Strong Trans Effect Research Articles

A comparative study of high-spin manganese and iron complexes

Different metal complexes of the general form M(OH) n (H2O)6– n have been studied for manganese and iron. Oxidation states considered for manganese are Mn(III), Mn(IV) and Mn(V) and for iron Fe(II), Fe(III) and Fe(IV). Oxygen containing ligands are used throughout with varying numbers of hydroxyl and water ligands. Some metal-oxo and some charged complexes were also studied. Large Jahn-Teller distortions were found for the Mn(III) and Fe(IV) complexes. Consequences of these distortions are that water ligands have to be placed along the weak JT-axis and that five-coordination by a loss of one of these water ligands is quite competitive with six-coordination in particular for manganese. For Fe(II) and Fe(III) lower coordinations than six are preferred due to the presence of two repulsive e g electrons. For the metal-oxo complexes five-coordination is also preferred due to the strong trans effect from the oxo ligand. All complexes studied have high-spin ground states. An interesting effect is that the spin is much more delocalized on the ligands for the iron complexes than for the manganese complexes. This effect, which is chemically important for certain iron enzymes, is rationalized by the large number of 3d electrons on iron. For manganese with only five 3d electrons no spin delocalization is needed to obtain the proper high-spin states.

Comparison of Isoelectronic Cyclopentadienyl, Indenyl, and Hydrotris(3,5-dimethylpyrazolyl)borate Complexes of Osmium(VI)

Osmium(VI) complexes with cyclopentadienyl, indenyl, and hydrotris(3,5-dimethylpyrazolyl)borate ligands result from the reaction between [Os(N)Ph2(py)2][BF4] and sodium cyclopentadienide, potassium indenide, or potassium hydrotris(3,5-dimethylpyrazolyl)borate. The molecular structures of the resulting complexes, CpOs(N)Ph2 (1), InOs(N)Ph2 (2), and Tp*Os(N)Ph2 (3), have been determined by X-ray diffraction analysis. The cyclopentadienyl-type ligand in each complex is distorted due to the strong trans effect of the nitrido group.

Synthesis, Structure, and Spectroscopic Properties of Ortho-Metalated Platinum(II) Complexes

The ortho-metalated Pt(II) complexes Pt(ppy)(CO)Cl (1), Pt(ptpy)(CO)Cl (2), and Pt(ppy)(Hppy)Cl (3) (where ppy and ptpy are respectively the ortho-C-deprotonated forms of 2-phenylpyridine and 2-p-tolylpyridine and Hppy is 2-phenylpyridine) have been prepared. The CO ligand is coordinated trans to the nitrogen atom of the ortho-metalated ligand and exerts a strong trans effect resulting in a relatively long Pt-N bond [2.114(19) {angstrom}]. This structure shows both the bidentate ppy ligand and the monodentate Hppy with the nitrogens of these ligands trans to each other. The UV/vis electronic absorption spectra of 1-3 have intense bands in the near-UV region ({approximately}375 nm) which have been assigned as metal to ligand charge transfer (MLCT) transitions, and higher energy bands were assigned as ligand-centered transitions. Each complex exhibits relatively long-lived structured emissions in the solid state at ambient temperature and at 77 K and 77 K glassy toluene solutions. These emissions are proposed to originate from triplet MLCT states. Notably, in solution both the lifetime and spectrum of 2 proved to be a function of the concentration, a phenomenon interpreted in terms of the propensity of square planar d{sup 8} complexes to oligomerize. In contrast, the more sterically hindered complex 3 displayed no such tendency towardmore » oligomerization.« less

Theoretical studies on the reaction of phosphoranes with anions

The reactions of phosphoranes with anions were studied by ab initio calculations at the HF/6-311 + +G(d,p) level. The reaction PH 5 + H − proceeds by equatorial H or axial H deprotonation, or adduct formation, depending on the orientation of the entering anion, the former prevailing overall. In the reaction PH 4X + H − (X = F, OH, NH 2, CN), the orientation of ligand X and the acidic hydrogen atoms in X = OH and NH 2 groups has a strong influence on deprotonation pathways but little effect on the addition process, with a strong trans effect of ligand X in ax-PH 4X. The reaction mode for PH 5X − → PH 4X. + H − was found to depend largely on the apicophilicity of X in PH 4X, giving axial phosphoranes for X = F and CN and the equatorial form for X = OH. PH 5NH 2 − has a C s structure and both axial H and equatorial H deprotonation lead to an eq-PH 4NH 2 product due to the strong preference for equatorial NH 2.

