0000000000025354
AUTHOR
Edmond Collange
New CpCrCl2(PR3) complexes: physical properties and reduction chemistry
Abstract Compounds CpCrCl2L ( L = PMe 2 Ph , 1 , PMePh 2 , 2 ; PPh 3 , 3 ) have been prepared. Their magnetic moment is in accord with the presence of three unpaired electron and a variable temperature 1H NMR investigation of 1 shows Curie-Weiss behavior. The 1H NMR, EPR and UV-visible spectra are in agreement with those of other previously reported compounds of the same family. An electrochemical investigation shows the accessibility of an irreversible reduction process. A parallel sodium reduction investigation of complexes CpCrCl2L (L = PMe3 and η1-dppe) suggests tjat the reduction process is followed by immediate chloride loss, and then by a ligand redistribution process to afford chrom…
Experimental and Computational Studies of Hydrogen Bonding and Proton Transfer to [Cp*Fe(dppe)H]
The present contribution reports experimental and computational investigations of the interaction between [Cp*Fe(dppe)H] and different proton donors (HA). The focus is on the structure of the proton transfer intermediates and on the potential energy surface of the proton transfer leading to the dihydrogen complex [Cp*Fe(dppe)(H2)]+. With p-nitrophenol (PNP) a UV/Visible study provides evidence of the formation of the ion-pair stabilized by a hydrogen bond between the nonclassical cation [Cp*Fe(dppe)(H2)]+ and the homoconjugated anion ([AHA]-). With trifluoroacetic acid (TFA), the hydrogen-bonded ion pair containing the simple conjugate base (A-) in equilibrium with the free ions is observed…
Generation, Characterization, and Electrochemical Behavior of the Palladium-Hydride Cluster [Pd3(dppm)3(3-CO)(3-H)]+ (dppm=Bis(diphenylphosphinomethane)
Addition of formate on the dicationic cluster [Pd(3)(dppm)(3)(mu(3)-CO)](2+) (dppm=bis(diphenylphosphinomethane) affords quantitatively the hydride cluster [Pd(3)(dppm)(3)(mu(3)-CO)(mu(3)-H)](+). This new palladium-hydride cluster has been characterised by (1)H NMR, (31)P NMR and UV/Vis spectroscopy and MALDI-TOF mass spectrometry. The unambiguous identification of the capping hydride was made from (2)H NMR spectroscopy by using DCO(2) (-) as starting material. The mechanism of the hydride complex formation was investigated by UV/Vis stopped-flow methods. The kinetic data are consistent with a two-step process involving: 1) host-guest interactions between HCO(2) (-) and [Pd(3)(dppm)(3)(mu(3…
Nature of (C5Me5)2Mo2O5in water–methanol at pH 0–14. On the existence of (C5Me5)MoO2(OH) and (C5Me5)MoO2+: a stopped-flow kinetic analysis
A stopped-flow analysis of compound Cp*2Mo2O5 (Cp* = η5-C5Me5) in 20% MeOH–H2O over the pH range 0–14 has provided the speciation of this molecule as well as the rate and mechanism of interconversion between the various species that are present in solution. The compound is a strong electrolyte in this solvent combination, producing the Cp*MoO2+ and Cp*MoO3− ions in equilibrium with a small amount of Cp*MoO2(OH), the latter attaining ca. 15% relative amount at pH 4. At low pH ( 6. The acid dissociation constant of Cp*MoO2(OH) has been measured directly (pK = 3.65 ± 0.02) while the pK for the protonation equilibrium leading to Cp*MoO3H2+ is estimated as 5. The prevalent pathway at high pH i…
Stopped-Flow and DFT Studies of Proton Transfer and Isomerization of 5-Amino-3-imino-1,2,6,7-tetracyano-3H-pyrrolizine and Its Related Base 2-(5-Amino-3,4-dicyano-2H-pyrrol-2-ylidene)-1,1,2-tricyanoethanide in Water: A Completely Sorted out Square Scheme
International audience; A complete kinetic study of pH-dependent isomerization of 5-amino-3-imino-1,2,6,7-tetracyano-3H-pyrrolizine (HL) and 2-(5-amino-3,4-dicyano-2H-pyrrol-2-ylidene)-1,1,2-tricyanoethanide (L‘-) in the pH range from −0.5 to +13 in aqueous solution, which spans over 7 orders of magnitude for the pseudo-first-order rates (log k from −4.8 to +2.5), has revealed for the first time the existence of the corresponding conjugate species L- and HL‘. The study has allowed the determination of the acid dissociation constants of HL (pKa) and HL‘ (pKa‘), as well as all of the individual forward and reverse isomerization rates of the acidic (HL/HL‘) and basic (L-/L‘-) forms. Although L…
Hydrogen bonding and proton transfer involving the trihydride complexes Cp*M(dppe)H 3 (M = Mo, W) and fluorinated alcohols: the competitive role of the hydride ligands and metal
International audience; The protonation of complexes Cp*M(dppe)H3 (dppe is ethylenebis(diphenylphosphine), M = Mo (1), W (2)) by a variety of fluorinated alcohols of different acid strength (FCH2CH2OH, CF3CH2OH, (CF3)2CHOH, and (CF3)3COH) was investigated experimentally by the variable temperature spectroscopic methods (IR, NMR) and stopped-flow technique (UV-Vis). The structures of the hydrogen-bonded and proton transfer products were studied by DFT calculations. In agreement with the calculation results, the IR data suggest that the initial hydrogen bond is established with a hydride site for complex 1 and with the metal site for complex 2. However, no intermediate dihydrogen complex foun…
Synthesis and structure of a new organometallic polyoxomolybdate,
Abstract Acidic aqueous solutions of the [Cp*MoO2(H2O)x]+ ion yield single crystals of the novel organometallic polyoxomolybdate Cp 2 ∗ Mo 6 O 17 via a slow protonolysis of the Mo–Cp* bond. This compound has subsequently been obtained selectively and in good yields from the combination of Cp 2 ∗ Mo 2 O 5 and four equivalents of MoO 4 2 - under acidic conditions. The X-ray structure of Cp 2 ∗ Mo 6 O 17 is analogous to other hexanuclear polyoxometallate ions but is the most distorted so far reported according to the continuous symmetry measure, the inner (μ6-O)Mo6 core featuring a large displacement of the central oxygen atom toward the organometallic moieties and away from the inorganic ones.
Unexpected Reaction of the Unsaturated Cluster Host and Catalyst [Pd3(3-CO)(dppm)3]2+ with the Hydroxide Ion: Spectroscopic and Kinetic Evidence of an Inner-Sphere Mechanism
The title cluster, [Pd(3)(mu(3)-CO)(dppm)(3)](2+) (dppm=bis(diphenylphosphino)methane), reacts with one equivalent of hydroxide anions (OH(-)), from tetrabutylammonium hydroxide (Bu(4)NOH), to give the paramagnetic [Pd(3)(mu(3)-CO)(dppm)(3)](+) species. Reaction with another equivalent of OH(-) leads to the zero-valent compound [Pd(3)(mu(3)-CO)(dppm)(3)](0). From electron paramagnetic resonance analysis of the reaction medium using the spin-trap agent 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), the 2-tetrahydrofuryl or methyl radicals, deriving from the tetrahydrofuran (THF) or dimethyl sulfoxide (DMSO) solvent, respectively, were detected. For both [Pd(3)(mu(3)-CO)(dppm)(3)](2+) and [Pd(3)(mu…