Oxidative stretching of metal-metal bonds to their limits

David W. Brogden, Yevgeniya Turov, Michael Nippe, Giovanni Li Manni, Elizabeth A. Hillard, Rodolphe Clérac, Laura Gagliardi, John F. Berry

Research output: Contribution to journalArticlepeer-review

23 Scopus citations

Abstract

Oxidation of quadruply bonded Cr2(dpa)4, Mo 2(dpa)4, MoW(dpa)4, and W2(dpa) 4 (dpa = 2,2′-dipyridylamido) with 2 equiv of silver(I) triflate or ferrocenium triflate results in the formation of the two-electron-oxidized products [Cr2(dpa)4]2+ (1), [Mo2(dpa)4]2+ (2), [MoW(dpa) 4]2+ (3), and [W2(dpa)4] 2+ (4). Additional two-electron oxidation and oxygen atom transfer by m-chloroperoxybenzoic acid results in the formation of the corresponding metal-oxo compounds [Mo2O(dpa)4]2+ (5), [WMoO(dpa)4]2+ (6), and [W2O(dpa) 4]2+ (7), which feature an unusual linear M···M≡O structure. Crystallographic studies of the two-electron-oxidized products 2, 3, and 4, which have the appropriate number of orbitals and electrons to form metal-metal triple bonds, show bond distances much longer (by >0.5 Å) than those in established triply bonded compounds, but these compounds are nonetheless diamagnetic. In contrast, the Cr-Cr bond is completely severed in 1, and the resulting two isolated Cr 3+ magnetic centers couple antiferromagnetically with J/k B= -108(3) K [-75(2) cm-1], as determined by modeling of the temperature dependence of the magnetic susceptibility. Density functional theory (DFT) and multiconfigurational methods (CASSCF/CASPT2) provide support for "stretched" and weak metal-metal triple bonds in 2, 3, and 4. The metal-metal distances in the metal-oxo compounds 5, 6, and 7 are elongated beyond the single-bond covalent radii of the metal atoms. DFT and CASSCF/CASPT2 calculations suggest that the metal atoms have minimal interaction; the electronic structure of these complexes is used to rationalize their multielectron redox reactivity.

Original languageEnglish (US)
Pages (from-to)4777-4790
Number of pages14
JournalInorganic chemistry
Volume53
Issue number9
DOIs
StatePublished - May 5 2014

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