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Synthesis and Characterization of [Ir(1,5-Cyclooctadiene)(mu-H)](4): A Tetrametallic Ir4H4-Core, Coordinatively Unsaturated Cluster

Yih, Kuang-Hway
Hamdemir, Isil K.
Mondloch, Joseph E.
Bayram, Ercan
Özkar, Saim
Vasic, Relja
Frenkel, Anatoly I.
Anderson, Oren P.
Finke, Richard G.
Reported herein is the synthesis of the previously unknown [Ir(1,5-COD)(mu-H)](4) (where 1,5-COD = 1,5-cyclooctadiene), from commercially available [Ir(1,5-COD)Cl](2) and LiBEt3H in the presence of excess 1,5-COD in 78% initial, and 55% recrystallized, yield plus its unequivocal characterization via single-crystal X-ray diffraction (XRD), X-ray absorption fine structure (XAFS) spectroscopy, electrospray/atmospheric pressure chemical ionization mass spectrometry (ESI-MS), and UV-vis, IR, and nuclear magnetic resonance (NMR) spectroscopies. The resultant product parallels-but the successful synthesis is different from, vide infra-that of the known and valuable Rh congener precatalyst and synthon, [Rh(1,5-COD)(mu-H)](4). Extensive characterization reveals that a black crystal of [Ir(1,5-COD)(mu-H)](4) is composed of a distorted tetrahedral, D-2d symmetry Ir-4 core with two long [2.90728(17) and 2.91138(17) angstrom] and four short Ir-Ir [2.78680 (12)-2.78798(12) angstrom] bond distances. One 1,5-COD and two edge-bridging hydrides are bound to each Ir atom; the Ir-H-Ir span the shorter Ir-Ir bond distances. XAFS provides excellent agreement with the XRD-obtained Ir-4-core structure, results which provide both considerable confidence in the XAFS methodology and set the stage for future XAFS in applications employing this Ir4H4 and related tetranuclear clusters. The [Ir(1,5-COD)(mu-H)](4) complex is of interest for at least five reasons, as detailed in the Conclusions section.