The Iron Triad

The reactions of bare M ions with organic substrates in the gas phase continue to attract attention. Comparative studies across the first row transition metals have been made with nitriles 233 and halobenzenes, and trends in the M+-CH3 dissociation energy have been interpreted.35 Collisional activation of the Fe propane complex by Xe atoms has been examined,  

Adsorption of ethylene on a hydrogen-covered Fe(lOO) surface occurs without reaction at 1 lOK, but at 160K reversible insertion occurs ro give surface Fe-Et groups. These do not react with further H2, but coadsorption of CO induces reductive elimination of ethane. Similar studies with other alkenes showed that the surface alkyls formed are predominantly teiminal. 1 

The influence of pyridine binding and spin state on the spectroscopic properties and electrochemistry of aryl iron porphyrin complexes has been studied. The reduction of styrene to ethylbenzene and 2,3-diphenylbutane catalysed by [(TPP)FeCl] is proposed to proceed via a o-Fe-CHMeRi intermediate. The phthalocyanine anion Na2[FePc] reacts with ROCBr to give Na(PcFeC R] (R = Ph, Pr), and similar alkynyl anions have been prepared with a hemin-like iron centre.55 

Insertion of [Fe(CO)5] into the four-membered ring of a-pinene gave a a, allyl complex which was used for further synthesis. Alkylation of tricarbonyl iron diene and cationic dienyl complexes also gave o.ti allyl species. A o, allyl lactone complex was used to form the lactone ring in the synthesis of valilalactone, a p-lactone esterase inhibitor,and a related allyl lactam complex has been derived from prolineJ  

Reasonable yields of [FpR] complexes were obtained by reaction of RLi or RMgBr with [Fpl] or [Fp(THF)][BF4] only when R was smallJ Irradiation of [Fp Me] in the presence of dppe gave [Cp Fe(dppe)Me], which could also be prepared by sequential treatment of [FeCl2(dppe)] with Cp Li and MeLiJ The synthesis of a chiral binaphthylcyclopentadiene and its complexation as [( n5-L)Fe(CO)2Me] has been described, and the complexes [Fe(CO)2R( J., Tj5,Ti5.L)Fe(CO)2R] 

Further ab initio calculations have i peared on the geometries and dissociation energies of FeCHn and FeCHn (n = l-3).24 Condensation of ground state Fe atoms witfi allene in an argon 

The reactions of bare Fe ions and related species in the gas phase continue to attract much interest. The remote functionalisation of 1,6-hexanediol by Fe occurs by C-H activation at C(3) and C(4).26 Functionalisation of 3-methyl-2-pentanone at C(4) is diastereoselective, probably because of the conformation of a chair-like intermediate. Reactions of Fe with anisoles and phenols have also been studied.28 Interaction of Fe with silanes gives both silene and silylene species, though the two are not interconvertible. The reactions of Fe(alkene)+ complexes with pentane were found to differ dramatically from those of bare Fe , and C-H and C-C activation were also observed in reactions of Fe(C2H4) with oxygen. 0,31 interaction of Fe(benzyne)+ with alkyl halides led to C-X or C-C addition followed by p-elimination and loss of HX.32 The gas phase reaction of Fe(NH2)Me with C2H4 is best explained by insertion into the Fe-C bond followed by P-elimination and loss of propene. The reaction of FeMe with 1-octyne also leads to C-C bond forming processes. 

The energetics of the decarboxylation of [Fe(CO)4(COOH)] in the gas phase have been studied by collision induced dissociation methods contrary to previous opinion, no additional base catalyst is necessary.53 Treatment of [Fe(CO)4(COR)]- (R = long chain alkyl) with CuCl provides a high yield route to the diketones RCOCOR.54 Reaction of [HFe(CO)4] with styrene gives [Fe2(CO)8]2-and ethylbenzene, presumably via a [Fe(CO)4(CHMePh)] intermediate.55 The interaction of Na2[Fe(CO)4] with [MnMe(CO)5] or [CpMo(CO)3Me] gave [Fe(CO)4Me] and the appropriate metal carbonylate in first order processes [ReMe(CO)5] reacted only slowly, and [FpMe] not at all.56 

The dipolar addition reaction between DMAD or dimethyl maleate and the diimine species [Fe(CNR)3(Pr N=C HCH=NPr )] (R = Bu , CH2Ph, Cy, 2,6-xylyl etc.) occurs to give complexes of type (4) in the case of [Fe(CO)2(CNR)(Pr N=CHCH=NPri)] there is a competition between CO and CNR insertion into the metallacycle. Compounds containing fused pyrrole rings arc also formed which on heating release substituted 2-vinylpyrroles. -64 similar cycloaddition also occurs between [Fe(C0)3(Bu N=CHCR=0)] (R = Me, Ph) and DMAD. 5 Purther details of the insertion of alkynes into vinylketene iron tricarbonyl complexes have appeared thermolysis of the insertion products gives cyclopentenediones or phenols. - 

