Mixed-Metal Cluster Chemistry. 13. Syntheses and Isomer Distribution Studies of Cp₂W₂Ir₂(μ-CO)₃(CO)_7-n(PR₃)_n(n= 1, 2; R = Ph, Me):  X-ray Crystal Structure of Cp₂W₂Ir₂(μ-CO)₃(CO)₆(PPh₃)

Abstract

Reactions of Cp2W2Ir2(CO)10 (1) with n equivalents of PPh3 and PMe3 (n = 1, 2) proceed in dichloromethane at room temperature to afford the clusters Cp2W2Ir2(μ-CO)3(CO)7 - n (PPh3) n (n = 1 (2), 2 (3)) and Cp2W2Ir2(μ-CO)3(CO)7 - n (PMe3) n (n = 1 (4), 2 (5)), respectively, in reasonable yields (38−63%). These products exhibit ligand fluxionality in solution, resolvable at low temperature into the constituent interconverting isomers. A structural study of one isomer of 2, namely 2a, reveals that the three edges of a WIr2 face of the tetrahedral core are spanned by bridging carbonyls and that the iridium-bound PPh3 ligates axially and the tungsten-bound cyclopentadienyl ligands coordinate apically and axially with respect to the plane of bridging carbonyls. Information from this crystal structure and 13C and 31P NMR spectral 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 carbonyl cluster complexes; these 1H−31P−13C correlation experiments, designed to elucidate P−C coupling networks involving phosphorus and carbonyl ligands (a “HPCO experiment”), benefit from the sensitivity enhancement gained from using proton detection. All the isomers of clusters 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 NMR spectroscopy, is consistent with the structural determination. A second configuration (2b, 4b: axial phosphine, axial Cp, apical Cp) is the only one identified (within the temperature range 183−293 K) for the PMe3-substituted cluster 4. Two isomers, both with radial phosphine, 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 two electropositive tungsten atoms may be polarizing the electron distribution toward the iridiums, although steric factors may also be involved.

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

“…The clusters 13 − 15 have been characterized by a combination of IR and 1 H NMR spectroscopies, SI mass spectrometry, and satisfactory microanalysis ( 13 and 15 only), while the unstable product 16 has been characterized by IR and 1 H NMR spectroscopies only. The spectroscopic features of 13 − 16 are similar to those of their cyclopentadienyl analogues, , but extra bands are observed in the solution IR spectra of some examples.

3 .

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Mixed-Metal Cluster Chemistry. 22. Synthesis and Crystallographic, Electrochemical, and Theoretical Studies of Alkyne-Coordinated Group 6−Iridium Clusters Linked by Phenyleneethynylene Groups

“…Transition-metal carbonyl cluster chemistry has been of enduring interest. , The redox properties of clusters have been of particular interest, clusters having been subjected to numerous detailed electrochemical studies. − A natural extension to these studies is to link electroactive cluster modules through unsaturated bridges and utilize electrochemical techniques to assess electronic communication, − but few examples of heterometallic clusters linked by unsaturated bridges exist, − and until our recent report none had been examined electrochemically. As part of a detailed study of group 6−iridium mixed-metal cluster chemistry, − we recently reported examples of cluster−alkyne adducts linked by phenylenevinylene bridges (Chart ) and their examination by cyclic voltammetry and UV−vis−near-IR spectroelectrochemistry . We have now expanded these studies to embrace bridging groups containing phenyleneethynylene units, the results from which are reported herein.…”

Mixed-Metal Cluster Chemistry. 21. Synthesis and Crystallographic and Electrochemical Studies of Alkyne-Coordinated Group 6−Iridium Clusters Linked by Phenylenevinylene Groups

“…Few examples of heterometallic clusters linked by unsaturated bridges exist, − and thus far none have been probed utilizing electrochemical techniques. We have been studying group 6−iridium clusters − and have recently reported cluster-containing oligourethanes in which the cluster units are linked via saturated bridges …”