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.     

Erratum

The reaction of Ir₆(CO)₁₆ with P(OPh)₃ in toluene yields Ir₆(CO)₁₂[P(OPh)₃]₄ which has been shown by X-ray diffraction to contain an octahedral cluster bearing four terminal P(OPh)₃ ligands, one face-bridging, three edge-bridging and eight terminal carbonyl groups. The carbonyl arrangement is different from that found in the analogous rhodium complex.     

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.     

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.     

Neutral substituted carbonyl clusters of iridium. Synthesis and X-ray characterization of tri-μ3-carbonyl-μ-carbonylheptacarbonylpentakis(trimethylphosphite)-octahedro-hexairidium

The reaction of Ir₆(CO)₁₆ with P(OMe)₃ in toluene yields Ir₆(CO)₁₁ [P(OMe)₃]₅ which has been shown by X-ray diffraction to contain an octahedral cluster of iridium atoms bearing five terminal trimethylphosphite ligands, three face-bridging, one edge-bridging and seven terminal carbonyl groups.     

Synthesis,stereodynamics, and reactivity of isonitrile derivatives of dodecacarbonyltetrairidium

The reaction of Ir₄₍CO)₁₂ with t-BuNC or MeNC in the presence of trimethylamine oxide in refluxing tetrahydrofuran provides the substituted iridium clusters Ir₄(CO)_12-x(RNC)_x] (χ  14; R  t-Bu, Me). The infrared and ¹³C NMR spectra of these molecules indicate that most of them adopt structures related to Ir₄(CO)₁₂, i.e., they have only terminal carbonyl ligands. The variable temperature ¹³C NMR spectra for Ir₄(CO)₁₁(t-BuNC) establish a carbonyl scrambling process which is the formal inverse of the C_3v→ T_d scrambling mechanism proposed for Rh₄(CO)₁₂. The kinetics of substitution of Ir₄(CO)₁₂ by t-BuNC have been studied. Each substitution step occurs by a ligand-dependent, overall second-order reaction at a rate much greater than for substitution by PPh₃. The observed differences between t-BuNC and PPh₃, can be rationalized on the basis of steric differences between the two ligands.     

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.     

Synthesis of [Ir3Rh(CO)12] and Fluxional Behaviour of Some of Its Substituted Derivatives

The redox condensation of [Ir(CO)₄]^–, [Ir(cod)(THF)₂]⁺, and [Rh(cod)(THF)₂]⁺ (cod = cycloocta-1,5-diene) followed by saturation with CO (1 atm) in THF afforded the first synthetic route to pure [Ir₃Rh(CO)₁₂] ( 1 ). Substitution of CO by monodentate ligands gave [Ir₃Rh(CO)₈(μ₂-CO)₃L] (L = Br^–, 2 ; I^–, 3 ; bicyclo[2.2.1]hept-2-ene, 4 ; PPh₃, 5 ). Clusters 2 – 5 have C_s symmetry with the ligand L bound to the basal Rh-atom in axial position. They are fluxional in solution at the NMR time scale due to two CO scrambling processes: the merry-go-round of basal CO's and changes of basal face. An additional process takes place in 5 above room temperature: the intramolecular migration of PPh₃ from the Rh- to a basal Ir-atom. Substitution of CO by polydentate ligands gave [Ir₃Rh(CO)_7–x(μ₂-CO)₃(η⁴-L)x] (L = bicyclo[2.2.1]hepta-2,5-diene (= norbornadiene; nbd), x = 1, 6 ; L = nbd, x = 2, 13 ; L = cod, x = 1, 7 ; L = cod x = 2, 15 ), [Ir₃Rh(CO)₇(μ₂-CO)₃(η²-diars)] (diars = 1,2-phenylenebis-(dimethylarsine); 8 ), [Ir₃Rh(CO)₇(μ₂-CO)₃(η⁴-L)] (L = methylenebis(diphenylphosphine), bonded to 2 basal Ir-atom ( 9a ) or one Ir- and one Rh-atom ( 9b )), [Ir₃Rh(CO)₆(μ₂-CO)₃(η⁴-nbd)PPh₃] ( 12 ), and [Ir₃Rh(CO)₆(μ₂-CO)₃(μ₃-L)] (L = 1,3,5-trithiane, 10 ; L = CH(PPh₂)₃, 11 ). Complexes 6 – 8 , 9a , 10 , and 11 have C_s symmetry, the others C₁ symmetry. They are fluxional in solution due to CO scrambling processes involving 1, 3, or 4 metal centres as deduced from 2D-EXSY spectra. Comparison of the activation energies of these processes with those of the isostructural Ir₄ and Ir₂Rh₂ compounds showed that substitution of Ir by Rh in the basal face of an Ir₄ compound slows the processes involving 3 or 4 metal centres (merry-go-round and change of basal face), but increases the rate of carbonyl rotation about an Ir-atom.     

