MoF₆ and WF₆: Nonrigid Molecules?

Abstract

Calculations reveal that the octahedral-trigonal prismatic-octahedral rearrangement has particularly low-energy barriers for MoF6, WF6, and (hypothetical) CrF6. Experimental evidence is obtained from the dynamic 19F NMR spectra of the derivatives CF3-CH2-O-MoF5, CF3-CH2-O-WF5, C6F5-O-MoF5, C6F5-O-WF5, and (CF3)3C-O-WF5. The ground-state structure of all these compounds is octahedral; at elevated temperatures the nonequivalent metal-bound fluorine atoms undergo an intramolecular exchange. The exchange mechanism could be a 3+3 or a 2+4 twist; calculations favor the 3+3 twist.

Tungsten(VI) and Tungsten(V) Fluoride Complexes

“…This may be yet another indication of the effect that d 0 transition metal complexes avoid 90° and 180° bond angles. Even octahedral WF 6 has a trigonal bipyramidal transition state only 11 kcal mol −1 higher in energy, so that the substituted derivative [C 6 F 5 OWF 5 ] shows intramolecular exchange of the different fluorine atoms at the high temperature limit 22…”

Contrasting Products in the Reactions of Cr, Mo, and W Atoms with H2O2: Argon Matrix Infrared Spectra and Theoretical Calculations

“…In addition the reaction of tungsten with CH 4 gave three hydrides, CH 3 WH, CH 2 WH 2 , and CH⋮WH 3 , and spectra were dominated by the most stable trihydride CH⋮WH 3 , and all three products were also observed for Mo, but in contrast CH 3 CrH is the most stable and the only chromium product trapped in solid argon ,, Both WF 6 and WCl 6 are stable molecules observed experimentally, while CrF 6 is calculated to be stable with respect to Cr−F dissociation. − Up to now there are no experimental data available for CrF 6 and CrCl 6 . …”

Facile Intermolecular Aryl−F Bond Cleavage in the Presence of Aryl C−H Bonds: Is the η2-Arene Intermediate Bypassed?

“…A 31 P NMR spectrum indicates that the fluorine is bound to the metal, exhibiting a doublet ( J F,P = 127.0 Hz) with 183 W satellites ( J W,P = 212.5 Hz). The 19 F NMR spectrum also shows this coupling ( J F,P = 127.0 Hz), but here 183 W satellites were not observed, even though 183 W− 19 F coupling has been detected in a few higher oxidation state complexes. − IR data show an absorption associated with an NO stretch at 1596 cm -1 , a feature significantly blue-shifted from common η 2 -coordinated arene−W 0 complexes (e.g., 1 : ν NO = 1564 cm -1 ) . Cyclic voltammetric data for 2 show only a broad oxidation wave with E p,a near 1.5 V (NHE), well beyond the normal range of TpW 0 (NO)(PMe 3 ) complexes .…”