bluuebunny/crossref_metadata_2025_split huggingface dataset:
Solid‐State CP/MAS 13C‐NMR Spectra of Oligolides derived from 3‐hydroxybutanoic acid
Authors: Riddell Frank G. , Seebach Dieter , Müller Hans‐Martin 
Published: December 2004

AbstractThe solid‐state CP/MAS 13C‐NMR spectra (cross‐polarization/magic‐angle spinning 13C‐NMR) of eight lower cyclic and one linear oligomers and several polymers of (R)‐3‐hydroxybutanoic acid (3‐HB) are reported. The polymeric samples of different origin and molecular weight give remarkably similar and well resolved spectra, indicating considerable similarity in the conformations of the molecules and homegeneity in the solid‐state environment. The crystalline cyclic oligomers 1–8 containing 3–9 units of 3‐HB give very well resolved spectra. The number of nonequivalent positions in the solid state can be identified and is in accord with structures from X‐ray diffraction where these were determined. The spectra of the oligolides become increasingly similar to those of the polymer as the ring size increases. This spectral evidence supports the view of a homogeneous and well defined conformation for the polymeric material (as proposed previously, based on other experiments).
The Chemistry of Coumarin Derivatives. Part 5. Unusual course of the reaction of 4‐hydroxycoumarin and aliphatic aldehydes
Authors: Appendino Giovanni , Cravotto Giancarlo , Nano Gian Mario , Palmisano Giovanni , Annunziata Rita 
Published: December 2004

AbstractThe reaction of 4‐hydroxycoumarin and certain aliphatic aldehydes affords 1:1 or complex 2:2 adducts besides (or in place) of the expected 2:1 bis(coumarin) adducts. Reaction with heptanal, cyclohexanecarbaldehyde, and pivalaldehyde are reported as representative. The structure of the reaction products was established by spectroscopical techniques, including X‐ray analysis, and their formation was mechanistically rationalized. Some of the 1:1 adducts are synthetically useful for the preparation of 3‐alkyl‐4‐hydroxycoumarins.
Enantioselective Copper‐Catalyzed 1,4‐Addition of Grignard Reagents to α,β‐Unsaturated Carbonyl Compounds
Authors: Spescha Maurus , Rihs Grety 
Published: December 2004

AbstractThe enantioselective copper‐catalyzed 1,4‐addition of Grignard reagents to α,β‐unsaturated carbonyl compounds was studied with the following CuI compounds as catalyst precursor and 1,2:5,6‐di‐O‐isopropylidene‐3‐thio‐α‐D‐glucofuranose (Hsiig) as chiral ligand: CuI, iodo[bis(dibutylsulfide)]copper(I), [Cu(siig)], [Cu(siig)(pp)] (pp =1,2‐bis)(diphenylphosphinoethene), and tetrakis[iodo(tributylphosphine)]copper(I). The addition of BuMg halides to cyclohex‐2‐en‐1‐one was tested under several reaction conditions. The chemical yields and regioselectivities for this reaction were, in all cases, larger than 90 and 98%, respectively, and independent of the experimental conditions. The enantioselectivity was strongly dependent on the reaction conditions and reached a maximum of 60%. Several other substrates were also tested in the above reaction. The X‐ray crystal structure for [Cu(siig)(pp)] was determined by X‐ray crystallography.
Assignment of 15N‐NMR resonances of vitamin B12 analogues by 2D‐[15N, 1H] long‐range correlation: Fully [15N]‐labelled Co‐β‐cyano‐5‐hydroxybenzimidazoylcobamide (factor III) and derivatives
Authors: Hollenstein† Roger , Stupperich Erhard 
Published: December 2004

AbstractThe 15N‐NMR spectra of vitamin B12 analogues obtained in fully 15N‐labelled form have been measured by direct and inverse (15N, 1H) correlated spectroscopy. All resonances, except those of the NH2 groups, have been assigned to individual N‐atoms. The influences on δ (N) are analyzed and discussed which are caused by changing the α‐face ligand from CN to H2O or CH3 and by switching the β‐face ligand from the base‐on to the base‐off state. An implication of the correct resonance assignment on biosynthetic pathways is demonstrated.
Structural Study of Pinacidil, a Potassium‐Channel Opener Belonging to the chemical class of N‐alkyl‐N″‐cyano‐N′‐pyridylguanidines
Authors: Pirotte Bernard , de Tullio Pascal , Masereel Bernard , Schynts Marc , Delarge Jacques , Dupont Léon 
Published: December 2004

