Iron. Ruthenium, and Osmium

The iron carbene complex (ri -CsHs) Fe(CO)(CH2) generated by the electron impact from (Ti -C5H5)Fe(C0)2CH20CH3 in the gas phase was fotmd to react with cyclohexene or n-donor bases such as NH3, CH3CN, or CD3CDO by displacement of ketene from the iron center (reaction 8.25). Methylene-carbon monoxide coupling was assumed to occur in the coordination sphere of iron during the reaction [51]. 

The formation of methyl acetate in up to 75% yield was observed in a stoichiometric reaction of methanol with the methylene-bridged complex Fe2(p-CH2)(CO)g (reaction 8.26). By coupling p-methylene with carbon monoxide to form a ketene-bridged intermediate in the reaction was postulated [52]. 

The vinylketene complex 5 was shown to undergo reversible loss of carbon monoxide to form vinylcarbene complex 6 (reaction 8.27) [53]. 

The formation of a stable (rj -C.G) ketene compound [(ri -CsHs) (C0)2Fe (CH2=C=0)][PF6 ] by carbonylation of an iron-methylidene complex ](ri -C5H5)(CO)2Fe+=CH2)][PF6 ] at 25 °C and 6 bar carbon monoxide pressure was described. Carbon-13 labeling study has shown that the electrophilic methylidene ligand picks up exogenous carbon monoxide and not a coordinated one [54]. 

The interconversion of methylene and ketene ligands on a triosmium duster was reported. It was found that a triosmium methylene complex in CH2CI2 solution readily adds two moles of carbon monoxide at 22 °C to yield the ketene derivative 9 (reaction 8.29). The formation of the ketene complex 9 from the methylene complex can be made reversible by heating under reduced pressure. Labeling experiments have shown that the ketene carbonyl derives from one of the initial Os3(CO)ii(p-CH2) carbonyl ligands and not from the added CO. This implies a preequilibrium between Os3(CO)xi(p-CH2) and a coordinatively unsaturated ketene complex that subsequently adds two moles of carbon monoxide to give the isolated product 9 [57,58], 

Mg2FeHfi and Mg2FeDg gave assignments (FeDg ) these are listed in Table 6.  

IR data have been reported for the reaction products of iron atoms with N2 and O2, trapped in low-temperature matrices. [ Fe(N3)(Pc ) 2( i-N)] has VasFeNFe at 997 cm (IR) and VjFeNFe at 478 cm (resonance Raman) vFe- 

Resonance Raman studies on vFe-His modes have been used to characterise a number of haem-containing systems. The resonance Raman spectra of deoxy- and oxy-complexes of o-substituted tetraphenyl and tetranaphthyl porphyrinato iron(II) derivatives with covalently linked proximal histidine show vFe-N(imidazole) in the range 201-223 cm k The dioxygen adducts have vFe-O2 modes at high wavenumbers (near 580 cm ), suggesting a decreased Fe-O-O angle.The resonance Raman spectra of the Fe(II) and Fe(III) forms of pea cytosolic ascorbate peroxidase both show two bands due to vFe-N(imidazole).  

The inelastic neutron scattering, IR and Raman spectra of the potassium salt of [FeCl5(H20)] gave the vibrational assignments shown in Table 

TR measurements on the reaction of O2 with mixed-valence cytochrome c oxidase gave evidence for the formation of a haem 3 oxoferryl, Fe =0, species. Raman data on the Fe-OH unit of ferric forms of two deletion derivatives of Rhizobium meliloti FixL showed that both high- and low-spin states were present. These had vFe-OH at 479, 539 cm respectively.  

Vinylic complexes of iron have been prepared by displacement of vinylic fluorine from perfluorocyclopentene to give (17), or of chlorine from what was thought to be 3,4-dichlorotetrafluorocyclobutene, but was in fact 

2-dichlorotetrafluorocyclobutene (arising from the presence of a large proportion of CF tCClj in the dichlorodifluoroethylene used to prepare the cyclobutene), to give (18). With triphenylphosphine, one carbonyl group of (18) was displaced. Authentic 3,4-dichlorotetrafluorocyclobutene in fact 

The fluorocarbon groups in (20) are assigned the trans disposition in view of the single strong i.r. carbonyl band, and it is argued that the three weak bands also observed for each compound arise from the lack of axial symmetry in the fluorocarbon groups, rather than from the presence of c -isomers. The stereochemistry about the double bond is firmly based on F n.m.r. spectroscopic correlations. 

