Showing papers on "Denticity published in 1994"

Synthesis and characterization of rigid bidentate nitrogen ligands and some examples of coordination to divalent palladium. X-ray crystal structures of bis(p-tolylimino)acenaphthene and methylchloro[bis(o,o'-diisopropylphenyl-imino)acenaphthene]palladium

Abstract: The synthesis and characterization of the rigid bidentate nitrogen ligands bis-(phenylimino)camphane (Ph-BIC) and a series of bis(arylimino)acenaphthenes (Ar-BIAN) is described. These ligands were synthesized by the reaction of camphorquinone or acenaphthenequinone with the corresponding (substituted) aniline in the presence of ZnCl2 or NiBr2, followed by removal of the metal salt in a subsequent step. NDDO calculations on p Tol-BIAN showed that the electronic properties of this ligand are comparable to the open-chain analogue Ph-DAB (DAB = 1,4-diaza-1,3-butadiene). The aromatic group on the imine N atom of Ar-BIAN ligands is orientated out of the bis(imino)acenaphthene plane, leading to the formation of syn and anti isomers for the ortho-substituted derivatives o-MeC6H4-BIAN and o-i PrC6H4-BIAN. In solution one isomer is observed for these ligands, but upon coordination to a Pd(Me)Cl fragment both syn and anti forms are present, as two isomers are formed. Furthermore, the attempted synthesis of bis(isopropylimino)cyclohexane is described, but it was found that a tautomeric imine-enamine compound is formed which coordinates to palladium(II) in a monodentate fashion, which could not be converted to a chelating ligand. The structures of p Tol-BIAN and Pd(Me)Cl(o,o′-i Pr2C6H3-BIAN) in the solid state were determined by X-ray diffraction. p Tol-BIAN is monoclinic, space group C2, a = 20.021(2), b = 8.7703(10), c = 5.5664(10) A, β = 103.37(1)°, Z = 2, final R = 0.040 for 963 reflections with I > 2.5σ(I). Pd(Me)Cl(o,o′-i Pr2C6H3-BIAN) is orthorhombic, space group Pbca, a = 11.440(2), b = 21.250(3), c = 27.087(2) A, Z = 8, final R = 0.043 for 2433 reflections with I > 2.0σ(I >).

Insertion of carbon monoxide and alkenes in palladium-carbon bonds of complexes containing rigid bidentate nitrogen ligands: the first example of isolated complexes in stepwise successive insertion reactions on the way to polyketones

Abstract: Facile successive insertion of carbon monoxide and strained alkenes has been observed for both neutral Pd(R)X(Ar-BIAN) and cationic [Pd(R)(MeCN)(Ar-BIAN)]SO 3 CF 3 complexes, i.e., complexes containing the rigid bidentate nitrogen ligands bis(arylimino)acenaphthene (Ar-BIAN; Ar=p-MeOC 6 H 4 (p-An), p-MeC 6 H 4 (p-Tol), o,o'-i-Pr 2 C 6 H 3 ), leading to the formation of new multiple insertion products of the type Pd{CH(R'CH(R')C(O)CH(R')CH(R')C(O0)R}X(Ar-BIAN). It appears that the rigidly chelating Ar-BIAN ligands have an activating effect on the insertion of CO and alkenes in palladium-carbon bonds as compared to other (bidentate) phosphorus and nitrogen ligands and a stabilizing effect on the Pd-acyl and Pd-alkyl complexes formed

