Reactions of (CF3)3BCO with amines and phosphines

Article abstract of DOI:10.1021/ic0515305

Reactions of tris(trifluoromethyl)borane carbonyl, (CF₃) ₃BCO, with ammonia yielded either a mixture of [NH ₄][(CF₃)₃BC(O)NH₂], [NH ₄][(CF₃)₃BCN], and [NH₄] ₂[{(CF₃)₃BC(O)}₂NH] or neat [NH ₄]₂[{(CF₃)₃BC(O)}₂NH] depending on the reaction conditions. The salt K[(CF₃) ₃BC(O)NH₂] was obtained as the sole product from the reaction of NH₃ with K[(CF₃)₃BC(O)F]. A simple synthesis for cyanotris(trifluoromethyl)borates, M[(CF₃) ₃BCN], was developed by dehydration of M[(CF₃) ₃BC(O)NH₂] (M = [NH₄], K) using phosgene. In addition, syntheses of the tris(trifluoromethyl)boron species [(CF ₃)₃BC(O)NHⁿPr]^-, [(CF ₃)₃BC(O)NMe₂]^-, and (CF ₃)₃BC(O)NMe₃, as well as of (CF ₃)₃BC(O)PMe₃, were performed. All species were characterized by multinuclear NMR spectroscopy. As far as neat substances resulted, IR and Raman spectra were recorded and their thermal behaviors were studied by differential scanning calorimetry. The interpretation of reaction pathways, structures, and vibrational spectra are supported by DFT calculations. The solid-state structure of K₂[{(CF₃) ₃BC(O)}₂NH]·2MeCN was determined by single-crystal X-ray diffraction.

Full text of DOI:10.1021/ic0515305

Inorg. Chem. 2006, 45, 669−678
Reactions of (CF3)3BCO with Amines and Phosphines
Maik Finze,*,†,‡ Eduard Bernhardt,† Helge Willner,*,† and Christian W. Lehmann*,§
Contribution from the FB C-Anorganische Chemie, Bergische UniVersita¨t Wuppertal,
Gaussstrasse 20, D-42097 Wuppertal, Germany, and the Max-Planck-Institut fu¨r Kohlenforschung,
Kaiser-Wilhelm-Platz 1, D-45470 Mu¨lheim an der Ruhr, Germany
Received September 8, 2005
Reactions of tris(trifluoromethyl)borane carbonyl, (CF3)3BCO, with ammonia yielded either a mixture of [NH4][(CF3)3-
BC(O)NH2], [NH4][(CF3)3BCN], and [NH4]2[ (CF3)3BC(O) 2NH] or neat [NH4]2[ (CF3)3BC(O) 2NH] depending on the
{
}
{
}
reaction conditions. The salt K[(CF3)3BC(O)NH2] was obtained as the sole product from the reaction of NH3 with
K[(CF3)3BC(O)F]. A simple synthesis for cyanotris(trifluoromethyl)borates, M[(CF3)3BCN], was developed by dehydration
of M[(CF3)3BC(O)NH2] (M
) [NH4], K) using phosgene. In addition, syntheses of the tris(trifluoromethyl)boron species
[(CF3)3BC(O)NHnPr]-, [(CF3)3BC(O)NMe2]-, and (CF3)3BC(O)NMe3, as well as of (CF3)3BC(O)PMe3, were performed.
All species were characterized by multinuclear NMR spectroscopy. As far as neat substances resulted, IR and
Raman spectra were recorded and their thermal behaviors were studied by differential scanning calorimetry. The
interpretation of reaction pathways, structures, and vibrational spectra are supported by DFT calculations. The
solid-state structure of K2[
{
(CF3)3BC(O)
}
2NH]
‚
2MeCN was determined by single-crystal X-ray diffraction.
Introduction
in 88% yield.14,15 In a series of recent publications, (CF3)3-
BCO was used as a versatile starting material for the
Chemical and thermal stable borate anions are of growing
interest because they are applied in many fields of chemistry,
biology, and physics.1-4 They can serve as ligands with
tunable properties in transition metal chemistry, for ex-
ample, [(C6F5)3BCN]-,5 [(CF3)3BCN]-,6 [B(CN)4]-,6-8 and
[CB11F11]2-,9 or as weakly coordinating anions,1,3,4,10 e.g.,
[B(C6F5)4]-,3 [B(CF3)4]-,11 [CHB11Cl11]-,12 and [CB11F12]-.13
Acidic solvolysis of one trifluoromethyl group of the
tetrakis(trifluoromethyl)borate anion, [B(CF3)4]-, in concen-
trated H2SO4 yields the unusual borane carbonyl, (CF3)3BCO,
synthesis of new borates and boranes with the (CF3)3B
fragment.14,16-20 The borane carbonyl reacts with nucleophiles
either under addition to the C atom of the carbonyl ligand
(7) Berkei, M.; Bernhardt, E.; Schu¨rmann, M.; Mehring, M.; Willner, H.
Z. Anorg. Allg. Chem. 2002, 628, 1734.
(8) Ku¨ppers, T.; Bernhardt, E.; Willner, H.; Rohm, H. W.; Ko¨ckerling,
M. Inorg. Chem. 2005, 44, 1015.
(9) Ivanov, S. V.; Rockwell, J. J.; Polyakov, O. G.; Gaudinski, C. M.;
Anderson, O. P.; Solntsev, K. A.; Strauss, S. H. J. Am. Chem. Soc.
1998, 120, 0, 4224.
(10) Lupinetti, A. J.; Havighurst, M. D.; Miller, S. M.; Anderson, O. P.;
Strauss, S. H. J. Am. Chem. Soc. 1999, 121, 11920.
(11) Bernhardt, E.; Henkel, G.; Willner, H.; Pawelke, G.; Bu¨rger, H. Chem.
Eur. J. 2001, 7, 4696.
(12) Reed, C. A. J. Chem. Soc., Chem. Commun. 2005, 1669.
(13) Strauss, S. H.; Ivanov, S. V.; Lupinetti, A. J. U.S. Patent 6,130,357,
2000.
(14) Finze, M.; Bernhardt, E.; Terheiden, A.; Berkei, M.; Willner, H.;
Christen, D.; Oberhammer, H.; Aubke, F. J. Am. Chem. Soc. 2002,
124, 15385.
* To whom correspondence should be addressed. Phone: (+49) 202-
439-2517 (H.W.); (+49) 211-81-13144 (M.F.); (+49) 208-306-2989
(C.W.L.). Fax: (+49) 202-439-3053 (H.W.). E-mail: willner@
uni-wuppertal.de (H.W.); maik.finze@uni-duesseldorf.de (M.F.);
lehmann@mpi-muelheim.mpg.de (C.W.L.).
† Bergische Universita¨t Wuppertal.
§ Max-Planck-Institut fu¨r Kohlenforschung.
‡ Present address: Institut fu¨r Anorganische Chemie und Strukturchemie
II, Heinrich-Heine-Universita¨t Du¨sseldorf, Universita¨tsstrasse 1, D-40225
Du¨sseldorf, Germany.
(15) Terheiden, A.; Bernhardt, E.; Willner, H.; Aubke, F. Angew. Chem.,
Int. Ed. 2002, 41, 799.
