Hieber-type reaction

A further novel method for demetallation provides even higher yields. Hieber-type reaction of the tricarbonyl(ri4-cydopentadienone)iron complex with sodium hydroxide to the corresponding hydride complex followed by ligand exchange with iodo-pentane affords an intermediate iodoiron complex, which is readily demetallated in the presence of air and daylight at room temperature (Scheme 1.4) [9]. Combining steps a-c in a one-pot procedure without isolation of the intermediate hydride complex gave yields of up to 98%. 

Scheme 4-6. Demetalation of tricarbonyl(cyclohexadienone)iron complexes based on Hieber-type reaction.

The first step is likely to be a so-called Hieber base reaction (0 in Scheme 1), describing a nucleophilic attack at metal-coordinated carbon monoxide by hydroxide. While eq. (3) is the prototypical example as first reported by Walter Hieber in 1932 [5], several other variants have since become known. For example, azides and alkyl/aryl anions attack metal carbonyls according to eqs. (4) and (5), yielding metal isocyanates (via a Curtius-type azide degradation step) and metal carbenes, respectively [6, 7]. 

In contrast to group 14, 15, and 16 elements, which have been introduced in a number of cases as naked mgms or elements, usage of bare group 13 metals for the preparation of mixed group 13/tm complexes is not widespread. Nevertheless, as early as in 1942, Hieber showed that bulk group 13 metals and a finely divided tm can be combined directly together in the presence of CO to form mixed mgm/Co clusters (mgm = Ga, In, Tl). These compounds represent the first examples of this reaction type. 

Another area of major interest in the field is that of mixed metal cluster systems. Hieber very early in the study of metal carbonyl chemistry was able to prepare mercury complexes of the type Fe(CO)4(HgCl)2. The related gold ° compounds were prepared in the 1960s by reaction of phosphine gold halides with carbonyl anions. 

The related reactions between Lewis bases, especially amines, and various metal carbonyl derivatives have been utilized largely by Hieber and coworkers to prepare a variety of metal carbonyl anions. Examples of reactions of this type are illustrated by the following equations ... 

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