Metal complex source reagents for MOCVD

Abstract: Metal organic chemical vapor deposition (MOCVD) source reagents useful for formation of metal-containing films, such as thin film copper oxide high temperature superconductor (HTSC) materials The source reagents have the formula MAyX wherein: M is a metal such as Cu, Ba, Sr, La, Nd, Ce, Pr, Sm, Eu, Th, Gd, Tb, Dy, Ho, Er, Tm Yb, Lu Bi, Tl, Y or Pb; A is a monodentate or multidentate organic ligand; y is 2 or 3; MAy is a stable sub-complex at STP conditions; and X is a monodentate or multidentate ligand coordinated to M and containing one or more atoms independently selected from the group consisting of atoms of the elements C, N, H, S, O, and F The ligand A may for example be selected from beta-diketonates, cyclopentadienyls, alkyls, perfluoroalkyls, alkoxides, perfluoroalkoxides, and Schiff bases The complexes of the invention utilize monodentate or multidentate ligands to provide additional coordination to the metal atom, so that the resulting complex is of enhanced volatility characteristics, and enhanced suitability for MOCVD applications

Zerovalent palladium and platinum complexes containing rigid bidentate nitrogen ligands and alkenes: synthesis, characterization, alkene rotation and substitution reactions. X-ray crystal structure of [Bis((2,6-diisopropylphenyl)imino)acenaphthene](maleic

Abstract: A number of zerovalent palladium and platinum M(NN)(alkene) complexes, containing the rigid bidentate nitrogen ligands bis(arylimino)acenaphthene (Ar-BIAN) and bis(phenylimino)camphane (Ph-BIC) have been synthetized and characterized. Stable complexes were obtained with electron poor alkenes, such as dimethyl fumarate, fumaronitrile, maleic anhydride, and tetracyanoethylene. Complexes bearing asymmetric Ar-BIAN or Ph-BIC ligands occurred as mixtures of isomers. From IR, UV, and 1 H and 13 C NMR spectroscopy and from substitution reactions it was concluded that the back-donation of electron density from the metal to the alkene is the major factor determining the stability of the complexes

Host-Guest Chemistry of a New Class of Macrocyclic Multidentate Lewis Acids Comprised of Carborane-Supported Electrophilic Mercury Centers?

Abstract: The synthesis and characterization of a family of carborane-supported macrocycles containing electrophilic mercury centers is described. These compounds are multidentate Lewis acids which have been demonstrated to bind anions such as C1-, Br, I-, and closo-BloHlo2- as well as uncharged nucleophilic species. The lithium salts of the anionic complexes (( 1,2-C2BloH10Hg)&)Li,(l.XnLi,; X = C1, Br, n = 1; X = I, n = 1 or 2) were synthesized from the reaction of closo-1,2-Li~-l,2-C~B~~H~~ with HgX2 (X = C1, Br, and I) in 70-80% yields. The free host ( 12lmercuracarborand-4 (1) was obtained by the removal of halide ions from 1.1~~- with AgOAc. The molecular structures of l-CILi, (l.Br)z- (benzo( 15)crown-5)3-Liz(H20)2, and l*Iz(AsPh4)2 have been determined from single-crystal X-ray diffraction studies. 1.ClLi crystallizes in the tetragonal space group P4/mcc, a = 14.3233(8) A, c = 11.2641(7) A, V = 2311 A3, z = 2 (l/! of the tetramer per asymmetricunit), R = 0.041, R, = 0.060. (l.Br)z(dibenzo( 1 5)crown-5)yLi2(H20)2 crystallizes

Stereo- and enantioselective alternating copolymerization of [alpha]-olefins with carbon monoxide -- Synthesis of chiral polymers

Abstract: Palladium(II) compounds of the type [PdL[sub 2](MeCN)[sub 2](MeCN)[sub 2]](BF[sub 4])[sub 2](L[sub 2] = chiral bidentate ligand) have been used as catalysts for the synthesis of chiral alternating [alpha]-olefin-carbon monoxide copolymers. For the synthesis of the chiral propylene-carbon monoxide copolymer and the ethylene-propylene-carbon monoxide terpolymer, chiral bidentate phosphines were employed as the ligand. The alternating styrene-carbon monoxide copolymers made thus far have been highly syndiotactic and since isotactic segments in the polymer backbone were required for chirality, a new ligand system was needed. When 2-pyridinecarboxaldehydeimine derivatives were used as the bidentate ligand, the ratio of isotactic to syndiotactic segments in the styrene-carbon monoxide copolymers was found to increase with increasing steric size of the substituent on the imine nitrogen, and when the enantiomerically pure 2-pyridinecarboxaldehyde-N-[alpha]-methylbenzylimine was employed, chiral alternating styrene-carbon monoxide copolymers were obtained. Finally, it appears that the optical rotations of the chiral copolymers were primarily due to the presence of stereogenic tertiary carbon centers in the polymer backbone with only minimal contribution from polymer conformation.

