Kinetic and thermodynamic acidity of hydrido transition-metal complexes.  3.  Thermodynamic acidity of common mononuclear carbonyl hydrides

Moore, Eric J.; Sullivan, Jeffrey M.; Norton, Jack R.

doi:10.1021/ja00269a022

Cited by 206 publications

(169 citation statements)

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“…As the HBF 4 molecule is not stable and the formation of ion pairs is not favored in acetonitrile solution, [10,11] it appears reasonable to assume that the attacking species in this case is the acetonitrile-solvated proton (H + MeCN ). In this case, the anion of the acid has a low coordinating ability; a species of the type [W 3 S 4 (BF 4 ) 3 + (two doublets at d = 13.5 and 10.3 ppm in the phosphorus spectrum with J P,F = 57 Hz and 92 Hz, respectively; one double doublet at d = À203.0 ppm in the fluorine spectrum with the same coupling constants) by abstraction of fluoride from the anion, this process occurs much more slowly than that of the stoppedflow measurements and does not cause any interference in the kinetic experiments.…”

Section: Resultsmentioning

confidence: 99%

Mechanism of the Reaction of the [W₃S₄H₃(dmpe)₃]⁺ Cluster with Acids: Evidence for the Acid‐Promoted Substitution of Coordinated Hydrides and the Effect of the Attacking Species on the Kinetics of Protonation of the Metal‐Hydride Bonds

Basallote

Feliz

Fernández‐Trujillo

et al. 2004

Chemistry A European J

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The cluster [W(3)S(4)H(3)(dmpe)(3)](+) (1) (dmpe=1,2-bis(dimethylphosphino)ethane) reacts with HX (X=Cl, Br) to form the corresponding [W(3)S(4)X(3)(dmpe)(3)](+) (2) complexes, but no reaction is observed when 1 is treated with an excess of halide salts. Kinetic studies indicate that the hydride 1 reacts with HX in MeCN and MeCN-H(2)O mixtures to form 2 in three kinetically distinguishable steps. In the initial step, the W-H bonds are attacked by the acid to form an unstable dihydrogen species that releases H(2) and yields a coordinatively unsaturated intermediate. This intermediate adds a solvent molecule (second step) and then replaces the coordinated solvent with X(-) (third step). The kinetic results show that the first step is faster with HCl than with solvated H(+). This indicates that the rate of protonation of this metal hydride is determined not only by reorganization of the electron density at the M-H bonds but also by breakage of the H-X or H(+)-solvent bonds. It also indicates that the latter process can be more important in determining the rate of protonation.

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Section: Resultsmentioning

confidence: 99%

Mechanism of the Reaction of the [W₃S₄H₃(dmpe)₃]⁺ Cluster with Acids: Evidence for the Acid‐Promoted Substitution of Coordinated Hydrides and the Effect of the Attacking Species on the Kinetics of Protonation of the Metal‐Hydride Bonds

Basallote

Feliz

Fernández‐Trujillo

et al. 2004

Chemistry A European J

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“…Given the EN difference at the metal−hydrogen bond, one may find it surprising that Co, Fe, and Mn hydridocarbonyls are Brønsted-Lowry acids in aqueous solution: HCo(CO) 4 is a strong acid [207], H 2 Fe(CO) 4 is comparable to acetic acid [208,209], and HMn(CO) 5 to "carbonic acid" [210]. This would seem to suggest that the hydrogen is protic.…”

Section: A-3 Ionic Approximation Against Brønsted-lowry Aciditymentioning

confidence: 99%

Toward a comprehensive definition of oxidation state (IUPAC Technical Report)

Karen

McArdle

Takats

2014

Pure and Applied Chemistry

105

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A generic definition of oxidation state (OS) is formulated: "The OS of a bonded atom equals its charge after ionic approximation". In the ionic approximation, the atom that contributes more to the bonding molecular orbital (MO) becomes negative. This sign can also be estimated by comparing Allen electronegativities of the two bonded atoms, but this simplification carries an exception when the more electronegative atom is bonded as a Lewis acid. Two principal algorithms are outlined for OS determination of an atom in a compound; one based on composition, the other on topology. Both provide the same generic OS because both the ionic approximation and structural formula obey rules of stable electron configurations. A sufficiently simple empirical formula yields OS via the algorithm of direct ionic approximation (DIA) by these rules. The topological algorithm works on a Lewis formula (for a molecule) or a bond graph (for an extended solid) and has two variants. One assigns bonding electrons to more electronegative bond partners, the other sums an atom's formal charge with bond orders (or bond valences) of sign defined by the ionic approximation of each particular bond at the atom. A glossary of terms and auxiliary rules needed for determination of OS are provided, illustrated with examples, and the origins of ambiguous OS values are pointed out. An electrochemical OS is suggested with a nominal value equal to the average OS for atoms of the same element in a moiety that is charged or otherwise electrochemically relevant.

