Carbon-carbon bond formation in the reductive coupling of trifluoroacetonitrile and pentafluorobenzonitrile - Synthetic routes to new perfluoroalkyl- and perfluoroaryl-substituted α-diimines: Versatile synthons for heterocycle synthesis

Article abstract of DOI:10.1016/j.ica.2004.09.002

Reductive coupling of perfluoroalkyl- and perfluoroaryl-nitriles with [(η⁵-C₅H₅)₂TiCl]₂ provides the corresponding μ-diiminatodititanium complexes. Protonolysis of the Ti-N bonds with ethereal HCl lib

Full text of DOI:10.1016/j.ica.2004.09.002

0
Inorganica Chimica Acta 357 (2004) 3902–3910
www.elsevier.com/locate/ica
Carbon–carbon bond formation in the reductive coupling of
trifluoroacetonitrile and pentafluorobenzonitrile – synthetic routes
to new perfluoroalkyl- and perfluoroaryl-substituted
a-diimines: versatile synthons for heterocycle synthesis
a,
a
a
b
Bruce N. Diel *, Peter J. Deardorff , Catherine M. Zelenski , Christopher Incarvito ,
b
Louise Liable-Sands , Arnold M. Rheingold
b
a
Chemical Sciences Division, Midwest Research Institute, 425 Volker Boulevard, Kansas City, MO 64110, USA
b
Department of Chemistry and Biochemistry, Crystallography Laboratory, University of Delaware, Newark, DE 19716, USA
Received 26 March 2004; accepted 7 September 2004
Available online 8 October 2004
Dedicated to Professor Tobin J. Marks on the occasion of his 60th birthday
Abstract
Reductive coupling of perfluoroalkyl- and perfluoroaryl-nitriles with [(g5-C5H5)2TiCl]2 provides the corresponding l-diiminato-
dititanium complexes. Protonolysis of the Ti–N bonds with ethereal HCl liberates the corresponding perfluoroalkyl- and perfluor-
1
oaryl-substituted a-diimines, two of which have been fully characterized by IR, H and 13C NMR, and X-ray crystallography.
ꢀ 2004 Elsevier B.V. All rights reserved.
1
1. Introduction
ported on the utilization of selected a-diimines
(R0 = –SiMe3) in dehalosilylation/ring-closure reactions
with SbCl3 or BiCl3, to provide the first examples of
Over the last two decades there have been many
significant developments in the applications of coordina-
tion complexes containing 1,4-diaza-1,3-butadiene (a-
diimine) ligands. Some of the most exciting recent
reports center on the utilization of such complexes as
luminescence labels for detection and photochemical
cleavage of DNA [1]. In addition, these ligand systems
have been examined extensively and more generally over
the last two decades for their variety of coordination
modes and reactivity of their coordination complexes
[2], as well as the applications of such complexes in or-
ganic synthesis and catalysis [3]. We have recently re-
2
Sb- and Bi-containing 1,3,2-diazaheteroles [4].
R
N
R'
R'
N
R
One of the most appealing attributes of the a-diimines,
which plays a significant role in the physical and chemical
1
Phenanthrenequinone-(9,10)-bis(trimethylsilyl)diimine and N,N0-
bis(trimethylsilyl)-1,2-diphenylethanediimine.
2
The general synthetic approach to and numbering sequence for
the 1,3,2-diazaheteroles is as shown below:
R
E
2
N1 3N
N
SiMe3
*
E
+
4
5
Me3Si
N
Corresponding author. Tel.: +1 8163605369; fax: +1 8167535359.
E-mail address: bdiel@mriresearch.org (B.N. Diel).
- 2 XSiMe3
X
X
R
R
R
0020-1693/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2004.09.002

B.N. Diel et al. / Inorganica Chimica Acta 357 (2004) 3902–3910
3903
properties of the resultant coordination compounds [1–
3], is their strong p-acceptor ability as a result of the ener-
getically low-lying LUMO [5]. We have recently reported
on the synthesis of the first examples of 2,3-perflu-
oroalkyl- or perfluoroaryl-substituted 1,4-diazabutadie-
nes [6]. Such systems can be expected to possess even
lower-lying LUMOs and, consequently, be even stronger
p-acceptor ligands. Additionally, these compounds have
proven to be very useful in the preparation of 1,3,2-dia-
zaheteroles containing elements from Groups 13 (Ga,
In), 15 (As, Sb, Bi) and 16 (Se, Te) [7]. However, for the
preparation of volatile Main Group element- or transi-
tion metal-containing compounds which might be appli-
cable to thin film deposition by CVD, the use of
Si-containing starting materials could result in unaccept-
able levels of Si-containing impurities in the CVD source
compounds, and deleterious Si-incorporation into the
resulting thin films. For these reasons we sought a
synthetic route to 2,3-perfluoroalkyl- or perfluoroaryl-
substituted 1,4-diazabutadienes that did not involve
Si-containing starting materials.
