Synthesis and Spectroscopic Characterization of Two Different Types of Heterobimetallic Glycolate Complexes of Niobium(V)

An entirely new class of heterobimetallic homoleptic glycolate complexes of the type Nb(OGO)₃{Ta(OGO)₂} [where G=CMe₂CH₂CH₂CMe₂ (G¹) (3); CMe₂CH₂ CHMe(G²) (4); CHMeCHMe (G³) (5); CH₂CMe₂CH₂ (G⁴) (6); CMe₂CMe₂(G⁵) (7); CH₂CHMeCH₂ (G⁶) (8); CH₂CEt₂CH₂ (G⁷) (9); CH₂CMe(Prⁿ)CH₂ (G⁸) (10)] have been prepared by the reactions of Nb(OGO)₂(OGOH) [G=G¹ (1a); G² (1b); G³ (1c); G⁴ (1d); G⁵ (1e); G⁶ (1f); G⁷ (1g); G⁸ (1h)] with Ta(OGO)₂ (OPrⁱ) (G=G¹ (2a); G² (2b); G³ (2c); G⁴ (2d); G⁵ (2e) G⁶ (2f); G⁷ (2g); G⁸ (2h). In addition to the novel derivatives (2)–(10), our earlier investigations on heterobimetallic glycolate-alkoxide derivatives have been extended to derivatives of the type Nb(OGO) [where M=A1 n=3, G=G³ (11);G⁴ (12); G⁶ (13) G⁷ (14); G^s (15); G⁹=CH₂CH₂CH₂ (16) and M=Ti (n=4, G=G⁴) (17), Zr(n=4,G=G⁴) (18)], which are conveniently prepared by the reactions of metalloligands Nb(OGO)₂(OGOH) [G=G³ (1c); G⁴ (1d); G⁶ (1f); G⁷ (1g); G⁸ (1h); G⁹ (1i)] with different metal alkoxides. All of these new complexes have been characterized by elemental analyses, molecular weight determinations, and spectroscopic (I.r. and ¹H, ²⁷Al-n.m.r.) studies. Structural features of the new derivatives have been elucidated on the basis of molecular weight and spectroscopic data.     

SYNTHESIS AND CHARACTERIzATION OF TRIPHENYLANTIMONY (V) (O-ALKYL,O-CYCLOALKYL AND O-ARYLTRITHIOPHOSPHATES)

Triphenylantimony (V) (O-alkyl,O-cycloalkyl and O-aryltrithiophosphates) of the type Ph ₃ Sb[S ₂ (S)P(OR)] (R = Me, Et, Pr ⁿ , Pr ⁱ , Bu ⁿ , Bu ^s , Bu ⁱ , Am ⁱ , Ph and C.h. = cyclohexyl) have been synthesized for the first time by the reaction of triphenylantimony (V) dibromide with potassium trithiophosphates in 1:1 molar ratio in methanol. These new compounds have been characterized by elemental analysis, molecular weight determinations, and spectroscopic (IR,¹³C and ³¹P NMR) studies. On the basis of these data trigonal bipyramidal geometry has been proposed for these compounds.     

Synthesis of ReI tricarbonyl complexes with various sulfur‐ and oxygen‐donating ligands: crystal structures of two ReI dinuclear structures bridged by S atoms

The synthesis and characterization of two dinuclear complexes, namely fac‐hexacarbonyl‐1κ³C,2κ³C‐(pyridine‐1κN)[μ‐2,2′‐sulfanediyldi(ethanethiolato)‐1κ²S¹,S³:2κ³S¹,S²,S³]dirhenium(I), [Re₂(C₄H₈S₃)(C₅H₅N)(CO)₆], ( 1 ), and tetraethylammonium fac‐tris(μ‐2‐methoxybenzenethiolato‐κ²S:S)bis[tricarbonylrhenium(I)], (C₈H₂₀N)[Re₂(C₇H₇OS)₃(CO)₆], ( 2 ), together with two mononuclear complexes, namely (2,2′‐bithiophene‐5‐carboxylic acid‐κ²S,S′)bromidotricarbonylrhenium(I), ( 3 ), and bromidotricarbonyl(methyl benzo[b]thiophene‐2‐carboxylate‐κ²O,S)rhenium(I), ( 4 ), are reported. Crystals of ( 1 ) and ( 2 ) were characterized by X‐ray diffraction. The crystal structure of ( 1 ) revealed two Re—S—Re bridges. The thioether S atom only bonds to one of the Re^I metal centres, while the geometry of the second Re^I metal centre is completed by a pyridine ligand. The structure of ( 2 ) is characterized by three S‐atom bridges and an Re…Re nonbonding distance of 3.4879 (5) Å, which is shorter than the distance found for ( 1 ) [3.7996 (6)/3.7963 (6) Å], but still clearly a nonbonding distance. Complex ( 1 ) is stabilized by six intermolecular hydrogen‐bond interactions and an O…O interaction, while ( 2 ) is stabilized by two intermolecular hydrogen‐bond interactions and two O…π interactions.     

