Asymmetric Bidentate Research Articles

Synthesis, characterization and crystal structure of a novel tris(2-aminoethyl) amine copper(II) complex with an asymmetric coordinated 4,5-diazafluorene-9-hydrazine

The compound, tris(2-aminoethyl)amine-4,5-diazafluorene-9-hydrazine copper(II) perchlorate complex, [Cu(C 6H 18N 4)(C 11H 8N 4](ClO 4) 2 ( 1), has been designed, synthesized and characterized. The X-ray analysis reveals that the copper(II) is coordinated by four nitrogen atoms from tis(2-aminoethyl)amine (tren) and two nitrogen atoms from 4,5-diazafluorene-9-hydrazine (dzfh) to form an unusual (4+1+1′) six-coordinate geometry. This structure is very rare, and to out knowledge, is a unique example of a tripodal copper(II) complex with an asymmetric bidentate phenanthroline derivative. The 110 K ESR and electronic reflectance spectra studies demonstrate that the coordinated geometry of copper(II) is quite similar to square-based pyramidal stereochemistry, instead of the trigonal bipyramidal stereochemistry, which is the common structure for [Cu(tren)L] 2+ (L = monodentate ligand) complexes. The electronic and variable-temperature ESR spectra in absolute DMF suggest that the two nitrogen atoms of the dzfh coordinate to the copper(II) ion in the two-dimensional fluxional model. For comparison, the complex, Cu(tren)(Py)(ClO 4) 2 (Py is pyridine) ( 2, was also

Regioselectivity of Nucleophilic Attack on [Pd(allyl)(phosphine)(imine)] Complexes: A Theoretical Study

Extended Huckel calculations help rationalize the observed regioselectivity of allylic alkylations catalyzed by Pd complexes containing either C2-symmetric or electronically asymmetric bidentate chiral ligands. Mixing of the empty high-lying π* into the LUMO, made up mostly of the antibonding combination between the dx2-y2 and the allyl nonbonding fragment orbitals, increases the electrophilicity of the carbon with the longest Pd−C bond as its weight in the LUMO increases.

Synthesis and spectral studies of some new palladium(II) and platinum(II) dithio complexes: The novel crystal structure of the palladium(II) dithiocarbimato complex

A new 4-aminophenyl ammonium dithiocarbamate ligand and its Pd II and Pt II complexes have been synthesized and characterized by analytical, magnetic and spectroscopic techniques. These complexes on reaction with strong base form novel anionic metal(II) dithiocarbimates, which have also been isolated and studied. The spectroscopic and magnetic data clearly indicate the bidentate bonding by the dithiocarbamate ligand in the complexes and which have square planar configurations. The single-crystal X-ray analysis of (Bu 4 nN) 2[Pd(S 2CNC 6H 4NH 2) 2] gave the first example of the structure of a dithiocarbimato complex. The Pd II complex has a square-planar configuration with the S 2CNC 6H 4NH 2 group coordinated as an asymmetric bidentate ligand forming a stable four-membered ring by chelation through the two sulfur atoms.

Synthesis, Characterization, and Crystal Structure of a Novel Copper(II) Complex with an Asymmetric Coordinated 2,2‘-Bipyridine Derivative: A Model for the Associative Complex in the Ligand-Substitution Reactions of [Cu(tren)L]2+?

The titled compound, (tris(2-aminoethyl)amine)(4,5-diazafluoren-9-one) copper(II) perchlorate, [Cu(C(6)H(18)N(4))(C(11)H(6)N(2)O)(ClO(4))(2)], 1, has been designed, synthesized, and characterized. The electronic and ESR spectra are very different from those of [Cu(tren)L](2+) complexes where L is monodentate ligand. The X-ray analysis revealed that the complex crystallizes in the monoclinic space group P2(1)/c, with a = 10.726(6) Å, b = 14.921(7) Å, c = 14.649(4) Å, beta = 95.13(3) degrees, and Z = 4. The copper(II) ion is coordinated by four nitrogen atoms from tris(2-aminoethyl)amine (tren) and two nitrogen atoms from 4,5-diazafluoren-9-one (dzf) to form an unusual six-coordinate (4 + 1 + 1') geometry. The structure is very rare, and to our knowledge, it is the first example of an asymmetric bidentate phenanthroline derivative metal complex. The structure could be used as a model of the associative complex in the ligand-exchange and ligand-substitution reactions of [Cu(tren)L](2+) and the catalytic mechanisms of enzymes involving copper sites. From the electronic and variable-temperature ESR spectra in solution, the possible mechanism of these reactions has also been proposed. As a comparison, the complex [Cu(tren)(ImH)(ClO(4))(2)], 2, was also synthesized and characterized, where ImH is imidazole.

