Hydrogen and Dihydrogen Bonds in the Reactions of Metal Hydrides

The dihydrogen bond-an interaction between a transition-metal or main-group hydride (M-H) and a protic hydrogen moiety (H-X)-is arguably the most intriguing type of hydrogen bond. It was discovered in the mid-1990s and has been intensively explored since then. Herein, we collate up-to-date experimental and computational studies of the structural, energetic, and spectroscopic parameters and natures of dihydrogen-bonded complexes of the form M-H···H-X, as such species are now known for a wide variety of hydrido compounds. Being a weak interaction, dihydrogen bonding entails the lengthening of the participating bonds as well as their polarization (repolarization) as a result of electron density redistribution. Thus, the formation of a dihydrogen bond allows for the activation of both the MH and XH bonds in one step, facilitating proton transfer and preparing these bonds for further transformations. The implications of dihydrogen bonding in different stoichiometric and catalytic reactions, such as hydrogen exchange, alcoholysis and aminolysis, hydrogen evolution, hydrogenation, and dehydrogenation, are discussed.

EPR detection and characterisation of a paramagnetic Mo(iii) dihydride intermediate involved in electrocatalytic hydrogen evolution

EPR spectroscopy and theoretical data show that the slow heterogeneous electron-transfer kinetics associated with the reduction of an 18-electron Mo(IV) acetato dihydride are a consequence of an η(2)-η(1) rearrangement of the carboxylate ligand which gives a unique paramagnetic 17-electron Mo(III) dihydride.

Preparation and substitution chemistry of [Bu4N]2[W6Cl8(p-OSO2C6H4CH3)6]. A useful precursor for pseudohalide, acetate, and organometallic complexes containing the [W6Cl8](4+) core

The tosylate (p-toluenesulfonate) cluster [Bu4N]2[W6Cl8(p-OSO2C6H4CH3)6] (1) has been prepared and characterized by IR and NMR spectroscopy, elemental analysis, and an X-ray crystal structure. This cluster complex is shown to be a useful starting material for the preparation of pseudohalide clusters, [Bu4N]2[W6Cl8(NCQ)6] (Q = O (2), S (3), and Se (4)), in high yields. Cluster 1 also serves as a precursor to the new cluster compounds: [Bu4N]2[W6Cl8(O2CCH3)6] (5), [Bu4N]2[W6Cl8((mu-NC)Mn(CO)2(C5H5))6] (6), [W6Cl8((mu-NC)Ru(PPh3)2(C5H5))6][ p-OSO2C6H4CH3]4 (7), and [W6Cl8((mu-NC)Os(PPh3)2(C5H5))6][ p-OSO2C6H4CH3]4 (8). X-ray crystal structures are reported for 1, 4, and 5.

Unexpectedly Lengthened N-H.Co Hydrogen Bonds?

Low-temperature crystal structures of QuinH(+)Co(CO)(4)(-), 1 (QuinH(+) = quinuclidinium), (DABCO)H(+)Co(CO)(3)P(p-tolyl)(3)(-), 2, and (DABCO)H(+)Co(CO)(3)PPh(2)(p-tolyl)(-), 3 (DABCO = 1,4-diazabicyclooctane), 2 and 3 as their acetonitrile solvates, demonstrate that these salts exhibit intermolecular N-H.Co hydrogen bonding between the cation and anion components. NMR and IR data demonstrate the persistence of these interactions in toluene solution. Such solution-state data, which examine solvated ion pairs, suggest little difference between these salts and the corresponding previously reported salts (DABCO)H(+)Co(CO)(3)L(-) (4, L = CO; 5, L = PPh(3)). However, in the solid state, the N-H.Co hydrogen bonds in 1-3 are some 0.1-0.15 Å longer than would be predicted from consideration of the structures of 4 and 5 and the aforementioned similarity to 4 and 5 in solution. In previous reports we have shown that major steric or electronic changes to the anion or cation have resulted in substantial changes (0.15-0.3 Å) in the N.Co [H.Co] separation for N-H.Co hydrogen bonds in related R(3)NH(+)Co(CO)(3)L(-) (L = CO, PR(3)) salts. In this report, we present examples in which small changes are made to the anion or cation remote from the N-H.Co hydrogen bond. In the solid state, the effect of these small changes on this hydrogen bond is subsumed by the effect of changes in the supramolecular structure. This clearly indicates the sensitivity of the geometry of these hydrogen bonds to the overall balance of intermolecular interactions in the solid state and as such is pertinent to current interest in weak (intermolecular) interactions for which characterization by X-ray crystallography is important.