Ruthenium, and Osmium

Cobalt. B and F NMR spectroscopy has been used to show [BF4] encapsulation in [Co4L6] , L = (73). A Co VCo exchange process for a pair of Schiff base diquinone complexes has been studied and AEff and determined.  

Serikpaeva, A.K. Il yasova, and Zh. Zhubatov, Izv. Minist. Nauki-Akad. Nauk Resp. Kaz., Ser. Khim., 1997, 97 (Chem. Abstr., 1998,128, 278 215). 

Moldrheim, B. Andersen, N.A. Froystein, and E. Sletten, Inorg. Chim. Acta, 1998, 273,41. 

Macchioni, G. Bellachioma, G. Cardaci, G. Cruciani, E. Foresti, P. Sabatino, and C. Zuccaccia, Organometallics, 1998,17, 5549. 

Ruthenium and Osmium.—The quenching of the luminescent excited state of [Ru(bipy)3]8+ has continued to receive attention.72-78 As discussed in last year s Report, controversy exists as to whether this process for Co111 complexes proceeds via electron-transfer (20) or energy-transfer (21). Navon and Sutin72 have obtained 

Other workers78 have unambiguously shown by luminescence quenching and flash photolysis studies that for the weak organic oxidants (3) and (4) and for 

Comparison of the quenching rate constants for 8[Ru(bipy)3]2+ by substituted nitrobenzenes with their reduction potentials74 

Two reports of a static contribution to the quenching of emission from Rum complexes have been published. Measurement of both phosphorescence lifetimes and intensities allowed Bolletta et al 7 to observe static quenching (through ion-pair formation) of 3[Ru(bipy)3]2+ by [Mo(CN)3]4- and [PtClJ2- in DMF. For [IrCle]3- only dynamic quenching was found. Demas and Addington78 77 

The quantum yield for pyridine photo-aquation (24) from [Ru(NH3)6(py)]2+ varies only slightly with wavelength in the range 436—254 nm, and photooxidation to give Ru,n is only important at 334nm.82e Similarly, only photo-aquation of [Ru(NH3)5(MeCN)]2+ is found on irradiation at 366 nm while photoredox reactions are very important at shorter wavelengths ( = 0.51 at 214 nm).889 For both complexes a CTTS state is implicated in the photoredox reactions. As H2 is a significant product for [Ru(NH3)6(MeCN)]2+ photolysis at 254 nm, particularly in the presence of propan-2-ol, steps (25) and (26) are probably important. 

Ruthenium and Osmium. - Much attention has been paid in the last few years to Ru as a hydrogenation catalyst and N activator in the synthesis of NH3. CO adsorption at the (100) face of Ru monocrystals has been studied by Thomas and Weinberg and Pfnizr et A continuous red 

Experiments on isotopic exchange (either CO/ CO or C 0/ C1 o)9 .ioo, 33 been of vital importance in the assessment of the surface stoicheiometry. Moreover Cant and Bell have proved in a similar way that 

Guglielminotti, L. Meda, G. Spoto, and A. Zecchina, Proceedings 3rd Italian Conf. on Catalysis , Rimini, Italy, Sept. 1982, p. 106. 

VIS-NIR diffuse reflectance spectroscopy, by which the processes taking place (decarbonylation, changes in the oxidation state, clustering of metal atoms) are monitored. 

The reaction between CO and H2 has been studied in many of the papers cited Formation of hydrocarbons (basically 

Ruthenium and Osmium.—Square-pyramidal compounds [M(X)(Y)(PPh3)3] exhibit a dynamic process in solution which according to P n.m.r. spectroscopy equilibrates apical and basal phosphine sites. The measured values of A5 (Table 5) are consistent with this being an intramolecular rearrangement (probably Berry pseudorotation) and since addition of PPh3 does not effect the process a bimolecular exchange is also excluded. 

Rhodium.—The temperature dependence of the n.m.r. spectra of trigonal-bipyramidal compounds [Rh(dtc)(RNC)a(olefin)] (dtc=Me2NCS2, R=/ -MeCsH4 or 2,4,6-MesC6H2, olefin=tcne, fumaronitrile, maleonitrile, or maleic anhydride)  

Kaneshima, Y. Yumoto, K. Kawakami, and Tanako, Inorg. Chim. Acta, 1976,18, 29. 

