Experimental and Theoretical Studies of Bis(perfluorovinyl)mercury, Hg(CF=CF₂)₂: Synthesis, Characterization, and Structure in the Gaseous and Crystalline Phases

Abstract

The low-temperature reaction between 2 equiv of (perfluorovinyl)lithium, derived from CF3CH2F and butyllithium, and mercury(II) chloride results in high yields of Hg(CFCF2)2. Complete characterization of the air- and moisture-stable liquid product is afforded by multinuclear (13C, 19F, 199Hg) NMR studies. Crystals of the compound [triclinic, P1̄; a = 4.956(4), b = 5.733(4), c = 6.394(4) Å; α = 104.57(5), β = 109.32(6), γ = 107.16(6)°; Z = 1] were obtained by slow cooling; an X-ray structural determination at 110 K represents the first such report for a (perfluorovinyl)metal complex. The mercury is coordinated linearly [r(Hg−C) = 1.998(5) Å], and π-stacking of the perfluorovinyl groups is observed. There is considerable variation in the C−F bond distances [1.286(6), 1.312(6), 1.362(6) Å] within each perfluorovinyl group. Structural data for the vapor-phase species were obtained by analysis of the electron-diffraction pattern. There appears to be free rotation of the perfluorovinyl groups around the Hg−C bonds, a significantly longer mercury−carbon distance [2.054(3) Å], and a similar, but smaller, variation in the C−F bond lengths. Theoretical optimization of the geometry at the MP2/DZP level predicts a shallow potential-energy minimum when the two perfluorovinyl groups are nearly perpendicular [Φ(CC···CC) = 98.2°] to one another. Analysis of the bonding in the molecule suggests that no significant d(Hg) → π*(CC) interaction is present.

Asymmetric fluoro-organomercurials. Part 2. The synthesis and characterisation of the fluorovinyl-mercurials RHgCXCF2 (R=Ph, Fc; X=F, Cl): The single crystal X-ray structures of PhHgCFCF2, FcHgCFCF2 and FcHgCClCF2

“…À90 ppm) to the metal. These assignments are consistent with the majority of previously reported trifluorovinyl compounds, but they do contrast the case of Hg(CF@CF 2 ) 2 , where the fluorine nucleus cis to mercury is observed to resonate at the lower frequency [15].…”

“…Hg interactions over their alkynyl analogues. Indeed, there is negligible evidence for such interactions in any of the present compounds (vide infra), or indeed the previously reported ClHgCCl@CF 2 [13] or Hg(CF@CF 2 ) 2 [15], which taken together with the conformations observed for 2 and 4 would seem to mitigate against a 'bent' geometry. It is, however, noted that the influence of the ferrocenyl fragment upon molecular packing cannot be quantified, and in lieu of further, appropriate, examples a definitive conclusion cannot be unequivocally reached.…”

“…A shortening of the C@C bond, relative to the averaged distance for Csp 2 @Csp 2 [1.299 Å ] [21], appears to be present in all three structures. This has been observed in nearly all structurally characterised fluorovinyl compounds, and has been attributed to librational effects [15], which become more pronounced with increasing mass of the metal/metalloid fragment. The C@C distances [d(C@C) 1.27(2) Å 1; 1.256(12) Å 2; 1.286(10) Å 4] are amongst the shorted yet observed for any fluorovinyl compound.…”

“…: Hg(C"CCF 3 ) 2 [9,10], Hg(CF@CF 2 ) 2 [11], BrHg(CF@CF 2 ) [11a,11b], Hg(C(CF 3 )@CF 2 ) 2 [12], ClHg(CF@CF 2 ) [13], Hg(CCl@CF 2 ) 2 [13], ClHg(CCl-@CF 2 ) [13] and (CH 2 @CH)Hg(CF@CF 2 ) [14], most of which are prepared using Grignard or organolithium reagents. Of these only two, ClHg(CF@CF 2 ) [13] and Hg(CF@CF 2 ) 2 [15], have been structurally characterised. We have sought to enhance the range of known asymmetric mercurials comprising the trifluorovinyl (CF@CF 2 ) and 1-chloro-2,2-difluorovinyl (CCl@CF 2 ) moieties.…”

Refractive indices of organo‐metallic and ‐metalloid compounds: A long‐range corrected DFT study

“…We hypothesize here that the discrepancy between the LC‐BLYP‐based refractive index of bis(perfluorovinyl)mercury and the experimental value might be attributed to the dimer formation. Although there are no structural data available for bis(perfluorovinyl)mercury in the liquid phase, its experimental crystal structure is known …”