Diamagnetic anisotropy of quadruple MoMo bonds: α-Mo2Cl4(diphosphine)2 complexes

Two components (χ_xV — χ′_hu and χ_xV — χ″_hu) of magnetic anisotropy of MoMo quadruple bonds have been obtained by using the X-ray crystallographic molecular structure and the low temperature ¹H NMR spectrum of α-Mo₂Cl₄[(C₆H₅)₂PCH₂CH₂P(p-RC₆H₄)₂]₂ [R  H (dppe), CH₃ (dpdt) and tert-C₄H₉ (dpdbp)]. The values of χ_xV — χ′_hu and χ_xV — χ″_hu for the dpdbp case are −(8470 ± 200) x 10⁻³⁶ and −(5540 ± 70) x 10⁻³⁶ m³ molecule⁻¹, respectively, which are several times as large as χ_xV — χ_hu (Mo³Mo). Through detailed examination of the ¹H NMR signals of the ethylene protons, conformational flexing of the chelate rings of α-Mo₂Cl₄(dpdbp)₂ has been recognized.     

On the stereochemistry of chiral (η5-C9H7)Rh(diphosphine) complexes

The dynamic behaviour of some indenyl complexes of the type (η⁵-C₉H₇)Rh(Ph₂PCHRCHR′PPh₂) (R = or ≠ R′) has been investigated, and the relevant energy barrier involved evaluated (10–11 kcal/mol). For the complexes in which the diphosphine has a C₁ symmetry (R ≠ R′), the energy differences between the two diastereometric conformations seem to depend on both steric and electronic factors.     

Coordination modes of diphosphines in silver(I)–diphosphine complexes mediated by 2,4,6-tri(2-pyridyl)-1,3,5-triazine (tptz)

Silver (I) complexes [Ag₂(tptz)(dppm)₂(DMF)](BF₄)₂·2DMF (1), [Ag(tptz)(dppe)]_n(BF₄)_n·2nH₂O·nMeOH (2), [Ag₂(tptz)₂(dppp)₂](BF₄)₂ (3) and [Ag₂(tptz)₂(dppb)](BF₄)₂ (4) were obtained from the reactions of AgBF₄ and diphosphine Ph₂P(CH₂) _nPPh₂ (L_pp, n=1–4) in the presence of 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) in MeOH–DMF. Single crystal analyses showed that the closed metallocyclic unit [Ag₂(L_pp)₂]²⁺ with double L_pp bridges was obtained in (1) and (3) with an odd number of n, while an open metallochain (Ag₂L_pp)²⁺ with a single bridge formed in (2) and (4) with n being even. Coordination modes for the diphosphines are directly related to the rigid tptz ligand with a large -system.     

Asymmetric hydrogenation of aromatic ketones using new chiral-bridged diphosphine/diamine-Ru(Ⅱ) complexes

<正>A series of chiral secondary alcohols were easily prepared by means of asymmetric hydrogenation of prochiral aromatic ketones using a new((R_(ax))-BuP)/(R,R)-DPEN-Ru(Ⅱ) complex catalyst system.The hydrogenation of 2-methylacetophenone in n-butanol (t-BuOK/Ru =45.6/1,S/C = 500,20 atm.of H_2,20℃,48 h) afforded(S)-1-(2'-methylphenyl)ethanol in 92%ee and99% conversion.     

trans-Fe(II)(H)2(diphosphine)(diamine) complexes as alternative catalysts for the asymmetric hydrogenation of ketones? A DFT study

New insights into the structural, electronic and catalytic properties of Fe complexes are provided by a density functional theory study of model as well as real [Fe(II)(H)(2)(diphosphine)(diamine)] systems. Calculations conducted using several different functionals on the trans- and cis-isomers of [Fe(II)(H)(2)(S-xylbinap)(S,S-dpen)] complexes show that, as with the [Ru(II)(H)(2)(diphosphine)(diamine)] complexes, the trans-[Fe(II)(H)(2)(diphosphine)(diamine)] complex is the more stable isomer. Analysis of the spin states of the trans-[Fe(II)(H)(2)(diphosphine)(diamine)] complexes also shows that the singlet state is significantly more stable than the triplet and the quintet, as with the [Ru(II)(H)(2)(diphosphine)(diamine)] complexes. Calculations of the catalytic cycle for the hydrogenation of ketones using two model trans-[M(II)(H)(2)(PH(3))(2)(en)] catalysts, where M = Ru and Fe, show that the mechanism of reaction as well as the activation energies are very similar, in particular: (i) the ketone/alcohol hydrogen transfer reaction occurs through the metal-ligand bifunctional mechanism, with energy barriers of 3.4 and 3.2 kcal mol(-1) for the Ru- and Fe-catalysed reactions, respectively; (ii) the heterolytic splitting of H(2) across the M[partial double bond, bottom dashed]N bond for the regeneration of the Ru and Fe catalysts has an activation barrier of 13.8 and 12.8 kcal mol(-1), respectively, and is expected to be the rate determining step for both catalytic systems. The reduction of acetophenone by trans-[M(II)(H)(2)(S-xylbinap)(S,S-dpen)] complexes along two competitive reaction pathways, shows that the intermediates for the Fe catalytic system are similar to those responsible for the high enantioselectivity of (R)-alcohol in those proposed trans-[Ru(II)(H)(2)(S-xylbinap)(S,S-dpen)] catalysed acetophenone hydrogenation reaction. Thus the high enantiomeric excess in the hydrogenation of acetophenone could, in principle, be achieved using Fe catalysts.     

