Hydrides, complex

The use of isotopic substitution to detennine stmctures relies on the assumption that different isotopomers have the same stmcture. This is not nearly as reliable for Van der Waals complexes as for chemically bound molecules. In particular, substituting D for H in a hydride complex can often change the amplitudes of bending vibrations substantially under such circumstances, the idea that the complex has a single stmcture is no longer appropriate and it is necessary to think instead of motion on the complete potential energy surface a well defined equilibrium stmcture may still exist, but knowledge of it does not constitute an adequate description of the complex. 

Finally, selective hydrogenation of the olefinic bond in mesityl oxide is conducted over a fixed-bed catalyst in either the Hquid or vapor phase. In the hquid phase the reaction takes place at 150°C and 0.69 MPa, in the vapor phase the reaction can be conducted at atmospheric pressure and temperatures of 150—170°C. The reaction is highly exothermic and yields 8.37 kJ/mol (65). To prevent temperature mnaways and obtain high selectivity, the conversion per pass is limited in the Hquid phase, and in the vapor phase inert gases often are used to dilute the reactants. The catalysts employed in both vapor- and Hquid-phase processes include nickel (66—76), palladium (77—79), copper (80,81), and rhodium hydride complexes (82). Complete conversion of mesityl oxide can be obtained at selectivities of 95—98%. 

Reduction of tosylhydrazone derivatives to the corresponding methylene analogs with metal hydride complexes provides an excellent solution to this problem. Soon after the discovery of this reaction it was recognized... 

Reaction of metal hydride complexes with N-nitrosoamides, e.g. Af-methyl-7V-nitrosourea ... 

Figure 2.68 Bond lengths in two 5-coordinate rhodium hydride complexes with bulky tertiary...

In synthesis (b), the initial product is a 5-coordinate (sp) iridium(III) hydride complex, which is rapidly oxidized in solution to the planar iridium(II) complex. Both of the compounds are paramagnetic with one unpaired electron, as expected for square planar d7 complexes. 

Hydride complexes are especially well characterized and important for iridium(III), with typical general formulae IrHX2L3, IrH2XL3, IrH3L3and IrH4L3". They are frequently readily interconvertible, as shown in Figure 2.85 for some diethylphenylphosphine complexes [156]. 

Recently two rare paramagnetic iridium(IV) hydride complexes have been reported [172]. 

One and, sometimes, two hydrogen atoms can be introduced into hydride complexes [98], A variety of synthetic routes has been utilized, using methods... 

---