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Vedavati G Puranik

Publications and source records attributed to Vedavati G Puranik.

At least 19 recordsLinked to original sources
PubMed2006

Facile synthesis of 1,3,7-trihydroxyxanthone and its regioselective coupling reactions with prenal: simple and efficient access to osajaxanthone and nigrolineaxanthone F.

A facile five-step synthesis of naturally occurring 1,3,7-trihydroxyxanthone has been described starting from 1,3,5-trimethoxybenzene via NBS-induced nuclear bromination, lithiation followed by an in situ benzoylation with methyl 2,5-dibenzyloxybenzoate, selective deprotection of the two benzyl groups, base-catalyzed intramolecular cyclization, and demethylations pathway with 62% overall yield. The regioselective coupling reactions of 1,3,7-trihydroxyxanthone with prenal in the presence of calcium hydroxide at room temperature and under thermal conditions at 140-150 degrees C have been demonstrated to exclusively obtain the natural products osajaxanthone in 75% yield and nigrolineaxanthone F in 98% yield, respectively.

Hydrogen Bonding↗
PubMed2006

Synthesis of tetrahydroxy perhydroaza-azulenes: tandem Johnson-Claisen rearrangement of D-glucose-derived allylic alcohols.

The Johnson-Claisen rearrangement of D-glucose-derived allylic alcohols 5a,b, afforded sugar-substituted gamma,delta-unsaturated ester in high yield. Conversion of the ester group to an azidomethyl group, epoxidation of the double bond and hydrogenation gave pyrrolidine ring skeletons 13a and 13b, which were transformed to tetrahydroxy perhydroaza-azulenes 1a and 1b, respectively. Glycosidase inhibitory activity was also evaluated.

Journal Article↗
PubMed2006

2,4,6-Tris(2-pyridyl)-1,3,5-triazine (tptz)-derived [Ru(II)(tptz)(acac)(CH3CN)]+ and mixed-valent [(acac)2Ru(III){(mu-tptz-H+)-}Ru(II)(acac)(CH3CN)]+.

Mononuclear [Ru(II)(tptz)(acac)(CH3CN)]ClO4 ([1]ClO4) and mixed-valent dinuclear [(acac)2Ru(III){(mu-tptz-Eta+)-}Ru(II)(acac)(CH3CN)]ClO4 ([5]ClO4; acac = acetylacetonate) complexes have been synthesized via the reactions of Ru(II)(acac)2(CH3CN)2 and 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz), in 1:1 and 2:1 molar ratios, respectively. In [1]ClO4, tptz binds with the Ru(II) ion in a tridentate N,N,N mode (motif A), whereas in [5]ClO4, tptz bridges the metal ions unsymmetrically via the tridentate neutral N,N,N mode with the Ru(II) center and cyclometalated N,C- state with the Ru(III) site (motif F). The activation of the coordinated nitrile function in [1]ClO4 and [5]ClO4 in the presence of ethanol and alkylamine leads to the formation of iminoester ([2]ClO4 and [7]ClO4) and amidine ([4]ClO4) derivatives, respectively. Crystal structure analysis of [2]ClO4 reveals the formation of a beautiful eight-membered water cluster having a chair conformation. The cluster is H-bonded to the pendant pyridyl ring N of tptz and also with the O atom of the perchlorate ion, which, in turn, makes short (C-H- - - - -O) contacts with the neighboring molecule, leading to a H-bonding network. The redox potentials corresponding to the Ru(II) state in both the mononuclear {[(acac)(tptz)Ru(II)-NC-CH3]ClO4 ([1]ClO4) >> [(acac)(tptz)Ru(II)-NH=C(CH3)-OC2H5]ClO4 ([2]ClO4) > [(acac)(tptz)Ru(II)-NH2-C6H4(CH3)]ClO4 ([3]ClO4) > [(acac)(tptz)Ru(II)-NH=C(CH3)-NHC2H5]ClO4 ([4]ClO4)} and dinuclear {[(acac)2Ru(III){(mu-tptz-H+)-}Ru(II)(acac)(NC-CH3)]ClO4 ([5]ClO4), [(acac)2Ru(III){(mu-tptz-H+(N+-O-)2)-}Ru(II)(acac)(NC-CH3)]ClO4 ([6]ClO4), [(acac)2Ru(III){(mu-tptz-H+)-}Ru(II)(acac)(NH=C(CH3)-OC2H5)]ClO4 ([7]ClO4), and [(acac)2Ru(III){(mu-tptz-Eta+)-}Ru(II)(acac)(NC4H4N)]ClO4 ([8]ClO(4))} complexes vary systematically depending on the electronic nature of the coordinated sixth ligands. However, potentials involving the Ru(III) center in the dinuclear complexes remain more or less invariant. The mixed-valent Ru(II)Ru(III) species ([5]ClO4-[8]ClO4) exhibits high comproportionation constant (Kc) values of 1.1 x 10(12)-2 x 10(9), with substantial contribution from the donor center asymmetry at the two metal sites. Complexes display Ru(II)- and Ru(III)-based metal-to-ligand and ligand-to-metal charge-transfer transitions, respectively, in the visible region and ligand-based transitions in the UV region. In spite of reasonably high K(c) values for [5]ClO4-[8]ClO4, the expected intervalence charge-transfer transitions did not resolve in the typical near-IR region up to 2000 nm. The paramagnetic Ru(II)Ru(III) species ([5]ClO4-[8]ClO4) displays rhombic electron paramagnetic resonance (EPR) spectra at 77 K (g approximately 2.15 and Deltag approximately 0.5), typical of a low-spin Ru(III) ion in a distorted octahedral environment. The one-electron-reduced tptz complexes [Ru(II)(tptz.-)(acac)(CEta3CN)] (1) and [(acac)2Ru(III){(mu-tptz-Eta+).2-}Ru(II)(acac)(CH3CN)] (5), however, show a free-radical-type EPR signal near g = 2.0 with partial metal contribution.

