A Versatile and Unprecedented Triply Bonded Dimolybdenum Carbonyl Anion

Abstract

Chemical reduction of [Mo 2 Cp 2 (µ-Cl)(µ-PA 2 )-(CO) 2 ] (A ) Cy, Ph, OEt) gives the corresponding alkaline metal salts of the triply bonded anions [Mo 2 -Cp 2 (µ-PA 2 )(µ-CO) 2 ] -, which exhibit both molybdenum and oxygen nucleophilic sites. The PCy 2 anion reacts easily with NH 4 + , [AuCl(PR 3 )], or MeI to give unsaturated dicarbonyls [Mo 2 Cp 2 (µ-X)(µ-PA 2 )(CO) 2 ] (X ) H, AuPR 3 , Me), while [Me 3 O]BF 4 gives the methoxycarbyne [Mo 2 Cp 2 (µ-COMe)(µ-PCy 2 )(µ-CO)] and allyl chloride rearranges to give the unsaturated alkenyl complex [Mo 2 -Cp 2 (µ-PCy 2 )(µ-CMeCH 2 )(CO) 2 ].

Reactivity of the unsaturated dimolybdenum anion [Mo2(η5-C5H5)2(μ-PCy2)(μ-CO)2]− towards electrophiles based on p- and d-block elements

“…Finally, we note that the chemical shifts for the bridging P atoms in compounds 5 (ca. 220 ppm), are comparable to those in compounds 3 (Table 1) or to those in the alkoxycarbyne complexes mentioned above [2,3].…”

“…These compounds turned out to be extremely sensitive to air and moisture, and all attempts to isolate them as pure materials led to their progressive decomposition. In spite of this, the available IR and 31 P NMR data are very similar to those previously measured for the alkoxycarbyne complexes [Mo 2 Cp 2 (l-COR)-(l-PCy 2 )(l-CO)] [R = Me, Et, i Pr, Cy, C(O)Ph] [2,3], then indicating a strong structural similarity. Thus, the IR spectra of compounds 3 exhibit a band in THF solution at ca.…”

“…As it will be shown below, the multisite reactivity exhibited by 1 towards C-based electrophiles is also found when faced to these new electrophiles, these being incorporated either to the dimetal site, to give heterometallic clusters with Mo 2 M (M = Sn, Au, Hg), Mo 2 Au 2 and Mo 4 Hg cores, or to the oxygen atom of the bridging carbonyl ligands, this leading to rather unstable silyloxycarbyne and isocarbonyl-bridged Mo 2 (l 3 -C:C:O-CO)M complexes (M = Ti, Zr). Some of these results were reported in our preliminary work on the reactivity of 1 [3].…”

“…Subsequent DFT calculations on this anion allowed us to describe more precisely this multiple bond as being composed of one r and two d components, with the latter ones also involving p-backbonding to the bridging carbonyls [4]. In our early report we found that this anion was reactive towards many different electrophiles, both based in p-block and in d-block elements, thus opening a new synthetic path to novel unsaturated derivatives that might be difficult or impossible to prepare from conventional (electron-precise) precursors [3]. Recently we have reported a detailed study of the reactivity of anion 1 towards C-based electrophiles RX revealing that, depending on the particular reagent being used, three different types of products can be formed: (a) alkyl-bridged complexes [Mo 2 Cp 2 (l-PCy 2 )(l-R)(CO) 2 ], (b) alkoxycarbyne-bridged complexes [Mo 2 Cp 2 (l-COR)(l-PCy 2 )(l-CO)], and (c) halide-bridged complexes [Mo 2 Cp 2 (l-PCy 2 )(l-X)(CO) 2 ] (X = Cl, Br, I).…”

“…This is specially so in the case of binuclear anions having multiple metalÀmetal bonds, of which only a few examples have been reported in the literature [2]. A few years ago we reported an efficient synthetic route to the dicyclohexylphosphide-bridged anion [Mo 2 Cp 2 (lPCy 2 )(l-CO) 2 ] À (1), for which a MoÀMo triple bond must be formulated under the Effective Atomic Number (EAN) formalism (Chart 1) [3]. Subsequent DFT calculations on this anion allowed us to describe more precisely this multiple bond as being composed of one r and two d components, with the latter ones also involving p-backbonding to the bridging carbonyls [4].…”