A full report (c/. Vol. 1, p. 169) of the photochemical reaction of dibromo-difluoromethane with pentacarbonyliron, to give a low yield of the complex (21), has now appeared. The compound (CF2Br)2Fe(CO)4 obtained in liquid-phase reactions is also obtained from photochemical reactions with 1,2-dibromotetrafluoroethane (thermal reactions lead only to general decomposition ), and is identified as the mononuclear complex 

The olefin complex (22 X,Y = F P,Q = Br) has also been prepared in low yield by a photochemical reaction of CFi CBra with pentacarbonyliron, together with a small amount of material formulated from its mass spectrum and an i.r. band at 1675 cm as the fenacyclopentene (23). A Russian patent claims that bis(halogenoperfluoroalkene)iron derivatives can be prepared by heating Fe(CO)s with CF2 CFX (X = Br, CF3, or CFiCFj) in an autoclave at 125—280° for 23—38 h.  

5 Iron, Ruthenium and Osmium.- The range of indenyl complexes 

When CpFe(CO)2(CH2Ph) is photolysed in the presence of PPh, CpFe(CO)2(PPhj) and (8) are formed. The scope of the 

Li[(CgH SiMe )Fe CO)2] has been investigated. The investigation of Cp-rich-sulphur systems continues with the report of the sulphur-rich complex (9).  

Anionic bimetallic dimers result from the reaction of [CpFe(C0)2] 

Spectroscopic results indicate an increasing stability of the complexes [CpFe(CO) P(OR)2)3 jj] as the degree of phosphite substitution increases. 

5 Iron, Ruthenium and Osmium. - In recent years, this group has provided the greatest number of publications dealing with metal carbonyl complexes. The year 2000 was no exeeption to this trend. The chemistry of the smaller elusters is, as usual, prominent. 

An interesting study to begin this section comes from Suzuki and co-workers who have used supported Fe(CO)s as a eatalyst to effect the eo-liquefaction of coal with polyethylene. Fundamental research has been reported by Schaefer et concerning the incorporation of formal Fe-Fe single, double, triple, and quadruple bonds in the structures of Fe2(CO)x (x = 9, 8,7,6). 

The biologjeal use of metal carbonyls was mentioned in the previous group. It appears here in the study of the origin of the anomalous Fe O stretehing mode in the CO eomplex of ascaris haemoglobin. 

Cedeno and Weitz have published an interesting study of the reaetions of Fe(CO)3 and Fe(CO)4 with C2CI4 in the gas phase monitored by transient infrared 

Other studies devoted to mononuclear iron complexes include evidence for a photoinduced haptotropic shift of the coordinated pyrrolyl ligand in (C5H5)(C4H4N)Fe(CO)2. The photochemistry was studied in low-temperature matrices and in room-temperature solution. The preparation and properties of carbonyliron complexes of l-aza-4-oxa-1,3-butadiene have also been described.  

6 Iron, Ruthenium, and Osmium - In this section of work Fp = Fe(CO)2Cp - and Rp = Ru(CO)2Cp is used throughout. The inclusion compounds of aromatic ruthenium complexes, e.g. (Bn)Ru(Cp) PF in a-cyclodextrin has been investigated and die mentioned example has been crystallographically characterised. Two transition m boryl complexes, FpB(OCeH40) and FpBPh2 have been reported the reaction of the former complex with Et2NH results in the formation of FpH and die aminoborane. Gas phase and solution studies have been carried out on the first pentafluorocyclopentadienyl complex ICp Rufn-CsFs)]. The redox chemistry of this complex is not unusual in any way.  

