The reaction of Ir4(CO)12 with bases

The reaction of Ir₄(CO)₁₂ with potassium hydroxide in methanol and/or with sodium in tetrahydrofuran leads to the carbonyliridate anions [HIr₄(CO)₁₁]^?, [Ir₆(CO)₂₂]^2?, [Ir₈(CO)₂₀]^2?, [Ir₆(CO)₁₅]^2? and [Ir(CO)₄]^? obtained as salts with bulky cations. From these, the tetranuclear carbonyl hydride H₂Ir₄(CO)₁₁ and the hexanuclear carbonyl compound Ir₆(CO)₁₆ are also obtained.     

Surface-Mediated Organometallic Synthesis: High-Yield Syntheses of [Ir4(CO)12], [Ir6(CO)15]2−, and [Ir8(CO)22]2− by Controlled Reduction of Silica-Supported IrCl3 or [Ir(cyclooctene)2(μ-Cl)]2 in the Presence of Na2CO3 or K2CO3

The controlled reductive carbonylation under 1 atm. of CO of [Ir(cyclooctene)₂(μ-Cl)]₂, supported on a silica surface added with an alkali carbonate such as Na₂CO₃ or K₂CO₃, can be directed toward the formation of [Ir₄(CO)₁₂], K₂[Ir₆(CO)₁₅] or K₂[Ir₈(CO)₂₂] by controlling (i) the nature and amount of alkali carbonate, (ii) the amount of surface water, and (iii) the temperature. [Ir₄(CO)₁₂] can also be prepared by direct controlled reductive carbonylation of IrCl₃ supported on silica in the presence of well controlled amounts of Na₂CO₃. These efficient silica-mediated syntheses are comparable to conventional synthetic methods carried out in solution or on the MgO surface. Like in strongly basic solution or on the MgO surface, the initially formed [Ir₄(CO)₁₂], the first step of nucleation which does not require a strong basicity of the silica surface, gives in a second time sequentially [Ir₈(CO)₂₂]^2? and [Ir₆(CO)₁₅]^2? according to reaction conditions and basicity of the silica surface.     

Double deoxygenation of PPN(NO2) using metal carbonyl clusters of cobalt,rhodium, and iridium

The reaction of PP(NO₂) with M₄(CO)₁₂ (M = Co, Rh) gives the nitrido clusters [M₆N(CO)₁₅]^? in 13 and 21% yields, respectively. A high yield synthesis (77%) of [Rh₆N(CO)₁₅)]^? directly from Rh₆(CO)₁₆ and PPN(NO₂) is also presented. PPN(NO₂) reacts with Ir₄(CO)₁₂ to give the new isocyanato cluster, [Ir₄(NCO)(CO)₁₁]^? in 34% yield, while the direct synthesis of this isocyanate product occurs in 77% yield from PPN(N₃) and Ir₄(CO)₁₂. Modifications of published procedures for the preparation of [N(C₂H₅)₄]₂ [Ir₆(CO)₁₅] and Ir₆(CO)₁₆ are reported that allow shorter reaction times and give higher yields. The reaction of Ir₆(CO)₁₆ with one equivalent of PPN(NO₂) generates a new cluster, PPN[Ir₆(CO)₁₅(NO)], in 57% yield which is proposed to contain a bent nitrosyl ligand. An additional equivalent of PPN(NO₂) gives (PPN)₂[Ir₆(CO)₁₅] in 84% yield with the evolution of N₂O as well as CO₂.     

Metal formyl complexes. Hydride transfer to group VIII transition metal carbonyl clusters

The reaction of LiBH(C₂H₅)₃ with Os₃(CO)₁₂ or Ir₄(CO)₁₂ leads to the formation of spectroscopically detectable formyl complexes. In the latter case, the complex is smoothly converted to [Ir₄(CO)₁₁H]^?, an expected decompositioFn complex of the corresponding polynuclear formyl complex, [Ir₄(CO)₁₁CHO]^?.     

