Cis Disposition Research Articles

Half-Sandwich Group 8 Borylene Complexes: Synthetic and Structural Studies and Oxygen Atom Abstraction Chemistry

Cationic terminal borylene complexes, synthesized by halide abstraction, offer a versatile platform on which to gauge the effects on the electronic structure of the metal−ligand bond brought about by variation in the borylene substituent and the metal/ligand framework. While the borylene substituent exerts a strong influence on boron-centered electrophilicity and hence on metal−ligand π character and bond length (e.g., from 1.792(8) Å for [Cp*Fe(CO)2(BMes)]+ to 2.049(4) Å for [CpFe(CO)2{B(NCy2)(4-pic)}]+), much smaller changes are effected by changes in the metal/ligand set. Introduction of stronger π donor ruthenium- and/or phosphine-containing fragments is readily brought about by extension of the halide abstraction approach; phosphines are readily introduced by carbonyl ligand substitution at the boryl precursor stage. Thus, the novel systems [CpRu(CO)2{B(NCy2)}]+[BArf4]−, [CpM(CO)(PMe3){B(NCy2)}]+[BArf4]− (M = Fe, Ru), and [(CpFe(CO){B(NCy2)})2(μ-dmpe)]2+[BArf4]−2 have been synthesized and structurally characterized. The effects of substitution at the metal on the M−B and B−N bonds are relatively minor {e.g., Fe−B and B−N bond lengths of 1.821(4), 1.347(5) Å and 1.859(6), 1.324(7) Å for [CpFe(CO)(PMe3){B(NCy2)}]+[BArf4]− and [CpFe(CO)2{B(NCy2)}]+[BArf4]−, respectively}, presumably reflecting, at least in part, the mutually cis disposition of the borylene and phosphine/carbonyl ligands. The utility of cationic complexes containing formally subvalent boron-based ligands in oxygen atom abstraction chemistry has been demonstrated by the conversion of a range of isocyanates, R′NCO, to the corresponding (metal-coordinated) isonitriles, [CpFe(CO)2(CNR′)]+. Moreover, with a view to modeling potential intermediates, the mechanism of related chemistry with carbodiimide substrates, R′NCNR′, has been investigated by structural and in situ ESI-MS approaches. While reactivity toward carbodiimides leads to the formation of a novel spirocyclic boronium complex, [CpFe(CO)2C(NCy)2B(NCy)2CNCy2]+[BArf4]− (for R′ = Cy), by a double-insertion process, DFT studies imply that the analogous product of isocyanate insertion is unlikely to be an intermediate on the pathway to isonitrile formation. The presence of a number of facile competing reaction pathways (including metathesis) and the thermodynamic stability of the spirocyclic product mean that the product distribution is better explained in terms of competing pathways, rather than differing extents of reaction along similar trajectories.

Protonation of the Side Group in β- and γ-Aminated Proline Analogues: Effects on the Conformational Preferences

This work shows the influence of the side-chain protonation on the conformational properties, relative stabilities, and peptide bond isomerization of four aminoproline isomers. Thus, this research has been useful to define the rules that allow control the conformation of aminoproline with the pH. Comparison of the results obtained using density functional theory calculations for the N-acetyl-N'-methylamide derivatives of the protonated isomers, which differ in the beta- or gamma-position of the substituent and its cis or trans relative disposition, with those reported for the corresponding neutral analogues (J. Phys. Chem. B 2008, 112, 14045) has allowed us to reach the following conclusions: (i) protonation of the amino group produces a reduction of the backbone conformational flexibility and a destabilization of the cis configuration of the amide bond involving the pyrrolidine nitrogen; (ii) the planarity of the peptide bond is broken in some cases to form strong side chain...backbone interactions, which induce a very significant pyramidilization at the amide nitrogen atom; (iii) as was also detected for the neutral analogues, the formation of side chain...backbone intraresidue interactions favor the cis disposition of the substituent; and (iv) protonation of the amino side group increases the energy gaps that separate the different investigated isomers resulting in an enhancement of the destabilization of the dipeptides with the substituent attached in a trans position.