Conformational isomerism in the chelate ring of [Rh(Cl)(CO)(PCN)] (PCN=( -diphenylphosphino-AW-dimethylbenzylamine) is thought to be responsible for the observed //-methyl group site exchange in the n.m.r. spectrum. The free energy of activation for the interchange is 8.8 kcal mol .  

Ruthenium and osmium are the first pair of platinum metals [1-13]. They exhibit oxidation states up to -f 8, the highest observed for any element, as in MO4 (M = Ru, Os) though this requires the use of the most electronegative elements, fluorine and oxygen, for stability. Generally, the H-2 and +3 states are the most important, along with -h4 for osmium however, there is a considerable chemistry of the ( osmyl and ruthenyl ) and 

M=N groups, as well as the classical hydride complexes OsH6(PR3)2, which also involve osmium(VI). 

Ruthenium and Osmium. The general methods by which osmium carbonyl clusters may be activated have been outlined. Routes to reactive substitution products of 

Stepwise deprotonation of [H4RU4(00)12] with KH yields [H4 wRu 4(00)12] ( = 1—3), the monoanion also resulting from the reaction between [H2Ru4(CO)is] and KH or that between [H4RU4(00)13] and methanolic KOH. X-ray studies on [PPN][HaRu4(CO)i2] have confirmed that two isomers exist, differing 

The reaction of [Ru 3(00)12] with pentamethylenediazirine leads to cleavage of the azo-bond and isolation of (30).  

Combined X-ray and neutron diffraction studies on [H20s3(CO)io] and [HOs3(CO)io(i a-CH=CH2)] have revealed the positions of the edge-bridging hydrides,confirming the structure proposed for the former. 

With hfb [H20s3(CO)io] gives [HOs3(CO)io(CF3CCHCF3)] which, unlike apparently related hydrocarbon vinyl complexes, contains the organic ligand bridging three metals in a manner best represented as in (32). 

Ruthenium, and Osmium.—Cyclo-octafluorotetramethylenetetra-carbonyliron (100), formed in the thermal reaction of tetrafluoroethylene with iron carbonyls, was one of the earliest reported fluoro-organo-derivatives of a transition metal. It may be more efficiently synthesized in a photochemical reaction. Ligands displace carbon monoxide from complex (100) to form complexes of the types (101) [L = PPhj, AsPhj, 

P(OPh) or P(OEt)J, (102) [L = P(OEt)3], and (103) [U = 2,2-bipyridyl, o-phenanthroline, or PhaP-CFIa-CHaPPha]. Ring cleavage results from reaction of complex (100) with H2SO4, SnCl4, S, Clj, PC1  

CFjiCFBr, CFjrCCU, CFsCFiCF, CFjCHiCFj, or (CFs) -CF CF (x = 2—4)]. Similar photochemical reactions of fluoro-olefins occur with the zero-valent (rf ) iron and ruthenium complexes rraHJ-[M(CO)3Lj] (L = phosphine or phosphite M = Fe or Ru), to give complexes of the type [M(CO)3La(fluoro-olefin)]. Thus, tetrafluoroethylene reacts with the complexes /ra -[Fe(CO)aLj] [L = (MeO)aP or (EtO)aP] to give complexes (104). Hexafluoropropene gives an analogous complex [L = (MeO)sP], while in the case of trifluoroethylene a five-membered iron heterocyclic 

Green and his co-workers have investigated the reactions of hexafluoro-but-2-yne with d complexes of the type /rfl 5-[M(CO)3L2] (M = Fe, Ru, or Os L = phosphine or phosphite) and found interesting variations within the periodic group. Photochemical reaction with iron complexes gave the cyclo-pentadienone complexes (112) [L = (EtO)3P or PhPMeJ. Reaction of 

Photochemical reaction of dibromodifluoromethane with pentacarbonyl-iron in the vapour phase produces the complex (119) with bridging difluoro- 

Diazoalkanes, R2CN2, react with a /i- -CsCPh ligand to form ji-n -allenyl 

Oxidation of i-vlnylidene complex [RU2(jt-L)(m-CO)(CO)2Cp21 (L - C=CH2) yields /i-ketene derivative (L - m-C(0)CH2) which readily decarbonylates producing the complex with L = W-CH2, whereas reduction forms (z-CHMe and n-C2U derivatives. Details are given for co-condensation reactions between arenes and Os atoms with the i -ray crystal structure of a dinuclear product, [OS2 (M-CHC6H3Me2-3,5) ( 7 -C6H3Me3-l, 3,5)2].  

