Synthesis of unsymmetrical formamidines and benzamidines: Structural studies of copper, cobalt and chromium complexes

Article abstract of DOI:10.1016/S0020-1693(03)00092-6

The preparation of new ligands capable of spanning linear chains of three metal atoms as well as mononuclear compounds of various geometries are reported. Reaction of triethyl orthoformate with 2-aminopyridine produces the key intermediate, ethylpyridylformimidate (1), in 60% yield. From this, by reaction with the appropriately substituted anilins the following pyridylformamidines were obtained: phenylpyridylformamidine (HPhPyF) (2); p-anisylpyridylformamidine (HAniPyF) (3); p-tolylpyridylformamidine (TolPyF) (4); 4-fluorophenylpyridylformamidine (HPh^FPyF) (5). The p-methyl analog of 1 was made, and from this the picolyl analog of 2 was made, phenylpicolylformamidine (HPhPcF) (7). The compound 2 reacted with CoCl₂ and CuCl₂·3H₂O to produce the tetrahedral complexes Co(HPhPyF)Cl₂ (8) and Cu(HPhPyF)Cl₂ (9). The quasitetrahedral compound Cu(PhPyF)₂ (10) was also prepared. The benzamidine analog of 2, PhN=C(Ph)N(H)Py (11) was prepared and from this the tetrahedral Co complex (12) analogous to 8 and the trichromium compound Cr₃(PhNC(Ph)NPy)₄Cl₂ (13) were made. The crystal structures of 8-13 were determined. The Cr₃ chain in 13 is unsymmetrical with Cr-Cr distances of 2.269(1) and 2.513(1) A?.

Full text of DOI:10.1016/S0020-1693(03)00092-6

Inorganica Chimica Acta 349 (2003) 165ꢀ172
/
www.elsevier.com/locate/ica
Synthesis of unsymmetrical formamidines and benzamidines:
structural studies of copper, cobalt and chromium complexes
F. Albert Cotton *, Peng Lei, Carlos A. Murillo *, Li-Sheng Wang
Department of Chemistry and Laboratory for Molecular Structure and Bonding, P.O. Box 30012 Texas A&M University, College Station,
TX 77842-3012, USA
Received 12 December 2002; accepted 15 January 2003
Abstract
The preparation of new ligands capable of spanning linear chains of three metal atoms as well as mononuclear compounds of
various geometries are reported. Reaction of triethyl orthoformate with 2-aminopyridine produces the key intermediate,
ethylpyridylformimidate (1), in 60% yield. From this, by reaction with the appropriately substituted anilins the following
pyridylformamidines were obtained: phenylpyridylformamidine (HPhPyF) (2); p-anisylpyridylformamidine (HAniPyF) (3); p-
tolylpyridylformamidine (TolPyF) (4); 4-fluorophenylpyridylformamidine (HPhFPyF) (5). The p-methyl analog of 1 was made, and
from this the picolyl analog of 2 was made, phenylpicolylformamidine (HPhPcF) (7). The compound 2 reacted with CoCl2 and
CuCl2×
Cu(PhPyF)2 (10) was also prepared. The benzamidine analog of 2, PhNꢀ
tetrahedral Co complex (12) analogous to 8 and the trichromium compound Cr3(PhNC(Ph)NPy)4Cl2 (13) were made. The crystal
/
3H2O to produce the tetrahedral complexes Co(HPhPyF)Cl2 (8) and Cu(HPhPyF)Cl2 (9). The quasitetrahedral compound
/C(Ph)N(H)Py (11) was prepared and from this the
˚
Cr distances of 2.269(1) and 2.513(1) A.
structures of 8ꢀ
# 2003 Published by Elsevier Science B.V.
/
13 were determined. The Cr3 chain in 13 is unsymmetrical with Crꢁ
/
Keywords: Transition metal compounds; Linear trichromium compounds; Unsymmetrical formamidines; Unsymmetrical benzamidine; Crystal
structures
1. Introduction
containing extended metal atoms in linear arrays, we
investigated the effects of other functionalized ligands
The development of multidentate ligands to support
linear chains of three or more metal atoms is being
actively pursued by both this laboratory [1] and else-
where [2]. Depending on the number of donor atoms on
the ligands, compounds with three, four, five, seven,
nine atoms in a linear array have been synthesized [1,2].
Generally, the ligands are symmetrical. Examples
(Scheme 1) are dpa (the anion of 2,6-dipyridylamine)
[1b], DPhIP (the anion of 2,6-di(phenylimino)-piperi-
dine) [3], BPAP (the dianion of 2,6-bisphenylaminopyr-
idine) [4], DPyF (the anion of dipyridylformamidine)
[1a]. As part of our ongoing study of complexes
on the metalꢀmetal interactions. Amidinate and for-
/
mamidinate ligands are attractive choices since dimetal
paddlewheel complexes with such ligands have been
intensively investigated and are well-understood [5] and
the synthesis of functionalized, symmetrical amidine and
formamidine ligands is not a difficult task [6].
Here we report the synthesis of a series of unsymme-
trical amidines and formamidines and their transition
metal complexes. The ligands (Scheme 2) include five
unsymmetrical formamidines with substituents ranging
from strong electron-donating groups, such as ꢁ
/OCH3,
to electron-withdrawing groups, e.g., F, and an unsym-
metrical benzamidine (N,N?-phenyl-pyridylbenzami-
dine). The metal complexes include mainly
mononuclear complexes with one example of a tri-
nuclear species; a large group of linear trinuclear species
is described in the following paper [7].
