Reaction Behavior of Decacarbonyldimetalates(2‐) (M = Cr and Mo) towards the Nitrosyl Carbonyls of Iron and Cobalt

The reaction of the nitrosyl carbonyl complexes [Fe(NO)₂(CO)₂] and [Co(NO)(CO)₃] with the decacarbonyldimetalates [M₂(CO)₁₀]^2– (M = Cr and Mo) in THF as the solvent at room temperature was investigated. Thereby a substitution of one nitrosyl ligand towards carbon monoxide was observed in each case. Both reactions afforded the known metalate complexes [Fe(NO)(CO)₃]^– and [Co(CO)₄]^–, respectively. These species were isolated as their corresponding PPN salts [PPN⁺ = bis(triphenylphosphane)iminium cation] in nearly quantitative yields. The products were unambiguously identified by their IR spectroscopic and elemental analytic data as well as by their characteristic colors and melting points.     

Addition of CCl4 to unsaturated compounds catalyzed by M3(CO)12 (M=Fe, Ru, Os)

The addition of CCl₄ to hex-1-ene and to the methyl ester ofN-(trans-cinnamoyl)-l-proline (2) catalyzed by M₃(CO)₁₂ or by the M₃(CO)₁₂+DMF system (M=Fe, Ru, Os) was studied. The use of ruthenium and osmium dodecacarbonyls in combination with DMF increases the yields of adducts CCl₃CH₂CHClC₄H₉ (4) and PhCHClCH(CCl₃)C(O)R′ (3) over those obtained in reactions catalyzed by the same carbonyls without DMF. In addition to adduct3, salts [M(CO₃)Cl₃]⁻[Me₂NH₂]⁺ were isolated from the products of the reaction between CCl₄ and1 in the presence of M₃(CO)₁₂+DMF (M=Ru, Os). These salts do not catalyze this reaction and apparently result from chain termination. Experimental results in favor of a coordination mechanism of the addition of CCl₄ to olefins in the presence of Ru₃(CO)₁₂ and Os₃(CO)₁₂ were obtained. Translated fromIzvestiya Akademii Nauk Seriya Khimicheskaya, No. 6, pp. 1174–1179, June, 1997.     

Interesting synthetic routes from the reinvestigation of the reaction of the M(CO)6 (M=Cr,Mo and W) species with KOH

Summary Reinvestigation of the reaction of M(CO)₆ (M=Cr, Mo or W) with KOH has been found to provide a very convenient route to the K[M₂H(CO)₁₀] compounds (M=Cr, Mo or W). The reaction involving Cr(CO)₆ yields new potassium derivatives containing [Cr₂(CO)₁₀]^2– and [HCr(CO)₅]^– species; also K[Cr₂D(CO)₁₀] is produced from the Cr(CO)₆/KOD interaction in C₂D₅OD. The reaction involving two different group 6 metal carbonyls yields [MM(CO)₁₀(-H)]^– (MM=CrMo, CrW or WMo) species as their K⁺ and PPN⁺ [bis(triphenylphosphine)iminium] salts.     

Polymerization Isomerism in Co-M (M = Cu,Ag, Au) Carbonyl Clusters: Synthesis,Structures and Computational Investigation

The reaction of [Co(CO)₄]⁻ (1) with M(I) compounds (M = Cu, Ag, Au) was reinvestigated unraveling an unprecedented case of polymerization isomerism. Thus, as previously reported, the trinuclear clusters [M{Co(CO)₄}₂]⁻ (M = Cu, 2; Ag, 3; Au, 4) were obtained by reacting 1 with M(I) in a 2:1 molar ratio. Their molecular structures were corroborated by single-crystal X-ray diffraction (SC-XRD) on isomorphous [NEt₄][M{Co(CO)₄}₂] salts. [NEt₄](3)represented the first structural characterization of 3. More interestingly, changing the crystallization conditions of solutions of 3, the hexanuclear cluster [Ag₂{Co(CO)₄}₄]²⁻ (5) was obtained in the solid state instead of 3. Its molecular structure was determined by SC-XRD as Na₂(5)·C₄H₆O₂, [PPN]₂(5)·C₅H₁₂ (PPN = N(PPh₃)₂]⁺), [NBu₄]₂(5) and [NMe₄]₂(5) salts. 5 may be viewed as a dimer of 3 and, thus, it represents a rare case of polymerization isomerism (that is, two compounds having the same elemental composition but different molecular weights) in cluster chemistry. The phenomenon was further studied in solution by IR and ESI-MS measurements and theoretically investigated by computational methods. Both experimental evidence and density functional theory (DFT) calculations clearly pointed out that the dimerization process occurs in the solid state only in the case of Ag, whereas Cu and Au related species exist only as monomers.     