Dual Metal Active Sites in an Ir1/FeOx Single‐Atom Catalyst: A Redox Mechanism for the Water‐Gas Shift Reaction

Herein, we report a theoretical and experimental study of the water‐gas shift (WGS) reaction on Ir₁/FeO_x single‐atom catalysts. Water dissociates to OH* on the Ir₁ single atom and H* on the first‐neighbour O atom bonded with a Fe site. The adsorbed CO on Ir₁ reacts with another adjacent O atom to produce CO₂, yielding an oxygen vacancy (O_vac). Then, the formation of H₂ becomes feasible due to migration of H from adsorbed OH* toward Ir₁ and its subsequent reaction with another H*. The interaction of Ir₁ and the second‐neighbouring Fe species demonstrates a new WGS pathway featured by electron transfer at the active site from Fe³⁺?O???Ir²⁺?O_vac to Fe²⁺?O_vac???Ir³⁺?O with the involvement of O_vac. The redox mechanism for WGS reaction through a dual metal active site (DMAS) is different from the conventional associative mechanism with the formation of formate or carboxyl intermediates. The proposed new reaction mechanism is corroborated by the experimental results with Ir₁/FeO_x for sequential production of CO₂ and H₂.     

New media in homogeneous catalysis: wet sodium or tetrabutylammonium hydrogensulfate salts for reppe syntheses catalyzed by a ru(ii) carbonyl complex

The ruthenium(II) complex fac-[Ru(CO)₂(H₂O)₃(C(O)C₂H₅)][CF₃SO₃] dissolved in aqueous tetrabutylammonium hydrogensulfate ([(CH₃(CH₂)₃)₄N][HSO₄]) or sodium hydrogensulfate (NaHSO₄) catalyzes the hydrocarboxylation of ethylene to propionic acid and additionally produces minor amounts of hydrocarbonylation products (diethyl ketone and propanal), under water-gas shift reaction conditions. This system is stable with a selectivity of 90% to propionic acid for high ethylene conversion. A turnover frequency of propionic acid, TOF(C₂H₅CO₂H)/24?h?=?5?×?10³ (TOF (C₂H₅CO₂H)?=?([(moles of C₂H₅CO₂H)/(moles of Ru)?×?rt)]?×?24?h) was achieved for Ru?=?7.45?×?10^?4?mol, [(CH₃(CH₂)₃)₄N][HSO₄]?=?80?g (2.36?×?10^?2?mol); H₂O?=?40?g (2.22?mol); CO?=?C₂H₄?=?20?g (total pressure?=?88?atm); T?=?150°C by a reaction time (rt) of 2.87?h. The countercation (sodium or tetrabutylammonium), the ruthenium concentration and the hydrogensulfate/H₂O ratio of the medium affect the catalytic reaction. A nonlinear dependence on total ruthenium concentration was shown. The data are discussed in terms of a potential catalytic cycle. Formation of propionic acid comes from hydrolysis, and formation of diethyl ketone and propanal comes from hydrogenolysis of the Ru-ketyl and Ru-acyl complexes, respectively.     

Intramolecular Dynamics of Tetranuclear Iridium Carbonyl Cluster Compounds. Part IV. Derivatives with monodentate ligands and edge-bridging bidentate ligands

