Sulfide oxidation with H2O2 catalyzed by manganese complex of N,N′,N″-tris(2-hydroxypropyl)-1,4,7-triazacyclononane

[MnL](ClO₄)₂ (L = N,N′,N″-tris(2-hydroxypropyl)-1,4,7-triazacyclononane) has been tested for catalyzing sulfide oxidation. In the presence of this complex, ethyl phenyl sulfide, butyl sulfide and phenyl sulfide are completely oxidized to the corresponding sulfoxides and sulfones with H₂O₂ as the oxidant. 2-Chloroethyl phenyl sulfide oxidation yield 2-chloroethyl phenyl sulfone and phenyl vinyl sulfone. In ethyl phenyl sulfide oxidation, effects of complex and H₂O₂ concentration and temperature on the reaction rate have been discussed. Through controlling reaction conditions, ethyl phenyl sulfoxide and ethyl phenyl sulfone may be produced selectively. The UV–Vis and electron paramagnetic resonance (EPR) studies on catalyst solution indicate that metal centre of the complex is transformed from Mn(II) to Mn(IV) after the addition of H₂O₂. At 25 °C, rate constant for ethyl phenyl sulfide oxidation is 4.38 × 10⁻³ min⁻¹.     

1,10-Phenanthroline-5,6-dione as a building block for the synthesis of homo- and heterometallic complexes

1,10-Phenanthroline-5,6-dione (C₁₂H₆N₂O₂ (1)) reacts with V(η⁶-mesitylene)₂ and Ti(η⁶-toluene)₂ affording coordination compounds of general formula M(O,O′---C₁₂H₆N₂O₂)₃ (M=Ti (2); M=V (3)) which further react with TiCl₄ or TiCp₂(CO)₂ yielding the tetrametallic species M(O,O′---C₁₂H₆N₂O₂---N,N′)₃(M′L_n)₃ (M=V, M′L_n=TiCl₄ (4); M=Ti, M′L_n=TiCp₂ (5); M=V, M′L_n=TiCp₂ (6)). The complex salt [Fe(N,N′---C₁₂H₆N₂O₂)₃][PF₆]₂ (7) has been obtained from iron(II) chloride tetrahydrate and 1 in the presence of NH₄PF₆. The reaction of 7 with TiCp₂(CO)₂ affords the tetrametallic derivative [Fe(N,N′---C₁₂H₆N₂O₂---O,O′)₃(TiCp₂)₃][PF₆]₂ (8). TiCl₂(THF)₂ reacts with MCp₂(O,O′---C₁₂H₆N₂O₂) to give MCp₂(O,O′---C₁₂H₆N₂O₂---N,N′)TiCl₂ (M=Ti (9); M=V (10)). By reaction of TiCp₂(O,O′---C₁₂H₆N₂O₂---N,N′)TiCl₂ (9) with C₁₂H₆N₂O₂, the bimetallic derivative TiCp₂(O,O′---C₁₂H₆N₂O₂---N,N′)TiCl₂(O,O′---C₁₂H₆N₂O₂) (11) has been prepared, which readily adds to TiCl₄, to give the trimetallic titanium derivative TiCp₂(O,O′---C₁₂H₆N₂O₂---N,N′)TiCl₂(O,O′---C₁₂H₆N₂O₂---N,N′)TiCl₄ (12). VCp₂(O,O′---C₁₂H₆N₂O₂---N,N′)TiCl₂ (10) reacts with the tris-chelate iron(II) cation 7 affording the heptametallic cationic complex [Fe(N,N′---C₁₂H₆N₂O₂---O,O′)TiCl₂(N,N′---C₁₂H₆N₂O₂---O,O′)VCp₂]₃ ⁺² isolated as the hexafluorophosphate 13.     

