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The reaction involves no changes in the oxidation state of the metal and can be viewed as splitting H 2 into hydride (which binds to the metal) and proton (which binds to the base). ML n x+ + base + H 2 ⇌ HML n (x-1)+ + Hbase + Such reaction are assumed to involve the intermediacy of dihydrogen complexes. Bifunctional catalysts activate H 2 ...
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.
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]
transfer of the second hydrogen atom from the metal to the alkyl group with simultaneous dissociation of the alkane ("reductive elimination") L n M(H)(CH 2 −CH 2 R) → L n M + CH 3 −CH 2 R. Alkene isomerization often accompanies hydrogenation. This important side reaction proceeds by beta-hydride elimination of the alkyl hydride ...
In general, complex metal hydrides have the formula M x M' y H n, where M is an alkali metal cation or cation complex and M' is a metal or metalloid.Well known examples feature group 13 elements, especially boron and aluminium including sodium aluminium hydride, NaAlH 4), lithium aluminium hydride, LiAlH 4, and lithium borohydride, (LiBH 4).
The reverse of olefin insertion into a metal-hydrogen bond is β-hydride elimination. The Principle of Microscopic Reversibility requires that the mechanism of β-hydride elimination follow the same pathway as the insertion of alkenes into metal hydride bonds. The first requirement for β-hydride elimination is the presence of a hydrogen at a ...
The distance between the metal and the hydrogen is typically 1.8–2.3 Å, and the M┄H−C angle is in the range of 90°–140°. The presence of a 1 H NMR signal that is shifted upfield from that of a normal aryl or alkane, often to the region normally assigned to hydride ligands.
Such reactions are subject to the usual parameters that affect other reactions in coordination chemistry, but steric effects are especially important in determining the stereochemistry and regiochemistry of the reactions. The reverse reaction, the de-insertion of CO and alkenes, are of fundamental significance in many catalytic cycles as well.