The fluxionality of [Ir₄(CO)₈(μ₂-CO)₃L] (L = Br^?, I^?, SCN^?, NO₂^?, P(4-ClC₆H₄)₃, PPh₃, P(4-MeOC₆H₄)₃, P(4-Me₂NC₆H₄)₃), as studied by 2D-¹³C-NMR in solution, is due to two successive scrambling processes: the merry-go-round of six basal CO's and CO bridging to alternative faces of the Ir₄ tetrahedron. The basicity of the ligand L has no significant effect on the activation parameters. The scrambling process of lowest activation energy in [Ir₄(CO)₇(μ₂-CO)₃(PMePh₂)₂] correspond to the two possible synchronous CO bridging about a unique face of the metal tetrahedron swapping the relative axial and radial positions of the ligands L. The disubstituted clusters [Ir₄(CO)₁₀(μ₂-L? L)] with one edge-bridging ligand have a ground-state geometry with three edge-bridging CO's (L? L = bis(diphenylphosphino)methane, bis(diphenylarsino)methane, bis(diphenylphosphino)propane) or with all terminal CO's (L? L = CH₃SCH₂SCH₃). In all cases, the fluxional process of lowest activation energy in the merry-go-round of six CO's about a unique triangular face. For the P and As donor ligands, this process is followed by the rotation of terminal CO's bonded to two Ir-atoms residing on the mirror plane of the unbridged intermediate.     

Synthesis and x-ray characterization of the [Ir6(CO)15COEt]-Anionic Cluster

The reaction of Ir₆(CO)₁₆ with a mixture of CO, H₂, and ethylene yields the [Ir₆(CO)₁₅COEt]^- anion, which has been shown by X-ray diffraction to contain an octahedral iridium cluster bearing a —bonded acyl group; the arrangement of the 11 terminal and 4 edge-bridging carbonyl groups is different from that found in both the analogous rhodium complex and the parent Ir₆(CO)₁₆ carbonyl.     

Iridium Cluster Chemistry: The Synthesis and the Solid State Structures of [HIr5(CO)12]2− and [HIr4(CO)10PPh3]−

The cluster [HIr₅(CO)₁₂]^2- (1) was prepared by condensation of [HIr₄(CO)₁₁]^- and [Ir(CO)₄]^- (molar ratio 1:1) in refluxing THF, with almost quantitative yields. Its solid state structure was determined by X-ray diffraction at low temperature on the salt [PPh₃CH₂Ph]₂[HIr₅(CO)₁₂]. The metal atoms define a trigonal bipyramidal arrangement. The hydride ligand was located indirectly as a bridge between apical and equatorial metal atoms. The phosphine-substituted cluster [HIr₄(CO)₁₀PPh₃]^- (2) was synthetized by CO displacement on [HIr₄(CO)₁₁]^-, in THF at room temperature. This reaction is selective, with no traces of polysubstitution products. In the solid state, the hydride and the triphenylphosphine are axially bound on basal iridium atoms; the terminal hydrogen atom was directly located by X-ray analysis at a Ir–H distance of 1.57(9) Å. On the contrary, two isomers are present in THF solution, and they interconvert rapidly at room temperature, as shown by¹H and ³¹P NMR spectra.     

New tetrahedral cluster compounds of iridium. Synthesis of the anions [Ir4(CO)11X]− (X = Cl,Br, I,CN, SCN) and x-ray structure of [PPh4] [Ir4(CO)11Br]

[Ir₄(CO)₁₁X]^? anions are obtained by reaction of halide and pseudo-halide ions with Ir₄(CO)₁₂. X-ray determination of the structure of [Ir₄(CO)₁₁Br]^? shows that the carbonyl arrangement differs from that of the parent Ir₄(CO)₁₂, and is similar to that known for Co₄(CO)₁₂; one terminal CO group in the basal M₃(CO)₉ moiety is replaced by the bromide ligand, and two of the bridging CO groups become markedly asymmetric.     

Facile Carbon–Fluorine Bond Activation and Subsequent Functionalisation of 1,1‐Difluoroethylene and Tetrafluoroethylene Promoted by Adjacent Metal Centres