Synthesis and characterisation of bite angle-dependent (η1-allyl)Rh and (η3-allyl)Rh complexes bearing diphosphine ligands. Implications for nucleophilic substitution reactions

Several novel rhodium allyl complexes have been prepared and their structures have been studied using NMR spectroscopy and X-ray crystallography. Depending on the bite angle of the ligand and the substitution pattern of the allyl group, two different coordination modes (η¹ and η³) have been observed for the allyl moiety. The activities of these Rh allyl complexes in the allylic alkylation reaction have been tested. We have shown that both coordination modes give active complexes in this reaction, but that the regioselectivity is dependent on the coordination mode of the allyl group.     

Models of the iron-only hydrogenase: Reactions of [Fe2(CO)6(μ-pdt)] with small bite-angle diphosphines yielding bridge and chelate diphosphine complexes [Fe2(CO)4(diphosphine)(μ-pdt)]

Reactions of [Fe₂(CO)₆(μ-pdt)] (1) (pdt = SCH₂CH₂CH₂S) and small bite-angle diphosphines have been studied. A range of products can be formed being dependent upon the nature of the diphosphine and reaction conditions. With bis(diphenylphosphino)methane (dppm), thermolysis in toluene leads to the formation of a mixture of bridge and chelate isomers [Fe₂(CO)₄(μ-dppm)(μ-pdt)] (2) and [Fe₂(CO)₄(κ²-dppm)(μ-pdt)] (3), respectively. Both have been crystallographically characterised, 3 being a rare example of a chelating dppm ligand in a first row binuclear system. At room temperature in MeCN with added Me₃NO · 2H₂O, the monodentate complex [Fe₂(CO)₅(κ¹-dppm)(μ-pdt)] (4) is initially formed. Warming 4 to 100 °C leads the slow conversion to 2, while oxidation (on alumina) gives [Fe₂(CO)₅(κ¹-dppmO)(μ-pdt)] (5). With bis(dicyclohexylphosphino)methane (dcpm), heating in toluene cleanly affords [Fe₂(CO)₄(μ-dcpm)(μ-pdt)] (6). With Me₃NO · 2H₂O in MeCN the reaction is not clean as the phosphine is oxidised but monodentate [Fe₂(CO)₅(κ¹-dcpm)(μ-pdt)] (7) can be seen spectroscopically. With 1,2-bis(diphenylphosphino)benzene (dppb) and cis-1,2-bis(diphenylphosphino)ethene (dppv) the chelate complexes [Fe₂(CO)₄(κ²-dppb)(μ-pdt)] (8) and [Fe₂(CO)₄(κ²-dppv)(μ-pdt)] (9), respectively are the final products under all conditions, although a small amount of [Fe₂(CO)₅(κ²-dppvO)(μ-pdt)] (10) was also isolated. Protonation of 2 with HBF₄ affords a cation with poor stability while with the more basic diiron centre in 6 readily forms the stable bridging-hydride complex [(μ-H)Fe₂(CO)₄(μ-dcpm)(μ-pdt)][BF₄] (11) which has been crystallographically characterised.     

Transition metal complexes derived from 2-hydroxyimino-3-(2′-hydrazonopyridyl)-butane

Summary The complexes of Mn^II, Co^II, Ni^II, Cu^II, Zn^II, Cd^II, Hg^II, Co^III and UO ₂ ²⁺ ions with 2-hydroxyimino-3-(2-hydrazonopyridyl)-butane (HL) have been synthesised and characterized by elemental analyses, molar conductivities, magnetic measurements and spectral (i.r., visible, n.m.r.) studies. I.r. spectra show that HL behaves as a neutral or mononegative ligand and binds in a bidentate and/or tridentate manner. Also, HL behaves as oxidizing agent towards Co^II forming diamagnetic Co^III complexes depending on the preparative conditions. Different stereochemistries are proposed for Mn^II, Co^III, Co^II, Ni^II and Cu^II on the basis of spectral and magnetic studies.     