Iridium(III) Complexes with Sulfonyl and Fluorine Substituents: Synthesis, Stereochemistry and Effect of Functionalisation on their Photophysical Properties

The synthesis and photophysical and electrochemical characterisation of new heteroleptic iridium complexes with electron-withdrawing sulfonyl groups and fluorine atoms bound to phenylpyridine ligands are reported. The emission energy of these materials strongly depends on the position of the sulfonyl groups and on the number of fluorine substituents. A 90 nm wide tuning range of photoluminescence from the blue-green (lambda(em)=468 nm) of iridium(III)bis[2-(4'-benzylsulfonyl)phenylpyridinato-N,C2'][3-(pentafluorophenyl)-pyridin-2-yl-1,2,4-triazolate] to the orange (lambda(em)=558 nm) of iridium(III)bis[2-(3'-benzylsulfonyl)phenylpyridinato-N,C2'](2,4-decanedionate) has been achieved. Emission quantum yields ranging from 47 to 71% have also been found for degassed solutions of the complexes, and a surprisingly high value of 16% was recorded for iridium(III)bis[2-(5'-benzylsulfonyl-3',6'-difluoro)phenylpyridinato-N,C2'](2,4-decanedionate) in air-equilibrated dichloromethane. A unusual stereochemistry of the benzylsulfonyl-substituted dimer and heteroleptic complexes has been detected by (1)H NMR spectroscopy, and is characterised by the mutual cis disposition of the pyridyl nitrogen atoms of the phenylpyridine ligands, which differs from the most common trans arrangement reported in the literature.

Conformational preferences of beta- and gamma-aminated proline analogues.

Quantum mechanical calculations have been used to investigate how the incorporation of an amino group to the Cbeta- or Cgamma-positions of the pyrrolidine ring affects the intrinsic conformational properties of the proline. Specifically, a conformational study of the N-acetyl-N'-methylamide derivatives of four isomers of aminoproline, which differ not only in the beta- or gamma-position of the substituent but also in its cis or trans relative disposition, has been performed. To further understand the role of the intramolecular hydrogen bonds between the backbone carbonyl groups and the amino side group, a conformational study was also performed on the corresponding four analogues of (dimethylamino)proline. In addition, the effects of solvation on aminoproline and (dimethylamino)proline dipeptides have been evaluated using a self-consistent reaction field model, and considering four different solvents (carbon tetrachloride, chloroform, methanol and water). Results indicate that the incorporation of the amino substituent into the pyrrolidine ring affects the conformational properties, with backbone...side chain intramolecular hydrogen bonds detected when it is incorporated in a cis relative disposition. In general, the incorporation of the amino side group tends to stabilize those structures where the peptide bond involving the pyrrolidine nitrogen is arranged in cis. The aminoproline isomer with the substituent attached to the Cgamma-position with a cis relative disposition is the most stable in the gas phase and in chloroform, methanol and water solutions. Replacement of the amino side group by the dimethylamino substituent produces significant changes in the potential energy surfaces of the four investigated (dimethylamino)proline-containing dipeptides. Thus, these changes affect not only the number of minima, which increases considerably, but also the backbone and pseudorotational preferences. In spite of these effects, comparison of the conformational preferences, i.e., the more favored conformers, calculated for different isomers of aminoproline and (dimethylamino)proline dipeptides showed a high degree of consistency for the two families of compounds.

Palladium and platinum complexes of chiral and achiral calix[4]arene bisphosphite ligands

Chiral and achiral p- tert-butyl-calix[4]arene bisphosphites ( L 1– L 3) have been synthesized by the reaction of p- tert-butyl-calix[4]arene and the phosphorodichloridites, ROPCl 2 [R = (1 S,2 R,5 R)-(+)- iso-menthyl ( L 1), (1 R,2 S,5 R)-(−)-menthyl ( L 2) or C 6H 4Bu t -4 ( L 3)]. These bisphosphites function as chelating ligands in palladium(II) and platinum(II) complexes which are formed in good yields by the reaction of PdCl 2(PhCN) 2, MCl 2(COD) (M = Pd or Pt) or PdMeCl(COD) with the respective calix[4]arene bisphosphite. Single crystal X-ray diffraction studies performed on the complexes [PdCl 2( L 1)], [PdCl 2( L 2)], [PdCl 2( L 3)] and [PtCl 2( L 3)] reveal a near square planar geometry around the metal with the two chloride ligands in a cis disposition. The crystal packing in the complexes [PdCl 2( L 1)] and [PdCl 2( L 2)], which crystallize in the chiral ( P6 122) space group, shows different hydrophobic channels with intermolecular C–H⋯Cl hydrogen bonding. The complexes [PdCl 2( L 3)] and [PtCl 2( L 3)] are isostructural and the molecules in the crystal lattice are linked by intermolecular C–H⋯Cl and C–H⋯O hydrogen bonds.