Synthesis and characterisation of heterobimetallic <Emphasis Type="Italic">N</Emphasis>-(hydroxyethyl)-salicylaldiminate–isopropoxide complexes of oxovanadium(V)

Soluble heterobimetallic-N-(hydroxyethyl) salicylaldiminate-alkoxide derivatives of the types [VO(L)₂{M(OPrⁱ)_n−1}] [M=Al (2) (n = 3); Ti (3), Zr (4) (n = 4); Nb (5), Ta (6) (n = 5)], [where L represents the dianionic N-(hydroxyethyl) salicylaldiminate group bonded to vanadium in a tridentate fashion involving both the oxygen atoms and azomethine nitrogen], have been prepared by the reactions of insoluble [VO(L)(LH)] (1) with different metal alkoxides in a 1:1 molar ratio in benzene. A monomeric heterobinuclear complex of the type [VO(η³-L)(μ-OPrⁱ)₂Al(η³-L)] (7) has been prepared by the equimolar reaction of [VO(η³-L)(μ-OPrⁱ)]₂ with [Al(η₃-L) (μ-OPrⁱ)]₂ in benzene. All these complexes have been characterised by elemental analyses, molecular weight measurements, and by spectroscopic (l.r., ¹H-, ²⁷Al- and ⁵¹V-n.m.r.) studies. The monomeric nature of (1) and (2) has been supported by their FAB-mass spectral studies.     

Elastic modulus of the crystalline phase of poly(cis 1,4-isoprene)

The crystalline elastic modulus of poly(cis 1,4-isoprene) has been measured by x rays and calculated by molecular mechanics. The experimental modulus is E = (2.3 ± 0.3) × 10⁹N m^?2. The calculated modulus is E = (8.8 ± 0.1) × 10⁹N m^?2 for chains in S⁺ cis S^?T conformation and E = (6.1 ± 0.1) × 10⁹N m^?2 for chains in S⁺ cis S+T conformation. The modulus calculated for a statistical structure including both conformation is E = (6.7 ± 0.1) × 10⁹N m^?2. The experimental modulus is thought to be a lower limit because of partial crystallinity of the sample. The chief mechanism of deformation is rotation around single bonds adjacent to the double bond.     

Synthesis of graft polymers with poly(isoprene) as main chain by living anionic polymerization mechanism

The graft polymers [poly(isoprene)‐graft‐poly(styrene)] (PI‐g‐PS), [poly(isoprene)‐graft‐poly(isoprene)] (PI‐g‐PI), [poly(isoprene)‐graft‐(poly(isoprene)‐block‐poly(styrene))] PI‐g‐(PI‐b‐PS), and [poly(isoprene)‐graft‐(poly(styrene)‐block‐poly(isoprene))] PI‐g‐(PS‐b‐PI) with PI as main chain were synthesized through living anionic polymerization (LAP) mechanism and the efficient coupling reaction. First, the PI was synthesized by LAP mechanism and epoxidized in H₂O₂/HCOOH system for epoxidized PI (EPI). Then, the graft polymers with controlled molecular weight of main chain and side chains, and grafting ratios were obtained by coupling reaction between PI^?Li⁺, PS^?Li⁺, PS‐b‐PI^?Li⁺, or PI‐b‐PS^?Li⁺ macroanions and the epoxide on EPI. The target polymers and all intermediates were well characterized by SEC,¹H NMR, as well as their thermal properties were also evaluated by DSC. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Preparation of 616X,6Y-Tris-O-(tert-butyldimethyl-silyl)-β-cyclodextrins,and Isolation and Regiochemical Determination of Five Positional Isomers

Abstract

Five positional isomers of 6¹,6^X,6^Y-tris-O-(tert-butyldimethylsilyl)-cyclomaltoheptaose (β-cyclodextrin, βCD) were prepared by reaction of β CD with tert-butyldimethylsilyl chloride in pyridine, and were isolated by HPLC and characterized by ¹³C NMR spectroscopy. The regiochemical determination of those positional isomers was carried out by the extended Körner's method, that is, by comparison with compounds obtained by additional monosilylation of 6¹, 6^X-bis-O-(tert-butyldimethylsilyl)-βCDs, and by conversion to the known compounds, 6¹,6^X,6^Y-tri-O-(toluene-sulfonyl)-βCDs.     