Chemical Bonding in Homoleptic Carbonyl Cations [M{Fe(CO)5}2]+ (M=Cu,Ag, Au)

Syntheses of the copper and gold complexes [Cu{Fe(CO)₅}₂][SbF₆] and [Au{Fe(CO)₅}₂][HOB{3,5-(CF₃)₂C₆H₃}₃] containing the homoleptic carbonyl cations [M{Fe(CO)₅}₂]⁺ (M=Cu, Au) are reported. Structural data of the rare, trimetallic Cu₂Fe, Ag₂Fe and Au₂Fe complexes [Cu{Fe(CO)₅}₂][SbF₆], [Ag{Fe(CO)₅}₂][SbF₆] and [Au{Fe(CO)₅}₂][HOB{3,5-(CF₃)₂C₆H₃}₃] are also given. The silver and gold cations [M{Fe(CO)₅}₂]⁺ (M=Ag, Au) possess a nearly linear Fe-M-Fe’ moiety but the Fe-Cu-Fe’ in [Cu{Fe(CO)₅}₂][SbF₆] exhibits a significant bending angle of 147° due to the strong interaction with the [SbF₆]⁻ anion. The Fe(CO)₅ ligands adopt a distorted square-pyramidal geometry in the cations [M{Fe(CO)₅}₂]⁺, with the basal CO groups inclined towards M. The geometry optimization with DFT methods of the cations [M{Fe(CO)₅}₂]⁺ (M=Cu, Ag, Au) gives equilibrium structures with linear Fe-M-Fe’ fragments and D₂ symmetry for the copper and silver cations and D_4d symmetry for the gold cation. There is nearly free rotation of the Fe(CO)₅ ligands around the Fe-M-Fe’ axis. The calculated bond dissociation energies for the loss of both Fe(CO)₅ ligands from the cations [M{Fe(CO)₅}₂]⁺ show the order M=Au (D_e=137.2 kcal mol⁻¹)>Cu (D_e=109.0 kcal mol⁻¹)>Ag (D_e=92.4 kcal mol⁻¹). The QTAIM analysis shows bond paths and bond critical points for the M−Fe linkage but not between M and the CO ligands. The EDA-NOCV calculations suggest that the [Fe(CO)₅]→M⁺←[Fe(CO)₅] donation is significantly stronger than the [Fe(CO)₅]←M⁺→[Fe(CO)₅] backdonation. Inspection of the pairwise orbital interactions identifies four contributions for the charge donation of the Fe(CO)₅ ligands into the vacant (n)s and (n)p AOs of M⁺ and five components for the backdonation from the occupied (n-1)d AOs of M⁺ into vacant ligand orbitals.     

Use of the Cationic Fragments [Ru(η5-C5H5) (MeCN)3]+ and [M(η6-C6H5R)(MeCN)3]+ (M=Os, Ru; R=H, Me) as Ionic Coupling Reagents in the Synthesis of the Clusters [Os4M2(CO)12(η6-C6H5R)], [Os4M(CO)12(η6-C6H6)(Au2dppm)] and [Os5Ru(CO)15(η5-C5H5)(AuPPh3)]*

The clusters [H₂Os₄M(CO)₁₂eta⁶-C₆H₆)] (M=Os, Ru) may be deprotonated to generate anions [Os₄M(CO)₁₂eta⁶-C₆H₆)]^2- which react with [M′eta⁶-C₆H₅R) (MeCN)₃]²⁺(M^′=Os, Ru; R=H, Me) to give the bicapped tetrahedral clusters [Os₄(CO)₁₂MM′eta⁶-C₆H₅R)₂]. Whereas [Os₄(CO)₁₂M₂eta⁶-C₆H₆)₂] (M=Os, Ru) have one Meta⁶-C₆H₆) unit in a site connected to three other metals, {3}, and one in a site connected to four other metals, {4}, [Os₄(CO)₁₂OsRueta⁶-C₆H₆)₂] has the Rueta⁶-C₆H₆) unit in the {3} site irrespective of whether the Os or Ru anion is capped. Coupling of these anions with Au₂dppm yields [Os₄M(CO)₁₂eta⁶-C₆H₆)(Au₂dppm)] (M=Os, Ru), which have the arene ligand in the axial site of a trigonal bipyramid and the digold unit capping two faces. Reduction of [H₂Os₅(CO)₁₅] with K/Ph₂CO and coupling with [Rueta⁵-C₅H₅)(MeCN)₃]²⁺yields the monoanion [Os₅(CO)₁₅Rueta⁵-C₅H₅)]^? which reacts with [AuPPh₃]⁺ generating [Os₅(CO)₁₅Rueta⁵-C₅H₅)(AuPPh₃)] with the “Ru(C₅H₅)” unit in the terminal {3} site.     

