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Hydrido-carbonyl chain clusters. Synthesis, solid state structure, and solution behavior of the tetranuclear open cluster anions [ReH(μ-H)(CO)] and [Re(μ-H)(CO)]

Organometallics, ISSN: 0276-7333, Vol: 16, Issue: 19, Page: 4129-4137
1997
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Article Description

The addition of [ReH(CO)] to the electronically unsaturated complex [Re(μ-H)(CO)] rapidly and selectively gives the anion [Re4H(W-H)2(CO)I?]' (2), containing an open chain tetranuclear metal skeleton, as revealed by a single-crystal X-ray analysis of its [NEt] salt. In the solid state the three metal-metal interactions display a staggered-eclipsed-staggered conformation, while in solution H and C NMR spectra have shown conformational freedom around the three Re-Re interactions and a dynamic process exchanging the two hydrides bound to the terminal HRe(CO) moiety, as well as the carbonyls trans to them (E -48(1) kJ/mol). A windshield-wiper motion of the HRe(CO) fragment around the two trans diaxial carbonyls, analogous to that previously observed in the related anions [ReH(μ-H)(CO)] and [ReH(μ-H)(CO)], is likely responsible for this exchange. The tetrametallic skeleton of the anion 2 in solution easily undergoes fragmentation to trinuclear species. Under CO atmosphere the clean formation of [ReH(CO)] and [ReH(μ-H)-(CO)] has been recognized. The anion 2 is formed (even if in lower yields) also by reaction Of [ReH(μ-H)(CO)] with "Re(CO)(THF)", obtained by treatment of [Re(CO)] with MeNO in THF. A C NMR investigation has clarified that such "Re(CO)(THF)" reagent is indeed a mixture of three eq-[Re(CO)L] species, containing THF, HO, and, in a minor amount, NMe, as labile L ligands. The reaction of the same eq-[Re(CO)L] species with [ReH(CO)] affords in good yields the tetranuclear cluster anion [Re(μ-H)(CO)}] (3). The single-crystal X-ray analysis of [NEt]3 has revealed also in this case a Re chain, with an all-staggered conformation, of idealized C symmetry. The low-temperature C NMR spectrum of the carbonyls has shown a higher symmetry in solution, suggesting conformational freedom around all of the Re-Re interactions.

Bibliographic Details

Mirka Bergamo; Tiziana Beringhelli; Giuseppe D'Alfonso; Pierluigi Mercandelli; Massimo Moret; Angelo Sironi

American Chemical Society (ACS)

Chemistry

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