Iron complexes cluster hydride

The synthetic methods used involve reaction of a cluster anion with [AuCIL], elimination of methane between a cluster hydride and [AuMeL] or addition of LAu+ units to metal-metal bonds. The emphasis here will be on structure and reactions of the complexes. Some examples of mixed gold clusters are given in Table 15, where it can be seen that most work has been on derivatives of clusters of iron, ruthenium and osmium. 

FeFe-enzyme - proton or hydrogen substrate binding and also the hydride-proton reaction exclusively occurs at the iron distal to the [4Fe-4S] cluster, suggesting that mononuclear iron complexes might also be viable catalysts. Consequently, Ott and coworkers have synthesized and characterized some stable pentacoordinated Fe(II) complexes with five ligands that nicely mimic the native ones and exhibit an open coordination site [163, 164]. This approach avoids the formation of the less reactive bridging hydrides that are found in the dinuclear complexes [153]. Catalytic H2 formation from weak acids at low overpotentials with promising TOF and catalyst stability could be demonstrated [164]. 

Some analogous rathenium- and osmium-bismuth clusters have been found. Examples include Bi2M3(CO)9 and H3BiM3(CO)9 (M = Ru, Os). The stmctures of the hydride compounds have both been determined and they are isostractural with the iron complexes as is Bi2Ru3(CO)9 withBi2Fe3(CO)9. The structure 0fBi2Os3(CO)9, on the other hand, has not been determined and its IR spectrum indicates that it probably has a different structure. A spirocyclic cluster [Ru2(CO)8(/X4-Bi)Ru3(CO)io(/x-Ft)] (39) has been reported. 

A similar reaction can be written for the [Fe] hydrogenases with a Fe-[4Fe-4S] complex replacing the nickel. Note that the nickel atom in the NiFe cluster, and the Fe-[4Fe-4S] sites are nearest to the electron carrier [4Fe-4S] clusters, indicating that electron transfer occurs through these atoms. The other atom in each of the centres is an iron atom with -CN and -CO ligands, and it seems likely that this is a binding site for hydride (Fig. 8.1). 

Heterometal alkoxide precursors, for ceramics, 12, 60-61 Heterometal chalcogenides, synthesis, 12, 62 Heterometal cubanes, as metal-organic precursor, 12, 39 Heterometallic alkenes, with platinum, 8, 639 Heterometallic alkynes, with platinum, models, 8, 650 Heterometallic clusters as heterogeneous catalyst precursors, 12, 767 in homogeneous catalysis, 12, 761 with Ni—M and Ni-C cr-bonded complexes, 8, 115 Heterometallic complexes with arene chromium carbonyls, 5, 259 bridged chromium isonitriles, 5, 274 with cyclopentadienyl hydride niobium moieties, 5, 72 with ruthenium—osmium, overview, 6, 1045—1116 with tungsten carbonyls, 5, 702 Heterometallic dimers, palladium complexes, 8, 210 Heterometallic iron-containing compounds cluster compounds, 6, 331 dinuclear compounds, 6, 319 overview, 6, 319-352... 

It should be clear from the discussion of Section 2 that all of these clusters can be unstable with respect to cluster degradation in the presence of Lewis bases with the formation of saturated fragment species (see Boron Hydrides and Polynuclear Organometallic Cluster Complexes). Thus, in the presence of an excess of phosphine, the reaction of [HFe3(CO)9(/u-H)2BH] changes from that shown in equation (10) to that shown in equation (12). The mononuclear boron and iron products demonstrate that both transition metal and main group element vertices are removed by base and the cluster is degraded. ... 

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