Interactions of Λ and Δ enantiomers of ruthenium(II) cationic complexes with achiral anionic porphyrins

The interactions between Lambda and Delta enantiomers of ruthenium(II)-phenanthroline cationic complex ([Ru(phen)(3)](2+)) and three anionic porphyrins have been characterized by absorption, circular dichroism (CD), fluorescence, and resonance light scattering (RLS). The three porphyrins used in this study have been chosen for the different number (two or four) and reciprocal (symmetrical, cis or trans) disposition of the anionic (4-sulphonatophenyl) peripheral groups in the meso positions. All the techniques evidence the formation of inorganic-organic hybrids. In particular, CD and fluorescence measurements show that the inorganic moiety is able to transfer to porphyrins not only chirality (as shown from the appearance of an induced CD signal (ICD) in the absorption region of porphyrins) but, most likely, also energy.

Platinum(II) complexes of 2-alkoxy-dibenzo[c.e][1,2]oxaphosphorines

2-Alkoxy-dibenzo[c.e][1,2]oxaphosphorines were prepared by the reaction of chloro-dibenzooxaphosphorine with alcohols and were converted to the cyclic phosphonates by oxidation and to the corresponding phosphonous boranes by reaction with borane-dimethylsulfide. Interaction of the alkoxy-dibenzooxaphosphorines with dichlorodibenzonitrileplatinum led to bis(dibenzooxaphosphorino)dichloroplatinum complexes exhibiting the P-ligands in the cis disposition. Relative energetics for the prepared cis and the theoretically possible trans isomers of the complexes along with their stereostructures were investigated by quantum chemical calculations.

Role of Axial Donors in the Ligand Isomerization Processes of Quadruply Bonded Dimolybdenum(II) Compounds

Quadruply bonded dimolybdenum(II) complexes with NP-R (2-(2-R)-1,8-naphthyridine; R = thiazolyl (NP-tz), furyl (NP-fu), thienyl (NP-th)) and 2,3-dimethyl-1,8-naphthyridine (NP-Me 2) have been synthesized by reactions of cis-[Mo2(OAc)2(CH3CN)6][BF4]2 with the corresponding ligands. The products cis-[Mo2(NP-tz)2(OAc)2][BF4]2 (1), trans-[Mo2(NP-fu)2(OAc)2][BF4]2 (2), trans-[Mo2(NP-th)2(OAc)2][BF4]2 (3), and trans-[Mo2(NP-Me2)2(OAc)2][BF4]2 (4) were isolated and characterized. The NP-R ligands with stronger R = pyridyl and thiazolyl donors result in cis isomers whereas the weaker furyl and thienyl appendages lead to compounds having a trans orientation of the ligands. The use of NP-Me2 leads to a trans structure with a tetrafluoroborate anion occupying one of the axial sites. Complete replacement of two acetate groups by acetonitrile in 1 and 2 resulted in the cis isomers [Mo2(NP-tz)2(CH3CN)4][OTf]4 (5) and [Mo2(NP-fu)2(CH3CN)4][OTf]4 (6) respectively. The combination of one acetate and two acetonitriles as ancillary ligands, however, yields trans-[Mo2(NP-tz)2(OAc)(CH3CN)2][BF4]3 (7) in the solid state as determined by X-ray crystallography. (1)H NMR spectra of the products are diagnostic of the cis and trans dispositions of the ligands. Solution studies reveal that the ligand arrangements observed in the solid state are mostly retained in the acetonitrile medium. The only exception is 7, for which a mixture of cis and trans isomers are detected on the NMR time scale. The isolation of trans compounds 2- 4 from the cis precursor [Mo2(OAc)2(CH3CN)6][BF4]2 indicates that an isomerization process occurs during the reactions. The mechanism involving acetate migration through axial coordination has been invoked to rationalize the product formation. Compounds 1- 7 were structurally characterized by single-crystal X-ray methods.