Iridium Cluster Chemistry: The Synthesis and the Solid-State Structure of [Ir11(CO)23]3−

The cluster [Ir₁₁(CO)₂₃]^3– was obtained by reaction of [Ir₁₀(CO)₂₁]^2– and [Ir(CO)₄]^– in refluxing MeCN, and its solid-state structure was determined on the salt [NEt₄]₃[Ir₁₁(CO)₂₃]. The metallic framework of D_3h symmetry is composed by three face-fused octahedra, all sharing a common edge. The cluster contains 9 edge bridging and 14 terminal carbonyl ligands, a disposition different from that of the two isomeric forms of the isoelectronic [Rh₁₁(CO)₂₃]^3–, both having, in the solid-state, more edge-bridging COs. Naked clusters of non-transition metals, found in binary and ternary materials, such as Cs₁₁O₃, display very similar trioctahedral polyedra.     

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.     

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.     

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.     

Reactions of metal carbonyl cluster complexes with multidentate phosphine ligands; reactions with bis(diphenylphosphino)methane

Reactions of Rh₆(CO)₁₆ with bis(diphenylphosphino)methane (dppm) gave Rh₆(CO)₁₄(dppm), Rh₆(CO)₁₂(dppm)₂, or Rh₆(CO)₁₀(dppm)₃, depending upon the reaction conditions. Rh₄(CO)₁₀(dppm) may be obtained from the reaction of Rh₄(CO)₁₂ with dppm, but this derivative rapidly decomposes in solution to give Rh₄(CO)₈(dppm)₂, Rh₆(CO)₁₄(dppm), and Rh₆(CO)₁₂(dppm)₂. Ir₄(CO)₁₀(dppm) and Ir₄(CO)₈(dppm)₂ have also been prepared, and their structures are discussed on the basis of infrared and ³¹P NMR spectroscopic data.     

Energy-dependent Electrospray Ionisation Mass Spectrometry of Carbonyl Clusters

The electrospray ionisation mass spectra (EDESI-MS) of Ru₆C(CO)₁₆(PPh₃) and Ir₄(CO)₁₁(PR₃) (PR₃=PPh₃, P(p-C₆H₄OMe)₃, P(p-C₆H₄NMe₂)₃, P(p-C₆H₄Cl)₃, P(OPh)₃, P(OMe)₃, PO₃C₅H₉) are described and the relative importance of carbonyl loss versus phosphine loss as a fragmentation pathway is assessed. Qualitatively, the phosphine ligands bind more strongly to Ir₄(CO)₁₁ clusters than to Ru₆C(CO)₁₆. The influence on the collision cell pressure on MS/MS spectra of transition metal carbonyl cluster anions is also explored showing that a greater, simultaneous, distribution of fragment ions is produced as the collision cell pressure is increased.Dedicated to Prof. Brian F. G. Johnson on the occasion of his retirement.     

Intramolecular Dynamics of Tetranuclear Iridium Carbonyl Cluster Compounds. Part V. Polysubstituted derivatives of [Ir4(CO)12]

The dynamic behaviour of twelve polysubstituted derivatives of [Ir₄(CO)₁₂] has been investigated in solution, using 2D-EXSY, and VT-³¹P- and ¹³C-NMR. [Ir₄(CO)₆(μ₂-CO)₃(η⁴-diarsine) PPh₃] and [Ir₄(CO)₆(μ₂-CO)₃(η⁴-nor-bornadiene)(PMePh₂)] exhibit two isomeric forms in solution, which interconvert through an intramolecular change of basal face. The related cluster [Ir₄(CO)₆(μ₂-CO)₃(η⁴-norbornadiene)PPh₃] exists as a single isomer in solution. It displays rotation of CO ligands about the apical Ir-atom, followed by two consecutive changes of basal face. The tetrasubstituted clusters with two chelating ligands [Ir₄(CO)₅(μ₂-CO)₃(η⁴-diolefin)₂] also exhibit rotation of apical CO's, the activation energy increases with greater steric hindrance of the radical ligands. A quantitative analysis of the ³¹P- and ¹³C-2D-EXSY spectra followed by simulation of the corresponding VT-NMR spectra of [IR₄(CO)₅(μ₂-CO)₃(μ₂-L)₂] (L = bis(diphenylphosphino)methane and 1,3-bis(diphenylphosphino)propane) revealed a pairwise averaging of the P-atoms, caused by two parallel changes of basal face averaging all CO ligands. In addition, the restricted rotation of ligands about the apical Ir-atom was identified at higher temperatures. The remaining clusters are either rigid on the NMR time scale, or display CO-scrambling about a single Ir-atom.     