Fluorescent ligands for the histamine H2 receptor: synthesis and preliminary characterization

3-[3-(Piperidinomethyl)phenoxy]alkyl, N-cyano-N′-[ω-[3-(1-piperidinylmethyl)phenoxy]alkyl]guanidine and 2-(5-methyl-4-imidazolyl)methyl thioethyl derivatives containing fluorescent functionalities were synthesized and the histamine H₂ receptor affinity was evaluated using the H₂ antagonist [¹²⁵I]-aminopotentidine. The compounds exhibited weak to potent H₂ receptor affinity with pK_i values ranging from <4 to 8.85. The highest H₂ receptor affinity was observed for N-cyano-N′-[ω-[3-(1-piperidinylmethyl)phenoxy]alkyl]guanidines substituted with methylanthranilate (13), cyanoindolizine (6) and cyanoisoindole (11) moieties via an ethyl or propyl linker.     

Synthesis and opioid activity of N,N-dimethyl-Dmt-Tic-NH-CH(R)-R' analogues: acquisition of potent delta antagonism

N,N-Dimethylation of the H-Dmt-Tic-NH-CH(R)-R′ series of compounds produced no significant affect on the high δ-opioid receptor affinity (K_i=0.035–0.454 nM), but dramatically decreased that for the μ-opioid receptor. The effect of N-methylation was independent of the length of the linker (R); however, the bioactivities were affected by the chemical composition of the third aromatic group (R′): phenyl (Ph) (5′–8′) elicited a greater reduction in μ-affinity (40–70-fold) compared to analogues containing 1H-benzimidazole-2-yl (Bid) (9-fold). The major consequences of N,N-dimethylation on in vitro bioactivity were: (i) a loss of δ-agonism coupled with the appearance of potent δ antagonism (4′–7′) (pA₂=8.14–9.47), while 1 exhibited only a 160-fold decreased δ agonism (1′) and the δ antagonism of 8 enhanced >10-fold (pA₂=10.62, 8′); and (ii) a consistent loss of μ-affinity resulted in enhanced δ-opioid receptor selectivity. With the exception of compound 1′, the change in the hydrophobic environment at the N-terminus and formation of a tertiary amine by N,N-dimethylation in analogues of the Dmt-Tic pharmacophore produced potent δ-selective antagonists.     

Selective addressing of heteroditopic ligands by iron(II) and platinum(II)

The heteroditopic ligand 4′-(4,7,10-trioxadec-1-yn-10-yl)-2,2′:6′,2″-terpyridine, 2, contains an N,N′,N″-donor metal-binding domain that recognizes iron(II), and a terminal alkyne site that selectively couples to platinum(II). This selectivity has been used to investigate routes to the formation of heterometallic systems. The single crystal structures of ligand 2 and the complex [Fe(2)₂][PF₆]₂ are reported.     

Lipase catalysed synthesis of diacyl hydrazines: an indirect method for kinetic resolution of chiral acids

The acylation of hydrazine, to afford the N,N′-diacyl derivatives, was catalysed by a number of lipases. The rates of the first and second steps depended on the lipase and the type of solvent used. Water, up to 0.4 M, had no detrimental effect on the yield and complete conversion to the N,N′-diacyl derivative was accomplished with some lipases. The hydrazide of 2-(4-isobutylphenyl)propanoic acid (ibuprofen), prepared by non-enzymatic reaction of ibuprofen methyl ester with hydrazine, acted as a nucleophile towards several lipases that do not accept ibuprofen derivatives as the acyl donor, but the enantiomer differentiation was inefficient in most cases. The best result was obtained with Pseudomonas lipoprotein lipase on EP 100 which formed the (R) enantiomer of the product (N-octanoyl-N′-2-(4-isobutylphenyl)propanoylhydrazine) with an enantiomeric ratio E of 26.     

X-ray crystal structure of Cu2(medpco-2H)Cl2, (medpco = N,N′-bis(2-N,N-dimethylaminoethyl)pyridine-2,6-dicarboxamide 1-oxide. Copper(II) complexes of a deprotonated binucleating pyridine N-oxide ligand

The X-ray structure is reported for the complex Cu₂(medpco-2H)Cl₂, (medpco = N,N′-bis-N,N-dimethylaminoethyl)pyridine-2,6-dicarboxamide 1-oxide. The complex is triclinic, , a=8.313(4), B=11.403(5), C=11.611(3) Å, =91.66(3), β=108.99(4), γ=109.60(3)° and Z=2. The deprotonated ligand (medpco-2H)²⁻ acts as a binulceating ligand, producing an N-oxide-bridged complex. Each copper in Cu₂(medpco-2H)Cl₂ is five-coordinate, being coordinated by a bridging N-oxide oxygen, a deprotonated amide nitrogen, a tertiary amine nitrogen and two bridging chlorides. The complex does not exhibit significant magnetic interaction, and this may be the result of distortion of the bridging geometry from planarity. A range of other, apparently N-oxide-bridged, complexes of the type Cu₂(medpco-2H)X₂ is reported. The complex Cu₂(medpco-2H)Br₂·H₂O is strongly antiferromagnetic, with magnetic data closely fitting the expected binuclear structure.     