Characterization of Vanadium(V) Complexes in Aqueous Solutions: Ethanolamine- and Glycine-Derived Complexes

Abstract: The preferred coordination geometry of vanadium(V) in aqueous solution with nitrogen- and oxygen-containing multidentate ligands has been determined. The ligands all contain at least two oxygen functionalities and one amine functionality and are derived from diethanolamine (DEA), glycine, and ethylenediaminetetraacetic acid (EDTA). The complexes of 17 ligands have been examined using a combination of 1 H, 13 C, 51 V, and 17 O NMR spectroscopy and IR and UV-vis spectrophotometries. When possible, correlations with solid-state structures have been made, although in several cases the structure in the solid state deviates from that observed in aqueous solution

Self-Assembly of Heteronuclear Supramolecular Helical Complexes with Segmental Ligands

Abstract: The segmental bidentatetridentate ligand 5-{2”[6”-( 1”'-(3,5- imethoxybenzyl)- 1'”H-benzimidazol-2”'- yl)-pyridin-2”-yl] - 1' -methyl- 1' H-benzimidazol-5'-ylmethy1l- 1 - methyl-2-(6””- ethylpyridine-2””-yl)- 1H -b enzimidazole (Ll) reacts with Fe(II), Zn(II), and Co(I1) in acetonitrile to give mononuclear head-to-head complexes [M(L1)2]2+ where the two tridentate units of the ligands are pseudo-octahedrally coordinated to M(I1). Detailed electrospray-mass spectrometeric (ES-MS), spectrophotometric, and ‘H-NMR studies show that a second metal ion can react with [M(L1)2]2+ to give homodinuclear C2-symmetrical head-to-head double helical complexes [M2(L1)2]4+ where the second cation is pseudotetrahedrally bound by the two remaining bidentate units of the ligands. When M = Fe(II), thermodynamic data show that the second metal ion is only weakly coordinated, while for M = Zn(II), Co(II), which display greater affinities for tetrahedral coordination, stable homodinuclear [ M2(L1)2I4+ are obtained in acetonitrile. Reaction of [Fe(L1)212+ with Ag(1) produces the self-assembled C2-symmetrical heterodinuclear double-helical complex [FeAg(L1)2I3+ where Fe(I1) occupies the pseudo-octahedral site defined by the two tridentate units of the ligands and Ag(1) lies in the remaining pseudotetrahedral site. Similarly, the trilepticligand l,l'-dimethyl-2,2'-bis[6-(methylpyridin- 2-yl)-S,S'-{pyridine-2,6-diylbis[( 1-methyl-1 H -benzimidazole-,5-diyl)methylene])bis[1 H -benzimidazole] (L2) reacts with Fe(1I) and Ag(1) (stoichiometricratio 1:2) to give the first self-assembled D2-symmetrical heterotrinuclear complex [FeAgz(L2)2]4+ where Fe(I1) is located in the central pseudo-octahedral site (bistridentate) and Ag(1) occupy the two capping pseudotetrahedral sites. 1H-NMR measurements are compatible with a double-helical or a catenate structure for [FeAgz(L2)2l4+. The selectivity of the self-assembly processes is discussed together with thermodynamic and structural factors required for the formation of helical heteropolynuclear complexes.

