Carbonyl hydride

The other ligands in a hydrido compound also influence the polarity of the M — H bond. The hydrogen atom may be bound as a terminal, bridging, or ligand  

Compounds of this type include [Co6H(CO)i5] (t=—13.2), [Nii2H(CO)2i]  

---

Covalent. Formed by most of the non-metals and transition metals. This class includes such diverse compounds as methane, CH4 and iron carbonyl hydride, H2Fe(CO)4. In many compounds the hydrogen atoms act as bridges. Where there are more than one hydride sites there is often hydrogen exchange between the sites. Hydrogens may be inside metal clusters. 

Remarkably few examples of this type of ring construction are available. The cobalt carbonyl hydride catalyzed hydroformylation of A/,A/ -diallylcarbamates has provided 3-pyrrolidinones (Scheme 61a) (81JOC4433). The pyrrole synthesis shown in Scheme 61b depends on Michael addition of ethyl a-lithioisocyanoacetate to ethyl a-isocyanocrotonate (77LA1174). 

Reduction of the pH of solutions of carbonylate anions yields a variety of protonated species and, from acid solutions, carbonyl hydrides such as the unstable, gaseous H2Fe(CO)4 and the polymeric liquids H2Fe2(CO)g and H2Fe3(CO)n are liberated. The use of ligand-replacement reactions to yield hydrides of higher nuclearity has already been noted. 

Carbonyl hydrides and carbonylate anions are obtained by reducing neutral carbonyls, as mentioned above, and in addition to mononuclear metal anions, anionic species of very high nuclearity have been obtained, often by thermolysis. These are especially numerous for Rh and in certain Rh, Rh and Rhi5 anions have structures conveniently visualized either as polyhedra encapsulating further metal atoms, or alternatively as arrays of metal atoms forming portions of hexagonal close packed or body... 

This also includes the decomposition of the more complex carbonyls such as the carbonyl hydrides and nytrosylcarbonyls. 

Reaction of Carbonyl Hydrides with Complexes of Group-IB. 

S.3.2.2.2. Reaction of Carbonyl Hydrides with Complexes of Group-IB Metals. 

Carbonyl hydrides react similarly with derivatives of Zn or Cd e.g., MnfCOIjH and MEt, (M = Zn, Cd) react on warming to give compounds containing Mn—M... 

On irradiation it is converted to the cobalt carbonyl hydride 8, as discussed above. The hydride then reacts with the olefin in a reaction sequence containing only thermal steps /10/. 

Some reactions of carbonyl hydrides will be illustrated in Chapter 22. Such species are involved in catalytic processes in which metal carbonyls function as hydrogenation catalysts. Generally carbonyl hydrides are obtained by acidifying solutions containing the corresponding carbonylate anion or by the reactions of metal carbonyls with hydrogen. The following reactions illustrate these processes ... 

In general, the carbonyl hydrides are slightly acidic, as is illustrated by the behavior of H2Fe(CO)4. 

A few metal carbonyl hydrides can be prepared by direct reaction of the metal with CO and H2, with the following being a typical reaction ... 

We have previously mentioned the class of compounds known as the carbonyl hydrides and now... 

Other carbonyl hydrides include H2Fe(CO)4, H2Fe3(CO)11( and HCo(CO)4. 

Some carbonyl hydrides, such as Cr2(CO)ml l, have the hydrogen atom in bridging positions as shown in the structure... 

Two hydrogen bridges are present in some carbonyl hydride complexes. This is illustrated by the structure of the [H2W2(CO)8]2 anion,... 

Many research groups have attributed the isomerization to a series of additions and eliminations of a cobalt carbonyl hydride. However, it has been shown that aldehydes may be found with formyl groups attached to a carbon atom other than the two of the double bond even under non-isomerizing conditions. Piacenti and co-workers (44, 45) studied the hydroformylation of [l-14C]propylene and of a>-deuterated a-olefins. Even for a-olefins with chain lengths up to C6, the formyl group was attached to all possible carbon atoms in the product mixture. However, in the deuterated experiments, deuterium was present only on carbons 2, 3, and a) of the resulting aldehydes. These results were explained by pro-... 

These effects of phosphines are explained by observing that the more strongly basic phosphines will dissociate to the least extent in solution (55, 56), Eqs. (26)-(27). The unsubstituted cobalt carbonyl hydride gives... 

---