Complexes In CH2Cl2 Research Articles

Electron-Transfer Properties of Cp*FeP5: Evidence for Dimerization Reactions following both Oxidation and Reduction

The redox reactions of Cp*Fe(η5-P5) (1; Cp* = η5-C5Me5) have been characterized in nonaqueous solvents by electrochemical methods. As anticipated by analogy with ferrocene, 1 may be both oxidized and reduced in one-electron processes. Both processes are irreversible by cyclic voltammetry but reversible by bulk electrolysis. In CH2Cl2 complex 1 oxidizes initially to 17-electron 1+ (Ep,a = 0.57 V vs Fc), which rapidly equilibrates to give the dimeric dication [12]2+. An ESR spectrum attributed to 1+ is consistent with a d5 iron sandwich complex. A dimerization rate constant for 1+ of kD(17) = 1.4 × 104 M-1 s-1 was determined from cyclic voltammetry (CV) data. The dimeric dication quantitatively re-forms neutral 1 upon rereduction. Complex 1 undergoes reduction (E1/2 = −2.00 V) to 19-electron 1-, which also appears to dimerize in THF; kD(19) = ca. 6 × 105 M-1 s-1. Reoxidation of the diamagnetic dimer [12]2- regenerates 1. The shifts in potential induced when replacing a cyclopentadienyl ring by a pentaphosphacyclopentadienyl ring, explicable in terms of the weaker electron-donating ability of the latter, are greater for the reductions than the oxidations, implying an increased P5 character to the LUMO of 1 compared to the HOMO. Possible structures of the dimeric ions are discussed in terms of known structural analogues and previously published molecular orbital descriptions.

Cu(I)-Binaphthyldiimine Catalyzed Asymmetric Cyclopropanation of Olefin with Diazoacetate

Chiral 1,1′-binaphthyl-N,N′-bis(2,6-dichloro-benzy-lidene)-2,2′-diamine (1) was found to be an effective ligand for the copper-catalyzed enantioselective cyclopropanation of olefin with l-menthyl diazoacetate. For example, the reaction of 1,1-diphenylethylene with l-menthyl diazoacetate in the presence of CuOTf-1 complex in CH2Cl2 at -40 °C gave the corresponding cyclopropanecarboxylate in 98% ee.

Electron-transfer chain catalysis for the cis-to-trans isomeric conversion of cis-[ReCl(CO)(Ph2PCH2CH2PPh2)2

The low temperature reaction of cis-[ReCl(NCC6H4Cl-4)(dppe)2] (dppe = Ph2PCH2CH2PPh2) with CO afforded cis-[ReCl(CO)(dppe)2] whose 31P-{1H} NMR spectrum has been analysed as an ABCD spin system. The latter complex in CH2Cl2 slowly converts into the corresponding trans isomer (which is oxidised at a higher oxidation potential and whose single crystal X-ray diffraction analysis is also reported) and this isomerisation is promoted by oxidation following an electron-transfer chain (ETC) catalytic process, with low net current flow. This behaviour has been investigated by digital simulation of the cyclic voltammograms at different temperatures and scan rates, which allowed an estimate of the rate constant and the activation parameters for the isomerisation. The relative values of the oxidation potential of the cis and trans isomers are interpreted on the basis of a metal dπ orbital splitting model, the ratio of the isomerisation equilibrium constants (for the pairs of oxidised and parent species) is estimated and the relevance of kinetic factors in the anodically induced isomerisation (which is favoured by the π-electron acceptance ability of the CO ligand) is shown.

Hydrogen-Bonded Complexes of Aromatic Crown Ethers with (9-Anthracenyl)methylammonium Derivatives. Supramolecular Photochemistry and Photophysics. pH-Controllable Supramolecular Switching

The (9-anthracenyl)methylammonium and (9-anthracenyl)benzylammonium tetrakis(hexafluorophosphate) salts give hydrogen-bonded complexes in CH2Cl2 with aromatic crown ethers containing dibenzo (DB) o...