Synthesis of new platinum(II) compounds with several bidentate and tridentate nitrogen-donor ligands. Structural analyses by 1H, 13C{ 1H} and 195Pt{ 1H} NMR spectroscopy and X-ray crystal structure

The reaction of the N-alkylaminopyrazole ( NN′) ligands 1-[2-(ethylamino)ethyl]-3,5-dimethylpyrazole (deae), 1-[2-( tert-butylamino)ethyl]-3,5-dimethylpyrazole (deat), or ( NN′ N) ligands bis[(3,5-dimethylpyrazolyl)methyl]ethylamine (bdmae) and bis[(3,5-dimethylpyrazolyl)ethyl]ethylamine (ddae) with [PtCl 2(CH 3CN) 2] affords a series of square-planar Pt(II) complexes with formula [PtCl 2( NN′)] ( NN′ = deae ( 1); deat ( 2)), [PtCl 2(bdmae)] ( 3), or [PtCl(ddae)]Cl ( 4). Treatment of complex 4 in the presence of AgBF 4 in CH 2Cl 2/methanol (3:1) gives [PtCl(ddae)](BF 4) ( 5). These Pt(II) complexes have been characterised by elemental analyses, conductivity measurements and IR, 1H, 13C{ 1H}, and 195Pt{ 1H} NMR spectroscopies. The 1H NMR spectroscopic studies of the complexes prove the rigid conformation of the ligands when they are complexed. The solid-state structure of complex 1 was determined by single crystal X-ray diffraction methods. The deae ligand is coordinated through the N pz and N amino atoms to the metallic centre, which completes its coordination with two chlorine atoms in cis disposition.

Organoiridium Quinolinolate Complexes: Synthesis, Structures, Thermal Stabilities and Photophysical Properties

AbstractThe syntheses, solid‐state structures, thermal properties and photophysics of a series of heteroleptic iridium(III) complexes with phenylpyridine as the cyclometalating ligands and quinolinolates are reported. The title compounds were formed by reaction of di‐μ‐chloro‐tetrakis[κ2(C2,N)‐2‐phenylpyridine]diiridium(III) with the corresponding 8‐hydroxyquinolines in 56 to 86 % yield. The crystal structures of two of the complexes have been determined. Both complexes show the two carbon ligands in a cis disposition and the 2‐phenylpyridine nitrogen atoms in a trans disposition. Assessment of the thermal stabilities of the compounds revealed huge differences depending on the substituents on the quinolinolato ligand. Most complexes are poor emitters in solution, in films and in OLEDs. Substitution of the quinolinolato ligand with electron‐withdrawing functional groups in the 5‐position caused additional absorption features in the visible region facilitating the finding of appropriate host materials for OLEDs and gave emission properties governed by the quinolinolato ligand.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Synthesis and characterization of palladium(II) complexes with chiral aminophosphine ligands: Catalytic behaviour in asymmetric hydrovinylation. Crystal structure of cis-[PdCl 2(PPh(( R)-NHCHCH 3Ph) 2) 2