(1) Krossing, I.; Raabe, I. Angew. Chem. 2004, 116, 2116.
(2) Davidson, M.; Hughes, A. K.; Marder, T. B.; Wade, K. Contemporary
Boron Chemistry; Royal Society of Chemistry: Cambridge, 2000.
(3) Marks, T. J.; Chen, E. X.-Y. Chem. ReV. 2000, 100, 1391.
(4) Reed, C. A. Acc. Chem. Res. 1998, 31, 325.
(5) Vei, I. C.; Pascu, S. I.; Green, M. L. H.; Green, J. C.; Schilling, R.
E.; Anderson, G. D. W.; Rees, L. H. J. Chem. Soc., Dalton Trans.
2003, 2550.
(16) Finze, M.; Bernhardt, E.; Lehmann, C. W.; Willner, H. J. Am. Chem.
Soc. 2005, 127, 10712.
(17) Finze, M.; Bernhardt, E.; Lehmann, C. W.; Willner, H. Chem. Eur. J.
2005, 11, 6653.
(18) Finze, M.; Bernhardt, E.; Willner, H.; Lehmann, C. W. Angew. Chem.,
Int. Ed. 2004, 43, 4159.
(19) Finze, M.; Bernhardt, E.; Willner, H.; Lehmann, C. W. Angew. Chem.,
Int. Ed. 2003, 42, 1052.
(6) Finze, M.; Bernhardt, E.; Berkei, M.; Willner, H.; Hung, J.; Waymouth,
R. M. Organometallics 2005, 24, 5103.
(20) Bernhardt, E.; Finze, M.; Willner, H.; Lehmann, C. W.; Aubke, F.
Angew. Chem., Int. Ed. 2003, 42, 2077.
10.1021/ic0515305 CCC: $33.50
Published on Web 12/20/2005
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 2, 2006 669

Finze et al.
or in a ligand-exchange reaction under loss of CO.14 With
hydrogen cyanide, (CF3)3BCO reacts to (CF3)3BNCH, which
is further deprotonated to the isocyanoborate anion
[(CF3)3BNC]- according to (eq 1).16
a storage Dewar vessel. The ampules were opened and flame-sealed
again by using an ampule key.23
2. Chemicals. (CF3)3BCO was synthesized as described previ-
ously from K[B(CF3)4].14,15 Labeled 15NH3 (isotopic enrichment:
99%) was obtained from Euriso-Top GmbH (Saarbru¨cken, Ger-
many). All dry solvents were obtained from Aldrich and stored
under dry N2 or Ar in 1 L round-bottom flasks equipped with valves
with PTFE stems (Young, London) and charged with molecular
sieves (4 Å). All other chemicals were obtained from commercial
sources and used without further purification.
+HCN, - CO
(CF3)3BCO -80 °C f RT, CH Cl 8
2
2
+Li[N(SiMe3)2], - HN(SiMe3)2
-20 °C f RT, toluene
(CF3)3BNCH
8 Li[(CF3)3BNC] (1)
This isocyanoborate anion quantitatively isomerizes to its
cyano isomer [(CF3)3BCN]- at elevated temperatures (eq 2).16
3. Synthetic Reactions. 3.1. Reaction of (CF3)3BCO with NH3.
A 250 mL round-bottom flask was charged at -196 °C with 3.56
g (14.5 mmol) of (CF3)3BCO followed by 20 mL of dry liquid
ammonia. The reaction vessel was placed into a cold bath kept at
-90 °C. The clear, colorless reaction mixture was warmed to -30
°C within 3 h. Subsequently, the excess of NH3 was removed under
reduced pressure. The white product mixture was investigated by
NMR spectroscopy in CD3CN solution: 39% [NH4][(CF3)3BC(O)-
NH2], 27% [NH4][(CF3)3BCN], 26% [NH4]2[(CF3)3BCO2], and 8%
[NH4]2[{(CF3)3BC(O)}2NH].
K[(CF3)3BNC]
9
∆8 K[(CF3)3BCN]
(2)
Both anions are isoelectronic to the parent borane carbonyl
(CF3)3BCO, and their use as ligands was demonstrated by
the synthesis of the Rh(I) complexes (PPh3)3RhCNB(CF3)3
and (PPh3)3RhNCB(CF3)3.21
A different route to [(CF3)3BCN]- was found in the
reaction of [(CF3)3BC(O)Hal]- (Hal ) Cl, Br) with
K[N(SiMe3)2] which was also extented to its higher homo-
logues [(CF3)3BCPnic]- (Pnic ) P, As) according to (eq
3).18
3.2. Synthesis of K[(CF3)3BCN] Using the Product Mixture
of Reaction 3.1. The product mixture of 3.1. was dissolved in 100
mL of dry acetonitrile in a 250 mL round-bottom flask. Phosgene
(60 mmol) and 9 mL of triethylamine were added in vacuo.
Overnight the stirred reaction mixture was allowed to warm to room
temperature. All volatiles were removed under reduced pressure.
Water (20 mL) and 30 mL of dichloromethane were added to the
residue. Subsequently, the mixture was treated with 2 mL of Et3N
and 1 mL of concentrated hydrochloric acid. The dichloromethane
layer was separated, and the remaining aqueous solution was
extracted twice with 25 mL of CH2Cl2. The combined colorless
dichloromethane phases were dried with anhydrous MgSO4 and
filtered. KOH (2 g) was dissolved in 5 mL of water and added to
the clear, colorless CH2Cl2 solution. The mixture was stirred
vigorously for 15 min. Subsequently, the dichloromethane was
removed under reduced pressure. After addition of 100 mL of
diethyl ether, K2CO3 was added until the aqueous phase became
greasy. The etheral phase was separated, and the greasy residue
was extracted twice with 20 mL of Et2O. The collected or-
ganic layers were dried over K2CO3 followed by filtration and
removal of the solvent. Colorless pure K[(CF3)3BCN] (2.34 g, 8.3
mmol, based on (CF3)3BCO: 57%) was obtained. Anal. Calcd for
C4BF9KN: C, 16.98; N, 4.95. Found: C, 16.79; N, 4.97.
3.3. K[(CF3)3BC(O)NH2]. Inside a drybox, 679 mg (2.2 mmol)
of K[(CF3)3BC(O)F] was weighed into a 50 mL round-bottom
flask. In vacuo, 5 mL of dry liquid NH3 was added. The reaction
mixture was held at -80 °C, and then it was warmed to -10 °C
overnight. The remaining liquid ammonia was removed under
reduced pressure, and the colorless residue was dissolved in 30
mL of Et2O. After addition of a few milliliters of a concentrated
aqueous K2CO3 solution, the reaction mixture was stirred for 15
min. A small amount of solid K2CO3 was added, and then the
etheral phase was decanted. The greasy residue was extracted
with two portions of diethyl ether (20, 10 mL). The combined
organic layers were dried with K2CO3 and subsequently filtered.
All volatiles were removed under reduced pressure yielding 552
mg (1.8 mmol, 83%) of K[(CF3)3BC(O)NH2]. Anal. Calcd for
C4H2BF9KNO: C, 15.96; H, 0.67; N, 4.65. Found: C, 16.14; H,
0.7; N, 4.64.