Molecular structure of [Tl(tpp)(O2CCF3)] and 19F dynamic nuclear magnetic resonance of it and [Tl(tmpp)(O2CCF3)][tpp = 5,10,15,20-tetraphenylporphyrinate, tmpp = 5,10,15,20-tetra(4-methoxyphenyl)porphyrinate

The crystal structure of (meso-5,10,15,20-tetraphenylporphyrinato)(trifluoroacetato)thallium(III), [Tl(tpp)(O2CCF3)], was determined. The co-ordination sphere of the Tl3+ ion is an approximate square-based pyramid in which the apical site is occupied by an asymmetric bidentate O2CCF3– group. The average Tl–N bond distance is 2.200(5)A and the Tl atom is displaced 0.741 A from the porphyrin plane. The Tl–O(1) and Tl–O(2) distances are 2.309(7) and 2.64(1)A, respectively. The extent of dissociation of [5,10,15,20-tetra(4-methoxyphenyl)porphyrinato](trifluoroacetato)thallium(III), [Tl(tmpp)(O2CCF3)], in CD2Cl2 was ≈4%. The free energy of activation at the coalescence temperature Tc was for the intermolecular trifluoroacetate exchange between ≈96 of [Tl(tmpp)(O2CCF3)] and ≈4% of CF3CO2H in CD2Cl2 solvent has been found to be ΔG238‡ 45.8 kJ mol–1 through 19F NMR temperature-dependent measurements. However, [Tl(tmpp)(O2CCF3)] and its homologue [Tl(tpp)(O2CCF3)] do not dissociate in [2H8]tetrahydrofuran. They undergo intramolecular CF3CO2– exchange in this solvent and ΔG212‡(or ΔG203‡) for this process was found to be 44.4 (or 42.0 kJ mol–1) for [Tl(tpp)(O2CCF3)]{or [Tl(tmpp)(O2CCF3)]} from 19F dynamic NMR spectroscopy. In the slow-exchange region the CF3 and carbonyl (CO) carbons of the CF3CO2– group in [Tl(tpp)(O2CCF3)] are separately located at δ 115.9 [1J(C–F)= 291, 3J(Tl–13C)= 239] and 156.5 [2J(C–F)= 37, 2J(Tl–13C)= 128 Hz] at – 100 °C.

Structure of human diferric lactoferrin refined at 2.2 A resolution.

The three-dimensional structure of the diferric form of human lactoferrin has been refined at 2.2 A resolution, using synchrotron data combined with a lower resolution (3.2 A) diffractometer data set. Following restrained least-squares refinement and model rebuilding the final model comprises 5330 protein atoms (691 residues), 2Fe(3+) and 2CO(3)(2-) ions, 469 solvent molecules and 98 carbohydrate atoms (eight sugar residues). Root-mean-square deviations from standard geometry are 0.015 A for bond lengths and 0.038 A for angle (1-3) distances, and the final crystallographic R-factor is 0.179 for all 39 113 reflections in the resolution range 8.0-2.2 A. A close structural similarity is seen between the two lobes of the molecule, with differences mainly in loops and turns. The two binding sites are extremely similar, the only apparent differences being a slightly more asymmetric bidentate binding of the carbonate ion to the metal, and a slightly longer Fe-O bond to one of the Tyr ligands, in the N-lobe site relative to the C-lobe site. Distinct differences are seen in the interactions made by two cationic groups, Arg210 and Lys546, behind the iron site, and these may influence the stability of the two metal sites. Analysis of interdomain and interlobe interactions shows that these are few in number which is consistent with the known flexibility of the molecule with respect to domain and lobe movements. Internal water molecules are found in discrete sites and in two large clusters (in the two interdomain clefts) and one tightly bound water molecule is present 3.8 A from the Fe atom in each lobe. The carbohydrate is weakly defined and has been modelled to a limited extent; two sugar residues of the N-lobe glycan and six of the C-lobe glycan. Only one direct protein-carbohydrate contact can be found.