Journal Article↗
PubMed2006

Crystal or low molecular mass organogel based on sugar-derived chiral pyrano[2,3-b]naphtho[1,2-e]pyrans.

[structure: see text] 2-C-Acetoxymethyl glycal derivatives reacted with beta-naphthol in the presence of InCl(3) (30 mol %) to give chiral pyrano[2,3-b]naphtho[1,2-e]pyrans in good to excellent yields via stereoselective Ferrier rearrangement-tandem cyclization. The major glucose-derived product exhibited crystal packing with C-H...O and C-H...pi (arene) interactions and the major galactose-derived product, a low molecular mass organogelator (LMOG), formed a rare type of micro tubular gel assembly in n-hexane.

Carbohydrates↗
PubMed2006

Metal-induced reductive ring opening of 1,2,4,5-tetrazines: three resulting coordination alternatives, including the new non-innocent 1,2-diiminohydrazido(2-) bridging ligand system.

Reaction of 3,6-diaryl-1,2,4,5-tetrazines (aryl = R = phenyl, 2-furyl or 2-thienyl) with 2 equiv of Ru(acac)2(CH3CN)2 results in reductive tetrazine ring opening to yield diruthenium complexes [(acac)2Ru(III)(dih-R(2-))Ru(III)(acac)2] bridged by the new 1,2-diiminohydrazido(2-) (dih-R(2-) = HNC(R)NNC(R)NH(2-)) ligands. rac/meso diastereoisomers could be detected and separated for the compounds with R = phenyl and 2-thienyl, all species are diamagnetic and were characterized by 1H NMR spectroscopy. Crystal structure determination of the meso isomers with R = phenyl and 2-thienyl confirmed the 1,2-diiminohydrazido formulation through long N-N (approximately 1.40 A) and short C=N(H) bonds (approximately 1.31 A), implying two bridged ruthenium(III) centers at about 4.765 A distance with strong antiferromagnetic coupling. The complexes undergo two reversible and well-separated one-electron reduction and oxidation processes, respectively. EPR Spectroscopy of the paramagnetic intermediates with comproportionation constants K(c) > 10(12) and UV-vis-NIR spectroelectrochemistry were used to identify the accessible redox states as [(acac)2Ru(II)(dih-R(2-))Ru(II)(acac)2]2-, [(acac)2Ru(II)(dih-R(*-))Ru(II)(acac)2]-, [(acac)2Ru(III)(dih-R(2-))Ru(III)(acac)2], [(acac)2Ru(III)(dih-R(*-))Ru(III)(acac)2]+, and [(acac)2Ru(III)(dih-R)Ru(III)(acac)2]2+. While the UV-vis-NIR spectroscopic response of [(acac)2Ru(dih-R)Ru(acac)2](0/-/2-) is very similar to that of [(bpy)2Ru(adc-R)Ru(bpy)2](4+/3+/2+), adc-R(2-) = 1,2-diacylhydrazido(2-), the EPR result indicating ligand-centered spin for [(acac)2Ru(II)(dih-R(*-))Ru(II)(acac)2]- despite deceptive NIR absorptions around 1400 nm reveals distinct differences in the electronic structures.