AbstractThe crystal structure of the potassium‐channel opener (R,S)‐pinacidil (2) was determined by X‐ray crystallography. Its N′, N″‐disubstitued N‐cyanoguanidine fragment was found to exhibit an unusual (Z,Z)‐conformation. X‐Ray and NMR data obtained with 2 are consistent with the predominance of the 4‐aminopyridine species over an iminopyridine tautomer in the solid state and in solution. These new structural informations may help further comparative studies of 2 and other potassium‐channel openers in elucidating structure‐activity relationships.
Novel Acetogenins from the Leaves of Annona purpurea
Authors: Cepleanu Felicitas , Ohtani Kazuhiro , Hamburger Matthias , Hostettmann Kurt , Gupta Mahabir P. , Solis Pablo 
Published: December 2004

AbstractThe CH2Cl2 extract of the leaves Annona purpurea L. (Annonaceae) showed strong brine shrimp toxicity and pronounced activity against larvae of the yellow‐fever mosquito Aedes aegypti. Activity‐directed fractionation of the extract by a combination of column chromatography on silica gel, filtration, and high‐pressure liquid chromatography led to the isolation of acetogenins 1–6 as the main active principles. The structures of two novel acetogenins named purpureacin 1(5) and purpureacin 2(6) were elucidated by spectroscopic analysis (UV, EI‐ and DCI‐MS, EI‐MS of Me3Si derivatives,1H‐ and 13C‐NMR). The configuration of 5 and 6 was not established due to the limited sample amount. Compounds 3–6 also showed antifungal activity against Candida albicans, and 5 was slightly active against Bacillus subtilis.
EHT Model Studies on Coordination‐Sphere Effects in the Elementary steps of d0 transition‐metal‐catalyzed Ziegler‐Natta polymerization
Authors: Mohr Roland , Berke Heinz , Erker Gerhard 
Published: December 2004

AbstractIn a theoretical investigation on Ziegler‐Natta catalysis, the influence of the coordination number and ligand type of model compounds in relevant reaction steps were studied. Thus, by using the MEHT method, insertion reactions of ethylene into Zr–CH3 and Zr–H bonds were analyzed in systems of the type [Zr(C2H4)R4R′]−[Zr(Cp)(C2H4)R2R′], and [Zr(Cp)(C2H4)R3R′]−(R=R′=CH3, R=CH3, R′=H). It was found that all processes do not have significant kinetic barriers, whereas the reverse reactions in particular the β‐hydride elimination have relatively high ones. The influence of coordination geometry and number on these transformations was found to be insignificant. While studying related conversions starting from [Zr(L)(C2H4)R3R′], [Zr(Cp)(C2H4)RR′(L)]+, and [Zr(Cp)(C2H4)R2R′(L)] (L = π‐donor, R=R′=CH3 or R=CH3, R′=H) compounds a pronounced π‐donor effect was observed. Methyl insertions in these cases showed a higher computed activation barrier than hydride migrations. An orbital basis for this phenomenon was provided and conclusions concerning chain‐length control in Ziegler‐Natta catalysis were drawn.
Highly Diastereoselective Aldol Reaction of Bicyclo[3.2.1]oct‐6‐en‐3‐ones and 8‐Oxabicyclo[3.2.1]oct‐6‐en‐3‐ones. (E)‐Selective conversion into α‐alkylidene ketones
Authors: Stohrer Ingo , Hoffmann H. Martin R. 
Published: December 2004

AbstractThe bicyclic ketones 1–6 entered into diastereoselective (> 95% d.e.) aldol reactions with a variety of aldehydes (Scheme 1 and Table 1). A representative series of aldols was converted (E)‐selectively into α,β‐unsaturated ketones by (i) spontaneous base‐promoted dehydration (Scheme 1 and Table 2) and also by (ii) conversion into brosylate and base‐mediated elimination with lithium diisopropylamide/N,N,N′,N′‐tetramethylethylenediamine (LDA/TMEDA; Scheme 2). The simple α‐methylidene ketones 17a and 18a were obtained via oxidation of the phenylselenides 19 and 20, respectively (Scheme 4). The tertiary aldol 27 was synthesized best by treatment of 1,3‐diketone 26 with Me4Zr (Table 4). In this fashion, the facile retro‐aldol reaction of 27 was suppressed effectively.
X‐Ray Molecular Structure of a Red Bilin Derivative from Chlorella protothecoides. 4th communication on chlorophyll catabolism
Authors: Engel Norbert , Gossauer Albert , Gruber Karl , Kratky Christoph 
Published: December 2004