Magnetic exchange through hydrogen bonds: structural and magnetic characterization of cis-hydroxoaquachromium(III) complexes of tetradentate and monodentate ligands

Abstract: The syntheses and characterization of a series of chromium(III) complexes of the general type cis-(CrA 4 (OH)-(OH 2 )] 2+ are described. The ligands A 4 used include 1,4,8,11-tetraazacyclotetradecane (cyclam), N,N'-bis(2-pyridylmethyl)-1,3-propandiamine (bispictn),... , and ammonia. The binuclear complex (Cr(bispic-Me 2 en)(OH)(OH 2 )](ClO 4 ) 2 , crystallizes in space group P2 1 /n of the monoclinic system with eight mononuclear formula units in a cell of dimensions a=14.381 (4) A, b=15.054(4) A, c=21.547(6) A, and β=105.94(2) o

Chapter 1 – Chemistry of iron and copper in radical reactions

Abstract: Iron and copper catalyze the formation of oxyradicals. This chapter discusses the chemistry of iron and copper in radical reactions and emphasizes on the quantitative aspects of metal-catalyzed oxyradical reactions. The structures of metal complexes, rate constants, and reduction potentials are also discussed. Under physiologically relevant conditions iron is, and copper is likely to be, bound to ligands other than water. The ligands influence rate constants and chelating agents that allow access to the metal react faster with hydrogen peroxide. For a catalyst to be effective, it should not be inactivated by the products formed. For the Fenton reaction, this means that the hydroxyl radical should not react with the ligand, and that the other product, the hydroxide anion, should not be able to displace the multidentate ligand from the iron(III) ion. Ligands also determine reduction potentials, and this can be used to generate conditions to prevent the Fenton reaction.

Linking Deprotonation and Denticity of Chelate Ligands. Rhenium(V) Oxo Analogs of Technetium-99m Radiopharmaceuticals Containing N2S2 Chelate Ligands

Abstract: The authors studied rhenium(V) oxo complexes of the polydentate ECH (ECH{sub 6} = (2R,7R)-2,7-dicarboxy-3,6-diaza-1,8-octanedithiol) and the tetramethylated ECH{sub 6} (TMECH{sub 6}) ligands by NMR spectroscopy. The coordination geometries of these complexes were explored with specific attention paid to the relationship between protonation and binding geometries.

Stereochemical Investigation of Bis(bidentate)-Palladium(II) Complexes. Transmission of Ring Chiralities between Chelating Amine Ligands via Their Prochiral N-Methyl Substituents

Abstract: Three diastereomeric palladium(II) complex cations containing the orthometalated (S)-dimethyl(1-(α-naphthyl)ethyl)amine together with the (R,R)-, (S,S)- and (R,S)- forms of N,N,N',N'-tetramethyl-2,3-butanediamine have been prepared separately as their pcrchlorate salts. The (S,R,R) isomer with [α] D +167 o (c 1.0, CH 2 Cl 2 ) crystallixes in the space group P2 1 2 1 2 1 with a=7.872 (3) A, b=15.843 (5) A, c=20.273 (6) A, Z=4, and R=0.0372.The square-planar geometry around palladium is slightly distorted. The (S,S,S) isomer with [α] D +87 o (c 1.0, CH 2 Cl 2 ) crystallizes in the spaces group P2 1 , with a=7.978 (2) A, b=20.856 (2) A, c=15.218 (2) A, β=90.06 (2) o , Z=4 and R=0.0362

2,2′:6′,2″-Terpyridine (terpy) acting as a fluxional bidentate ligand. Part 4. cis-[M(C6F5)2(terpy)](M = Pd or Pt): nuclear magnetic resonance studies of their solution dynamics and crystal structure of cis-[Pd(C6F5)2(terpy)]