synthetic methods. We report herein, the reductive cou-
pling of trifluoroacetonitrile and pentafluorobenzonitrile,
to yield the corresponding l-diimino titanium dimers (1,
2). Treatment of these l-diimino titanium dimers with
ethereal HCl liberates the free diimines, 1,1,1,4,4,4-hexa-
fluoro-2,3-butanediimine 3, and 1,2-di(pentafluorophe-
nyl)-ethanediimine 4, respectively (Scheme 1). Both
diimines, along with their recently reported N,N0-bis(tri-
methylsilyl)-substituted analogues represent the first
examples of perfluoroalkyl- or perfluoroaryl-substituted
a-diimines. These diimines are very stable compounds,
isolable in good-to-high yields, and have been fully char-
acterized by 1H NMR, 13C NMR, IR and X-ray structure
determinations. As an added benefit of this synthetic ap-
proach, the (g5-C5H5)2TiCl2 produced from the HCl/
Et2O reaction can be recovered and recycled with good
efficiency, making this a very attractive synthetic route
to these novel ligand systems and versatile synthons for
heterocycle synthesis.
Finally, we describe an example of the utilization of
one of these a-diimines (3) in the synthesis of 1-dimethy-
lamido-4,5-bis(trifluoromethyl)-1,3,2-diazastibole 5.
Organotransition metal-based reactions forming car-
bon–carbon bonds, and the efficacy of metal-coordina-
tion for stabilization of reactive ligands are among the
most fundamental organic chemical transformations
mediated by transition metal complexes [8,9]. To date,
reductive coupling reactions and insertion reactions are
successfully used with most transition metals, to con-
struct C–C bonds via either stoichiometric or catalytic
processes [9]. The reductive coupling of nitriles, as a syn-
thetic approach to otherwise unknown a-diimines,
embodies both themes of carbon–carbon bond formation
and stabilization of reactive ligands. There are several re-
ported examples of the use of transition metals to effect
either two-electron [10–14] (producing a diiminato lig-
and) or four-electron [15,16] (producing an enediimido
ligand) reductive coupling of nitriles. Of these previous
reports, the two-electron reductive coupling reactions
involving Ti and Zr appeared most promising as general
2. Experimental
All manipulations were performed under an inert
atmosphere (purified argon) by using standard Schlenk
and cannula techniques or a glove-box. Solvents were
purified using standard techniques. The [(g5-C5H5)2-
TiCl]2 was prepared by reduction of [(g5-C5H5)2TiCl2]
with Li3N [17]. Dimethylaminodichlorostibine, Me2-
NSbCl2, was prepared via the exchange reaction of
SbCl3 and Sb(NMe2)3 (2:1 molar ratio) [18]. Trifluoro-
acetonitrile (Oakwood Research Chemicals), penta-
fluorobenzonitrile (Lancaster), and 1-methylpyrrolidine
(Aldrich) were used as received. NMR spectra were re-
corded at 300 K with a Varian VXR300 spectrometer
operating at 300 MHz for 1H; TMS was used as internal
R CN
( R = -CF3, -C6F5 )
Cl
Cl
Cl
N
Ti
Ti
2
Ti
< -78˚C
C
R
Warm to RT
LiN3
Cl
N
Ti
H N
R
R
R
HCl/Et2O
+
2 Cp2TiCl2
R
N H
N
Ti
Cl
R = -CF3, -C6F5
Scheme 1.

3904
B.N. Diel et al. / Inorganica Chimica Acta 357 (2004) 3902–3910
reference. Melting points were obtained with a TA
Instruments DSC 910S Differential Scanning Calorime-
ter, which was calibrated using an elemental In stand-
ard. Mass spectral data were collected on a Fisons
MD-800 quadrupole mass spectrometer using full scan
analysis. Schwartzkopf Microanalytical Laboratories,
Inc., Woodside, NY, performed the elemental analyses.
C34H20N2F10Cl2Ti2: C, 50.22; H, 2.48; N, 3.44. Found:
C, 50.43; H, 2.61; N, 3.32%.
2.3. Synthesis of 1,1,1,4,4,4-hexafluoro-2,3-butanediimine
(3)
In a 1.0 L two-necked reaction flask with stopcock,
fitted with an overhead stirrer and vented addition fun-
nel, 150.0 g (243 mmol) of [l-[1,1,1,4,4,4-hexafluoro-2,
3-butanediiminato(2-)-N:N0]]tetrakis(g5–2,4-cyclopenta-
dien-1-yl)dichlorodititanium (1) was suspended in
approximately 500 mL anhydrous diethyl ether. Ethe-
real HCl (HCl/diethyl ether, 1.0 M, 510 mL/510 mmol)
was added to the vented addition funnel. The reaction
mixture was cooled to approximately ꢀ78 ꢁC (dry ice/
isopropanol bath), and the ethereal HCl was added
dropwise over approximately 1 h. The reaction mixture
was allowed to warm slowly to approximately 0 ꢁC (ice/
water bath), and the mixture stirred at this temperature
for an additional 1–3 h. Upon completion of reaction,
the volatile components were vacuum transferred into
a separate 1.0 L flask, leaving behind (g5-C5H5)2TiCl2,
which can be recycled back to [(g5-C5H5)2TiCl]2 {over-
all 75% yield of [(g5-C5H5)2TiCl]2} for re-use. The vola-
tile components are then atmospherically distilled to
yield first, the solvent (ether), and then the product
2.1. Synthesis of [l-[1,1,1,4,4,4-hexafluoro-2,3-butane-
diiminato(2-)-N:N0]]tetrakis(g5–2,4-cyclopentadien-1-
yl)dichlorodititanium (1)
In the glove box, 64.1 g (150 mmol) of [(g5-
C5H5)2TiCl]2 was weighed into a two-necked 1.0 L reac-
tion flask w/stopcock. The flask was brought out of the
glove box, attached to the Schlenk line, and approxi-
mately 500 mL of anhydrous toluene added via cannula.