The cis- and trans-effects of cyanide in substitution at platinum(II)

The cis- and trans-[Pt(am)2Cl2] isomers (am = dimethylamine, pyridine, 4-cyanopyridine, 4-chloropyridine, 2-methylpyridine, 4-methylpyridine, 2,4-dimethylpyridine, 4-ethylpyridine, morpholine or piperidine), react rapidly with excess CN– in methanol to form the corresponding cis- and trans-[Pt(am)2(CN)2] species which then react further to give [Pt(CN)4]2–. The kinetics of the slow step, [Pt(am)2(CN)2]+ CN–→[Pt(am)(CN)3]–+ am, has been studied. In spite of the strong trans effect of CN– the trans species are all more reactive than the corresponding cis isomers. The second-order rate constants are sensitive to the nature of am; plots of log k2 against the pKa of Ham+ are linear but the slope for the trans isomers (–0.27) is much greater than that for the cis isomers (–0.07). The rate constants for the displacement of o-methyl substituted pyridines are smaller than predicted from their basicity. This steric hindrance effect is much more marked in the trans isomers. The complexes with am = NH3 and NH2Me are similarly less reactive than might be predicted but the effect is the same in both isomers. The results are explained in terms of the trans effect of cyanide and its effect upon the intrinsic reactivities and nucleophilic discriminations of the substrates.

Stereoselective formation and reactions of tetraalkylaurates(III)

Reactions of cis- (or trans-) dimethylalkyl(triphenylphosphine)gold(III), Au(R 1)(R 2) (R 3)(PPh 3) with alkyllithiums (R 4Li) lead to selective displacement of the triphenylphosphine ligand by the alkyl anion to give square planar cis- (or trans-)tetraalkylaurates(III), [Au(R 1) (R 2)(R 3)(R 4)] − Li + (R 1 = Me, R 2 = R 3 = Me or Et, R 4 = Me, Et, nPr, nPr, nBu or Ph) in benzene. The reactions are stereoselective and no isomerization is observed. Rates of the reactions between the trialkylgold(II) complex and alkyllithiums are first order in the concentration of the gold(III) complex, and an associative mechanism involving the neutral trimethylgold(III) complex and alkyllithiums for the formation of tetraalkylaurates(III) has been proposed as a result from the kinetic study. Hydrolyses of cis- or trans-dimethyldiethylaurates(III) in the presence of triphenylphosphine afford cis-methyldiethyl(triphenylphosphine) gold(III) or trans-di-methylethyl(triphenylphosphine)gold(III) with liberation of an equimolar amount of the corresponding alkane, reflecting the strong trans effect of the alkyl group in the reaction. Molecular structure of cis-methyldiethyl (triphenylphosphine)gold(III) has been unequivocally determined by X-ray structure analysis (monoclinic, P2 1 / c, a 10.972(6), b 19.898(9), c 10.683(7) Å, γ 112.42(4)°, V 2156(2) Å 3, R = 7.8, R w = 11.6 for 3947 reflections (| F o| ⪢ 3 | F o|).

Darstellung, Schwingungsspektren und Normalkoordinatenanalyse der Chloro-Bromo-Technetate(IV), [TcCl„Br6_n]2-, n = 0-6 / Preparation, Vibrational Spectra and Normal Coordinate Analysis of Chloro-Bromo-Technetates(IV), [TcCln Br6-n]2-, n = 0-6

