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.     

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.     

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.     

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.     

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 .     

Photochemical reactions of metal carbonyls [M(CO)6 (M = Cr,Mo and W), Re(CO)5Br,Mn(CO)3Cp] with 2-hydroxyacetophenone methanesulfonylhydrazone (apmsh)

Five new complexes, [M(CO)₅(apmsh)] [M = Cr; (1), Mo; (2), W; (3)], [Re(CO)₄Br(apmsh)] (4) and [Mn(CO)₃(apmsh)] (5) have been synthesized by the photochemical reaction of metal carbonyls [M(CO)₆] (M = Cr, Mo and W), [Re(CO)₅Br], and [Mn(CO)₃Cp] with 2-hydroxyacetophenone methanesulfonylhydrazone (apmsh). The complexes have been characterized by elemental analysis, mass spectrometry, f.t.-i.r. and ¹H spectroscopy. Spectroscopic studies show that apmsh behaves as a monodentate ligand coordinating via the imine N donor atom in [M(CO)₅(apmsh)] (1–4) and as a tridentate ligand in (5).     

Fluxional Behaviour of Isocyanide Derivatives of Dodecacarbonyltetrairidium

The fluxional behaviour of [Ir₄(CO)₁₁(t-BuNC)] ( 1 ) and [Ir₄(CO)₁₁(ArNC)] (Ar = 4-methoxyphenyl, 4-tolyl, phenyl, 4-chlorophenyl, 4-nitrophenyl; 2 – 5 ) has been investigated by 2D and variable-temperature ¹³C-NMR. These techniques give new evidence of the processes responsible for CO exchange, namely two successive merry-go-rounds causing Cotton-like scrambling and a CO rotation about one metal center.     

Intramolecular Dynamics of Tetranuclear Iridium Carbonyl Cluster Compounds. Part III. Crystallographic and dynamic evidence for the intermediate of the ‘merry-go-round’ process in nonacarbonyl-μ3-(1,3,5-trithiane)-tetrairidium

The title complex crystallises in two C_3v, isomeric forms differing in carbonyl-ligand arrangement. In solution, the isomer 1b with three edge-bridging carbonyls on a common face of the metal tetrahedron converts via an endothermic equilibrium into the isomer 1u with no bridging carbonyls. The latter was shown by ¹³C-NMR to be the intermediate of the ‘merry-go-round’ process which exchanges the sites of the basal CO's.     

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.     

Intramolecular Dynamics of Tetranuclear Iridium Carbonyl Cluster Compounds. Part 1. Bromotri-μ-carbonyloctacarbonyltetrairidate(1–)

A 2D and variable-temperature ¹³C-NMR study indicates that a CO-site exchange occurs in the title complex via several consecutive processes, the first being a ‘merry-go-round’ of the basal CO's, the second a switch of basal face not involving unbridged intermediates.     

XPS characterization of SiO2-supported iridium producedin situ from Ir4(CO)12

The initial stage of Ir₄(CO)₁₂ physisorption on SiO₂ from solutions and the subsequent modifications induced by heating under different atmospheres are discussed with the help of XPS results obtained on samples treatedin situ. Ir₄(CO)₁₂ is shown to physisorb as crystallites. A good dispersion of crystallites on SiO₂ is obtainedvia heating at 373 K under Ar. Ir₄(CO)₁₂-supported clusters can be reduced to metal under mild conditions, with complete loss of ligands on controlled heating under Ar or H₂. The final products of the process are metal clusters, which are obtained at different nuclearities, depending on the duration of the process. We present the first report on the obtainment of Ir on SiO₂ at the same Ir4f_7/2 binding energy (b.e.) of bulk Ir.     

Crystal Structure of Tricarbonyl-[2,3-η:O-σ-(7,7-dimethoxy-5,6-dimethylidenebicyclo[2.2.1]hept-2-ene)]iron

The product of the reaction of [Fe(benzalacetone)(CO)₃] with 7,7-dimethoxy-5,6-dimethylidenebicyclo[2.2.1] hept-2-ene is tricarbonyl-[2,3-η:O-σ-(7,7-dimethoxy-5,6-dimethylidenebicyclo [2.2.1]hept-2-ene)]iron. Crystals are monoclinic, space group P2¹/c with a = 6.612(2), b = 11.610(4), c = 18.604(6) Å, and β = 95.91(2)°. The coordination at the metal atom is trigonal bipyramidal. The equatorial sites are occupied by 2 CO's and by the midpoint of the endocyclic double bond of the organic ligand. The axial sites are occupied by one CO group and the O-atom of one MeO group of the C(OMe)₂ bridge. It is an uncommon example of a d⁸ metal carbonyl complex bearing an O-bonded ligand.     