The flask was freeze-thaw degassed and 30.88 g (325
mmol) trifluoroacetonitrile, CF3CN, condensed into
the flask at liquid nitrogen temperature (ꢀ196 ꢁC).
The reaction mixture was allowed to warm to approxi-
mately ꢀ78 ꢁC (dry ice/isopropanol bath), and stirred
at this temperature for approximately 4–8 h, after which
time it was allowed to warm to room temperature. After
stirring at room temperature for approximately 12–20 h,
the mixture was filtered, and the bright yellow precipi-
tate washed with anhydrous pentane until the washings
were clear and colorless. The yellow microcrystalline
solid was dried in vacuo to yield 87.9 g (95%) of [l-[1,
1,1,4,4,4-hexafluoro-2,3-butanediiminato(2-)-N:0]]tetra-
kis(g5-2,4-cyclopentadien-1-yl)dichlorodititanium (1).
Elemental Anal. Calc. for C24H20N2F6Cl2Ti2: C, 46.71;
H, 3.27; N, 4.54. Found: C, 46.85; H, 3.55; N, 4.39%.
1,1,1,4,4,4-hexafluoro-2,3-butanediimine
(2),
H–
N@C(CF3)–(CF3)C@N–H [35.5 g, 185 mmol (76%)];
b.p. = 80–81 ꢁC, m.p. = 52.9 ꢁC. Elemental Anal. Calc.
for C4H2N2F6: C, 25.01; H, 1.05; N, 14.59; F, 59.35.
Found: C, 25.03; H, 1.12; N, 14.53; F, 59.28%. 13C[1H]
NMR (d; CD2Cl2) 158.7 ppm (>C@N–; q, J2 = 33.47
1
Hz), 117.6 ppm (–CF3, q, J1 = 282.1 Hz). H NMR (d;
CD2Cl2) 12.07 ppm (–NH). Infrared mC@N = 1718 cmꢀ1
.
2.2. Synthesis of tetrakis(g5–2,4-cyclopentadien-1-yl) [l-
[1,2-di(pentafluorophenyl)ethanediiminato(2-)-N:N0]]
dichlorodititanium (2)
2.4. Synthesis of 1,2-di(pentafluorophenyl)-ethanediimine
(4)
In the glove box, 21.35 g (50 mmol) of [(g5-
C5H5)2TiCl]2 was weighed into a two-necked 500 mL
reaction flask w/stopcock. The flask was brought out of
the glove box, attached to the Schlenk line, and approxi-
mately 200 mL of anhydrous toluene added via cannula.
The reaction mixture was cooled to approximately ꢀ78
ꢁC (dry ice/isopropanol bath), and 13.6 mL (21.3 g, 110
mmol) pentafluorobenzonitrile was added dropwise, via
syringe. The reaction mixture was stirred at this temper-
ature for approximately 4–8 h, after which time it was al-
lowed to warm to room temperature. After stirring at
room temperature for approximately 12–20 h, the mix-
ture was filtered, and the red-orange precipitate washed
with anhydrous pentane until the washings were clear
and colorless. The red-orange solid was dried in vacuo
to yield 30.5 g (75%) of tetrakis(g5–2,4-cyclopentadien-
1-yl) [l-[1,2-di(pentafluorophenyl)ethanediiminato(2-)-
N:N0]] dichlorodititanium (3). Elemental Anal. Calc. for
In a 500 mL two-necked reaction flask with stopcock,
fitted with an overhead stirrer and vented addition
funnel, 50.0 g (61.5 mmol) of tetrakis(g5–2,4-cyclopen-
tadien-1-yl) [l-[1,2-di(pentafluorophenyl)ethanediimi-
nato(2-)-N:N0] dichlorodititanium (2) was suspended in
approximately 200 mL anhydrous diethyl ether. Ethe-
real HCl (HCl/diethyl ether, 1.0 M, 130 mL/130 mmol)
was added to the vented addition funnel. The reaction
mixture was cooled to approximately ꢀ78 ꢁC (dry ice/
isopropanol bath), and the ethereal HCl was added
dropwise over approximately 1 h. The reaction mixture
was allowed to warm slowly to approximately 0 ꢁC (ice/
water bath), and the mixture stirred at this temperature
for an additional 1–3 h. Upon completion of reaction,
the reaction mixture was filtered through a fritted funnel
and the precipitate [(g5-C5H5)2TiCl2] was washed with
2 · 50 mL ether. The solvent was removed in vacuo,
and the residue was re-dissolved in approximately 100

B.N. Diel et al. / Inorganica Chimica Acta 357 (2004) 3902–3910
3905
1
mL anhydrous CH2Cl2, and filtered again to remove
insoluble materials. The CH2Cl2 solution was cooled
overnight at approximately ꢀ70 to ꢀ80 ꢁC (dry ice/iso-
propanol), and then filtered cold to yield the orange
crystalline product 1,2-di(pentafluorophenyl)-ethanedii-
mine (4), H–N@C(C6F5)–(C6F5)C@N–H [15.5 g, 40
mmol (65%)]. Elemental Anal. Calc. for C14H2N2F10:
C, 43.32; H, 0.52; N, 7.22; F, 48.94. Found: C, 43.43;
H, 0.61; N, 7.32; F, 48.81%. 13C[1H] NMR (d; CD2Cl2)
158.2 ppm (>C@N–; t, J3 = 13.3 Hz), 112.4 ppm (i, t,
J2 = 23.6 Hz), 138.4 ppm (dt, J1 = 253.3 Hz), 142.7
(dm, J1 = 254.1 Hz), 144.5 ppm (dd, J1 = 248.9 Hz).