Aminophosphanes with bulky amino groups: Molecular structure,coupling constants 1J(31P, 15N) and 2J(31P, 29Si), and isotope‐induced chemical shifts 1Δ14/15N(31P)

The preferred conformation of aminophosphanes with bulky amino groups ( 1–20 ) was determined by NMR spectroscopy in solution, in two cases in the solid state ( 11,17 ) and in one case ( 11 ) by X‐ray crystallography. Trimethylsilylaminodiphenylphosphanes Ph₂PN(R)SiMe₃ (R = Bu ( 1 ), Ph ( 2 ), 2‐pyridyl ( 3 ), 2‐pyrimidyl ( 4 ), Me₃Si ( 5 )), amino(chloro)phenylphosphanes Ph(Cl)PNRR′ (R = Bz, R′ = Me ( 6 ), R = Bz, R′ = ^tBu ( 7 ), R = Et, R′ = Ph ( 8 )), amino(chloro)tert‐butylphosphanes ^tBu(Cl)PNRR′ (R = R′ = ⁱPr ( 9 ), R = Me, R′ = ^tBu ( 10 ), R = Bz, R′ = ^tBu ( 11 ), R = H, R′ = ^tBu ( 12 ), R = Et, R′ = Ph ( 13 ), R = ⁱPr, R′ = Ph ( 14 ), R = Bu, R′ = Ph ( 15 ), R = Bz, R′ = Ph ( 16 ), R = R′ = Ph ( 17 ), R = R′ = Me₃Si ( 18 )), 3‐tert‐butyl‐2‐chloro‐1,3,2‐oxazaphospholane ( 19 ), and benzyl(tert‐butyl)aminodichlorophosphane ( 20 ) were studied by ¹H, ¹³C, ¹⁵N, ²⁹Si, and ³¹P NMR spectroscopy. In all cases, the more bulky substituent at the nitrogen atom prefers the syn‐position with respect to the assumed orientation of the phosphorus lone pair of electrons. Many of the derivatives studied adopt this preferred conformation even at room temperature. Numerous signs of coupling constants ¹J(³¹P, ¹⁵N), ²J(³¹P, ¹³C), and ²J(³¹P, ²⁹Si) were determined. Low temperature NMR spectra were measured for derivatives for which rotation about the P N bond at room temperature is fast, showing the presence of two rotamers at low temperature. The respective conformation of these rotamers could be assigned by ¹³C, ¹⁵N, and ³¹P NMR spectroscopy. Isotope‐induced chemical shifts ¹Δ^15/14N(³¹P) were determined for all compounds at natural abundance of ¹⁵N by using Hahn‐echo extended polarization transfer experiments. The molecular structure of 11 in the solid state reveals pyramidal surroundings of the nitrogen atom and mutual trans‐positions of the tert‐butyl groups at phosphorus and nitrogen. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:667–676, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10084     

Manganese-Mediated Formic Acid Dehydrogenation

A robust and rapid manganese formic acid (FA) dehydrogenation catalyst is reported. The manganese is supported by the recently developed, hybrid backbone chelate ligand ^tBuPNNOP (^tBuPNNOP=2,6-(di-tert-butylphosphinito)(di-tert-butylphosphinamine)pyridine) ( 1 ) and the catalyst is readily prepared with MnBrCO₅ to form [(^tBuPNNOP)Mn(CO)₂][Br] ( 2 ). Dehydrohalogenation of 2 generated the neutral five coordinate complex (^tBuPNNOP)Mn(CO)₂ ( 3 ). Dehydrogenation of FA by 2 and 3 was found to be highly efficient, exhibiting turnover frequencies (TOFs) exceeding 8500 h⁻¹, rivaling many noble metal systems. The parent chelate, ^tBuPONOP (^tBuPONOP=2,6-bis(di-tert-butylphosphinito)pyridine) or ^tBuPNNNP (^tBuPNNNP=2,6-bis (di-tert-butylphosphinamine)pyridine), coordination complexes of Mn were synthesized, respectively affording [(^tBuPONOP)Mn(CO)₂][Br] ( 4 ) and [(^tBuPNNNP)Mn(CO)₂][Br] ( 5 ). FA dehydrogenation with the hybrid-ligand supported 2 exhibits superior catalysis to 4 and 5 .     