Complex [OS3Br2(CO)2 g], with a linear chain structure, undergoes substitution and fragmentation on reaction with phosphines, probably by radical processes. Linear [0s3Cl(C0)] gCp] is converted thermally into ir/angw/o-cluster [0s3(/i-Cl) (COlgCp).  

Reduction of the ON bond in substituted benzonltriles on a RU3 cluster is and the reversibility of related imide-amide-nitrene 

Cleavage of phosphine ligands on ruthenium clusters has been studied thus, on thermolysis [Ru3(( -dppe)2(CO)8] yields [Ru3(( -H) ( 3-PPhCHPPh(CgH4) (( -dppm)- C0)-7] and [RU3(( 3 PPh) (( 3-CHPPh2) (/ -dppm) (00)7] reaction of [Ru3(( -dppm) (COj O hydrogen gives [Ru3 ( -H)(( 3-PPhCH2PPh2)(CO)g] and 

Black-brown RuBr3 has roughly octahedral coordination of ruthenium (Ru-Br 2.46-2.54 A) with short Ru-Ru contacts (2.73 A) [17]. Black RUI3 has a similar structure. Neither is particularly soluble in water. 

It has a VF4 type puckered sheet structure with 6-coordinated ruthenium four fluorines bridge, two non-bridging ones are trans with the terminal distances shorter as expected (Table 1.1). It is paramagnetic (/Xeff = 3.04/xb at room temperature). 

Green RuFs, sublimeable in vacuo (65°C, 10 torr (1.33 x 10 Pa)) can be made by fluorination 

A second, red form has recently been reported from mass spectral evidence, it may be a trimer. In the gas phase at 120°C, it consists mainly of a trimer (with octahedrally coordinated Ru) [18]. 

RuFg is made by fluorination of RuFs under forcing conditions  

The outer-sphere electron transfer reaction between [Fe(CN)6] and [Co(NH3)5H20] has been studied as a function of temperature and pressure in a variety of water-glycerol solvent mixtures. While AV remains essentially constant at 28 cm moP both A/f and A5 increase with an increase in the viscosity of the solvent. The intramolecular electron transfer processes in (NH3)5CoLFe(CN)5 complexes, where L is 3,3 -dimethyl-4,4 -bipyridine, 4,4 -bipyridylacetylene, 2,7-diazapyrene, and 3,8-phenathroline, have been studied. The activation free energies display an inverse dependence on the Fe-Co distance and, when corrected for solvent reorganization energies, are relatively constant at 14.0 0.5 kcal moP.  

The electron self-exchange rate constants for several Fe(II)/Fe(III) porphyrin couples have been measured by H NMR line-broadening techniques in 5 1 acetone/water at -20 The relative rate constants for the [Fe(P)(l-MeIm)2] couples, P = octaethylporphyrin chlorin isobacteriochlorin, have been attributed to differences in outer-sphere reorganization, related to the steric bulk. The rate-determining step in the metallopophyrin-catalyzed reductions of dioxygen by substituted ferrocenes is the electron transfer between the ferrocene and the metalloporphyrin (M = Fe, Co, and The Marcus relationship provides a 

A number of publications detail both triruthenium and triosmium chemistry. Thus in a series of papers, Bruce and co-workers describe the preparation and reactivity of complexes [ M3(CO) (p-Ph2PC4PPh2) M 3(CD)n)] (M=M =Ru or Os M=Ru,M =Os) in which trinuclear 

The molecular structures surveyed in this Chapter are mostly those of various iron complexes. There are relatively few reports of investigations of compounds of osmium. Cluster molecules of various types have been intensively studied. 