Addition von kationischen Lewis‐Säuren [M′Ln]+ (M′Ln = Fe(CO)2Cp,Fe(CO)(PPh3)Cp,Ru(PPh3)2Cp,Re(CO)5, ${1 \over 2}$ Pt(PPh3)2, W(CO)3Cp an die anionischen Thiocarbonyl‐Komplexe [HB(pz)3(OC)2M(CS)]− (M = Mo,W; pz = 3,5‐dimethylpyrazol‐1‐yl)

Addition of Cationic Lewis Acids [M′L_n]⁺ (M′L_n = Fe(CO)₂Cp, Fe(CO)(PPh₃)Cp, Ru(PPh₃)₂Cp, Re(CO)₅, Pt(PPh₃)₂, W(CO)₃Cp to the Anionic Thiocarbonyl Complexes [HB(pz)₃(OC)₂M(CS)]⁻ (M = Mo, W; pz = 3,5‐dimethylpyrazol‐1‐yl) Adducts from Organometallic Lewis Acids [Fe(CO)₂Cp]⁺, [Fe(CO)(PPh₃)Cp]⁺, [Ru(PPh₃)₂Cp]⁺, [Re(CO)₅]⁺, [ Pt(PPh₃)₂]⁺, [W(CO)₃Cp]⁺ and the anionic thiocarbonyl complexes [HB(pz)₃(OC)₂M(CS)]⁻ (M = Mo, W) have been prepared. Their spectroscopic data indicate that the addition of the cations occurs at the sulphur atom to give end‐to‐end thiocarbonyl bridged complexes [HB(pz)₃(OC)₂MCSM′L_n].     

Ruthenafuran Complexes Supported by the Bipyridine-Bis(diphenylphosphino)methane Ligand Set: Synthesis and Cytotoxicity Studies

Mononuclear and dinuclear Ru(II) complexes cis-[Ru(κ²-dppm)(bpy)Cl₂] (1), cis-[Ru(κ²-dppe)(bpy)Cl₂] (2) and [Ru₂(bpy)₂(μ-dpam)₂(μ-Cl)₂](Cl)₂ ([3](Cl)₂) were prepared from the reactions between cis(Cl), cis(S)-[Ru(bpy)(dmso-S)₂Cl₂] and diphosphine/diarsine ligands (bpy = 2,2′-bipyridine; dppm = 1,1-bis(diphenylphosphino)methane; dppe = 1,2-bis(diphenylphosphino)ethane; dpam = 1,1-bis(diphenylarsino)methane). While methoxy-substituted ruthenafuran [Ru(bpy)(κ²-dppe)(C^O)]⁺ ([7]⁺; C^O = anionic bidentate [C(OMe)CHC(Ph)O]⁻ chelate) was obtained as the only product in the reaction between 2 and phenyl ynone HC≡C(C=O)Ph in MeOH, replacing 2 with 1 led to the formation of both methoxy-substituted ruthenafuran [Ru(bpy)(κ²-dppm)(C^O)]⁺ ([4]⁺) and phosphonium-ring-fused bicyclic ruthenafuran [Ru(bpy)(P^C^O)Cl]⁺ ([5]⁺; P^C^O = neutral tridentate [(Ph)₂PCH₂P(Ph)₂CCHC(Ph)O] chelate). All of these aforementioned metallafuran complexes were derived from Ru(II)–vinylidene intermediates. The potential applications of these metallafuran complexes as anticancer agents were evaluated by in vitro cytotoxicity studies against cervical carcinoma (HeLa) cancer cell line. All the ruthenafuran complexes were found to be one order of magnitude more cytotoxic than cisplatin, which is one of the metal-based anticancer agents being widely used currently.     

