Ultrafast and long-time excited state kinetics of an NIR-emissive vanadium(iii) complex I: synthesis,spectroscopy and static quantum chemistry

In spite of intense, recent research efforts, luminescent transition metal complexes with Earth-abundant metals are still very rare owing to the small ligand field splitting of 3d transition metal complexes and the resulting non-emissive low-energy metal-centered states. Low-energy excited states decay efficiently non-radiatively, so that near-infrared emissive transition metal complexes with 3d transition metals are even more challenging. We report that the heteroleptic pseudo-octahedral d²-vanadium(iii) complex VCl₃(ddpd) (ddpd = N,N′-dimethyl-N,N′-dipyridine-2-yl-pyridine-2,6-diamine) shows near-infrared singlet → triplet spin–flip phosphorescence maxima at 1102, 1219 and 1256 nm with a lifetime of 0.5 μs at room temperature. Band splitting, ligand deuteration, excitation energy and temperature effects on the excited state dynamics will be discussed on slow and fast timescales using Raman, static and time-resolved photoluminescence, step-scan FTIR and fs-UV pump-vis probe spectroscopy as well as photolysis experiments in combination with static quantum chemical calculations. These results inform future design strategies for molecular materials of Earth-abundant metal ions exhibiting spin–flip luminescence and photoinduced metal–ligand bond homolysis.

Vanadium is an abundant and cheap metal but near-infrared luminescent vanadium complexes are extremely rare with largely unexplored photophysics and photochemistry. We delineate the photodynamics of VCl₃(ddpd) to infer novel design strategies.     

Stereospecificity of the reaction of (+)-(4S, 5S)-4-(4-nitrophenyl)-1-aza-3,7-dioxabicyclo[3.3.0]octane with methyl iodide

The MINDO3, MNDO, AM1, and PM3 methods have been used to optimize the geometries of (+)-(4S,5S)-4-(4-nitrophenyl)-1-aza-3,7-dioxabicyclo[3.3.0]octane and (+)-(4S,5S)-4-phenyl-1-aza-3,7-dioxabicyclo-[3.3.0]octane. It has been shown that the stereospecificity, of the reaction of the former with methyl iodide is due to the high stability of one of the possible conformers. Pharmacy Faculty 28, University of the Auvergne, Henri Dunant Place, Clermont-Ferrand, France; Samara State University, Samara 443011, Russia; Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1424–1427, October, 1999.     

(+)-(1S,2S,5R)-8-联苯薄荷醇的合成

以(R)-( )-pu legone为起始原料,经1,4-加成,还原两步反应合成了手性辅助试剂( )-(1S,2S,5R)-8-联苯薄荷醇及其差向异构体(-)-(1R,2S,5R)-8-联苯薄荷醇,总产率95%。其结构经1H NMR,13C NMR,IR,MS和X-射线衍射仪表征。     

Synthesis of the Enantiomerically Enriched Macrocyclic Lactones (+)-(S)- and (−)-(R)-Phoracantholide I and (+)-(S)-Tetradecan-13-olide

Synthesis of two naturally occurring macrocyclic lactones is described. (?)-(R)-Phoracantholide I ((?)- 1 ; Scheme 2) was synthesized by asymmetric and chemoselective reduction of the side-chain C?O group of (?)4-(1-nitro-2-oxocyclohexyl)butan-2-one ((?)- 6 ) with (R)-Alpine-Hydride (47% ee). It was shown that the formation of only one diastereoisomer of the hemiacetal 5 , by methylation with (i-PrO)₂TiMe₂ of ketoaldehyde (?)- 2 is thermodynamically controlled. (+)-(S)-Tetradecan-13-olide ((+)- 10 ) was obtained by reduction of diketone (±)- 11 with optically active borohydrides followed by denitration (Scheme 3).     

Chemistry of baker's yeast reduction products: Use of optically active (S)-(+)-1-(p-toluenesulfonyl)propan-2-ol and (S)-(+)-1-(phenylsulfonyl)propan-2-ol in synthesis.

The utility of the title compounds in the preparation of optically active lactones and alcohols is detailed.     

Optically Active Alkylvinylpyridines: Synthesis of (+)-(S)-6-(1-Methylpropyl)-2-Vinylpyridine

A generalizable procedure for the preparation of optically active 6-alkyl-2-vinylpyridines from chiral 2-alkylpyridines without loss of optical purity is reported.     