Abstract: 2,2′:6′,2″-Terpyridine reacted with trans-[M(C6F5)2(diox)2](M = Pd or Pt, diox = 1,4-dioxane) to form the square-planar complexes cis-[M(C6F5)2(terpy)] in which the terpyridine acts as a bidentate chelate ligand. In solution these complexes are fluxional with the terpyridine oscillating between equivalent bidentate modes by a mechanism consisting of a ‘tick-tock’ twist of the metal moiety through an angle equal to the N–M–N angle of the metal centre. Rates of this fluxion were measured by NMR spectroscopy from the exchange effects on the 1H signals of the aromatic hydrogens and in the 19F signals of two C6F5 groups. The ΔG‡ values for the fluxion were ca. 71 and 94 kJ mol–1 for the complexes of PdII and PtII respectively. At below-ambient temperatures further changes in the 19F NMR spectra of both complexes were interpreted in terms of varying rates of rotation of the unco-ordinated pyridine ring, with the rates of rotation of the C6F5 rings being substantially slower at all temperatures and not separately measurable. The lowest-temperature spectra suggested the presence of a pair of degenerate rotamers each having the planes of both C6F5 rings and the unco-ordinated pyridine ring closely parallel and orthogonal to the remainder of the ligand ring system. The crystal structure of [Pd(C6F5)2(terpy)] confirms the bidentate chelate bonding of terpy with a N–Pd–N angle of 77.9°, and the pendant ring oriented at an angle of 46° to the adjacent co-ordinated ring.

Synthesis of Silver(I) Complexes with the Bis(diphenylphosphanyl)‐o‐carborane Ligand. Crystal Structure of [Ag(phen){(PPh2)2C2B10H10}]ClO4 and [Ag{(SPPh2)2CH2}{(PPh2)2C2B10H10}]ClO4 · CH2Cl2

Abstract: Silver(I) perchlorate or nitrate react readily with bis(di-phenylphosphanyl)-o-carborane to give the complexes [AgX{(PPh2)2C2B10H10}] [X = ClO4 (1), NO3, (2)]. The perchlorate ligand is weakly bound to the silver atom and thus can be displaced by other ligands affording the three-coordinated complexes [AgL{(PPh2)2C2B10H10}]ClO4 [L = PPh3 (3), PPh2Me (4), AsPh3 (5), C5H4NCOOH (6), C9H6NCOOH (7), SPPh3 (8)]. Compounds 3 and 4 can also be obtained by reaction of [Ag(OClO3)PR3] with the diphosphane. Treatment of complex 1 with bidentate ligands leads to the cationic four-coordinated [Ag(LL){(PPh2)2C2B10H10}]ClO4 [LL = (PPh2)2C2B10H10 (9), bipy (10), phen (11), (SPPh2)2CH2 (12)] or to the neutral [Ag(S2CNR2){(PPh2)2C2B10H10}] [NR2 = NEt2 (13), NC4H8 (14)]. The crystal structures of 11 and 12 have been established by X-ray crystallography. In both complexes the silver(I) atoms exhibit tetrahedral coordination by two phosphorus and two nitrogen or two sulfur atoms, respectively.

Synthesis and characterization of diorganotin(IV) derivatives of 2-mercaptopyridine and crystal structure of diphenyl pyridine-2-thiolatochlorotin(IV)

Abstract: Diorganotin(IV) derivatives of 2-mercaptopyridine (HSPy), R2Sn(SPy)2, R2SnCl(SPy) (R = Me, iPr, nBu, tBu, Cy, Ph) and Cy2SnBr(SPy), were obtained from R2SnX2 (X = Cl, Br) and NaSPy. Ph2SnCl(SPy) crystals, as determined by singlecrystal X–ray diffraction, are monoclinic in the space group P21/n. Tin forms with the bidentate SPy ligand a four–membered chelate ring with a short NSnS bite angle of 64.8(1)° leading to a heavily distorted trigonal–bipyramidal environment about tin. Apical Cl–Sn–N angle = 156.1(1)° equatorial C–Sn–C angle = 121.9(2)°. From 119Sn Mossbauer and IR data, analogous structures are inferred for the other solid compounds R2SnX(SPy), and distorted octahedral molecular structures for the solid compounds R2Sn(SPy)2 with R in the trans position, and sulfur atoms and nitrogen–donor atoms each in cis positions. According to IR and 1H, 13C and 119Sn NMR data, the solid–state molecular structures are retained in chloroform solution.

