Iron triad

Called the Iron Triad on the periodic chart, the elements are ... 

These six metals located beneath the iron triad on the periodic chart are very much alike. The first three are called the light platinum triad. The heavy platinum triad includes the other two and platinum itself. They are usually found together in nature and are used for similar things. All are shiny and beautiful and they do not tarnish or rust. 

The compounds MOs3(CO)i3H3 (M = Mn, Re) are clearly analogous to the carbonyl hydrides of the iron triad and are more conveniently discussed in the next section. 

Whereas, plahnum complexes are used predominantly as efficient catalysts in the hydrosilylation of carbon-carbon mulhple bonds, cobalt and iron triad complexes play a cmcial role in the catalysis of other processes, such as the hydrosi-lylahon of C=0 and C=N, dehydrogenative silylation, sUylcarbonylahon, and silylation with vinylsilanes and disilanes. 

The earliest examples were provided by the work of Stone et al. on reactions of zero-valent Pt complexes with carbonyls of the iron triad (10,36,37). Thus... 

Exclusive formation of silylstyrenes 76 is achieved when the reactions of styrene and 4-substituted styrenes with HSiEt3 are catalyzed by Fe3(CO)i2 or Fe2(CO)9100. Other iron-triad metal carbonyl clusters, Ru3(CO)i2 and Os3(CO)i2, are also highly active catalysts, but a trace amount of hydrosilylation product 77 is detected in the Ru-catalyzed reactions and the Os-catalyzed reactions are accompanied by 3-12% of 77 (equation 31)100. Mononuclear iron carbonyl, Fe(CO)5, is found to be inactive in this reaction100. 

In 1993, Murai s group examined the effectiveness of the iron-triad carbonyl complexes Fe(CO)5, Fe2(CO)9 and Fe3(CO)12 as catalysts for the reaction of styrene with triethylsilane [47]. Whereas Fe(CO)5 showed no catalytic activity, Fe2(CO)9 and Fe3(CO)12 formed selectively P-silylstyrene 57a and ethylbenzene 58. Interestingly, Fe3(CO)12 is the catalyst that exhibited the highest selectivity. This trinuclear iron carbonyl catalyst was also successfully applied in the reaction of different para-substituted styrenes with Et3SiH giving only the (E)-P-triethylstyrenes in 66-70% yield (Scheme 4.23). 

The reaction of carbonylmetalates with trinuclear clusters provides, in many cases, a convenient synthesis of tetranuclear clusters. This reaction was first explored by Knight and Mays (105, 106), who allowed [Mn(CO)5] and [Re(CO)5] to react with trimeric clusters of the iron triad. A summary of the products that they obtained on using Os3(CO)12 as the starting trimer is shown in Scheme 3. Of particular mechanistic... 

An extension of this category should include the mixed pseudohalogen X—HgX. Thus in the iron triad, cationic products have been prepared with mercuric chloride. 

The stannylene SnR2[R = CH(SiMe3)2] reacts in different ways with the three dode-cacarbonyls of the iron triad, M3(CO)i2(M = Fe, Ru, Os). A diiron product and a planar pentametallic triruthenium product are formed (equations 129 and 130). The osmium carbonyl did not react264. 

Kinetic studies have shown that electrophilicity in the iron triad is strongly metal dependent with Fe Ru, Os, and the nucleophilic reactivity order is PPh3 > P(0-tBu)3. Adducts 237 (PR3 = phosphites) react with water to give the cyclohexadienyl phosphonate complexes 239. Complex 235 is a effective catalyst for the conversion of phosphites to HP(0)(0R)2 (99,146,147) [Eq. (29)]. In a similar fashion, benzene ruthenium dications... 

Clusters based on homonuclear trimetal units are dominated by those containing transition metals from the iron triad. Clusters constructed on a Co3 framework are the only additional examples in this section. The first cluster to be reported was Co3(CO)9BNEt3 (22). This arises from the reaction of [Co(CO)4] with BBr3 in the presence of NEt3 and is clearly related to the triosmium systems of Shore et al. discussed above (Fig. 7)... 

Interestingly, the only example of oxidative cluster aggregation in the iron triad is the formation of [Ru6(CO)i8H] in the reaction of [Ru3(CO)nH] with mineral acids (31). 

More recent work with nitrido clusters within the iron triad revealed chemical shifts in the expected region. For instance, [Ru6N(CO),6] appears at 538 ppm (NH4 ) 91) which can be compared to the carbon resonance of [Ru6C(CO),6] which is at 461.2 ppm (CH4) 112). Although the value is not twice as large as it is at least larger than the carbon resonance. Of the approximately 15 compounds measured, a range from —450 to —620 ppm is observed. Because many of the compounds are closely related some useful trends have appeared. 

Group VIII Fe, Ru, Os. Five-coordinated complexes of the iron triad metals M(0) and M(I) undergo oxidative addition with alkyl, aryl and acyl halides to give 6-... 

A good general review of group IVB-iron triad species is A. Bonny, Coord. Chem Rev., 25, 229 (1978). 

A series of osmium carbonyl complexes have been prepared by the reaction of OsO-with CO or decomposition of Os3(CO)i2 [226] and a mononuclear homoleptic osmium carbonyl complex, Os(CO)5, is also known. It is a volatile, colorless liquid and is the most robust M(CO)5 type complex of the iron triad against both oxidation and heat but it gradually loses CO to form Os3(CO)i2. Multinuclear osmium carbonyl clusters such as Os3(CO),2, Os5(CO)i6, Os5(CO)i9, Os6(CO)ig, 087(00)2, and OsgfCO).. have also been reported [227]. In this section, several carbonyl complexes based on Os3(CO)j2are described. 

The Iron Triad, Platinum Group, and Coinage Metals... 

The nearly identical atomic radii of the iron triad—iron, cobalt, and nickel —help explain the similar chemistry of these three elements. The similarities among the platinum group elements in Periods 5 and 6 emphasize the fact that there is little difference between the atomic radii of the elements in these periods in which inner d orbitals are being filled. The coinage metals show the expected similarity among elements in the same group. 

The mechanism of cooperativity has also been probed by the substitution of other metalloporphyrins into the globin for example, zinc porphyrins have been used for their excited triplet-state properties,"" manganese porphyrins for their EPR activity, and ruthenium porphyrins as a member of the iron triad." ... 

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