ℴ,V=896.5(2) å3, Z=2,R(F)=0.046, andRw(F)=0.051. The presence of both propiconazole (2R.4S)- and (2S,4R)-enantiomers enables the formation of a crystalline racemic modification, while the diastereomeric propiconazole (2R,4R)- and (2S,4S)-enantiomers are viscous oils. In the absence of its enantiomorphic partner, the propiconazole (2R,4S)- or (2S,4R)-enantiomers remain as viscous oils rather than form chiral crystals.

Cis,trans-isomerization of the dibenzylideneacetone ligand: Intramolecular quenching effected by ferrocenyl group substitutions and coordination with Pd(0) and Pt(0)☆

Abstract The structural properties, UV—visible absorption and emission spectra and emission lifetimes of the dibenzylideneacetone ligand (dba), 4-ferrocenyldibenzylideneacetone (dba-Fc) and diferrocenylideneacetone (dFca) in solution and in the solid state are reported. The primary non-sensitized cis,trans-isomerization reactions of dba at 298 K in solution were investigated by 1 H nuclear magnetic resonance (NMR), UV—visible and Fourier transform IR spectroscopy. The photoinduced cis,trans-isomerization reaction exhibits a large photochemical quantum yield (Φ cis,trans = 0.85 ± 0.05) and is not affected by the presence of oxygen in solution. In contrast, dba-Fc, dFca and the M 2 (dba) 3 complexes (M  Pd, Pt) are photochemically inert, even under prolonged broad band irradiation (more than 48 h). An efficient intramolecular energy transfer quenching mechanism is proposed involving energy transfer from the upper intraligand excited states to the lower triplet ligand field states in the dba-Fc and dFca compounds and to the lower triplet metal-to-ligand charge transfer state in the M 2 (dba) 3 complex. Finally, the reported results on the delayed fluorescence of dba (τ e = 28.5 ± 2.0 μs) provide the lower energy limit for the non-luminescent triplet state of dba ( E T ≥ 13 880 cm −1 ).

Rigidified acetylcholine mimics: conformational requirements for binding to neuronal nicotinic receptors.

Rigidified derivatives have been designed and synthesized assuming the g+t conformer of acetylcholine (N-C-C-O=+60 degrees, C-C-O-C=180 degrees ) as active conformation for binding to cytisine sensitive neuronal nicotinic receptors. The SAR of the compounds evaluated, along with those of more flexible analogues, support the g+t conformer hypothesis and highlight the stringent steric limitation of this nicotinic receptor sub-type. Compound 3e has low microM affinity for cytisine sensitive nicotinic receptor binding sites while being selective with regard to the alpha-bungarotoxin sensitive subclass. We also report few compounds with microM affinity for the alpha-bungarotoxin sensitive subclass.

Solution- and solid-state stereochemistry of (–)-α-lobeline hydrochloride and hydrobromide, a respiratory-stimulant drug

The solid-state structure of (–)-α-lobeline hydrobromide has been determined by single crystal X-ray diffraction analysis. (–)-α-Lobeline hydrobromide gives crystals belonging to the orthorhombic P212121 space group, and at 298 K: a= 6.0100(3), b= 11.7177(4), c= 28.977(2)A, V= 2040.7(2), Z= 4, R(F)= 0.030, and Rw(F)= 0.022. The (2R,6S,CβS)-absolute configuration was determined from the effects of anomalous dispersion of the bromine atom. The N-methyl group exists in an axial configuration similar to that previously described for the hydrochloride salt. However, in the hydrobromide salt the β-hydroxyphenethyl residue exhibits a different conformation from that noted for the hydrochloride salt. 1H and 13C NMR spectroscopy for the hydrochloride salt dissolved in CD2Cl2 shows axial- and equatorial-N-methyl solution-state diastereoisomers in the ratio ca. 5 : 1, respectively. The major contributors to the time-averaged structures of the salt in D2O and the free base in CDCl3 also show axial N-methyl orientations. Conformational differences for the acetophenonyl and β-hydroxyphenethyl moieties were found in the two N-methyl epimers, as well as in the time-averaged salt (D2O) and free base (CDCl3) structures. The putative bioactive conformation of the nicotine agonist was found to have a different acetophenonyl arm conformation than that found in both crystals.