Synthesis of (-)-(S)-3-sec-butyl- and (+)-(S)-5-sec-butyl-2(1H)-pyridinone

Optically active (+)-(S)-5-sec-butyl- and (-)-(S)-3-sec-butyl-2(1H)-pyridinone are synthesized and the relationship between optical activity and minimum optical purity of the latter is determined.     

Stabilised phosphorus(I) and arsenic(I) iodide: readily-synthesised reagents for low oxidation state main group chemistry

Herein we report a surprisingly facile and clean synthesis of base-stabilised phosphorus(I) and arsenic(I) iodide salts, which are reagents that provide convenient access to new low oxidation state main group compounds.     

Efficient syntheses of four stable-isotope labeled (1R)-menthyl (1S,2S)-(+)-2-phenylcyclopropanecarboxylates

Many carbenoid cyclopropanation reactions promoted by chiral catalysts give product mixtures reflecting impressive diastereo- and enantioselectivities. Few provide a single chiral product efficiently. This limitation has been overcome in cyclopropanations of styrene and isotopically labeled styrenes with alpha-diazoacetates. Convenient syntheses on a 20 g scale of each of four chiral isotopically labeled (1R)-menthyl (1S,2S)-2-phenylcyclopropanecarboxylates (the 1-d-3-(13)C, 1,(3S)-d2, 1,2,(3S)-d3, and 1,3,3-d3 isotopomers) of better than 99% ee have been realized.     

A general enantioselective approach to jasmonoid fragrances: synthesis of (+)-(1R,2S)-methyl dihydrojasmonate and (+)-(1R,2S)-magnolione

Methyl dihydrojasmonate 1 and magnolione 3 are of both academic and industrial interest. In this paper, we describe a flexible, high-yielding route to diastereomerically pure (+)-cis-(1R,2S)-methyl dihydrojasmonate 1 and the first synthesis of (+)-cis-(1R,2S)-magnolione 3, both with enantiomeric excesses up to 93%. The two syntheses diverged from the same advanced intermediate 5, readily available from the enantioenriched hydroxymethyl delta-lactone (-)-(3aS,4S,6aR)-6. The olfactory properties of (1R,2S)-1 and (1R,2S)-3 are reported.     

Highly enantioselective approach to indolizidines: preparation of (+)-(1S,8aS)-1-hydroxyindolizidine and (-)-slaframine

A highly stereoselective approach to (-)-slaframine and its probable biosynthetic precursor (+)-(1S,8aS)-1-hydroxyindolizidine has been developed based on a diastereofacially selective cycloaddition of dichloroketene with a chiral dienol ether.     

On the kinetics of formation of an excited charge-transfer state in 4-(9-anthryl)N,N-dimethylaniline

The kinetics of formation of an excited charge-transfer (CT) state in 4-(9-anthryl)-N,N-dimethylaniline have been studied by means of steady-state and nanosecond time-resolved fluorescence. It is concluded that the excited CT state is formed irreversibly at room temperature in ethyl acetate on a timescale shorter than 54 picoseconds.     

HPLC in photokinetics: Determination of reaction mechanism and photochemical quantum yields of (E)-1-phenylpropene

Summary A combined method of high-performance liquid chromatography and UV-absorption spectroscopy is described for use in dynamic systems. It provides a way of obtaining detailed mechanistic information as well as quantitative data (rate constants, quantum yields), even though neither mechanism nor photoproducts are known. The kinetic treatment of the photoreaction of (E)-1-phenylpropene was successful, showing a photo-isomerization and a parallel step. Information on this additional step is obtained by using HPLC to observe the changes in the concentrations of the reactants' selectivity. The necessity of process control is demonstrated.Dedicated to Prof. Ernst Bayer on the occasion of his 60^th anniversary.     

Synthesis of the Juvenoid (S)-(+)-Hydroprene from L-(-)-Menthol

The versatile chiral synthon methyl (R)-5,5-dimethoxy-3-methylpentanoate has been prepared for the first time via ozonolytic decyclization of (R)-4-menthenone, which is available from L-(-)-menthol. The optically pure juvenoid (S)-(+)-hydroprene can be prepared from the synthon     

Phosphorus(I) iodide: a versatile metathesis reagent for the synthesis of low oxidation state phosphorus compounds

An improved method for the synthesis of cyclic low oxidation state P cations is presented. The only byproducts of the reaction of phosphorus triiodide with chelating phosphines are readily removed, resulting in an easily accessible P(I) reagent with an anion that can be readily replaced through salt metathesis chemistry. These P(I) salts are surprisingly stable, even in O2 and moisture, and the origin of this unusual stability is elucidated using density functional theory calculations.     