Tetrairidium carbonyl clusters of mono- and di-olefins

The reactions of NEt₄ [Ir₄(CO)₁₁ Br] (I) with mono- and di-olefins in the presence of AgBF₄ gave high yields ( > 90%) of Ir₄(CO)₁₁ (olefin) (II) and Ir4(CO)₁₀(η⁴-diolefin) (III). Oxidation of Ir₄(CO)₁₁ (L = PPh₃, AsPh₃) in the presence of an excess of diolefin by 1 eq. ON(CH₃)₃ gave the clusters Ir₄(CO)₉L(η⁴-diolefin) (IV) and Ir₄(CO)₇L(η⁴-diolefin)₂ (V). Sulphur dioxide quantitatively displaces the monoolefin ligand from II to give Ir₄(CO)₉(μ₂-CO)₂(μ₂-SO₂), which is the first example of a tetrairidium- SO₂ cluster.     

Salts of Anionic Metal Carbonyl Clusters with Cryptand[2.2.2](Na+), DB‐18‐crown‐6(Na+), and Paramagnetic Cp*2Cr+ Cations Obtained by Reduction

Reduction of neutral metal clusters (Co₄(CO)₁₂, Ru₃(CO)₁₂, Fe₃(CO)₁₂, Ir₄(CO)₁₂, Rh₆(CO)₁₆, {CpMo(CO)₃}₂, {Mn(CO)₅}₂) by decamethylchromocene (Cp*₂Cr) or sodium fluorenone ketyl in the presence of cryptand[2.2.2] and DB‐18‐crown‐6 was studied. Nine new salts with paramagnetic Cp*₂Cr⁺, cryptand[2.2.2](Na⁺), and DB‐18‐crown‐6(Na⁺) cations and [Co₆(CO)₁₅]^2– ( 1 , 2 ), [Ru₆(CO)₁₈]^2– ( 3 – 4 ) dianions, [Rh₁₁(CO)₂₃]^3– ( 6 ) trianions, and new [Ir₈(CO)₁₈]^2– ( 5 ) dianions were obtained and structurally characterized. The increase of nuclearity of clusters under reduction was shown. Fe₃(CO)₁₂ preserves the Fe₃ core under reduction forming the [Fe₃(CO)₁₁]^2– dianions in 7 . The [CpMo(CO)₃]₂ and [Mn(CO)₅]₂ dimers dissociate under reduction forming mononuclear [CpMo(CO)₃]^– ( 8 ) and [Mn(CO)₅]^– ( 9 ) anions. In all anions the increase of negative charge on metal atoms shifts the bands attributed to carbonyl C–O stretching vibrations to smaller wavenumbers in agreement with the elongation of the C–O bonds in 1 – 9 . In contrast, the M–C(CO) bonds are noticeably shortened at the reduction. Magnetic susceptibility of the salts with Cp*₂Cr⁺ is defined by high spin Cp*₂Cr⁺ (S = 3/2) species, whereas all obtained anionic metal clusters and mononuclear anions are diamagnetic. Rather weak magnetic coupling between S = 3/2 spins is observed with Weiss temperature from –1 to –11 K. That is explained by rather long distances between Cp*₂Cr⁺ and the absence of effective π–π interaction between them except compound 7 showing the largest Weiss temperature of –11 K. The {DB‐18‐crown‐6(Na⁺)}₂[Co₆(CO)₁₅]^2– units in 2 are organized in infinite 1D chains through the coordination of carbonyl groups of the Co₆ clusters to the Na⁺ ions and π–π stacking between benzo groups of the DB‐18‐crown‐6(Na⁺) cations.     

Trimethylphosphite derivatives of the mixed cobalt—iridium tetranuclear cluster Co2Ir2(CO)12

Up to four carbonyl groups of Co₂Ir₂(CO)₁₂ have been replaced by trimethylphosphite to form tetranuclear clusters of formula Co₂Ir₂(CO)_12?n[P(OMe)₃]_n. The clusters do not exhibit the redistribution of the metal core which is observed in the case of mixed cobalt—rhodium clusters. Attachment of three or four trimethylphosphites to the metal skeleton of the cluster inhibits the scrambling of the carbonyl groups.     

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]^?.     

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.