Halogenation behaviour of bidentate ligand-bridged derivatives of [Ru3(CO)12] and [Os3(CO)12]

Reaction of the ligand-bridged derivatives [M₃(CO)₁₀{μ-(RO)₂PN(Et)P(OR)₂}] and [M₃(CO)₈{μ-(RO)₂PN(Et)P(OR)₂}₂] (M = Ru or Os; R = Me or Prⁱ) with halogens leads to the formation of cationic products [M₃(μ-X)(CO)₁₀{μ- (RO)₂PN(Et)P(OR)₂}]⁺ and [M₃(μ-X)(CO)₈{μ-(RO)₂PN(Et)P(OR)₂}₂]⁺ (X = Cl, Br or I) in which the halogen bridges an opened edge of the metal atom framework; the crystal structure of [Ru₃(μ-I)(CO)₈{μ-(MeO)₂PN(Et)P(OMe)₂}₂]PF₆ is reported.     

Transition metal nitrosyl compounds. Part XIV(1). The oxidation of carbon monoxide by nitric oxide using [M(NO)2(PPh3)2]n+ (M=Fe,Ru or Os; n=0. M=Co,Rh or Ir; n=1)

Summary Carbon monoxide reacts with the cationic dinitrosyls [M(NO)₂(PPh₃)₂]⁺ (M = Rh, Ir) under ambient conditions to produce CO₂, N₂O and the tricarbonyl cations, (M(CO)₃(PPh₃)₂]⁺. The cationic tricarbonyls are reconverted into the dinitrosyl reactants on treatment with NO atca. 80°. The Ru(NO)₂(PPh₃)₂ and Os(NO)₂(PPh₃)₂ complexes react similarly with CO but under more vigorous conditions whereas the corresponding dinitrosyls of cobalt and iron do not undergo this reaction under similar conditions. A pentacoordinate dinitrosyl intermediate [M(NO)₂(CO)(PPh₃)₂]ⁿ⁺ is proposed and a mechanism for the catalytic oxidation of CO by NO is presented. Studies of Pt(N₂O₂)PPh₃)₂ establish that a dinitrogcn dioxide intermediate, produced by the coupling of two nitrosyl ligands, is reasonable.     

Structure of (BEDT-TTF)-Based Organic Metals with Photochromic Nitroprusside Anion (BEDT-TTF)4M[FeNO(CN)5]2, where M = Na+, K+, NH+4, Tl+, Rb+, and Cs+

The crystal and molecular structures of a family of three-component radical cation salts bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF), (BEDT-TTF)₄M[NP]₂, where M = Na⁺, K⁺, NH⁺ ₄, Tl⁺, Rb⁺, and Cs⁺and NP is the nitroprusside anion [FeNO(CN)₅]^2–, are studied by X-ray structure analysis. These salts are isostructural and behave as stable metals down to helium temperatures. Their structures are characterized by radical cation layers of the "-type alternating with layers of complex anions [M⁺(NP^2–)₂]^3–. The conducting radical cation system and photochromic nitroprusside anion in the crystals were shown to affect each other. On the one hand, this changes the geometric parameters of the nitroprusside anion as compared to those of the Na₂[NP] · 2H₂O crystals in the ground state and, on the other hand, makes the geometries of the two crystallographically independent BEDT-TTF molecules with a different number of shortened contacts with the anion different. Based on the data of crystallochemical analysis of the (BEDT-TTF)₄M[FeNO(CN)₅]₂structures, we suggest their possible routes of chemical modification with the purpose of changing their physical properties.     

Substituted metal carbonyls: [{{(p-MeOC6H4)2Te}M(CO)4}]2 (M = Mn or Re) in the presence of an O-atom transfer reagent

Two novel telluroether-disubstituted metal carbonyls, [(R₂Te)M(CO)₄]₂(M = Mn or Re; R = p-MeOC₆H₄), were prepared from [M₂(CO)₁₀] by an oxygen atom transfer. The axial CO is replaced by the telluroether when [M₂(CO)₁₀] reacts with a new kind of oxygen transfer reagent, R₂TeO, under mild conditions. The products were characterized by elemental analysis, i.r., ¹H- and ¹³C-n.m.r., and FAB-mass spectra. The configuration of the substituted carbonyl is unique, i.e. the 1, l-diax isomer.     

