Calorimetric investigation of the reaction of 1,5-cyclooctadiene with complexes of the type (acac)M(olefin)2 [M = Rh(I), Ir(I)]

The enthalpies of reaction of the complexes (acac)M(olefin)₂ (acac=acetyl-acetonate, M=Rh(I), Ir(I); olefin=ethylene, propene, vinyl chloride, vinyl acetate, methyl acrylate and styrene) with 1,5-cyclooctadiene in n-heptane, according to the reaction [(acac)M(olefin)₂ + 1,5COD → (acac)M(1,5COD) + 2 olefin]_n.heptane have been determined by solution calorimetry. From these results the influence of substituent R in the olefin CH₂CHR on the M---(CH₂CHR) displacement enthalpy has been derived. It is concluded that π back-bonding is slightly more important in the Ir---olefin bond than in the Rh---olefin bond. Furthermore, the data show that, as a result of steric factors which inhibit the approach of solvent molecules, solvation enthalpies are not additive.     

Complexes de l'iridium avec le cyclooctadiène-1,5 IV. Le di-υ-chloro-bis(π-cylooctadiène-1,5)-bis(π-ether diallylique)-diiridium

Di-μ-chlorobis(π-cycloocta-1,5-diene)diiridium, (I), reacts with allyl alcohol to give a complex, (II), of (I) and diallyl ether and byproducts: propene, propanal and diallyl ether. The same complex is readily obtained by direct reaction of (I) and diallyl ether. Some physicochemical properties (II) are described (IR spectra, stability, reactivity, etc.). Its structure is discussed, and a mechanism for the transformation of allyl alcohol during the reaction is given.     

Synthesis of 2,3-disubstituted benzofurans by platinum-olefin-catalyzed carboalkoxylation of o-alkynylphenyl acetals

The PtCl2-catalyzed cyclization reaction of o-alkynylphenyl acetals 1 in the presence of 1,5-cyclooctadiene produces 3-(alpha-alkoxyalkyl)benzofurans 2 in good to high yields. For example, the reaction of acetaldehyde ethyl 2-(1-octynyl)phenyl acetal (1a), acetaldehyde ethyl 2-(cyclohexylethynyl)phenyl acetal (1c), and acetaldehyde ethyl 2-(phenylethynyl)phenyl acetal (1f) in the presence of 2 mol % of platinum(II) chloride and 8 mol % of 1,5-cyclooctadiene in toluene at 30 degrees C gave the corresponding 2,3-disubstituted benzofurans 2a, 2c, and 2f in 91, 94, and 88% yields, respectively.     

Structural characterization of cyclopentadienyl(duroquinone)cobalt dihydrate

The structure of cyclopentadienyl(duroquinone)cobalt dihydrate, (C₅H₅)Co-[(CH₃)₄C₆O₂]·2H₂O, has been determined by three-dimensional X-ray analysis. The crystal structure consists of discrete cyclopentadienyl(duroquinone)cobalt molecules linked together by a complex network of hydrogen bonds between water molecules and duroquinone oxygen atoms. Each (C₅H₅)Co[(CH₃)₄C₆O₂] molecule consists of a cobalt atom sandwiched between a cyclopentadienyl ring and a duroquinone ring. A detailed comparison of the molecular parameters of this complex with those of closely related complexes is given. Crystallographic evidence that the metal---duroquinone interaction in cyclopentadienyl(duroquinone)cobalt dihydrate is considerably stronger than that in the electronically-equivalent 1,5-cyclooctadiene(duroquinone)nickel complex is given not only by the metal---C(olefin) distances being 0.12 Å (av) shorter in the duroquinone---cobalt complex [viz., 2.104(8) Å vs. 2.222(7) Å] but also by the much greater C_2v-type distortion of the duroquinone ring from the planar D_2h configuration in free duroquinone. The compound crystallizes with two formula species in a triclinic unit cell of symmetry P and reduced cell dimensions á = 8.60 Å, b = 9.00 Å, c = 10.15 Å, = 87° 34′, β = 84° 10′, γ = 73° 44′. Least-squares refinement yielded final unweighted and weighted discrepancy factors of R₁ = 10.8% and R₂ = 12.0%, respectively, for 2481 independent diffraction maxima collected photographically.     

Potentiometric study of chloro complexes of some divalent transition metal cations in dimethyl sulphoxide at 25°C

Formation of the chloro complexes of manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II) in DMSO has been studied potentiometrically at 25°C. The con- centration stability constants for the ionic strength of 0.1 mol kg are derived and discussed. The stability of the divalent transition metal cations towards the chloride anion follows the sequence Mn &> Co &> Ni << Cu &> Zn disobeying the Irving-Williams series.     