* Corresponding author. Tel.: ꢁ
9351.
E-mail
murillo@tamu.edu (C. Murillo).
/
1-409-845-4432; fax: ꢁ
/
1-409-845-
Cotton),
addresses:
cotton@tamu.edu (F.A.
0020-1693/03/$ - see front matter # 2003 Published by Elsevier Science B.V.
doi:10.1016/S0020-1693(03)00092-6

166
F.A. Cotton et al. / Inorganica Chimica Acta 349 (2003) 165ꢀ172
/
2.2. Preparations
2.2.1. Preparation of ethyl pyridylformimidate (1)
2-aminopyridine (18.8 g, 0.200 mol), triethylorthofor-
mate (50 ml, excess) and two drops of 2 M HCl were
charged into a 200 ml flask. The flask was heated slowly
using a heating mantle. At approximately 110 8C,
ethanol began to distill. When 95% of the theoretical
amount of ethanol had been collected, the flask was
allowed to cool slowly. The excess of triethyl orthofor-
Scheme 1.
mate was removed by vacuum distillation at 115ꢀ
using a water aspirator (:25 mmHg). Upon further
heating the final product, a pale yellow liquid, distilled
at 177ꢀ
180 8C. Yield, 14.1 g, 60%. 1H NMR (300 MHz,
/
120 8C
/
/
acetone-d6, d): 8.52 (s, 1H), 8.35 (d, 1H), 7.81 (s, 1H),
7.42 (m, 2H), 4.26 (q, 2H), 1.33 (t, 3H).
2.2.2. Preparation of N,N?-phenylpyridylformamidine
(HPhPyF, 2)
A 50 ml acid-free flask were charged with ethyl
pyridylformimidate (4.62 g, 30.0 mmol) and freshly
distilled aniline (2.79 g, 30.0 mmol). The mixture
solidified upon stirring for 5 min generating heat. White
needle crystals, were obtained by recrystallization from
toluene. Yield: ꢀ
85%. 1H NMR (300 MHz, acetone-d6,
d): 9.05 (broad, 1H), 8.52 (s, 1H), 8.38 (d, 1H), 7.64 (m,
/
1H), 7.45 (m, 2 H), 7.01 (m, 2H), 6,52 (m, 3H). Low
): m/z 198 [Mꢁ
1]ꢁ
(100%).
resolution mass spectrum (FABꢁ
/
/
Scheme 2.
2.2.3. Preparation of N,N?-anisylpyridylformamidine
(HAniPyF, 3)
This was made similarly to 2 by using anisidine
instead of aniline as white needle-like crystals with a
yield greater than 80%. 1H NMR (300 MHz, acetone-d6,
d): 9.08 (broad, 1H), 8.56 (s, 1H), 8.30 (d, 1H), 7.64 (m,
1H), 7.45 (m, 2H), 6.82 (d, 2H), 6.36 (d, 2H), 2.38 (s,
2. Experimental
2.1. General procedures
3H). Low resolution mass spectrum (FABꢁ
/
): m/z 228
Ethyl orthoformate, aniline, p-anisidine, p-toluidine,
p-fluroaniline, benzanilide, phosphorus pentachloride,
2-aminopyridine, and methyllithium (1 M in cumene/
THF) were obtained from Aldrich. Benzanilide was
purified by recrystallization from ethanol. Cobalt
[Mꢁ
/
1]ꢁ(100%).
2.2.4. Preparation of N,N?-tolylpyridylformamidine
(HTolPyF, 4)
This was prepared similarly to 2 by substituting
aniline by toluidine. Yield: 82% (after recrystallization
from toluene). 1H NMR (300 MHz, acetone-d6, d): 9.10
(broad, 1 H), 8.48(s, 1H), 8,25 (d, 1H), 7.68 (m, 1H),
7.50 (m, 2H), 6.79 (d, 2H), 6.31 (d, 2H), 2.35 (s, 3H).
dichloride, CrCl2 and CuCl2×/3H2O were purchased
from Strem Chemicals Inc. All solvents were freshly
distilled from appropriate drying agents under nitrogen.
All routine operations were carried out under N2 unless
otherwise noted. 1H NMR spectra were obtained on
Varian XL-200 and XL-300 spectrometers. IR spectra
were recorded on a Perkin-Elmer 16PC FT-IR spectro-
meter. Cyclic voltammograms were obtained on a BAS
100 electrochemical analyzer. Magnetic measurements
were done at room temperature using powder on a
magnetic susceptibility balance (Johnson Matthey Che-
micals Limited). Elemental analyses were performed by
Canadian Microanalytical Service, Ltd.
Low resolution mass spectrum (FABꢁ
/
): m/z 212 [Mꢁ
/
1]ꢁ(100%).