Journal Article↗
PubMed2006

Synthesis, characterization, X-ray structure and DNA photocleavage by cis-dichloro bis(diimine) Co(III) complexes.

Complexes of the type [Co(LL)2Cl2]Cl, where LL = N,N'-ethylenediamine (en), 2,2'-bipyridine (bpy), 1,10-phenanthroline (phen), 1,10-phenanthroline-5,6-dione (phendione) and dipyrido[3,2-a:2',3'-c]phenazine (dppz) have been synthesized and characterized by elemental analyses, IR, UV-visible and NMR spectroscopy. Crystal structure of [Co(phendione)2Cl2]Cl x 0.5 HCl x 3.5 H2O has been solved and refined to R = 0.0552. The crystal is monoclinic with space group C2/c; a = 25.730(2) A, b = 12.375(1) A, c = 18.979(2) A, beta = 119.925(1) degrees and Z = 8. The DNA binding characteristics of the complexes, investigated by covalent binding assay, viscosity measurements and competitive binding fluorescence measurements show that the complexes interact with DNA covalently except the complex containing the planar dppz ligand which intercalates within the base pairs of DNA. The complexes containing en, phen and phendione cleave plasmid pBR 322 DNA upon irradiation under aerobic conditions while the complex containing the dppz ligand cleaves DNA upon irradiation under inert atmosphere. Molecular modeling studies show that the minimized structure of [Co(phendione)2Cl2]+, maintained the octahedral structure while binding to the N7 of guanines and the ligand fits into the major groove without disrupting the helical structure of the B-DNA.

2,2'-Dipyridyl↗
PubMed2005

Preorganizing linear (self-complementary) quadruple hydrogen-bonding arrays using intramolecular hydrogen bonding as the sole force.

[structures: see text] In this article we describe a rational approach for prefixing multiple cooperative binding sites in an ideal spatial arrangement on a structurally rigid backbone, constrained exclusively by intramolecular hydrogen bonding. The idea is exemplified by the ability of the self-assembling constructs 1a-e and 2a,b to form hydrogen-bonded dimers, whose structural preorganization has been solely effected by intramolecular hydrogen bonding. The readily accessible amidinourea backbone has been used as a common platform for the construction of a variety of such self-assembling systems. ESI mass spectrometry and single-crystal X-ray diffraction studies have been particularly effective in investigating the self-assembling propensities of these systems. Remarkably, most the H-bonded dimers reported herein undergo an unusual mode of self-assembly, using intermolecular four-membered ring hydrogen-bonded interaction, affording extended supramolecular networks.

Journal Article↗
PubMed2005

2,5-Dioxido-1,4-benzoquinonediimine (H2L2-), a hydrogen-bonding noninnocent bridging ligand related to aminated topaquinone: different oxidation state distributions in complexes [{(bpy)2Ru}2(mu-H2L)]n (n=0,+,2+,3+,4+) and [{(acac)2Ru}2(mu-H2L)]m (m=2-,-,0,+,2+).

