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A new experimental study was carried out to determine the accurate rate constant and activation parameters for the isomerization process of the [[Cp*Fe(dppe)[H.sub.2]].sup.+] system when the counterion is either B[F.sub.4.sup.-] or C[F.sub.3]CO[O.sup.-]. The isomerization rate constant is found to be essentially independent of the nature and quantity of strong acid.

The direct and independent observation of the kinetics at the same temperature, is performed for the faster protonation of the hydride ligand site in complex Cp*FeH(dppe) and for the isomerization of the resulting Cp*Fe(H2)(dppe)(super +) intermediate to the thermodynamically preferred classical dihydride product. Strong evidence is obtained in favor of a direct isomerization process, not involving the reversible deprotonation of the hydride site and protonation of the metal site.

A study is conducted to examine the interaction of the ruthenium hybride complex CpRuH(CO)(PCy3) with proton donors HOR of different strength in hexane and is compared with data in dichloromethane. The protonation of a transition metal hydride appears as a complicated process in which hydride basicity, proton donor strength and secondary interactions among the acids and the bases present, and concentration effects are relevant.

Low-temperature IR and NMR studies combined with DFT calculations revealed the mechanistic complexity of apparently simple reactions between Mn(I) complex fac-[(dppm)Mn(CO)3H] and Lewis acids (LA = Ph3C+, B(C6F5)3) involving the formation of so-far elusive meridional hydride species mer-[(dppm)Mn(CO)3H⋯LA] and unusual dearomatization of the Ph3C+ cation upon hydride transfer. [ABSTRACT FROM AUTHOR]

The (carbonyl)dihydride complex [(triphos)Ru(CO)[H.sub.2]] (2) has been synthesized by reaction of the ruthenate [(triphos)Ru[H.sub.3]]K (triphos = MeC[(C[H.sub.2]P[Ph.sub.2]).sub.3]) with ethanol saturated with CO. A single crystal X-ray analysis and IR and NMR experiments have shown that 2 adopts in both the solid state and solution an octahedral coordination geometry with a facial triphos ligand, two cis terminal hydrides, and a terminal carbonyl. The reaction of hexafluoro-2-propanol (HFIP) with 2 has been studied in C[H.sub.2] [Cl.sub.2] solution by IR and NMR spectroscopy. The proton donor interacts with a terminal hydride of 2 forming a rather strong hydrogen bond. The resulting H-bonded adduct [{(triphos)Ru(CO)(H)H}***{HOCH [(C[F.sub.3]).sub.2]}] (2a) has fully been characterized by in situ NMR and IR techniques. Compound 2a is in equilibrium with the nonclassical [[eta].sup.2]-[H.sub.2] complex [[(triphos)Ru(CO)H([H.sub.2])].sup.+] (2b), which can independently be prepared by protonation of 2 with a strong protic acid at low temperature. Unequivocal characterization of the dihydrogen complex (2b) has been achieved by a multifaceted spectroscopic investigation ([T.sup.obs.sub.1min] = 0.005 s (200 MHz), [J.sub.H,D] [approximately equal to] 30 Hz, DQCC = 78.3 kHz). A combined IR and NMR study of the proton transfer reaction involving 2 and HFIP in C[H.sub.2][Cl.sub.2] to give, first, the H-bonded adduct (2a) and, then, the dihydrogen complex (2b) has demonstrated that all these species are in equilibrium in the temperature range from 190 to 260 K. The thermodynamic parameters for the formation of 2a have independently been determined by NMR and IR methods, while those for the formation of 2b have been obtained by IR spectroscopy. An energetic profile for the reaction sequence 2 [right arrow] 2a [right arrow] 2b is proposed and discussed. Key words: hydrides, hydrogen bonding, ruthenium, IR spectroscopy, NMR spectroscopy.

The adducts that precede the formation of nonclassical dihydrogen complexes during the protonation of rhenium hydrides were analyzed via calculations based on density functional theory (DFT). DFT analysis of the formation of dihydrogen complexes from rhenium hydrides with perfluoro-tert-butyl alcohol indicated the presence of intermolecular hydrogen bonding which led to the formation of two type of complexes. However, the strength of the hydrogen bonds formed by the rhenium hydride complexes was less than those of related tungsten systems.

A study was conducted to determine whether the hydride ligand of WH(CO)2(NO)L2 complexes act as a proton acceptor in intermolecular W-H...H-O bonding. Infrared and nuclear magnetic resonance spectra in hexane, toluene-d8 and CD2Cl2 solutions provided evidence that hydrogen bonding highly influences the protonation of the metal hydrides. Tests were performed to confirm this result.

The interaction of a series of [Ni(PR12NR22)2]2+ complexes 1–4 (where PR12NR22=1,5‐R2‐3,7‐R1‐1,5‐diaza‐3,7‐diphosphacyclooctane; R1=o‐Py, Ph; R2=CHPh2, p‐Tol) with H2 is reversible yielding the products of heterolytic splitting of dihydrogen in the metal coordination sphere ‐ [NiH(PR12NR22)(PR12NR22H)]2+. Experiments conducted with parahydrogen allowed to see the signal at about −4 ppm corresponding to the metal‐bound H2 in the nickel dihydrogen complex [Ni(η2−H2)(PPh2NCHPh22)2]2+ (3‐H2) – the short‐living non‐classical intermediate, which so far has been revealed only computationally. [ABSTRACT FROM AUTHOR]

We describe an efficient protocol for the regioselective isomerization of terminal alkenes employing a previously described bifunctional Ir‐based PC(sp3)complex (4) possessing a hemilabile sidearm. The isomerization, catalyzed by 4, results in a one‐step shift of the double bond in good to excellent selectivity, and good yield. Our mechanistic studies revealed that the reaction is driven by the stepwise migratory insertion of Ir−H species into the terminal double bond/β‐H elimination events. However, the selectivity of the reaction is controlled by dissociation of the hemilabile sidearm, which acts as a selector, favoring less sterically hindered substrates such as terminal alkenes; importantly, it prevents recombination and further isomerization of the internal ones. [ABSTRACT FROM AUTHOR]