title: Fluoride ion complexation by a B(2)/Hg heteronuclear tridentate Lewis acid.
abstract: The reaction of [Li(THF)(4)][1,8-mu-(Mes(2)B)C(10)H(6)] with HgCl(2) affords [1,1'-(Hg)-[8-(Mes(2)B)C(10)H(6)](2)] () or [1-(ClHg)-8-(Mes(2)B)C(10)H(6)] (), depending on the stoichiometry of the reagents. These two new compounds have been characterized by (1)H, (13)C, (11)B and (199)Hg NMR, elemental analysis and X-ray crystallography. The cyclic voltammogram of in THF shows two distinct waves observed at E(1/2) -2.31 V and -2.61 V, corresponding to the sequential reductions of the two boron centers. Fluoride titration experiments monitored by electrochemistry suggest that binds tightly to one fluoride anion and more loosely to a second one. Theses conclusions have been confirmed by a UV-vis titration experiment which indicates that the first fluoride binding constant (K(1)) is greater than 10(8) M(-1) while the second (K(2)) equals 5.2 (+/- 0.4) x 10(3) M(-1). The fluoride binding properties of have been compared to those of [1-(Me(2)B)-8-(Mes(2)B)C(10)H(6)] () and [1-((2,6-Me(2)-4-Me(2)NC(6)H(2))Hg)-8-(Mes(2)B)C(10)H(6)] (). Both experimental and computational results indicate that its affinity for fluoride anions is comparable to that of but significantly lower than that of the diborane . In particular, the fluoride binding constants of , and in chloroform are respectively equal to 5.0 (+/- 0.2) x 10(5) M(-1), 1.0 (+/- 0.2) x 10(3) M(-1) and 1.7 (+/- 0.1) x 10(3) M(-1). Determination of the crystal structures of the fluoride adducts [S(NMe(2))(3)][-mu(2)-F] and [S(NMe(2))(3)][-mu(2)-F] along with computational results indicate that the higher fluoride binding constant of arises from a strong chelate effect involving two fluorophilic boron centers.
authors.affiliation: Chemistry TAMU 3255, Texas A & M University, College Station, Texas 77843-3255, USA.
authors.forename: Christopher L
authors.initials: CL
authors.lastname: Dorsey
authors.forename: Pawel
authors.initials: P
authors.lastname: Jewula
authors.forename: Todd W
authors.initials: TW
authors.lastname: Hudnall
authors.forename: James D
authors.initials: JD
authors.lastname: Hoefelmeyer
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Taylor
authors.forename: Nicole R
authors.initials: NR
authors.lastname: Honesty
authors.forename: Ching-Wen
authors.initials: CW
authors.lastname: Chiu
authors.forename: Marcus
authors.initials: M
authors.lastname: Schulte
authors.forename: François P
authors.initials: FP
authors.lastname: Gabbaï
mesh_terms: D001880:Boranes / Q000737:chemistry; D001895:Boron / Q000737:chemistry*; D004563:Electrochemistry; D005459:Fluorides / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008628:Mercury / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011789:Quantum Theory; D013057:Spectrum Analysis
chemical_list: D001880:Boranes; D009942:Organometallic Compounds; D008628:Mercury; D001895:Boron; D005459:Fluorides