Silver(I) perchlorate complexes of N,N ′-bis(trans-cinnamaldehyde)ethylenediimine (ca2en)

Three silver(I) complexes, [Ag(ca₂en)(PPh₃)]ClO₄ (1), [Ag(ca₂en)(PPh₃)₂]ClO₄ (2) and [Ag(ca₂en)₂]ClO₄ (3), where ca₂en?=?N,N′-bis(trans-cinnamaldehyde)ethylenediimine, have been synthesized and characterized spectroscopically. The crystal structure of (1) was determined by X-ray diffraction methods. Crystal data for 1: C₃₈H₃₅AgClN₂O₄P, triclinic, P 1, a?=?12.086(2), b?=?18.204(2), c?=?8.550(2) Å, α?=?102.69(1), β?=?105.85(1), γ?=?91.47(1)°, V?=?1758.0(5) ų, Z?=?2, R(F)?=?0.070, wR (F)?=?0.064, T?=?296?K. The coordination geometry of the Ag atom is distorted trigonal involving two N atoms of ca₂en and one P atom of triphenylphosphine (PPh₃).     

Copper(II) and palladium(II) complexes of N,N′-bis(2-hydroxyethyl)stilbenediamine

A new 1,2-diamine ligand, N,N-bis(2-hydroxyethyl)stilbenediamine (L), has been prepared by reduction of the condensation product of benzaldehyde with 2-aminoethanol with Al amalgam. Mononuclear complexes of the [CuL(H₂O)]X₂ type where X=Cl^– or AcO^– with Cu^II and PdLCl₂ with palladium(II) have been prepared and characterized by elemental analysis and i.r., u.v.–vis. or ¹H-n.m.r. spectroscopy.     

Transition metal complexes derived from N-isonicotinamido-N′-benzoylthiocarbamide (H2IBTC)

Summary The synthesis and characterization of Cr^III, Mn^II, Fe^III, Co^II, Ni^II, Cu^II, Zn^II, Cd^II and UO _inf2 ^sup2+ complexes of N-isonicotinamido-_N-benzoylthiocarbamide (H₂IBTC) are reported. I.r. spectral data show that the ligand behaves in a bidentate, tridentate and/or tetradentate manner. Different stereochemistries are proposed for Cr^III, Mn^II, Fe^III, Co^II, Ni^II and Cu^II complexes on the basis of spectral and magnetic studies. The i.r. data indicate that the carbonyl oxygen of the benzoyl moiety is the backbone of chelation in most complexes.     

The reactions of [Fe2(η-Cp)2(CNAr)4] complexes with halogens and tin(II) halides

Summary [Fe₂(-Cp)₂(CNAr)₄] (2) (540-01, C₆H₄Me-2, C₆H₄Et-2, C₆H₃Me₂-2,4, C₆H₃Me₂-2,6, C₆H₃(Me)Et-2,6, C₆H₃Et₂-2,6 or C₆H₃ i-Pr₂-2,6) react with I₂ to give [Fe(-Cp)(CNAr)₂I], but with Br₂[Fe(-Cp) (CNAr)₃]⁺ salts are the only products; IBr gives a mixture of the two. With SnX₂ (X = F, Cl, Br or I) in refluxing n-butanol, (2) gives isolable [{Fe(-Cp)(CNAr)₂}₂SnX₂] only when the CNAr ligands have two ortho substituents, otherwise decomposition occurred. When X = F, [Fe(-Cp) (CNAr)₂SnF₃] was also obtained from this reaction. Attempts to prepare [Fe(-Cp)(CNAr)₂X] (X = Cl or Br) by reaction of (2) with HX in the presence of air gave rather unstable products which with SnX₂ formed [Fe(-C₅H₅)-(CNAr)₂SnX₃]. Similar compounds, [Fe(-Cp) (CNAr)₂ SnX₂I], were obtained from [Fe(-Cp)-(CNAr)₂I] and SnX₂ (X = Cl or Br but not I). All of these complexes are much less stable than their Fe(-Cp)(CO)₂ counterparts; all decompose in solution to [Fe(-Cp)(CNAr)₃]⁺ which then break down to unidentified species. X-ray diffraction studies show that in [Fe(-Cp)(CNC₆H₃-i-Pr₂-2,6)₂I] and [{Fe(-Cp)(CNC₆H₃Me₂-2,6)₂}₂SnBr₂] there is pseudo-octahedral coordination about Fe. In the latter there is also distorted tetrahedral coordination about Sn so that its structure is very similar to that of [{Fe(-Cp)(CO)₂}₂SnCl₂]. Spectroscopic studies show that in all complexes rotation of the aryl rings of the CNAr ligands cannot be slowed in solution, and that there is free rotation about all 540-02 bonds.     

Synthesis and reactions of ν2-(2-formylphenyl)tetracarbonylmanganese(I) complexes; cyclopentaanulation of a diterpenoid

Reaction of tetracarbonylmangenese(I) complexes derived from a diterpenoid aryl aldehyde or aryl methyl ketone with acetylene or ethylene leads to cyclopentaannulation to give 1H-inden-1-ols or 1H-indan-ols, respectively.     

