Hydrides trans effect

Kinetic inertness, evidently caused by the electronic configuration, leads to a remarkable unreactivity of the Rh-H bond to hydrolysis. In the absence of air, it is unaffected by ammonia solution in dilute solution, the ammonia tram to hydride is reversibly replaced by water, showing that the hydride has a trans-effect parallel to its trans-influence. 

Kinetic study [141] of complexes of the type trans-Pt(PEt3)2XCl was of great value in establishing the strong trans-effect of hydride (Table 3.13) examination of the data for a wide range of reactions gives rise to a series... 

As already mentioned, a purely 7r-bonding mechanism cannot account for the position of hydride in trans-effect and trans-influence series. Overall, therefore, a major role (though not necessarily the only one) for <7-bonding is implied. 

The anion [Ir4(CO)nH]- is stable under a CO atmosphere (trans-effect of hydride ), whereas under nitrogen it rapidly gives brown products of higher nucleari-ty, which are not yet well-characterized9. The dianion [Ir4(CO)i0H2]2 has also been recently characterized102. ... 

Trans effect, 543-545 Transferrins, 937 Transition metal hydrides, acidities of. 643... 

Transfer of a hydride to another ligand on substitution is also possible (equation 59). Alternatively, substitution reactions can occur without loss of the H ligand. This is common where only one H is present (equation 60). The presence of the coordinated hydrogen can even encourage such reactions by its high trans effect and perhaps even by transfer to a CO (or related ligand, where one is present) to give a transient formyl and an open site (equation 61). 

As mentioned earlier, steric effects can be important in determining the outcome of the hydride abstraction reaction. This is particularly vexing in cases where an alkyl substituent is present at the sp carbon of the cyclohexadiene complex. For example, complexes such as (47 equation 19) are untouched by trityl cation, provided traces of acid are not present (these are formed by hydrolysis of the trityl tetra-fluoroborate due to atmospheric moisture, and will cause rearrangement of the diene complex). This is due to the fact that only the hydride trans to the Fe(CO)3 group can be removed, and the methyl substituent prevents close approach to this hydrogen. 

The latter is outside the scope of organometallic chemistry, but within the first two topics the work involved three main themes olefin and acetylene complexes, alkyl and aryl complexes, and hydride complexes. As continuous subsidiary themes throughout ran the complex chemistry of tertiary phosphines and such ligands, the nature of the trans effect, and the nature of the coordinate bond. All the work from 1947 to 1969 was carried out in the Butterwick Research Laboratories, later renamed Akers Research Laboratories, of Imperial Chemical Industries Ltd., and I am indebted to that Company and particularly to Mr. R. M. Winter, the Company s Controller of Research, and Sir Wallace Akers, its Director of Research, who in 1947, made available to me the opportunity to develop my research in my own way, in those laboratories. 

Hydride is also one of the highest Trans Effect and Trans Influence ligands. Structures of hydride complexes often show rather long M L bond lengths trans to H. H2 is a low trans effect ligand, however, and a trans H M (H2) arrangement is found in many nonclassical hydrides. 

---