Optically active ligands of type Ph 2PNHR (R = ( R)-CHCH 3Ph, ( a); ( R)-CHCH 3Cy, ( b); ( R)-CHCH 3Naph, ( c)) and PhP(NHR) 2 (R = ( R)-CHCH 3Ph, ( d); ( R)-CHCH 3Cy, ( e)) with a stereogenic carbon atom in the R substituent were synthesized. Reaction with [PdCl 2(COD) 2] produced [PdCl 2P 2] ( 1) (P = PhP(NHCHCH 3Ph) 2), whose molecular structure determined by X-ray diffraction showed cis disposition for the ligands. All nitrogen atoms of amino groups adopted S configuration. The new ligands reacted with allylic dimeric palladium compound [Pd(η 3-2-methylallyl)Cl] 2 to gave neutral aminophosphine complexes [Pd(η 3-2-methylallyl)ClP] ( 2a– 2e) or cationic aminophosphine complexes [Pd(η 3-2-methylallyl)P 2]BF 4 ( 3a– 3e) in the presence of the stoichiometric amount of AgBF 4. Cationic complexes [Pd(η 43-2-methylallyl)(NCCH 3)P]BF 4 ( 4a– 4e) were prepared in solution to be used as precursors in the catalytic hydrovinylation of styrene. 31P NMR spectroscopy showed the existence of an equilibrium between the expected cationic mixed complexes 4, the symmetrical cationic complexes [Pd(η 3-2-methylallyl)P 2]BF 4 ( 3) and [Pd(η 3-2-methylallyl)(NCCH 3) 2]BF 4 ( 5) coming from the symmetrization reaction. The extension of the process was studied with the aminophosphines ( a– e) as well as with nonchiral monodentate phosphines (PCy 3 ( f), PBn 3 ( g), PPh 3 ( h), PMe 2Ph ( i)) showing a good match between the extension of the symmetrization and the size of the phosphine ligand. We studied the influence of such equilibria in the hydrovinylation of styrene because the behaviour of catalytic precursors can be modified substantially when prepared ‘ in situ’. While compounds 3 and bisacetonitrile complex 5 were not active as catalysts, the [Pd(η 3-2-methylallyl)(η 2-styrene) 2] + species formed in the absence of acetonitrile showed some activity in the formation of codimers and dimers. Hydrovinylation reaction between styrene and ethylene was tested using catalytic precursors solutions of [Pd(η 3-2-methylallyl)LP]BF 4 ionic species (L = CH 3CN or styrene) showing moderate activity and good selectivity. Better activities but lower selectivities were found when L = styrene. Only in the case of the precursor containing Ph 2PNHCHCH 3Ph ( a) ligand was some enantiodiscrimination (10%) found.

New Mono- and Polynuclear Alkynyl Complexes Containing Phenylacetylide as Terminal or Bridging Ligand. X-ray Structures of the Compounds NBu4[Pt(CH2C6H4P(o-tolyl)2-κC,P)(C⋮CPh)2], [Pt(CH2C6H4P(o-tolyl)2-κC,P)(C⋮CPh)(CO)], [{Pt(CH2C6H4P(o-tolyl)2-κC,P)(μ-C⋮CPh)}2], and [{Pt(CH2C6H4P(o-tolyl)2-κC,P)(C⋮CPh)2Cu}2

This work describes the synthesis of the compounds Q[Pt(C∧P)(C⋮CPh)2] (Q = Li+ (1), NBu4+ (2). C∧P = CH2C6H4P(o-tolyl)2-κC,P) and their use as precursors for the preparation of homo- and heteropolynuclear complexes by reactions with Lewis acid species of transition metals, M (M = Cu(I), Ag(I), Tl(I), Pd(II), Pt(II)). These reactions give rise to heteropolynuclear complexes that exhibit different bonding patterns for the bridging alkynyl ligands, depending on M. The reaction of 2 with readily available M+ (M = Cu, Ag) species affords the discrete tetranuclear clusters [{Pt(C∧P)(C⋮CPh)2M}2] (M = Cu (3), Ag (4)). The X-ray structure of 3 shows that in this complex both “Pt(C∧P)(C⋮CPh)2” fragments are connected by two d10 metal centers and are stabilized by alkynyl bridging ligands, showing the stronger preference of the MI centers (MI = Cu, Ag) for the electron-rich alkynyl units than for the basic Pt(II) center. However, the reaction of 2 with TlPF6 rendered the tentatively tetranuclear complex [{Pt(C∧P)(C⋮CPh)2Tl}2] (5), containing Pt→Tl dative bonds, which shows the higher affinity of thallium for the electron density of platinum(II) than for the alkynyl units. Moreover, the reaction of (NBu4)[Pt(C∧P)(C⋮CPh)2] (2) with the neutral complex [Pd(C6F5)2(THF)2] yields the compound (NBu4)[Pt(C∧P)(C⋮CPh)2Pd(C6F5)2] (11), in which the two alkynyl ligands are η2-bonded to Pd(II) in such a way that the “cis-Pt(C⋮CPh)2“ fragment acts as a chelate ligand toward Pd(II). Meanwhile the reactions with the cationic and neutral Pt(II) complexes [Pt(C∧P)(THF)2]+ and [Pt(C6F5)2(THF)2] produce the complexes [{Pt(C∧P)(μ-C⋮CPh)}2] (6) and (NBu4)[Pt(C∧P)(μ-C⋮CPh)2Pt(C6F5)2] (12), both containing the double μ2-η2(σ,π)-alkynyl bridging system “Pt2(μ-C⋮CPh)2” as a consequence of an alkynylating process. This bridging system “Pt2(μ-C⋮CPh)2” can be broken by neutral ligands, L, to give mono(σ-alkynyl) complexes of Pt(II). Thus, the complexes [Pt(C∧P)(C⋮CPh)L] (L = CO (7), py (8), tht (9), PPh3 (10)) have been obtained by reaction of 6 with L in a 1:2 molar ratio. When L = PPh3, the substitution reaction takes place with stereoretention, but not when L = CO, py, tht, as was conclusively established by an X-ray study on the complex [Pt(CH2C6H4P(o-tolyl)2)(CCPh)(CO)] (7). The cis or trans disposition of the two σ-C-donor ligands (C(C∧P), σ-C⋮CPh) around the Pt center in complexes 6−10 and 12 seems to depend as much on the transphobia of pairs of trans ligands (T) as on the steric requirements of those in the cis configuration.