Kinetic analyses of biomass tar pyrolysis using the distributed activation energy model by TG/DTA technique

Volatile compounds of iridium(I): (acetylacetonato)(1,5-cyclooctadiene)iridium(I) Ir(acac)(cod), (methylcyclopentadienyl) (1,5-cyclooctadiene)iridium(I) Ir(Cp’)(cod), (pentamethylcyclopentadienyl)(dicarbonyl) iridium(I) Ir(Cp*)(CO)₂ and (acetylacetonato)(dicarbonyl)iridium(I) Ir(acac)(CO)₂ were synthesized and identified by means of element analysis, NMR-spectroscopy, mass spectrometry. Thermal properties in solid phase for synthesized iridium(I) complexes were studied by means of thermogravimetric analysis in inert atmosphere (He). By effusion Knudsen method with mass spectrometric registration of gas phase composition the temperature dependencies of saturated vapor pressure were measured for iridium(I) compounds and the thermodynamic characteristics of vaporization processes enthalpy ΔH _T* and entropy ΔS _T⁰ were determined. The energy of intermolecular interaction in the crystals of complexes was calculated.     

Ligand migrations during the formation of some palladium-rhodium heterodinuclear complexes

A new Pd(I)-Rh(II) heterodinuclear complex, trans-(NC)₂---(CH₃0)₃PRh(μ-dppm)₂PdC1 (2a), was prepared by treatment of [(cod)RhCI]₂ with (CH₃0)₃P and trans-(NC)₂Pd(dppm)₂ (1) (dppm = bis(diphenylphosphino)methane, COD = 1,5-cyclooctadiene) and characterized by ³¹P NMR spectroscopy and single-crystal X-ray structure determination. The single crystal of complex 2a is triclinic; its space group

Full-size image

, = 94.43(3), β = 106.55(3), γ = 87.86(3)°. The Rh---Pd bond distance is 2.7835(5) Å. The molecular structure of this complex suggests that its formation reaction includes: (i) ligand migrations of the Cl⁻ from the Rh center to the Pd center and the two CN⁻ groups from the Pd center to Rh center; (ii) the intermetallic one-electron transfer indicated by the alteration from Rh(I) and Pd(II) to Rh(1I) and Pd(I) respectively; (iii) the Pd(I)---Rh(II) bond formation by pairing one electron from Rh(II) with one electron from Pd(I). The differences of chemical shifts of the phosphorus atoms coordinated to the Pd center in the Pd---Ag complexes and the Pd---Rh complexes are discussed.     

Synthesis and Characterization of a Bis(&mgr;-beta-diketonato)bis((1,2,5,6-eta)-1,5-dimethyl-1,5- cyclooctadiene)disilver Complex. An Intermediate in the Synthesis of an Isomerically Pure (beta-Diketonato)((1,2,5,6-eta)-1,5-dimethyl-1,5-cyclooctadiene)copper(I) Complex

Dimethyl-1,5-cyclooctadiene (DMCOD) is synthesized by the Ni-catalyzed dimerization of isoprene and consists of 80% 1,5-dimethyl-1,5-cyclooctadiene (1,5-DMCOD) and 20% 1,6-dimethyl-1,5-cyclooctadiene (1,6-DMCOD). Reaction of Hhfac (1,1,1,5,5,5-hexafluoro-2,4-pentanedione) with Ag(2)O in the presence of DMCOD results in the formation of isomeric Ag(I) species. Repeated recrystallizations yield an isomerically pure compound ((1,5-DMCOD)Ag(hfac))(2) that was characterized by X-ray crystallography and (1)H and (13)C NMR and IR spectroscopy. X-ray crystallography revealed a dinuclear complex with a short Ag-Ag spacing (3.0134(3) ? at -150 degrees C and 3.0278(5) ? at -20 degrees C) and bridging hfac ligands (&mgr;(2) bonding). The overall geometry around the Ag atoms is a deformed tetrahedron with two short Ag-O bonds (2.375 ? average) and two Ag-diene bonds. The methyl groups of the 1,5-DMCOD ligand are pointed toward the center of the molecule. Decomposition of the silver complex in a biphasic HCl (1 M)/CH(2)Cl(2) mixture liberates isomerially pure 1,5-DMCOD; this diene is subsequently used to synthesize isomerically pure (1,5-DMCOD)Cu(hfac). The latter compound was characterized by (1)H and (13)C NMR and IR spectroscopy and is a useful liquid precursor for Cu CVD. Crystallographic data: C(30)H(34)Ag(2)F(12)O(4), monoclinic, P2(1)/c (No. 14), Z = 4; at -150 degrees C, a = 12.428(1) ?, b = 11.071(1) ?, c = 24.520(2) ?, beta = 101.98(1) degrees; at -20 degrees C, a = 12.597(1) ?, b = 11.191(1) ?, c = 24.641(2) ?, beta = 102.08(1) degrees.     