The reactivities of terminal acetylides has been examined in the complexes 

The reaction of the dimers (Fp 2, Fp 2 with isocyanides in the presence of a catalytic quantity of triethylborane to give a mono substituted product is proposed to go via a radical chain process.The photoelectron spectra of the n -acetylides CpFe(CO 2C=CR R = H, Bu and Ph have been analysed and show significant interaction of the ir-orbitals with the metal dx orbitals based on the splitting of metal-based ionization bands, shifts in Cp-based and acetylide based ionizations, changes in ionization cross sections (Hel/Hell) and the vibrational fine structure in the metal based ionizations. The 19e complex [CpFtffCsMee) has been used as an electron reservoir in the multiple electron reduction of Buckminster fullerene.  

In a continuation of Ru benzothitqrhene chemistry the reactitnis of 2-benzo[b]thienyl complexes with CF3SO3H has been described the syndiesis of [Cp(PMe3)2Ru(Ti -(S)-BT)] and Cp(CO)(PPh3)Ru(n -(S)-BT)] complexes in which protonation occurs in the 2-position 

The crystal structures of the following have also been reported  

6 Iron, Ruthenium, and Osmium The use of metallocenes, pardculariy ferrocene in 

Dynamic NMR studies of ring rotations in phenyl and r-bu l substituted fiarocenes and ruthenocencs have been undertaken.  

New metallocene-based ligands continue to be develcqied and new complexes of existing 

Ferrocene l,l -dicarboxaldehyde has been prepared directly from dilithioferrocene and DMF. Similarly a new synthesis of diferrocenylketones has been reported from bromo-ferrocene. The stepwise alkylation of diethylcyclopentadiene and the reaction of 2,3,4,5--tetraethylcyclopent-2-enone with ethyl magnesium bromide has been used to prepare pentaethyl-cyclopentadiene en route to decaethylfenocene.  

A number of skeletal mode assignments, including vM-M modes have been made for Fe3EE (CO)9 (E,E = S, Se, Te), Co2FeS(CO)9 and Os3S2(CO)9L (L = 

The resonance Raman spectra of cyanide adducts of cytochrome P450cam and its T252A and D251N mutants gave assignments to vFe N (near 480 cm ) and 5Fe-C-N (near 560 cm ) modes Similar experiments on the oxygensensor FixL and its derivatives showed characteristic shifts in vFe-CN and vFe-02 on replacement of Ilc209 by an Ala residue  

Resonance Raman data for the ferric Chlamydomoms haemoglobin cyanide complex include vFe-CN at 440 cm - lower than in other globins. vFe-His was tentatively assigned to 315 cm. Significant shifts were seen in vFe-CN for several mutant forms of the haemoglobin  

The IR spectra of the spin-transition complexes [Fe(L)3] , where L = IH-l,2,4-triazole and derivatives, showed characteristic shifts in vFeN modes between the high-spin and low-spin states. A resonance Raman band (180-250 cm ) was ascribed to iron-ligand out-of-plane modes in mutant H93G myoglobin - its position is markedly dependent on the nature of the axial ligand. A normal-coordinate analysis shows that this band has vFe-L character, but also a significant contribution from iron-haem doming.  

Picosecond TR of carbonmonoxy Coo A (a CO-sensing transcriptor activator) shows vFe-His at 211 cm immediately after photolytic CO-loss. vFe-N(His) is at 231 cm in cytochrome d from Alcaligentes xylosoxidansP Ultrafast time-resolved IR was used to probe myoglobin dynamics via vFe-His This mode was seen at 244 cm in the resonance Raman spectrum of the ferrous form of flavohaemoglobin from E. coli and at 211 cm for the SoxB-type cytochrome c oxidase from Bacillus stearothermophilusP  

Cluster conqiounds of iron were also represented in 1994 widi die preparadon of the boron-containing clusters [HFe5(CO)j5B], [HFe5(CO) P and 

The reactions of the radtenium conqtlex RuClH(COXPPh3)3 with alljdic amines have been reported . 

The osmium hydrido-catbonyl H2Os3(CO)]0 has featured in an interesting stucty by Aime et al where its reactions wito sitn(de ligands (CO, NH3 and H2S) were examined. Osmiiim carbotiyl-hydride anions (eg. [H30s4(C0) 2r) 1 l cen (uepared on silica firom [Os(CO)3Cl2]2 in toe presence of K2CO3 and toe reactions of 

A detailed study of the osmium clusters Os5(CO) g(CN Bu) and Os5(CO) 5(CN%u) has been publiBhed ch highlights tiie site selectivity of the CN%u ligand in the cluster. X-ray data is also provided. Osmium also figures in a shufy 29 devoted to the solution structure and dynamics of (/u-H)083(CO)io(M-Me). The authors make use of the H and NMR spectra of die comfdex to draw didr conclusions. Two quite enormous osmium cluster carbonyls, [OS t(CO)35]2 and [Os2q(CO)4q]2, have been prepared by Johnson ero/.  

