Boron monofluoride

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Boron monofluoride
Names
Other names
Boron fluoride

Boron(I) fluoride
Fluoroboronene

Fluoroborylene
Identifiers
3D model (
JSmol
)
ChemSpider
ECHA InfoCard
 100.033.970 Edit this at Wikidata
EC Number
  • 237-383-0
UNII
  • InChI=1S/BF/c1-2 checkY
    Key: YFSQMOVEGCCDJL-UHFFFAOYSA-N checkY
SMILES
  • [BH0]F
  • [B-]=[F+]
  • [B-2]#[F+2]
Properties
BF
Molar mass 29.81 g·mol−1
Thermochemistry
200.48 J K−1 mol−1
Std enthalpy of
formation
(ΔfH⦵298)
 115.90 kJ mol−1
Related compounds
dinitrogen, nitrosonium, cyanide, acetylide
Related compounds
 aluminium monofluoride
aluminium monochloride
aluminium monoiodide
gallium monofluoride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Boron monofluoride or fluoroborylene is a chemical compound with the formula BF, one atom of

dinitrogen; each molecule has 14 electrons.[1]

Structure

The experimental B–F bond length is 1.26267 Å.[2][3][4] Despite being isoelectronic to the triple-bonded species CO and N2, computational studies generally agree that the true bond order is much lower than 3. One reported computed bond order for the molecule is 1.4, compared with 2.6 for CO and 3.0 for N2.[5]

Lewis dot diagram structures show three formal alternatives for describing bonding in boron monofluoride.

BF is unusual in that the dipole moment is inverted with fluorine having a positive charge even though it is the more electronegative element. This is explained by the 2sp orbitals of boron being reoriented and having a higher electron density. Backbonding, or the transfer of π orbital electrons for the fluorine atom, is not required to explain the polarization.[6]

Preparation

Boron monofluoride can be prepared by passing boron trifluoride gas at 2000 °C over a boron rod. It can be condensed at liquid nitrogen temperatures (−196 °C).[7]

Properties

Boron monofluoride molecules have a dissociation energy of 7.8 eV or heat of formation −27.5±3 kcal/mole[1][8] or 757±14 kJ/mol.[2] The first ionization potential is 11.115 eV.[2] The spectroscopic constants vibrational frequency ωe of BF+ (X 2Σ+) is 1765 cm−1 and for neutral BF (X 1Σ+) it is 1402.1 cm−1.[2][9] The anharmonicity of BF is 11.84 cm−1.[9]

Reactions

BF can react with itself to form polymers of boron containing fluorine with between 10 and 14 boron atoms. BF reacts with BF3 to form B2F4. BF and B2F4 further combine to form B3F5. B3F5 is unstable above −50 °C and forms B8F12. This substance is a yellow oil.[7]

BF reacts with acetylenes to make the 1,4-diboracyclohexadiene ring system. BF can condense with

2-butyne forming 1,4-difluoro-2,3,5,6-tetramethyl-1,4-diboracyclohexadiene. Also, it reacts with acetylene to make 1,4-difluoro-1,4-diboracyclohexadiene.[7] Propene reacts to make a mix of cyclic and non-cyclic molecules which may contain BF or BF2.[2]

BF hardly reacts with C2F4 or SiF4.[2] BF does react with arsine, carbon monoxide, phosphorus trifluoride, phosphine, and phosphorus trichloride to make adducts like (BF2)3B•AsH3, (BF2)3B•CO, (BF2)3B•PF3, (BF2)3B•PH3, and (BF2)3B•PCl3.[2]

BF reacts with oxygen: BF + O2 → OBF + O; with chlorine: BF + Cl2 → ClBF + Cl; and with nitrogen dioxide BF + NO2 → OBF + NO.[10]

Ligand

A naïve analysis would suggest that BF is isoelectronic with carbon monoxide (CO) and so could form similar compounds to

Lewis acidic; it tends to form higher-order bonds to metal centers, and can also bridge between two or three metal atoms (μ2 and μ3).[11]

Working with BF as a ligand is difficult due to its instability in the free state.[12] Instead, most routes tend to use derivatives of BF3 that decompose once coordinated.

In a 1968 conference report, Kämpfer et al claimed to produce Fe(BF)(CO)4 via reaction of

transition element is due to Vidovic and Aldrige, who produced [(C5H5)Ru(CO)2]2(μ2-BF) (with BF bridging both ruthenium atoms) in 2009.[15] To make the compound, Vidovic and Aldridge reacted NaRu(CO)2(C5H5) with (Et2O)·BF3; the boron monofluoride ligand then formed in-place.[14]

Vidovic and Aldridge also developed a substance with the formula (PF3)4FeBF by reacting iron vapour with B2F4 and PF3.[2] Hafnium, thorium, titanium, and zirconium can form a difluoride with a BF ligand at the low temperature of 6K. These come about by reacting the atomic metal with BF3.[2]

The first fully characterized molecule featuring BF as a terminal ligand was synthesized by Drance and Figueroa in 2019, by

sterically hindering the formation of a dimer. In the molecule, boron is double-bonded to iron.[16]

FBScF2, FBYF2, FBLaF2, and FBCeF2 have been prepared in a solid neon matrix by reacting atomic metals with boron trifluoride.[17]

References

  1. ^
    doi:10.1063/1.1696932
    .
  2. ^
    doi:10.1039/C0SC00508H
    .
  3. doi:10.1063/1.1725063
    .
  4. ISSN 0022-2852
    .
  5. doi:10.1021/ed100758t
    .
  6. PMID 25531385
    .
  7. ^
    ISBN 0-12-023614-1
    .
  8. ISBN 9781483224343
    .
  9. ^
    doi:10.1039/F29837900483
    .
  10. doi:10.1021/j100269a036. Archived
    (PDF) from the original on June 1, 2022.
  11. PMID 20143841
    .
  12. doi:10.1016/j.poly.2012.02.003
    .
  13. ^ Drance et al. 2019: "Previously, Vidovic and Aldridge reported that two equivalents of the ruthenium-based nucleophile Na[CpRu(CO)2] (Cp, cyclopentadienyl; [C5H5]−) reacts with boron trifluoride diethyl etherate (BF·
    3    Et
    2    O    ) with the formal loss of two equivalents of sodium fluoride (NaF) to produce the bridging BF complex ((μ2-BF)[CpRu(CO)2]2) (20). The latter is the only crystallographically characterized compound in which BF functions as a ligand to a metal center."
  14. ^
    doi:10.1016/j.ica.2010.07.013
    .
  15. PMID 19373822
    .
  16. S2CID 78094683
    .
  17. doi:10.1021/acs.inorgchem.8b02801
    .
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