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Ternary metal hydrides have the formula A x MH n, where A + is an alkali or alkaline earth metal cation, e.g. K + and Mg 2+.A celebrated example is K 2 ReH 9, a salt containing two K + ions and the ReH 9 2− anion.
Classical transition metal hydride feature a single bond between the hydrogen centre and the transition metal. Some transition metal hydrides are acidic, e.g., HCo(CO) 4 and H 2 Fe(CO) 4. The anions potassium nonahydridorhenate [ReH 9] 2− and [FeH 6] 4− are examples from the growing collection of known molecular homoleptic metal hydrides. [16]
Protonation of metal hydroxides gives aquo complexes: L n M−OH + H + ⇌ L n M−OH + 2 where L n is the ligand complement on the metal M. Thus, aquo ligand is a weak acid, of comparable strength to acetic acid (pK a of about 4.8). [6] In principle but not very commonly, metal hydroxides undergo deprotonation, yielding oxo complexes:
The pK a of HMn(CO) 5 in water is 7.1. [8] It is thus comparable to hydrogen sulfide, a common inorganic acid, in its acidity.. A common reaction involving HMn(CO) 5 is substitution of the CO ligands by organophosphines, as occurs both thermally and photochemically.
The greater stabilization that results from metal-to-ligand bonding is caused by the donation of negative charge away from the metal ion, towards the ligands. This allows the metal to accept the σ bonds more easily. The combination of ligand-to-metal σ-bonding and metal-to-ligand π-bonding is a synergic effect, as each enhances the other.
Muetterties's work on boron hydride clusters led to the work on several polyhedral borane anions such as B 12 H 12 2−. [7] [8] He was an inventor on some basic findings with the polyhedral borate anions. [9] In addition to the polyhedral boranes, the program explored pi-allyl, fluoroalkyl, and boron hydride complexes of the transition metals.
In hydrogenation, the resulting alkyl ligand combines with a second hydride to give the alkane. Analogous reactions apply to the hydrogenation of alkynes: an alkenyl ligand combines with a hydride to eliminate an alkene. Migratory insertion of an alkene into a metal hydride. The middle image depicts the transition state.
An often studied dihydrogen complex of iron, [HFe(H 2)(dppe) 2] +.. The usual method for characterization is 1 H NMR spectroscopy.The magnitude of spin–spin coupling, J HD, is a useful indicator of the strength of the bond between the hydrogen and deuterium in HD complexes.