The First Complex of Benzilbis(thiosemicarbazone) acting as Bridging Ligand only through the Sulfur Atom

AbstractThe first complex with benzilbis(thiosemicarbazone) LH6 acting only as a bridge between two metallic centres through the sulfur atoms, was obtained from the reaction with methylmercury chloride. This complex shows a 1:2 ligand : mercury ratio and has been spectroscopically characterized and recrystallized in toluene. The ligand acts as a dianion, with an intermediate situation between cis and trans dispositions, and it is bonded to both methylmercury moieties through the sulfur atoms, giving a binuclear complex with linear CS coordination for the mercury atoms.

Pd(II) complexes containing N-alkyl-3-pyridine-5-trifluoromethyl pyrazole ligands: Synthesis, NMR studies and X-ray crystal structures

Palladium [PdCl 2( L)] complexes with N-alkylpyridylpyrazole derived ligands [2-(5-trifluoromethyl-1 H-pyrazol-3-yl)pyridine ( L 1 ), 2-(1-ethyl-5-trifluoromethyl-1 H-pyrazol-3-yl)pyridine ( L 2 ), 2-(1-octyl-5-trifluoromethyl-1 H-pyrazol-3-yl)pyridine ( L 3 ), and 2-(3-pyridin-2-yl-5-trifluoromethyl-pyrazol-1-yl)ethanol ( L 4 ) were synthesised. The crystal and molecular structures of [PdCl 2( L)] ( L = L 2 , L 3 , L 4 ) were resolved by X-ray diffraction, and consist of monomeric cis-[PdCl 2( L)] molecules. The palladium centre has a typical square-planar geometry, with a slight tetrahedral distortion. The tetra-coordinate metal atom is bonded to one pyridinic nitrogen, one pyrazolic nitrogen and two chlorine ligands in cis disposition. Reaction of L ( L 2 , L 4 ) with [Pd(CH 3CN) 4](BF 4) 2, in the ratio 1M:2L, gave complexes [Pd( L)] 2(BF 4) 2. Treatment of [PdCl 2( L)] ( L = L 2 , L 4 ) with NaBF 4 and pyridine (py) and treatment of the same complexes with AgBF 4 and triphenylphosphine (PPh 3) yielded [Pd( L)(py) 2](BF 4) 2 and [Pd( L)(PPh 3) 2](BF 4) 2 complexes, respectively. Finally, reaction of [PdCl 2( L 4 )] with 1 equiv of AgBF 4 yields [PdCl( L 4 )](BF 4).