Structure and Reactivity of (η-C5R5)Mo(NO)2−Halide, −Halomethyl, and −Alkyl Complexes: Consecutive Aerobic Methylene and Nitrosyl Ligand Oxidation

Cp‘Mo(NO)2(CH2X) complexes are isolated in 80−90% yield after the treatment of the Cp‘Mo(NO)2X complexes in CH2Cl2 with ethereal diazomethane in the presence of Cu powder (Cp‘ = η-C5H5 (Cp), η-C5(CH3)5 (Cp*); X = Cl, Br). The Cp‘Mo(NO)2(CH2I) derivatives are obtained in over 90% yield by treating the Cp‘Mo(NO)2(CH2Cl) derivatives with NaI in THF. Four new halomethyl complexes have been characterized by X-ray crystallography and are compared to the related CpMo(NO)2Br, Cp*Mo(NO)2Cl, and Cp*Mo(NO)2(CH3) derivatives. The structural data and IR data indicate the donor properties of the halomethyl ligands to be intermediate between halide and alkyl ligands. The Cp‘Mo(NO)2(CH2X) complexes react initially with O2 to give CH2O and the regeneration of the parent Cp‘Mo(NO)2X complexes. The Cp‘Mo(NO)2Cl complexes react with O2 after an induction period to give the well-known Cp‘MoO2Cl complexes, NO2, NOCl, and N2O. Exposure of CpCr(NO)2(CH(CH3)Br) to 18O2 gives 18OCH(CH3) and 16O-labeled CpCr(NO)2Br. The Cp‘Mo(NO)2−alkyl complexes react with O2 to give the corresponding Cp‘MoO2−alkyl derivatives in 40−70% yield (alkyl = CH3, CH2CH3). Electrochemical data show the Mo complexes to oxidize at 0.2−0.3 V lower than the Cr congeners.

One-Electron Oxidation of Metalloporphycenes As Studied by Radiolytic Methods

One-electron and two-electron oxidations of 2,7,12,17-tetrapropylporphycene (H2TPrPc) and its Fe, Co, Ni, Cu, and Sn complexes in CH2Cl2, CCl4, and 2-PrOH solutions have been studied by radiolytic techniques. Formation and decay of intermediates formed upon one-electron oxidation have been followed by kinetic spectrophotometric pulse radiolysis, and the absorption spectra of stable oxidation products have been recorded following γ-radiolysis. H2TPrPc is oxidized to the π-radical cation and then to the dication, which is stable in aprotic solvents but is transformed to a different product in 2-PrOH. Similar oxidation to the π-radical cation and then to the dication was observed for the CuII, SnIV, CoIII, and FeIII porphycenes. CoII and NiII porphycenes underwent radiolytic oxidation to form stable CoIII and NiIII products. The stability of the latter is in contrast with previous electrochemical observations, and the difference is ascribed to the effect of the axial ligand.

Structure, characterization and photoreactivity of monomeric dioxovanadium(V) Schiff-base complexes of trigonal-bipyramidal geometry

Five mononuclear cis-dioxovanadium(V) complexes of tridentate Schiff bases derived from salicylaldehyde and its derivatives and 8-aminoquinoline have been synthesized and characterized. Single-crystal X-ray analyses were performed with [VO2L1]1 and [VO2L2]2(L1 and L2 denote the [1 + 1] Schiff-base anions derived from salicylaldehyde or naphthaldehyde and 8-aminoquinoline). While the structure of 2 was refined to a final R= 0.074 (R′= 0.055), that of 1 was refined only to R= 0.134 (R′= 0.139) due to its poor diffraction quality. The complexes contain cis-oxo groups in the equatorial plane and a trigonal-bipyramidal geometry around the vanadium at which the Schiff base binds meridionally. Photoirradiation of these complexes in CH2Cl2 yielded chloride-bound VO3+ species, as studied using absorption and 51V NMR spectroscopy. These species are convertible back to the dioxovanadium(V) complexes upon addition of water to the photoirradiated solution.

Synthesis of sterically hindered bis(imidazole) proligands and an exploration of their co-ordination chemistry with copper(II)

Five new sterically hindered bis(imidazole) proligands have been synthesised: 1,2-bis(1-ethyl-4-phenylimidazol-2-yl)ethane (L1), bis(1-ethyl-4-phenylimidazol-2-yl)-(L2) and bis(1-methyl-4-phenylimidazol-2-yl)-dimethyl methane (L3), α, α′-bis(4,5′-diphenylimidazol-1-yl)-o-(L4) and m-xylene (L5). They have been characterised analytically and spectroscopically (1H NMR and mass) and L1 and L2 have been crystallised and characterised by X-ray crystallography. Complexation reactions were attempted with Cu(BF4)2·4.5H2O but only L1 formed a simple monomeric complex, [CuL12][BF4]2. The CuII is co-ordinated by four nitrogen atoms, Cu–Nav 2.01 A, in an essentially square-planar environment. The X-band EPR spectrum of solid [CuL12][BF4]2(g⊥≈1.967, g∥≈2.214, A∥≈196 × 10–4 cm–1) is consistent with a tetragonal ligand field but the Q-band spectrum of a frozen solution of the complex in CH2Cl2–toluene (10 : 1) at 77 K indicates a small rhombic distortion (gx≈2.034, gy≈2.052 and gz≈2.229, Az≈198 × 10–4 cm–1). In CH2Cl2 the complex displays a quasi-reversible CuII–CuI couple with an oxidation peak at +0.74 V and a coupled reduction at –0.07 V (scan rate of 0.2 V s–1). The complexes [CuL42][BF4]2·H2O and [CuL52][BF4]2·H2O appear to be polymeric with bridging ligands. Compound L3 reacted with Cu(BF4)2·4.5H2O to form [H2L3][BF4]2 which has been characterised by X-ray crystallography; L2 reacts similarly.