Water-Soluble Organometallic Compounds. 8[1]. Synthesis, Spectral Properties, and Crystal Structures of 1,3,5-Triaza-7-phosphaadamantane (PTA) Derivatives of Metal Carbonyl Clusters: Ru3(CO)9(PTA)3 and Ir4(CO)7(PTA)5

The syntheses of Ru₃(CO)₉(PTA)₃ and Ir₄(CO)₇(PTA)₅ were accomplished through the thermal reactions of Ru₃(CO)₁₂ or Ir₄(CO)₁₂ with the water-soluble phosphine, PTA(1,3,5-triaza-7-phosphaadamantane). The ruthenium derivative was shown by X-ray crystallography to consist of a triangular Ru₃ core with three nearly equal Ru–Ru bonds, with each ruthenium atom bearing an equatorially positioned PTA ligand. In Ir₄(CO)₇(PTA)₅ the iridium atoms define a tetrahedron which is bridged on three edges by CO ligands. One basal iridium atom contains two PTA ligands, while the other two basal and the apical iridium atoms each possess one PTA ligand in their coordination spheres. Although, Ru₃(CO)₉(PTA)₃ is only sparingly soluble in pure water, it is very soluble in aqueous solution of pH<4. Indeed the triruthenium cluster can be extracted reversibly between an aqueous and an organic phase (e.g., CH₂Cl₂) by changing the pH of the aqueous phase. On the other hand the more highly PTA substituted cluster, Ir₄(CO)₇(PTA)₅, exhibits good solubility in aqueous solution (pH 7 and below) and a variety of organic solvents. Both cluster derivatives are stable in deoxygenated, aqueous solutions for extended period of time (>24 h).     

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.     

New tetrahedral clusters of iridium. Crystal and molecular structure of μ3-phenylphosphidotri-μ-carbonyltricarbonyltetrakis(triphenylphosphine)-tetrahedro-tetrairidium

The reaction of Ir₄(CO)₁₂ with PPh₃ in toluene, under forcing conditions, yields a mixture of products, one of which has been identified by X-ray diffraction as Ir₄(μ₃-PPh)(μ₂-CO)₃(CO)₃(PPh₃)₄. It is the first iridium cluster to contain four triphenylphosphine groups and a phenylphosphido ligand. The metal tetrahedron displays a trigonal pyramidal distortion with average apical and basal edges of 2.747 and 2.894 », respectively. The latter value is ca. 0.18 » longer than the usual metal-metal bond length in iridium tetrahedra.     

Metal—olefin bonding. X-ray structures of trichloro-1,6-bis(diphenylphosphino)-trans-hex-3-enerhodium(III) and dichlorocarbonyl-1,6-bis(diphenylphosphino)-trans-hex-3-eneruthenium(II)

X-ray structures have been determined for the olefin-containing complexes RuCl₃(BDPH) and RuCl₂(CO)(BDPH); BDPH = 1,6-bis(diphenylphosphino)-trans-hex-3-ene. Both compounds crystallise in space group Pbca with eight molecules in unit cells of dimensions RhCl₃(BDPH) a 16.109(8), b 20.359(12), c 17.194(4) Å; RuCl₂(CO)(BDPH) a 16.279(1), b 20.160(1), c 17.334(1) Å. Least-squares refinement returned residuals, R, of 0.030 and 0.067 respectively. In the ruthenium complex the CO and one Cl ligand are statistically interchanged. Both complexes are characterised by weak metal—olefin bonding and a twisted olefin orientation. The geometries are compared with those in other Ir^I and Ir^III complexes containing the BDPH ligand.     

