3074 Organometallics, Vol. 25, No. 12, 2006
Finze et al.
used without further purification. All dry solvents were obtained
from Aldrich and transferred under an Ar atmosphere into 1 L
round-bottom flasks equipped with valves with PTFE stems (Young,
London) and charged with molecular sieves (4 Å).
Single-Crystal X-ray Diffraction. Crystals of (PPh3)3RhCNB-
(CF3)3 and (PPh3)3RhNCB(CF3)3‚1.5CH2Cl2 suitable for X-ray
diffraction were obtained by slow diffusion of pentane into
dichloromethane solutions. Diffraction data were collected at 100
K on a KappaCCD diffractometer (Bruker AXS) using Mo KR
radiation (λ ) 0.71073 Å) and either a graphite monochromator
(for the isocyanide) or a focusing graded multilayer mirror
(XENOCS). Frames were integrated using DENZO, and an empiri-
cal absorption correction (scalepack) was applied.23 Crystal struc-
tures were determined using SHELXS-97,24 and full-matrix least-
squares refinements based on F2 were performed using SHELXL-
97.25 Molecular structure diagrams were drawn using the program
Diamond.26 A summary of experimental details and crystal data is
collected in Table 5. X-ray crystallographic files in CIF format have
been deposited at the Cambridge Crystallographic Center under the
deposition numbers CCDC-252111 for (PPh3)3RhCNB(CF3)3 and
CCDC-252112 for (PPh3)3RhNCB(CF3)3‚1.5CH2Cl2. Copies 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).
Figure 6. 15N{1H} NMR spectrum of (PPh3)3Rh15NCB(CF3)3.
Hz, cis P). These values are close to those found for (PPh3)3-
Rh15NCBPh3 (Table 4).5
In the 11B and 19F NMR spectra of both Rh(I) complexes
only broad singlets are observed, due to the quadrupolar moment
of the 11B nuclei. A dynamic effect, for example ligand
exchange, as reason for the line broadening can be excluded
because (i) no significant temperature dependence of the signal
shape is observed, (ii) a similar line broadening was found for
(CF3)3BNCMe13 and (CF3)3BCNMe,22 and (iii) in the 19F{11B}
NMR spectra sharp signals are observed. The 1J(13CF3,19F) and
4J(19F,19F) coupling constants as well as the 1∆19F(12/13C)
isotopic shifts derived from 19F{11B} experiments are listed in
Table 4. There is nearly no difference in δ(11B) and only a small
change in δ(19F) between the noncoordinated borate anions and
(PPh3)3RhCNB(CF3)3 as well as (PPh3)3RhNCB(CF3)3, respec-
tively (Table 4).
Raman Spectroscopy. 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 (DPY 301 II-N-OEM-500, Coherent,
Lu¨beck, Germany).
UV Spectroscopy. The solids were dissolved in dry dichlo-
romethane and transferred into a glass cell (d ) 5 cm, V ) 20 mL)
equipped with quartz windows (Suprasil, Heraeus, Hanau) and a
valve with a PTFE stem (Young, London). The UV spectra were
recorded on a Perkin-Elmer Lambda 900 spectrometer in the range
200-700 nm.
Summary and Conclusion
1
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
The first examples of transition metal complexes of
[(CF3)3BCN]- and [(CF3)3BNC]- derived from reactions of
(PPh3)3RhCl with the potassium borates are presented. Their
high thermal stabilities make them promising candidates for
further chemistry and give a first insight into the application
potential of [(CF3)3BCN]- and [(CF3)3BNC]- in coordination
chemistry. The complexes are investigated by Raman, UV, and
NMR spectroscopy, and their structures were determined by
single-crystal X-ray diffraction.
A comparison of the CN stretching band positions and the
structural parameters of (PPh3)3RhCNB(CF3)3 and (PPh3)3-
RhNCB(CF3)3 with those of (PPh3)3RhCNBPh3 and (PPh3)3-
RhNCBPh35,8 indicate that the tris(trifluoromethyl)borate ligands
have a stronger trans effect and are stronger π-acceptors/weaker
σ-donors. This trend is related to the higher Lewis acidity of
(CF3)3B in comparison with Ph3B, in agreement with the data
of [(PPh3)3RhNCMe]+,9,10 having the even stronger Lewis acid
Me+.
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 to TMS (0.03% v/v) and CFCl3 (0.1% v/v) as
internal standards and 15% (v/v) BF3‚OEt2 in CD3CN, 85% (v/v)
H3PO4 in H2O, and 10% (v/v) MeNO2 in CD3CN as external
standards. Concentrations of the investigated samples were in the
range 0.1-1 mol L-1. The samples for NMR spectroscopic studies
were prepared in 5 mm NMR tubes, equipped with special valves
with PTFE stems (Young, London),27 and dry CD2Cl2 was used as
solvent. 31P NMR spectra of (PPh3)3RhC14NB(CF3)3 and (PPh3)3-
RhC15NB(CF3)3 were simulated using the program gNMR.21
DSC Measurements. Thermoanalytical measurements were
made with a Netzsch DSC204 instrument. Temperature and
sensitivity calibrations in the temperature range 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
Experimental Section
temperature range 20-600 °C with a heating rate of 5 K min-1
;
General Considerations. Apparatus. The reactions involving
air-sensitive compounds were performed under an 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.
throughout this process the furnace was flushed with dry nitrogen.
For the evaluation of the output, the Netzsch Protens4.0 software
was employed.
(23) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307.
(24) Sheldrick, G. M. SHELXS-97, Program for Crystal Structure
Solution; University of Go¨ttingen: Germany, 1997.
K[(CF3)3BNC] and K[(CF3)3BCN] were synthesized as described
previously.11 (PPh3)3RhCl was obtained from Strem Chemicals and
(25) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure
Refinement; University of Go¨ttingen: Germany, 1997.
(26) Diamond-Visual Crystal Structure Information System, Ver. 2.1;
Crystal Impact GbR, 1996-1999.
(22) Finze, M.; Bernhardt, E.; Willner, H.; Lehmann, C. W. Inorg. Chem.
2006, 45, 669.
(27) Gombler, W.; Willner, H. Int. Lab. 1984, 84.