2.2.5. Preparation of N,N?-4-
fluorophenylpyridylformamidine (HPhFPyF, 5)
This was synthesized similarly to 2 by reacting 4-
fluoroaniline with ethyl pyridylformamidinate. The final
product was recrystallized from toluene. Yield: 76%. 1H
NMR (300 MHz, acetone-d6, d): 9.12 (broad, 1H), 8.30

F.A. Cotton et al. / Inorganica Chimica Acta 349 (2003) 165ꢀ
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167
(s, 1H), 8.19 (d, 1H), 7.68 (m, 1H), 7.48 (m, 2H), 6.72 (d,
2H), 6.44 (d, 2H). Low resolution mass spectrum
gas inlet. Then 17.5 g of recrystallized benzanilide (89
mmol) and 18.5 g of PCl5 (89 mmol) were mixed under a
nitrogen flow. The mixture was heated at 110 8C for 30
min and then at 160 8C for 90 min, giving a slightly
yellow solution. To this solution were added, slowly
through the dropping funnel, 8 ml of pyridine followed
by a 2-aminopyridine solution (8.4 g, 89 mmol in 20 ml
of pyridine). The mixture became violet after 10 min and
the temperature was maintained at 160 8C for 8 h. The
flask was then cooled to 90 8C and 50 ml of water was
added through the dropping funnel. The mixture was
(FABꢁ
/
): m/z 216 [Mꢁ
1]ꢁ (100%).
/
2.2.6. Preparation of ethyl 4-picolylformimidate (6)
The preparation was similar to that of 1. Ethyl 4-
picolylformimidate was distilled at 168ꢀ171 8C under
/
reduced pressure. Yield: 44%. 1H NMR (300 MHz,
acetone-d6, d): 8.35 (d, 1H), 7.80 (s, 1H), 7.42 (m, 2H),
4.28 (q, 2H), 2.37 (s, 3H), 1.33 (t, 3H).
2.2.7. Preparation of N,N?-phenylpicolylformamidine
(HPhPcF, 7)
further cooled to room temperature and a violetꢀred
/
solid was collected after filtration on a Buchner funnel.
The solid was put in 50 ml of ethyl alcohol and turned
yellow after stirring. The yellow solid was collected on a
Buchner funnel and the filtrate was saved. The solid was
ground in a mortar and then treated with 100 ml of
This was prepared similarly to 2 by reacting freshly
distilled aniline with ethylpicolylformamidine. The pro-
duct was recrystallized in toluene. Yield: 80%. 1H NMR
(300 MHz, acetone-d6, d): 9.04 (broad, 1H), 8.34 (s,
1H), 8.25 (d, 1H), 7.44 (m, 2H), 7.05 (m, 2H), 6.62 (t,
1H), 6.46 (d, 2H). Low resolution mass spectrum
ammonia solution (28ꢀ30%), followed by heating to
/
60 8C in air for 1 h. The mixture was filtered and the
solid was collected; the filtrate was saved. Ethyl ether
(500 ml) was added to the solid to extract the product.
The extract was filtered and the volume of the filtrate
was reduced to approximately 20 ml using a water
aspirator. The cream-colored solid was collected on a
Buchner funnel and the filtrate was saved. The solid was
dried under vacuum overnight (yield 7.0 g). Further
work-up on the combined filtrates gave another 3.8 g of
product. Overall yield: 10.8 g (45%). 1H NMR (d,
CDCl3): 13.25 (NH, broad, 1H), 8.31 (pyridyl a-H,
(FABꢁ
/
): m/z 212 [Mꢁ
1]ꢁ (100%).
/
2.2.8. Preparation of Co(HPhPyF)Cl2 (8)
To a flask charged with 2 (210 mg, 1.10 mmol) and
CoCl2 (130 mg, 1.00 mmol) was added 20 ml of THF.
After stirring for 2 h the mixture was bright blue. The
solid was collected by filtration, and it was washed with
2ꢂ20 ml of THF. This was dried under vacuum for 1 h.
/
Yield: 82%. Blue crystals were obtained by slow diffu-
sion of ether into a methanol solution of the compound.
broad, 1H), 7.8ꢀ
Low resolution mass spectrum (FABꢁ
(100%), 180 [Mꢀ
NHpy]ꢁ (85%). IR (cm, KBr disk):
/
6.7 (phenyl and pyridyl protons, 13H).
2.2.9. Preparation of Cu(HPhPyF)Cl2 (9)
The ligand 2 was dissolved in 15 ml of THF. This was
/
): m/z 273 [M]ꢁ
/
slowly added to a methanol solution of CuCl2×
/
3H2O
3229 (m), 3059 (m), 1646 (s), 1575 (s) 1526 (s), 1488 (w),
1461 (w), 1434 (s), 1321 (s), 1252 (w), 1230 (m), 1148 (w),
1111 (m), 1092 (m), 1071 (w), 1025 (w), 992 (w), 922 (w),
776 (s), 698 (s), 627 (w) and 530 (m). A crystal suitable
for X-ray structure determination was obtained by slow
(170 mg, 1.00 mmol). A brownꢀred precipitate formed
/
immediately. The mixture was stirred for 1 h. The solid
was collected by filtration and was washed with 20 ml
THF. This was dried under vacuum for 1 h. Yield: 72%.
Red crystals were obtained by slow diffusion of ether
into a methanol/MeCN (1:1) solution of the compound.
diffusion of hexanes into a benzene solution of PhNꢀ
/
C(Ph)NH-2-py.
