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Anand Sundararaman

Publications and source records attributed to Anand Sundararaman.

6 recordsLinked to original sources
PubMed2006

Electronic communication and negative binding cooperativity in diborylated bithiophenes.

The bifunctional conjugated organoboranes Ar2B-bt-BAr2, which contain 2,2'-bithiophene (bt) linkers and different aryl substituents on boron (3: Ar = p-tBuC6H4; 4: Ar = C6F5; 5: Ar = C6F5, Fc; Fc = ferrocenyl), have been synthesized. The electronic communication between the boron centers and cooperativity effects in the binding of pyridine have been investigated by a comprehensive study using X-ray crystallography, DFT calculations, cyclic voltammetry, 1H and 19F NMR, and UV visible absorption and emission spectroscopy. A comparison of the single-crystal X-ray structures of 4 and 4Py2 revealed a strongly diminished bond alternation in the thiophene rings for 4, indicative of a high degree of electronic delocalization. DFT calculations are in good agreement with the structural features determined from the X-ray analysis and, consistent with the experimental absorption and emission data, predict a smaller HOMO-LUMO gap for green luminescent 4 in comparison to blue luminescent 3. The complexation of pyridine to the two boron centers was further investigated by 1H and 19F NMR for 4 and by 1H NMR and UV-visible absorption spectroscopy for 3. We found that binding of the first pyridine molecule to one of the boryl groups significantly lowers the Lewis acidity of the other boryl group. For 3, the interaction parameter a, which provides a measure of communication between the boron sites, was determined to be a = 0.23 by UV-visible titration and 0.21 by 1H NMR spectroscopy. Further enhanced electronic communication was observed for the more highly Lewis acidic fluorinated derivative 4, for which a = 0.025 according to 19F and 1H NMR spectroscopy.

Binding Sites↗
PubMed2005

A family of main-chain polymeric Lewis acids: synthesis and fluorescent sensing properties of boron-modified polythiophenes.

A new family of main-chain organoborane polymeric Lewis acids (PTh-BAr) that contain Lewis acidic boron groups embedded into a polythiophene backbone has been prepared under mild conditions through tin-boron exchange reaction. When phenyl and pentafluorophenyl groups are attached to boron, blue and green luminescence is observed, respectively, while the attachment of ferrocenyl substituents leads to a characteristic red color. The incorporation of readily accessible highly Lewis acidic groups into the conjugated polymer backbone provides an opportunity for sensing of Lewis basic substrates. For instance, treatment of the polymer containing phenyl substituents on boron with pyridine leads to efficient quenching of the fluorescence, while the polymer containing ferrocenyl groups changes color from dark red to light orange.

Boron↗
PubMed2005

Binding cooperativity of two different Lewis acid groups at the edge of ferrocene.

The binding properties of heteronuclear bidentate Lewis acids, in which an organoboron and an organotin moiety are attached adjacent to each other at one of the Cp rings of ferrocene, have been studied. Treatment of [1,2-fc(SnMe2Cl)(BClMe)] (1-Cl) (fc = ferrocenediyl) with one equivalent of pyridine or 4-dimethylaminopyridine (DMAP) resulted in diastereoselective complexation of boron. Adducts 2 and 3 have been studied by multinuclear NMR, and the stereoselectivity of complexation was further confirmed by single crystal X-ray diffraction of 2. The importance of cooperative effects that involve an intramolecular B-ClSn interaction on the diastereoselectivity is evident from comparison with binding studies on the phenyl-substituted analogue [1,2-fc(SnMe2Cl)(BPhMe)] (1-Ph). Complexation of 1-Ph led to diastereomeric mixtures of adducts 4 and 5, respectively, which were identified by multinuclear NMR including NOESY experiments. The solid-state structure of one of the diastereomers of 5 was confirmed by X-ray crystallography. Facile isomerization was found in solution and the barrier of activation was determined by VT NMR studies (4: Delta(#)(298) = 54.9+/-0.4 kJ mol(-1); 5: Delta(#)(298) = 70.3+/-0.1 kJ mol(-1)). Competitive binding of pyridine to 1-Cl and [FcB(Cl)Me] (Fc = ferrocenyl) showed that cooperative effects between tin and boron lead to significant Lewis acidity enhancement. Binding of a second nucleophile in the presence of excess of base occurred also at boron. The novel zwitterionic complexes [1,2-fc(BMe(py)2)(SnMe2Cl2)] (6) and [1,2-fc(BMe(dmap)(2))(SnMe(2)Cl2)] (7) formed, which consist of boronium cation and stannate anion moieties. The structure of 7 in the solid-state was confirmed by X-ray crystallography. Multinuclear NMR data and competition experiments indicate weak binding of chloride to tin in 7 and partial dissociation in solution.

Journal Article↗
PubMed2005

Cuprophilic and pi-stacking interactions in the formation of supramolecular stacks from dicoordinate organocopper complexes.

The unsupported organocopper pyridine complexes C6F5Cu(py) (2) and [C6F5Cu]2(4,4'-bipy) (3) form supramolecular structures that are unprecedented in organocopper chemistry; one-dimensional chains of copper atoms with Cu...Cu distances of 2.8924(3) angstroms in the blue-luminescent complex are likely associated with cuprophilic interactions, whereas multiple perfluoroarene-arene interactions dominate in the supramolecular assembly of 3.

Journal Article↗
PubMed2002

Well-defined boron-containing polymeric lewis acids.

A general new route to well-defined polymeric Lewis acids via borylation of silylated polymers is reported. Trimethylsilylated polystyrene (PS-Si) of controlled molecular weight and low polydispersity (PDI < 1.15) was obtained via atom transfer radical polymerization (ATRP) of 4-(trimethylsilyl)styrene. The functional polymer PS-Si was quantitatively borylated using BBr3 to give poly(4-dibromoborylstyrene) (PS-B), a novel soluble boron-containing polymeric Lewis acid. PS-B readily reacted with nucleophiles serving as a precursor to a family of new polymers with boron centers of variable Lewis acidity. Reaction of PS-B with Cu(C6F5) gave the highly Lewis acidic polymer poly[4-bis(pentafluorophenyl)borylstyrene], the first polymeric analogue of tris(pentafluorophenyl)borane.

Journal Article↗