A Cobalt(I) Pincer Complex with an η2‐Caryl−H Agostic Bond: Facile C−H Bond Cleavage through Deprotonation,Radical Abstraction,and Oxidative Addition

The synthesis and reactivity of a Co^I pincer complex [Co(ϰ³P,CH,P‐P(CH)P^NMe‐iPr)(CO)₂]⁺ featuring an η²‐ C_aryl−H agostic bond is described. This complex was obtained by protonation of the Co^I complex [Co(PCP^NMe‐iPr)(CO)₂]. The Co^III hydride complex [Co(PCP^NMe‐iPr)(CNtBu)₂(H)]⁺ was obtained upon protonation of [Co(PCP^NMe‐iPr)(CNtBu)₂]. Three ways to cleave the agostic C−H bond are presented. First, owing to the acidity of the agostic proton, treatment with pyridine results in facile deprotonation (C−H bond cleavage) and reformation of [Co(PCP^NMe‐iPr)(CO)₂]. Second, C−H bond cleavage is achieved upon exposure of [Co(ϰ³P,CH,P‐P(CH)P^NMe‐iPr)(CO)₂]⁺ to oxygen or TEMPO to yield the paramagnetic Co^II PCP complex [Co(PCP^NMe‐iPr)(CO)₂]⁺. Finally, replacement of one CO ligand in [Co(ϰ³P,CH,P‐P(CH)P^NMe‐iPr)(CO)₂]⁺ by CNtBu promotes the rapid oxidative addition of the agostic η²‐C_aryl−H bond to give two isomeric hydride complexes of the type [Co(PCP^NMe‐iPr)(CNtBu)(CO)(H)]⁺.     

New Chromium Enolates

Three new (η²‐acrylate)(η⁶‐arene)dicarbonylchromium complexes are reported. They were obtained either by CO/acrylate exchange in [Cr(η⁶‐benzene)(CO)₃] ( 1 ) via the photolytically generated η²‐cyclooctene intermediate or by arene exchange in [Cr(η²‐methyl acrylate)(η⁶‐benzene)(CO)₂] ( 3 ) (Scheme 1). On crystallization, [Cr(η²‐methyl acrylate)(η⁶‐o‐xylene)(CO)₂] ( 5 ) underwent partial resolution. The degree of this resolution was analyzed via X‐ray crystal‐structure determination (Fig. 1) and was correlated to the CD spectra in solution (Fig. 6), thus allowing the assignment of the absolute configuration. The reaction of [Cr(η²‐acrylate)(η⁶‐benzene)(CO)₂] complexes with cyclopentad‐1,3‐diene or 1H‐indene afforded new (η⁶‐cyclopenta‐2,4‐dien‐1‐yl)‐ or (η⁶‐1H‐inden‐1‐yl)(η³‐oxaallyl)chromium complexes (Scheme 2). A mechanism is proposed that involves arene‐ligand substitution by the diene ligand, initiated by haptotropic rearrangement of the acrylate from a η²‐ to a η⁴‐coordination mode, followed by hydride migration from the diene to the acrylate (Scheme 3). An X‐ray crystal‐structure determination of [Cr(CO)₂(η⁵‐1H‐inden‐1‐yl){η³‐CH(CH₂CF₃)C(O)OEt}] ( 8 ) reveals a metal enolate that is best described as η³‐oxaallyl species (Fig. 2). A shorter, more‐efficient route to the [Cr(η⁵‐1H‐inden‐1‐yl)(η³‐oxaallyl)] complexes was devised via the reaction of [Cr(CO)₂(η²‐cyclooctene)(η⁶‐1H‐indene)] with methyl acrylate (Scheme 4).     

Quenching of biacetyl (3Au) molecules by near-resonant and off-resonant collisional partners

Laser-induced time-resolved phosphorescence has been used to evaluate the quenching of gaseous biacetyl (³A_u) molecules by various molecules at 25°C. The quenching of biacetyl (³A_u) molecules by biacetyl itself was not detectable under our experimental conditions, and a pressure-independent lifetime of 1.70 ± 0.08 msec was found. The bimolecular rate constants (units of l/mol·sec) for quenching of the ³A_u molecules by cis-2-pentene, trans-2-pentene, cis-1,3-pentadiene, trans-1,3-pentadiene, and oxygen were found to be (3.3 ± 1.9) × 10³, (4.0 ± 0.2) × 10⁴, (3.9 ± 0.1) × 10⁸, (1.3 ± 0.1) × 10⁸, and (5.2 ± 0.4) × 10⁸, respectively.     

