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  • 1
    Electronic Resource
    Electronic Resource
    Intramolecular Dynamics of Tetranuclear Iridium Carbonyl Cluster Compounds. Part VPart IV: [1].. Polysubstituted derivatives of [Ir4(CO)12] (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 754-770 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770317
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  • 2
    Electronic Resource
    Electronic Resource
    Synthesis of [Ir3Rh(CO)12] and Fluxional Behaviour of Some of Its Substituted Derivatives (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1869-1885 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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 Cs 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 Cs 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.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770718
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  • 3
    Electronic Resource
    Electronic Resource
    Variable-Temperature and -Pressure 31P-NMR Study of the Intramolecular PPh3 Migration in the Cluster Compound [Ir2Rh2(CO)11PPh3] (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 547-553 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770216
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  • 4
    Electronic Resource
    Electronic Resource
    Synthesis, Reactivity, and Fluxional Behaviour of [Ir2Rh2(CO)12], and Crystal Structure of [Ir2Rh2(CO)8(norbornadiene)2] (1993)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 76 (1993), S. 2913-2925 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19930760815
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