(1R,5S)-(+)-Nopinone of High Enantiomeric Purity

Commercial β-pinene of 87% ee can be upgraded to the 98plus;% ee level by simple treatment with silver perchlorate. A solid complex is obtained whose formation is more rapid when two like enantiomers are involved. Simple dissolution of this precipitate in water releases the enantioenriched hydrocarbon from which (+)-nopinone of high enantiomeric purity is obtained via ozonolysis.     

Luminescence of dimeric Tl(I)-complexes: Metal-metal interaction in the electronically excited state

Summary Dimeric diethyldithiocarbamatethallium(I) [Et ₂NCS₂Tl]₂ shows a red emission at _max=608 nm which undergoes a huge Stokes shift with regard to the excitation maximum at =246 nm. It is suggested that the emission originates from a sp excited state which is characterized by strong metal-metal bonding.

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Lumineszenz von dimeren Tl(I)-Komplexen: Metall-Metall-Wechselwirkung im elektronisch angeregten Zustand (Kurze Mitt.)

Zusammenfassung Dimeres Thallium(I)diethyldithiocarbamat [Et ₂NCS₂Tl]₂ zeigt eine rote Emission mit _max=608 nm und eine große Stokes'sche Verschiebung im Bezug auf das Anregungsmaximum von =246 nm. Die Emission wird einem sp angeregten Zustand zugeordnet, der durch eine starke Metall-Metall Wechselwirkung charakterisiert ist.

     

New Chiral Diamines of the Dioxolane Series: (+)-(4S,5S)-2,2-Dimethyl-4,5-bis(diphenylaminomethyl)- 1,3-dioxolane and (+)-(4S,5S)-2,2-Dimethyl-4,5-bis(methyl- aminomethyl)-1,3-dioxolane

The reaction of sodium diphenylamide with 2,2-dimethyl-4,5-bis(tosyloxymethyl)-1,3-dioxolane gave (+)-(4S,5S)-2,2-dimethyl-4,5-bis(diphenylaminomethyl)-1,3-dioxolane, which was brought into complex formation with cobalt chloride. Treatment of 2,2-dimethyl-4,5-bis(tosyloxymethyl)-1,3-dioxolane with sodium N-methylanilide resulted in cleavage of the SÄO bond in the p-toluenesulfonate moiety with formation of N-methyl-N-phenyl-p-toluenesulfonamide and 4,5-bis(hydroxymethyl)-2,2-dimethyl-1,3-dioxolane disodium salt. Diethyl (4R,5R)-2,2-dimethyl-1,3-dioxolane-4,5-dicarboxylate reacted with methylamine to give the corresponding dicarboxamide which was reduced with lithium aluminum hydride to (4S,5S)-2,2-dimethyl-4,5-bis(methylaminomethyl)-1,3-dioxolane having chiral carbon and nitrogen atoms.     

Racemization of (S)-(+)-10,11-dimethoxyaporphine and (S)-(+)-aporphine: efficient preparations of (R)-(−)-apomorphine and (R)-(−)-aporphine via a recycle process of resolution

Efficient preparations of (R)-(−)-apomorphine (R)-1 and (R)-(−)-aporphine (R)-2 based on a recycle process of resolution are described. In this recycle process of resolution, (RS)-(±)-10,11-dimethoxyaporphine 3 as the precursor of 1, and (RS)-(±)-aporphine 2 were successfully resolved into both enantiomers with (+)-dibenzoyltartaric acid (DBTA). The desired (R)-3 and (R)-2 were obtained and then, respectively, transformed to compound (R)-1, the hydrochloride salt of (R)-1, diacetate compound 4 and the hydrochloride salt of (R)-2; while the undesired (S)-3 and (S)-2 were racemized to obtain a racemate, which was suitable for further resolution. A method for the racemization of the undesired (S)-3 and (S)-2 was extensively studied, in order to obtain high-yielding racemization conditions. A plausible mechanism for the racemization of (S)-3 and (S)-2 was also proposed.