Redox state of the partially reduced cytochrome aa3-cyanide complex

The low-spin ferric cyanide complex of beef heart cytochrome aa₃ can be partially reduced by stoichiometric additions of ferrous cytochrome c or by similar additions of N,N,N′,N′-tetramethyl-p-phenylene diamine. In both cases the initial ratio of cytochrome c oxidized: cytochrome a reduced or Wurster's Blue: cytochrome a reduced approximates the value 2. It is concluded that the binding of a single HCN prevents the reduction of both cytochrome a₃ and its associated EPR-invisible Cu atom.     

H NMR study of the interaction of N,N′,N″-triacetyl chitotriose with Ac-AMP2, a sugar binding antimicrobial protein isolated from Amaranthus caudatus

The interaction between Ac-AMP2, a lectin-like small protein with antimicrobial and antifungal activity isolated from Amaranthus caudatus, and N,N′,N″-triacetyl chitotriose was studied using ¹H NMR spectroscopy. Changes in chemical shift and line width upon increasing concentration of N,N′,N″-triacetyl chitotriose to Ac-AMP2 solutions at pH 6.9 and 2.4 were used to determine the interaction site and the association constant K_a. The most pronounced shifts occur mainly in the C-terminal half of the sequence. They involve the aromatic residues Phe¹⁸, Tyr²⁰ and Tyr²⁷ together with their surrounding residues, as well as the N-terminal Val-Gly-Glu segment. Several NOEs between Ac-AMP2 and the N,N′,N″-triacetyl chitotriose resonances are reported.     

Studies of the cation complexing ability of crowns Part I. Synthesis, characterization and crystal structure of diazacrowns and their barium complexes

A number of N,N′-bis(4-substituted phenyl)-1,7-diaza-12-crown-4 and N,N′-bis(4-substituted phenyl)-1, 10-diaza-18-crown-6 (where the substituents are OCH₃, CH₃, H, Cl, respectively) have been prepared by cyclization reaction of a ditosylate with the appropriately substituted diol. These new macrocyclic ligands have been characterized by means of elemental analysis, IR, ¹H NMR and MS spectra. The crystal structures of N,N′-bis(4-chlorophenyl)-1,10-diaza-18-crown-6 (21) and its complex with barium thiocyanate Ba(SCN)₂ (22) have been determined by single crystal X-ray diffraction. The crystallographic data are as follows: 21: C₂₄H₃₂Cl₂N₂O₄, orthorhombic, P2₁2₁2₁, A=4.852(1), B=11.989(2), C=41.231(8) Å, V=2398.7(8) ų, Z=4; 22: C₂₆H₃₂Cl₂N₄O₄S₂Ba, monoclinic, P2₁/c, A=8.801(2), B=11.653(9), C=15.756(6) Å, ß=105.96(3)°, V=1553.7(14) ų, Z=2. In the complex, the Ba atom is eight-coordinate (O(1), O(2), O(1)′, O(2)′, N(1), N(1)′, N(21), N(21)′) to form a distorted D_6h geometry with the Ba atom at the center of crystallographic symmetry.     