Rhodium and iridium complexes of N-heterocyclic carbenes: Structural investigations and their catalytic properties in the borylation reaction

Bridged and unbridged N-heterocyclic carbene (NHC) ligands are metalated with [Ir/Rh(COD)₂Cl]₂ to give rhodium(I/III) and iridium(I) mono- and biscarbene substituted complexes. All complexes were characterized by spectroscopy, in addition [Ir(COD)(NHC)₂][Cl,I] [COD = 1,5-cyclooctadiene, NHC =  1,3-dimethyl- or 1,3-dicyclohexylimidazolin-2-ylidene] (1, 4), and the biscarbene chelate complexes 12 [(η⁴-1,5-cyclooctadiene)(1,1′-di-n-butyl-3,3′-ethylene-diimidazolin-2,2′-diylidene)iridium(I) bromide] and 14 [(η⁴-1,5-cyclooctadiene)(1,1′-dimethyl-3,3′-o-xylylene-diimidazolin-2,2′-diylidene)iridium(I) bromide] were characterized by single crystal X-ray analysis. The relative σ-donor/π-acceptor qualities of various NHC ligands were examined and classified in monosubstituted NHC-Rh and NHC-Ir dicarbonyl complexes by means of IR spectroscopy. For the first time, bis(carbene) substituted iridium complexes were used as catalysts in the synthesis of arylboronic acids starting from pinacolborane and arene derivatives.     

Electrocatalytic reactions in organized assemblies: Part III. Reduction of allyl halides by bipyridyl derivatives of cobalt in anionic and cationic micelles

Reduction of allyl halides to 1,5-hexadiene at glassy carbon electrodes was catalyzed by tris(2,2'-bipyridyl) cobalt(II) and tris(4,4'-dimethyl-2,2'-bipyridyl)cobalt(II) in aqueous solutions of 0.1 M SDS or 0.1 M CTAB. An organocobalt(I) intermediate was observed by its separate voltammetric reduction peak in each system studied. This intermediate undergoes an internal redox reaction to form 1,5-hexadiene and Co(II). Small micellar enhancements of reaction rates found for tris(2,2'-bipyridyl) cobalt(II) in 0.1 M CTAB can be attributed to reactant compartmentalization in the micelles. Observed chemical rates followed the order CTAB > SDS = acetonitrile. For tris(4,4'-dimethyl-2,2'-bi-pyridyl) Co(II) in CTAB, catalysis was limited by adsorption of the Co(I) form at the electrode. Preliminary work with bis(2,2'-bipyridyl)-(4,4'-dihexadecyl-2,2'-bipyridyl)cobalt(II) showed that its catalytic utility in 0.1 M SDS was equivalent to that of the most efficient system studied, i.e. tris(2,2'-bipyridyl)Co(II) in 0.1 M CTAB.     

Synthesis and utilization of alternative chain transfer agent in cobalt catalyzed 1,3-butadiene polymerization reaction to produce cis-polybutadiene rubber

The cyclodimerization of 1,3-butadiene was performed to synthesize 1,5-cyclooctadiene by using nickel-phosphite based catalyst system. The optimization of cyclodimerization reaction was done to achieve up to 80% selectivity towards 1,5-cyclooctadiene. 1,5-Cyclooctadiene, thus synthesized, was subsequently employed as a chain transfer agent (CTA) for controlling the molecular weight (M.W.) of cis-polybutadiene rubber (BR) in cobalt-complex catalyzed 1,3-butadiene polymerization reaction. The M.W. of BR was reduced from 6.7 to 1.88 × 10⁵ g/mol by escalating the concentration of 1,5-cyclooctadiene from 0% to 0.5% with respect to 1,3-butadiene (monomer) concentration. Similar reducing trend was observed for the Mooney viscosity and gel content of BR with increasing 1,5-cyclooctadiene concentration. The efficacy of 1,5-cyclooctadiene as a CTA for 1,3-butadiene polymerization reaction was further explored by conducting polymerization reaction in various solvents and at higher monomer conversion (∼70%). The effect of 4-vinyl cyclohexene, which was a dominant byproduct during cyclodimerization of 1,3-butadiene, was also investigated. The presence of 4-vinyl cyclohexene has shown adverse effect in the polymerization reaction and was not functioning as a chain transfer agent. Finally, a feasibility of replacement of commercially used gaseous CTA, 1,2-butadiene, by in-house synthesized liquid CTA, 1,5-cyclooctadiene, was also investigated.     