AbstractThe molecular structure of a chlorophyll a catabolite isolated from the culture medium of bleached Chlorella protothecoides cells has been determined by X‐ray diffraction; the crystal structure shows a distorted helical arrangement of the pyrrole rings and consists of symmetrical dimers located at a crystallographic diad, which are stabilized by six intermolecular H‐bonds.
Synthesis, Structure, and Reactivity of Secosteroids Containing a Medium‐Size Ring. Part 35. Photooxidations of some (Z)‐ and (E)‐1(10)‐unsaturated 5,10‐secosteroids in acetone solution
Authors: Lorenc Ljubinka B. , Pavlović Vladimir D. , Mihailović Mihailo Lj. , Krstić Natalija M. 
Published: December 2004

AbstractUV Irradiation of (Z)‐ and (E)‐1(10)‐unsaturated 5,10‐secosteroids 1–4 in acetone solution effected, besides (Z/E)‐isomerization, (i) a stereospecific epoxidation (only in the presence of O2), which, depending on the configuration ((Z) or (E)) in the starting steroid, gave cis‐epoxides 5 and 8 (from the (Z)‐compounds 1 and 3) or trans‐epoxides 6,9, and 10 (from the (E)‐compounds 2 and 4), and (ii) oxidative acetone addition to the olefinic double bond producing 1‐acetonyl derivatives 7 and 11a, b.
Rhodium(I)‐Catalyzed ‘Metallo‐Ene’ Cyclizations/β‐Eliminations
Authors: Oppolzer Wolfgang , Fürstner Alois 
Published: December 2004

AbstractOctadienyl carbonates 5 provide cyclic 1,4‐dienes 6 when treated with Rh1 complexes (1–10 mol‐%) at 80°. Similar cyclization of cyclohexenyl acetate 8 affords cis‐ fused hexahydroindene 9. Analogous ring closures of nonadienyl carbonate 10 yield preferably the cis‐divinypyrrolidine 11 with Rh1 catalysis but the trans‐isomer 12 when catalyzed by Pd0. Azaoctadienyl carbonate 5a undergoes elimination with [RhH(PPh3)4] (5 mol‐%, 80°) in MeCN giving acyclic triene. 7.
Phenylenbis(silandiyl‐triflate) als neuartige Synthesebausteine für vielfältig strukturierte Organosilizium‐Polymere
Authors: Uhlig Wolfram 
Published: December 2004

Phenylenebis(silandiyl triflates) – New Synthetic Building Blocks for Variously Structured Organosilicon PolymersOrtho‐, meta‐, and para‐substituted phenylenebis(silandiyl triflates) are prepared as new useful building blocks for the synthesis of polymers with a regular alternating arrangement of an organosilicon unit and a π‐electron system (phenylene or ethynylene) in the backbone. Such polymers can be used as photoresists, semiconducting materials or precursors of silicon carbide. The phenylenebis(silandiyl‐triflates) 5a–c are obtained by protodesilylation of the corresponding (allylsilyl)‐ or [(diethylamino)silyl]benzenes 3a–c and 4a–c, respectively, with trifluoromethanesulfonic acid. Reactions with dinucleophiles like Li2C2 and Ph2Si(OH)2 lead to variously structured organosilicon polymers (see Eqns. 11 and 12), which are characterized by spectroscopic methods.
The Protonation of [Pt3(m̈‐CO)3(PCy3)3]
Authors: Dahmen Klaus‐Hermann , Imhof Daniel , Venanzi Luigi M. 
Published: December 2004

AbstractThe cluster [Pt3(m̈‐CO)3(PCy3)3] can be protonated with HBF4 · OEt2 to form the cluster [Pt3(m̈‐CO)3(PCy3)3](m̈3‐H) +BF (2). This unstable compound was isolated and characterised by NMR and IR spectroscopy.
β ‐Cyclodextrin‐Mediated Regioselective Hydrolysis of 5,10,15,20‐tetrakis[2,4‐bis(pivaloyloxy)phenyl]‐21H,23H ‐porphine
Authors: Matile Stefan , Hansen Thorsten , Stocker Achim , Woggon Wolf‐Dietrich 
Published: December 2004