Kinetics of ligand substitution in bis(N-alkylsalicylaldiminato)nickel(II) complexes: A search for kinetically-effective aromatic ring stacking

The square-planar bis chelate complexes Ni(R-sal)₂ (= bis(N-alkyl)salicylaldiminato)nickel(II)) with R = (CH₂)₂Ph (I; Ph = phenyl), (CH₂)₃Ph (II), (CH₂)₄Ph (III) and (CH₂)₂(4-hydroxyphenyl) (IV) were prepared and characterized. ComplexesII and III meet the steric requirements for intramolecular aromatic ring stacking. Stopped-flow spectrophotometry was used to study the kinetics of ligand substitution in complexesI–IV by H₂salen (=N,N′-disalicylidene-ethylenediamine) in acetone. For the substitution of the two bidentate ligands in Ni(R-sal)₂ only one step is kinetically observed which follows a second-order rate law, rate =k[H₂salen] [Ni(R-sal)₂], with k = 43.4 (I), 64.0 (II), 87.0 (III) and 49.5 (IV) M⁻¹ s⁻¹ at 298 K. It is found, therefore, that the size of k does not change significantly upon lengthening of the alkane chain in Ni(Ph(CH₂)_nsal)₂ from n = 2 to 4 and that there is no kinetic evidence for intramolecular stacking interactions. The equilibrium constants and thermodynamic parameters for the formation of the bis adductsIII·(py)₂ and III·(MeOH)₂ in acetone are reported.     

Design and properties of mixed metal multinuclear molecules: Part 1. Molecular structures of [Ag(PR3)2]2[Ni(mnt)2] type complexes (R=Me, Et, Cy and MNT=maleonitriledithiolate) and [AgL]2[Ni(mnt)2] type complexes with chelating diphosphines (L=dppf and dppm)

The trinuclear complexes [Ag(PR₃)₂]₂[Ni(mnt)₂] and [AgL]₂[Ni(mnt)₂] have been prepared by reactions of (NEt₄)₂[Ni(mnt)₂] and Ag₂SO₄ with alkyl phosphines (PR₃=P(CH₃)₃ (PMe₃) for 1, P(C₂H₅)₃ (PEt₃) for 2 and P(C₆H₁₁)₃ (PCy₃) for 3), or with chelating diphosphines (L=1,1′-bis(diphenylphosphino)ferrocene (dppf) for 4 and bis(diphenylphosphino)methane (dppm) for 5). The structures of all the complexes have been determined by X-ray crystallography. Interactions between the [Ag(PR₃)₂]⁺ and [Ni(mnt)₂]²⁻ groups occur in compounds 1 and 2 with Ni---Ag distances of 3.063(4) and 2.9311(6) Å, respectively. Only one sulfur atom of each mnt ligand bridged [Ag(PR₃)₂]⁺ cations and [Ni(mnt)₂]²⁻ anions in compound 1 through 3 with Ag---S distances of about 2.7 Å. There is no interaction between Ag and Ni in compound 3 due to the flexibility of the cyclohexyl groups. Interactions between [AgL]⁺ and [Ni(mnt)₂]²⁻ groups also occur in compound 4 with a much shorter Ag---Ni distance of 2.7213(7) Å, while silver atoms and the NiS₄ plane in compound 4 make a chair conformation with Ag---S distances of about 2.8 Å. In compound 5, dppm bridges two silver atoms, and interaction between silver atoms occurs at a distance of 2.9859(11) Å, and only one sulfur atom of mnt is used to bridge Ni and Ag atoms with Ag---S distances of 2.582(3) and 2.663(3) Å.     

Reactions of the haloalcohols HO(CH2)nCl (n = 2, 3) with platinum(II) - alkynyl and -alkyne complexes. X-ray crystal structure of trans-[Pt(Me) {C(OCH2CH2Cl) (CH2Ph)} (PPh3)2] [BF4]