The bridging fluoroolefin ligands in the complexes [Ir₂(CH₃)(CO)₂(μ‐olefin)(dppm)₂][OTf] (olefin=tetrafluoroethylene, 1,1‐difluoroethylene; dppm=μ‐Ph₂PCH₂PPh₂; OTf^?=CF₃SO₃^?) are susceptible to facile fluoride ion abstraction. Both fluoroolefin complexes react with trimethylsilyltriflate (Me₃SiOTf) to give the corresponding fluorovinyl products by abstraction of a single fluoride ion. Although the trifluorovinyl ligand is bound to one metal, the monofluorovinyl group is bridging, bound to one metal through carbon and to the other metal through a dative bond from fluorine. Addition of two equivalents of Me₃SiOTf to the tetrafluoroethylene‐bridged species gives the difluorovinylidene‐bridged product [Ir₂(CH₃)(OTf)(CO)₂(μ‐OTf)(μ‐C?CF₂)(dppm)₂][OTf]. The 1,1‐difluoroethylene species is exceedingly reactive, reacting with water to give 2‐fluoropropene and [Ir₂(CO)₂(μ‐OH)(dppm)₂][OTf] and with carbon monoxide to give [Ir₂(CO)₃(μ‐κ¹:η²‐C?CCH₃)(dppm)₂][OTf] together with two equivalents of HF. The trifluorovinyl product [Ir₂(κ¹‐C₂F₃)(OTf)(CO)₂(μ‐H)(μ‐CH₂)(dppm)₂][OTf], obtained through single C? F bond activation of the tetrafluoroethylene‐bridged complex, reacts with H₂ to form trifluoroethylene, allowing the facile replacement of one fluorine in C₂F₄ with hydrogen.     

Diphosphine ligand chelation and bridging and regiospecific ortho metalation in the reaction of 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) with Ir4(CO)12: X-ray diffraction structures of Ir4(CO)7(μ-CO)3(bpcd), Ir4(CO)5(μ-CO)3(bpcd)(μ-bpcd), and HIr4(CO)4(μ-CO)3(bpcd)[μ-PhP(C6H4)CC(PPh2)C(O)CH2C(O)]

Me₃NO activation of the tetrairidium cluster Ir₄(CO)₁₂ (1) in presence of the diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) furnishes the bpcd-substituted clusters Ir₄(CO)₁₀(bpcd) (3) and Ir₄(CO)₈(bpcd)₂ (4) as the minor and major products, respectively. Cluster 3 has been isolated as the sole observable product from the reaction of [Ir₄(CO)₁₁Br][Et₄N] (2) with bpcd in presence of AgBF₄ at room temperature. Both 3 and 4 have been isolated and fully characterized in solution by spectroscopic methods. The solid-state structure of 3 reveals that the ancillary bpcd ligand is bound to a single iridium center, with chelating and bridging bpcd ligands found in the X-ray structure of cluster 4. Cluster 4 is unstable at room temperature and slowly loses CO to afford the hydride-bridged cluster HIr₄(CO)₄(μ-CO)₃(bpcd)[μ-PhP(C₆H₄)CC(PPh₂)C(O)CH₂C(O)] (5). Cluster 5 has been fully characterized in solution by IR and NMR spectroscopies, and the C–H bond activation attendant in the ortho metalation step is shown to occur regioselectively at one of the aryl groups associated with the bridging bpcd ligand. The redox properties of clusters 3–5 have been explored and the electrochemical behavior discussed with respect to extended Hückel MO calculations and related diphosphine-substituted cluster compounds prepared by our groups.     

Solution Equilibria in Trialkyl-Phosphite Derivatives of [Ir4(CO)12]. Crystal Structure of [Ir4(CO)11{P(OCH2)3CEt}]

The monosubstituted [Ir₄(CO)₁₁L] clusters (L = P(OPh)₃, 1 ; L = P(OMe)₃, 2 ; L = P(OCH₂)₃CEt, 3 ) were obtained in good yields by the reaction of [Ir₄(CO)₁₁ I ]^? with the corresponding phosphite. In the solid state, cluster 3 has a C_s geometry with all terminal ligands as shown by an X-ray analysis. Three isomers are present in solution: one with terminal ligands ( A ) and two with three edge-bridging CO's and with L in axial ( B ) or radial ( C ) position (see Scheme). The thermodynamic and kinetic parameters of isomerisations B ? A and A ? C were determined by simulation of the variable-temperature ³¹P-NMR spectra. The three isomers correspond to three minima on the kinetic pathway of CO scrambling, whose relative energies vary independently within a small range (1–9 kJ mol^?1 at 298 K). At low temperature, isomer C is always the least stable and is not observed for 1 which bears the most bulky phosphite ligand. The isomerisations are due to two intramolecular merry-go-rounds of CO groups about two unequivalent faces of the unbridged species A .     