1H NMR (d; CD2Cl2) 12.42 ppm (–NH). Infrared
34.54 ppm (–CH3, s). H NMR (d; CD2Cl2) 2.49 ppm
(–CH3, s).
2.7. X-ray crystallography
Table 1 lists the crystallographic data for compounds 3
and 4 [19]. ORTEP diagrams showing the solid-state
structures and atom-numbering schemes are given in
Figs. 1 and 2; selected bond lengths and bond angles
are presented in the figure captions. The sample of 3 con-
sisted of colorless blocks measuring ca. 0.45 mm along the
thin dimension and 0.6 mm along the other two dimen-
sions. A single crystal whose visual appearance was sim-
ilar to the bulk sample measuring 0.45 · 0.5 · 0.6 mm,
was selected and mounted in n-paraffin oil on the tip of
a glass fiber and placed in a cold stream of nitrogen on
the diffractometer. The crystals sublime readily at room
temperature and thus had to be mounted at low temper-
ature, achieved by cooling the oil and sample with dry ice.
No evidence of symmetry higher than monoclinic was ob-
served. The systematic absences in the diffraction data
were consistent with the space group P21/c which yielded
chemically reasonable and computationally stable results
of refinement. The structure was initially phased by direct
methods and completed by normal difference Fourier
techniques. Full-matrix least-squares refinement was
based on F2. All non-hydrogen atoms were refined with
anisotropic displacement coefficients. The hydrogen
atoms on the imine-nitrogens could not be located from
the difference map and were ignored. The final residual,
based on 4rF data, was 5.62%.
m
C@N = 1657 cmꢀ1
.
2.5. Recovery and recycle of [(g5-C5H5)2TiCl2]
From the original 64.1 g (150 mmol) of [(g5-
C5H5)2TiCl]2 used in the preparation of 1, after the
HCl/Et2O cleavage of 3 and removal by distillation,
the remaining finely divided bright red solids were
washed, on a coarse frit, (3 · 75 mL) with cold Et2O,
and dried in vacuo, to yield 31.82 g (127.8 mmol,
85.2%) of [(g5-C5H5)2TiCl2] (ꢁ98% pure, by 1H
NMR). This [(g5-C5H5)2TiCl2] was reduced with Li3N
according to the method reported by Kilner et al. [17],
to produce 48.04 g of [(g5-C5H5)2TiCl]2 (112.5 mmol,
88%).
2.6. Synthesis of 1-Dimethylamido-4,5-bis(trifluoro-
methyl)-1,3,2-diazastibole (5)
The sample of 4 consisted of crystalline yellow blades
measuring ca. 0.1 mm along the thin dimension and 0.2–
0.5 mm along the other two dimensions. Many of the
crystals were striated, and likely twinned, fused blades
but a single crystal was selected whose visual appearance
was otherwise similar to the bulk sample; it measured
0.1 · 0.1 · 0.4 mm. The crystal was mounted in a nitro-
gen flushed thin-walled capillary and placed in a cold
stream of nitrogen on the diffractometer. No evidence
of symmetry higher than triclinic was observed in the
diffraction data. E-statistics suggested the centro-sym-
To a solution of 2 (2.95 g, 15.34 mmol) and 2.61 g
(3.19 mL, 30.7 mmol) 1-methylpyrrolidine, in 100 mL
anhydrous diethyl ether at 0 ꢁC was added slowly, via
a solids addition tube, 3.63 g (15.3 mmol) Me2NSbCl2.
