Mixed-Metal Cluster Chemistry. 19. Crystallographic, Spectroscopic, Electrochemical, Spectroelectrochemical, and Theoretical Studies of Systematically Varied Tetrahedral Group 6-Iridium Clusters
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- 作者：Nigel T. Lucas ; Jonathan P. Blitz ; Simon Petrie ; Robert Stranger ; Mark G. Humphrey ; Graham A. Heath ; and Vincent Otieno-Alego
- 刊名：Journal of the American Chemical Society
- 出版年：2002
- 出版时间：May 8, 2002
- 年：2002
- 卷：124
- 期：18
- 页码：5139 - 5153
- 全文大小：238K
- 年卷期：v.124,no.18(May 8, 2002)
- ISSN：1520-5126
文摘
A systematically varied series of tetrahedral clusters involving ligand and core metal variationhas been examined using crystallography, Raman spectroscopy, cyclic voltammetry, UV-vis-NIR and IRspectroelectrochemistry, and approximate density functional theory, to assess cluster rearrangement toaccommodate steric crowding, the utility of metal-metal stretching vibrations in mixed-metal clustercharacterization, and the possibility of tuning cluster electronic structure by systematic modification ofcomposition, and to identify cluster species resultant upon electrochemical oxidation or reduction. The60-electron tetrahedral clusters MIr3(CO)11-x(PMe3)x(
5-Cp) [M = Mo, x = 0, Cp = C5H4Me (5), C5HMe4(6), C5Me5 (7); M = W, Cp = C5H4Me, x = 1 (13), x = 2 (14)] and M2Ir2(CO)10-x(PMe3)x(5-Cp) [M = Mo,x = 0, Cp = C5H4Me (8), C5HMe4 (9), C5Me5 (10); M = W, Cp = C5H4Me, x = 1 (15), x = 2 (16)] have beenprepared. Structural studies of 7, 10, and 13 have been undertaken; these clusters are among the moststerically encumbered, compensating by core bond lengthening and unsymmetrical carbonyl dispositions(semi-bridging, semi-face-capping). Raman spectra for 5, 8, WIr3(CO)11(5-C5H4Me) (11), and W2Ir2(CO)10(5-C5H4Me)2 (12), together with the spectrum of Ir4(CO)12, have been obtained, the first Raman spectrafor mixed-metal clusters. Minimal mode-mixing permits correlation between A1 frequencies and clustercore bond strength, frequencies for the A1 breathing mode decreasing on progressive group 6 metalincorporation, and consistent with the trend in metal-metal distances [Ir-Ir < M-Ir < M-M]. Cyclicvoltammetric scans for 5-15, MoIr3(CO)11(5-C5H5) (1), and Mo2Ir2(CO)10(5-C5H5)2 (3) have been collected.The [MIr3] clusters show irreversible one-electron reduction at potentials which become negative oncyclopentadienyl alkyl introduction, replacement of molybdenum by tungsten, and replacement of carbonylby phosphine. These clusters show two irreversible one-electron oxidation processes, the easier of whichtracks with the above structural modifications; a third irreversible oxidation process is accessible for thebis-phosphine cluster 14. The [M2Ir2] clusters show irreversible two-electron reduction processes; thetungsten-containing clusters and phosphine-containing clusters are again more difficult to reduce than theirmolybdenum-containing or carbonyl-containing analogues. These clusters show two one-electron oxidationprocesses, 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 tungstenby molybdenum, and replacement of phosphine by carbonyl. The reversible one-electron oxidation of 12has 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 insolution with an all-terminal carbonyl geometry, in contrast to 12 for which an isomer with bridging carbonylsis apparent in solution. Approximate density functional calculations (including ZORA scalar relativisticcorrections) have been undertaken on the various charge states of W2Ir2(CO)10(5-C5H5)2 (4). Thecalculations suggest that two-electron reduction is accompanied by W-W cleavage, whereas one-electronoxidation proceeds with retention of the tetrahedral core geometry. The calculations also suggest that thelow-energy NIR band of 12+ arises from a 
(W-W) 
*(W-W) transition.
5-Cp) [M = Mo, x = 0, Cp = C5H4Me (5), C5HMe4(6), C5Me5 (7); M = W, Cp = C5H4Me, x = 1 (13), x = 2 (14)] and M2Ir2(CO)10-x(PMe3)x(5-Cp) [M = Mo,x = 0, Cp = C5H4Me (8), C5HMe4 (9), C5Me5 (10); M = W, Cp = C5H4Me, x = 1 (15), x = 2 (16)] have beenprepared. Structural studies of 7, 10, and 13 have been undertaken; these clusters are among the moststerically encumbered, compensating by core bond lengthening and unsymmetrical carbonyl dispositions(semi-bridging, semi-face-capping). Raman spectra for 5, 8, WIr3(CO)11(5-C5H4Me) (11), and W2Ir2(CO)10(5-C5H4Me)2 (12), together with the spectrum of Ir4(CO)12, have been obtained, the first Raman spectrafor mixed-metal clusters. Minimal mode-mixing permits correlation between A1 frequencies and clustercore bond strength, frequencies for the A1 breathing mode decreasing on progressive group 6 metalincorporation, and consistent with the trend in metal-metal distances [Ir-Ir < M-Ir < M-M]. Cyclicvoltammetric scans for 5-15, MoIr3(CO)11(5-C5H5) (1), and Mo2Ir2(CO)10(5-C5H5)2 (3) have been collected.The [MIr3] clusters show irreversible one-electron reduction at potentials which become negative oncyclopentadienyl alkyl introduction, replacement of molybdenum by tungsten, and replacement of carbonylby phosphine. These clusters show two irreversible one-electron oxidation processes, the easier of whichtracks with the above structural modifications; a third irreversible oxidation process is accessible for thebis-phosphine cluster 14. The [M2Ir2] clusters show irreversible two-electron reduction processes; thetungsten-containing clusters and phosphine-containing clusters are again more difficult to reduce than theirmolybdenum-containing or carbonyl-containing analogues. These clusters show two one-electron oxidationprocesses, 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 tungstenby molybdenum, and replacement of phosphine by carbonyl. The reversible one-electron oxidation of 12has 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 insolution with an all-terminal carbonyl geometry, in contrast to 12 for which an isomer with bridging carbonylsis apparent in solution. Approximate density functional calculations (including ZORA scalar relativisticcorrections) have been undertaken on the various charge states of W2Ir2(CO)10(5-C5H5)2 (4). Thecalculations suggest that two-electron reduction is accompanied by W-W cleavage, whereas one-electronoxidation proceeds with retention of the tetrahedral core geometry. The calculations also suggest that thelow-energy NIR band of 12+ arises from a (W-W) *(W-W) transition.