Pnic(SiMe3)3
[(CF3)3BC(O)Hal]- + K[Pnic(SiMe3)2]
8
-20 oC f RT
[(CF3)3BCPnic]- + (Me3Si)2O + KHal
(Hal ) Cl, Br; Pnic ) N, P, As) (3)
In this contribution we report on (i) the synthesis of the
carbamoyl complexes [(CF3)3BC(O)NR1R2]- (R1 ) H, Me,
nPr; R2 ) H, Me), [{(CF3)3BC(O)}2NH]2- and (CF3)3BC-
(O)PnicMe3 (Pnic ) N, P), (ii) the dehydration of K[(CF3)3-
BC(O)NH2] yielding K[(CF3)3BCN], (iii) the solid-state
structure of K2[{(CF3)3BC(O)}2NH]‚2MeCN determined by
X-ray diffraction, and (iv) DFT calculations supporting the
interpretation of reaction pathways and the assignments of
the vibrational spectra.
The new borate anions may be used as ligands in
organometallic chemistry.
Experimental Section
General Procedures and Reagents. 1. Apparatus. Volatile
materials were manipulated in glass vacuum lines of known volume
equipped with valves with PTFE stems (Young, London) and with
a capacitance pressure gauge (Type 280E, Setra Instruments, Acton,
MA). The reactions involving air-sensitive compounds were
performed under a N2 or Ar atmosphere using standard Schlenk
line techniques. Solid materials were manipulated inside an inert
atmosphere box (Braun, Munich, Germany) filled with argon, with
a residual moisture content of less than 1 ppm. Reactions were
performed either in round-bottom flasks equipped with valves with
PTFE stems (Young, London) and fitted with PTFE-coated
magnetic stirring bars or in 5 mm o.d. NMR tubes attached to
rotational symmetric valves (Young, London).22 Volatile compounds
were stored in flame-sealed glass ampules under liquid nitrogen in
3.4. K[(CF3)3BCN] by Dehydration of K[(CF3)3BC(O)NH2].
The synthesis was performed analogous to reaction 3.2. K[(CF3)3-
(21) Finze, M.; Bernhardt, E.; Willner, H.; Lehmann, C. W. Organome-
tallics, in preparation.
(22) Gombler, W.; Willner, H. Int. Lab. 1984, 84.
(23) Gombler, W.; Willner, H. J. Phys. E: Sci. Instrum. 1987, 20, 1286.
670 Inorganic Chemistry, Vol. 45, No. 2, 2006

Reactions of (CF3)3BCO with Amines and Phosphines
Table 1. Crystallographic Data of K2[{(CF3)3BC(O)}2NH]‚2MeCN at
BC(O)NH2] (242 mg, 0.9 mmol) was dissolved in 10 mL of dry
CH3CN and 1 mL of Et3N. At -196 °C, 4 mmol of phosgene was
added. The workup was performed as described for reaction 3.2.
Yield: 213 mg (0.8 mmol, 94%).
100 K
empirical formula
C12H7B2F18K2N3O2
667.03
fw [g mol-1
color
]
colorless
3.5. K2[{(CF3)3BC(O)}2NH]. A 100 mL round-bottom flask was
charged at -196 °C with 1.18 g (4.8 mmol) of (CF3)3BCO.
Subsequently, 50 mL of diethyl ether were added. The reaction
mixture was warmed to -80 °C. A 250 mL round-bottom flask
filled with 29 mmol of NH3 was kept at -196 °C and connected
to the other reaction vessel. The valves between the two flasks were
opened, and subsequently, the ammonia was allowed to warm to
room temperature and to diffuse into the reaction mixture. Under
vigorous stirring, the reaction mixture was warmed to room
temperature overnight. A clear, colorless two-phase system was
obtained. The solvent and the excess of NH3 were removed under
reduced pressure, and pure colorless [NH4]2[{(CF3)3BC(O)}2NH]
remained in the flask. Analogous to synthesis 3.3., [NH4]2[{(CF3)3-
BC(O)}2NH] is transformed in Et2O into the corresponding potas-
sium salt using aqueous solutions of KOH and K2CO3. Yield: 552
mg (1.8 mmol, 83%). Anal. Calcd for C8HB2F18K2NO2: C, 16.43;
H, 0.17; N, 2.39. Found: C, 16.52; H, < 0.2; N, 2.40.
cryst syst, space group
unit cell dimensions
monoclinic, C2/c (no. 15)
a [Å]
b [Å]
c [Å]
â [deg]
V [Å3]
Z
14.4824(2)
11.0174(1)
29.0305(3)
90.17(1)
4632.04(9)
8
1.910
4.21-30.70
0.0468
F
calc [Mg m-3
θ range [deg]
]
R1, [I > 2σ(I)]a
wR2, all datab
GOF on F2
0.1013
1.067
a R1 ) (∑||Fo| - |Fc||)/∑|Fo|. b wR2 ) [∑w(Fo - Fc )2/∑w(Fo )2]1/2
,
2
2
2
2
weight scheme w ) [σ2(Fo) + (0.0352P)2 + 7.6786P]-1; P ) (max(0,Fo )
2
+ 2Fc )/3).
magnetic stirring bar. The reaction mixture was first warmed to
-30 °C and then under stirring to room temperature. A colorless
solid precipitated from the solution. After 2 h at room temperature,
all volatiles were removed in vacuo. (CF3)3BC(O)NMe3 was
identified as the main product by NMR spectroscopy (78%). Slow
decomposition of the trimethylamine adduct in acetonitrile solution
to unknown products was observed by NMR spectroscopy.
3.12. (CF3)3BC(O)PMe3. Analogous to reaction 3.11., (CF3)3-
BC(O)PMe3 was synthesized from the borane carbonyl and PMe3.
Yield: 520 mg (1.6 mmol, 99%). Anal. Calcd for C7H9BF9PO: C,
26.12; H, 2.82. Found: C, 26.75; H, not observed. An analysis of
the hydrogen content was not possible because the peak was
interfered by an artifact.
3.13. (CF3)3BCNMe. K[(CF3)3BCN] (205 mg, 0.7 mmol) was
weighed into a cylindrical reaction vessel (V ) 10 mL) equipped
with a valve with a PTFE stem (Young, London), fitted with a
PTFE-coated magnetic stirring bar. At -196 °C, 5 mL of CF3S(O)2-
OMe was added. The reaction mixture was allowed to warm to
room temperature, yielding a colorless solution. During the course
of the reaction, a solid slowly precipitated from the solution. After
5 h at room temperature, the excess of methyltriflate was removed
in vacuo. The colorless residue was extracted three times with CH2-
Cl2 (20, 20, 10 mL), and the organic phases were filtered through
a glass frit packed with Celite. After removal of the solvent, a
colorless solid was obtained. Yield: 127 mg (0.5 mmol, 71%). Anal.
Calcd for C5H3BF9N: C, 23.20; H, 1.17; N, 5.41. Found: C, 22.75;
H, 0.8; N, 4.66. In a similar way, the 15N-labeled compound was
obtained.
3.6. K[(CF3)3BC(O)15NH2] and K2[{(CF3)3BC(O)}215NH]. The
isotopically labeled compounds were synthesized by the same
procedures as described for the natural compounds.