AbstractThe four peripheral ester moieties of the title compound 5 are regioselectively hydrolyzed under mild conditions in the presence of β ‐cyclodextrin (10), providing a new entry to tetraphenylporphyrin derivatives with differently substituted Ph groups in the meso‐positions. UV, 1H‐NMR and mass spectroscopy of the inclusion complex 9 of 2,6‐O‐dimethyl‐β‐cyclodextrin (12) and 5 indicate a stoichiometry of 2:1 for 10/5. Moreover, calculations confirm NOE experiments consistent with the fact that the cyclodextrins 10 and 12 approach the Ph groups of the porphyrin with the small opening of the cavity (primary face).
Enantioselective Reduction of Electrophilic CC Bonds with sodium tetrahydroborate and ‘semicorrin’ cobalt catalysts
Authors: Misun Marian , Pfaltz Andreas 
Published: December 2004

Abstract‘Semicorrin’ cobalt complexes, prepared in situ from cobalt(II) chloride and the corresponding ligands, are efficient catalysts for the enantioselective reduction of electrophilic CC bonds with NaBH4. The best selectivities (> 90% ee) are achieved with α,β‐unsaturated carboxamides and carboxylates. Analogous α,β‐unsaturated nitriles, sulfones, and phosphonates afford enantiomeric excesses of 50–70%. Interestingly, in the reduction of α,β‐unsaturated sulfones, the highest enantioselectivities were obtained with unsymmetrical ‘semicorrins’, whereas in all other cases C2‐symmetric ‘semicorrins’ proved to be superior.
Acid‐Catalysed Backbone Rearrangement of cholesta‐6,8(14)‐dienes
Authors: Liu Rong‐Ming , Chillier Xavier F. D. , Kamalaprija Philippe , Burger Ulrich , Gülaçar Fazil O. 
Published: December 2004

AbstractRearrangement of 5α‐ and 5β‐cholesta‐6,8(14)‐dienes (13a and 13b, resp.) in the presence of anhydrous toluene‐4‐sulfonic acid in acetic acid leads to 5α‐ and 5β‐12(13 → 14)‐abeo‐cholesta‐8,13(17)‐dienes (15a and 15b, resp.) via 5α‐ and 5β‐cholesta‐8,14‐dienes (14a and 14b, resp.), respectively. Epimerization at C(20) of the spirosteradienes 15a and 15b occurs with increasing reaction time. Molecular‐mechanics calculation of the relative stabilities of these compounds and of congeners thereof is in agreement with the observed reaction pathway.
Metal Complexes with Macrocyclic Ligands. Part XLII. Tetraazamacrocyclic nickel(II) complexes with a methylthio or a methoxy pendant chain as model for cofactor F430
Authors: Schmid Claudio L. , Kempf Christian , Taubert Andreas , Neuburger Markus , Zehnder Margareta , Kaden Thomas A. , Bujno Krzysztof , Bilewicz Renata 
Published: December 2004

AbstractThe 14‐membered macrocyclic Ni2+ complexes of 1 and 2, with a methylthio pendant chain, and those of 3 and 4, with a methoxy pendant chain, have been synthesized and their chemistry has been studied. Solution spectra in H2O, MeCN, and DMF indicate no participation of the side‐chain donor group in metal coordination. This is also the case in the solid state as shown by the X‐ray structures of the Ni2+ complexes with 1 and 2, in which a tetrahedrally distorted square‐planar geometry around the Ni2+ results by the coordination of the four N‐atoms of the macrocycle. Cyclic voltammetry of these complexes in MeCN reveals that Ni2+ is reversibly reduced to Ni+ between −0.7 and −0.8 V vs. SCE. For the complexes with 1 and 2, the thioether bond is cleaved at more negative potentials, whereby a thiol group is formed. This thiol group is then oxidized at ca. +0.7 V vs. SCE, when a glassy C electrode is used, or at ca. 0 V vs. SCE at a dropping Hg electrode. No cleavage of the ether bond in the complexes with 3 and 4 is observed under similar conditions. Reduction of the Ni2+ complexes of 1 and 2 with Na‐amalgam in DMF produces small amounts of methane only in the case of 1, indicating the importance of the proximity between the NiI centre and the MeS group.
The X‐Ray Crystal Structure and Packing of a Hexakis‐adduct of C60: Temperature dependence of weak CH…︁O interactions
Authors: Seiler Paul , Isaacs Lyle , Diederich François 
Published: December 2004