The symmetrically dinuclear title compounds were isolated as diamagnetic [(bpy)2Ru(mu-H2L)Ru(bpy)2](ClO4)2 (1-(ClO4)2) and as paramagnetic [(acac)2Ru(mu-H2L)Ru(acac)2] (2) complexes (bpy=2,2'-bipyridine; acac- = acetylacetonate = 2,4-pentanedionato; H2L = 2,5-dioxido-1,4-benzoquinonediimine). The crystal structure of 22 H2O reveals an intricate hydrogen-bonding network: Two symmetry-related molecules 2 are closely connected through two NH(H2L2-)O(acac-) interactions, while the oxygen atoms of H2L2- of two such pairs are bridged by an (H2O)8 cluster at half-occupancy. The cluster consists of cyclic (H2O)6 arrangements with the remaining two exo-H2O molecules connecting two opposite sides of the cyclo-(H2O)6 cluster, and oxido oxygen atoms forming hydrogen bonds with the molecules of 2. Weak antiferromagnetic coupling of the two ruthenium(III) centers in 2 was established by using SQUID magnetometry and EPR spectroscopy. Geometry optimization by means of DFT calculations was carried out for 1(2+) and 2 in their singlet and triplet ground states, respectively. The nature of low-energy electronic transitions was explored by using time-dependent DFT methods. Five redox states were reversibly accessible for each of the complexes; all odd-electron intermediates exhibit comproportionation constants K(c)>10(8). UV-visible-NIR spectroelectrochemistry and EPR spectroscopy of the electrogenerated paramagnetic intermediates were used to ascertain the oxidation-state distribution. In general, the complexes 1n+ prefer the ruthenium(II) configuration with electron transfer occurring largely at the bridging ligand (mu-H2Ln-), as evident from radical-type EPR spectra for 13+ and (+. Higher metal oxidation states (iii, iv) appear to be favored by the complexes 2m; intense long-wavelength absorption bands and RuIII-type EPR signals suggest mixed-valent dimetal configurations of the paramagnetic intermediates 2+ and 2-.

Journal Article↗
PubMed2005

Stereospecific route to 5,11-methanomorphanthridine alkaloids via intramolecular 1,3-dipolar cycloaddition of nonstabilized azomethine ylide: formal total synthesis of (+/-)-pancracine.

The core structure of the complex pentacyclic 5,11-methanomorphanthridine alkaloids is constructed stereospecifically in one step employing an intramolecular [3 + 2]-cycloaddition of nonstabilized azomethine ylide as the key step. The strategy is demonstrated by accomplishing the formal total synthesis of (+/-)-pancracine. [reaction: see text]

Alkaloids↗
PubMed2005

Effect of 2-(2-Pyridyl)azole-based ancillary ligands (L1-4) on the electrophilicity of the nitrosyl function in [RuII(trpy)(L1-)4)(NO)]3+ [trpy = 2,2':6',2' '-Terpyridine]. synthesis, structures, and spectroscopic, electrochemical, and kinetic aspects.

Ruthenium nitrosyl complexes [Ru(trpy)(L(1-4))(NO)](3+) (13-16) [trpy = 2,2':6',2' '-terpyridine, L(1) = 2-(2-pyridyl)benzoxazole, L(2) = 2-(2-pyridyl)benzthiazole, L(3) = 2-(2-pyridyl)benzimidazole, L(4) = 1-methyl-2-(2-pyridyl)-1H-benzimidazole] were obtained in a stepwise manner starting from [Ru(II)(trpy)(L(1-4))(Cl)]ClO(4) (1-4) -->[Ru(II)(trpy)(L(1-4))(H(2)O)](ClO(4))(2) (5-8) --> [Ru(II)(trpy)(L(1-4)) (NO(2))]ClO(4) (9-12) --> [Ru(II)(trpy)(L(1,2,4))(NO)](ClO(4))(3) (13, 14, 16)/[Ru(II)(trpy)(L(3))(NO)](ClO(4))(2)(NO(3)) (15). Crystal structures of 1, 2, 4, 9, 12, 13, 15, and 16 established the stereoretentive nature of the transformation processes. Though the complexes of L(1), L(3), and L(4) were isolated in the isomeric form A (pi-acceptor trpy and azole ring in the equatorial plane and the pyridine and chloride donors in the axial positions), complexes of L(2) preferentially stabilized in form B (trpy and pyridine in the equatorial plane and the azole ring and chloride donors in the axial positions). The nu(NO) stretching frequency varied in the range of 1957-1932 cm(-1), 13 >> 14 approximately 15 > 16, primarily depending on the electronic aspects of L as well as the isomeric structural forms. The coordinated nitrosyl function underwent successive reductions of [Ru(II)-NO(+)](3+) --> [Ru(II)-NO(*)](2+) and [Ru(II)-NO(*)](2+) --> [Ru(II)-NO(-)](+), and the first reduction potential follows the order 14 > 13 >> 15 approximately 16. The nearly axial EPR spectra having nitrogen hyperfine splittings (A approximately 26 G) at 77 K of 13(-)-16(-) with g approximately 2.0 established that the reduction process is largely centered around the nitrosyl function. Despite an appreciably high nu(NO), the complexes were found to be unusually stable even in the aqueous medium. They transformed slowly and only partially into the corresponding nitro derivatives in H(2)O (k approximately 10(-4) s(-1) and K = 0.4-3.8). The chloro (1-4), aqua (5-8), and nitro (9-12) derivatives displayed reasonably strong emissions near 700 nm at 77 K (phi = 10(-1)-10(-2)). The aqua derivative 7 was found to interact with the calf thymus and the circular form of p-Bluescript SK DNA.