Redox Non‐Innocence and Isomer‐Specific Oxidative Functionalization of Ruthenium‐Coordinated β‐Ketoiminate

This article deals with isomeric ruthenium complexes [Ru^III(L^R)₂(acac)] (S=1/2) involving unsymmetric β‐ketoiminates (AcNac) (L^R=R‐AcNac, R=H ( 1 ), Cl ( 2 ), OMe ( 3 ); acac=acetylacetonate) [R=para‐substituents (H, Cl, OMe) of N‐bearing aryl group]. The isomeric identities of the complexes, cct (cis‐cis‐trans, blue, a ), ctc (cis‐trans‐cis, green, b ) and ccc (cis‐cis‐cis_, pink, c ) with respect to oxygen (acac), oxygen (L) and nitrogen (L) donors, respectively, were authenticated by their single‐crystal X‐ray structures and spectroscopic/electrochemical features. One‐electron reversible oxidation and reduction processes of 1 – 3 led to the electronic formulations of [Ru^III(L)(L ^? )(acac)]⁺ and [Ru^II(L)₂(acac)]^? for 1 ⁺‐ 3 ⁺ (S=1) and 1^? – 3^? (S=0), respectively. The triplet state of 1 ⁺‐ 3 ⁺ was corroborated by its forbidden weak half‐field signal near g≈4.0 at 4 K, revealing the non‐innocent feature of L. Interestingly, among the three isomeric forms ( a – c in 1 – 3 ), the ctc ( b in 2 b or 3 b ) isomer selectively underwent oxidative functionalization at the central β‐carbon (C?H→C=O) of one of the L ligands in air, leading to the formation of diamagnetic [Ru^II(L)(L ′ )(acac)] (L ′ =diketoimine) in 4 / 4′ . Mechanistic aspects of the oxygenation process of AcNac in 2 b were also explored via kinetic and theoretical studies.     

[3+2] Cycloadditions of Metallo Nitrile Ylides and Metallo Nitrile Imines with Metal Carbonyl,Thiocarbonyl, and Isocyanide Complexes: Heterodimetallic Systems with Bridging Heterocycles [1]

The reactions of [Re(CO)₆]⁺, [FeCp(CO)₂CS]⁺ and [FeCp(CNPh)₃]⁺ with the metallo nitrile ylides [M^–{C⁺=N–C^–(H)CO₂Et}(CO)₅]^– (M = Cr, W) and the chromio nitrile imine [Cr^–{C⁺=N–N^–H}(CO)₅]^– (generated by mono‐α‐deprotonation of the parent isocyanide complexes) to give neutral 5‐metallated 1,3‐oxazolin‐ ( 1 ), 1,3‐thiazolin‐ ( 2 ), imidazolin‐ ( 3 , 4 ), 1,3,4‐oxdiazolin‐ ( 5 ), 1,3,4‐thiadiazolin‐ ( 6 ) and 1,3,4‐triazolin‐2‐ylidene ( 8 ) chromium and tungsten complexes represent the first all‐organometallic versions of Huisgen’s 1,3‐dipolar cycloadditions. The formation of 6 and 8 is accompanied by partial decomposition to (OC)₅Cr–C≡N–FeCpL₂ {L = CO ( 7 ), CNPh ( 9 )}. The structures of 4a and 5 have been characterized by X‐ray diffraction.     

β‐Diketiminate‐Stabilized Magnesium(I) Dimers and Magnesium(II) Hydride Complexes: Synthesis,Characterization, Adduct Formation,and Reactivity Studies