The mixed chloro-bromo-technetates(IV), [TcClnBr6-n 2-, n = 1-5, have been separated for the first time by ion exchange chromatography on diethylaminoethyl-cellulose. Due to the stronger trans-effect of Br as compared to Cl, the ligand exchange reactions of [TcBr6 2- with HCl and of [TcCl6]2- with HBr proceed stereospecifically, to form either cis/fac- or trans/merspecies for n = 2, 3, 4, respectively. To avoid photoisomerization the compounds have to be handled in the absence of light. The IR and Raman spectra of the ten chloro-bromo-techne-tates(IV), including the pure geometrical isomers, have been recorded at low temperature (80 K) and completely assigned to structures of point groups Oh, D4h, C4v, C3v, and C2v, supported by normal coordinate analysis based on a general valence force field. Due to the different trans-influences Cl < Br in asymmetric Cl′—Tc— Br′ axes, the Tc— Br′ bonds are strengthened and the Tc—Cl′ bonds are weakened, as indicated by valence force constants, for Tc—Br′ on average 6% higher and for Tc—Cl′ 10% lower, as compared with the values calculated for symmetric Br—Tc—Br and CI—Tc—Cl axes, respectively.

Darstellung, Schwingungsspektren und Normalkoordinatenanalyse von Chloro-Bromo-Rhodaten(III) / Preparation, Vibration Spectra and Normal Coordinate Analysis of Chloro-Bromo-Rhodates(III)

The mixed chloro-bromo-rhodates(III) [RhClnBr6-n]3-, n = 1-5, have been separated for the first time by ion exchange chromatography on diethylaminoethyl-cellulose. Due to the stronger trans-effect of Br, as compared with Cl, on treatment of [RhBr6]3- with conc. HCl nearly pure cis/fac-isomers for n = 2, 3, 4 are formed. The reaction of [RhCl6]3- with conc. HBr yields mixtures of the cis/trans-isomers for n = 2, 4, which cannot be separated, but mer-[RhCl3Br3]3 is formed stereospecifically. The IR and Raman spectra of all isolated mixed ligand complexes are completely assigned according to point groups Oh, D3d, C4v, C3v and C2v, supported by normal coordinate analyses based on a general valence force field. The good agreement of calculated and observed frequencies confirms the assignments. Due to the stronger trans-influence of Br as compared to Cl, in all asymmetric Cl—Rh—Br axes the Rh—Br bonds are strengthened and the Rh—Cl bonds are weakened, indicated by valence force constants for Rh—Br approximately 14% higher, for Rh—Cl 10% lower, as compared with the values calculated for symmetric Br—Rh—Br and Cl—Rh—Cl axes, respectively.

The mechanical nature of the trans-effect in ligand substitution reactions of square-planar complexes

The kinetic trans-effect in associative ligand substitution reactions of square-planar complexes is explained theoretically on the basis of the angular deformability of the bond in the trans-activating ligands. The ability of these ligands, under the condition of low energy input, to leave the plane of the complex determines the ease with which the transition of the complex into the pentacoordinate state takes place in the substitution process. The most general property of ligands exhibiting a strong trans-effect is the large angular unfolding of the donor orbital in the direction of the central atom. This facilitates coordination between the bond-cleaving process and the formation of chemical bonds in the intermediate compound.

Thiol competition for Et 3PAuS-albumin: a nonenzymatic mechanism for Et 3PO formation

Thiols (RSH = 2,3,4,6-tetra- O-acetyl-β-l- d-thioglucose, β-1- d-thioglucose, and glutathione) can displace either the albumin or the triethylphosphine from the protein-gold complex, AlbSAuPEt 3. The albumin is displaced in preference to triethylphosphine, but irreversible oxidation of the latter eventually shifts the equilibria toward Et 3PO and AlbSAuSR. Albumin disulfide bonds are the probable oxidants. Neither O 2 nor oxidized glutathione substantially enhanced the rate or extent of Et 3PO formation. The labilization of the phosphine in AlbSAuPEt 3 is attributed to a strong trans effect of the albumin thiolate, Cys-34. The 31P NMR chemical shifts of various thiolato(triethylphosphine)gold(I) complexes are correlated directly with the affinity of the thiols for gold and inversely with their p K sh values. Deacetylated auranofin (1-thio-β- d-glucopyranosato- S) (triethylphosphine)gold(I) reacts with the mercaptalbumin and oxidized mercaptalbumin (putatively AlbSOH) forms of bovine serum albumin to form AlbSAuPEt 3 with displacement of the thioglucose ligand.