2.2.10. Preparation of Cu(PhPyF)2 (10)
2.2.12. Preparation of CoCl2(h2-PhNꢀ
(12)
/
C(Ph)NH-2-py)
To a flask charged with CuCl2×/3H2O (170 mg, 1.00
mmol), HPhPyF (197 mg, 1.00 mmol) and an excess of
copper wire (1.00 g) was added 40 ml MeCN. The
mixture was refluxed under air for 8 h, forming a yellow
solution over the copper wire, and then it was allowed to
cool slowly to room temperature. After 24 h, the color
changed to deep purple and a lot of deep-purple, block-
shaped crystals deposited on the glass walls. From these
crystals, one suitable for X-ray crystallographic study
was selected. The crystals were separated manually from
the unreacted copper wire. Yield: 44%.
PhNꢀ/C(Ph)NH-2-pyridyl (137 mg, 0.500 mmol) and
CoCl2 (65 mg, 0.500 mmol) were mixed in 10 ml of
THF. The mixture was stirred for 1 h producing a bright
blue suspension. The solid was allowed to settle and the
colorless supernatant liquid was decanted. The solid was
washed with 10 ml of ethyl ether and dried under
vacuum for 2 h. Yield: 150 mg, 74%. Anal. Calc. for
C18H15N3CoCl2: C, 53.60; H, 3.72; N, 10.42. Found: C,
53.58; H, 3.75; N, 10.32. IR (cmꢃ1, KBr disk): 3270 (m),
3199 (m), 3077 (m), 1624 (m), 1603 (s), 1519 (s), 1472 (s),
1352 (m), 1263 (m), 1221 (m), 1117 (m), 1025 m), 933
(w), 867 (w), 782 (s), 700 (s), 538 (w), 513 (w), 420 (w).
2.2.11. Preparation of PhNꢀ
/
C(Ph)NH-2-py (11)
A 250 ml three-neck flask was equipped with a
dropping funnel, a condenser with a gas outlet, and a
Low resolution mass spectrum (m/z): 367 ([Mꢀ
/
Cl]ꢁ,
100%). UVꢀ
/
Vis (EtOH, cmꢃ1): 608 nm (300), 550 nm

168
F.A. Cotton et al. / Inorganica Chimica Acta 349 (2003) 165ꢀ172
/
(150). Powder magnetic susceptibility measurement
(room temperature): 5.3mB. Sea blue crystals, obtained
by slow diffusion of ethyl ether into an ethyl alcohol
solution, were used for X-ray structure determination.
polarization effects using PROCOR [11] (for FAST
data) or SAINT [12] (for SMART data), and then further
corrected for absorption using SORTAV [13] (for FAST
data) or SADABS [14] (for SMART data). The positions of
heavy atoms were found by the direct methods using
SHELXS-97 [15] Subsequent cycles of least-squares re-
finement followed by difference Fourier syntheses
revealed the positions of the non-hydrogen atoms. All
hydrogen atoms were placed in idealized positions.
Important crystallographic data are given in Table 1.
2.2.13. Preparation of Cr3(PhNC(Ph)N-2-py)4Cl2 (13)
PhNC(Ph)NH-2-py (273 mg, 1.00 mmol) was dis-
solved in 15 ml of THF. To this solution was added 1.1
ml of MeLi (1 M in THF/cumene). The mixture was
stirred for 1 h and the solution was then transferred to a
Schlenk tube containing chromium dichloride (123 mg,
1.00 mmol). The mixture turned to a violet suspension
immediately. Stirring was continued for 1 h. The solvent
was then removed under reduced pressure and 20 ml of
CH2Cl2 was added to the violet residue. After 1 h of
stirring, the suspension was filtered through Celite and
the solvent of the filtrate was removed. Acetonitrile (10
ml) was added to the violet residue giving a violet
solution. Diethyl ether (30 ml) was added to the solution
causing the precipitation of a yellowish green solid. The
supernatant liquid was filtered off and the solid was
washed with 10 ml of ether. The solid was then dried
under vacuum for 1 h. Yield: 160 mg. The product was
crystallized by slow diffusion of hexanes into a methyl-
ene chloride solution that contained a small amount of
THF. Yield: 75 mg, 23%. Low resolution mass spectrum
Selected bond lengths and angles are listed in Tables 2ꢀ
/
4.
3. Results and discussion
3.1. Synthetic considerations
Five unsymmetrical formamidines were synthesized in
two steps with excellent yield and facile separations.
First, reactions of aminopyridine derivatives with ethyl
orthoformate form pyridyl formimidate (Scheme 3a);
then the unsymmetrical formamidines are obtained by
reacting the formimidate with the corresponding aniline
derivatives, as shown in Scheme 3b. For the first
reaction, the use of a catalytic amount of acid and an
excess of ethyl orthoformate are critical for the success
of the reaction. However, the second reaction must be
carried out in an acid-free environment as trace amounts
of acid cause the unsymmetrical formamidines to
disproportionate into the corresponding symmetrical
formamidines, as shown in Scheme 4. For comparison,
when ethyl phenylformimidate was used as a starting
material instead of ethyl pyridylformimidate, there is no
reaction at room temperature. At higher temperatures
such as those that were used to distill out ethanol, a
mixture of unsymmetrical and symmetrical formami-
dines were obtained as evidenced by the mass spectrum.
The separation was extremely difficult since the unsym-
metrical formamidines decompose in contact with silica
gel. Therefore, the method described in Scheme 3b is the
only good way to prepare the unsymmetrical formami-
dines.