Molecular structure of [CpRu(PPh3)2(C6H11SH)]BF4·CH2Cl2

The structure of the [CpRu(PPh3)2(C6H11SH)]BF4·CH2Cl2 complex was determined by X-ray diffraction techniques; triclinic space group $$P\bar 1$$ ,a=12.567(1),b=13.409(1),c=14.733(1) A, α=95.380(7), β=111.041(7), γ=96.454(8)°,V=2278.5(4) A3,Z=2,R=0.056,R w=0.088. The Ru is attached to two triphenylphosphine ligands, a cyclopentadienyl and the S atom of the cyclohexylthiol. The Ru−S distance is 2.389(2) A and the S−H distance is 1.23 A.

The extraction of sodium and potassium picrates with poly[(benzo-16-crown-5)maleimide], poly[(benzo-15-crown-5) maleimide-alt-α-methylstyrene] and benzo-15-crown-5

The distribution of complexes of sodium picrate and potassium picrate with poly[(benzo-15-crown-5)maleimide], poly[(benzo-15-crown-5)maleimide-alt-α-methylstyrene] and benzo-15-crown-5 (b15/5) between water and CH2Cl2 was investigated. Concentration of Na-ion with homopolymer in CH2Cl2 was 52%, while the concentration of complex of alternating copolymer and b15/5 with Na-ion was 22% and 20% respectively. Concentration of K-ion complex in CH2Cl2 with homopolymer and alternating copolymer was 90% and with b15/5 the concentration of complex was 40%. The large difference in the complexation ability of Na-ion and K-ion with homopolymer and alternating copolymer is considered to be the consequence of the formation of 1:1 complex with Na-ion and 2:1 complex with K-ion.

Charge Transfer Interaction of Caffeine with π and σ Electron Acceptors

Abstract Solid 1:1 CT molecular complexes of caffeine with π-acceptors (DDQ, TCNE, CHL) and with the [sgrave]-acceptor (I2) are synthesized and characterized. Spectral characteristics and thermodynamic properties of such CT complexes in CH2 Cl2 are investigated. Formation constant values of the CT complexes in various solvents are determined in the temperature range 10–25°C and discussed in terms of nature of the electron acceptor as well as solvent polarity. It is concluded that, the donor orbital of caffeine has both n and m characters.

Electrochemical, electron spin resonance and nuclear magnetic resonance investigations of tertiary phosphine complexes of nickel. Part 2. [NiIL4]+, [NiI(L–L)2]+and their precursors (L = monodentate phosphine, L–L = bidentate diphosphine)

The complexes [Ni(L–L)2]2+ and [NiX(L–L)2]+[L–L =cis-C2H2(PPh2)2-1,2, C6H4(PPh2)2-1,2, C6H4(PMePh)(PPh2)-1,2 or C6H4(PBunPh)(PPh2)-1,2; X = Cl or Br] have been prepared and characterized. Phosphorus-31 NMR spectroscopy reveals the presence of stereoisomers of [Ni(L–L)2]2+ when L–L is unsymmetrically substituted, and the results for the case L–L = C6H4(PBunPh)(PPh2)-1,2 are presented and analysed. Electrochemical studies of the above complexes in CH2Cl2 and of CH2Cl2 solutions containing nickel(II) and an excess of ligand L = PMePh2 or PBunPh2 or L–L = C6H4(PMePh)2-1,2 have been made. Two successive one-electron metal-based reductions were observed for the [Ni(L–L)2]2+ complexes. The halide-containing complexes showed complex redox behaviour involving loss of halide upon one-electron reduction to form the stable [NiI(L–L)2]+ species. Electron spin resonance studies of nickel(I) complexes obtained upon controlled-potential reduction of these systems have been made. Data from both electrochemical and ESR studies show effects due to variations in the structure of the phosphine ligands. The most important factor is the nature of the interphosphorus linkage, but effects due to changes in the substituents at phosphorus are also observed. The electrochemical and ESR properties of [Ni(PPh2R)4]+ are very sensitive to the nature of the alkyl substituent R.