3.7. K[(CF3)3BC(O)NHnPr]. A NMR tube22 was charged with
100 mg (0.33 mmol) of K[(CF3)3BC(O)F]. nPrNH2 (1.3 mmol) and
1 mL of CD2Cl2 were added in a vacuum at -196 °C. The reaction
mixture was warmed to room temperature and shaken subsequently.
After a small portion of solid K2CO3 was added, the NMR tube
was shaken again. According to the NMR spectra, K[(CF3)3BC-
(O)NHnPr] was the only product.
3.8. K[(CF3)3BC(O)NMe2]. K[(CF3)3BC(O)F] (94 mg, 0.31
mmol) was transferred into a NMR tube,22 and at -196 °C, 1 mL
of CD3CN was added in vacuo. Under a N2 atmosphere, 0.5 mL of
Me2NSiMe3 was transferred into the NMR tube using a syringe.
The reaction mixture was shaken and then investigated by NMR
spectroscopy. K[(CF3)3BC(O)NMe2] was identified as the sole
product.
3.9. Reaction of (CF3)3BCO with HN(SiMe3)2. A 50 mL round-
bottom flask was charged at -196 °C with 430 mg (1.8 mmol) of
(CF3)3BCO and 5 mL of HN(SiMe3)2. The reaction mixture was
warmed from -50 °C to room temperature and stirred overnight.
The excess of disilazane was removed under reduced pressure. The
NMR spectroscopic investigation revealed the following products:
27% [(CF3)3BCN]- and 73% further unidentified (CF3)3B deriva-
tives. The assigned NMR data of the main product (59%) are 19F
2
NMR: δ ) -61.2 ppm (q, JB,F ) 26.6 Hz); 11B-NMR: δ )
2
-18.3 ppm (decet, JB,F ) 26.6 Hz).
4. Instrumentation. 4.1. Single-Crystal X-Ray Diffraction.
Crystals of K2[{(CF3)3BC(O)}2NH]‚2MeCN suitable for X-ray
diffraction were obtained by slow diffusion of dichloromethane
vapor into an acetonitrile solution. Diffraction data were collected
at 100 K on a KappaCCD diffractometer (Bruker AXS) using Mo
KR radiation (λ ) 0.71073 Å) and a graphite monochromator.
Crystal structures were determined using SHELXS-97,24 and full-
matrix least-squares refinements based on F2 were performed using
SHELXL-97.25 Integration and empirical absorption corrections
(DENZO scalepack)26 were applied. Figures of the molecular
structure were drawn using the program Diamond.27 A summary
3.10. K[(CF3)3BC(O)NHMe]. Inside a drybox, 98 mg (0.38
mmol) of (CF3)3BCNMe was weighed into a beaker with a magnetic
stirring bar. After the addition of 5 mL of CH2Cl2, 1 mL of a
concentrated aqueous K2CO3 solution was added while stirring. The
dichloromethane layer was discarded, and the aqueous phase was
extracted three times with diethyl ether (20, 20, 10 mL). The
combined etheral phases were predried with K2CO3, filtered, and
then dried with molecular sieves (4 Å) in a N2 atmosphere. After
filtration, the solvent was removed under reduced pressure. Yield:
64 mg (0.2 mmol, 53%). In an analogous manner, the 15N-labeled
compound was obtained.
(24) Sheldrick, G. M. SHELXS-97, Program for Crystal Structure Solution;
University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(25) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure Refine-
ment; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
3.11. (CF3)3BC(O)NMe3. (CF3)3BCO (145 mg, 0.59 mmol), 5
mL of CH2Cl2, and 1.8 mmol of NMe3 were condensed into a
cylindrical reaction vessel (V ) 15 mL) equipped with a valve with
a PTFE stem (Young, London) and fitted with a PTFE-coated
(26) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307.
Inorganic Chemistry, Vol. 45, No. 2, 2006 671

Finze et al.
Scheme 1. Reaction of (CF3)3BCO with Liquid Ammonia (Observed Borates Are Printed in Bold Letters)
of experimental details and crystal data is collected in Table 1. An
X-ray crystallographic file in CIF format for K2[{(CF3)3BC-
(O)}2NH]‚2MeCN has been deposited at the Cambridge Crystal-
lographic Data Center under the deposition number CCDC-253572.
A copy of the data can be obtained free of charge on application
to CCDC, 12 Union Road, Cambridge CB21EZ, UK (fax: (+44)-
1223-336-033; e-mail: deposit@ccdc.cam.ac.uk).
98 program suite.34 Geometries were optimized and energies were
calculated with the 6-311++G(d) basis set, and all structures
represent true minima on the respective hypersurface (no imaginary
frequency). Diffuse functions were incorporated because improved
energies are obtained for anions.35 All energies presented herein
are zero-point corrected, and for enthalpies and free energies, the
thermal contributions are included for 298 K.
4.2. Vibrational Spectroscopy. Infrared spectra were recorded
at room temperature on an IFS 66v FTIR instrument (Bruker,
Karlsruhe, Germany). A DTGS detector, together with a KBr/Ge
beam splitter was used in the region of 5000-400 cm-1. Raman
spectra were recorded on a Bruker RFS 100/S FT Raman
spectrometer using the 1064 nm excitation (500 mW) of a Nd:
YAG laser.
Results and Discussion
1. Synthetic Aspects. The reaction of (CF3)3BCO with
liquid ammonia results in a mixture of the borates [NH4]-
[(CF3)3BC(O)NH2], [NH4][(CF3)3BCN], [NH4]2[(CF3)3BCO2],
and [NH4]2[{(CF3)3BC(O)}2NH], as rationalized in Scheme
1. Ammonia adds to the carbonyl C atom of (CF3)3BCO
yielding (CF3)3BC(O)NH3 as the intermediate. Subsequently,
most of the (CF3)3BC(O)NH3 is deprotonated by ammonia,
yielding [NH4][(CF3)3BC(O)NH2]. Similar reactions of NH3
with other borane carbonyls yielding carbamoyl complexes
have been observed, for example, [NH4][H3BC(O)NH2]36,37
and [NH4]2[1,12-B12H10{C(O)NH2}2].38,39
1
4.3. NMR Spectroscopy. H, 19F, 31P, and 11B NMR spectra
were recorded at room temperature on a Bruker Avance DRX-300
spectrometer operating at 300.13, 282.41, 121.49, or 96.29 MHz
1
for H, 19F, 31P, and 11B nuclei, respectively. 13C and 15N NMR
spectroscopic studies were performed at room temperature on a
Bruker Avance DRX-500 spectrometer, operating at 125.758 or
50.678 MHz for 13C and 15N nuclei, respectively. The NMR signals
were referenced against TMS and CFCl3 as internal standards and
BF3‚OEt2 in CD3CN, H3PO4 in H2O and MeNO2 in CD3CN as
external standards. Concentrations of the investigated samples were
(27) Diamond-Visual Crystal Structure Information System, Ver. 2.1, 1996-
1999.
(28) Morris, G. A.; Freeman, R. J. Am. Chem. Soc. 1979, 101, 760.
(29) Witanowski, M.; Stefaniak, L.; Webb, G. A. Annu. Rep. NMR
Spectrosc. 1986, 18, 1.
in the range of 0.1-1 mol L-1
.
