Rational Synthesis and Characterization of the Mixed-Metal Organometallic Polyoxometalates [Cp*Mo_xW_6–xO₁₈]⁻ (x = 0, 1, 5, 6)

Abstract

The reaction between the oxometallic complexes Cp*(2)M(2)O(5) and Na(2)M'O(4) (M, M' = Mo, W) in a 1:10 molar ratio in an acidic aqueous medium constitutes a mild and selective entry into the anionic Lindqvist-type hexametallic organometallic mixed oxides [Cp*Mo(x)W(6-x)O(18)](-) [x = 6 (1), 5 (2), 1 (3), 0 (4)]. All of these compounds have been isolated as salts of nBu(4)N(+) (a), nBu(4)P(+) (b), and Ph(4)P(+) (c) cations and two of them (1 and 3) also with the n-butylpyridinium (nBuPyr(+), d) cation. The compounds have been characterized by elemental analyses, thermogravimetric analyses, electrospray mass spectrometry, and IR spectroscopy. The molecular identity and geometry of compounds 1c, 2a, and 2c have been confirmed by single-crystal X-ray diffraction. Density functional theory calculations on models obtained by replacing Cp* with Cp (I-IV) have provided information on the assignment of the terminal M═O and bridging M-O-M vibrations.

Investigation of the reaction of [Cp*2M2O5] (M = Mo, W) with hydrogen peroxide and tert-butylhydroperoxide in MeCN; implications for olefin epoxidation catalyzed by organomolybdenum and organotungsten compounds

“…The precipitates that were isolated from the controlled decomposition of [Cp*2M2O5] with a small excess of aqueous H2O2 have been analyzed by IR spectroscopy and by elemental analysis. -1 for the nBu4N + salt, 967 cm -1 for the nBu4P + and Ph4P + salts, and 962 cm -1 for the n-butylpyridinium salt [44]) and for 1 (966 cm -1 [10]). The IR pattern of the solid isolated from the controlled decomposition of [Cp*2W2O5] is similar, with a sharp band centered at 974 cm -1 and a broader band centered at 776 cm -1 .…”

“…The structure of 3 is affected by severe disorder and no reliable structural information beyond confirmation of the chemical constitution may be inferred. The Lindqvist anion [Mo6O19] 2is reported in another > 130 structurally characterized salts according to the Cambridge structural database, whereas the [Cp*Mo6O18] 2ion is already reported for the above mentioned polymorph of the [C5Me5O] + salt [42], for the nBu4N + salt [43] and for the Ph4P + salt [44]. A detailed discussion of these structures is not warranted.…”

Oxo-Replaced Polyoxometalates: There Is More than Oxygen

“…Carbon (Pauling EN: 2.55) is the only element of group 14 known so far substituting oxygen in POM structures (Table S1). Carbon-based ligands have been shown to replace one 49 or two 50 terminal O t sites in the Lindqvist archetype (Figure 1A), but with completely different underlying chemical principles as purely electron-donating or π-accepting ligands. So far, there are no reports on the replacement of oxygen by carbon for other POM archetypes.…”

“…In [Mo VI 6 O 18 (η 5 -Cp*)] (Figure 3D), 49 the Mo-Cp* bond (2.31 Å) is significantly longer than the O t bond (1.68 Å) that it replaces. The phenomena that the central oxygen atom μ 6 -O largely moves to the Mo ion bearing the Cp* ligand (Figure 3D) and that additional surface charges probably extend to the terminal oxygen atoms in trans-position in anions Cp*Mo 6 and Cp* 2 Mo 6 are explained by trans-influence.…”

Electronic properties of polyoxometalate derivatives [(C2B9H11) M'M5O18]n‐ (M' = TiIV, MoVI, WVI; M = MoVI, WVI): Protonation, Electronic Spectra, and Redox Properties

“…Klemperer et al have synthesized and analyzed a class of Lindqvist POMs‐supported organometallic compounds, such as [( η 5 ‐C 5 R 5 )TiMo 5 O 18 ] 3− , [( η 5 ‐C 5 R 5 )TiW 5 O 18 ] 3− , and [( η 5 ‐C 5 R 5 )Mo 6 O 18 ] − (R = H (Cp), CH 3 (Cp*)) . Recently, a series of mixed‐metal organometallic Lindqvist POMs [Cp*Mo x W 6− x O 18 ] − ( x = 0, 1, 5, 6) have also been synthesized by Taban‐Çalışkan et al Among these compounds, the Cp/Cp* ligand has been used as an ancillary ligand, because it has the ability to stabilize both low and high formal oxidation states in POMs …”