Complete photodissociation of [FpR] (R = Et, Pr) and their indenyl analogues in a molecular beam experiment gives species arising from -elimination and Fe-alkyl bond homolysis the ratio of the two processes is similar for Cp and indenyl, showing that ring-slippage is not important., 76 

The dialkyl-iron complexes cis-[FeMe (dmpe) J cis-[FeMeo (dmpm) t trans-[Fe (Bz) (dmpm) 2 6 4 2 2  

The methyliron complexes [Fe(CO)2 (I) (Me) (pdiipl.l [pdmp = o-phenylenebis(dimethylphosphine)] and fac-[Fe(CO) Me(CO) have been prepared from the acyl complex [Fe(CO)2 C(0)Me (I)(pdmp)] 

The reactions of a variety of alkylmetal carbonyl complexes, including [Fe(Cp)(00)2(Me)] and [Os(CO) (Me)2 , with various metal hydrides (such as [ReH(CO) ], [OsH2(CO) ], [MnH(CO)g], and [WH(CO)2(Cp)]) have been shown to lead to dinuclear complexes or polynuclear hydrides with the organic products eliminated usually being aldehydes although alkane elimination is also seen.  

The synthesis of a number of 6-co-ordinate nitrosyl alkyl-and aryl-iron porphyrin complexes, and their electrochemical 

Syntheses and 5C-ray crystal structures of a number of carbido cluster complexes containing iron have been reported. Such com- 

1 The Iron Triad. - Quantum mechanical calculations have suggested that it should be possible to synthesise the complex [Fe(CO)4C] if the carbon ligand is stabilised by a Lewis Acid such as Addition of TMSOTf and Bu NBr to 

Several reports on the synthesis and reactivity of complexes containing metal-aryl bonds have appeared. Thus, reaction of the N,A-dimethylbenzylamine complex [Ru(Cl)(C6H4CH2NMe2)(riCC6H6)] with ethylene affords 2-vinyl-AT,N-dimethylbenzylamine and [Ru(Cl)(MeCH2C6H4CH2NMe2)(ri -C6H6)] (formed 

A series of vinylidene and allenylidene complexes have been synthesised from reaction of [tnpodCpL2RuCl], tripodCph2 = MeC(CH2-r -C5H4)(CH2-r -PPh2)2, with terminal alkynes and the barrier to rotation about the Ru-C bond of the vinylidene species measured using P NMR spectroscopy. Addition of D2O to either the cyclohexenylvinylidene species [Ru(PNP)Cl2 C = CH(C = CHCH2CH2CH2CH2) ] or the vinylvinylidene complex [Ru(PNP)Cl2 C = CHC(R) = CH2 ] [R = Me, Ph PNP 

C = CH(C02Me) (ri -C5H5)2]. The molecular quadratic and cubic optical non- 

Complexes 15 and 16 containing a,a-(diphenylphosphino)allyl ligands are formed from thermolysis of the corresponding allyl species 14, whereas, heating 17 affords the hexa-l,3,5-triene-2,6-diyl complex 18.  

2 Metal Carbon o-Bonds Involving Group 8,9, and 10 Metals 2.1 The Iron Triad 

The crystal structure of [PPN][Fe(C0)4 CH(Me)C02Et)], formed by insertion of ethyl acrylate into [HFe(CO)4] , has been published. Reaction of [Fe(CO)4]2- with the acetylide cluster 

The synthesis and crystal structures of [Cr(CO)3(ri6-arene)] complexes where arene = Fp Ph, (ii-C9H7)Fe(CO)2Ph, and Fp(p-tol) have been described in each case the Fp units are bent away from the chromium primarily because of electronic factors. Aryl complexes with one or more Fp 

The syntheris, diermal behaviour, and electrochemistry of [Fp(CO(CX2)3CX Fp] QC = H, F) have been reported. The redox-catalysed carbcmylation of [CpFe(CX))CL)(Me)] (L = various phosphines) in MeCN is prtqtosed to involved n d formation of [CpFe(L)(NCMe)(COMe)] then rate-limiting reaction widi The crystal structure and molecular mechanics of 

The first example of Me to CO conversion is achieved by reaction of [Ru(OEP)Me] with the TEMPO radical trap, leading to [Ru(OEP)(CO)].141 The complex [Ru(OEP)Me2] undergoes le oxidation and reduction with NaCioHg and Ag+ respectively one equivalent of Ag+ produces [Ru(OEP-p.-CH2)Me] with a CH2 group bridging the Ru and a porphyrin nitrogen. 142 Electrochemistry of [Ru(OEP)At2] (Ar = X = H, OMe, Cl, F) showed that the cation 

CoCH with aliphatic alkanes and cyclic hydrocarbons 

Metallacyclo-hexanes and -heptanes have also been made, and their 

Photoreversible oxidative reductive elimination reactions have been described for 

A convenient synthesis of a ferracyclopentane complex involves the reaction of [Pe(CO).] with tetramethylenebis(trifluoro- 

The chemistry of organoiron complexes derived from the com-plexation of vinyl ethers with [Fe (Cp) (CO) 2 I , in which the 

Evans and C. J. Newell, Inorg. Chim. Acta, 1978, 31, L387. 

