Hydrido Carbonyl Clusters

High-nuclearity carbonyl clusters, 30 123-222, see also specific metal and clusters decrease in cluster nuclearity, 30 152 interstitialhydrido, NMR data, 30 168 large hydrido clusters, structure, 30 168-172... 

Another class of synthesis reaction is deprotonation of a hydrido metal carbonyl cluster on a basic surface. For example, [H4Os4(CO)i2] reacts with MgO or with y-Al203 to give [H3Os4(CO)i2], which is part of a surface ion pair on the support (Budge, Scott, and Gates, 1983). 

Reaction of Fe3(CO)12 with 3-pentyn-l-ol gives the hydrido cluster 4, formed by coupling of an allenylidene unit with a coordinated carbonyl ligand and methoxy group. In contrast, reaction with the isomeric alkyne 2-methyl-3-butyn-2-ol affords a binuclear iron complex.18 Treatment of Fe3(p3-S)2(CO)9 with Me3NO affords the vinylferrocene complex 5, whereas the similar reaction with Fe3(p3-Te)2(CO)9 gives no cluster products.19... 

These studies have Indicated that simple rhodium carbonyl complexes, e.g., mono- and binuclear species are Involved in the fragmentation and aggregation reactions of rhodium carbonyl clusters under high pressures of carbon monoxide and hydrogen. They indicate that it is possible to write formal equations for such reactions in the case of rhodium carbonyl anionic hydrido clusters (equation 25) and for the more particular situation when there are not hydrides present (equation 26)... 

The reactions of HNCC with the nucleophiles X and [NO 2] are treated separately because they may either lead to the formation of reduced species, as discussed in Section or follow the same trends as the reactions with CO and PR 3 discussed above. The outcome of the reaction seems to depend on the nature of the individual cluster considered. For example, simple addition of iodide with opening up of the metal polyhedron has been observed in the formation of [Os5C(CO)i5l] and [Os5(CO)ijH2l] (65, 76) from OssC(CO)i5 and Os5(CO)ijH2, respectively. Alternatively, reaction of this nucleophile with Rh6(CO)ig results in the formation of the substituted products [Rh6(CO)i5l] and [Rh6(CO)i4l2] (Scheme 37). In contrast, the binary carbonyls Os (CO) (m = 6, 7, 8 n = 18, 21, 23) are reduced to their respective dianions (Section II,C,2), while the hydrido clusters Os (CO) H2 (m = 6,7,8 n = 18,20,22) are deprotonated by halides (Section II,B). 

In contrast, when thiophenes react with triosmium carbonyl clusters it is C-H bond activation that occurs in preference to C-S bond cleavage. The direct reaction of [Os3(CO)i2], or the -acetonitrile complex [Os3(CO)io(NCMe)2], with thio-phene results in the oxidative addition of a C-H bond to give the exo- and endo isomers of the n, -thienyl hydrido cluster [Os3(//-H)(/z-C4H3S)(CO)io] (21a, 22a) (Scheme 7). These isomers are in rapid equilibrium at room temperature. The complex [Os3(/i-H)2(/X3-C4H2S)(CO)9] (23a) also results from his reaction, presumably by additional thermal C-H bond activation and decarbonylation of the thienyl complex. This cluster contains a triply bridging cyclic alkyne ligand related to /i3-benzyne. " ... 

Metal carbonyl clusters are also numerous. In addition to dinuclear carbonyls such as M2(CO)io (M = Mn, Tc, Re), many hydrido clusters and ionic species exist which contain three or more metal atoms [M3H3(CO)i2] (M = Mn, Tc, Re), Mn3(CO)i (linear compound, 1)4 ), and Re3(/i-H)(CO)i4 (the Re —Re —Re angle is 90°). Rhenium forms a number of tetranuclear compounds. Some of them have a butterfly structure while others adopt a triangle of rhenium atoms with one Re attached to it Re4(/i3-H)4(CO)i2, [(Re4( -H)4(CO)i3] , [Re4( -H)6(CO)i4], and [Re4(CO)i6]. Rhenium also forms mixed metal carbonyls possessing several metal atoms (Table 3.14). There are numerous clusters of the group 7 metals containing cyclopentadienyl groups, ... 

The cyclometallation of simple phenoxides can be achieved at mono- and polymetallic centres via oxidative addition pathways. The cluster carbonyl [Os3(CO)i2] initially reacts with phenol to produce the hydrido, phenoxide [Os3(/i2-H)(iU.2-OPh)(CO)ii] which on subsequent thermolysis yields the nonacarbonyl whose structural parameters are consistent with a 1,3-cyclohexadienone bonding description (Eq. 6.59).2°4... 

Retaining the theme of metal carbonyl clusters, capping considerations in transition-metal clusters have been discussed with reference to [Sb2Co4(CX))] g( A-CX))], and [Bi2Co4(CO)jQ( i-CO)]" 28. An infrared spectroscopic study of the formation of carbonyl rhodium clusters on a rhodium electrode produced by oxidation reduction cycles in acidic solution 2 has also been published. Electrochemistry with ruthenium carbonyls >21 osmium carbonyls 2 jg also reported. Muon spin rotation in a metal-cluster carbonyl compound has been communicated and, lastly, a proton spin-lattice NMR relaxation study of hydride carbonyl clusters has been reported. This provides a method for determining distances involving hydrido ligands... 

It usually occurs at the carbon atom of a linear carbonyl ligand. For example the nucleophilic attack of an OH group on a coordinated CO gives rise, via elimination, to the formation of anionic hydrido clusters ... 

In addition to the electron-precise 48e hydrido cluster anion 2, the 47e-radical anion, [Fe3(CO)nl 3, is regarded as a key intermediate in reductive transformation of nitroaromatics to anilines or their carbonylated derivatives. The radical 3 is formed via a redox disproportionation reaction upon treatment of 1 with halide (Cl, Br, I ) or pseudohalide (NCO ) in THF in contrast to the reactions of the Ru and Os derivatives, which afford the diamagnetic substituted anions, [M3(CO)io(/t-X)] Treatment of iron carbonyls such as 1 with trimethylamine iV-oxidc or... 

Interstitial hydrido, in high-nuclearity carbonyl clusters, NMR data, 30 168 Intracellular calcium-binding proteins, 46 442, 443-456... 

Several examples of direct ring phosphorus interaction with transition metals are now known [279-287]. For example, reaction of N3P3CI6 with Na2Fe2(CO)g affords a novel spirocyclic diiron octa carbonyl derivative (Scheme 25) [282, 283]. The diiron spiro derivative acts as a template for the construction of several transition metal clusters. Some of the other examples where ring phosphorus atom is involved in interaction with transition metals are summarized in Scheme 25. The ring phosphorus atoms in hydrido phos-phazenes, N3P3R4R H also coordinates to transition metals. This has been discussed in an earlier section (vide supra). 

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