TRIMETHYLTIN CHLORIDE AND PSEUDOHALIDE COMPLEXES OF TRYPTOPHAN

Abstract Organotin chloride and pseudohalide complexes of tryptophan of the type Me3SnX. Tryp (Me = methyl, X = Cl, SCN, N3, CN and NCO; Tryp = tryptophan) were prepared by the addition reactions of tryptophan with trimethyltin chloride and the appropriate pseudohalide prepared in situ. The complexes were characterized by elemental analyses, spectroscopic (IR, NMR) studies, melting point and conductance measurements. Melting point and conductance measurements show them to be stable and non-electrolytes in DMSO. The spectroscopic data indicate that tryptophan coordinates with tin covalently through its carboxylate group as an asymmetric bidentate ligand. It is suggested that the complexes have an octahedral geometry.

Synthesis, resolution and reactions of (±)-1-(dimethylarsino)-2-(methylphenylphosphino)benzene. Crystal and molecular structure of [(S), (S)]-(+)589-{2-[1-(dimethylamino)ethyl]phenyl-C1,N}[1-(dimethylarsino)-2-(methylphenylphosphino)benzene-As,P]palladium(II) hexafluorophosphate

Asymmetric bidentate (±)-1-(dimethylarsino)-2-(methylphenylphosphino)benzene has been prepared by the reaction of sodium dimethylarsenide with (±)-1-chloro-2-(methylphenylphosphino)benzene in tetrahydrofuran. Its resolution has been achieved by the separation by fractional crystallisation of a pair of internally diastereomeric palladium(II) complexes containing the racemic ligand and orthometallated (S)-dimethyl(1-phenylethyl)amine. The optically pure antipodes have α±32°(589 nm, dichloromethane). The absolute configuration of the R enantiomer of the ligand has been assigned by a crystal-structure determination of the least-soluble diastereomeric complex [(S),(S)]-(+)589-{2-[1-(dimethylamino)ethyl]phenyl-C1, N}[1-(dimethylarsino)-2-(methylphenylphosphino)benzene-As,P]palladium(II) hexafluorophosphate. Chemoselective cleavage of the dimethylarsino moiety of the free benzene derivative occurs in the presence of lithium metal in tetrahydrofuran.

Optically active asymmetric bidentate ligands. Crystal and molecular structure of [SP-4-4-(R),(R)]-(–)589-{1-[1-(dimethylamino)ethyl]naphthyl-C2,N}[1-(diphenylphosphino)-2-(methylphenylphosphino)ethane-P,P′]-palladium(II) hexafluorophosphate

Asymmetric bidentate (±)-1-(diphenylphosphino)-2-(methylphenylphosphino)ethane has been resolved by the separation by fractional crystallisation of internally diastereomeric palladium(II) complexes containing the racemic ligand and orthometallated (R)-dimethyl[1-(1-naphthyl)ethyl]amine. The absolute configuration of the S enantiomer of the ligand has been assigned by a crystal structure determination of the least-soluble diastereomeric palladium(II) complex (R,R)-(–)589-{1-[1-(dimethylamino)ethyl]naphthyl-C2,N}[1-(diphenylphosphino)-2-(methylphenylphosphino)ethane-P,P′]palladium(II) hexafluorophosphate. The X-Ray analysis also showed the methylphenylphosphino group of the di(tertiary phosphine) to be trans to the amino group of the resolving agent. This trans arrangement is retained in dichloromethane but facile intermolecular cis–trans isomerisation occurs in more polar solvents. Chemoselective cleavage of a phenyl group from the diphenylphosphino moiety of the free diphosphine occurred in the presence of lithium in tetrahydrofuran to give a separable 1 : 1 diastereomeric mixture of (R*,R*)- and (R*,S*)-1-(ethylphenylphosphino)-2-(methylphenylphosphino)ethane upon further reaction with bromoethane.