The preparation and characterization of a series of magnesium(II) iodide complexes incorporating β‐diketiminate ligands of varying steric bulk and denticity, namely, [(ArNCMe)₂CH]^? (Ar=phenyl, (^PhNacnac), mesityl (^MesNacnac), or 2,6‐diisopropylphenyl (Dipp, ^DippNacnac)), [(DippNCtBu)₂CH]^? (^tBuNacnac), and [(DippNCMe)(Me₂NCH₂CH₂NCMe)CH]^? (^DmedaNacnac) are reported. The complexes [(^PhNacnac)MgI(OEt₂)], [(^MesNacnac)MgI(OEt₂)], [(^DmedaNacnac)MgI(OEt₂)], [(^MesNacnac)MgI(thf)], [(^DippNacnac)MgI(thf)], [(^tBuNacnac)MgI], and [(^tBuNacnac)MgI(DMAP)] (DMAP=4‐dimethylaminopyridine) were shown to be monomeric by X‐ray crystallography. In addition, the related β‐diketiminato beryllium and calcium iodide complexes, [(^MesNacnac)BeI] and [{(^DippNacnac)CaI(OEt₂)}₂] were prepared and crystallographically characterized. The reductions of all metal(II) iodide complexes by using various reagents were attempted. In two cases these reactions led to the magnesium(I) dimers, [(^MesNacnac)MgMg(^MesNacnac)] and [(^tBuNacnac)MgMg(^tBuNacnac)]. The reduction of a 1:1 mixture of [(^DippNacnac)MgI(OEt₂)] and [(^MesNacnac)MgI(OEt₂)] with potassium gave a low yield of the crystallographically characterized complex [(^DippNacnac)Mg(μ‐H)(μ‐I)Mg(^MesNacnac)]. All attempts to form beryllium(I) or calcium(I) dimers by reductions of [(^MesNacnac)BeI], [{(^DippNacnac)CaI(OEt₂)}₂], or [{(^tBuNacnac)CaI(thf)}₂] have so far been unsuccessful. The further reactivity of the magnesium(I) complexes [(^MesNacnac)MgMg(^MesNacnac)] and [(^tBuNacnac)MgMg(^tBuNacnac)] towards a variety of Lewis bases and unsaturated organic substrates was explored. These studies led to the complexes [(^MesNacnac)Mg(L)Mg(L)(^MesNacnac)] (L=THF or DMAP), [(^MesNacnac)Mg(μ‐AdN₆Ad)Mg(^MesNacnac)] (Ad=1‐adamantyl), [(^tBuNacnac)Mg(μ‐AdN₆Ad)Mg(^tBuNacnac)], and [(^MesNacnac)Mg(μ‐tBu₂N₂C₂O₂)Mg(^MesNacnac)] and revealed that, in general, the reactivity of the magnesium(I) dimers is inversely proportional to their steric bulk. The preparation and characterization of [(^tBuNacnac)Mg(μ‐H)₂Mg(^tBuNacnac)] has shown the compound to have different structural and physical properties to [(^tBuNacnac)MgMg(^tBuNacnac)]. Treatment of the former with DMAP has given [(^tBuNacnac)Mg(H)(DMAP)], the X‐ray crystal structure of which disclosed it to be the first structurally authenticated terminal magnesium hydride complex. Although attempts to prepare [(^MesNacnac)Mg(μ‐H)₂Mg(^MesNacnac)] were not successful, a neutron diffraction study of the corresponding magnesium(I) complex, [(^MesNacnac)MgMg(^MesNacnac)] confirmed that the compound is devoid of hydride ligands.     

Sensitivity of Positive Ion Mode Electrospray Ionization Mass Spectrometry in the Analysis of Thiol Metabolites

High signal intensities of glutathione (GSH), [GSH+H]⁺ (m/z 308), cysteine (CySH), [CySH+H]⁺ (m/z 122), and homocysteine (hCySH), [hCySH+H]⁺ (m/z 136), are observed in ESI MS with on‐line electrochemistry (EC). Dimers formed by H‐bonding, which are not electrochemical products, are detected as [2GSH+H]⁺ (m/z 615), [2CySH+H]⁺ (m/z 243) and [2hCySH+H]⁺ (m/z 271) together with disulfide dimers GSSG, CySSCy and hCySSCyh, [GSSG+H]⁺ (m/z 613), [CySSCy+H]⁺ (m/z 241) and [hCySSCyh+H]⁺ (m/z 269). When dopamine is present a thiol/dopamine quinone (DAQ) adduct is observed. Formation of this adduct is proposed to occur by an electrochemical mechanism during ESI. Catalysis of thiol oxidation and analysis of thiol mixtures is addressed.     