A New Optically Active Monodentate Phosphine Ligand, (R)-(+)-3-Diphenylphosphino-3′-methoxy-4,4′-biphenanthryl (MOP-phen): Preparation and Use for Palladium-Catalyzed Asymmetric Reduction of Allylic Esters with Formic Acid

Abstract: (R)-(+)-3-Diphenylphosphino-3'-methoxy-4,4'-biphenanthryl (MOP-phen, 8) was prepared starting with (-)-3,3'-dihydroxy-4,4'-biphenanthryl. The absolute configuration of (+)-8 was determined to be R by X-ray crystal structure analysis of its π-allylpalladium complex. The monodentate optically active phosphine 8 was found to be a more enantioselective ligand than (R)-(+)-2-diphenylphosphino-2'-methoxy-1,1'-binaphthyl (MOP, 1a) for palladium-catalyzed asymmetric reduction of allylic esters with formic acid giving optically active olefins of up to 85% ee

Tetracyanoquinodimethane Derivatives of Macrocyclic Nickel(II) Complexes. Synthesis and Crystal Structure of Bis(7,7,8,8-tetracyanoquinodimethanido)(1,8-bis(2-hydroxyethyl)-1,3,6,8,10,13-hexaazacyclotetradecane)nickel(II)

Abstract: The reactivity of the dichloro(1,8-disubstituted-1,3,6,8,10,13-hexaazacyclotetradecane)nickel(II) complex [NiCl 2 L R ] (R=C 2 H 4 OH, C 2 H 5 , CH 2 C 6 H 5 ) toward LiTCNQ leads to a complete replacement of the chloride groups by the anionic TCNQ .- with formation of complexes of formulas (NiL R (TCNQ) 2 ]. The crystal structure of the hydroxyethyl derivative has been solved. The nickel atom is hexacoordinated surrounded by four nitrogens of the macrocyclic ligand and two axial monodentate TCNQ .- ligands, being the first nickel-TCNQ complex showing σ-bonds between the organic acceptor and the metal atom

Dioxygen and carbon monoxide uptake by iridium(I) complexes stabilized by mixed N,P-donor ligands

Abstract: The preparation of a new family of iridium(I) complexes with the mixed-donor bidentate ligands o-Ph 2 PC 6 H 4 -CH=NR (PNalkyl) (R=Et, Pr i , Bu i ) is described. In these complexes, the iridium center is coordinated by two PNalkyl ligands in a square-planar environment. All [(PNalkyl) 2 Ir] + compounds undergo reversible electron transfer to the Ir(0) oxidation state as well as irreversible oxidation to Ir(III). Only for R=Bu t is the Ir(II) oxidation state accessible through a reversible oxidation process. For comparative purposes, the electrochemical behavior of the Rh(I) congeners [(PNalkyl) 2 Rh]PF 6 has been investigated

Thermodynamics of Several 1:1 and 1:2 Complexation Reactions of the Borate Ion with Bidentate Ligands. 11B NMR Spectroscopic Studies1

Abstract: The borate ion, B(OH) 4 -, is capable of forming anionic complexes of both 1:1 and 1:2 stoichiometries with bidentate chelating ligands. The reactions are B(OH) 4 -+H 2 X↔BX - +2H 2 O (K 1 ) and BX - +H 2 X↔BX 2 - +2H 2 O (K 2 ). Reactions with 1,2-ethanediol, 1,2-propanediol, glycolic acid, lactic acid, and oxalic acid are reported. The successive reactions of the diols with B(OH) 4 - are shown to be thermodynamically similar. In marked contrast, the successive addition of the more acidic α-hydroxy carboxylic acids is characterized by very different thermodynamic parameters for each step