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: 11.44). 05/2002; 124(18):5139-53. DOI: 10.1021/ja0173829
Source: PubMed

ABSTRACT 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.

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    ABSTRACT: Reaction between the tetrahedral cluster compound Mo2Ir2(CO)10(η5-C5H4Me)2 (1) and 2-iodo-5-(oct-1‘-ynyl)thiophene afforded the pseudooctahedral cluster Mo2Ir2{μ4-η2-Me(CH2)5C2-5-C4H2S-2-I}(CO)8(η5-C5H4Me)2 (17) by formal insertion of the alkyne CC group into the Mo−Mo bond. Similar reactions of 1 or W2Ir2(CO)10(η5-C5H4Me)2 (2) with heterocyclic di- or triynes afforded the related mono-, di-, or tricluster compounds [M2Ir2(CO)8(η5-C5H4Me)2]2{μ8-η4-Me(CH2)5C2-2-C4H2E-5-C2(CH2)5Me} [E = S, M = Mo (20), W (21); E = Se, M = Mo (30), W (31)], [M2Ir2(CO)8(η5-C5H4Me)2]2{μ8-η4-Me(CH2)5C2-2-C4H2S-5-(E)-CHCH-2-C4H2S-5-C2(CH2)5Me} [M = Mo (22), W (24)], M2Ir2{μ4-η2-Me(CH2)5C2-2-C4H2S-5-(E)-CHCH-2-C4H2S-5-CC(CH2)5Me}(CO)8(η5-C5H4Me)2 [M = Mo (23), W (25)], [M2Ir2(CO)8(η5-C5H4Me)2]3{μ12-η6-Me(CH2)5C2-2-C4H2S-5-C2-2-C4H2S-5-C2(CH2)5Me} [M = Mo (26), W (28)], and [M2Ir2(CO)8(η5-C5H4Me)2]2{μ8-η4-Me(CH2)5C2-2-C4H2S-5-C2-2-C4H2S-5-CC(CH2)5Me} [M = Mo (27), W (29)]. Compounds 27 and 29 correspond to the 1,2-dicluster adducts of the linear triyne Me(CH2)5CC-5-C4H2S-2-CC-2-C4H2S-5-CC(CH2)5Me. No 1,3-dicluster isomer was isolated from direct reaction, but the molybdenum-containing 1,3-dicluster isomer was prepared by exploiting organic reaction chemistry on precoordinated functionalized alkyne ligands. Thus, Sonogashira coupling of 17 with trimethylsilylacetylene and subsequent desilylation gave Mo2Ir2{μ4-η2-Me(CH2)5C2-5-C4H2S-2-CCR}(CO)8(η5-C5H4Me)2 [R = SiMe3 (18), H (19)]. Sonogashira coupling of 17 and 19 gave the 1,3-isomer [Mo2Ir2(CO)8(η5-C5H4Me)2]2{μ8-η4-Me(CH2)5C2-2-C4H2S-5-CC-2-C4H2S-5-C2(CH2)5Me} (32), as well as the homocoupling product [Mo2Ir2(CO)8(η5-C5H4Me)2]2{μ8-η4-Me(CH2)5C2-2-C4H2S-5-CCCC-2-C4H2S-5-C2(CH2)5Me} (33). The identities of 21, 29, and 31 were confirmed by single-crystal X-ray diffraction studies. Cyclic voltammetric scans for these complexes all show a reversible/quasi-reversible oxidation followed by an irreversible oxidation process. Dicluster compounds linked by one heterocycle, and tricluster compounds, show two reduction processes, whereas dicluster compounds with longer bridges reveal only one reduction process.
