Mixed-Metal Cluster Chemistry. 19. Crystallographic, Spectroscopic, Electrochemical, Spectroelectrochemical, and Theoretical Studies of Systematically Varied Tetrahedral Group 6−Iridium Clusters

University of Canberra, Canberra, Australian Capital Territory, Australia
Journal of the American Chemical Society (Impact Factor: 12.11). 05/2002; 124(18):5139-53. DOI: 10.1021/ja0173829
Source: PubMed


A systematically varied series of tetrahedral clusters involving ligand and core metal variation has been examined using crystallography, Raman spectroscopy, cyclic voltammetry, UV-vis-NIR and IR spectroelectrochemistry, and approximate density functional theory, to assess cluster rearrangement to accommodate steric crowding, the utility of metal-metal stretching vibrations in mixed-metal cluster characterization, and the possibility of tuning cluster electronic structure by systematic modification of composition, and to identify cluster species resultant upon electrochemical oxidation or reduction. The 60-electron tetrahedral clusters MIr(3)(CO)(11-x)(PMe(3))(x)(eta(5)-Cp) [M = Mo, x = 0, Cp = C(5)H(4)Me (5), C(5)HMe(4) (6), C(5)Me(5) (7); M = W, Cp = C(5)H(4)Me, x = 1 (13), x = 2 (14)] and M(2)Ir(2)(CO)(10-x)(PMe(3))(x)(eta(5)-Cp) [M = Mo, x = 0, Cp = C(5)H(4)Me (8), C(5)HMe(4) (9), C(5)Me(5) (10); M = W, Cp = C(5)H(4)Me, x = 1 (15), x = 2 (16)] have been prepared. Structural studies of 7, 10, and 13 have been undertaken; these clusters are among the most sterically encumbered, compensating by core bond lengthening and unsymmetrical carbonyl dispositions (semi-bridging, semi-face-capping). Raman spectra for 5, 8, WIr(3)(CO)(11)(eta(5)-C(5)H(4)Me) (11), and W(2)Ir(2)(CO)(10)(eta(5)-C(5)H(4)Me)(2) (12), together with the spectrum of Ir(4)(CO)(12), have been obtained, the first Raman spectra for mixed-metal clusters. Minimal mode-mixing permits correlation between A(1) frequencies and cluster core bond strength, frequencies for the A(1) breathing mode decreasing on progressive group 6 metal incorporation, and consistent with the trend in metal-metal distances [Ir-Ir < M-Ir < M-M]. Cyclic voltammetric scans for 5-15, MoIr(3)(CO)(11)(eta(5)-C(5)H(5)) (1), and Mo(2)Ir(2)(CO)(10)(eta(5)-C(5)H(5))(2) (3) have been collected. The [MIr(3)] clusters show irreversible one-electron reduction at potentials which become negative on cyclopentadienyl alkyl introduction, replacement of molybdenum by tungsten, and replacement of carbonyl by phosphine. These clusters show two irreversible one-electron oxidation processes, the easier of which tracks with the above structural modifications; a third irreversible oxidation process is accessible for the bis-phosphine cluster 14. The [M(2)Ir(2)] clusters show irreversible two-electron reduction processes; the tungsten-containing clusters and phosphine-containing clusters are again more difficult to reduce than their molybdenum-containing or carbonyl-containing analogues. These clusters show two one-electron oxidation processes, the easier of which is reversible/quasi-reversible, and the more difficult of which is irreversible; the former occur at potentials which increase on cyclopentadienyl alkyl removal, replacement of tungsten by molybdenum, and replacement of phosphine by carbonyl. The reversible one-electron oxidation of 12 has been probed by UV-vis-NIR and IR spectroelectrochemistry. The former reveals that 12(+) has a low-energy band at 8000 cm(-1), a spectrally transparent region for 12, and the latter reveals that 12(+) exists in solution with an all-terminal carbonyl geometry, in contrast to 12 for which an isomer with bridging carbonyls is apparent in solution. Approximate density functional calculations (including ZORA scalar relativistic corrections) have been undertaken on the various charge states of W(2)Ir(2)(CO)(10)(eta(5)-C(5)H(5))(2) (4). The calculations suggest that two-electron reduction is accompanied by W-W cleavage, whereas one-electron oxidation proceeds with retention of the tetrahedral core geometry. The calculations also suggest that the low-energy NIR band of 12(+) arises from a sigma(W-W) --> sigma*(W-W) transition.

