An in situ generated catalyst from readily available RuH(2)(PPh(3))(4), an N-heterocyclic carbene (NHC) precursor, NaH, and acetonitrile was developed. The catalyst showed high activity for the amide synthesis directly from either alcohols or aldehydes with amines. When a mixture of an alcohol and an aldehyde was reacted with an amine, both of the corresponding amides were obtained with good yields. Homogeneous Ru(0) complexes such as (eta(4)-1,5-cyclooctadiene)(eta(6)-1,3,5-cyclooctatriene)ruthenium [Ru(cod)(cot)] and Ru(3)(CO)(12) were also active in the amidation of an alcohol or an aldehyde with the help of an in situ generated NHC ligand.

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The polyanionic water-soluble and non-mu-oxo-dimer-forming iron porphyrin iron(III) 5(4),10(4),15(4),20(4)-tetra-tert-butyl-5(2),5(6),15(2),15(6)-tetrakis[2,2-bis(carboxylato)ethyl]-5,10,15,20-tetraphenylporphyrin, (P(8-))Fe(III) (1), was synthesized as an octasodium salt by applying well-established porphyrin and organic chemistry procedures to bromomethylated precursor porphyrins and characterized by standard techniques such as UV-vis and (1)H NMR spectroscopy. A single pK(a1) value of 9.26 was determined for the deprotonation of coordinated water in (P(8-))Fe(III)(H(2)O)(2) (1-H(2)()O) present in aqueous solution at pH <9. The porphyrin complex reversibly binds NO in aqueous solution to give the mononitrosyl adduct, (P(8-))Fe(II)(NO(+))(L), where L = H(2)O or OH(-). The kinetics of the binding and release of NO was studied as a function of pH, temperature, and pressure by stopped-flow and laser flash photolysis techniques. The diaqua-ligated form of the porphyrin complex binds and releases NO according to a dissociative interchange mechanism based on the positive values of the activation parameters DeltaS() and DeltaV() for the "on" and "off" reactions. The rate constant k(on) = 6.2 x 10(4) M(-1) s(-1) (24 degrees C), determined for NO binding to the monohydroxo-ligated (P(8-))Fe(III)(OH) (1-OH) present in solution at pH >9, is markedly lower than the corresponding value measured for 1-H(2)O at lower pH (k(on) = 8.2 x 10(5) M(-1) s(-1), 24 degrees C, pH 7). The observed decrease in the reactivity is contradictory to that expected for the diaqua- and monohydroxo-ligated forms of the iron(III) complex and is accounted for in terms of a mechanistic changeover observed for 1-H(2)O and 1-OH in their reactions with NO. The mechanistic interpretation offered is further substantiated by the results of water-exchange studies performed on the polyanionic porphyrin complex as a function of pH, temperature, and pressure.

A stopped-flow study of the Cp*MoO3- protonation at low pH (down to zero) in a mixed H2O-MeOH (80:20) solvent at 25 degrees C allows the simultaneous determination of the first acid dissociation constant of the oxo-dihydroxo complex, [Cp*MoO(OH)2]+ (pKa1 = -0.56), and the rate constant of its isomerization to the more stable dioxo-aqua complex, [Cp*MoO2(H2O)]+ (k-2 = 28 s-1). Variable-temperature (5-25 degrees C) and variable-pressure (10-130 MPa) kinetics studies have yielded the activation parameters for the combined protonation/isomerization process (k-2/Ka1) from Cp*MoO2(OH) to [Cp*MoO2(H2O)]+, viz., DeltaH++= 5.1 +/- 0.1 kcal mol-1, DeltaS++ = -37 +/- 1 cal mol-1 K-1, and DeltaV++ = -9.1 +/- 0.2 cm3 mol-1. Computational analysis of the two isomers, as well as the [Cp*MoO2]+ complex resulting from the dissociation of water, reveals a crucial solvent effect on both the isomerization and the water dissociation energetics. Introducing a solvent model by the conductor-like polarizable continuum model and especially by explicitly inclusion of up to three water molecules in the calculations led to the stabilization of the dioxo-aqua species relative to the oxo-dihydroxo isomer and to the substantial decrease of the energy cost for the water dissociation process. The presence of a water dissociation equilibrium is invoked to account for the unusually low effective acidity (pKa1' = 4.19) of the [Cp*MoO2(H2O)]+ ion. In addition, the computational study reveals the positive role of external water molecules as simultaneous proton donors and acceptors, having the effect of dramatically lowering the isomerization energy barrier.