Structurally nonrigid molecular complexes (HF)n(H2O)m (n + m ≥ 2) and their spectroscopic features

The problem of the formation and stability of structurally nonrigid, donor—acceptor molecular complexes is considered. These complexes are formed between the molecules of water and hydrogen fluoride, the latter being the hydrolysis product of the chemical, radiochemical, and metallurgical industrial wastes. Based on the results of ab initio quantum-chemical calculations of the potential energy surfaces by the Hartree—Fock—Roothaan method, the equilibrium configurations of the (H₂O) _n (HF) _m complexes (n : m = 1 : 1; 1 : 2; 2 : 1; 2 : 2; and 3 : 3) were determined. These configurations are necessary for correct interpretation of the IR absorption spectra and for routine remote monitoring of such environmentally hazardous complexes in the Earth atmosphere. The harmonic vibrational frequencies of the (H₂O) _n (HF) _m complexes (n + m 2) were calculated and the interaction energies between the monomers were found. The influence of UV radiation on the (H₂O) _n (HF) _n complexes (n = 1—3) upon the transition from the ground to the lowest excited singlet electronic state was studied. Characteristic spectroscopic features of the (H₂O) _n (HF) _m complexes were established.     

Synthesis and structure of novel dinitrosyl iron complexes [Fe2(μ-SCH2CH2NHR)2(NO)4]

Two novel dinitrosyl iron complexes with thiolate bridging ligands [Fe₂(μ-SCH₂CH₂NHR)₂(NO)₄] (R = Ac, Boc), derived from the cysteamine complex [Fe₂(μ-SCH₂CH₂NH₃)₂(NO)₄]²⁺ are described. The complex with acylated cysteamine is characterized by X-ray diffraction analysis. The cysteamine complex is a convenient precursor for modification of the bridging ligand.     

Malatoplatinum(II) complexes – carboplatin analogs

A series of new neutral dicarboxylatoplatinum(II) complexes, containing D(+), L(−) or DL-malate dianion and ethylenediamine, 1-ethylimidazole or 1-propylimidazole as amine ligands, have been synthesized and characterized by elemental analysis, t.l.c., conductance, i.r., n.m.r., mass spectra (m/z) and electronic spectra. The new cytotoxic malatoplatinum(II) complexes are very soluble in water and resist hydrolysis. Their reactivity against glutathione is comparable with the reactivity of carboplatin, which suggests that these new complexes may be promising candidates in the search for low toxicity platinum cytostatics. This revised version was published online in June 2006 with corrections to the Cover Date.     

μ-phenoxo-bridged binuclear copper(II) complexes

Summary Two -phenoxo-bridged binuclear copper(II) complexes, [Fsal(GG)₂Cu₂Cl₃]·H₂O (1) containing an exogenous chloride-bridge and [Fsal(GG)₂Cu₂(OH)](ClO₄)₂·H₂O (2) containing an exogenous hydroxide-bridge, where {Fsal(GG)₂ = 2,6-bis[N-(acetylglycine)-imino-methylene]-4-methylphenol}, were synthesized. The complexes were characterized be several spectroscopic methods. According to variable temperature magnetic susceptibility measurements (4–300 K), the hydroxide-bridged complex (2) has a weak antiferromagnetic spin exchange integral (J =- 23.6 cm), while the chloride complex (1) has an unusual weak ferromagnetic spin exchange integral (J = + 30.9 cm); both complexes have similar optical spectra in the aqueous solutions.     

Ruthenium(II) complexes of 2-(2′-pyridyl)naphthoimidazole: synthesis,characterization and DNA-binding studies

The perchlorate salts of two new ruthenium(II) complexes incorporating 2-(2′-pyridyl)naphthoimidazole are synthesized in good yield. Complexes [Ru(phen)₂(PYNI)]²⁺ (phen = 1,10-phenanthroline) 1 and [Ru(dmp)₂(PYNI)]²⁺ (dmp = 2,9-dimethyl-1,10-phenanthroline, PYNI = 2-(2′-pyridyl)naphthoimidazole) 2 are fully characterized by elemental analysis, FAB-MS, ES-MS, ¹H NMR and cyclic voltammetric methods. The DNA-binding behavior of the complexes have been studied by spectroscopic titration, viscosity measurements and thermal denaturation. Absorption titration and thermal denaturation studies reveal that these complexes are moderately strong binders of calf-thymus DNA (CT-DNA), with their binding constants spanning the range (2.73–5.35) × 10⁴ M^?1. The experimental results show that 1 interacts with calf thymus DNA (CT-DNA) by intercalative mode, while 2 binds to CT-DNA by partial intercalation.