AbstractThe crystal structure and packing of the C60 hexakis‐adduct 1 has been determined from accurate X‐ray diffraction measurements. The largest deformations on the C60 surface occur within the bridged pyracylene subunits; the bridgehead 6–6 bond lengths of the four cyclopropane and the two cyclohexene rings, attached in pseudo‐octahedral positions, are close to 1.6 Å. Significant deformations also occur in the remaining part of the C60 skeleton, not bridged to any of the functional groups. The crystal packing, analyzed at 270, 230, and 180 K is characterized by a three‐dimensional network of 14 weak CH…︁O interactions. For most of these, H…︁O and C…︁O distances decrease on cooling the crystal specimen, indicating that they are attractive in nature. On the other hand, the shortest, nearly linear C(sp3)H…︁O contact seems to be repulsive, since cooling of the crystal specimen leads to significantly longer H…︁O and C…︁O distances and to a reduction of the CH…︁O linearity. Probably as a result of this intermolecular expansion, strain is produced in the crystal. Depending on the crystal‐mounting procedure, this can lead either to a disordered structure (below ca. 200 K), or to destruction of the crystal specimen.
Preparation of α,α‐Dibromocyclobutanones from Olefins: A simple procedure for the regioselective functionalization of olefins
Authors: Chaumeil Hélène , Le Drian Claude 
Published: December 2004

AbstractDibromoketene is prepared by in‐situ Zn dehalogenation of tribromoacetyl bromide in the presence of POCl3. Under these conditions, the cycloaddition of dibromoketene with olefins 5 yields α,α‐dibromocyclobutanones 2, which are cleaved with alkoxides to yield β‐dibromomethyl esters 4. Several examples are given. For monosubstituted olefins, the functionalization is regioselective, the methoxycarbonyl group being introduced at the terminal C‐atom.
Asymmetric Synthesis of the Alkaloids mayfoline and N(1)‐acetyl‐N(1)‐deoxymayfoline
Authors: Kuehne Paul , Linden Anthony , Hesse Manfred 
Published: December 2004

AbstractThe total syntheses of the spermidine alkaloids (−)‐mayfoline (11) and (+)‐N(1)‐acetyl‐N(1)‐deoxymayfoline (12) are described. These macrocyclic lactams belong to the most interesting conjugates of the polyamine derivatives very commonly found in nature. The enantioselective syntheses were achieved through resolution of the methyl 3‐amino‐3‐phenylpropanoate (2) by recrystallization of its (+)‐L‐tartrate salt. Construction of the 13‐membered ring ensued through condensation, reductive ring expansion (internal bond cleavage), and finally a transamidation reaction involving a second ring expansion.
Nucleic‐Acid Analogs with Restricted Conformational Flexibility in the Sugar‐Phosphate Backbone (‘Bicyclo‐DNA’). Part 6. Probing the influence of torsion angle γ on DNA‐duplex stability: Syntheis and properties of oligodeoxynucleotides containing [(3′S,5′S)‐2′‐deoxy‐3′,5′‐ethano‐β‐D‐ribofuranosyl]adenine and ‐thymine (‘5′‐epi‐bicyclodeoxynucleosides’)
Authors: Litten J. Christopher , Leumann Christian 
Published: December 2004

AbstractThe synthesis of the thymine‐ and adenine‐containing 5′‐epi‐bicyclodeoxynucleosides 7 and 8 as well as of the corresponding building blocks 13 and 14 for oligonucleotide syntheis according to the phosphoramidite methodology is described. A conformational analysis of 7 and 8 by 1H‐NMR spectroscopy, refined by molecular modeling, shows the preferred conformation of the furanose unit in these nucleosides to be of the 1′‐exo/2′‐endo type. The 5′‐OH group on the carbocyclic ring prefers to be axially oriented, thus placing torsion angle γ in the unusual –syn‐clinal (–sc) range. These epi‐bicyclodeoxynucleosides were successfully incorporated into DNA decamers. From UV/melting curves of such decamers with DNA and RNA complements, a duplex destabilization of −2 to −9° per residue was observed. An oligonucleotide built completely from 5′‐epi‐bicyclothymidine shows no detectable affinity to its DNA or RNA complement anymore. CD Spectra of duplexes containing 5′‐epi‐bicyclodeoxynucleotide units are very similar to the natural reference systems, indicating no major structural changes. A molecular‐dynamics simulation of a heptamer duplex containing one 5′‐epibicyclothymidine residue in the center reveals a conformational change of its carbocyclic unit placing torsion angle γ in the (for the free mononucleoside unfavorable) –anti‐clinal (–ac) conformation in the duplex. The role of torsion angle γ on DNA duplex stability is discussed.
The Synthesis and Characterization of New Optically Active ‘dimeric’ ‘pineno’‐[4,5]‐fused 2,2′‐bipyridines linked without spacer or by small spacer groups
Authors: Fletcher Nicholas C. , Keene F. Richard , Ziegler Marco , Stoeckli‐Evans Helen , Viebrock Heiko , von Zelewsky Alex 
Published: December 2004