Chiral Lewis acids derived from 1,8-naphthalenediylbis-(dichloroborane): Mechanistic aspects

Chiral Lewis acids derived from 1,8-Naphthalenediylbis(dichloroborane), a novel bidentate Lewis acid, have been found to be active catalysts for the asymmetric Diels-Alder reaction. Utilizing chiral ligands derived from amino acids, a range of enantioselectivities have been achieved with cyclopentadiene and various α,β-unsaturated aldehydes. Some mechanistic aspects of this novel asymmetric bidentate catalyst have been addressed.

Structural characterization of bidentate carboxylate derivatives of copper(I) bistriphenylphosphine

The complexes (Ph 3P) 2Cu(carboxylate) (carboxylate = acetate ( 1), hippurate ( 2), vinyl acetate ( 3), fluorenate ( 4)) have been prepared and their solid-state structures determined crystallographically. The copper(I) center in all four structures exhibits a distorted tetrahedral geometry, with varying degrees of asymmetric bidentate binding of the carboxylate ligand. For example, in complex 2 the hippurate ligand displays the greatest extent of asymmetry with the two CuO bond distances differing by 0.234(6) Å. The structures of all four derivatives were each shown to be the same both in the solid-state and in dichloromethane solution based on infrared spectroscopy. The magnitude of Δ ( v a(CO 2 −)- v s(CO 2 −)) in these copper(I) derivatives, determined to be quite similar to the corresponding ionic values, is used as constituting a diagnosis for asymmetric bidentate binding of the carboxylate ligand. Although all four complexes are structurally quite similar, only the fluorenate derivative which affords a resonance-stabilized carbanion upon carbon dioxide extrusion undergoes the decarboxylation reaction. Crystal data for 1: space group P2 1/ c, a = 18.085(5), b = 10.977(2), c = 17.979(5) Å, β = 115.62(2)°, Z= 4, R =3.91%. Crystal data for 2: space group P 1 , a = 9.96(2), b = 14.68(3), c = 14.96(3) Å , a = 115.46(14), β = 97.54(16), η = 102.31(15)°, Z = 2, R=5.84%. Crystal data for 3: space group P 1 , a = 12.755(3), b = 13.125(2), c = 12.572(2) Å, α = 118.85(1), β = 105.85(1), η = 97.65(1)°, Z = 2, R =4.08%. Crystal data for 4: space group P 1 , a = 11.554(1), b = 15.217(2), c = 15.285(2) Å, α = 63.71(1), β = 79.08(1), η = 75.20(1)°, Z = 2, R = 7.6%.

Formation and structure of mono- and di-bismuth hydroxide and fluoride complexes in molten NH4NO3· 1.5H2O at 50 °C

The formation of bismuth hydroxide and fluoride complex species in NH4NO3· 1.5H2O has been investigated by potentiometric, NMR and Raman spectroscopy and large-angle X-ray scattering (LAXS) methods at 50 °C. Complexes with the formal composition BiOH2+, Bi2OH5+, BiF2+ and Bi2F5+ were detected. The stability constants, as derived from potentiometry, are; β*11[BiOH2+]=(5.6 ± 0.1)× 10–3 mol kg–1, β*21[Bi2OH5+]=(3.37 ± 0.02)× 10–2, β11[BiF2+]=(1.54 ± 0.02)× 104 kg mol–1 and β21[Bi2F5+]=(7.3 ± 0.5)× 103 kg2 mol–2. 19F NMR shift studies indicate that the predominant contribution to the Bi–F bonding character is most likely to be electrostatic. 14N NMR and Raman spectroscopic experiments on a number of compositions in the system Bi(NO3)3· 4.5H2O–(H,NH4)(F,NO3)· 1.5H2O indicate the presence of nitrate ions convalently bonded to bismuth. The Raman spectra show a loss of degeneracy of the internal ν3 and ν4 nitrate vibration modes in the 1300 and 700 cm–1 regions, respectively, and a residual contribution to the ν1 band of NO3– at 1048 cm–1 due to direct bismuth–nitrate interactions. A weak polarized band at 240 cm–1 is assigned to a Bi—O2NO stretching vibration. Intensity correlations in the 1050 cm–1 region yield a coordination number of four for the bismuth nitrate complex in an acidic melt. The quantitative analysis suggests that nitrate ions are released upon formation of bismuth hydroxide and fluoride complexes. Results of the structural investigation on the [Bi(NO3)4(OH2)2]– complex, supported by ab initio calculations, reveal a slightly asymmetric bidentate coordination of NO3–., dBi–O(NO3)= 2.52, 2.69 and 4.30 Å, dBi–N(NO3)= 3.08 Å. Rather long Bi—OH2 contacts (2.90 Å) were obtained. The Bi—Bi distances in Bi2OH5+ Bi2F5+ are 3.70 Å, implying a bent structure (C2v symmetry). The large Bi—Bi separations and negligible Bi—Bi orbital overlap (as revealed by ab initio calculations) indicate that these complexes may be stabilized by bridging nitrate ions. Approximate MO calculations suggest that a monodentate bridging configuration is the most stable one.