Variable-Temperature and -Pressure 31P-NMR Study of the Intramolecular PPh3 Migration in the Cluster Compound [Ir2Rh2(CO)11PPh3]

The reaction of [Ir₂Rh₂(CO)₁₂] with 1 mol-equiv. of PPh₃ yields [Ir₂Rh₂(CO)₁₁PPh₃] ( 1 ) as a mixture of two isomers with the phosphine ligand axially bound either to one basal Rh-atom in the kinetically preferred isomer 1 R or to one basal Ir-atom in the thermodynamically preferred isomer 11 . Both isomers are fluxional on the ¹³C-NMR time scale at low temperature due to CO scrambling. Around room temperature, a new type of fluxional process starts to operate which is responsible for the isomerisation 1R?11 , i.e. the intramolecular migration of the reputedly inert PPh₃ ligand from one metal centre to another. The activation volumes of conversions 1R → 11 and 11 → 1R are both positive, indicating that the migration of PPh₃ is dissociative in character. This article reports the first application of variable pressure ³¹P-NMR to mechanistic studies.     

Neue Phosphor-verbrückte Übergangsmetallcarbonyl-Komplexe Die Kristallstrukturen von [Re2(CO)7(PtBu)3], [Co4(CO)10(PtBu)2], [Ir4(CO)6(PtBu)6] und [Ni4(CO)10(PiPr)6]

New Phosphorus-bridged Transition Metal Carbonyl Complexes. The Crystal Structures of [Re₂(CO)₇(P^tBu)₃], [Co₄(CO)₁₀(P^tBu)₂], [Ir₄(CO)₆(P^tBu)₆], and [Ni₄(CO)₁₀(PⁱPr)₆], (P^tBu)₃ reacts with [Mn₂(CO)₁₀], [Re₂(CO)₁₀], [Co₂(CO)₈] and [Ir₄(CO)₁₂] to form the multinuclear complexes [M₂(CO)₇(P^tBu)₃] (M = Re ( 1 ), Mn ( 5 )), [Co₄(CO)₁₀(P^tBu)₂] ( 2 ) and [Ir₄(CO)₆(P^tBu)₆] ( 3 ). The reaction of (PⁱPr)₃ with [Ni(CO)₄] leads to the tetranuclear cluster [Ni₄(CO)₁₀(PⁱPr)₆] ( 4 ). The complex structures were obtained by X-ray single crystal structure analysis: ( 1 : space group P1 (Nr. 2), Z = 2, a = 917.8(3) pm, b = 926.4(3) pm, c = 1 705.6(7) pm, α = 79.75(3)°, β = 85.21(3)°, γ = 66.33(2)°; 2 : space group C2/c (Nr. 15), Z = 4, a = 1 347.7(6) pm, b = 1 032.0(3) pm, c = 1 935.6(8) pm, β = 105.67(2)°; 3 : space group P1 (Nr. 2), Z = 4, a = 1 096.7(4)pm, b = 1 889.8(10)pm, c = 2 485.1(12) pm, α = 75.79(3)°, β = 84.29(3)°, γ = 74.96(3)°; 4 : space group P2₁/c (Nr. 14), Z = 4, a = 2 002.8(5) pm, b = 1 137.2(8) pm, c = 1 872.5(5) pm, β = 95.52(2)°).     

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.     

Reactivity of Cyanide and Thiocyanate Towards the Nitrosyl Carbonyl [Co(CO)3(NO)]

The reaction of equimolar amounts of [Co(CO)₃(NO)] and [PPN]CN, PPN⁺ = (PPh₃)₂N⁺, in THF at room temperature resulted in ligand substitution of a carbonyl towards the cyanido ligand presumably affording the complex salt PPN[Co(CO)₂(NO)(CN)] as a reactive intermediate species which could not be isolated. Applying the synthetic protocol using the nitrosyl carbonyl in excess, the title reaction afforded unexpectedly the novel complex salt PPN[Co₂(μ-CN)(CO)₄(NO)₂] ( 1 ) in high yield. Because of many disorder phenomena in crystals of 1 the corresponding NBu₄⁺ salt of 1 has been prepared and the molecular structure of the dinuclear metal core in NnBu₄[Co₂(μ-CN)(CO)₄(NO)₂] ( 2 ) was determined by X-ray crystal diffraction in a more satisfactory manner. In contrast to the former result, the reaction of [PPN]SCN with [Co(CO)₃(NO)] yielded the mononuclear complex salt PPN[Co(CO)₂(NO)(SCN-κN)] ( 3 ) in good yield whose molecular structure in the solid was even determined and its composition additionally confirmed by spectroscopic means.