Nitrido-Azido-Komplexe des Molybdän(VI): Synthese und Kristallstruktur von MoN(N3)2[HB(3,5-Me2pyz)3] und MoN(N3)Cl[HB(3,5-Me2pyz)3] / Nitrido Azido Complexes of Molybdenum(VI): Synthesis and Crystal Structure of MoN(N3)2[HB(3,5-Me2pyz)3] and MoN(N3)Cl[HB(3,5-Me2pyz)3

The reaction of MOCl4 (C2H5CN)2 with (CH3)3SiN3 and subsequent addition of Na[HB(3,5-Me2pyz)3] yields the nitrido azido complexes MoN(N3)2[HB(3,5-Me2pyz)3] and MoN(N3)Cl[HB(3,5-Me2pyz)3]. The two complexes crystallize from toluene as mixed crystals (space group P21/n, a = 1630.6, b = 878.0, c = 1675.5 pm, β = 112.67°, Z = 4). Crystallographic equivalent positions are occupied in a 4:1 ratio by diazido and monoazido monochloro complexes. The central Mo atom exhibits a sixfold coordination in form of a distorted octahedron with the nitrido ligand and one of the three pyrazol rings in axial positions. The triply bonded nitrido nitrogen atom (Mo≡N 164.2 pm) causes a strong trans effect, resulting in a long Mo-N6 bond (245 pm) to the trans positioned pyrazole nitrogen atom. The Mo-N distances in the equatorial plane are Mo-N2 215 and Mo-N4 216 pm, respectively. The nitrido complexes are remarkably stable against hydrolysis, probably due to steric shielding by the [HB(3,5-Me2pyz)3]- ligand. ν(Mo≡N) is observed at 1025 cm-1

The formation and reactivity of sulfito complexes of tetraethylenepentamine-cobalt(III): X-ray structure of αα-[co(tetren)SO 3]ClO 4

The synthesis of complexes of the type Co(tetren)-OH 2 3+ (tetren = tetraethylenepentamine) and their reactions with sulfite to produce O- and S-bonded isomers were studied in detail. The linkage isomerization reaction of αβS-Co(tetren)OSO 2 + to αβS-Co(tetren)SO 3 + is accompanied by a geometrical isomerization to αα-Co(tetren)SO 3 +. The latter species was isolated as pure crystals and an X-ray structure was determined. The structure data clearly show the strong trans effect of the sulfito ligand, which may account for the geometrical isomerization process.

Unsymmetrisch substituierte alkin- und dialkinkomplexe von wolfram(IV) und molybdän(IV). Die kristallstruktur von [W 2Cl 8(PhCCCCSiMe 3)(pyridin) 2

The unsymmetrically substituted alkyne ClCCSiMe 3 and the dialkynes PhCCCCSiMe 3 and PhCCSiMe 2CCPh react with tungsten hexachloride in CCl 4, in the presence of C 2Cl 4 as a reducing agent, and with molybdenum pentachloride in CCl 4, respectively, to form the alkyne complexes [MoCl 4-(ClCCiMe 3)] 2 ( 1), [WCl 4(ClCCSiMe 3)] 2 ( 2), [WCl 4(PhCCCCSiMe 3)] 2 ( 3), [W 2Cl 8(PhCCCCSiMe 3)] x ( 4), [W 2Cl 8(PhCCSiMe 2CCPh)] x ( 5), [Mo 2Cl 8-(PhCCSiMe 2CCPh)] x ( 6). In all cases the alkyne ligand is side-on coordinated to the metal (η 2), the bonding features correspond to the cyclopropene type. The coordination number of the metal is 7; the complexes 1–3 are dimerised via MCl 2M bridges and the bifunctional complexes 4–6 are polymerised via analogous bridges. In 3, the tungsten atom is coordinatd to the alkyne group adjacent to the phenyl substituent. In the molybdenum compounds the alkyne ligand is cleaved with Lewis bases such as pyridine or diethyl ether forming solvate complexes of molybdenum(IV), whereas in the corresponding tungsten complexes only the chloro bridges are cleaved. The pyridine adducts [W 2Cl 8(PhCCCCSiMe 3)(pyridine) 2] ( 7) and [W 2Cl 8(PhCCSiMe 2CCPh)(pyridine) 2] ( 8) are described in further detail. All complexes are characterized by elemental analyses, mass and IR spectra, the tungsten compounds (as ether adducts) also by their 13C NMR spectra. 7 was obtained in single crystals and has been subjected to a X-ray diffraction study. It crystallises in the monoclinic space group P2 1/ c with four formula units per unit cell (4154 independent, observed reflexions, R = 0.096) and with the lattice constants a 880.0(6), b 2866.0(20), c 1501.2(10) pm; β 94.4(3)°. EAch tungsten atom is surrounded by four chlorine atoms in equatorial positions, both alkyne groups are bonded side-on (η 2) to the tungsten atoms, whereas the N atoms of the pyridine molecules are located trans to the alkyne groups. The CC bond lengths of the alkyne groups are 125 pm (adjacent to the phenyl substituent) and 140 pm (adjacent to the SiMe 3 group), respectively. A strong trans-effect of the two alkyne groups is observed, resulting in shifting the tungsten atoms out of the Cl 4 planes by about 33 pm. The dihedral angle of 94.9°, enclosed by the two WC 2 planes, is remarkable.