Synthesis of the first lanthanide complexes of dialkyl α-hydroxyiminophosphonates; ambivalent ligand bonding in the PrIIIand NdIIIcomplexes of diisopropyl α-hydroxyiminopropylphosphonate (L1), [PrL13Cl3] and [NdL12(NO3)3(H2O)

Lanthanide complexes of dialkyl α-hydroxyiminophosphonates (RO)2P(O)C(R′)N(OH)(L1–L3), where R = Et or Pri and R′= Me or Et, have been prepared for the first time; the crystal structures of two complexes of L1(R = Pri, R′= Et) have been determined, showing nine-co-ordination geometry in both cases with asymmetric bidentate ligands in [PrL13Cl3] and monodentate bonding in [NdL12(NO3)3(H2O)] demonstrating that the ambivalent nature of the new ligands allow formation of neutral complexes.

The synthesis and characterization of an Mo 4MoCl 4(LL) 2 compound with LL=Ph 2PCH 2PMe 2

The preparation and structural characterization of a new Mo 4Mo complex with an interesting asymmetric bidentate phosphine Mo 4MoCl 4(μ-dmdppm) 2 (dmdppm=Ph 2PCH 2PMe 2) is reported. The Mo 4Mo bond distance in Mo 4MoCl 4(μ-dmdppm) 2 (2.1523(9) Å) is longer than those in either Mo 4MoCl 4(μ-dppm) 2 (2.138(1) Å) or Mo 4MoCl 4(μ-dmpm) 2 (2.125(4) Å) due to the presence of a twist about the Mo 4Mo axis of 17.56°. The crystal structure of Mo 4MoCl 4(μ-dmdppm) 2 is fully described. Crystallographic data for this compound are as follows: (1) P2 1/ c with a=12.552(6), b=17.223(3), c=18.582(9) Å, V=3989(3) Å 3 and Z=4.

Metal phenoxyalkanoic acid interactions—36. The preparation and crystal structures of tetraaquabis(2-phenoxybenzoato)nickel(ii) dihydrate, diaquabis(4-fluorophenoxyacetato)zinc(ii), catena-diaquabis(phenoxyacetato)cobalt(ii) and tetrakis-μ-[(pentafluorophenoxy)acetato(o,o′)] bis[aquacopper(ii)

The structures of four complexes involving divalent first-row transition metals and phenoxy substituted carboxylic acids have been determined by X-ray diffraction. These are tetraaquabis(2-phenoxybenzoato)nickel(II) dihydrate (1), diaquabis(4-fluorophenoxyacetato)zinc(II) (2), diaquabis(phenoxyacetato)cobalt(II) (3) and tetrakis-μ-(pentafluorophenoxyacetato)bis[aquacopper(II)] (4). Complex 1 is regular octahedral with trans-related unidentate carboxylate [Ni—O (carboxylate) 2.031(1) Å] and four waters [Ni—O 2.049, 2.104(2) Å]. Complex 2 has a skew trapezoidal bipyramidal stereochemistry, involving four oxygens from two asymmetric bidentate carboxylates [Zn—O 2.107, 2.332(3) Å] and two waters [Zn—O 1.989(4) Å]. The polymeric complex 3 is isomorphous and isostructural with the manganese(II) analogue, with centrosymmetric octahedral CoO 6 stereochemistry comprising four bonds to carboxylate oxygens (both bridging) [Co—O 2.076, 2.087(3) Å] and two to waters [Co—O 2.134(3) Å]. Complex 4 is a pseudo-centrosymmetric tetracarboxylate bridged dimer of the copper(II) acetate hydrate type with a Cu—Cu separation of 2.644(4) Å. Bond distances to copper are 1.96(1) (average, equatorial) and 2.15(1) Å (average, axial, to water).