Antibacterial activity of a new class of tris homoleptic Ru (II)-complexes with alkyl-tetrazoles as diimine-type ligands

Herein, we describe a new family of tris chelate homoleptic Ru (II) complexes, [Ru(N^N) ₃ ] ²⁺ , where the role of the diimine-type ligands (N^N) was fulfilled by 2-pyridyl (PTZ) or 2-quinolyl tetrazole (QTZ) derivatives decorated with various alkyl substituents at the N-2 position of the tetrazole ring. The new Ru (II) complexes with general formula [Ru (PTZ-R) ₃ ] ²⁺ and [Ru (QTZ-R) ₃ ] ²⁺ , were obtained as mixtures of facial (fac) and meridional (mer) isomers, as suggested by NMR (¹H, ¹³C) experiments, and confirmed in the case of mer-[Ru (QTZ-Me) ₃ ] ²⁺ , by X-ray crystallography. The photophysical behavior of the tetrazole-based [Ru(N^N) ₃ ] ²⁺ type species was investigated by UV–vis absorption spectroscopy, providing trends typical of polypyridyl Ru (II) complexes. The new homoleptic complexes fac/mer- [Ru (PTZ-R) ₃ ] ²⁺ and fac/mer- [Ru (QTZ-R) ₃ ] ²⁺ have been assessed for any eventual antimicrobial activity towards two different bacteria such as Gram-negative Escherichia coli and Gram-positive Deinococcus radiodurans. Whereas being inactive toward E. coli, the response of agar disks diffusion tests suggested that some of the new fac/mer Ru (II) complexes could inhibit the growth of D. radiodurans. This effect was further investigated by determining the growth kinetics in liquid medium of D. radiodurans exposed to the fac/mer- [Ru (PTZ-R) ₃ ] ²⁺ and fac/mer- [Ru (QTZ-R) ₃ ] ²⁺ complexes at different concentrations. The outcome of these experiments highlighted that the turn-on of the growth inhibitory effect took place as the linear hexyl chain was appended to the PTZ or QTZ scaffold, suggesting also how the inhibitory activity appeared more pronouncedly exerted by the facial isomers fac- [Ru (PTZ-Hex) ₃ ] ²⁺ and fac- [Ru (QTZ-Hex) ₃ ] ²⁺ (MIC = ca. 3.0 μg/ml) with respect to the corresponding meridional isomers (MIC = ca. 6.0 μg/ml).     

Absolute rate constants for the addition of hydroxymethyl radicals to alkenes in methanol solution

Absolute rate constants and their temperature dependencies were determined for the addition of hydroxymethyl radicals (CH₂OH) to 20 mono- or 1,1-disubstituted alkenes (CH₂ = CXY) in methanol by time-resolved electron spin resonance spectroscopy. With the alkene substituents the rate constants at 298 K (k₂₉₈) vary from 180 M^?1s^?1 (ethyl vinylether) to 2.1 middot; 10⁶ M^?1s^?1 (acrolein). The frequency factors obey log A/M^?1s^?1 = 8.1 ± 0.1, whereas the activation energies (E_a) range from 11.6 kJ/mol (methacrylonitrile) to 35.7 kJ/mol (ethyl vinylether). As shown by good correlations with the alkene electron affinities (EA), log k₂₉₈/M^?1s^?1 = 5.57 + 1.53 · EA/eV (R² = 0.820) and E_a = 15.86 ? 7.38 · EA/eV (R² = 0.773), hydroxymethyl is a nucleophilic radical, and its addition rates are strongly influenced by polar effects. No apparent correlation was found between E_a or log k₂₉₈ with the overall reaction enthalpy. © 1995 John Wiley & Sons, Inc.     

Mononukleare und mehrfach verbrückte dinukleare Phthalocyaninate(1–/2–) des Yttriums durch Solvenz‐kontrollierte Kondensation; kleine Solvenz‐Cluster als Liganden

