Martin Putala

Study on the synthesis of nonracemic C2-symmetric 1,1′-binaphthyl-2,2′-diyl bridged ferrocene. Stereochemical result of the cross-coupling reactions controlled by Pd(II) or Pd(IV) complex intermediacy

Abstract Palladium catalyzed Negishi, Suzuki and Stille cross-coupling reactions of enantiopure 2,2′-diiodo-1,1′-binaphthyl with the corresponding 1,1′-dimetalloferrocenes gave the C 2 -symmetric binaphthyl bridged ferrocene 1-1,1′-(1,1′-binaphthyl-2,2′-diyl)ferrocene ( 1 ). The latter was obtained by Stille coupling with the bis(trimethylstannyl) derivative but not with the bis(tributylstannyl) one. Products of alkyl group transfer from tin to binaphthyl were obtained as the main products in both cases. The stereochemical result of these cross-coupling reactions in the positions 2 and 2′ of 1,1′-binaphthyl depends on the reactivity of 1,1′-dimetalloferrocenes. Negishi coupling proceeds stereoconservatively (affording enantiopure product 1 ). Complete racemization of binaphthyl moiety occurs during the reactions with less reactive boron and tin organometallics. Proposed different reaction pathways include C 1 -symmetric palladium(II) intermediate in the former and configurationally unstable C 2 -symmetric pallada(IV)cyclic intermediate in the latter cases. In contrast to the cross-coupling reactions, free radical arylation of ferrocene with enantiopure 1,1′-binaphthyl-2,2′-bisdiazonium salt gave predominantly oligomeric binaphthyl bridged ferrocenes and only traces of the partially racemized product 1 .

New metallocene complexes of Nb and Ta with functionalized diazoalkanes

The reaction of Cp2MH3, where M  Nb or Ta, with N2CPh2, N2CPh(o-C6H4Br) and N2CHCOOEt was thoroughly studied. It was shown that the primary products of the reaction are the complexes Cp2M(H)(η1-N2CRR′) (2). The complexes 2 are readily oxidized by air to give polymeric (Cp2MO)n, N2CRR′ and RR′CN2CRR′. Interaction of an excess of N2CPh(o-C6H4Br) with Cp2NbH3 leads to a 17-electron complex Cp2Nb( NNCPho-C6H4)2 (6) with two σ-N pyrazole ligands. Finally the reaction of Cp2NbH3 with N2CHCOOEt gives an unusual dimeric complex Cp2Nb2(η5-C5H4C(COOEt)N μ-N)2. The complexes 2 were found to undergo easily substitution of a hydride ligand for a halogen atom. The results of X-ray analysis of the complexes 6 and Cp2Nb(Cl)-η1-N2CPh(o-C6H4Br) are provided.

Diastereoselective reaction of (MP)-pentahelicene-7,8-dione with trans-cyclohexane-1,2-diamine. Thermal and photochemical transformations of its product

Abstract The reaction of the title compounds and the transformations of the product, 3 were investigated with an emphasis on the stereochemistry. The primary interaction of the title compounds is feebly stereoselective. The diastereoisomers of product 3 exhibit free energies differing by ca. 16 kJ/mol; diastereoisomerization by helix inversion takes place during the reaction. The most stable diastereoisomers of the intermediate 8 and the product 3 show opposite helicities, which allows isolation of the product 3 in diastereoisomeric ratios from 19:81 to >99:1 depending on solvent and temperature. The free energies of activation for helix inversions of 3 were determined by time-dependent 1H NMR. The predicted configuration of the more stable diastereoisomer of 3 was confirmed by chemical correlation to be (M,R,R). The four stereoisomers of 3 were separated by analytical enantioselective HPLC and characterized by on-line circular dichroism. Irradiation of 3 afforded the 2-substituted benzimidazole derivative 9.

Semiconducting Organic Molecular Materials

Semiconducting Organic Molecular Materials This feature article gives an overview of recent advances in development of high performance molecular organic semiconductors for field-effect transistors with emphasis on the structure of molecular materials and requirements for high-performance.

Fluoride anion sensing using colorimetric reagents containing binaphthyl moiety and urea binding site

Four 1,1′-binaphthalene based bis-urea derivatives bearing aryl groups at end-on nitrogen atoms IIIa–d were synthesized as potential sensor molecules. These receptors show characteristic UV-VIS spectral changes on complexation with anions and they exhibit selective recognition of F− over other halide anions. Interaction of a fluoride anion with urea NH groups was confirmed by 1H NMR data. The presence of an electron-withdrawing nitro group in N′-aryls (receptors IIIa and IIIb) appeared to be necessary for naked-eye colorimetric detection. These receptors show dramatic color change from light-yellow to orange (IIIa) or to orange-red (IIIb) in the presence of guest fluoride anions already at concentrations of 10−5 mol dm−3 of the receptor and host.

A chiroptical binaphthopyran switch: amplified CD response in a polystyrene film

Enantiopure 10,10′-bi(naphtho[2,3-b]pyran) (5a) has been prepared from (R)-BINOL by using the attachment of 1,1-diphenylallyl alcohol to positions 3 and 3′ of the binaphthalene via Heck coupling as a key step. The irradiation of 5a in solution with UV light at 313 nm caused photochemical opening of only one of the pyran rings, accompanied by minor changes in the CD spectrum. Thermal ring closure occurred spontaneously with an activation barrier of 74 kJ mol−1. When 5a was immobilised in a polystyrene film, an improved switching performance, both in terms of fatigue resistance (>10 cycles) and CD signal amplitude (>100 mdeg, >6:1 signal ratio of open/closed forms), was observed.

The chemistry of hydride, halide and alkyl niobocene complexes with coordinated diazoalkanes

Abstract The complexes Cp 2 Nb ( H )(η 1 - NNCPhAr ) ( ArPh )) ( 1 ) or o- C 6 H 4 Br ( 2 ) ) were found to undergo easy substitution of a hydride ligand for a halogen atom by the reaction of 1 with various alkylhalides with high yields of Cp 2 Nb(X)( η 1 -NNCPh 2 ) (XCl ( 4 ), Br ( 5 ) or I ( 6 ), Cp 2 Nb ( Br )(η 1 - NNC ( Ph )-o- C 6 H 4 Br ) ( 7 ) and 5 were found to be formed in a halogen exchange reaction, and also by the thermolysis of 2 . Halide diazoalkane niobocene complexes clearly exhibit marked polarity of the metal centre. Nucleophilic substitution of bromine in 5 yielded Cp 2 Nb ( Me )(η 1 - NNCPh 2 ) ( 8 ) . The results of X-ray analysis of 7 are provided.

New phenanthrene-based organic semiconductor material for electronic devices

This work describes the thin-film fabrication technology and characterization of devices based on organic semiconductor 3,6-bis(5`-hexyl-2,2`-bithiophen-5-yl)phenanthrene (H2T36Phen). The surface morphology, optical, and electrical properties are investigated for thin organic films. It demonstrates that the solution-based depositions require different substrate surface treatment than the evaporation-based deposition.