Journal Article↗
PubMed2005

Unusual monodentate binding mode of 2,2'-dipyridylamine (L) in isomeric trans-(acac)2RuII(L)2, trans-[(acac)2RuIII(L)2]ClO4, and cis-(acac)2RuII(L)2 (acac = acetylacetonate). synthesis, structures, and spectroscopic, electrochemical, and magnetic aspects.

The reaction of cis-Ru(acac)2(CH3CN)2 (acac = acetylacetonate) with 2,2'-dipyridylamine (L) in ethanolic medium resulted in facile one-pot synthesis of stable [(acac)2RuIII(L)]ClO4 ([1]ClO4), trans-[(acac)2RuII(L)2] (2), trans-[(acac)2RuIII)L)2]ClO4 ([2]ClO4), and cis-[(acac)2RuII(L)2] (3). The bivalent congener 1 was generated via electrochemical reduction of [1]ClO4. Although in [1]+ the dipyridylamine ligand (L) is bonded to the metal ion in usual bidentate fashion, in 2/[2]+ and 3, the unusual monodentate binding mode of L has been preferentially stabilized. Moreover, in 2/[2]+ and 3, two such monodentate L's have been oriented in the trans- and cis-configurations, respectively. The binding mode of L and the isomeric geometries of the complexes were established by their single-crystal X-ray structures. The redox stability of the Ru(II) state follows the order 1 < 2 << 3. In contrast to the magnetic moment obtained for [1]ClO4, mu = 1.84 muB at 298 K, typical for low-spin Ru(III) species, the compound [2]ClO4 exhibited an anomalous magnetic moment of 2.71 muB at 300 K in the solid state. The variable-temperature magnetic measurements showed a pronounced decrease of the magnetic moment with the temperature, and that dropped to 1.59 muB at 3 K. The experimental data can be fitted satisfactorily using eq 2 that considered nonquenched spin-orbit coupling and Weiss constant in addition to the temperature-independent paramagnetism. [1]ClO4 and [2]ClO4 displayed rhombic and axial EPR spectra, respectively, in both the solid and the solution states at 77 K.

Journal Article↗
PubMed2005

1,3-Dipolar cycloaddition reaction of D-glucose-derived nitrone with allyl alcohol: synthesis of 2-hydroxy-1-deoxycastanospermine analogues.

[reaction: see text] The synthesis and evaluation of glycosidase inhibitory activity of polyhydroxylated indolizidine alkaloids namely 2-hydroxy-1-deoxycastanospermine 3a,b and 2-hydroxy-1-deoxy-8a-epi-castanospermine 3c,d is reported. The key step involves the intermolecular 1,3-dipolar cycloaddition of allyl alcohol to d-glucose-derived nitrone 4, followed by tosylation, that afforded four diastereomeric sugar-substituted isoxazolidines 5a-d with the desired regioselectivity. The one-pot conversion of 5a-d to pyrrolidines 8a-d by hydrogenolysis, removal of 1,2-acetonoide functionality, and hydrogenation afforded corresponding target molecules 3a-d.

Glucose↗
PubMed2005

Larvicidal activity of Acacia nilotica extracts and isolation of D-pinitol--a bioactive carbohydrate.

A low-molecular-weight, sugar-like compound other than glucose, fructose, sucrose, or myo-inositol showing lipophilic nature was isolated from the EtOH extract of Acacia nilotica. The structure of the compound was determined by spectral methods. This alicyclic polyalcohol was found to be D-pinitol (= 3-O-methyl-D-chiro-inositol; 1). The configuration of the compound was confirmed by single-crystal X-ray analysis. The compound 1 is known from Soybean, Australian mangroves, Fagonia indica, Arachis hypogaea, etc., but we have isolated this compound for the first time from the aerial parts of A. nilotica. Very few references have been cited for compound 1 for its entomological activity, and there are no reports on mosquitoes. Therefore, the crude extracts of A. nilotica were tested for its biological activity against mosquito larvae. Acetone extract at 500-ppm concentration showed chronic toxicity against Aedes aegypti and Culex quinquefasciatus IVth instar mosquito larvae. Such a biological activity has been observed for the first time for this plant. This study could be a stepping stone to a solution for destroying larval species as well as consumption of such a widely grown, problem weed, A. nilotica. This larvicidal agent, since it is derived from plant, is eco-friendly, cost effective, non-hazardous to non-target organisms and would be safe unlike commercially available insecticides.