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“…[7] From Norton×s measurements in CH 3 CN, the pK a of 8.3 determined for [CoH(CO) 4 ] indicates that it is of comparable acidity to HCl in that solvent. [9] The molybdenum hydride [Mo(Cp)(CO) 3 H] is less acidic, with a pK a of 13.9. [9] Tilset and co-workers found [10] that one-electron oxidation of metal hydrides can produce super-acids, with a pK a of À6.0 estimated in CH 3 CN for the radicalcation complex [Mo(Cp)(CO) 3 H] + ¥ .…”

Section: Introductionmentioning

confidence: 99%

“…[9] The molybdenum hydride [Mo(Cp)(CO) 3 H] is less acidic, with a pK a of 13.9. [9] Tilset and co-workers found [10] that one-electron oxidation of metal hydrides can produce super-acids, with a pK a of À6.0 estimated in CH 3 CN for the radicalcation complex [Mo(Cp)(CO) 3 H] + ¥ . For our purposes, we need a dihydride or dihydrogen complex as the proton donor rather than a monohydride, and it is abundantly clear that such complexes can have ample acidity.…”

Section: Introductionmentioning

confidence: 99%

Catalytic Ionic Hydrogenations

Bullock

2004

Chemistry A European J

284

206

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Catalytic ionic hydrogenation of ketones occurs by proton transfer to a ketone from a cationic metal dihydride, followed by hydride transfer from a neutral metal hydride. This contrasts with traditional catalysts for ketone hydrogenation that require binding of the ketone to the metal and subsequent insertion of the ketone into a M-H bond. Ionic hydrogenation catalysts based on the inexpensive metals molybdenum and tungsten have been developed based on mechanistic understanding of the individual steps required in the catalytic reaction.

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Kinetic and thermodynamic acidity of hydrido transition-metal complexes. 3. Thermodynamic acidity of common mononuclear carbonyl hydrides

Cited by 206 publications

References 0 publications

Mechanism of the Reaction of the [W₃S₄H₃(dmpe)₃]⁺ Cluster with Acids: Evidence for the Acid‐Promoted Substitution of Coordinated Hydrides and the Effect of the Attacking Species on the Kinetics of Protonation of the Metal‐Hydride Bonds

Mechanism of the Reaction of the [W₃S₄H₃(dmpe)₃]⁺ Cluster with Acids: Evidence for the Acid‐Promoted Substitution of Coordinated Hydrides and the Effect of the Attacking Species on the Kinetics of Protonation of the Metal‐Hydride Bonds

Toward a comprehensive definition of oxidation state (IUPAC Technical Report)

Catalytic Ionic Hydrogenations

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Kinetic and thermodynamic acidity of hydrido transition-metal complexes. 3. Thermodynamic acidity of common mononuclear carbonyl hydrides

Cited by 206 publications

References 0 publications

Mechanism of the Reaction of the [W3S4H3(dmpe)3]+ Cluster with Acids: Evidence for the Acid‐Promoted Substitution of Coordinated Hydrides and the Effect of the Attacking Species on the Kinetics of Protonation of the Metal‐Hydride Bonds

Mechanism of the Reaction of the [W3S4H3(dmpe)3]+ Cluster with Acids: Evidence for the Acid‐Promoted Substitution of Coordinated Hydrides and the Effect of the Attacking Species on the Kinetics of Protonation of the Metal‐Hydride Bonds

Toward a comprehensive definition of oxidation state (IUPAC Technical Report)

Catalytic Ionic Hydrogenations

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Mechanism of the Reaction of the [W₃S₄H₃(dmpe)₃]⁺ Cluster with Acids: Evidence for the Acid‐Promoted Substitution of Coordinated Hydrides and the Effect of the Attacking Species on the Kinetics of Protonation of the Metal‐Hydride Bonds

Mechanism of the Reaction of the [W₃S₄H₃(dmpe)₃]⁺ Cluster with Acids: Evidence for the Acid‐Promoted Substitution of Coordinated Hydrides and the Effect of the Attacking Species on the Kinetics of Protonation of the Metal‐Hydride Bonds