The Me2NSbCl2 was slow to dissolve in the initially col-
orless solution. As dissolution ensued, an orange color-
ation developed simultaneously; orange-yellow solids
precipitated subsequently. After stirring for approxi-
mately 4 h at 0 ꢁC, the orange solids were separated
by filtration on a coarse frit, and washed (3 · 25 mL)
3
ꢀ
with cold diethyl ether . Subsequently, the 2-dimethyl-
metric space group option, P1. The structure was ini-
amino-4,5-bis(trifluoromethyl)-1,3,2-diazastibole 5 (cf.
[4]) is recrystallized from hot THF; yield 4.14 g (11.63
mmol, 76%). Elemental Anal. Calc. for C6H6N3F6Sb:
C, 20.25; H, 1.70; N, 11.81; F, 32.03; Sb, 34.21. Found:
C, 20.41; H, 1.80; N, 11.62; F, 32.21; Sb, 34.45%.
13C[1H] NMR (d; CD2Cl2) 153.1 ppm (>C@N–; q,
J2 = 35.9 Hz), 123.1 ppm (–CF3, q, J1 = 282.1 Hz),
tially phased by direct methods and completed by
normal difference Fourier techniques. Full-matrix
least-squares refinement was based on F2. All non-hy-
drogen atoms were refined with anisotropic displace-
ment coefficients. Hydrogen atoms were treated as
idealized contributions. The final residual, based 4rF
data, was 7.53% (see Tables 2 and 3).
3
Heating of the reaction mixture can result in significant conver-
3. Results and discussion
sion of the desired 2-dimethylamido-4,5-bis(trifluoromethyl)-1,3,2-
diazastibole (5) to the corresponding 2-chloro-4,5-bis(trifluoro-
methyl)-1,3,2-diazastibole, presumably via protonolysis (HCl) of the
Sb–N(Me)2 bond.
We have recently described the synthesis and
structural characterization of the first examples of

3906
B.N. Diel et al. / Inorganica Chimica Acta 357 (2004) 3902–3910
Table 1
Crystallographic data collection parameters for 1,1,1,4,4,4-hexafluoro-2,3-butanediimine, H–N@C(CF3)–(CF3)C@N–H (3) and 1,2-di(pentafluor-
ophenyl)-ethanediimine, H–N@C(C6F5)–(C6F5)C@N–H (4)
3
4
Molecular formula
Formula weight
Temperature (K)
C4H2N2F6
192.08
273(2)
C14H2N2F10
388.18
203(2)
˚
Wavelength (A)
0.71073
monoclinic
P21/c
0.71073
triclinic
Crystal system
Space group
Unit cell dimensions
ꢀ
P1
˚
a (A)
8.2752(2)
9.1660(3)
9.1194(2)
9.2321(2)
˚
b (A)
˚
c (A)
8.8411(3)
90
13.2012(2)
99.8845(7)
a (ꢁ)
b (ꢁ)
c (ꢁ)
93.2369(6)
90
669.54(2)
106.7253(5)
107.6820(9)
972.39(4)
3
˚
V (A )
Z
4
1.906
3
1.989
Dcalc (gm/cmꢀ3
)
Absorption coefficient (mmꢀ1
F(000)
)
0.236
376
0.221
570
Crystal dimensions (mm)
Crystal color
0.60 · 0.50 · 0.45
colorless block
2.47–23.99
0.40 · 0.10 · 0.10
yellow blade
1.68–24.99
h Range for data collection (ꢁ)
Limiting indices
Reflections collected
ꢀ9 6 h 6 8, ꢀ10 6 k 610, ꢀ9 6 l 6 10
2877
1028 (0.0330)
ꢀ10 6 h 6 10, ꢀ10 6 k 6 10, ꢀ15 6 l 6 15
5761
3217 (0.0476)
Independent reflections (Rint
Absorption correction
Refinement method
)
none
none
full-matrix least-squares on F2
1028/0/109
1.906
full-matrix least-squares on F2
3217/0/352
1.733
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
R indices (all data)
R1 = 0.0562, wR2 = 0.2023
R1 = 0.0593, wR2 = 0.2098
0.755 and ꢀ0.261
R1 = 0.0753, wR2 = 0.1921
R1 = 0.1013, wR2 = 0.2131
0.384 and ꢀ0.650
ꢀ3
˚
Largest difference peak and hole (e A
)
Fig. 1. Molecular structure of 1,1,1,4,4,4-hexafluoro-2,3-butanediimine, H–N@C(CF3)–(CF3)C@N–H (3), with 30% thermal ellipsoids, showing the
atomic numbering scheme.
1,3,2-diazastibole and 1,3,2-diazabismole ring com-
pounds, prepared via the dehalosilylation/ring closure
reactions between N,N0-bis(trimethylsilyl)-a-diimines
and either SbCl3 or BiCl3 [4]. To expand the range
of diazaheteroles available and to explore the physico-
chemical properties and applications of these novel
heterocycles further, we have recently developed syn-
theses of the first 2,3-perfluoroalkyl- and 2,3-perfluor-
oaryl-substituted 1,4-diazabutadienes [6]. For certain
applications, or in those instances where dehalosilyla-

B.N. Diel et al. / Inorganica Chimica Acta 357 (2004) 3902–3910
3907
Fig. 2. Molecular structure of 1,2-di(pentafluorophenyl)-ethanediimine, H–N@C(C6F5)–(C6F5)C@N–H (4), with 30% thermal ellipsoids, showing
the atomic numbering scheme.
