Cyano- and Isocyanotris(trifluoromethyl)borates:  Syntheses, Spectroscopic Properties, and Solid State Structures of K[(CF₃)₃BCN] and K[(CF₃)₃BNC]

Abstract

A two step synthesis to the isocyanotris(trifluoromethyl)borate anion, [(CF3)3BNC]-, and its isomerization to the cyanotris(trifluoromethyl)borate anion, [(CF3)3BCN]-, at temperatures above 150 degrees C are presented. In the first step (CF3)3BNCH was obtained by reacting (CF3)3BCO with hydrogen cyanide followed by deprotonation of the HCN adduct with Li[N(SiMe3)2] in toluene. The thermal behavior of K[(CF3)3BNC] and K[(CF3)3BCN] were investigated by differential scanning calorimetry (DSC), and K[BF4] was identified as a major solid decomposition product. The enthalpy of the isocyanide-cyanide rearrangement, deltaH(iso) = -35 +/- 4 kJ mol(-1), was obtained from DSC measurements, and the activation energy, E(a) = 180 +/- 20 kJ mol(-1), from kinetic measurements. The isomerization was modeled as an intramolecular reaction employing DFT calculations at the B3LYP/6-311+G(d) level of theory yielding a reaction enthalpy of deltaH(iso) = -36.1 kJ mol(-1) and an activation energy of E(a) = 155.7 kJ mol(-1). The solid-state structures of K[(CF3)3BNC] and K[(CF3)3BCN] were determined by single-crystal X-ray diffraction. Both salts are isostructural and crystallize in the orthorhombic space group Pnma (no. 62). In the crystals the borate anions possess C(s) symmetry, while for the energetic minimum C3 symmetry is predicted by DFT calculations. The borate anions have been characterized by IR and Raman spectroscopy as well as by NMR spectroscopy. The assignment of the IR and Raman bands is supported by their calculated wavenumbers and intensities. The spectroscopic and structural properties of both borate anions are compared to the properties of the isoelectronic borane carbonyl (CF3)3BCO and the [B(CF3)4]- anion as well as to those of other related species.

Ethynylmonocarba-closo-dodecaborates: M[12-HCC-closo-1-CB11H11] and M[7,12-(HCC)2-closo-1-CB11H10] (M=Cs+, [Et4N]+)

“…The expected form of the signals with four lines of equal intensities and equal distances is not observed and distorted quartets are found. Partially collapsed signals are well known in NMR spectroscopy of boron compounds and they are a general phenomenon that occurs if a nucleus A couples to a nucleus B with spin > 1/ 2 and an inverse spin-lattice relaxation rate r 1 that is close to the respective coupling constant n J(A,B) [68][69][70][71][72]. In addition, the increased intensity of the two central lines of the quartets is to some extend due to the underlying partially collapsed septet of the corresponding 10 B isotopomer that has a relative intensity of 20%.…”

Salts of the Cobalt(I) Complexes [Co(CO)5]+ and [Co(CO)2(NO)2]+ and the Lewis Acid–Base Adduct [Co2(CO)7COB(CF3)3]

“…[23,24] Nitriles in place of [Co 2 (CO) 8 ] react with (CF 3 ) 3 BCO in an analogous manner yielding XCN·BA C H T U N G T R E N N U N G (CF 3 ) 3 (X = CH 3 , H). [16,17,25] Reaction (1) proceeds in anhydrous HF (aHF) solution in a different way, whereby the proton acts as oxidizing agent [Eq. (2)] and [Co(CO) 5 ]A C H T U N G T R E N N U N G [(CF 3 ) 3 BF] was isolated in 72 % yield.…”

Magnesium Cyanide or Isocyanide?

“…[9] This essential isotropic coordinative behavior of the spinning cyanide anion is typical for ionic metal cyanides and explains its description as ap seudohalide. [13] Trimethylsilyl cyanide, Me 3 SiCN,w as shown to contain small but significant quantities of Me 3 SiNC. [10] More covalently bound main-group CN compounds generally prefer cyanide connectivity.F or example,o rganic nitriles (RCN) are thermodynamically more stable than the corresponding isonitriles (RNC).…”

“…[10] More covalently bound main-group CN compounds generally prefer cyanide connectivity.F or example,o rganic nitriles (RCN) are thermodynamically more stable than the corresponding isonitriles (RNC). [13][14][15][16][17][18] Forionically bound CN À ,for example,LiCN,the cyanide/isocyanide energy differences become negligible while,atthe same time,the transition states for isomerization are lowered as well. [12] Likewise,t he anion [(CF 3 ) 3 B À CN] À is 8.4 kcal mol À1 lower in energy than [(CF 3 ) 3 B À NC] À .…”