Mixed-Metal Cluster Chemistry. 13. Syntheses and Isomer Distribution Studies of Cp2W2Ir2(-CO)3
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- 作者：Susan M. Waterman ; Mark G. Humphrey ; Jeanne Lee ; Graham E. Ball ; and David C. R. Hockless
- 刊名：Organometallics
- 出版年：1999
- 出版时间：June 21, 1999
- 年：1999
- 卷：18
- 期：13
- 页码：2440 - 2451
- 全文大小：216K
- 年卷期：v.18,no.13(June 21, 1999)
- ISSN：1520-6041
文摘
Reactions of Cp2W2Ir2(CO)10 (1) with n equivalents of PPh3 and PMe3 (n = 1, 2) proceedin dichloromethane at room temperature to afford the clusters Cp2W2Ir2(
r.gif">-CO)3(CO)7-n(PPh3)n(n = 1 (2), 2 (3)) and Cp2W2Ir2(r.gif">-CO)3(CO)7-n(PMe3)n (n = 1 (4), 2 (5)), respectively, inreasonable yields (38-63%). These products exhibit ligand fluxionality in solution, resolvableat low temperature into the constituent interconverting isomers. A structural study of oneisomer of 2, namely 2a, reveals that the three edges of a WIr2 face of the tetrahedral coreare spanned by bridging carbonyls and that the iridium-bound PPh3 ligates axially and thetungsten-bound cyclopentadienyl ligands coordinate apically and axially with respect to theplane of bridging carbonyls. Information from this crystal structure and 13C and 31P NMRspectral data have been employed to assign coordination geometries for the isomers of 2-5.NMR studies included development and use of 2D triple-resonance experiments with carbonylcluster complexes; these 1H-31P-13C correlation experiments, designed to elucidate P-Ccoupling networks involving phosphorus and carbonyl ligands (a "HPCO experiment"), benefitfrom the sensitivity enhancement gained from using proton detection. All the isomers ofclusters 2-5 contain a carbonyl-bridged WIr2 basal plane and an apical tungsten atom;ligands can be approximately coplanar (radial) to the basal plane or below the plane (axial).The configuration of 2a (axial phosphine, axial Cp, apical Cp), as assigned by NMRspectroscopy, is consistent with the structural determination. A second configuration (2b,4b: axial phosphine, axial Cp, apical Cp) is the only one identified (within the temperaturerange 183-293 K) for the PMe3-substituted cluster 4. Two isomers, both with radialphosphine, axial phosphine, axial Cp, apical Cp configurations, have been identified for 5,namely 5a and 5b; it is likely that isomers of 3 adopt the same configurations. The WIr2-bridged form is seen exclusively across the isomers, indicating that the presence of twoelectropositive tungsten atoms may be polarizing the electron distribution toward theiridiums, although steric factors may also be involved.
r.gif">-CO)3(CO)7-n(PPh3)n(n = 1 (2), 2 (3)) and Cp2W2Ir2(r.gif">-CO)3(CO)7-n(PMe3)n (n = 1 (4), 2 (5)), respectively, inreasonable yields (38-63%). These products exhibit ligand fluxionality in solution, resolvableat low temperature into the constituent interconverting isomers. A structural study of oneisomer of 2, namely 2a, reveals that the three edges of a WIr2 face of the tetrahedral coreare spanned by bridging carbonyls and that the iridium-bound PPh3 ligates axially and thetungsten-bound cyclopentadienyl ligands coordinate apically and axially with respect to theplane of bridging carbonyls. Information from this crystal structure and 13C and 31P NMRspectral data have been employed to assign coordination geometries for the isomers of 2-5.NMR studies included development and use of 2D triple-resonance experiments with carbonylcluster complexes; these 1H-31P-13C correlation experiments, designed to elucidate P-Ccoupling networks involving phosphorus and carbonyl ligands (a "HPCO experiment"), benefitfrom the sensitivity enhancement gained from using proton detection. All the isomers ofclusters 2-5 contain a carbonyl-bridged WIr2 basal plane and an apical tungsten atom;ligands can be approximately coplanar (radial) to the basal plane or below the plane (axial).The configuration of 2a (axial phosphine, axial Cp, apical Cp), as assigned by NMRspectroscopy, is consistent with the structural determination. A second configuration (2b,4b: axial phosphine, axial Cp, apical Cp) is the only one identified (within the temperaturerange 183-293 K) for the PMe3-substituted cluster 4. Two isomers, both with radialphosphine, axial phosphine, axial Cp, apical Cp configurations, have been identified for 5,namely 5a and 5b; it is likely that isomers of 3 adopt the same configurations. The WIr2-bridged form is seen exclusively across the isomers, indicating that the presence of twoelectropositive tungsten atoms may be polarizing the electron distribution toward theiridiums, although steric factors may also be involved.