Mononuclear and Multiply Bridged Dinuclear Phthalocyaninates(1–/2–) of Yttrium by Solvent Controlled Condensation; Small Solvent Clusters as Ligands Green chlorophthalocyaninato(2–)yttrium(III), [Y(Cl)pc^2–] forms when yttrium chloride is heated with o‐phthalonitrile in 1‐chloronaphthalene. Black cis‐di(chloro)phthalocyaninato(1‐)yttrium(III), ^cis[Y(Cl)₂pc^–] is obtained as a stable intermediate by partial reduction. Both complexes are soluble in many O‐donor solvents and pyridine. The solubility in water is remarkable: [Y(Cl)pc^2–] dissolves with green, ^cis[Y(Cl)₂pc^–] with red‐violet color. Typical absorptions of the pc^2– ligand are observed at 14800 and 29700 cm^–1. A solvent dependent monomer‐dimer equilibrium is found for the pc^– radical. The monomer with absorptions at 12100 and 19900 cm^–1 is favored in non‐polar solvents, while in polar solvents the dimer with absorptions at 8700, 13200 and 18600 cm^–1 is preferred. cis‐Tri(dimethylformamide)chlorophthalocyaninato(2–)yttrium(III) etherate ( 1 ) crystallises from a solution of [Y(Cl)pc^2–] in MeOH/dmf, cis‐tetra(dimethylsulfoxide)phthalocyaninato(2–)yttrium(III) chloride etherate methanol disolvate ( 2 ) from thf/dmso, μ‐di(chloro)‐μ‐di〈di(pyridine)(μ‐water)〉di(phthalocyaninato(2–)‐ yttrium(III)) ( 5 ) from py, and cis‐(chloro)pyridine(triphenylphosphine oxide)phthalocyaninato(2–)yttrium(III) semi‐etherate ( 3 ) is obtained from a solution of [Y(Cl)pc^2–] and triphenylphosphine oxide in py. 1 condenses in MeOH yielding a (1 : 1)‐mixture ( 4 ) of μ‐di(chloro)di(〈trans‐(diwaterdimethanol)〉〈dimethanol〉phthalocyaninato(2–)yttrium(III)) ( 4 a ) and μ‐di(chloro)di(dimethylformamide〈dimethanol〉phthalocyaninato(2–)yttrium(III)) ( 4 b ); co‐ordinatively bound solvent clusters are in brakets. The structures of 1 – 5 have been established by X‐ray crystallography. Apart from 3 with hepta‐co‐ordinated yttrium, the metal ion prefers octa‐co‐ordination, and the bond arrangement around Y³⁺ is always a distorted quadratic antiprism. In the dinuclear complexes obtained by solvent controlled condensation both antiprisms share an edge by two μ‐Cl atoms in 4 , while in 5 the antiprisms are face‐shared by two trans positioned μ‐Cl atoms and μ‐O atoms, respectively. In 5 , the bent ^b〈{py}₂(μ‐H₂O)〉 cluster is stabilised by a combined interplanar bonding of pyridine by short N…H–O bonds (d(N…O) = 2.664(7) Å; 2.81(2) Å) and strong van‐der‐Waals interactions with the ecliptic pc^2– ligands. 4 a and 4 b contain the dimeric methanol cluster 〈(MeOH)₂〉, and 4 a in addition the cyclic heterotetrameric trans‐diwaterdimethanol cluster, trans^c〈(H₂O)₂(MeOH)₂〉. The neutral clusters co‐ordinatively bound to the Y atom are compared with structurally established cluster‐anions of type 〈(OMe)(MeOH)〉^–, linear ^l〈(OMe)(MeOH)₂〉^–, cyclic ^c〈(OH)₃(H₂O)₃〉^3–, ^b〈{H₂O}₂(μ‐O)〉^2–, and ^b{H₂O}₂(μ‐F)〉^–.     

A Cobalt(I) Pincer Complex with an η2‐Caryl−H Agostic Bond: Facile C−H Bond Cleavage through Deprotonation,Radical Abstraction,and Oxidative Addition

The synthesis and reactivity of a Co^I pincer complex [Co(?³P,CH,P‐P(CH)P^NMe‐iPr)(CO)₂]⁺ featuring an η²‐ C_aryl?H agostic bond is described. This complex was obtained by protonation of the Co^I complex [Co(PCP^NMe‐iPr)(CO)₂]. The Co^III hydride complex [Co(PCP^NMe‐iPr)(CNtBu)₂(H)]⁺ was obtained upon protonation of [Co(PCP^NMe‐iPr)(CNtBu)₂]. Three ways to cleave the agostic C?H bond are presented. First, owing to the acidity of the agostic proton, treatment with pyridine results in facile deprotonation (C?H bond cleavage) and reformation of [Co(PCP^NMe‐iPr)(CO)₂]. Second, C?H bond cleavage is achieved upon exposure of [Co(?³P,CH,P‐P(CH)P^NMe‐iPr)(CO)₂]⁺ to oxygen or TEMPO to yield the paramagnetic Co^II PCP complex [Co(PCP^NMe‐iPr)(CO)₂]⁺. Finally, replacement of one CO ligand in [Co(?³P,CH,P‐P(CH)P^NMe‐iPr)(CO)₂]⁺ by CNtBu promotes the rapid oxidative addition of the agostic η²‐C_aryl?H bond to give two isomeric hydride complexes of the type [Co(PCP^NMe‐iPr)(CNtBu)(CO)(H)]⁺.