1 Read
  • [Show abstract] [Hide abstract]
    ABSTRACT: The pseudooctahedral monocluster compounds M2Ir2(μ4-η2-R1C2R2)(μ-CO)4(CO)4(η5-C5H4Me)2 (M = Mo, R2 = Ph, R1 = H (12), Ph (13), Me (14); M = W, R2 = Ph, R1 = Me (15); M = Mo, R1 = n-hexyl, R2 = C6H4-4-CHO (16), C6H4-4-CH2P(O)(OEt)2 (17)) have been prepared from reactions between the tetrahedral cluster compounds M2Ir2(CO)10(η5-C5H4Me)2 and the alkynes R1C2R2. Similar reactions between tetrahedral cluster precursors and di- or triynes have afforded the related compounds [M2Ir2(μ-CO)4(CO)4(η5-C5H4R)2]2(μ8-η4-R1C2BC2R1) (R = H, R1 = H, B = 4-C6H4-(E)-CHCH-4-C6H4, M = Mo (18); R = Me, R1 = n-hexyl, B = 4-C6H4, M = Mo (19), W (20); R = Me, R1 = n-hexyl, B = 4-C6H4-(E)-CHCH-4-C6H4, M = Mo (22), W (23); R = Me, R1 = n-hexyl, B = 4-C6H4-(E)-CHCH-4-C6H4-(E)-CHCH-4-C6H4, M = Mo (24); R = Me, R1 = H, B = (CH2)2, M = W (27)), [Mo2Ir2(μ-CO)4(CO)4(η5-C5H4Me)2]3{μ12-η6-1,3,5-C6H3[(E)-CHCHC6H4-4‘-C2(CH2)5Me]3} (25), and W2Ir2(μ4-η2-R1C2R2)(μ-CO)4(CO)4(η5-C5H4Me)2 (R1 = n-hexyl, R2 = 4-C6H4CC(CH2)5Me (21); R1 = H, R2 = (CH2)2CCH (26)). Compounds 18−20 and 22−25 contain two or three cluster units linked by unsaturated bridges, while 27 contains two cluster units linked by a saturated bridge. Compound 22 was prepared in lower yield by coupling 16 and 17 under Emmons−Horner conditions. Structural studies of examples of mono- (15), di- (22), and tricluster (25) compounds have been undertaken. Cyclic voltammetric scans for 12−15, 19, 20, 22−24, 27 and the related cluster W2Ir2(μ4-η2-PhC2Ph)(μ-CO)4(CO)4(η5-C5H4Me)2 (4) have been collected. All compounds show a reversible/partially reversible oxidation, followed by an irreversible oxidation process; potentials for the former increase on replacement of tungsten by molybdenum and alkyne substituent variation Me < H < Ph. UV−vis−near-IR spectroelectrochemical studies of the first oxidation process for 12, 15, and 20 show similar spectral progressions for these mono- and dicluster compounds. The reductive cyclic voltammetric scans for 4, 12−15, 22−24, and 27 all show one irreversible reduction process; compounds 19 and 20, distinguished by possessing the shortest unsaturated bridge, show two reduction processes.
    Organometallics 12/2002; 22(2). DOI:10.1021/om020203r · 4.13 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Reactions of MoIr3(μ-CO)3(CO)8(η-C5H5) (1) with stoichiometric amounts of isocyanides afford the ligand-substituted clusters [MoIr3(μ-CO)3(CO)8−n(L)n(η-C5H5)] (L=CNBut, n=1 (3), 2 (4), 3 (5); L=CNC6H3Me2-2,6, n=1 (6), 2 (7), 3 (8)) in moderate to excellent yields (13–75%). Single-crystal X-ray studies of 3 and 6 reveal that the isocyanides occupy coordination sites on an apical cluster core metal atom, a first for ligand-substituted derivatives of 1. In contrast, reaction of Mo2Ir2(μ-CO)3(CO)7(η-C5H5)2 (2) with one or two equivalents of CNBut affords Mo2Ir2(μ-CO)2(CNBut)2(CO)6(η-C5H5)2 (9) as the only major product. A single-crystal X-ray study of 9 reveals an unprecedented carbonyl configuration about the pseudotetrahedral cluster core.
    Journal of Organometallic Chemistry 07/2003; 678(1-2):72-81. DOI:10.1016/S0022-328X(03)00438-8 · 2.17 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Transition metal carbonyl clusters incorporating group 6 (molybdenum, tungsten) and iridium atoms in a tetrahedral or butterfly-shaped four-atom cluster core, together with carbonyl, cyclopentadienyl and alkyne ligands, have been synthesized and incorporated into oligourethanes, and their optical limiting properties assessed by open-aperture Z-scan (ns pulses, 523 nm) and time-resolved pump-probe studies (ps pulses, 527 nm). The Z-scan studies reveal that the tetrahedral [M2Ir2] cluster cores (M = Mo, W) displayed a greater effective nonlinear absorption coefficent beta(2) than the [MoIr3] cores; the tungsten example, W2Ir2(CO)(10)(eta-C5H5)(2), exhibited the highest response. Substitution at the cyclopentadienyl group (including incorporation into a polymer backbone) had little effect on the response measured. A time-resolved investigation of the alkyne-adduct Mo2Ir2(mu(4)-eta(2)-MeC2Ph)(CO)(8)(eta-C5H4Me)(2) using picosecond pulses at 527 nm reveals optical-power-limiting behaviour that results from electronic processes [specifically, a fast nonlinear absorption process followed by reverse saturable absorption involving long-lived (> 1000 ps) metastable excited states].
    01/2003: pages 318-325;
Show more