Inorganic Molecules.—Three compounds with the iron atom in tetrahedral co-ordination have been investigated. The molecule [Fe(NO)2(Ph2- 

In the iron(iii) complex [FeaOCsalenlal.CHaCl, the co-ordination poly-hedra around the iron atoms are distorted square pyramids, sharing a common apex occupied by the bridging oxygen (2). The four donor atoms 

Various octahedral complexes have been studied. The crystal structure of the compound Fe Cl2,4HaO consists of octahedral units of trans-[FeCla(H20)4], held together by hydrogen bonds of the type O-H Cl, with O Cl distances ranging from 3.15 to 3.23 A. The two Fe-O bond lengths are 2.08 and 2.12 A, and the Fe-Cl bond length is 2.53 A. In the molecule ci [Fe i(H)8 P Ph(OEt)a 4], the octahedron around the iron atom is tetrahedrally distorted. The Fe-P bonds cis and trans to the hydrido ligands and the Fe-H bond are 2.128(2), 2.150(2), and 1.51(4) A, respeo 

The Fe-S, S-C, and C-C distances in the chelate ring of the 1,2-dithiolato ligand are 2.195(3), 1.702(9), and 1.36(2) A, respectively. The iron complex (4) in [Fe (imidazole)2(dimethylglyoximato)a],2MeOH is centrosymmetric by crystallographic requirements. In the tetragonally distorted octahedron around the iron atom the axial Fe-N(im) and the two equatorial Fe-N(dmg) 

Complexes [Ru2(it-R-dab) C0)n] (n - 6, R-dab - PH-CHCH-NR) react with carbodiimides or thiofluorenone-S-oxide (C gHgC S-O) by C-C coupling to form new bridging ligands reactions of the same R-dab complexes (n 5 or 6) with Hg afford oxidative-addition products and when R 5 11 a linear 

Carboxylato bridged binuclear species reported include the catalytlcally active IRU2(m-02CC5H4F-P)2(C0)5(H20)]1 and [RU2(m-02CEt)2(CO)4L2] (L solvent) which in the absence of L associates via Ru-0 Interactions. Coi )lexas (Ru2(m-RCONH)2 s- r2 ° ( ) )2 2l bol) are produced by 

Eighteen /i-alkylidene complexes [Ru2(m CRr )(H0)2CP2] have been synthesised from [RU2(/i lfO)2Cp2 and their isomerisation, protonation and themolysis 

Bensene, formed by dehydrogenation of cyclohexadiene, is co-ordinated in a face capping mode in [083(n3-n ) C6H5)(C0)9] (8) a similar 

Oxidative addition of furan to [OS3(CO)io(HCIfe)2] produces [083 s-H)(n-n2-C4H30)(CO)iol. Competitive oxidative addition reactions of oB-unsaturated aldehydes form clusters [Os3(m H)( I )(CO)3o3 RC CHCHO 

R = H) gives similar butadienethiolate complexes. Tr-Complexation of thiophene in compounds of the type 123 activates the heterocycle relative toward other nucleophiles, such as OMe , SMe , SEt , S(i-Pr) , andCH(COOMe)2. The products 127 include the ring-opened butadiene-thiolate framework. 

Thermal arene exchange of tetramethylthiophene with [(/ -cymene)RuCl2]2 affords 130 (89JA8828), which on reaction with AgBE4 and excess tetramethylthiophene yields 131. The Ru—S thiophenic cluster, 132, was synthesized by reaction of 130 with (Mc3Si)2S followed by anionic metathesis and formation of the PFg salt. The coordination geometry around each ruthenium atom is pseudooctahedral. 

The TiVS) coordination of thiophene was proposed for [(ri -Cp)Ru(PPh3)2(Ti -C4H4S)] prepared from [CpRu(PPh3)2Cl], thiophene, and AgBp4 (76JA689, 

84JA5379, 85OM1909). However, this complex undergoes the t] transformation to yield 123 (R = = H) simply on standing in solution 

The reaction of thiophene with Ru3(CO)l2 leads to the disintegration of the heteroring and formation of 140 (R = H) and 141 (R = H) [92JCS(D)2423, 94AGE1381]. 2-Methylthiophene reacts differently and yields both the product of the C—H bond cleavage as a mixture of exo-, 142, and endo-, 143, isomers, cluster 140 (R = Me), and the product of the C—S bond cleavage, 141 (R = Me). 