The Fe, Ru and Os carbonyls have, as in previous years, attracted a great deal of work. The reactions of KHFe(CO)4 with various phosphites have been described . The eventual reaction products depend on the nature of the phosphite and the temperature. In the gas phase, the reactions of iron carbonyl cations with atomic hydrogen and atomic nitrogen have 

The still relatively new technique of time-resolved infrared (TRIR) spectroscopy has been used by Turner and co-workers to investigate the photochemical substitution reactions of [CpFe (CO)2 ] o in hydrocarbon and THF solution at room temperature and the kinetics and mechanism of photosubstitution in this molecule are examined by Zhang and Brown.  

Polynuclear carbonyls containing Fe, Ru and Os again figure prominently in this report The reactive anion 

Mechanistic studies include an investigation into the fluxional behaviour of the M3(CO)j2 carbonyls (M = Fe, Ru. Os) and the rather larger [HMioC(CO) 24) (M = Ru, Os) clusters. Mann has applied the concept of the concerted bridge opening/closing mechanism to the fluxionality of 

Of biological interest, Sakan et al have detected the Fe-CO stretching Raman band for the transient species formed from photodissociated carboxy-myoglobin .  

The earliest attempts to measure the rate of exchange between ferrous and ferric ions in aqueous media utilised the diffusion separation technique. Little agreement was obtained by the different workers Diffusion separation factors, found to be 0.5 , 1.4, 3.5 and 1.2, illustrate the difficulty of the technique. The isotopes used to label the iron were either Fe or Fe, and exchange was found to be complete in hours or many days in perchlorate media. 

Silverman and Dodson made the first detailed isotopic study of this exchange system using the separation afforded by the addition of 2,2 -dipyridyl at pH 5, followed by the precipitation of the ferric iron with either ammonia or 8-hydro-xyquinoline. Dodson , using this separation method, had previously obtained an overall rate coefficient of 16 l.mole sec at 23 °C for 0.4 M perchloric acid media. The exchange in perchlorate and perchlorate-chloride media was found to conform to a rate law, first order with respect to both total ferrous and ferric ion concentrations, with an observed rate constant (k bs) dependent on the hydrogen-ion concentration, viz. 

This dependence was interpreted in terms of an [ ]-independent pathway Fe3++Fe  

From intercepts and slopes of plots of versus values of ki and 

IONS OF SAME METAL IN DIFFERENT OXIDATION STATES 

Photo-oxidation of ferrocene by CCI4 in solution can normally only be effected by u.v. irradiation. However it has been observed that the reaction may be carried out with visible light in cetyltrimethylammonium chloride micelles, albeit with low quantum yield.It is suggested that the main effect of micellization may be an increase in the oxidation potential of ferrocene or alternatively that a CTTS state of ferrocene is involved under these conditions. The ring substitution of ruthenocene by irradiation in 1 1 (v/v) solutions of ethanol with CCI4, CHCI3, or CH2CI2 proceeds by a mechanism similar to that previously found for ferrocene. Other reports consider the synthesis of ferrocenyl thioesters and the photooxidation of ferrocene.  

Visible (A 400 nm) excitation of [CpFe(p-xylene)] PF6 in the presence of a suitable ligand L, e.g. isonitriles, phosphines, or CO, leads to expulsion of the p-xylene and formation of [CpFeLj] . In acidic aqueous solution the product is Fe +.  

Yokota and T. Sato, Kokagaku Torortkai Koen Yoshishu, 1979, 192 Chem. Abstr., 1980,93, 25561. 