15N NMR spectra were obtained
by direct measurements or for compounds having a hydrogen
available for polarization transfer with the INEPT method.28,29
4.4. DSC Measurements. Thermoanalytical measurements were
made with a Netzsch DSC204 instrument. Temperature and
sensitivity calibrations in the temperature range of 20-500 °C were
carried out with naphthalene, benzoic acid, KNO3, AgNO3, LiNO3,
and CsCl. About 5-10 mg of the solid samples were weighed and
contained in sealed aluminum crucibles. They were studied in the
(30) Kohn, W.; Sham, L. J. Phys. ReV. A 1965, 140, 1133.
(31) Becke, A. D. Phys. ReV. B 1988, 38, 3098.
(32) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(33) Lee, C.; Yang, W.; Parr, R. G. Phys. ReV. B 1988, 41, 785.
(34) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.;
Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels,
A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone,
V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.;
Clifford, S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;
Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R.
L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara,
A.; Gonzalez, C.; Challacombe, M.; Gill, P. M. W.; Johnson, B. G.;
Chen, W.; Wong, M. W.; Andres, J. L.; Head-Gordon, M.; Replogle,
E. S.; Pople, J. A. Gaussian 98, revision A.6; Gaussian, Inc.:
Pittsburgh, PA, 1998.
temperature range of 20-500 °C with a heating rate of 5 K min-1
;
throughout this process, the furnace was flushed with dry nitrogen.
For the evaluation of the output, the Netzsch Protens4.0 software
was employed.
4.5. Computational Calculations. Quantum chemical calcula-
tions were performed to support the interpretation of the experi-
mental results in this study. DFT calculations30 were carried out
using Becke’s three-parameter hybrid functional and the Lee-
Yang-Parr correlation functional (B3LYP)31-33 with the Gaussian
(35) Rienstra-Kiracofe, J. C.; Tschumper, G. S.; Schaefer, H. F., III; Nandi,
S.; Ellison, G. B. Chem. ReV. 2002, 102, 231.
672 Inorganic Chemistry, Vol. 45, No. 2, 2006

Reactions of (CF3)3BCO with Amines and Phosphines
The [(CF3)3BC(O)NH2]- anion is dehydrated by unreacted
(CF3)3BCO, resulting in [NH4][(CF3)3BCN] and [NH4]2-
[(CF3)3BCO2] in equimolar amounts. The postulated tran-
sient [(CF3)3BC(NH)OC(O)B(CF3)3]2- is very likely,
since this dimeric borate anion is similar to the known
[{(CF3)3BC(O)}2O]2- dianion.17
of the [(CF3)3BC(O)NH2]- anion is quantitative by treatment
with phosgene in the presence of triethylamine (eq 6).
[(CF3)3BC(O)NH2]- + OCCl2 + 2Et3N CH CN8
3
RT
[(CF3)3BCN]- + 2[Et3NH]Cl + CO2 (6)
The formation of [NH4]2[{(CF3)3BC(O)}2NH] as side
product is rationalized by deprotonation of the intermediate
[(CF3)3BC(OH)NHC(O)B(CF3)3]-. Due to a low local con-
centration of NH3, the deprotonation of (CF3)3BC(O)NH3 is
incomplete. Hence, (CF3)3BC(O)NH3 rearranges to (CF3)3-
BC(OH)NH2, which reacts with (CF3)3BCO to the [{(CF3)3-
BC(O)}2NH]2- dianion. The selective synthesis of salts with
the [{(CF3)3BC(O)}2NH]2- anion were achieved by diffusion
of gaseous ammonia into solutions of (CF3)3BCO in diethyl
ether (eq 4).
N-Alkylamide derivatives of the type [(CF3)3BC(O)NR1R2]-
were obtained by three different routes: (i) reaction of amines
with K[(CF3)3BC(O)F] (eq 7),
[(CF3)3BC(O)F]- + 2nPrNH2 CH CN8
3
RT
[(CF3)3BC(O)NH nPr]- + [nPrNH3]F (7)
(ii) reaction of R2NSiMe3 with K[(CF3)3BC(O)F] (eq 8) and
[(CF3)3BC(O)F]- + Me2NSiMe3 CD CN8
3
RT
[(CF3)3BC(O)NMe2]- + Me3SiF (8)
(iii) alkylation of [(CF3)3BCN]- (eq 9) followed by hydroly-
sis (eq 10).
CF3
S(O) OMe8
2
K[(CF3)3BCN] CF3S(O)2OMe
(CF3)3BCNMe + KCF3SO3 (9)
Due to the lower basicity of diethyl ether in comparison
to ammonia, the carbene complex (CF3)3BC(OH)NH2 is
present in the reaction mixture instead of [(CF3)3BC(O)NH2]-.
Hence, (CF3)3BCO reacts with the N atom of (CF3)3BC(OH)-
NH2 and after deprotonation [{(CF3)3BC(O)}2NH]2- is
obtained and isolated as the colorless salt K2[{(CF3)3BC-
(O)}2NH], which according to DSC measurements under-
goes a phase transition at 104 °C and decomposes at 185
°C. The close relationship to the acetylacetonate anion,
[{MeC(O)}2CH]-, whose coordination chemistry is well
studied,40,41 makes [{(CF3)3BC(O)}2NH]2- a possible can-
didate as a bidentate ligand.
2(CF3)3BCNMe + K2CO3 + H2O H O8
2
2K[(CF3)3BC(O)NHMe] + CO2 (10)
(CF3)3CC(O)NMe2, which is isoelectronic to the
[(CF3)3BC(O)NMe2]- anion, is formed by the reaction of
(CF3)3CC(O)Cl with Me2NH,43,44 analogous to the synthesis
of [(CF3)3BC(O)NHnPr]- shown in eq 7.
The main product of the reaction of (CF3)3BCO with
trimethylamine is the colorless inner salt (CF3)3BC(O)NMe3.
PMe3 reacts with the borane carbonyl to (CF3)3BC(O)PMe3
as the sole product.
Pure K[(CF3)3BC(O)NH2] was obtained from the reaction
of K[(CF3)3BC(O)F] with liquid NH3 (eq 5).
CH2Cl2
NH3
(CF3)3BCO + Me3Pnic
8
[(CF3)3BC(O)F]- + 2NH3
8
C
-80 f -10 o
[(CF3)3BC(O)NH2]- + [NH4]F (5)
(CF3)3BC(O) Pnic Me3 (Pnic ) N, P) (11)
The adduct H3BC(O)NMe3 obtained from NMe3 and
H3BCO,36,37,45 is stable only at temperatures below -45 °C
and decomposes at elevated temperatures to H3BNMe3 and
CO.36,37,45 In contrast, (CF3)3BC(O)NMe3 decomposes slowly
K[(CF3)3BC(O)NH2] is a colorless solid which undergoes
a phase transition at 74 °C and decomposes at 215 °C. The
main thermal decomposition product is K[(CF3)3BCN] (60%,
NMR spectroscopy), besides the borates K[C2F5BF3] (32%),
K[(CF3)3BF] (5%), and K[BF4] (3%). The latter three salts
were observed also when reacting KF with the gas-phase
decomposition products of (CF3)3BCO.42 The dehydration
46
in solution at room temperature but no (CF3)3BNMe3 is
formed, and if triethylamine is used in place of NMe3, the
mixture turns black when warming up (>-30 °C) and slow
gas evolution is observed.