The dependence of photoinduced energy transfer on the orientation of the acceptor with respect to the π-plane of the donor in naphthalene-linked crown ether–Tb complexes

The photoinduced energy transfer (ET) from naphthalene (N) to Tb³⁺ has been studied in the complexes of Tb³⁺ ion with 2,3-naphtho-17-crown-5 ether(I), 2,3-naphtho-20-crown-6 ether(II), 1,8-naphtho-21-crown-6 ether(III) and 1,5-naphtho-22-crown-6 ether(IV), respectively, using nitrate (NO₃⁻) ion as the counter anion in EtOH glass at 77 K. The ligands are so designed that the Tb³⁺ ion can be complexed with a predetermined orientation with respect to the naphthalene molecular plane. In systems I and II, the Tb³⁺ ion is along the Z-axis; in system III, it is along the Y-axis and in IV, it is along the X-axis, where Z- and Y- are the molecular in-plane long and short axes of the naphthalene molecular plane respectively and X- is the out-of plane axis perpendicular to the naphthalene molecular plane. Present studies indicate that the efficiency of energy transfer (ET) and the quenching of naphthalene phosphorescence show a strong dependence on the orientation of the acceptor metal ion (Tb³⁺) with respect to the π-plane of the donor naphthalene moiety. The ET studies suggest that an exchange mechanism involving the lowest (ππ^*) triplet state of N and the ⁵D₄ state of Tb³⁺ ion is predominantly operating. Our observation further indicates that for a given orientation in a complex the emission intensity of the various transitions (⁵D₄ → ⁷F_J, J=2–6) for Tb³⁺, vis-a-vis ET efficiency varies considerably with ΔJ values (=0, +1 and +2).     

Enantioselective hydrogen transfer reactions from propan-2-ol to ketones catalyzed by pentacoordinate iridium(I) complexes with chiral Schiff bases

Some diastereoisomeric pentacoordinate complexes of the type [Ir(COD)-(NNR)I] (COD = cis,cis-1,5-cyclooctadiene; NNR = 2-pyridinal-1-phenylethylimine (PPEI) (I), 2-acetylpyridine-1-phenylethylimine (APPEI) (II)) have been synthesized. The complexes are active and selective catalysts for asymmetric hydrogen transfer from propan-2-ol to prochiral ketones. Optical yields of up to 84% have been obtained in the reduction of t-butyl phenyl ketone. The structure and absolute configuration of complexes I and II were determined by X-ray diffraction.     

Competition between π–π stacking and hydrogen bonding in (1:2) picrates of 1,5-diamino-3-oxapentane, 1,8-diamino-3,6-dioxaoctane and 1,5-diamino-3-azapentane—solid state studies

Crystallographic studies of (2:1) salts of picric acid with 1,5-diamino-3-oxapentane (1OPICR), 1,8-diamino-3,6-dioxaoctane (2OPICR) and 1,5-diamino-3-azapentane (1NPICR) showed significant conformational change of the picrate ion due to numerous electrostatic, H-bonding and π–π stacking interactions present in the crystal lattice. In particular, intermolecular N–HO H-bonds were found to cause significant twisting of the o-NO₂ groups from the plane of the benzene ring, whereas overlapping of the picrate ions due to electrostatic interactions and π–π stacking caused flattening of the molecule. Analysis of the geometry of 74 picrate ions found in the Cambridge Crystallographic Database, in their various crystallochemical environments, showed that competition between essentially weak but numerous intermolecular interactions of different types led to systematic changes in geometric parameters within the picrate ion. In particular, relations found between the C1–C2–N–O (C1–C6–N–O) torsion angle and the endocyclic C1–C2–C3 (C1–C6–C5) valence angle can be explained on the basis of competition between resonance effects of the o-NO₂ group and π–π stacking.     

