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Transition metal hydride complexes are usually amphoteric, not only acting as hydride donors, but also as Bronsted–Lowry acids. A simple additive ligand acidity constant equation (LAC for short) allows the estimation of the acid dissociation constant KaLAC of diamagnetic transition metal hydride and dihydrogen complexes. It is remarkably successful in systematizing diverse reports of over 450 reactions of acids with metal complexes and bases with metal hydrides and dihydrogen complexes, including catalytic cycles where these reactions are proposed or observed. There are links between pKaLAC and pKaTHF, pKaDCM, pKaMeCN for neutral and cationic acids. For the groups from chromium to nickel, tables are provided that order the acidity of metal hydride and dihydrogen complexes from most acidic (pKaLAC −18) to least acidic (pKaLAC 50). Figures are constructed showing metal acids above the solvent pKa scales and organic acids below to summarize a large amount of information. Acid–base features are analyzed for c...

This Review highlights stoichiometric reactions and elementary steps of catalytic reactions involving cooperative participation of transition-metal hydrides and main group Lewis acids. Included are reactions where the transition-metal hydride acts as a reactant as well as transformations that form the metal hydride as a product. This Review is divided by reaction type, illustrating the diverse roles that Lewis acids can play in mediating transformations involving transition-metal hydrides as either reactants or products. We begin with a discussion of reactions where metal hydrides form direct adducts with Lewis acids, elaborating the structure and dynamics of the products of these reactions. The bulk of this Review focuses on reactions where the transition metal and Lewis acid act in cooperation, and includes sections on carbonyl reduction, H2 activation, and hydride elimination reactions, all of which can be promoted by Lewis acids. Also included is a section on Lewis acid–base secondary coordination sph...

Transition-metal hydride radical cations (TMHRCs) are involved in a variety of chemical and biochemical reactions, making a more thorough understanding of their properties essential for explaining observed reactivity and for the eventual development of new applications. Generally, these species may be treated as the ones formed by one-electron oxidation of diamagnetic analogues that are neutral or cationic. Despite the importance of TMHRCs, the generally sensitive nature of these complexes has hindered their development. However, over the last four decades, many more TMHRCs have been synthesized, characterized, isolated, or hypothesized as reaction intermediates. This comprehensive review focuses on experimental studies of TMHRCs reported through the year 2014, with an emphasis on isolated and observed species. The methods used for the generation or synthesis of TMHRCs are surveyed, followed by a discussion about the stability of these complexes. The fundamental properties of TMHRCs, especially those pert...

This Feature Article intends to provide an overview of a variety of catalytic isomerization reactions that have been performed using well-defined transition metal hydride precatalysts. A particular emphasis is placed on the underlying mechanistic features of the transformations discussed. These have been categorized depending upon the nature of the substrate and in most cases discussed following a chronological order.

Hydrogen bonding to transition metal hydride complexes and its role in the proton transfer process has been a subject of the authors' research interest in recent years. The present microreview analyzes the relationships of kinetic and thermodynamic parameters of dihydrogen bonding, MH···HA, proton transfer, yielding [M(η 2 -H 2 )] species, and subsequent steps such as [M(η 2 -H 2 )] to [M(H) 2 ] isomerization or H 2 evolution on the basis of all data acquired so far. It aims at showing the factors that determine the stability of the species involved, the physico-chemical (thermodynamic and kinetic) origin of the effects observed, and, ideally, allow one to better govern the hydrides reactivity.

Calcium magnesium nickel tetrahydride, CaMgNiH4, and its deuteride were prepared by sintering ternary metal alloy powders at 450–460 °C under 100–130 bar hydrogen (deuterium) pressure, and characterized by X-ray and neutron powder diffraction. The compound crystallizes with a cubic structure (space group P2132a = 6.7414(4) A (hydride) and 6.7301(4) A (deuteride) at 298 K) that contains [NiD4]4− complex ions in which two types of deuterium atoms surround nickel in an ordered, nearly regular tetrahedral configuration with bond distances [Ni−D1] = 1.597(9) and [Ni-3 × D2] = 1.602(8) A, and bond angles in the range [DNiD] = 107.6(5)°−111.3(5)°. The thermal stability as measured from pressure-composition isotherms on the hydride is ΔHdes = −129(3) kJ (mol H2)−1.

Ca4Mg4Fe3H22 and its deuteride were synthesized by reaction of binary CaMg with iron wire at 500–530 °C and 100–155 bar hydrogen (deuterium) pressure. The cubic structure was established from X-ray single-crystal and neutron powder diffraction: space group P43m, a=6.7151(6)A (hydride) and 6.7016(4) A (deuteride) at 295 K. It contains three types of deuterium atoms: two surrounding iron octahedrally with bond distances [Fe–4D1] = 1.583(3) A and [Fe–2D2] =1.562(5) A , and one situated in a tetrahedral hole formed by one magnesium and three calcium atoms with bond distances [Mg–D3] =1.808(7) A and [Ca–D3] = 2.388(9) A .

The activation of metal hydrogen bonds toward alkyne insertion and carbonyl reduction in NO substituted transition metal hydride complexes is discussed. MO theoretical treatment elucidates a genuine nitrosyl effect and enhanced hydricity for this class of compounds. This is traced in NMR based M-H bond ionicity measurements and reactivity studies.

We have investigated the band structure of the new tetragonal quaternary mixed alkali-alkaline earth transition metal hydride PdSr 2 LiH 5 by means of the ab initio augmented plane wave method. We find this material to be metallic. The total density of states as well as its partial wave analysis have been used to investigate the origin of the electronic states. In this hydride, like in superconducting PdH, the palladium d bands are essentially filled and the H-s states have a non-negligible contribution at the Fermi energy. We find the electronic contribution to the electron-optical phonon coupling constant to be sizeable, although smaller than in PdH.

Publisher Summary This chapter discusses the spectroscopy of multinuclear magnetic resonance in solution, which is one of the most important analytical methods in structural studies of transition-metal hydride complexes. Among different nuclei, the proton plays the main role because 1H NMR provides direct information about spectral properties of the hydride ligands. In addition, the proton, being a nonquadrupolar and long-relaxing nucleus, gives rise to well-resolved NMR spectra that are very conveniently analyzed. The NMR signals of quadrupole nuclei are usually broadened because of rapid relaxation and sometimes they even become unobservable. This situation relates to the well-known difficulties in the realization of the NMR experiments of such nuclei. The energy of interaction of the nuclear quadrupole moment, Q, with the molecular electric field gradient, EFG, can be experimentally measured as the nuclear-quadrupole coupling constant, NQCC. EFG and NQCC are very sensitive to changes in electronic distribution in the molecule, intermolecular association, and solid-state effects.

Dicarbonyl(η3-1,1,2,3,4,4-hexafluoro-2-butenyl)(triphenyl-phosphine)cobalt(I) was isolated at the first time from the reaction of tetracarbonylhydridocobalt(I) with hexafluorobuta-1,3-diene and triphenylphosphine.

Cet article presente des travaux concernant la reactivite d'une serie de complexes trinucleaires carbonyles de l'osmium et du ruthenium: effet isotopique du deuterium au cours de reactions d'echanges de coordinats ou de transfert d'hydrogene, cinetique et mecanisme