The chloro complexes trans-[Pt(Me)(Cl)(PPh₃)₂], after treatment with AgBF₄, react with 1-alkynes HC---C---R in the presence of NEt₃ to afford the corresponding acetylide derivatives trans-[Pt(Me) (C---C---R) (PPh₃)₂] (R = p-tolyl (1), Ph (2), C(CH₃)₃ (3)). These complexes, with the exception of the t-butylacetylide complex, react with the chloroalcohols HO(CH₂)_nCl (n = 2, 3) in the presence of 1 equiv. of HBF₄ to afford the alkyl(chloroalkoxy)carbene complexes trans-[Pt(Me) {C[O(CH₂)_nCl](CH₂R) } (PPh₃)₂][BF₄] (R = p-tolyl, N = 2 (4), N = 3 (5); R=Ph, N = 2 (6)). A similar reaction of the bis(acetylide) complex trans-[Pt(C---C---Ph)₂(PMe₂Ph)₂] with 2 equiv. HBF₄ and 3-chloro-1-propanol affords trans-[Pt(C---CPh) {C(OCH₂CH₂CH₂Cl)(CH₂Ph) } (PMe₂Ph)₂][BF₄] (7). T alkyl(chloroalkoxy)-carbene complex trans-[Pt(Me) {C(OCH₂CH₂Cl)(CH₂Ph) } (PPh₃)₂][BF₄] (8) is formed by reaction of trans-[Pt(Me)(Cl)(PPh₃)₂], after treatment with AgBF₄ in HOCH₂CH₂Cl, with phenylacetylene in the presence of 1 equiv. of n-BuLi. The reaction of the dimer [Pt(Cl)(μ-Cl)(PMe₂Ph)]₂ with p-tolylacetylene and 3-chloro-1-propanol yields cis-[PtCl₂{C(OCH₂CH₂CH₂Cl)(CH₂C₆H₄-p-Me}(PMe₂Ph)] (9). The X-ray molecular structure of (8) has been determined. It crystallizes in the orthorhombic system, space group Pna2₁, with a = 11.785(2), B = 29.418(4), C = 15.409(3) Å, V = 4889(1) ų and Z = 4. The carbene ligand is perpendicular to the Pt(II) coordination plane; the PtC(carbene) bond distance is 2.01(1) Å and the short C(carbene)-O bond distance of 1.30(1) Å suggests extensive electronic delocalization within the Pt---C(carbene)---O moietry.     

A seven-coordinate manganese(II) complex formed with the single heptadentate ligand N,N,N′-tris(2-pyridylmethyl)-N′-(2-salicylideneethyl)ethane-1,2-diamine

The new disymmetric ligand N,N,N′-tris(2-pyridylmethyl)-N′-(2-salicylideneethyl)ethane-1,2-diamine (LH) has been synthesized in the search of a novel type of manganese complex to mimic the active site of the water-oxidizing enzyme in photosystem II. The complex [Mn(II)L]ClO₄ has been obtained and characterized by X-ray diffraction techniques. It crystallizes in the monoclinic space group Pn with the following unit cell parameters: a=10.164(3), b=10.122(4), c=14.166(5) Å, β=93.48(2)° and Z=2. The manganese ion is heptacoordinated with the coordination being achieved by only one ligand; it is bonded to the oxygen atom of the phenolate group in an axial position, the imino and the three pyridine nitrogen atoms in an equatorial position and the two amine atoms in a pseudo-axial position. The coordination polyhedron is best described as a distorted monocapped trigonal prism. This structure was compared with the seven-coordinated Mn(II) complexes deposited in the Cambridge Structured Database (CSD). The redox potential of the Mn(III)/Mn(II) couple was determined by cyclic voltammetry.     

One-dimensional polymeric chlorocadmate(II) systems of N-methylpiperazinium and N,N′-dimethylpiperazinium compounds: synthesis, structural and thermal properties