Table 2
Our first attempts at removal of the diimine ligands
focused on metathesis of 1 (60 ꢁC, various solvents)
with, e.g., SbCl3, to yield [(g1-C5H5)2TiCl2] and the de-
sired 2-chloro-1,3,2-diazastibole [4], analogous to previ-
ously reported titanacyclopentadiene metathesis
reactions [20]. However, the reactions were unsuccessful,
˚
Bond lengths (A) and angles (ꢁ) for 1,1,1,4,4,4-hexafluoro-2,3-butane-
diimine, H–N@C(CF3)–(CF3)C@N–H (3)
F(1A)–C(1A)
F(3A)–C(1A)
C(1A)–C(2A)
F(1B)–C(1B)
F(3B)–C(1B)
C(1B)–C(2B)
1.328(3) F(2A)–C(1A)
1.339(3) N(1A)–C(2A)
1.527(4) C(2A)–C(2A)#1
1.340(3) F(2B)–C(1B)
1.340(3) N(1B)–C(2B)
1.539(3) C(2B)–C(2B)#2
1.342(4)
1.271(3)
1.506(5)
1.352(3)
1.267(3)
1.498(5)
5
6
yielding CF3CN , multiple Cp-containing products ,
and no solution-phase products with 13C NMR reso-
nances attributable to either the –CF3 or the imine
(>C@N–) carbons. Reaction of 1 with Me3SiBr was sim-
ilarly unsuccessful, yielding CF3CN, multiple Cp-con-
taining products, no products with 13C NMR
resonances attributable to either the –CF3 or the imine
F(1A)–C(1A)–F(3A)
F(3A)–C(1A)–F(2A)
F(3A)–C(1A)–C(2A)
107.7(2) F(1A)–C(1A)–F(2A)
106.7(2) F(1A)–C(1A)–C(2A)
111.0(2) F(2A)–C(1A)–C(2A)
108.0(2)
111.2(2)
112.1(2)
122.5(2)
107.4(2)
107.6(2)
112.1(2)
N(1A)–C(2A)–C(2A)#1 121.1(3) N(1A)–C(2A)–C(1A)
C(2A)#1–C(2A)–C(1A) 116.3(2) F(1B)–C(1B)–F(3B)
F(1B)–C(1B)–F(2B)
F(1B)–C(1B)–C(2B)
F(2B)–C(1B)–C(2B)
N(1B)–C(2B)–C(1B)
107.3(2) F(3B)–C(1B)–F(2B)
110.5(2) F(3B)–C(1B)–C(2B)
7
carbon, and Me3SiF . The products of the control reac-
tion (1, benzene-d6, 60 ꢁC) also consisted of CF3CN,
multiple Cp-containing products, and no other products
with 13C NMR resonances attributable to either the –
CF3 or the imine carbon. Although the reactions de-
scribed were not fruitful for the removal/transfer of
the ligand, they were informative with regard to the
apparent oxidative decoupling 8 of the l-diimine ligand.
The reversible nature of this nitrile reductive-
111.7(2) N(1B)–C(2B)–C(2B)#2 121.7(3)
122.0(2) C(2B)#2–C(2B)–C(1B) 116.2(2)
tion/ring-closure reactions would not work, an alterna-
tive synthesis of these same perfluoroalkyl- and per-
fluoroaryl-substituted which
Si-containing starting materials, was necessary.
The organotitanium(III)-mediated reductive coupling
of trifluoroacetonitrile and pentafluorobenzonitrile
provides convenient synthetic access to the novel perflu-
oroalkyl- and perfluoroaryl-substituted diazabutadie-
nes, 2 and 4. Teuben and De Boer first reported the
use of the one-electron (per Ti) reductant, [(g1-
C5H5)2TiCl]2, for the reductive coupling of acetonitrile,
a-diimines,
avoids
5
The metathesis reactions with SbCl3, SbBr3, Me3SiBr (and control
reactions) were conducted in screw-cap (w/septum) NMR tubes to
enable GC/MS analysis of the head-space gas(es) after reaction. Mass
spectral data were collected on a Fisons MD-800 quadrupole mass
spectrometer using full scan analysis.
6
One of these is tentatively assigned as titanocene dichloride [(g1-
4
2,2-dimethylpropionitrile and benzonitrile . In these
C5H5)2TiCl2], the others are not yet assigned.