1-Methyl-1-siiacyclobutane reacts with [FeaCCO) ] to give the complexes (10) and (11)- The cationic complex formed by the reaction of [Fe(CNMe)e] + with acetamidine has been shown by A -ray diffraction methods to possess the structure (12).  

Carbon-13 studies on the carbon dioxide bridged complex anion [(OQioHOs,-Cw-C02)0se(C0)i7] , prepared by treatment of the anion [OssH(CO)ii] with [Ose(CO)is], establish that the carbon of the CO2 bridge originates from the [Os (CO)i8]. Carbido complexes [Os6C(HKOP(OMe)OP(OMe)aKCO)i83 (20) and [Os6C(HXOP(OMe)J(CO)iJ (21) obtained by the pyrolysis of [Os8(CO)n- 

A kinetic study of migratoiy ins on of [Fe(T) -C9H7XCO)2(R)] induced by pho hines has been carried out to distinguish structural and electronic parameters  

The energetics of propane C-H and C-C activation by gas phase Fe+ and Ni+ has been investigated and suggested initial C-H insertion.22 An ion cyclotron resonance study of remote C-H bond activation in aliphatic nitriles by [FeMe]+ shows end on nitrogen coordination and activation of the (0, (w-l), and (o)-2) positions.23 

Protonation of [Ru(Ti -C5Me5)]2(n-OMe)2 with triflic acid and reaction with 2-chlorocyclo-hexanol in refluxing THF produced green crystals of [Ru(ii -C5Me5)]3(ti2-Cl)2( i2-CO)(p3-CCl) 2+ as the triflate salt in 80% yield.26 [Ru(ri5-C5Me5)(NO)(Me)2] reacts with a tetraarylboronic acid in 

Reaction of trans, rraru-[Ru(Cl)2(PBu3)2(CO)2] widi Me3Sn(MT h produces the bisfacetylide) while the use of the reagents Me3SnOC-R-OCSnMe3 where R is a phenyl or Inphenyl spacer 

Surface bound ethylidene groups have been modelled in an infrared study by inter aUa, 

Manotti Lanfredi, and A. Tiripicchio, Inorg. Chim. Acta, 1980, 42, 255. 2 C. Jangala, E. Rosenberg, D. Skinner, S. Aime. L. Milone, and E. Sappa, Inorg. Chem., 1980, 19, 1571. 

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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. 

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... 

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 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." ... 

Among the iron triad metals most complexes are iron Tc-allyl adducts from dienes. This may be fortuitous or owing to an electronic property of the heavier elements. The ruthenium diene complex XXIXa shows no tendency to undergo insertion s, but the origin of this may be steric, as indicated by the protonation of (CO)3Ru(butadiene), which goes via complex XXIXb and yields XXXa S ... 

The reactivity of tungstenocene, W(Cp- 7 )2 , is similar to that observed for zero-valent alkyl phosphine complexes of the iron triad. Generation of tungstenocene in aromatic solvents gives aryl hydrides in moderate to good yields. The various routes to the coordinatively unsaturated intermediate include photolysis of W(Cp-> )2H2 or W(Cp- 7 )2CO, removal of H2 from W(Cp->/ )2H2 by hydrogenation of a diene or thermolysis of alkyl hydrides, W(Cp-j/ )2HR °. 

S.4.3 Reactions of propargyl alcohols with metal carbonyl clusters of the iron triad... 

There are numerous /i4-carbide- and nitride-containing clusters examples from the iron-triad include [M4C(CO)i3] (M = Fe, and [M4N(CO)i2] (M = Fe,... 

The metal clusters of the iron triad M3(CO)i2, 4 M = Fe, 5 M = Ru, and 6 M = Os, despite being some of the simplest carbonyl clusters known, are fascinating molecules, which still present interesting structural and dynamic problems. Because of their simplicity, they have been, and indeed remain, archetypal molecules for discussions on fluxional mechanisms. The two heavier congeners 5 and 6 have a clearer and less complicated history. In the solid state they are isostructural, and possess... 

Group IVI3 derivatives of the iron triad carbonyls. A. Bonnv, Coord. Chem. Rev., 1978, 25,... 

Bonny, A., Group IVB Derivatives of the Iron Triad Carbonyls, Coord. Chem. Rev. 25 [1978] 229/73. 

Metallocenes of the iron triad and some other cuclopentadienyl complexes undergo metallation reactions of the ring and therefore show aromatic properties as in the acylation reactions. Both metallation and acylation occur more easily than in the case of benzene. 

Spectroscopic studies on metal carbonyl complexes were relatively abundant in 1993. They include Iridium carbonyl complexes investigated via NMR O NMR studies on (mesitylene)M CO)3 complexes (M = Cr, Mo, W) an interesting NMR method for optimizing the study of slow chemical exchange has been announced natural abundance 0 NMR spectra of metal carbonyl clusters of the iron triad . 

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