(36) Burg, A. B.; Schlesinger, H. I. J. Am. Chem. Soc. 1937, 59, 780.
(37) Carter, J. C.; Parry, R. W. J. Am. Chem. Soc. 1965, 87, 2354.
(38) Knoth, W. H.; Sauer, J. C.; Miller, H. C.; Mutterties, E. L. J. Am.
Chem. Soc. 1964, 86, 115.
(39) Knoth, W. H.; Sauer, J. C.; Balthis, J. H.; Miller, H. C.; Muetterties,
E. L. J. Am. Chem. Soc. 1967, 89, 4842.
(42) Finze, M.; Bernhardt, E.; Za¨hres, M.; Willner, H. Inorg. Chem. 2004,
43, 490.
(43) Cherbukov, Y. A.; Aronov, Y. A.; Fedin, E. I.; Petrovskii, P. V.;
Knunyants, I. L. Dokl. Akad. Nauk SSSR 1966, 169, 128.
(44) Cherbukov, Y. A.; Knunyants, I. L. IzV. Akad. Nauk SSSR, Ser. Khim.
1967, 346.
(40) Crabtree, R. H. The Organometallic Chemistry of the Transition Metals,
2nd ed.; Wiley: New York, 1994.
(41) Elschenbroich, C. Organometallchemie; 4th ed.; Teubner, B. G., Ed.;
Verlag/GWV Fachverlage GmbH, Wiesbaden, 2003.
(45) Carter, J. C.; Moye´, A. L.; Luther III, G. W. J. Am. Chem. Soc. 1974,
96, 3071.
(46) Brauer, D. J.; Bu¨rger, H.; Do¨rrenbach, F.; Krumm, B.; Pawelke, G.;
Weuter, W. J. Organomet. Chem. 1990, 385, 161.
Inorganic Chemistry, Vol. 45, No. 2, 2006 673

Finze et al.
Table 2. Calculateda Enthalpies of the Reactions of (CF3)3BCO with
NH3 and Me3Pnic (Pnic ) N, P)
(CF3)3BCO + X3Pnic f
(CF3)3BC(O)PnicX3
(CF3)3BCO + X3Pnic f
(CF3)3BPnicX3 + CO
base
∆H(298 K) [kJ mol-1
]
∆H(298 K) [kJ mol-1
]
NH3
Me3N
Me3P
-46.1
-33.6
-57.4
-124.5
-87.2
-121.8
a B3LYP/6-311++G(d).
Figure 1. View of the [{(CF3)3BC(O)}2NH]2- anion in the crystal structure
of K2[{(CF3)3BC(O)}2NH]‚2MeCN.
Table 3. Selected Bond Parameters of the [{(CF3)3BC(O)}2NH]2- Ion
in the Potassium Salt and from DFT Calculationsa,b
exptl
calcd
exptl
calcd
bond lengths [Å]
1.217 B-C(O)
1.414 B-CF3
1.011 C-F
C-O
C-N
N-H
1.227(2)
1.397(2)
0.822(26)
1.636(3)
1.626(4)
1.358(5)
1.665
1.648
1.372
bond angles [deg]
O-C-N
B-C-O
120.73(16) 121.7
121.59(16) 121.0
B-C-N
117.59(16) 117.3
(O)C-B-CF3 109.48(16) 110.0
torsion angles [deg]
4.7 O-C-N-H 175.2
O-C-N-C(O)
6.6
175.3
Figure 2. Coordination sphere of one K+ chelated by two [{(CF3)3BC-
(O)}2NH]2- anions in the crystal structure of K2[{(CF3)3BC(O)}2NH]‚
2MeCN.
a B3LYP/6-311++G(d). b Mean values of different bond lengths and
angles.
Solid (CF3)3BC(O)PMe3 is thermally stable up to 142 °C.
The residue of the decomposition contains no (CF3)3BPMe3.
The reaction of PH3 with the borane carbonyl yields a light
yellow solid, which is insoluble in acetonitrile and in
water. In contrast to PMe3 and PH3, PF3 does not react with
(CF3)3BCO, neither in the gas phase (p(PF3) ) 3 bar) nor in
CD2Cl2 solution at room temperature.
2. DFT Calculations. Thermochemical data derived from
DFT calculations (B3LYP/6-311++G(d)) of CO exchange
reactions and additions to the carbonyl C atom of (CF3)3-
BCO with ammonia, NMe3, and PMe3, respectively, are listed
in Table 2. All six reactions are exothermic. For all examples,
the exchange reactions are thermochemically favored over
the respective addition reactions, in sharp contrast to the
experimental findings. The formation of stable adducts is
kinetically favored, and so no ligand exchange occurs. If no
stable adduct is formed, e.g., with acetonitrile, immediately
CO is released and (CF3)3BNCMe is obtained.14
The increased enthalpy of the reaction of the borane
carbonyl with PMe3 in comparison to NMe3 parallels the
trend in thermal stability: while (CF3)3BC(O)PMe3 is stable
in acetonitrile solution at room temperature and up to 142
°C in the solid state, (CF3)3BC(O)NMe3 slowly decomposes
in MeCN solution at room temperature.
3. Solid State Structure of K2[{(CF3)3BC(O)}2NH]‚
2MeCN. The potassium salt of the [{(CF3)3BC(O)}2NH]2-
anion crystallizes as solvate with two molecules of aceto-
nitrile per formula unit in the monoclinic space group C2/c
(no. 15). Selected bond parameters are collected in Table 3
and are compared to values derived from DFT calculations
(B3LYP/6-311++G(d)). In Figure 1, an anion in the crystal
structure is depicted. In the solid state, the anions have no
symmetry (C1), whereas for the energy minimum of the gas-
phase structure, C2 symmetry is calculated. However, the
deviations between experimental and theoretical bond pa-
rameters are small.
In the crystal lattice, the borate anions form layers parallel
to the c axis which are rotated (Figure S1). Two different
types of potassium cations are present in the crystals which
are both located on the C2 axis. One-half of the cations are
coordinated by four O atoms of two chelating borate anions
with distances of 2.655(1) and 2.723(1) Å, as well as six
fluorine atoms (2.861(1)-2.970(1) Å) (Figure 2). The second
half of the K+ cations are coordinated by two N atoms of
two acetonitrile molecules (2.852(2) Å), two nonchelating
oxygen atoms (2.802(2) Å), and six fluorine atoms (2.991-
(2)-3.183(2) Å). All contacts represent weak interionic
interactions.47
4. Vibrational Spectroscopy. K[(CF3)3BC(O)NH2],
K2[{(CF3)3BC(O)}2NH] (Figure 3), and (CF3)3BC(O)PMe3
(Figure 4), as well as the reaction mixture obtained from
(CF3)3BCO and NMe3, were investigated by IR and Raman
spectroscopy. Due to the large number of vibrational modes,
the spectra are complex and only those of the simplest
[(CF3)3BC(O)NH2]- anion were assigned in detail with the
aid of the predicted spectrum obtained from DFT calculations
(Table S1).