Reactions of [Ru3(CD)i2] towards a variety of reagents are reported. These include the formation of simple adducts from the addition of tris(dimethylphosphino)methane, hexaphosphaferrocenes, l,2-0-isopropylidene-a-D-glucofuian, Ph2PCH2C(0)Ph, and cyclic thioethers. A large number of publications document the oxidative-addition of carbon- 

A variety of RU2- and Rug-complexes containing silicon-substituted cyclic polyolefins have been prepared and one of these, [RugCCgHgSiMegCHg-CH3iMe2)(CO)s], has been shown to contain an unusual -hydrocarbon ligand bridging both ruthenium atoms. The reactions of [Ru2(CO)e(DAB)] 

Single-step reactions have been reported for the preparation of [Ru2(CO)4-(PBuS)2Cm-X)2] (X=OaCH, OaCMe) and [Ru2(CO)4(PBut3)j( -X)2] (X=C1, Br, ).  

An 2f-ray study of the diamagnetic complex, [(Me3P)4Ru0x-CHa)2Ru(At-CH2)2-Ru(PMe3)4l+, shows an almost linear array of Ru atoms. Bond length considerations suggest a Ru —Ru —Ru formation that would, however, be expected 

232 Jangala, E. Rosenberg, D. Skinner, S. Aime, L. Milone, and E. Sappa, Inorg. Chem., 1980, 19, 1571. 

Spectroscopic studies on [Os3(CO)i2H2] are consistent with the hydrides being on the terminal osmium atoms, which are linear with staggered carbonyls. Whereas fragmentation of [Ru3(CO)i2] occurs on irradiation in the presence of triphenylphosphine, [Os3(CO)ia] gives [Os3(CO)ia a (PPh3)x] 2, 3) with 

Acetonitrile derivatives of [0 3(CX ),2] have been used extensively in the preparation of new triosmium complexes. Thus, [Os3(CO) (McCN)l reacts with (Cp3)2P-N=PPh, and 3,3- 

Publications on pentanuclear clusters include reports on the substitution chemistry, reactivity towards allyl halides, and high temperature thermolysis of [Ru,(CX ) ((X-PPhi)( i -Cy Ph2)], the latter giving the isomer [Rus(CO) ([i-PPh2)(M. -HTi)(li -C2Ph)], a result 

RUO4 can be isolated by heating a dry sample mixed with NaBiOi in a quartz boat placed in a tube flushed with moist oxygen [9]. 

Ruthenium (osmium) is stripped from the organic solvent with 1 M H2SO4 in the presence of NaSCN, and the absorbance of the resulting ruthenium- (or osmium-) thiocyanate complex measured directly. 

The chloride-, bromide-, and thiocyanate complexes of ruthenium(IIl) and osmium(IV) can be extracted from acid solutions by oxygen-containing solvents, also in the presence of TBP or amines [10,12-15]. Osmium has been separated from Ru after conversion into Osle and extraction with TO A [16]. From mixtures of thiocyanate complexes of Ru and Os, only the Os complex can be extracted into diethyl ether containing a small amount of peroxide [14]. Poljmrethane foam has also been used for separating Ru and Os as their thiocyanate complexes [17,18]. 

Ruthenium can be separated from osmium by extraction as the ion-pair of perruthenate [Ru(VIII)] with tetraphenylarsonium ion [19] or with benzyltributylammonium chloride [20]. 

Ruthenium has been extracted from semiconducting materials using bis-(2- 

R = Me). In the reaction of benzamido complex CRU2(PhCONH) Cl] with PPh, phenyl group transfer occurs to form [Ru2 u-Ph2POC(Ph)N 2  

Carboxylato-bridged RU2 units are present in structurally characterised complexes C RU2(P-O2CR)2(CO) (RCOOH) ] 

Full details are published for syntheses, from CRU2(p-CO)(u-COC2Ph2)  

Mechanistic studies of kinetic H-lsotope effects on p-H and CO migrations in some trinuclear Ru and Os clusters are reported.  

The structurally characterised anion COs (p-NO) (CO) has a lower activation barrier for CO scrambling than related hydrldo-bridged clusters.Protonations of complexes COs-(CO), (MeCM) 3 (n =1,2) occur, and the structure of [Os (p-H) (CO) j q(M6CN) 2] is reported. 