Characterization of a New Tetranuclear Cluster of Palladium, (Pd4(dppm)4(H))

The recently discovered and characterized [Pd4(dppm)4(H)]2+ cluster catalyst (1; dppm = Ph2PCH2PPh2), slowly evolves in the presence of the reducing tetraphenylborate anion, to generate a new diamagnetic cluster [Pd4(dppm)4(H)]+ (2). The evolution of this starting material 1, has been monitored using NMR (1H and 31P), UV-vis and ESR spectroscopy. This new 56-electron Pd cluster has been characterized from X-ray crystallography, and consists of a cyclic species exhibiting an approximate puckered square structure. The Pd2 bond distances are 2.7367(10) and 2.7495(11)A and indicate the presence of weak bonding. The diagonal Pd···Pd separations are 3.646(10) and 3.590(10)A indicating that the square is relatively symmetric. Such a structure is unprecedented for “Pdx(dppm)x” species. Although not formally observed from the X-ray data, the hydride is assumed to be fluxional as found in 1. The cyclic voltammogram for 2 exhibits an irreversible reduction wave at —1.65V vs SCE which is greater than that found for 1, and corroborates the lower oxidation state for Pd (+1/2). The Pd-H bonding scheme and MO symmetry for a model cluster where the hydride has been placed at the center of the Pd4 frame, have been addressed qualitatively using the EHMO model. These calculations demonstrate clearly that the Pd-H bonding is strong. Charakterisierung eines neue tetranuklearen Clusters von Palladium, [Pd4(dppm)4(H)]— Der kurzlich als Katalysator beschriebene und strukturell charakterisierte Pd4(dppm)4(H)22+ Cluster (1, dppm = Ph2PCH2PPh2) wandelt sich in Gegenwart des reduzierenden Tetraphenylboratanions langsam in die neue diamagnetische Clusterspezies [Pd4(dppm)4(H)]+ (2) um. Die schrittweise Veranderung von 1 wird durch 1H und 31P-NMR sowie durch UV-VIS und ESR-Spektroskopie verfolgt. Den Ergenissen der Rontgenstrukturanalyse zufolge besteht der neue 56-Elektronen Pd4-Cluster aus einer zyklischen Einheit mit einer angenahert (leicht gewellten) quadratischen Struktur. Die Pd2-Abstande betragen 2, 7367 (10) und 2, 7495 (11)A und weisen auf schwache Bindungen hin. Die diagonalen Pd···Pd-Abstande von 3, 646 (10) und 3, 590 (10)A zeigen, dass die Pd4-Anordnung relativ symmetrisch und damit unerwartet fur eine “Pdx(dppm)x“-Spezies ist. Obwohl das H-Atom bei der Strukturanalyse nicht direkt beobachtet werden konnte, wird es analog zu der Situation in 1 als zwischen den Pd-Atomen schnell fluktuierend angenommen. Das Cyclovoltamogramm zeigt fur 2 ein Signal fur eine irreversible Reduktion bei —1, 65 Volt (vs SCE), groser als diejenige fur 1, wodurch die Annahme der niedrigen Oxidationsstufe der Pd-Atome unterstutzt wird. Das PdH-Bindungsproblem und die Symmetrie der MOs eines Modellclusters, in dem sich das H-Atom im Zentrum des Pd4-Gerusts befindet, wurde qualitativ durch das EHMO-Modell beschrieben. Nach diesen Modellrechnungen ist die PdH-Bindung als stark anzusehen.

Upper-rim monofunctionalization of calix[4]arene by organometallic diphenylphosphinorhodium complexes

Monofunctionalization of the calix[4]arene upper-rim is achieved by lithiation with BunLi, followed by phosphination with Ph2PCl of monobromotetra-n-propoxycalix[4]arene; subsequent reactions with [Cp*RhIIICl2]2 and Cp*RhI(CO)2 provide the corresponding Cp*[Ph2(calix)P]RhIIICl2, which can be converted to Cp*[Ph2(calix)P]RhIII(H)2 and Cp*[Ph2(calix)P]RhI(CO), respectively.

The stereochemistry of a nine-membered ring analogue of nefopam, a nonnarcotic analgesic drug

The solid-state structure of a (±)-homonefopam hydrogenfumarate salt having an-O(CH2)3N-fragment was determined by single-crystal X-ray diffraction analysis. Homonefopam hydrogenfumarate gave crystals belonging to the monoclinicP21/c space group, and at ambient temperaturea=10.220(1),b=18.187(2),c=10.687(2)A,Β=94.43(1)‡,V=1980.5(5)å3 Z=4,R(F)=0.039,Rw=0.039,RW (F)=0.025. The1H NMR spectrum of homonefopam hydrochloride in CD2Cl2 solution showed two species (7:1 ratio) at the prototropic shift-nitrogen inversion slow exchange limit. The solution-state major species has the same conformation andtrans-to-phenyl axial N-methyl disposition found in the crystal as evidenced by three antiperiplanar vicinal3J (HH) coupling constants in the oxytrimethyleneamino fragment and vicinal coupling constants involving theN-H proton. TheR-ratio method was used to estimate 64(2)‡ O-C(3)-C(4)-C(5) and 75(3)‡ C(3)-C(4)-C(5)-N(6) dihedral angles for the major species in CD2Cl2 solution in accord with its proposed structure. The finding of C(3)-C(4) bond time-averaged magnitude3J (HH) values and severe broadening of signals from other minor species protons suggests conformational heterogeneity for the solution-state minor species.