Synthesis,Reactivity, and Fluxional Behaviour of [Ir2Rh2(CO)12], and Crystal Structure of [Ir2Rh2(CO)8(norbornadiene)2]

The synthesis of [Ir₂Rh₂(CO)₁₂] ( 1 ) by the literature method gives a mixture 1 /[IrRh₃(CO)₁₂] which cannot be separated using chromatography. The reaction of [Ir(CO)₄]^? with 1 mol-equiv. of [Rh(CO)₂(THF)₂]⁺ in THF gives pure 1 in 61% yield. Crystals of 1 are highly disordered, unlike those of its derivative [Ir₂Rh₂(CO)₅(μ₂-CO)₃(norbornadiene)₂] which were analysed using X-ray diffraction. The ground-state geometry of 1 in solution has three edge-bridging CO's on the basal IrRh₂ face of the metal tetrahedron. Time averaging of CO's takes place above 230 K. The CO site exchange of lowest activation energy is due to one synchronous change of basal face, as shown by 2D- and VT-¹³C-NMR. Substitution of CO by X^? in 1 takes place at a Rh-atom giving [Ir₂Rh₂(CO)₈(μ₂-CO)₃X]^? (X = Br, I). Substitution by bidentate ligands gives [Ir₂Rh₂(CO)₇(μ₂-CO)₃(η⁴-L)] (L = norbornadiene, cycloocta-1,5-diene) where the ligand L is chelating a Rh-atom of the basal IrRh₂ face. Carbonyl substitution by tridentate ligands gives [Ir₂Rh₂(CO)₆(μ₂-CO)₃(μ₃-L)] (L = 1,3,5-trithiane, tripod) with L capping the triangular basal face of the metal tetrahedron. Carbonyl scrambling is also observed in these substituted derivatives of 1 and is mainly due to the rotation of three terminal CO's about a local C₃ axis on the apical Ir-atom.     

Supported metals and metal oxides as promoters for the metal dimer and cluster catalysed co substitution reaction

Promotional effects due to PtO₂, PdO, Pd/C and Pd/CaCO₃ on the metal dimer or cluster (e.g. [(η⁵-C₅H₅)Fe(CO)₂]₂, Ru₃(CO)₁₂, Ir₄(CO)₁₂) catalysed reaction between metal carbonyls and isonitriles are shown to lead to enhanced reaction rates for the metal carbonyl substitution reaction.     

Unsaturation in homoleptic tetranuclear iridium carbonyls: a comparison of density functional theory with the MP2 method in metal cluster structures

The lowest energy Ir₄(CO)₁₂ structure is predicted by density functional theory to be a triply bridged structure analogous to the experimental structures for its lighter congeners M₄(CO)₉(??-CO)₃ (M=Co, Rh). The experimental unbridged structure for Ir₄(CO)₁₂ is predicted to lie ~6?kcal/mol above the triply bridged structure. However, the MP2 method predicts the unbridged structure for Ir₄(CO)₁₂ to be the lowest energy structure by ~9?kcal/mol over the triply bridged structure. The lowest energy Ir₄(CO)₁₁ structure is predicted to be a doubly bridged structure with a central tetrahedral Ir₄ unit. A higher energy Ir₄(CO)₁₁ structure at ~18?kcal/mol above this global minimum is found with an unusual ??₄-CO group bridging all four atoms of a central Ir₄ butterfly. This Ir₄(CO)₈(??-CO)₂(??₄-CO) structure is analogous to the lowest energy Co₄(CO)₁₁ structure found in a previous theoretical study, as well as Rh₄(CO)₄(??-CO)₄(PBu ₃ ^t )₂(PtPBu ₃ ^t )(??₄-CO), which has been synthesized by Adams and coworkers. The Ir₄ tetrahedron is remarkably persistent in the more highly unsaturated Ir₄(CO) _n (n?=?10, 9, 8) structures with relatively little changes in the Ir?CIr distances as carbonyl groups are removed. This appears to be related to the spherical aromaticity in the tetrahedral Ir₄ structures.     