AbstractLinked chiral bipyridines 2–4 are prepared by combining two optically active ‘pineno’‐[4,5]‐fused 2,2′‐bipyridines in a stereoselective reaction (Scheme 1). These potential ligands are new members of the ‘chiragen’ family, and are characterized by NMR spectroscopy and, in the case of 2 and 3 by single‐crystal X‐ray analysis. A new synthesis of ‘dipineno’‐[4,5;4′,5′]‐fused 2,2′ ‐bipyridine 8 is described, which, when coupled, gives additional four chiral centres to the analogous ‘chiragen’ series ( → 9). Analysis of the CD spectra allowed conformational information about the solution species to be determined.
The Enantioselective Synthesis of β‐Amino Acids, their α‐hydroxy derivatives, and the N‐terminal components of bestatin and microginin
Authors: Jefford Charles W. , McNulty James , Lu Zhi‐Hui , Wang Jian Bo 
Published: December 2004

AbstractL‐Aspartic acid by tosylation, anhydride formation, and reduction with NaBH4 was converted into (3S)‐3‐(tosylamino)butan‐4‐olide (8; Scheme 1). Tretment of 8 with ethanolic trimethylsilyl iodide gave the N‐protected deoxy‐iodo‐β‐homoserine ethyl ester 9. The latter, on successive nucleophilic displacement with lithium dialkyl‐cuprates ( → 10a–e), alkaline hydrolysis ( → 11a–e), and reductive removal of the tosyl group, produced the corresponding 4‐substituted (3R)‐3‐aminobutanoic acids 12a–e (ee > 99%). Electrophilic hydroxylation of 8 ( → 19; Scheme 3), subsequent iodo‐esterification ( → 21; Scheme 4), and nucleophilic alkylation and phenylation afforded, after saponification and deprotection, a series of 4‐substituted (2S, 3R)‐3‐amino‐2‐hydroxybutanoic acids 24 including the N‐terminal acids 24e ( =3) and 24f ( =4) of bestatin and microginin (de > 95%), respectively.
Singlet‐Oxygen (1Δg) Production by Ruthenium(II) complexes containing polyazaheterocyclic ligands in methanol and in water
Authors: Garcìa‐Fresnadillo David , Georgiadou Yiola , Orellana Guillermo , Braun André M. , Oliveros Esther 
Published: December 2004

AbstractIn the context of our studies on ruthenium(II) complexes containing polyazaheterocyclic ligands, we have determined the rate constants of quenching by molecular oxygen (kq) of the metal‐to‐ligand charge‐transfer‐excited state of a series of homoleptic [RuL3] complexes (where L stands for 2,2′‐bipyridine (bpy), 1,10‐phenanthroline (phen), 2,2′‐bipyrazine (bpz), 4,7‐diphenyl‐1,10‐phenanthroline (dip), diphenyl‐1,10‐phenanthroline‐4,7‐disulfonate (dpds), and 1, 10‐phenanthroline‐5‐octadecanamide (poda)) in H2O and in MeOH. These compounds are singlet‐oxygen (O2(1Δg)) sensitizers, and quantum yields of singlet‐oxygen production (ΨΔ) in both solvents are also reported. Values of kq and ΨΔ depend on the nature of the ligand L and on the solvent, ΨΔ values showing a large range of variation (0.2 to 1.0). In MeOH, the only pathway for quenching of the excited [RuL3] complexes by molecular oxygen is energy transfer: the fraction of quenched excited states yielding singlet oxygen (ƒ) is unity for all compounds in the series investigated. Changing from MeOH to H2O has several remarkable effects: higher kq and lower ΨΔ values are observed; ƒ drops to ca. 0.5 except for [Ru(bpz)3]2+. In fact, [Ru(bpz)3]2+ is by far the weakest reductant in the series and behaves differently from the other complexes, with lowest kq and ΨΔ values and a ƒ equal to 1 in both solvents. Results are interpreted on the basis of the role played by charge‐transfer interactions between the sensitizer excited state and molecular oxygen in the quenching mechanism. RuII Complexes based on the 4,7‐diphenyl‐1, 10‐phenanthroline (dip) ligand are very efficient and stable singlet‐oxygen sensitizers with ΨΔ values close to unity in air‐saturated MeOH.