Compound 10 was synthesized by mixing CuCl2,
copper metal and the neutral ligand HPhPyF in
MeCN under reflux. The reaction condition here was
chosen to be very similar to the one used in the
preparation of Cu3(dpa)4Cl2 [16] with the hope of
making a tricopper analogue. However, the reaction
yielded only a mononuclear species.
The compound, N,N?-phenylpyridylbenzamidine (11),
is known but the literature preparation gave only an
18% yield [17]. Our synthesis (Eqs. (1) and (2)) was
achieved by a modification of a method reported for the
synthesis of benzamidine. Because 2-aminopyridine is
less nucleophilic than aniline, reaction (2) requires 8 h
(m/z): 1280 ([ꢁ
/
Cl]ꢁ, 42%), 920 ([Cr2(PhNC(Ph)N-2-
Vis (THF, cmꢃ1): 655 nm (210),
py)3]ꢁ, 100%). UVꢀ
/
590 nm (420), 508 nm (490), 413 nm (1420). IR (KBr,
cmꢃ1): 1598 (m), 1512 (m), 1464 (s), 1430 (s), 1385 (s),
1306 (m), 1274 (w), 1210 (w), 1160 (w), 1019 (w), 946
(m), 798 (s), 781 (s), 752 (w), 703 (s), 627 (w), 541 (w),
532 (w), 444 (s). Cyclic voltammetry (CH2Cl2, vs. Ag/
AgCl): a reversible oxidation at E1/2
susceptibility at room temperature: 5.3mB.
ꢄ0.15 V. Magnetic
/
2.3. Crystallography
For compound 12 data were collected on a Nonius
CAD 4 diffractometer at ꢃ
were obtained from 25 strong reflections in the range of
30.24ꢀ36.588 (2u). Absorption corrections were based
/
125 8C. Unit cell parameters
/
on a series of c-scans. Details of the procedure have
been described previously [8]. For compounds 11 and
13, data were collected on a Nonius FAST area-detector
diffractometer at ꢃ60 8C using the program MADNES
/
[9]. The cell dimensions were determined by the refine-
ment of 171 and 250 reflections for 11 and 13,
respectively (20.200
/
2u 046.268). Absorption correc-
/
tions were carried out by averaging multiple equivalent
measurements. The procedure for the FAST data
collection in our laboratory has been detailed earlier
[4]. For compounds 8, 9 and 10, data were collected on a
Bruker SMART 1000 CCD area detector system. Cell
parameters were obtained using SMART software [10]. In
both cases, the data were corrected for Lorentz and

F.A. Cotton et al. / Inorganica Chimica Acta 349 (2003) 165ꢀ
/172
169
Table 1
Crystallographic data
8
9
10
11
12
13
Empirical for-
mula
fw
C
12H11C12CoN3 C12H14C12CuN3 C24H20CuN6 C18H15N3
C18H15N3CoCl2 C72H56N12Cr1Cl2(CH2Cl2)1.64
(C5H14 0.52(C4H3O)0.42
1565.18
-
)
327.07
P21/c
331.68
¯
P1
456.00
¯
P1
273.33
P21/n
403.16
P212121
11.592(1)
11.787(1)
12.919(1)
90
¯
P1
Space group
˚
/
/
/
a (A)
˚
13.338(2)
12.795(2)
7.9981(13)
7.5991(7)
9.6871(9)
10.0425(9)
97.642(2)
111.090(2)
105.646(2)
642.05(10)
1.716
9.0546(7)
10.3920(8)
12.102(1)
90.894(1)
98.220(2)
110.891(1)
1050.2(1)
1.442
14.547(7)
5.967(2)
16.77(1)
90
12.806(3)
14.941(3)
20.306(4)
79.77(2)
86.82(1)
87.79(1)
3816(1)
1.362
b (A)
˚
c (A)
a (8)
b (8)
95.067(3)
92.889(2)
90
90
90
g (8)
3
V (A )
˚
1359.7(4)
1.598
1453.8(12)
1.249
1765.2(3)
1.517
d (g cmꢃ3
)
Z
4
213(2)
0.0342, 0.0822
2
213(2)
0.0298, 0.0742
2
213(2)
4
4
148(2)
2
213(2)
T (K)
R1 a, wR2
213(2)
0.0767,
0.1675
0.0638,
0.1889
1.085
b
0.0274,
0.0728
0.0298, 0.0756 0.0745, 0.1786
0.0359, 0.0782 0.0922, 0.2046
[I ꢀ2s(I)]
/
R1 a, wR2
(all data)
0.0428, 0.0876
0.0400, 0.0799
1.052
0.0301,
0.0752
1.048
b
Quality of fit c 1.097
1.049
1.097
a
R1ꢄ
/
ajjFojꢃ
wR2ꢄ
[a[w(Fo2ꢃ
Quality of fitꢄ
[a[w(Fo2ꢃ
/
jFcjj/ajFoj.
2 2
/
b
c
2 2 12
//
/
Fc ) ]/aw(Fo ) ], wꢄ
/
1/[s2(Fo2)ꢁ
Nparams), based on all data.
/
(aP)2ꢁ
/
bP], where Pꢄ
/
[max(0 or (Fo2)ꢁ2(Fc2)]/3.