Acacia↗
PubMed2004

Diruthenium complexes [((acac)2RuIII)2(mu-OC2H5)2], [((acac)(2RuIII)2(mu-L)](ClO4)2, and [((bpy)(2RuII)2(mu-L)](ClO4)4 [L = (NC5H4)2-N-C6H4-N-(NC5H4)2, acac = acetylacetonate, and bpy = 2,2'-bipyridine]. synthesis, structure, magnetic, spectral, and photophysical aspects.

Paramagnetic diruthenium(III) complexes (acac)(2)Ru(III)(mu-OC(2)H(5))(2)Ru(III)(acac)(2) (6) and [(acac)(2)Ru(III)(mu-L)Ru(III)(acac)(2)](ClO(4))(2), [7](ClO(4))(2), were obtained via the reaction of binucleating bridging ligand, N,N,N',N'-tetra(2-pyridyl)-1,4-phenylenediamine [(NC(5)H(4))(2)-N-C(6)H(4)-N-(NC(5)H(4))(2), L] with the monomeric metal precursor unit (acac)(2)Ru(II)(CH(3)CN)(2) in ethanol under aerobic conditions. However, the reaction of L with the metal fragment Ru(II)(bpy)(2)(EtOH)(2)(2+) resulted in the corresponding [(bpy)(2)Ru(II) (mu-L) Ru(II)(bpy)(2)](ClO(4))(4), [8](ClO(4))(4). Crystal structures of L and 6 show that, in each case, the asymmetric unit consists of two independent half-molecules. The Ru-Ru distances in the two crystallographically independent molecules (F and G) of 6 are found to be 2.6448(8) and 2.6515(8) A, respectively. Variable-temperature magnetic studies suggest that the ruthenium(III) centers in 6 and [7](ClO(4))(2) are very weakly antiferromagnetically coupled, having J = -0.45 and -0.63 cm(-)(1), respectively. The g value calculated for 6 by using the van Vleck equation turned out to be only 1.11, whereas for [7](ClO(4))(2), the g value is 2.4, as expected for paramagnetic Ru(III) complexes. The paramagnetic complexes 6 and [7](2+) exhibit rhombic EPR spectra at 77 K in CHCl(3) (g(1) = 2.420, g(2) = 2.192, g(3) = 1.710 for 6 and g(1) = 2.385, g(2) = 2.177, g(3) = 1.753 for [7](2+)). This indicates that 6 must have an intermolecular magnetic interaction, in fact, an antiferromagnetic interaction, along at least one of the crystal axes. This conclusion was supported by ZINDO/1-level calculations. The complexes 6, [7](2+), and [8](4+) display closely spaced Ru(III)/Ru(II) couples with 70, 110, and 80 mV separations in potentials between the successive couples, respectively, implying weak intermetallic electrochemical coupling in their mixed-valent states. The electrochemical stability of the Ru(II) state follows the order: [7](2+) < 6 < [8](4+). The bipyridine derivative [8](4+) exhibits a strong luminescence [quantum yield (phi) = 0.18] at 600 nm in EtOH/MeOH (4:1) glass (at 77 K), with an estimated excited-state lifetime of approximately 10 micros.

Journal Article↗
PubMed2004

Synthesis, structure, redox, NLO and DNA interaction aspects of [((L'-'")2RuII)3(mu3-L)]3+ and [(L')2RuII(NC5H4S-)]+[L3- = 1,3,5-triazine-2,4,6-trithiolato, L'-'" = arylazopyridine].