Nitrido-zido-Komplexe des Molybdän(VI): Synthese und Kristallstruktur von MoN(N3)2Cl(terpy)/ Nitrido Azido Complexes of Molybdenum(VI): Synthesis and Crystal Structure of MoN(N3)2Cl(terpy)

Abstract MoN(N3)2Cl(terpy) is formed by the reaction of MoCl4(C2H5CN)2 with (CH3)3SiN3 and subsequent addition of terpy. This complex appears also as the main product o f the heterogeneous reaction between MoCl3(terpy) and (CH3)3SiN3. It crystallizes in the monoclinic space group P 21/c with the lattice parameters a = 875.5, b = 1041.4, c = 1891.3 pm, β = 97.00°, Z = 4. The central Mo atom is seven-coordinated in the form of a slightly distorted pentagonal bipyramid, the nitrido and chloro ligands being in axial positions. The triply bonded nitrido ligand ( Mo - N 1 = 166.2 pm) causes a strong trans effect, resulting in a long Mo-Cl distance of 271.9 pm.

Über die Staudinger-Reaktion mit Tantaltetrachloridazid. Die Kristallstruktur von Tantal(V)-(triphenylphosphinimino)tetrachlorid, Ta[NP(C6H5)3]Cl4 / On the Staudinger Reaction with Tantalum Tetrachloride Azide. The Crystal Structure of Tantalum(V)(triphenyl-phosphinimino)tetrachloride, Ta[NP(C6H5)3]Cl4

[TaCl4N3]2 reacts easily with PPh3 yielding TaCl4(NPPh3 ) , TaCl4(NPPh3)(NHPPh3) and TaCl5 . The latter are supposed to be products of the reaction of primarily formed TaCl4(NPPh3)2-TaCl4 + with the solvent ClCH2-CH2Cl. TaCl4(NPPh3) crystallizes in the monoclinic system with the space group P21/c. The crystal structure shows centrosymmetric dimers, in which the Ta atoms are linked together by asymmetric Cl bridges. The phosphinimino ligand is coordinated trans to the Cl bridge and causes a strong trans effect. A linear P = N = Ta group with double bonds of P = N = 159.3 and Ta = N = 180,1 pm is observed.

Darstellung und Schwingungsspektren von Chloro-Bromo-Platinaten(IV) einschließlich der Stereoisomeren / Preparation and Vibrational Spectra of Chloro-Bromo-Platinates(IV) Including Stereoisomers