The chlorocadmate(II) systems of (H₂me₂pipz)[Cd₂Cl₆(H₂O)₂] (1) and (H₂mepipz)₂[Cd₃Cl₁₀(H₂O)] (2) (L = me₂pipz = N,N′-dimethylpiperazine; L′ = mepipz = N-methylpiperazine) were prepared and their structural and thermal properties investigated. Compound 1 is monoclinic, space group P2₁/c, A = 7.664(1), B = 7.472(4), C = 15.347(1) Å, β = 99.468(7)°, Z = 2, R = 0.024. The crystal structure consists of organic cations and infinite one-dimensional chains of [CdCl₃(H₂O)]_n³⁻ anions. Each Cd atom is octahedrally surrounded by bridged and terminal chlorine atoms and by a water molecule, which is in trans position with respect to the terminal chlorine atom. Inter- and intrachain hydrogen bond interactions between the terminal chlorine atoms and the water molecules contribute to the crystal packing. Compound 2 is orthorhombic, space group Cmc2₁, A = 15.286(3), B = 13.354(3), C = 13.154(3) Å, R = 0.023. The crystal structure consists of organic dications and infinite chains of [Cd₂Cl₆(CdCl₄H₂O]_n⁴⁻ units running along the [001] axis. Each unit is formed of regularly alternate six-coordinated Cd atoms, one of them linking one pentacoordinated Cd atom which completes its coordination througha water molecule. A strong hydrogen bond interaction involving the organic dication and the inorganic chain contributes to the crystal packing. Differential hydrogen bond interaction involving the organic dication and the inorganic chain contributes to the crystal packing. Differential scanning calorimetry measurements did not show the presence of any structural phase transitions. The structures are compared with those of (H₂pipz)[Cd₂Cl₆(H₂O)₂] (3), (H₂mepipz)[Cd₂Cl₆(H₂O)₂]·H₂O (4) and (H₂mepipz)[Cd₂Cl₆] (5) (L = pipz = piperazine, L′ = mepipz = N-ethylpiperazine).     

Synthesis, magnetism and crystal structure of [V2O2(μ-OH)2(tpen)]I2·4H2O; a binuclear complex containing the syn-{VO(μ-OH)2VO} core (tpen = tetrakis(2-pyridylmethyl)ethylenediamine)

The reaction of N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine (tpen) with VCl₃ in CH₃CN yields Cl₃V(tpen)VCl₃ which was hydrolyzed in water in the presence of oxygen affording [V₂O₂(μ-OH)₂(tpen)]I₂·2H₂O, the crystal structure of which has been determined. Asyn-{OV(μ-OH)₂VO}²⁺ core has been identified where the V(IV) centers are antiferromagnetically coupled (J = −150 cm⁻¹;g = 1.80).     

Conformational characterization of square planar nickel(II) tetraaza macrocyclic complexes by proton NMR. Crystal structure of [Ni(13aneN4)]ZnCl4

Conformations in solution of several diamagnetic nickel(II) complexes of macrocyclic tetraaza ligands are elucidated using proton NMR. There are six possible configurational isomers of planar [Ni(13aneN₄)]²⁺ (13aneN₄ = 1,4,7,10-tetraazacyclotridecane due to the orientation of the N---H protons above or below the plane of the macrocyle. Using NMR it is shown that in aqueous solution the [Ni(13aneN₄)]²⁺ complex has the R,S,R,S or trans-II configuration. A single-crystal X-ray study demonstrates the same configuration of the nitrogen atoms in the complex [Ni(13aneN₄)]ZnCl₄. In the case of the 14-membered ring macrocyle cyclam (cyclam = 1,4,8,11-tetraazacyclotetradecane), previous NMR studies revealed the presence, in aqueous solution, of the previously unobserved trans-I or R,S,R,S isomer, whose spectrum is examined in greater detail here. Solution structures of nickel(II) complexes of bicyclam (1,5,8,12-tetraazabicyclo[10.2.2]hexadecane) and dachden (N, N′-bis(2-aminoethyl)-1,4-diazacycloheptane) are also reported.     

Syntheses and structures of palladium(II) and platinum(II) complexes with tridentate (Ph2PCH2CH2CH2)2S and its arsenic analogue

A series of square-planar complexes [MLCl]ClO₄ (M = Pd(II), Pt(II); L = bis(3-(diphenylphosphino)propyl)sulfide (psp), bis(3-(diphenylarsino)propyl)sulfide (asa)) have been prepared and characterized. The X-ray crystal structures of two of them have been determined: [Pd(psp)Cl]ClO₄, P2₁/c, A = 12.519(2), B = 15.766(2), C = 16.501(2) Å, β = 105.22(1)°, Z = 4; and [Pt(asa)Cl]ClO₄, P2₁/c, a = 12.583(5), B = 16.007(6), C = 16.549(6) Å, β = 104.89(3)°, Z = 4. In both structures, there is a conformational disorder between the chair and skew-boat orientation in one of the two six-membered chelate rings. The C---H…O hydrogen bond between the hybrid ligand and the perchlorate counter ion that induces the conformational disorder is discussed.     