    Organometallics 09/2003; 22(18):3659-3670. DOI:10.1021/om030253b · 4.25 Impact Factor
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    ABSTRACT: The reaction of Mo2Ir2(μ-CO)3(CO)7(η5-C5H5)2 and Ir(Ctriple bond; length of mdashCCH2OH)(CO)(PPh3)3 in refluxing toluene gives the molybdenum–iridium cluster MoIr2(μ3-η2-C6H4)(μ-PPh2)(μ-CO)2(CO)4(η5-C5H5) (1) in low yield. Mo2Ir2(μ-CO)3(CO)6(PPh3)(η5-C5H5)2 (2) is a possible intermediate en route to 1; reaction of Mo2Ir2(μ-CO)3(CO)7(η5-C5H5)2 and Ir(Ctriple bond; length of mdashCCH2OH)(CO)(PPh3)3 in refluxing dichloromethane affords low yields of 2, and thermolysis of the latter in refluxing toluene gives modest yields of 1. A structural study reveals that 1 consists of a triangular MoIr2 core with a molybdenum-bound cyclopentadienyl group, two terminal carbonyls at each of the iridium atoms, one carbonyl bridging each of the Mo–Ir bonds, and a PPh2 moiety spanning the Ir–Ir linkage. The cluster coordination sphere is completed by a face-capping benzyne ligand that ligates η1- to each iridium atom and η2- to the group 6 metal. A structural study of 2 confirms the tetranuclear Mo2Ir2 core with molybdenum-bound cyclopentadienyl groups, six terminal and three-edge-bridging carbonyls, the latter deployed about an MoIr2 face, and a triphenylphosphine ligand ligated axially with respect to the carbonyl-bridged plane. Reaction of 1 with PPh3 in refluxing toluene gives MoIr2(μ3-η2-C6H4)(μ-PPh2)(μ-CO)2(CO)3(PPh3)(η5-C5H5) (3) in low yield. While X-ray structural authentication of 3 has thus far proven elusive, theoretical studies indicate that an equatorially substituted structure is favored energetically over the axially-substituted isomer by around 20 kJ mol−1, but this energy difference is not sufficiently large so as to exclude formation of the axial isomer experimentally.
    Polyhedron 03/2013; 52:957-962. DOI:10.1016/j.poly.2012.07.018 · 2.05 Impact Factor
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    ABSTRACT: Reactions of the tetrahedral clusters Mo2Ir2(μ-CO)3(CO)7(η5-L)2 (L = C5H5, C5HMe4) with the molybdenum alkylidyne complex Mo(≡CC6H4OMe-4)(CO)2{(N2C3H3)3BH-κ3N,N′,N″} afford the pentanuclear clusters Mo3Ir2(μ4-C)(μ3-CC6H4OMe-4)(μ-O)(CO)6{(N2C3H3)3BH-κ3N,N′,N″}(η5-C5H5)2 (1; 62%) and Mo3Ir2(μ3-CC6H4OMe-4)(μ3-η2-CO)(μ-CO)(CO)6{(N2C3H3)3BH-κ3N,N′,N″}(η5-C5Me4H)2 (2; 65%), respectively, while the reaction of Mo2Ir2(μ-CO)3(CO)7(η-C5H5)2 with W(≡CC≡CSiMe3)(CO)2{(N2C3H3)3BH-κ3N,N′,N″} yields the butterfly cluster Mo2Ir2(μ4-η2-SiMe3C2C≡W(CO)2{(N2C3H3)3BH-κ3N,N′,N″})(μ-CO)4(CO)4(η5-C5H5)2 (3; 60%). The identities of 1–3 have been confirmed by single-crystal X-ray diffraction studies. Cluster 1 contains μ4-carbido and μ-oxido ligands resulting from CO cleavage. Cluster 2, with sterically more encumbering tetramethylcyclopentadienyl ligands that arrest CO cleavage, possesses a μ3-η2-CO ligand with a weak CO bond (1.272(7), 1.257(7) Å). Cluster 2 could not be converted into an analogue of cluster 1. The reaction with alkyne is more facile than the reaction with alkylidyne; cluster 3 results from addition of the C≡C bond (rather than the W≡C bond) across the Mo–Mo vector.
    Organometallics 03/2012; 31(7):2582–2588. DOI:10.1021/om201053s · 4.25 Impact Factor