Factors influencing the site of electroreduction in rhodium porphyrins

The electrochemistry of rhodium(III) porphyrins containing bound phosphine, isocyanide, or carbene axial ligands was investigated by cyclic voltammetry and UV-visible spectroelectrochemistry in tetrahydrofuran (THF) and methylene chloride (CH2Cl2) containing tetrabutylammonium hexafluorophosphate (TBAPF6) as supporting electrolyte. The investigated compounds are represented as [(TPP)Rh(L)2]PF6, (TPP)Rh(L')PF6, or (TPP)Rh(PF3)(OH), where TPP is the dianion of tetraphenylporphyrin, L = PPh3, PPh2Me, PPhMe2, and CNCH2Ph, and L' = :C(NHCH2Ph)2. The addition of one electron to these complexes leads to one of two different reduction products depending upon the temperature and the specific set of axial ligands. Some of the complexes are reversibly reduced by one electron to give a transient Rh(III) porphyrin pi anion radical while others are irreversibly reduced under the same solution conditions to give dimeric [(TPP)Rh]2. In several cases, the addition of one electron gives a Rh(II) dimer at room temperature but a Rh(III) pi anion radical at low temperature. The UV-visible data suggest that all of the investigated rhodium(III) porphyrins are initially reduced at the porphyrin pi ring system, and this is also the conclusion based on electrochemical criteria relating the potentials for oxidation and reduction of each metalloporphyrin in nonaqueous media. The absolute potential difference between E1/2 for the first room temperature oxidation of a given complex in CH2Cl2 and the first low-temperature reduction of the same species in THF (where the reaction is reversible) ranges between 2.22 and 2.32 V, suggesting that both electrode reactions involve the porphyrin pi ring system. One of the species, (TPP)Rh(PF3)(OH), undergoes a slow conversion of the electrogenerated pi anion radical to dimeric [(TPP)Rh]2, and this reaction was followed as a function of time by thin-layer UV-visible spectroelectrochemistry in THF. Exchange equilibria involving bound PPh3 and THF axial ligands were also studied in methylene chloride or tetrahydrofuran by UV-visible spectroscopy. Both [(TPP)Rh(PPh3)]+ and [(TPP)Rh(PPh3)2]+ are converted to [(TPP)Rh(PPh3)(THF)]+ in neat THF, but the addition of 1.0 equiv of PPh3 to these solutions leads to [(TPP)Rh(PPh3)2]+ as identified by UV-visible spectroscopy. The formation constant for this reaction was calculated as 103.1 using spectrophotometric methods.

Synthesis, X‐Ray Crystal Structure, and Fluxional Behaviour of fac‐[Ru(CH3CO2)2(PPh3)3] · 2 CH3CO2H

Abstract[Ru2(μ‐O2CCH3)4(O2CCH3)] reacts with excess triphenylphosphane in acetic acid to give fac‐[Ru(O2CCH3)2(PPh3)3] · 2CH3CO2H (1), which crystallizes in the triclinic space group P 1− with Z=2. The three phosphane ligands are in the sterically congested facial configuration, and the distorted octahedral geometry around the metal is completed by a unidentate and chelating acetate. A variable temperature 31P{1H}‐NMR study of the complex in CH2Cl2 showed the three phosphanes to be inequivalent at low temperature. On raising the temperature two separate coalescence processes are observed, ultimately making all of the phosphanes equivalent at room temperature. Complex 1 shows slight catalytic activity for the ring‐opening polymerization of bicyclo[2.2.1]hept‐2‐ene (norbornene).

Nucleophilic Attack on Dichloromethane. Synthesis and Structure ofmer-[Cu(2-(Aminomethyl)Pyridine)3]2+

Abstract Solutions of copper(II) β-diketone complexes in CH2Cl2 or CHCl3 react with 2-(aminomethyl)pyridine (AMP) to produce Cu(AMP)3 2 +, which precipitates as its chloride salt. mer-[Cu(AMP)3]Cl2·CH2Cl2 is monoclinic, space group P21/c; a = 11.072(1), b = 22.306(3), c = 11.388(2) A; β = 117.39(2)°; Z = 4; R = 0.076; R w = 0.068 for 375 parameters and 3477 reflections with I > I σ (I). The mer-Cu(AMP)3 2 + ion has a tetragonally distorted octahedral geometry; distances from Cu to two trans-oriented pyridine N atoms are elongated (2.420(5) and 2.437(5) A), while the third is normal (2.060(4) A). Distances from Cu to the equatorial NH2 N atoms range from 2.012(5) to 2.048(5) A. The chloride ion in this compound is produced by nucleophilic attack of AMP on the CH2Cl2 solvent.