/
/
/
Fc2)2]/(Nobs
ꢃ
/
rather than 20 min as in the synthesis of benzamidine.
We obtained a 45% (unoptimized) yield. Further
purification of the benzanilide could perhaps improve
the yield further by reducing the formation of a tarry
material.
Treatment
of
chromium
dichloride
with
Li(PhNC(Ph)N-2-py), which was obtained by deproto-
nation of N,N?-phenylpyridylbenzamidine with methyl-
lithium,
generated
the
trinuclear
compound
Cr3(PhNC(Ph)N-2-py)4Cl2 (13) in THF at room tem-
perature. The method of preparation is different from
that for Cr3(dpa)4Cl2, where the reaction must be
carried out in refluxing THF. When this reaction was
carried out at the reflux temperature of THF, the target
complex could not be isolated.
PhNHC(O)PhꢁPCl50 PhNꢀC(Cl)PhꢁHClꢂ
ꢁP(O)Cl3
(1)
(2)
PhNꢀC(Cl)PhꢁNH2-2-py 0 PhNꢀC(Ph)NH-2-py
ꢁHClꢂ
Table 2
Selected bond lengths (A) and angles (8) for compounds 8, 9, 10 and 12
˚
8
9
10
12
Bond lengths
Co(1)ꢁ
Co(1)ꢁ
Co(1)ꢁ
Co(1)ꢁ
/
N(3)
1.982(2)
2.015(2)
Cu(1)ꢁ
/
N(3)
N(1)
Cl(3)
Cl(2)
1.961(2)
2.000(2)
Cu(1)ꢁ
/
N(6)
N(1)
N(3)
N(4)
1.9205(13) Co(1)ꢁ
1.9258(14) Co(1)ꢁ
1.9852(14) Co(1)ꢁ
1.9890(14) Co(1)ꢁ
/
N(1)
N(3)
Cl(1)
Cl(2)
1.989(3)
2.006(3)
2.223(1)
2.239(1)
1.296(4)
1.370(5)
1.384(5)
/N(1)
Cu(1)ꢁ
/
Cu(1)ꢁ
/
/
/Cl(2)
2.2172(11) Cu(1)ꢁ
/
2.2292(7) Cu(1)ꢁ
2.2482(7) Cu(1)ꢁ
1.347(3)
1.296(3)
1.388(3)
/
/
/Cl(13)
2.247(9)
1.346(3)
1.291(4)
1.393(3)
Cu(1)ꢁ
/
/
/
N(2)ꢁ
N(3)ꢁ
N(2)ꢁ
/
C(6)
C(6)
C(5)
N(2)ꢁ
N(3)ꢁ
N(2)ꢁ
/
C(6)
C(6)
C(5)
N(1)ꢁ
C(7)ꢁ
C(8)ꢁ
/
C(7)
1.332(2)
1.308(2)
1.361(2)
N(1)ꢁ
N(2)ꢁ
N(2)ꢁ
/
C(27)
C(27)
C(31)
/
/
/N(2)
/
/
/
/N(3)
/
Bond angles
N(3)ꢁCo(1)ꢁ
N(3)ꢁCo(1)ꢁ
N(1)ꢁCo(1)ꢁ
N(3)ꢁCo(1)ꢁ
N(1)ꢁCo(1)ꢁ
Cl(2)ꢁCo(1)ꢁ
C(5)ꢁN(1)ꢁ
C(5)ꢁN(1)ꢁ
C(1)ꢁN(1)ꢁ
/
/
N(1)
Cl(2)
Cl(2)
Cl(3)
Cl(3)
93.21(9)
116.73(9)
110.19(8)
112.10(8)
109.48(8)
113.23(4)
117.7(2)
123.7(2)
118.5(2)
N(3)ꢁ
N(3)ꢁ
N(1)ꢁ
N(3)ꢁ
N(1)ꢁ
Cl(3)ꢁ
C(5)ꢁN(1)ꢁ
C(5)ꢁN(1)ꢁ
C(1)ꢁN(1)ꢁ
/
Cu(6)ꢁ
Cu(1)ꢁ
Cu(1)ꢁ
Cu(1)ꢁ
Cu(1)ꢁ
Cu(1)ꢁ
/
N(1)
Cl(3)
Cl(3)
Cl(2)
Cl(2)
93.10(8)
138.41(7)
99.80(6)
98.44(6)
135.50(6)
99.40(3)
117.1(2)
125.6(2)
117.3(2)
N(6)ꢁ
N(6)ꢁ
N(1)ꢁ
N(6)ꢁ
N(1)ꢁ
N(3)ꢁ
N(3)ꢁ
C(7)ꢁN(1)ꢁ
C(7)ꢁN(2)ꢁ
/
Cu(6)ꢁ
Cu(1)ꢁ
Cu(1)ꢁ
Cu(1)ꢁ
Cu(1)ꢁ
Cu(1)ꢁ
C(8)ꢁ
/
N(1)
N(3)
N(3)
N(4)
N(4)
N(4)
141.77(6)
101.21(6)
92.92(6)
N(1)ꢁ
N(1)ꢁ
Cl(1)ꢁ
N(3)ꢁCo(1)ꢁ
N(1)ꢁCo(1)ꢁ
N(3)ꢁCo(1)ꢁ
C(27)ꢁN(1)ꢁ
C(27)ꢁN(1)ꢁ
C(27)ꢁN(2)ꢁ
/