Especially the vibrational spectra of K[(CF3)3BC(O)NH2]
and K2[{(CF3)3BC(O)}2NH] display in the range of 100-
1300 cm-1 the band pattern typical for (CF3)3B spe-
cies.11,14,48,49 In the Raman spectrum of (CF3)3BC(O)PMe3,
this trend is not as clear due to additional strong bands
associated with the PMe3 moiety (Figure 4).
Characteristic bands for the carbamoyl complexes are the
CO stretches which are observed (calculated) at 1696 cm-1
(1624 cm-1) for K[(CF3)3BC(O)NH2], at 1756 (1694) and
1725 cm-1 (1662 cm-1) for K2[{(CF3)3BC(O)}2NH], at 1993
(47) Shannon, R. D. Acta Crystallogr., Sect. A: Found. Crystallogr. 1976,
32, 751.
(48) Pawelke, G.; Bu¨rger, H. Coord. Chem. ReV. 2001, 215, 243.
(49) Pawelke, G.; Bu¨rger, H. Appl. Organomet. Chem. 1996, 10, 147.
674 Inorganic Chemistry, Vol. 45, No. 2, 2006

Reactions of (CF3)3BCO with Amines and Phosphines
(Figure 3, Table S1). In the Raman spectrum, only νs(NH)
can be observed. In the range from 3300 to 3800 cm-1, a
series of bands are found in the spectra of K2[{(CF3)3BC-
(O)}2NH] due to overtones (Figure 3).
5. NMR Spectroscopy. Multinuclear NMR spectroscopy
of the carbamoyl complexes (CF3)3BC(O)NMe3 and (CF3)3-
BC(O)PMe3 allowed their detailed characterization due to
small line widths (Table S2). This is unexpected, since in
general, broad lines are a typical feature for 11B NMR spectra
and NMR spectra of nuclei that interact with 11B due the
quadrupolar moment of 11B.50-52 Investigated nuclei are 1H,
11B, 13C, 15N, 19F, and 31P, and the chemical shifts and
coupling constants are collected in Table 4.
In Figure 5 the 11B and in Figure 6 the 19F, as well as
19F{11B}, NMR spectra of [(CF3)3BC(O)NH2]-, [(CF3)3BC-
(O)NHMe]-, [{(CF3)3BC(O)}2NH]2-, and their 15N isoto-
pomers are depicted. The 11B and 19F NMR chemical shifts
of [(CF3)3BC(O)NH2]-, [(CF3)3BC(O)NHR]- (R ) Me,
nPr) and [{(CF3)3BC(O)}2NH]2- are similar to those of
[(CF3)3BC(O)OH]-,14 while δ(11B) and δ(19F) of [(CF3)3BC-
(O)NMe2]- are shifted to higher values (Table 4). The 11B
NMR signals are split into decets, and the 19F NMR signals
into quartets due to the 2J(11B,19F) couplings. The 11B NMR
spectra of the three carbamoyl complexes are split into
2
doublets due to J(11B,15N) with values of 5.2-6.2 Hz. In
the case of [(CF3)3BC(O)NH2]-, only one 3J(1H,11B) coupling
is observed, which is due to the interaction with the trans
proton. In general, trans couplings are larger than the respec-
tive cis couplings.53 Similarly, the proton in [{(CF3)3BC-
(O)}2NH]2-, which does not couple to 11B, is in the cis
position to the B atom. It is further concluded that in
[(CF3)3BC(O)NHMe]- the proton is positioned cis to the B
atom, in accordance with steric considerations. The 19F nuclei
of [(CF3)3BC(O)15NH2]-, [(CF3)3BC(O)15NHMe]-, and
[{(CF3)3BC(O)}215NH]2- couple to the respective 15N nucleus
and 4J(15N,19F) range from 0.8 to 1.0 Hz. While for
[(CF3)3BC(O)15NHMe]- and [{(CF3)3BC(O)}215NH]2- the
5J(1H,19F) couplings were observed, in the 19F{11B} NMR
Figure 3. IR and Raman spectra of K2[{(CF3)3BC(O)}2NH] (top) and
K[(CF3)3BC(O)NH2] (bottom).
5
spectrum of [(CF3)3BC(O)15NH2]-, no J(1H,19F) coupling
was found.
The chemical shifts and coupling schemes in the 11B and
19F NMR spectra of (CF3)3BC(O)PnicMe3 (Pnic ) N, P)
are similar to related (CF3)3B-C(O) derivatives (Table 4,
2
Figure S2).14 In the trimethylphosphan adduct, J(11B,31P)
Figure 4. IR and Raman spectra of (CF3)3BC(O)PMe3 (IR spectrum as
Nujol mull).
) 44.5 Hz and 4J(19F,31P) ) 4.4 Hz are observed. The much
larger line widths in the NMR spectra of (CF3)3BC(O)NMe3
are remarkable in comparison to those of its phosphorus
analogue.
The 15N NMR spectra of [(CF3)3BC(O)NH2]-, [(CF3)3BC-
(O)NHMe]-, and [{(CF3)3BC(O)}2NH]2- display the 1J
couplings between 1H and 15N (Figure S3). Furthermore, the
spectra of [(CF3)3BC(O)NH2]- and [(CF3)3BC(O)NHMe]-
cm-1 (1800 cm-1) for (CF3)3BC(O)NMe3, and at 1815 cm-1
(1679 cm-1) for (CF3)3BC(O)PMe3. As a first approximation,
ν(CO) is a measure for the bonding between the carbonyl C
atom and the N or P base: the stronger the C(O)-X bond
becomes, the lower is ν(CO). Hence, trimethylamine is
weakest bound, and in (CF3)3BC(O)PMe3, the C-P bond
strength is significantly increased in accordance with their
thermal behaviors. The strongest C-N interactions are
present in the borate anions [(CF3)3BC(O)NH2]- and
[{(CF3)3BC(O)}2NH]2-.
(50) Hubbard, P. S. J. Chem. Phys. 1970, 53, 985.
(51) Halstead, T. K.; Osment, P. A.; Sanctuary, B. C.; Tagenfeldt, J.; Lowe,
I. J. J. Magn. Reson. 1986, 67, 267.
(52) Wrackmeyer, B. In Annu. Rep. NMR Spectrosc.; Webb, G. A., Ed.;
Academic Press Ltd: London, 1988; Vol. 20, p 61.
(53) Hesse, M.; Meier, H.; Zeeh, B. Spektroskopische Methoden in der
organischen Chemie, 2nd ed.; Georg Thieme Verlag: Stuttgart, 1984.
In the IR spectrum of K[(CF3)3BC(O)NH2], two N-H
bands are found at 3707 (νas(NH)) and 3564 cm-1 (νs(NH))
Inorganic Chemistry, Vol. 45, No. 2, 2006 675

Finze et al.
676 Inorganic Chemistry, Vol. 45, No. 2, 2006

Reactions of (CF3)3BCO with Amines and Phosphines
Figure 6. 19F (black) and 19F{11B} NMR spectra (grey) of [{(CF3)3BC-
(O)}2NH]2-, [(CF3)3BC(O)NH2]-, and [(CF3)3BC(O)NHMe]- (19F{11B}
NMR spectra: 15N-labeled anions).