The effect of solvents on the stability of the products of electrochemical reactions of iron, ruthenium, and osmium carbonyl cluster compounds

The electrochemical reactions of carbonyl cluster compounds M₃(CO)₁₂ (M = Fe, Ru, Os) were compared with those of [Fe₅C(CO)₁₄]^2? and [Fe₆C(CO)₁₆]^2? in different aprotic solvents. The stability of electrochemically generated products of these clusters in the studied solvents was shown to grow in the following order: tetrahydrofuran < acetone < dichloromethane < acetonitrile.     

Reactions of [Ru(CO)3Cl2]2 with aromatic nitrogen donor ligands in alcoholic media

The reactions of mono‐ and bidentate aromatic nitrogen‐containing ligands with [Ru(CO)₃Cl₂]₂ in alcohols have been studied. In alcoholic media the nitrogen ligands act as bases promoting acidic behaviour of alcohols and the formation of alkoxy carbonyls [Ru(N–N)(CO)₂Cl(COOR)] and [Ru(N)₂(CO)₂Cl(COOR)]. Other products are monomers of type [Ru(N)(CO)₃Cl₂], bridged complexes such as [Ru(CO)₃Cl₂]₂(N), and ion pairs of the type [Ru(CO)₃Cl₃]^? [Ru(N–N)(CO)₃Cl]⁺ (N–N = chelating aromatic nitrogen ligand, N = non‐chelating or bridging ligand). The reaction and the product distribution can be controlled by adjusting the reaction stoichiometry. The reactivity of the new ruthenium complexes was tested in 1‐hexene hydroformylation. The activity can be associated with the degree of stability of the complexes and the ruthenium–ligand interaction. Chelating or bridging nitrogen ligands suppresses the activity strongly compared with the bare ruthenium carbonyl chloride, while the decrease in activity is less pronounced with monodentate ligands. A plausible catalytic cycle is proposed and discussed in terms of ligand–ruthenium interactions. The reactivity of the ligands as well as the catalytic cycle was studied in detail using the computational DFT methods. Copyright © 2005 John Wiley & Sons, Ltd.     

1,3-diaryltriazenido complexes of ruthenium(I), (II) and (III), and of osmium(III), rhodium(III) and iridium(III)

The synthesis and characterization of the platinum metal—1,3-diaryltriazenido complexes [Ru(ArNNNAr)(CO)₃]₂, [Ru(ArNNNAr)₂]₂, cis-Ru(ArNNNAr)₂(CO)₂, MX₂(ArNNNAr)(PPh₃)₂ (M = Ru, Os; X = Cl, Br) and M′(ArNNNAr)₃ (M′= Ru, Os, Rh and Ir) are reported. Axial ligand substitution in [Ru(ArNNNAr)(CO)₃]₂ and adduct formation by [Ru(ArNNNAr)₂]₂ are described. In contrast to other known Ru(II)/Ru(II) “lantern” molecules, the species [Ru(ArNNNAr)₂]₂ have measured magnetic moments equivalent to ca one unpaired electron per dimer, which are presumably due to population of the spin states σ²π⁴δ²π^*4 and σ²π⁴δ²π^*3σ^*1.     

Binuclear metal carbonyl dab complexes : VII. A 13C NMR investigation of MM′(CO)6(DAB) complexes (M = M ′ = Fe,Ru; M = Mn,Re and M′ = Co; DAB = 1,4-diazabutadiene). Dynamic behaviour of σ2-N, σ2-N′, η2-C=N coordinated dab in MnCo(CO)6(DAB) and local scrambling of the carbonyl groups

The ¹³C NMR spectra of MM′(CO)₆(DAB) complexes (M = M′ = Fe, Ru; M = Mn, Re and M′ = Co; DAB = 1,4-diazabutadiene) show very characteristic features which are directly related with the bonding mode of the DAB ligand to the binuclear metal carbonyl fragment. In these complexes the DAB ligand is σ²-N, μ²-N′, η²-C=N or σ²-N, σ²-N′, η²-C=N coordinated. Chemical shifts of about 175 ppm are observed for the σ-coordinated imine fragments and about 60 or 80 ppm for the η²-C=N coordinated imine fragments.In MnCo(CO)₆[diacetylbis(cyclopropylimine)] the DAB ligand is fluxional, and the changes in the spectra when recorded at various temperatures can be interpreted in terms of an exchange between the σ- and π-coordinated part of the DAB ligand.The homodinuclear M₂(CO)₆(DAB) complexes (M = Fe or Ru) contain M(CO)₃ fragments on which the carbonyl groups are involved in a local scrambling process with very different activation parameters (T_c = ?50°C and +85°C).MCo(CO)₆(DAB) complexes (M = Mn, Re), which contain a semi-bridging carbonyl group according to the crystal structure, show rapid interchange of this carbonyl group with the terminal carbonyl groups on cobalt. The electronic balance is kept in equilibrium by an internal compensation within the DAB ligand.     