7
Within the limits of the experiment, all of the starting Me3SiBr
previous reports, the electron-transfer/reductive-cou-
pling step requires forcing conditions (e.g., several
hours, to days, at toluene reflux). In contrast, with the
perfluorinated nitriles described herein, the reductive
coupling occurs rapidly (2–4 h), even at ꢀ78 ꢁC. The
l-diimino-titanium dimers that result are only margin-
ally soluble and attempts to obtain X-ray quality crys-
tals to structurally characterize the intact bridged
dimer have not been successful.
was converted to Me3SiF. This reaction is currently under study to
determine the mechanism for the apparent C–F activation and F-atom
transfer. There is a precedent for Lewis acidic metal-induced [e.g.,
Ti(IV)] C–F activation. see for example: (a) Suzuki, K. Pure & Appl.
Chem. 1994, 66, 1557; (b) Kiplinger, J.L.; Richmond, T.G.; Osterberg,
C.E. Chem. Rev. 1994, 94, 373.
8
This terminology requires that we assume a formal ligand
[
(ꢀ)N@C(CF3)–(CF3)C@N(ꢀ)] charge of (ꢀ2) and assign a correspond-
ing formal oxidation state of +4 for each Ti, to maintain electroneu-
trality. Although we have not yet identified any reduced titanium
species as products of this reaction, since we constructed this ligand via
a reductive coupling (Scheme 1), we refer to the reverse as an oxidative
decoupling.
4
For example, reductive coupling of acetonitrile at [(g5-
C5H5)2TiCl]2 requires refluxing in toluene for 3–4 days.

3908
B.N. Diel et al. / Inorganica Chimica Acta 357 (2004) 3902–3910
Table 3
˚
Bond lengths (A) and angles (ꢁ) for 1,2-di(pentafluorophenyl)-ethanediimine, H–N@C(C6F5)–(C6F5)C@N–H (4)
F(1A)–C(1A)
F(3A)–C(3A)
F(5A)–C(5A)
F(10A)–C(10A)
F(12A)–C(12A)
N(1A)–C(7A)
C(1A)–C(2A)
C(2A)–C(3A)
C(4A)–C(5A)
C(6A)–C(7A)
C(8A)–C(14A)
C(9A)–C(14A)
C(11A)–C(12A)
C(13A)–C(14A)
F(2B)–C(2B)
F(4B)–C(4B)
N(1B)–C(7B)
C(1B)–C(6B)
C(3B)–C(4B)
C(5B)–C(6B)
C(7B)–C(7B)#1
1.355(5)
1.329(5)
1.336(5)
1.345(5)
1.336(6)
1.200(6)
1.357(6)
1.374(6)
1.364(6)
1.488(6)
1.486(6)
1.396(6)
1.379(8)
1.385(7)
1.339(5)
1.337(6)
1.202(6)
1.385(7)
1.383(7)
1.379(7)
1.536(9)
F(2A)–C(2A)
F(4A)–C(4A)
F(9A)–C(9A)
F(11A)–C(11A)
F(13A)–C(13A)
N(2A)–C(8A)
C(1A)–C(6A)
C(3A)–C(4A)
C(5A)–C(6A)
C(7A)–C(8A)
C(9A)–C(10A)
C(10A)–C(11A)
C(12A)–C(13A)
F(1B)–C(1B)
F(3B)–C(3B)
F(5B)–C(5B)
C(1B)–C(2B)
C(2B)–C(3B)
C(4B)–C(5B)
C(6B)–C(7B)
1.348(5)
1.338(5)
1.325(5)
1.345(6)
1.323(5)
1.176(6)
1.376(6)
1.370(6)
1.396(6)
1.540(6)
1.359(7)
1.359(7)
1.375(7)
1.350(6)
1.325(5)
1.329(5)
1.360(7)
1.373(7)
1.373(7)
1.502(7)
F(1A)–C(1A)–C(2A)
C(2A)–C(1A)–C(6A)
F(2A)–C(2A)–C(3A)
F(3A)–C(3A)–C(4A)
C(4A)–C(3A)–C(2A)
F(4A)–C(4A)–C(3A)
F(5A)–C(5A)–C(4A)
C(4A)–C(5A)–C(6A)
C(1A)–C(6A)–C(7A)
N(1A)–C(7A)–C(6A)
C(6A)–C(7A)–C(8A)
N(2A)–C(8A)–C(7A)
F(9A)–C(9A)–C(10A)
C(10A)–C(9A)–C(14A)
F(10A)–C(10A)–C(11A)
F(11A)–C(11A)–C(10A)
C(10A)–C(11A)–C(12A)
F(12A)–C(12A)–C(11A)
F(13A)–C(13A)–C(12A)
C(12A)–C(13A)–C(14A)
C(13A)–C(14A)–C(8A)
F(1B)–C(1B)–C(2B)
C(2B)–C(1B)–C(6B)
F(2B)–C(2B)–C(3B)
F(3B)–C(3B)–C(2B)
C(2B)–C(3B)–C(4B)
F(4B)–C(4B)–C(3B)
F(5B)–C(5B)–C(4B)
C(4B)–C(5B)–C(6B)
C(5B)–C(6B)–C(7B)
N(1B)–C(7B)–C(6B)
C(6B)–C(7B)–C(7B)#1
118.1(4)
123.1(4)
119.7(4)
120.2(4)
119.8(4)
119.8(4)
118.0(4)
121.8(4)
121.9(4)
123.6(4)
116.6(4)
117.9(4)
118.2(4)
121.9(4)
120.1(4)
120.5(5)
120.3(5)
120.2(5)
119.1(5)
121.2(5)
122.2(4)
117.3(4)
123.1(5)
118.9(4)
121.4(5)
119.0(4)
119.1(5)
118.5(4)
121.4(4)
123.9(4)
123.9(4)
116.3(5)
F(1A)–C(1A)–C(6A)
F(2A)–C(2A)–C(1A)
C(1A)–C(2A)–C(3A)
F(3A)–C(3A)–C(2A)
F(4A)–C(4A)–C(5A)
C(5A)–C(4A)–C(3A)
F(5A)–C(5A)–C(6A)