Figure 5. 11B NMR spectra of [{(CF3)3BC(O)}2NH]2-, [(CF3)3BC(O)NH2]-,
and [(CF3)3BC(O)NHMe]- (spectra in gray: 15N-labeled anions).
are split into distorted quartets due to the interaction with
11B. The signal of the [{(CF3)3BC(O)}2NH]2- anion is split
into a septet with an intensity distribution of 1:2:3:4:3:2:1,
in accordance with two equivalent 11B nuclei coupling to
15N.
The highly coupled 31P NMR spectrum of (CF3)3BC(O)-
PMe3 (Figure 7), consists of a quartet (2J(11B,31P) ) 44.5
Hz) of decets (2J(1H,31P) ) 14.4 Hz) of decets (4J(19F,31P)
) 4.4 Hz).
In Figure 8 the 13C NMR spectra of [(CF3)3BC-
(O)NHR]- (R ) H, Me), [(CF3)3BC(O)NMe2]-, and
[{(CF3)3BC(O)}2NH]2- and in Figure S4 in the Supporting
Information the 13C NMR spectrum of (CF3)3BC(O)PMe3
are presented. The chemical shifts of the CF3 groups are in
the typical region of similar compounds.11,14 The 13C nuclei
of the CF3 groups couple to three 19F nuclei (1J(13C,19F),
quartet), to 11B (1J(11B,13C), quartet), and to six 19F nuclei
(3J(13C,19F), septet). The resonance frequency of the carbonyl
C atom of (CF3)3BC(O)PMe3 (δ(13C) ) 229.7 ppm) is shifted
to a higher value compared to (CF3)3B derivatives with
carbamoyl ligands (δ(13C) ) ∼187 ppm). Besides the
1J(11B,13C) coupling of the signals of the carbonyl C atoms,
a series of further couplings are assigned (Table 4). For
Figure 7. 31P NMR spectra of (CF3)3BC(O)PMe3.
[(CF3)3BC(O)NHMe]- and [(CF3)3BC(O)NMe2]-, the signals
of the methyl groups are observed. The very broad signals
of the methyl groups of [(CF3)3BC(O)NMe2]- at 35.0 and
Inorganic Chemistry, Vol. 45, No. 2, 2006 677

Finze et al.
spectrum of [(CF3)3BC(O)NH2]-, only the signal at 6.1 ppm
3
shows a J coupling to 11B (4.2 Hz). Taking the results of
11B NMR spectroscopy into account, this proton is in trans
position to boron. In the case of [{(CF3)3BC(O)}2NH]2- and
[(CF3)3BC(O)NHR]- (R ) Me, nPr), the 5J(1H,19F) coupling
(0.8-1.0 Hz) was found in the 1H{11B} NMR spectra
(Lorentz-Gauss processing54,55). For (CF3)3BC(O)PMe3,
6
even the J(1H,19F) coupling (0.3 Hz) is observed. Similar
long-range, through-space couplings have been reported for
(CF3)3CC(O)NMe2.43
Summary and Conclusion
Reactions of the borane carbonyl (CF3)3BCO with selected
amines and phosphines were studied. The exclusive attack
at the carbonyl C atom is remarkable, although ligand
exchange under release of CO is thermodynamically favored,
as predicted by DFT calculations. This behavior contrasts
the reactions of HCN and nitriles with (CF3)3BCO where
only exchange products are obtained.14
Especially the syntheses of [(CF3)3BC(O)NH2]- using
either (CF3)3BCO or K[(CF3)3BC(O)F] are of interest be-
cause [(CF3)3BC(O)NH2]- salts are starting materials for
the syntheses of [(CF3)3BCN]- salts.16 Recently, the po-
tential of [(CF3)3BCN]- as a novel ligand was demonstrated
by the synthesis of (PPh3)3RhNCB(CF3)3.21 Furthermore, the
straightforward preparation of the dimeric borate anion
[{(CF3)3BC(O)}2NH]2- promises to enable its application as
a bidentate chelating ligand in transition metal chemistry.
In the crystal structure of K2[{(CF3)3BC(O)}2NH]‚2MeCN,
the chelating ability of the diborate anion is already
demonstrated.
The novel (CF3)3B compounds are extensively character-
ized by multinuclear NMR spectroscopy and by vibrational
spectroscopy, as well as their thermal properties. Noteworthy
are their well-resolved, highly coupled NMR spectra, which
are unusual for 11B NMR spectroscopy.14, 52
Acknowledgment. Financial support by the Deutsche
Forschungsgemeinschaft, DFG, is acknowledged. Further-
more, we are grateful to Merck KGaA (Darmstadt, Germany)
for providing chemicals used in this study. We thank Mr.
M. Za¨hres (University Duisburg-Essen) for performing some
NMR measurements and Mrs. R. Bru¨lls (University Duis-
burg-Essen) for the elemental analyses.
Figure 8. [{(CF3)3BC(O)}2NH]2- 13C{1H} (top, 14N) and 13C{19F} NMR
,
spectra (bottom, 14N); [(CF3)3BC(O)NH2]-, 13C{1H} (top, 14N) and
13C{19F} NMR spectra (bottom, 15N); [(CF3)3BC(O)NHMe]-, 13C{1H}
(top, 15N) and 13C{19F} NMR spectra (bottom, 14N); [(CF3)3BC(O)NMe2]-,
13C{1H} (top, 14N) and 13C{19F} NMR spectra (bottom, 14N).
Supporting Information Available: A view of the unit cell of
K2[{(CF3)3BC(O)}2NH]‚2MeCN; plots of the 15N and 1H
NMR spectra of [(CF3)3BC(O)NH2]- and [{(CF3)3BC(O)}2NH]2-
;
a figure of the 11B and 19F NMR spectra of (CF3)3BC(O)NMe3
and (CF3)3BC(O)PMe3 and a plot of the 13C NMR spectrum of
(CF3)3BC(O)PMe3; a table with the calculated energies, ZPCs and
enthalpies; a table with the experimental (K+ salt), as well as
calculated vibrational data of the [(CF3)3BC(O)NH2]- anion; and
a table with NMR spectroscopic relaxation rates and line widths.
This material is available free of charge via the Internet at
http://pubs.acs.org.
37.5 ppm, respectively, are explained by slow rotation of
the NMe2 group. In contrast, the rotation of the NHMe group
in [(CF3)3BC(O)NHMe]- and the NH2 group in [(CF3)3BC-
(O)NH2]- are frozen because neither the 13C nor the 1H NMR
spectra show any broadening for the respective signals.
The 1H chemical shifts of the carbamoyl groups (Table 4,
Figure S5) are similar to δ(1H) of related organic com-
1
pounds.53 Two different signals are found in the H NMR
IC0515305
spectrum of the [(CF3)3BC(O)NH2]- anion, due to the
(54) Ferrige, A. G.; Lindon, J. C. J. Magn. Reson. 1978, 31, 337.
(55) Lindon, J. C.; Ferrige, A. G. Prog. NMR Spectrosc. 1980, 14, 27.
1
hindered rotation of the NH2 group. In the H{14N} NMR
678 Inorganic Chemistry, Vol. 45, No. 2, 2006