Co(1)ꢁ
Co(1)ꢁ
Co(1)ꢁ
/
N(3)
92.6(1)
115.59(9)
112.26(4)
106.51(9)
111.16(9)
117.45(9)
120.6(3)
120.6(3)
131.8(3)
/
/
/
/
/
/
/
/Cl(1)
/
/
/
/
/
/
/
/
Cl(2)
/
/
/
/
/
/
93.19(6)
/
/
Cl(1)
Cl(2)
Cl(1)
/
/
/
/
/
/
102.05(6)
134.18(6)
124.75(16)
117.94(14)
124.61(15)
/
/
/
/Cl(3)
/
/Cl(2)
/
/
/
/
/
/
C(1)
/
/
C(1)
/
/
N(2)
/
/
C(11)
C(11)
C(31)
/
/
Co(1)
/
/
Cu(1)
Cu(1)
/
/
C(5)
/
/
/
/
Co(1)
/
/
/
/C(8)
/
/

170
F.A. Cotton et al. / Inorganica Chimica Acta 349 (2003) 165ꢀ172
/
Table 3
˚
Selected bond lengths (A) and angles (8) for 11
N(2)ꢁ
N(2)ꢁ
N(2)ꢁ
N(2)ꢁ
N(1)ꢁ
N(3)ꢁ
N(3)ꢁ
/
C(1)
1.380(4)
1.401(4)
3.130(4)
0.89(4)
C(1)ꢁ
C(1)ꢁ
N(1)ꢁ
N(1)ꢁ
C(12)ꢁ
N(3)ꢁC(1)ꢁ
N(3)ꢁC(1)ꢁ
N(2)ꢁC(1)ꢁ
/
N(2)ꢁ
/
C(11)
128.5(3)
120.7(3)
122.9(3)
112.9(3)
124.2(3)
121.5(3)
125.9(3)
112.6(3)
/
C(11)
C(1A)
H(2)
/
N(3)ꢁ
/C(31)
/
/
C(11)ꢁ
C(11)ꢁ
/C(12)
/
/
/N(2)
/
H(2A)
C(1)
C(31)
2.25(5)
1.279(4)
1.414(4)
/
C(11)ꢁ
/N(2)
/
/
/
N(2)
/
/
/
C(21)
/
/
C(21)
Fig. 1. The molecular structure of 8 with ellipsoids drawn at the 45%
probability level. The hydrogen atoms are omitted.
Table 4
˚
Selected bond lengths (A) and angles (8) for 13
able. The observed Nꢁ
smaller than those in the ideal geometry possibly due to
the backbone constraint of the ligand but similar to
/
Mꢁ
/
N angles are substantially
Cr(1)ꢁ
Cr(2)ꢁ
Cr(1)ꢁ
Cr(3)ꢁ
Cr(1)ꢁ
Cr(1)ꢁ
Cr(1)ꢁ
Cr(1)ꢁ
Cr(2)ꢁ
Cr(2)ꢁ
Cr(2)ꢁ
Cr(2)ꢁ
Cr(3)ꢁ
Cr(3)ꢁ
Cr(3)ꢁ
Cr(3)ꢁ
/
Cr(2)
Cr(3)
Cl(1)
Cl(2)
N(1)
N(2)
N(3)
N(4)
N(5)
N(6)
N(7)
N(8)
N(9)
N(10)
N(11)
N(12)
2.269(1)
2.513(1)
2.499(2)
2.456(2)
2.130(5)
2.122(5)
2.146(5)
2.092(5)
2.047(5)
2.033(5)
2.039(5)
2.043(4)
2.112(5)
2.184(5)
2.114(5)
2.125(5)
Cr(1)ꢁ
Cr(2)ꢁ
Cl(2)ꢁCr(3)ꢁ
N(4)ꢁCr(1)ꢁ
N(4)ꢁCr(1)ꢁ
N(2)ꢁCr(1)ꢁ
N(4)ꢁCr(1)ꢁ
N(2)ꢁCr(1)ꢁ
N(1)ꢁCr(1)ꢁ
N(4)ꢁCr(1)ꢁ
N(2)ꢁCr(1)ꢁ
N(1)ꢁCr(1)ꢁ
N(3)ꢁCr(1)ꢁ
N(4)ꢁCr(1)ꢁ
N(2)ꢁCr(1)ꢁ
N(1)ꢁCr(1)ꢁ
/
Cr(2)ꢁ
/
Cr(3)
178.70(5)
178.37(6)
171.57(7)
172.3(2)
90.1(2)
92.1(2)
87.9(2)
88.7(2)
170.2(2)
87.4(1)
85.4(1)
84.5(1)
85.9(1)
94.2(1)
93.0(1)
95.8(1)
/
/
Cr(1)ꢁ
/Cl(1)
/
/
/Cr(2)
/
/
/
N(2)
N(1)
N(1)
N(3)
N(3)
N(3)
Cr(2)
Cr(2)
Cr(2)
Cr(2)
Cl(1)
Cl(1)
Cl(1)
those in Co(Hdpa)Cl2 (Hdpaꢀ
Individual values are listed in Table 2. The Cꢁ
distances of the formamidinate (in 8 and 9) and/or
amidinate (in 10) groups should not be equivalent as one
would expect for a neutral ligand. Indeed they are not.