C(1A)–C(6A)–C(5A)
C(5A)–C(6A)–C(7A)
N(1A)–C(7A)–C(8A)
N(2A)–C(8A)–C(14A)
C(14A)–C(8A)–C(7A)
F(9A)–C(9A)–C(14A)
F(10A)–C(10A)–C(9A)
C(9A)–C(10A)–C(11A)
F(11A)–C(11A)–C(12A)
F(12A)–C(12A)–C(13A)
C(13A)–C(12A)–C(11A)
F(13A)–C(13A)–C(14A)
C(13A)–C(14A)–C(9A)
C(9A)–C(14A)–C(8A)
F(1B)–C(1B)–C(6B)
F(2B)–C(2B)–C(1B)
C(1B)–C(2B)–C(3B)
F(3B)–C(3B)–C(4B)
F(4B)–C(4B)–C(5B)
C(5B)–C(4B)–C(3B)
F(5B)–C(5B)–C(6B)
C(5B)–C(6B)–C(1B)
C(1B)–C(6B)–C(7B)
N(1B)–C(7B)–C(7B)#1
118.8(4)
120.9(4)
119.3(4)
120.0(4)
120.4(4)
119.8(4)
120.2(4)
116.1(4)
122.1(4)
119.5(4)
124.1(4)
117.7(4)
119.9(4)
119.9(5)
120.0(5)
119.3(5)
120.2(5)
119.6(5)
119.6(4)
117.0(4)
120.8(4)
119.6(4)
121.6(5)
119.5(4)
119.6(5)
120.4(5)
120.5(5)
120.0(4)
116.5(4)
119.6(4)
119.8(6)
coupling M diimine oxidative-decoupling, observed also
for metal(alkyne)2 M metallacyclopentadiene systems, is
currently under study by us through both experimental
and theoretical investigations [21].
Treatment of these l-diimino titanium dimers (1
and 2) with ethereal HCl at ꢀ78ꢁ does liberate the free
diimines, 1,1,1,4,4,4-hexafluoro-2,3-butanediimine 3,
and 1,2-di(pentafluorophenyl)-ethanediimine 4, respec-
tively (Scheme 1) in good-to-high yields. Both
diimines, along with their recently reported [6] N,N0-
bis(trimethylsilyl)-substituted analogues are the first
examples of perfluoroalkyl- or perfluoroaryl-substi-
tuted -diimines. As an added benefit, the [(g5-
C5H5)2TiCl2] produced from the HCl/Et2O reaction

B.N. Diel et al. / Inorganica Chimica Acta 357 (2004) 3902–3910
3909
can be recovered and recycled with good efficiency
Acknowledgement
{75% overall, unoptimized, based on the recovered
amount of [(g5-C5H5)2TiCl]2 and starting amount of
[(g5-C5H5)2TiCl]2}, making this a very attractive syn-
thetic route to these novel ligand systems and synthons
for heterocycle synthesis.
The research described in this article was supported
by the Department of Energy, Division of Materials Sci-
ences, Office of Basic Energy Sciences (Grant No. DE-
FG02-96ER45603).
The 1,1,1,4,4,4-hexafluoro-2,3-butanediimine, H–
N@C(CF3)–(CF3)C@N–H (3), crystallizes in the mono-
clinic space group, P21/c. There are two half molecules,
each on a crystallographic inversion center, in the asym-
metric unit, and four molecules in the unit cell. The struc-
ture reveals extensive hydrogen bonding between the
imine (@N–H) hydrogens and a fluorine atom (F3) of
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9
˚
adjacent molecules, on the order of 2.939 A . The 1,2-
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(C6F5)C@N–H (4), crystallizes in the triclinic space
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These diimines can be employed in HCl-elimination/
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We have developed a convenient organotransition
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[19] Crystal data collection and refinement parameters for compounds
3 and 4 are given in the supplementary materials. Data was
collected with a Siemens P4 diffractometer equipped with a
SMART/CCD detector. All software and sources of the scattering
factors are contained in the SHELXTL (version 5.03) program
library (G. Sheldrick, Siemens XRD, Madison, WI). Program
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9
Packing diagrams are provided in the Supplementary Material.

3910
B.N. Diel et al. / Inorganica Chimica Acta 357 (2004) 3902–3910
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[22] B.N. Diel, P.J. Deardorff, in press.