Solution NMR structure of a human FGF‐1 monomer, activated by a hexasaccharide heparin‐analogue

The 3D structure of a complex formed by the acidic fibroblast growth factor (FGF-1) and a specifically designed synthetic heparin hexasaccharide has been determined by NMR spectroscopy. This hexasaccharide can substitute natural heparins in FGF-1 mitogenesis assays, in spite of not inducing any apparent dimerization of the growth factor. The use of this well defined synthetic heparin analogue has allowed us to perform a detailed NMR structural analysis of the heparin-FGF interaction, overcoming the limitations of NMR to deal with the high molecular mass and heterogeneity of the FGF-1 oligomers formed in the presence of natural heparin fragments. Our results confirm that glycosaminoglycans induced FGF-1 dimerization either in a cis or trans disposition with respect to the heparin chain is not an absolute requirement for biological activity.

Exploring the coordination chemistry and reactivity of hemilabile N-alkylaminopyrazole ligands towards Pd(II)

Reaction of the N-alkylaminopyrazole ( NN′ N) ligands bis[(3,5-dimethyl-1-pyrazolyl)methyl]ethylamine ( bdmae) and bis[(3,5-dimethyl-1-pyrazolyl)methyl]isopropylamine ( bdmai) with [PdCl 2(CH 3CN) 2] in a 1:1 M/L ratio in CH 2Cl 2 produces cis-[PdCl 2( NN′ N)] ( NN′ N = bdmae ( 1), bdmai ( 2)). The solid state structure of complex 1 was determined by X-ray diffraction studies. The bdmae ligand is coordinated through the two N pz atoms to the metal atom, which completes its coordination with two chlorine atoms in a cis disposition. Treatment of the corresponding ligand with [PdCl 2(CH 3CN) 2] in 1:1 M/L ratio in the presence of AgBF 4 and metathesis with NaBPh 4 in CH 2Cl 2/CH 3OH (3:1) gave [PdCl( bdmae)](BPh 4) ( 3), and in the presence of NaBPh 4 in CH 2Cl 2/CH 3CN (3:1) gave [PdCl( bdmai)](BPh 4) ( 4). Complexes 1 and 2 were again obtained when complexes 3 and 4 were heated under reflux in a solution of Et 4NCl in acetonitrile. These Pd(II) compounds were characterised by elemental analyses, conductivity measurements, IR, 1H and 13C{ 1H} NMR, HMQC and NOESY spectroscopies. The NMR studies of the complexes prove the rigid conformation of the ligands when they are complexed.

Titanium Complexes of Dialkanolamine Ligands: Synthesis and Structure

AbstractSynthesis of the title compounds, viz. [RN(CH2CH2O)(CHR1CR2R3O)]Ti(OiPr)2 (13–15) and [RN(CH2CH2O)(CHR1CR2R3O)]2Ti (18–28), by the reaction of one ortwo equivalents of the corresponding dialkanolamines RN(CH2CH2OH)(CHR1CR2R3OH) (1–12) with Ti(OiPr)4 is reported. Other routes to [RN(CH2CH2O)(CHR1CR2R3O)]2Ti, such as the reaction of Ti(CH2Ph)4 with dialkanolamine and the reaction of TiCl4(THF)2 with dialkanolamine/Et3N were also tested. Dimeric titanocane 16, [PhCH2N(CH2CH2O)2Ti(OMe)2]2, was obtained from the reaction of one equivalentof dialkanolamine 3 with CpTi(OMe)3. PhCH2N(CH2CH2O)2Ti(OMenth)2 (17) was prepared from the transalkoxylation reaction of 15 with two equivalents of menthol. The composition and structures of all novel compounds were established by 1H and 13C NMR spectroscopy as well as elemental analysis data. The possible solution structure features of 13–28 are discussed. The single‐crystal X‐ray diffraction study oftitanocane 16 clearly indicates a dimeric structure for this compound in the solid state. According to X‐ray data, compounds [PhCH2N(CH2CH2O)2]2Ti (19), [MeN(CH2CH2O)(CH2CHPhO)]2Ti (20), [MeN(CH2CH2O)(CH2CPh2O)]2Ti (23), erythro‐[MeN(CH2CH2O)(CHPhCHPhO)]2Ti (24), threo‐[MeN(CH2CH2O)(CHPhCHPhO)]2Ti (25), and {MeN(CH2CH2O)[CH(CH2)4CHO]}2Ti (27) possess a monomeric structure with a hexacoordinate titanium atom in the solid state. Among them complexes 19, 20, 23, 25, and 27 are characterized by a cis disposition of the nitrogen atoms in the coordination environment of the Ti atom, while nitrogen atoms in 24 occupy trans positions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Synthesis of new palladium(II) compounds with several bidentate nitrogen-donor ligands: Structural analyses by 1H and 13C{ 1H} NMR spectroscopy and crystal structures