Stable cationic 17-electron [LM(CO)3]+ species (L = 1,4,7-tribenzyl-1,4,7-triazacyclononane; M = Cr, Mo, W): synthesis, spectroscopic properties, and reactivity. Crystal structure of [LMo(CO)3](PF6).cntdot.dmf

The neutral 18-electron complexes LM(CO)3 (L = 1,4,7-tribenzyl-1,4,7-triazacyclononane; M = Cr, Mo, W) were prepd. from M(CO)6 and L in DMF at 150 Deg. Oxidn. of these diamagnetic complexes in CH2Cl2 with [FeCp2]PF6 (Cp = cyclopentadienyl) affords the 17-electron species [LM(CO)3]PF6 in good yields. Magnetic susceptibility measurements and ESR spectroscopy confirm the presence of 1 unpaired electron per cation in these materials. The crystal structure of [LMo(CO)3](PF6).DMF has been detd. by x-ray crystallog. (trigonal, space group R.hivin.3, a 18.299(4), c 24.852(7) .ANG., Z = 9, R = 0.085, Rw = 0.078). The Mo atom is in a pseudooctahedral environment of 3 facially coordinated amine N atoms and 3 carbonyl ligands. The cation possesses crystallog. imposed C3 symmetry. Cyclic voltammetry reveals a reversible one-electron oxidn. of LM(CO)3 species in DMF at -0.545 V vs [FeCp2]+/[FeCp2] for the Cr complex at -0.23 V for the Mo complex and at -0.305 V for the W complex. At more anodic potentials a second irreversible oxidn. wave has been obsd. The reactivity of the [LM(CO)3] species has been briefly investigated.

Arene σ,π complexes: synthesis and electrochemistry of (η6-1,4-C6H4XFp)Cr(CO)3 (where X = H, Me, Cl, or OMe; Fp = (η5-C5H5)Fe(CO)2)

The bimetallic complexes (η6-1,4-C6H4XFp)Cr(CO)3 (where X = H, Me, Cl, or OMe; Fp = (η5-C5H5)Fe(CO)2) were synthesized in 32–80% yields by the reaction of NaFp with (η6-1,4-C6H4XF)Cr(CO)3 (where X = H, Me, or OMe) or (η6-1,4-C6H4Cl2)Cr(CO)3. They were fully characterized by conventional spectroscopic techniques. In these complexes, the arenes are σ bound to the Fp group and π bound to the Cr(CO)3 group. The 13C NMR data suggest that a synergic substituent–arene–Fp π interaction is occurring. Cyclic voltammetric studies of these complexes in CH2Cl2 show that they are oxidized reversibly to give stable radical cations, and confirm that the Fp substituents are strong net electron donors to the Cr(CO)3 fragments. Keywords: bimetallic, iron, chromium, arene, oxidation.

A new synthesis and the electrochemical behaviour of nickel(II) dithiophosphate and dithiophosphinate complexes

The [Ni(S2PR2)2] complexes (R=i-PrO, PhO, or Et) can be conveniently prepared by reaction of [Ni{P(OPh)3}4] with [R2P(S)S]2 (R=i-PrO, PhO, or Et) in refluxing CHCl3. The electrochemical behaviour of the complexes in CH2Cl2 and MeCN has been studied by cyclic voltammetry and coulometry. The oxidation of complexes at a glassy carbon reveals an e.c. mechanism. The [Ni(S2PR2)2] complexes undergo a one-electron irreversible reduction.

ChemInform Abstract: Synthesis of Dihydromorphinones from Dihydrocodeinones.

A preparative method was proposed for obtaining dihydromorphinones based on the O-demethylation of dihydrocodeinones using the AlCl3·Me2S complex in CH2Cl2.

Selective recognition of neutral molecules: 1H n.m.r. Study of the complexation of CH2Cl2 and CH2Br2 by cryptophane-D in solution and crystal structure of its CH2Cl2cavitate

The complexation of CH2Cl2 and CH2Br2 by cryptophane-D (2), a new bis-cyclotribenzyl cavitand, has been studied by 1H n.m.r. spectroscopy and the structure of the internal 1 : 1 (2)·CH2Cl2 complex (cavitate) has been determined by single crystal X-ray crystallography.