Zur reaktivität komplexgebundener carbocyclen: XV. Neue wege zu indenyl-diolefen-komplexen von cobalt und rhodium

The formation of (indenyl)rhodium(diolefin) complexes is described, using bis(indenyl) magnesium. On protonation of these complexes an η⁵-η⁶ shift of the indenyl ligand is observed. The corresponding cobalt complexes are obtained by lithium reduction of bis(indenyl)cobalt in the presence of the diolefin. The bidentate ligand 1,5-cyclooctadiene is readily replaced in these complexes by carbon monoxide. All compounds were characterised by ¹³C NMR spectroscopy.     

Evidence for a reactive (alkene)peroxoiridium(III) intermediate in the oxidation of an alkene complex with O2

An (alkene)peroxoiridium(III) complex, [Ir(L)(cod)(O(2))] [where LH = PhN=C(NMe(2))NHPh and cod = 1,5-cyclooctadiene], was identified as an intermediate in the reaction of the Ir(I) precursor [Ir(L)(cod)] with O(2) and characterized by spectroscopic methods. Decay of the intermediate and further reaction with 1,5-cyclooctadiene produced 4-cycloocten-1-one.     

Cyclic homo- and cooligomerization of 2-cyclopropylbutadiene with 1,3-dienes

Conclusions We were the first to study the cyclic homo- and cooligomerization of 2-cyclopropyl-1,3-butadiene with butadiene and isoprene in the presence of catalysts based on nickel. The conditions were found for obtaining 1,5-dicyclopropyl-1,5-cyclooctadiene, 1-cyclopropyl-1,5-cyclooctadiene, 1-cyclopropyl-5-methyl-1,5-cyclooctadiene, and 1-cyclopropyl-5,9 (8)-dimethyl-1,5,9-cyclododecatriene.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2634–2636, November, 1979.     

The actual mercurating species in the mercuration of aromatic amines and the aminomercuration of olefins

The reactivity of π- and σ- N-mercurated and C-mercurated amines as electrophiles towards olefins and aromatic amines is studied under different reaction conditions. Depending on the ionic or covalent character of the starting mercury(II) salt, dissociated species or π-complexes 3 respectively, are found to be the most plausible mercurating species in the aminomercuration process. By contrast, complexes 3' do not react with aromatic amines unless the former undergo prior dissociation.     

Mechanistic implications of an asymmetric intermediate in catalytic C-C coupling by a dinuclear nickel complex

An asymmetric nickel-nickel bonded intermediate was isolated in the reaction of biphenylene with bis(1,5-cyclooctadiene)nickel and i-Pr(3)P, where three of the four carbons are σ-bonded to one nickel. Mechanistic investigations support reactivity as a formal Ni(III)-Ni(I) complex; reductive elimination of cis-disposed Ni-C bonds from a single nickel centre directly provides a dinuclear Ni(I)-Ni(I) complex, a reaction relevant to dinuclear catalysis.     

Direct in situ synthesis of cationic N-heterocyclic carbene iridium and rhodium complexes from neat ionic liquid: Application in catalytic dehydrogenation of cyclooctadiene

A direct synthetic route to cationic N-heterocyclic carbene (NHC) complexes of rhodium and iridium from neat dialkyl-imidazolium ionic liquids (ILs) has been found. The method uses complexes bearing basic anionic ligands, [M(COD)(PPh₃)X], X = OEt, MeCO₂, which react with the inactivated imidazolium cation in the absence of external bases yielding one M-NHC moiety and the free protonated base. This new one-pot synthesis leaving pure, catalytically active IL solutions is faster, cleaner and more efficient than traditional syntheses of such NHC complexes. The observed reactivity also gives insight into NHC incorporation of rhodium and iridium catalyzed reactions performed in common dialkyl-imidazolium ILs.The complexes synthesised in this manner are compared with their bis-phosphine analogues in terms of activity for catalytic dehydrogenation of 1,5-cyclooctadiene and 1,3-cyclooctadiene in neat [BMIM][NTf₂] as solvent. Even at high temperature, no ligand exchange reaction is observed with [(COD)M(PPh₃)₂] [NTf₂] catalysts. As expected, the yields of all the reactions were low, iridium was much more active in C-H activation than rhodium and the NHC ligands were more stable than triphenylphosphine. For all catalysts, the isomerisation of 1,5-cyclooctadiene is the major reaction. However, the phosphine-NHC complex of iridium seems to be more selective for dehydrogenation than its bis-phosphine counterpart, which is more active in transfer-hydrogenation and less stable under the applied conditions. Different reaction conditions were tried in order to optimise selectivity for dehydrogenation over isomerisation and transfer-hydrogenation. Surprisingly, with 1,3-cyclooctadiene as substrate selectivity for dehydrogenation is much higher than with 1,5-cyclooctadiene for all catalysts.