Ligand connected metal clusters. The molecular structures and solid state packing of {Ru3(CO)11}2(bis(diphenylphosphino)ethane) and {Ru3(CO)11}2(1,4-bis(diphenylphosphino)benzene)

The preparation and structural characterization of {Ru₃(CO)₁₁}₂(1,4-bis(diphenylphosphino)benzene), a modified synthesis of 1,4-bis(diphenylphosphino)benzene, and the structural characterization of {Ru₃(CO)₁₁}₂(bis(diphenylphosphino)ethane) are reported. In both compounds two metal cluster units are connected through ditertiary-phosphine ligands. Both molecules consist of centrosymmetric units in which the diphosphine ligands are largely covered by the triangular ruthenium clusters. No direct interaction between the two cluster units occurs within individual molecules. Molecular packing in the solid state is dominated by interactions between sets of carbon monoxide ligands in motifs that were previously identified in the solid state structure of the parent cluster, Ru₃(CO)₁₂.     

Alkene rotation in [Ru(η-C5H5) (L2) (η-alkene][CF3SO3] with L2 = iPr- or pTol-diazabutadiene. X-ray crystal structure of [Ru(η-C5H5(pTol-DAB) (η-ethene][CF3SO3]

Reaction of RuCl(η⁵-C₅H₅(pTol-DAB) with AgOTf (OTf = CF₃SO₃) in CH₂Cl₂ or THF and subsequent addition of L′ (L′ = ethene (a), dimethyl fumarate (b), fumaronitrile (c) or CO (d) led to the ionic complexes [Ru(η⁵-C₅H₅)(pTol-DAB)(L′)][OTf] 2a, 2b and 2d and [Ru(η⁵-C₅H₅)(pTol-DAB)(fumarontrile-N)][OTf] 5c. With the use of resonance Raman spectroscopy, the intense absorption bands of the complexes have been assigned to MLCT transitions to the iPr-DAB ligand. The X-ray structure determination of [Ru(η⁵-C₅H₅)(pTol-DAB)(η²-ethene)][CF₃SO₃] (2a) has been carried out. Crystal data for 2a: monoclinic, space group P2₁/n with A = 10.840(1), b = 16.639(1), C = 14.463(2) Å, β = 109.6(1)°, V = 2465.6(5) ų, Z = 4. Complex 2a has a piano stool structure, with the Cp ring η⁵-bonded, the pTol-DAB ligand σN, σN′ bonded (Ru-N distances 2.052(4) and 2.055(4) Å), and the ethene η²-bonded to the ruthenium center (Ru-C distances 2.217(9) and 2.206(8) Å). The C = C bond of the ethene is almost coplanar with the plane of the Cp ring, and the angle between the plane of the Cp ring and the double of the ethene is 1.8(0.2)°. The reaction of [RuCl(η⁵-C₅H₅)(PPh)₃ with AgOTf and ligands L′ = a and d led to [Ru(η⁵-C₅H₅)(PPh₃)₂(L′)]OTf] (3a) and (3d), respectively. By variable temperature NMR spectroscopy the rottional barrier of ethene (a), dimethyl fumarate (b and fumaronitrile (c) in complexes [Ru(η⁵-C₅H₅)(L₂)(η²-alkene][OTf] with L₂ = iPr-DAB (a, 1b, 1c), pTol-DAB (2a, 2b) and L = PPh₃ (3a) was determined. For 1a, 1b and 2b the barrier is 41.5±0.5, 62±1 and 59±1 kJ mol⁻¹, respectively. The intermediate exchange could not be reached for 1c, and the ΔG^# was estimated to be at least 61 kJ mol⁻. For 2a and 3a the slow exchange could not be reached. The rotational barrier for 2a was estimated to be 40 kJ mol⁻. The rotational barier for methyl propiolate (HC≡CC(O)OCH₃) (k) in complex [Ru(η⁵-C₅H₅)(iPr-DAB) η²-HC≡CC(O)OCH₃)][OTf] (1k) is 45.3±0.2 kJ mol⁻¹. The collected data show that the barrier of rotational of the alkene in complexes 1a, 2a, 1b, 2b and 1c does not correlate with the strength of the metal-alkene interaction in the ground state.