Decacarbonylbis(methylcyclopentadienyl)‐tetrahedro‐diiridiumdimolybdenum and decacarbonylbis(tetramethylcyclopentadienyl)‐tetrahedro‐diiridiumdimolybdenum dichloromethane hemisolvate

The two title compounds, [Mo₂Ir₂(C₆H₇)₂(CO)₁₀] and [Mo₂Ir₂(C₉H₁₃)₂(CO)₁₀]·0.5CH₂Cl₂, respectively, or collectively [Mo₂Ir₂(μ‐CO)₃(CO)₇(η⁵‐C₅H_5?nMe_n)₂] (n = 1 or 4), have a pseudo‐tetrahedral Mo₂Ir₂ core geometry, an η⁵‐­C₅H_5?nMe_n group ligating each Mo atom, bridging carbonyls spanning the edges of an MoIr₂ face and seven terminally bound carbonyl groups.     

Heat of formation of Benzophenone Oxide

The heat of formation of benzophenone oxide, Ph₂CO₂, was measured using photoacoustic calorimetry. The enthalpy of the reaction Ph₂CN₂ + O₂ → Ph₂CO₂ + N₂ was found to be ?48.0 ±0.8 kcal mol^?1 and ΔH_f(Ph₂CN₂) was determined by measuring the reaction enthalpy for Ph₂CN₂ + EtOH → Ph₂CHOEt + N₂ (?53.6 ±1.0 kcal mol^?1). Taking ΔH_f(PhCHOEt) = ?10.6 kcal mol^?1 led to ΔH_f(Ph₂CN₂) = 99.2 ± 1.5 kcal mol^?1 and hence to ΔH_f(Ph₂CO₂) = 51.1 ± 2.0 kcal mol^?1. The results imply that the self-reaction of benzophenone oxide i.e., 2Ph₂CO₂ → 2Ph₂CO + O₂ is exothermic by ?76.0 ±4.0 kcal mol^?1.     

The reaction of bis[tricarbonyl(triphenylphosphine)iridium],Ir2(CO)6(PPH3)2, with diazonium salts

The reaction of Ir₂(CO)₆(PPh₃)₂ with p-substituted aryldiazoniurn salts gives the o-metalated complexes [Ir(CO)₂(NHNC₆H₃R) (PPh₃)]₂²⁺ 2BF₄^?. These react with KOH in ethanol to give the deprotonated derivatives, and with halogens to give halogenated derivatives by cleavage of the carbonmetal bond.     

Chemistry of iridium carbonyl : I. Chemical and structural characterization of the tetranuclear anions [Ir4(μ-CO)3(CO)8(COOR)]-

1 The anions [Ir₄(CO)₁₁(COOR)^- (R  Me, Et) have been prepared by reacting Ir₄(CO)₁₂ with alkali alkoxides in dry alcohol and under an atmosphere of carbon monoxide. The reaction of [Ir₄(CO)₁₁(COOMe)]^- with primary and secondary alcohols (EtOH, PrⁱOH) gives rise to specific alcoholysis. The anions [Ir₄(CO)₁₁(COOR)^- react with acids in THF solution to give quantitatively Ir₄(CO)₁₂. The chemical, spectroscopic and crystallographic characterization of the tetranuclear anions are reported.