/
dipyridylamine) [18].
N
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
For example, in compound 8, the distance of a Cꢁ
/N
/
/
/
˚
N(2), is long, 1.346(3) A, and the
single bond, C(6)ꢁ
/
/
/
/
distance for a carbonꢀ
/
nitrogen double bond, C(6)ꢁN(3)
/
/
/
/
˚
is short, 1.291(4) A.
/
/
/
/
/
/
The structure of 10 (Fig. 2) shows two PhPyF ligands
chelating a heavily distorted tetrahedral copper(II)
center, like that found in Cu(dpa)2 [19]. There are three
nitrogen atoms in a plane indicating that the ligand is
anionic. Evidence of the anionic nature of the ligand
/
/
/
also comes from the equivalence of Cꢁ
/
N distances in the
formamidinate. In compound 10, those distances are
˚
almost equal, 1.332(2) and 1.308(2) A, which strongly
suggest the existence of a delocalized system.
Scheme 3.
Scheme 4.
3.2. Structural studies
Compounds 8, 9, and 12 have similar structures with a
1:1 metal/ligand ratio. The crystal structures for these
three compounds display a distorted tetrahedral metal
center chelated by a neutral ligand through two nitrogen
atoms to form a six-member ring, and two chloride
atoms. The molecular structure of 8 is shown in Fig. 1 as
an example. In all three compounds, the Mꢁ
/
N distances
Fig. 2. A drawing of the molecular structure of 10 with ellipsoids
drawn at the 45% probability level and hydrogen atoms omitted.
˚
(:
/
2.00 A) and Nꢁ
/
Mꢁ
/
N angles (:
/
938) are compar-

F.A. Cotton et al. / Inorganica Chimica Acta 349 (2003) 165ꢀ
/172
171
The molecular structure of 13 is shown in Fig. 4. It
consists of an essentially linear but unsymmetrical Cr36ꢁ
chain coordinated by a spiral set of N,N?-phenyl-2-
pyridylbenzamidinato ligands and two chloro anions at
axial positions. It is interesting that of the several
possible regioisomers, the one seen here has three
ligands orientated in one direction and the other in the
opposite direction. The average Crꢁ
the outer chromium atoms are 2.123(5) and 2.134(5) A,
substantially longer than the average CrꢁN bond length
involving central chromium atom (2.04(15) A). The
Cr(1)ꢁCl(1) bond is essentially colinear with the metal
chain (Cr(2)ꢁCr(1)ꢁCl(1) 178.37(6)8) whereas the
Cr(3)ꢁCl(2) bond at the other end of the molecule is
slightly bent away from the three ꢁphenyl groups
(Cr(2)ꢁCr(3)ꢁCl(2) 171.57(7)8), which indicates the
repulsive interaction between Cl(2) atom and the three
adjacent ꢁphenyl groups. The two CrꢁCr bond lengths
are not equal (2.269(1) and 2.513(1) A). These distances
are indicative of an elongated quadruple bond and an
isolated CrII ion, which is consistent with the unsymme-
trical arrangement of the wrapping ligands and in
accord with the magnetic moment. Further discussion
on this and other compounds with linear trichromium
units is presented in the following paper [7].
/
N bond lengths of
˚
/
˚
/
/
/
Fig. 3. A drawing showing the dimeric nature of 11 with ellipsoids
drawn at the 40% probability level.
/
/
/
/
The X-ray structure of N,N?-phenylpyridylbenzami-
dine, 11, shows that this unsymmetrical benzamidine
forms a dimer in the solid state (Fig. 3) as it is often
found in symmetrical formamidines and benzamidines
[17]. The amidine molecules adopt syn-, anti-geometry.
This arrangement is preferred because of the presence of
weak intramolecular hydrogen bonding involving the H-
/
/
˚
atom in the amidine nitrogen atoms and the pyridyl
˚
H) is 2.25(5) A long
groups. The hydrogen bond (N
/
ꢀ ꢀ ꢀ
/
and almost linear (170(3)8). The bond length of the
amino nitrogen atom to its adjacent carbon atoms is
˚
1.380(4) and 1.401(4) A, indicative of single bonds. The
C bond angle at the amino nitrogen atom is
4. Supplementary material
Cꢁ
/
128.5(3)8. The bond lengths of the amidine nitrogen
atom to its neighboring carbon atoms are 1.279(4) and
˚
1.414(4) A which can be assigned as double and single
Crystallographic data in CIF format for compounds
8ꢀ/13 have been deposited at the Cambridge Crystal-
lographic Data Centre, CCDC Nos. CCDC 199350ꢀ
/
bonds, respectively. The CꢀN double bond position is
/
199359, respectively. Copies of CIFs are available free
of charge from The Director, CCDC, 12 Union Road,
located close to the phenyl group, rather than the
pyridyl substituent, which is consistent with the assign-
Cambridge, CB2 1EZ, UK (fax: ꢁ44-1223-336-033;
/
ment of the Cꢀ
/
N double bond in Eq. (2).
email: deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.
ac.uk).
Acknowledgements
We thank the National Science Foundation and the
NIRT (Nanoscale Science and Engineering (NIRT
Grant DMR-0103455) and the Telecommunications
and Information Task Force at Texas A&M University.
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