The reaction of [PdCl 2(CH 3CN) 2] with N-alkylaminopyrazole ( NN′) ligands, 1-[2-(ethylamino)ethyl]-3,5-dimethylpyrazole ( deae), 1-[2-( i propylamino)ethyl]-3,5-dimethylpyrazole ( deai), and 1-[2-( t butylamino)ethyl]-3,5-dimethylpyrazole ( deat), affords a series of square planar Pd(II) complexes [PdCl 2( NN′)] ( NN′ = deae ( 1), deai ( 2) and deat ( 3)). The solid-state structures of complexes 1 and 3 were determined by single crystal X-ray diffraction studies. The NN′ ligands are coordinated through the N pz and N amine atoms to the metal atom, which completes its coordination with two chlorine atoms in a cis disposition. These palladium(II) compounds were characterised by elemental analyses, conductivity measurements, IR, 1H and 13C{ 1H} NMR spectroscopies. The NMR studies of the complexes prove the rigid conformation of the ligands when they are complexed.

Stereomutations of Atropisomers of Sterically Hindered Salophen Ligands

[structure: see text] The stereomutations in nonsymmetrical salophen ligands 1-4 were studied by means of dynamic NMR and HPLC methods. DNMR experiments showed that in DMSO-d(6) hindered ligands 2-4 exist in two chiral conformations, depending on whether the imine carbon atoms are in a cis or trans disposition with respect to the plane of the central o-phenylenediamine ring, the latter being more stable by 1.0 kcal mol(-1). Owing to its higher dipole moment, in the apolar solvent C(6)D(6) the cis conformer is destabilized with respect to the trans one, in agreement with the results of ab initio calculations. In DMSO-d(6) solution the two conformers are in equilibrium through the less hindered rotation about the C6-N7 bond aligned to the a(6,7) axis, and the interconversion barriers range from 18.4 to 19.3 kcal mol(-1). The enantiomerization process is a two step-process that implies sequential rotations around the C6-N7 and the C1-N8 bonds, so that the rate determining step is the slower rotation around the more hindered C1-N8 bond aligned to the a(1,8) axis, and the energy barriers range from 21.4 to 21.9 kcal mol(-1). These values compare well with those determined by chromatography on an enantioselective HPLC column at low temperature, thus confirming that DNMR and DHPLC can be conveniently employed as complementary techniques.

Synthesis and characterisation of new N1-alkyl-3,5-dipyridylpyrazole derived ligands. Study of their reactivity with Pd(II) and Pt(II)

Two new pyrazole-derived ligands, 1-ethyl-3,5-bis(2-pyridyl)pyrazole ( L 1) and 1-octyl-3,5-bis(2-pyridyl)pyrazole ( L 2), both containing alkyl groups at position 1 were prepared by reaction between 3,5-bis(2-pyridyl) pyrazole and the appropriate bromoalkane in toluene using sodium ethoxide as base. The reaction between L 1, L 2 and [MCl 2(CH 3CN) 2] (M = Pd(II), Pt(II)) resulted in the formation complexes of formula [MCl 2( L)] (M = Pd(II), L = L 1 ( 1); M = Pd(II), L = L 2 ( 2); M = Pt(II), L = L 1 ( 3); M = Pt(II), L = L 2 ( 4)). These complexes were characterised by elemental analyses, conductivity measurements, infrared, 1H, 13C{ 1H} NMR and HMQC spectroscopies. The X-ray structure of the complex [PtCl 2( L 2)] ( 4) was determined. In this complex, Npyridine and Npyrazole donor atoms coordinate the ligand to the metal, which complete its coordination with two chloro ligands in a cis disposition.