The Use of the Electron-Reservoir Complexes [Fe(I)Cp(arene)] for the Electrocatalytic Synthesis of Redox-Reversible Metal-Carbonyl Clusters Containing Ferrocenyldiphenylphosphine

Starting from [M₃(CO)₁₂] (M = Fe or Ru) and [CH₃CCo₃(CO)₉], the electron-tranfer-chain catalyzed synthesis of new Fe, Ru, and Co carbonyl clusters in which one or several carbonyl ligands have been selectively substituted by one or several ferrocenyldiphenylphosphine (FDPP) ligands has been achieved using the electron-reservoir complexes [Fe(I)Cp(arene)] as electrocatalysts. The number of FDPP ligands selectively introduced can be chosen from one per cluster for the three clusters up to one per metal for the Ru and Co clusters. The advantage of this family of electrocatalysts is that the driving force for the initiation step can be varied by changing the number of methyl groups on the rings. The FDPP substituted clusters show one reversible wave by cyclic voltammetry.     

Synthesis, characterization and photophysics of bimetallic manganese(I) and ruthenium(II) complexes

A series of new manganese(I) and ruthenium(II) monometallic and bimetallic complexes made of 2,2′-bipyridine and 1,10-phenanthroline ligands, [Mn(CO)₃(NN)(4,4′-bpy)]⁺, [{(CO)₃(NN)Mn}₂(4,4′-bpy)]²⁺ and [(CO)₃(NN)Mn(4,4′-bpy)Ru(NN)₂Cl]²⁺ (NN = 2,2′-bipyridine, 1,10-phenanthroline; 4,4′-bpy = 4,4′-bipyridine) are synthesized and characterized, in addition to already known ruthenium(II) complexes [Ru(NN)₂Cl(4,4′-bpy)]⁺ and [Cl(NN)₂Ru(4,4′-bpy)Ru(NN)₂Cl]²⁺. The electrochemical properties show that there is a weak interaction between two metal centers in Mn–Ru heterobimetallic complexes. The photophysical behavior of all the complexes is studied. The Mn(I) monometallic and homobimetallic complexes have no detectable emission. In Mn–Ru heterobimetallic complexes, the attachment of Mn(I) with Ru(II) provides interesting photophysical properties.     

Controlled-Potential Coulometric Determination of Ruthenium in Ru(OH)Cl3 with Microwave Sample Preparation

A procedure for the controlled-potential coulometric (CPC) determination of ruthenium is proposed. The procedure is based on the redox reaction [Ru(CO)Cl₅]^2–/[Ru(CO)Cl₄(H₂O)]^2– followed by the synthesis of the [Ru(CO)Cl₅]^2– depolarizing complex under microwave irradiation. The procedure was used in the analysis of a domestic commercial Ru(OH)Cl₃ preparation.     

Protonation of a series of diphosphazane- and diphosphine-bridged derivatives of iron and ruthenium: dependence of the nature of the hydride ligand on the metal and the bridging diphosphorus ligand

Protonation of the dinuclear compounds [M₂(μ-CO)(CO)₄(μ-R₂PYPR₂)₂] by HBF₄ or HPF₆ leads to the formation of crystalline cationic hydrido products [M₂H(CO)₅(μ-R₂PYPR₂)₂]X and [M₂(μ-H)(μ-CO)(CO)₄(μ-R₂PYPR₂)₂]X (X = BF₄ or PF₆) in which the hydride ligand is terminal for M = Ru, Y = N(Et) and R = OMe or OPrⁱ and bridging for M = Fe, Y = CH₂ and R = Me or Ph, for M = Fe, Y = N(Et) and R = OMe, OEt, OPrⁱ or OPh and for M = Ru, Y = CH₂ and R = Ph; the fluxional behaviour of [Ru₂H(CO)₅{μ-(RO)₂PN(Et)P(OR)₂}₂]⁺ (R = Me or Prⁱ) in solution is described.