The mixed chloro-bromo complexes [PtClnBr6-n]2-, n = 1-5, are separated by ion exchange chromatography on diethylaminoethylcellulose. The separation of corresponding stereoisomers for n = 2, 3, 4 is not possible. Due to the stronger trans-effect of Br compared with Cl, on treatment of [PtBrß]2- with Cl- in the presence of Br2 nearly pure cis-isomers, and by reaction of [PtClsBr]2- and cis-fPtC^Bro]2- with Br~/Br2 completely pure transisomers are formed. The stereoselectivity of the successive ligand exchange reactions is better than in corresponding series of Re, Os and Ir. The highly resolved vibrational spectra allow the distinction of the mixed ligand complexes as well as the estimation of purity of the isomers. All allowed stretching frequencies are observed and assigned according to point groups D4h, C4V, C3V and C2V. Especially in the ν(Pt-Br) region it is possible to distinguish bands arising either from symmetric Br-Pt-Br or asymmetric Cl-Pt-Br axes. The UV/VIS spectra exhibit systematic hypsochromic shifts on the successive exchange of Br-ligands by Cl. A critical discussion of the literature concerning chloro-bromo-platinates- (IV) shows the importance of effective separation processes for the isolation of pure mixed ligand complexes

METAL ISOTOPE EFFECT ON METAL-LIGAND VIBRATIONS: V. CIS AND TRANS Ni(II) PHOSPHINE-HALIDE COMPLEXES

Abstract Infrared spectra (4000–200 cm−1) have been reported for Ni(DPE)X2 where X is Cl, Br and I and DPE is 1,2-bis(diphenylphosphino)ethane. The Ni[sbnd]X and Ni[sbnd]P stretching bands have been assigned based on the observed isotopic shifts due to the 58Ni-62Ni substitution. The Ni[sbnd]X stretching frequencies are always lower and the Ni[sbnd]P stretching frequencies are always higher in the cis-complexes such as Ni(DPE)X2 than in the corresponding trans-complexes such as Ni(PEt3)2X2. These differences between cis and trans configurations have been attributed to the strong trans-effect of phosphine ligands.

The development of coordination chemistry in the Soviet Union

The report involves a review of the most important work on coordination chemistry carried out in the Soviet Union during this decade in the field of platinum metals, rare earth elements, actinides, as well as complex compounds of elements from various groups of the D. I. Mendeleev Periodic System. The results obtained on studying heteropolyacids and complexes with different new types of ligands, including complexons, are described, new data on coordination chemistry of organo-element compounds are reported, and the results of the study of complex compounds and of the nature of their chemical bonding as obtained by various physicochemical methods are characterized. Mention is made of studies concerned with explaining the phenomenon of complex formation in terms of the DI. Mendeleev Periodic Law. The report shows the development of coordination chemistry in the Soviet Union by its main research centres. Soon after its publication, the coordination theory developed by Werner gained considerable support in Russia. An important contribution in this respect was made by Chugaev, discoverer of the well-known reactions for nickel with dimethyiglyoxime, for osmium with thiourea, etc. Since 1904 he had been engaged in research on the chemistry of complex compounds, at first those of nickel and cobalt and later of various platinum metals. It was Chugaev who originated synthesis of a series of pentammine derivatives of platinum(iv), before unknown. He discovered the extraordinary strength of five-membered rings in complex compounds and the regularities of their formation1. In 1910 Chugaev published a monograph, On the Chemical Structure of Complex Compounds, in which he popularized and further developed Werner's ideas. The investigations of Chugaev and hi co-workers laid down the foundation for a large scientific school in the Soviet Union, which carries on extensive research on the chemistry of complex compounds of platinum and other elements. In 1926 (Cherniayev2, while studying nitrite complexes of platinum, discovered the trans-effect, which proved to be of great importance for the further development of the chemistry of complex compounds. Gel'man3 discovered a strong trans-effect of unsaturated organic molecules of the ethylene and acetylene type, which act as electron donors in the formation of coordination compounds.

Oxidation by Transition Metal Complexes. I. Oxidation of Styrene and Triphenylphosphine Catalyzed by O2-Ir Complex

Abstract In order to investigate the oxidation reaction which is catalyzed by transition metal complexes in a homogeneous system under mild conditions, the oxidation reactions of styrene and triphenylphosphine catalyzed by various iridium complexes have been studied. The Vaska complex (IrX(CO)(PPh3)2) and the biphosphine chelate complex have been found to be effective as oxidation catalyst. It was found that the SnCl3 ligand which has a strong trans effect promotes the oxidation of styrene. For the sake of comparison with the iridium compounds, oxidation with palladium salts was also studied.