Recent reports on the photochemistry of CpFe(CO)2-derivatives include the observation of CpFe(CO)2Me following irradiation of CpFe(CO)2PbMe3, the formation of the orthometallated derivative (10) and the elimination of Ph2MeSiH upon irradiation of CpFe(CO)2SiMePh2 and P(OPh)3, the photodecarbonyla-tion of CpFe(CO)2(tra/z5 -COCH=CHR) (R = Me or Ph) to give the corresponding alkenyl complex CpFe(CO)2( ranj -CH=CHR), and the observation of CpFe(CO)(m.t.h.f.)I upon photolysis of CpFe(CO)2l in methyltetrahydro-furan. The photoelimination of ethylene from CpFe(CO)2Et, giving CpFe(CO)2H, has been monitored in low-temperature matrices.In the same report it is also shown that the initial photoprocess in the conversion of (11) into 

Gerhartz, G. Ellerhorst, P. Dahler, and P. Eilbracht, Liebigs Ann. Chem., 1980, 1296. 

Homoleptic mononuclear thiolate complexes have been prepared for Fe(II) with sterically hindered substituents as in [Fe(SC6H3-2,6-Mes)2], [Fe(S-Mes )3], which is trigonal planar, or [Fe(SC6H4NR2)4] which is tetrahedral. Dinuclear derivatives of the type [Fe2(ER)4] (E=S, Se) have been obtained for several R groups. Other stoichiometries have been reported 

---

Table 25.1 Some properties of the elements iron, ruthenium and osmium...

Table 25.2 Standard reduction potentials for iron, ruthenium and osmium in acidic aqueous solution...

In the iron, ruthenium, and osmium derivatives, there are eases of r] re-switeh on thermolysis followed by the elimination of small ligands. Organo-ruthenium speeies eontaining pyrazol-l-ylborate or -methane ligands with bulky substituents often have uneoordinated pyrazol-l-yl moieties and agostie R—B(C) - - - M interaetion. The latter sometimes influenees the properties of the jj -eoordinated speeies as well. 

Pauling, L. Evidence from Bond Lengths and Bond Angles for Enneacovalence of Cobalt, Rhodium, Iridium, Iron, Ruthenium, and Osmium in Compounds with Elements of Medium Electronegativity Proc. Natl. Acad. Sci. (USA) 1984, 81, 1918-1921. 

Kramer, J., Redel, E., Thomann, R. and Janiak, C. (2008) Use of ionic liquids for the synthesis of iron, ruthenium, and osmium nanopartides from their metal carbonyl precursors. Organometallics,... 

The electroactive units in the dendrimers that we are going to discuss are the metal-based moieties. An important requirement for any kind of application is the chemical redox reversibility of such moieties. The most common metal complexes able to exhibit a chemically reversible redox behavior are ferrocene and its derivatives and the iron, ruthenium and osmium complexes of polypyridine ligands. Therefore it is not surprising that most of the investigated dendrimers contain such metal-based moieties. In the electrochemical window accessible in the usual solvents (around +2/-2V) ferrocene-type complexes undergo only one redox process, whereas iron, ruthenium and osmium polypyridine complexes undergo a metal-based oxidation process and at least three ligand-based reduction processes. 

The mononuclear metal carbonyls contain only one metal atom, and they have comparatively simple structures. For example, nickel tetracarbonyl is tetrahedral. The pentacarbonyls of iron, ruthenium, and osmium are trigonal bipyramidal, whereas the hexacarbonyls of vanadium, chromium, molybdenum, and tungsten are octahedral. These structures are shown in Figure 21.1. 

This observation may well explain the considerable difference between metal-olefin and metal-acetylene chemistry observed for the trinuclear metal carbonyl compounds of this group. As with iron, ruthenium and osmium have an extensive and rich chemistry, with acetylenic complexes involving in many instances polymerization reactions, and, as noted above for both ruthenium and osmium trinuclear carbonyl derivatives, olefin addition normally occurs with interaction at one olefin center. The main metal-ligand framework is often the same for both acetylene and olefin adducts, and differs in that, for the olefin complexes, two metal-hydrogen bonds are formed by transfer of hydrogen from the olefin. The steric requirements of these two edgebridging hydrogen atoms appear to be considerable and may reduce the tendency for the addition of the second olefin molecule to the metal cluster unit and hence restrict the equivalent chemistry to that observed for the acetylene derivatives. 

---