The trinuclear complexes [(L'-'")2RuII)3(mu3-L)](ClO4)3, [1] (ClO4)3-[3](ClO4)3 (L = trianionic form of 1,3,5-triazine-2,4,6-trithiol; N(p)C(5)H(4)N=N(a)-C6H4(R), R = H (L'), m-Me (L"), p-Me (L'")) and the analogous mononuclear complex [(L')2RuII(NC5H4S-)]ClO4 [4] ClO4 were synthesized. Crystal structures of [1](ClO4)3 and [4]ClO4 were determined. [1](3+)-[3](3+) exhibit three successive oxidative couples corresponding to Ru(II)Ru(II)Ru(III)<==>Ru(II)Ru(II)Ru(II); Ru(II)Ru(III)Ru(III)<==>Ru(II)Ru(II)Ru(III); Ru(III)Ru(III)Ru(III)<==>Ru(II)Ru(III)Ru(III) where the mixed valent states are moderately coupled. The complexes display multiple reductions associated with the azo functions of the ancillary ligands (L'-'"). The energy of the Ru(II)-based lowest energy MLCT transitions (533-558 nm) involving the pi* level of azoimine chromophore of L'-'" varies depending on the nuclearity as well as substituents in the ligand framework and follows the order: [1](3+) > [2](3+) > [3](3+) > [4](+). The complexes exhibit reasonably high third-order non-linear optical properties with gamma= (0.90-2.45) [times] 10(-29) esu. The interactions of the trinuclear complexes [((L')2RuII)3(mu3-L)]3+[1]3+, [((bpy)2RuII)3((mu3-L)]3+[5]3+ and [((phen)2RuII)3((mu3)-L)]3+[6]3+(bpy = 2,2'-bipyridine and phen = 1,10-phenanthroline) with the circular and linear forms of p-Bluescript DNA show reduced ethidium bromide fluorescence on gel electrophoresis.

Azo Compounds↗
PubMed2004

Stepwise synthesis of [Ru(trpy)(L)(X)](n+) (trpy = 2,2':6',2' '-terpyridine; L = 2,2'-dipyridylamine; X = Cl-, H2O, NO2-, NO+, O2-). Crystal structure, spectral, electron-transfer, and photophysical aspects.

Ruthenium-terpyridine complexes incorporating a 2,2'-dipyridylamine ancillary ligand [Ru(II)(trpy)(L)(X)](ClO(4))(n) [trpy = 2,2':6',2' '-terpyridine; L = 2,2'-dipyridylamine; and X = Cl(-), n = 1 (1); X = H(2)O, n = 2 (2); X = NO(2)(-), n = 1 (3); X = NO(+), n = 3 (4)] were synthesized in a stepwise manner starting from Ru(III)(trpy)(Cl)(3). The single-crystal X-ray structures of all of the four members (1-4) were determined. The Ru(III)/Ru(II) couple of 1 and 3 appeared at 0.64 and 0.88 V versus the saturated calomel electrode in acetonitrile. The aqua complex 2 exhibited a metal-based couple at 0.48 V in water, and the potential increased linearly with the decrease in pH. The electron-proton content of the redox process over the pH range of 6.8-1.0 was calculated to be a 2e(-)/1H(+) process. However, the chemical oxidation of 2 by an aq Ce(IV) solution in 1 N H(2)SO(4) led to the direct formation of corresponding oxo species [Ru(IV)(trpy)(L)(O)](2+) via the concerted 2e(-)/2H(+) oxidation process. The two successive reductions of the coordinated nitrosyl function of 4 appeared at +0.34 and -0.34 V corresponding to Ru(II)-NO(+) --> Ru(II)-NO* and Ru(II)-NO* --> Ru(II)-NO(-), respectively. The one-electron-reduced Ru(II)-NO* species exhibited a free-radical electron paramagnetic resonance signal at g = 1.990 with nitrogen hyperfine structures at 77 K. The NO stretching frequency of 4 (1945 cm(-1)) was shifted to 1830 cm(-1) in the case of [Ru(II)(trpy)(L)(NO*)](2+). In aqueous solution, the nitrosyl complex 4 slowly transformed to the nitro derivative 3 with the pseudo-first-order rate constant of k(298)/s(-1) = 1.7 x 10(-4). The chloro complex 1 exhibited a dual luminescence at 650 and 715 nm with excited-state lifetimes of 6 and 1 micros, respectively.

Journal Article↗
PubMed2003

Chelation-control in nucleophilic addition to Cr(CO)3-complexed aryl aldehydes.

One or more methoxy groups on the benzylic carbon at the ortho-position of tricarbonylchromium-complexed aryl aldehydes (2, 3 or 4) permit chelation-controlled addition of nucleophiles to the carbonyl function in the presence of Lewis acids. In the absence of a Lewis acid additive, a complementary set of diastereomeric products are obtained.

Journal Article↗