Hieber complex

Although this catalytic reaction appeared to be of synthetic interest, it has since then neither been applied in synthesis nor further developed. This might be attributed in part to problems with reproducibility and catalyst stability under the reaction conditions, although the Hieber complex was used in a stoichiometric manner for the preparation of a variety of 7i-allyl-Fe complexes. These latter compounds served as starting materials for a plethora of subsequent reactions [34]. The results obtained by Nakanishi and coworkers on the stability and reactivity of n-allyl-Fe-nitrosyl complexes proved such intermediates to be reactive towards a variety of nucleophiles however, the Fe complexes formed upon nucleophilic substitution were catalytically inactive. Hence, in order to maintain the catalytic activity, the formation of intermediate 7i-allyl-Fe complexes had to be circumvented. About 3 years ago we started our research in this field and envisioned the use of a monodentate ligand to be a suitable way to stabilize the proposed catalytically active G-allyl complex. The replacement of one CO by a non-volatile basic ligand was thought to prevent the formation of the catalytically inactive 7t-allyl-Fe complex (Scheme 7.21). 

First hydrido complex of a transition metal prepared by W. Hieber and F. Leutert. 

In 1931, Hieber and Leutert reported Fe(CO)4(H)2 not only as the first iron hydride complex but also as the first transition-metal hydride complex (FeH2 was reported in 1929 from FeCl2 and PhMgBr under a hydrogen atmosphere. However, it exists only in a gas phase) [2, 3]. The complex synthesized from Fe(CO)5 and OH (Scheme 1) is isolable only at low temperature and decomposes at room temperature into Fe(CO)5, Fe(CO)3, and H2. 

Apart from this mechanistic hypothesis, another scenario, with a ferrate complex as intermediate, may be possible. In 1928, Hieber discovered that Fe(CO)5 78 underwent a disproportionation in the presence of ethylenediamine 122 [97-101]. Depending on the reaction temperature, different ferrate complexes were formed that incorporated a [Fe(en)3] cation (en = ethylenediamine) and mono-, di- or trinuclear ferrate anions (Scheme 32) [102-107]. As the reaction discussed above is also performed with amines at high temperatures, these ferrates may well be involved in the catalytic cycle of the carbonylation discussed above. 

Nickel tetracarbonyl may be prepared in the laboratory by the Hieber process, a disproportion reaction of several nickel compounds of organic thio acids, such as nickel(II) phenyldithiocarbamate, (CeHs— NH—C(=S)—S)2Ni, with carbon monoxide under controlled conditions. In such disproportionation reactions, the divalent nickel ion converts to a tetravalent nickel complex (Hieber. H. 1952. Z.anorg.Chem., 269, pp. 28). The overall reaction is ... 

Hieber and coworkers first prepared the pentacarbonyl hydride complex of rhenium1 by protonation of the corresponding pentacarbonyl anion, [Re(CO)5] . Modified versions of the original syntheses have been reported,2 but these procedures still require extensive vacuum-line manipulations. Furthermore, the yield of ReH(CO)s is only 30% based on pure Na[Re(CO)s],1,3 which means that the overall yield from Re2(CO)i0 is much lower. 

Studies of complexes involving cobalt have a long history a report by Hieber in 1942 (34) described the syntheses of [E Co(CO)4 3] (24, E = Ga 25, E = In 26, E = Tl) from the respective Group 13 metal, cobalt metal, and CO under high pressures. Later work by Graham (5J) described the syntheses... 

Finally, we note a number of higher nuclearity iron-containing clusters. Hieber (74) reported a complex formulated as [Sn2Fe5(CO)2o], 62, although no structural details were presented. Hieber also described a complex formulated as [PbFe3(CO)12], but later work by Whitmire (71) indicates that this compound is probably the tetrairon species, 56. Mackay and Nicholson (75) have described the synthesis and structures of three polynuclear species [Fe2(CO)7 //-E(Fe2(CO)8) 2] (63, E = Ge 64, E = Sn) and [Fe3(CO)10- //-Ge(Fe2(CO)8) 2], 65, from reactions involving germanium or tin... 

Anionic clusters are good nucleophiles (see Section III,A) and are often easy to make. On the other hand, the electrophilic nature of most monometallic complexes is obvious from ligand substitutions. The combination of these properties makes a strategy for cluster expansion. This strategy was used for the first time by Hieber (130) in making Fe4(CO)fc from Fe3(CO),7 and Fe(CO)s. It is probably active in many syntheses of large metal carbonyl clusters because the Re, Os, Rh, Ir, Ni, and Pt clusters involved are almost always anionic. However, simple stoichiometries can rarely be written for such reactions (122). This route makes mixed metal clusters accessible, e.g.,... 

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%. 

The structures of the isoelectronic hydridocarbonyls H2Fe(CO)4 and HCo(CO)4 were the central theme of numerous studies over a period of many years after their discovery by Hieber. Because of their very similar physical characteristics, these complexes were considered to be pseudo nickel tetracarbonyls (H2Fe = HCo = Ni) in which, even then, the... 

The chemistry of the metal carbonyl hydrides and metal carbonylates remained the principal research topic for Hieber until the 1960s. He mentioned in his account [25], that it was a particular pleasure for him that in his laboratory the first hydrido carbonyl complexes of the manganese group, HMn(CO)5 and HRe(CO)5, were prepared by careful addition of concentrated phosphoric acid to solid samples of the sodium salts of the [M(CO)5] anions, giving the highly volatile hydrido derivatives in nearly quantitative yield [45, 46]. In contrast to HCo(CO)4 and its rhodium and iridium analogues, the pentacarbonyl hydrido compounds of manganese and rhenium are thermally remarkably stable, and in... 

In the last three decades of the twentieth century, following Walter Hieber s retirement, four aspects of the research on mono- and polynuclear metal carbonyl complexes found particular attention. These were the preparation of highly reduced carbonyl metallate anions, the generation of stable metal carbonyl cations, the matrix isolation of uncharged metal carbonyls obeying or not the 18-electron rule and, last but not least, the giant metal carbonyl clusters. 

There are several examples of iron(I) complexes in which the +1 oxidation state is stabilized by coordination of carbon monoxide or arsine ligands. In an early paper217 Hieber and Lagally... 

The first complexes to be made, by W. Hieber in the 1930s, were HCo(CO)4 and H2Fe(CO)4, but their structures and the nature of the M—H bond were not known... 

Controlled reduction of carbonyls often leads to dinuclear compounds. This may involve attack by the reduced species on the umeacted starting material. The complex chemistry of iron carbonyls, going back to the pioneering work of Hieber and Hein, is a good example (equation 46). 

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