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Ruthenium and osmium have hep crystal stmetures. These metals have properties similar to the refractory metals, ie, they are hard, britde, and have relatively poor oxidation resistance (see Refractories). Platinum and palladium have fee stmetures and properties akin to gold, ie, they are soft, ductile, and have excellent resistance to oxidation and high temperature corrosion. 

The residue, which contains Ir, Ru, and Os, is fused with sodium peroxide at 500°C, forming soluble sodium mthenate and sodium osmate. Reaction of these salts with chlorine produces volatile tetroxides, which are separated from the reaction medium by distillation and absorbed into hydrochloric acid. The osmium can then be separated from the mthenium by boiling the chloride solution with nitric acid. Osmium forms volatile osmium tetroxide mthenium remains in solution. Ruthenium and osmium can thus be separately purified and reduced to give the metals. 

Syntheses from Dry Metals and Salts. Only metaUic nickel and iron react direcdy with CO at moderate pressure and temperatures to form metal carbonyls. A report has claimed the synthesis of Co2(CO)g in 99% yield from cobalt metal and CO at high temperatures and pressures (91,92). The CO has to be absolutely free of oxygen and carbon dioxide or the yield is drastically reduced. Two patents report the formation of carbonyls from molybdenum and tungsten metal (93,94). Ruthenium and osmium do not react with CO even under drastic conditions (95,96). 

A Belgian patent (178) claims improved ethanol selectivity of over 62%, starting with methanol and synthesis gas and using a cobalt catalyst with a hahde promoter and a tertiary phosphine. At 195°C, and initial carbon monoxide pressure of 7.1 MPa (70 atm) and hydrogen pressure of 7.1 MPa, methanol conversions of 30% were indicated, but the selectivity for acetic acid and methyl acetate, usehil by-products from this reaction, was only 7%. Ruthenium and osmium catalysts (179,180) have also been employed for this reaction. The addition of a bicycHc trialkyl phosphine is claimed to increase methanol conversion from 24% to 89% (181). 

Ruthenium and osmium are generally found in the metallic state along with the other platinum metals and the coinage metals. The major source of the platinum metals are the nickel-copper sulfide ores found in South Africa and Sudbury (Canada), and in the river sands of the Urals in Russia. They are rare elements, ruthenium particularly so, their estimated abundances in the earth s crustal rocks being but O.OOOl (Ru) and 0.005 (Os) ppm. However, as in Group 7, there is a marked contrast between the abundances of the two heavier elements and that of the first. 

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...

Ruthenium and osmium have no oxides comparable to those of iron and, indeed, the lowest oxidation state in which they form oxides is -t-4. RUO2 is a blue to black solid, obtained by direct action of the elements at 1000°C, and has the rutile (p. 961) structure. The intense colour has been suggested as arising from the presence of small amounts of Ru in another oxidation state, possibly - -3. 0s02 is a yellowish-brown solid, usually prepared by heating the metal at 650°C in NO. It, too, has the rutile structure. 

Ruthenium and osmium form only disulfides. These have the pyrite structure and are diamagnetic semiconductors this implies that they contain M . RuSc2, RuTc2, OsSc2 and OsTc2 are very similar. All 6 dichalcogenides are obtained directly from the elements. 

As already noted (p. 1073), the platinum metals are all isolated from concentrates obtained as anode slimes or converter matte. In the classical process, after ruthenium and osmium have been removed, excess oxidants are removed by boiling, iridium is precipitated as (NH4)2lrCl6 and rhodium as [Rh(NH3)5Cl]Cl2. In alternative solvent extraction processes (p. 1147) [IrClg] " is extracted in organic amines leaving rhodium in the aqueous phase to be precipitated, again, as [Rh(NH3)5Cl]Cl2. In all cases ignition in H2... 

Organometallic chemistry of pyrrole is characterized by a delicate balance of the ti N)- and -coordination modes. Azacymantrene is an illustration of the considerable nucleophilicity of the heteroatom. However, azaferrocene can be alkylated at C2 and C3 sites. Ruthenium and osmium, rhodium, and iridium chemistry revealed the bridging function of pyrroles, including zwitterionic and pyrrolyne complex formation. The ti (CC) coordination of osmium(2- -) allows versatile derivatizations of the heteroring. 

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