Optically active asymmetric bidentate ligands. Crystal and molecular structure of {(R), (S)-(–)589-2-[1-(dimethylamino)ethyl]phenyl-C2,N}[1-(diphenylphosphino)-2-(methylphenylphosphino) benzene-P,P′]palladium(II) hexafluorophosphate

Optically active asymmetric bidentate ligands. Crystal and molecular structure of {(R), (S)-(–)₅₈₉-2-[1-(dimethylamino)ethyl]phenyl-C²,N}[1-(diphenylphosphino)-2-(methylphenylphosphino) benzene-P,P′]palladium(<scp>II</scp>) hexafluorophosphate

Resolutions involving metal complexation. Optical resolution and photochemical rearrangement of (.+-.)-(2-mercaptoethyl)methylphenylphosphine

The asymmetric bidentate (±)-(2-mercaptoethyl)methylphenylphosphine has been resolved by the fractionial crystallization of a pair of diastereomeric thiolato-S-bridged dipalladium(II) complexes containing the deprotonated form of the ligand and ortho-metalated (R)-(1-(dimethylamino)ethyl)naphthalene. In order to recover the resolved ligand from the less soluble diastereomer of the dipalladium complex, the terminal palladium resolving unit was displaced with ethane-1,2-diamine, and the residual (thiolato)palladium(II) complex was treated with benzyl bromide.

Crystal and molecular structures of tris (p‐methoxyphenyl)‐ and tris(2,4, 6‐trimethylphenyl)tin(IV) acetates

AbstractThe crystal and molecular structures of tris(p‐anisyl)tin acetate (1) (p‐anisyl = p‐methoxyphenyl) and trimesityltin acetate (2) (mesityl = 2,4,6‐trimethylphenyl) have been determined. Both have monomeric structures with the acetate group acting as an asymmetric bidentate ligand. Bond valence analysis of (1) and (2) and other Ph3SnO2CR suggest however that the carboxylate ligand effectively occupies a single bonding position at tin. Thus in (1) and (2) the tin atom is in a chemical environment equivalent to that found in four‐coordinate R3Sn‐X systems based on tetrahedral geometry.

Group 15 Metal Complexes With Carboxylic Acids. Preparation and Crystal Structure of Polymeric Ammonium Aquabis[(+)-tartrato(2-)]bismuthate(III) Hydrate

The crystal structure of the bismuth(III) complex with (+)-tartaric acid, ammonium aquabis [(+)-tartrato (2-)] bismuthate (III) hydrate, has been determined by X-ray methods and refined to a residual R 0.020 for 1288 observed reflections. Crystals are orthorhombic, space group P 212121 with Z 4 in a cell of dimensions a 7.4712(4), b 10.856(1), c 17.609(3) � . Each nine-coordinate MO9 bismuth centre comprises three bidentate α-hydroxy carboxy residues from two tartrato (2-) ligands (with one bridging), an asymmetric bidentate carboxylato (O,O') group, and a water. The Bi-O range is 2.372(7)-2.738(6) � [mean 2.509(6) &gt;� ]. The resultant structure is a linear polymer which is stabilized by extensive hydrogen-bonding interactions.

Crystal structure of the complex between carboxypeptidase A and the biproduct analog inhibitor l-benzylsuccinate at 2·0 Å resolution

The X-ray crystal structure of the Carboxypeptidase A- l-benzylsuccinate complex has been refined at 2·0 Å resolution to a final R-factor of 0·166. One molecule of the inhibitor binds to the enzyme active site. The terminal carboxylate forms a salt link with the guanidinium group of Arg145 and hydrogen bonds with Tyr248 and Asn144. The second carboxylate group binds to the zinc ion in an asymmetric bidentate fashion replacing the water molecule of the native structure. The zinc ion moves 0·5 Å from its position in the native structure to accommodate the inhibitor binding. The overall stereochemistry around the zinc can be considered a distorted tetrahedron, although six atoms of the co-ordinated groups lie within 3·0 Å from the zinc ion. The key for the strong inhibitory properties of l-benzylsuccinate can be found in its ability both to co-ordinate the zinc and to form a short carboxylcarboxylate-type hydrogen bond (2·5 Å) with Glu270.