W2Cl4(NHR)2(PR′3) 3 Molecules. 3. Bidentate Phosphine Complexes of Bis(tert-butylamido)tetrachloroditungsten. Preparation and Structural Characterization of cis,cis-W2Cl4(NHCMe3)2(L-L) (L-L = dmpm, dmpe, dppm, dppe)

Article abstract of DOI:10.1021/ic960906z

Four new triply-bonded ditungsten complexes of the formula cis,cis-W₂Cl₄(NHCMe₃)₂(L-L) (L-L = dmpm (1), dmpe (2), dppm (3), dppe (4)) have been prepared by reaction of W₂Cl₄(NHCMe₃)₂(NH ₂CMe₃)₂ with the appropriate bidentate phosphines (L-L) in hydrocarbon solvents. These complexes are the first triply-bonded complexes of the form W₂Cl₄(NHR)₂(L-L) where L-L groups are bidentate phosphines. The molecular structures have been investigated by X-ray crystallography. Crystal data are as follows: for 1, monoclinic space group P2₁/n, a = 13.807(1) ?, b = 11.835(2) ?, c = 15.348(1) ?, β= 109.19(2)°, Z = 4; for 2, P2₁/n, a = 14.144(2) ?, b = 11.991(1) ?, c = 15.662(2) ?, β= 109.50(1)°, Z = 4; for 3-CH₂Cl₂, P2₁/c, a = 18.777(6) ?, b = 10.273(2) ?, c = 21.082(3) ?, β= 94.11(6)°, Z = 4; for 4, P2₁/n, a = 11.938(1) ?, b = 18.583(3) ?, c = 17.606(2) ?, β = 106.54(6)°, Z = 4. The W-W bond lengths for 1, 2, 3-CH₂Cl₂ and 4 are 2.3247(4), 2,3274(5), 2.328(1), and 2.3452(5) ?, respectively, which are consistent with a formal W≡W bond. The W-P and W-Cl distances are similar in all of the complexes reported. The average W-N distance of 1.905(7) ? is indicative of a W-N double bond having some N → W π character. No orientational disorder of the central ditungsten units was observed. While strong N-H?Cl hydrogen bonding is retained in these diphosphine complexes, each molecule deviates from an eclipsed geometry with torsion angles involving the hydrogen-bonded N and Cl atoms being in the range 12.8-22.0°. It is also noteworthy that all complexes are highly twisted and display exceptionally large torsional angles for the bridging diphosphines across the W≡W bond (1, 46.2°; 2, 59.9°; 3-CH₂Cl₂, 43.6°; 4, 56.8°). As far as the stereochemistry of each molecule is concerned, the structure analyses reveal that the final product in each case was the cis,cis isomer of W₂Cl₄(NHCMe₃)₂(L-L) with the P and N atoms mutually cis on each W atom. In addition to the structural data for these complexes, IR, ³¹P{¹H} and ¹H NMR spectroscopy, and mass spectrometry have been used to characterize the complexes.

Full text of DOI:10.1021/ic960906z

80
Inorg. Chem. 1997, 36, 80-85
W2Cl4(NHR)2(PR′3)2 Molecules. 3. Bidentate Phosphine Complexes of
Bis(tert-butylamido)tetrachloroditungsten. Preparation and Structural Characterization of
cis,cis-W2Cl4(NHCMe3)2(L-L) (L-L ) dmpm, dmpe, dppm, dppe)
F. Albert Cotton,* Evgeny V. Dikarev, and Wai-Yeung Wong
Department of Chemistry and Laboratory for Molecular Structure and Bonding, Texas A&M University,
College Station, Texas 77843-3255
ReceiVed August 1, 1996X
Four new triply-bonded ditungsten complexes of the formula cis,cis-W2Cl4(NHCMe3)2(L-L) (L-L ) dmpm (1),
dmpe (2), dppm (3), dppe (4)) have been prepared by reaction of W2Cl4(NHCMe3)2(NH2CMe3)2 with the appropriate
bidentate phosphines (L-L) in hydrocarbon solvents. These complexes are the first triply-bonded complexes of
the form W2Cl4(NHR)2(L-L) where L-L groups are bidentate phosphines. The molecular structures have been
investigated by X-ray crystallography. Crystal data are as follows: for 1, monoclinic space group P21/n, a )
13.807(1) Å, b ) 11.835(2) Å, c ) 15.348(1) Å, â ) 109.19(2)°, Z ) 4; for 2, P21/n, a ) 14.144(2) Å, b )
11.991(1) Å, c ) 15.662(2) Å, â ) 109.50(1)°, Z ) 4; for 3‚CH2Cl2, P21/c, a ) 18.777(6) Å, b ) 10.273(2) Å,
c ) 21.082(3) Å, â ) 94.11(6)°, Z ) 4; for 4, P21/n, a ) 11.938(1) Å, b ) 18.583(3) Å, c ) 17.606(2) Å, â )
106.54(6)°, Z ) 4. The W-W bond lengths for 1, 2, 3‚CH2Cl2, and 4 are 2.3247(4), 2.3274(5), 2.328(1), and
2.3452(5) Å, respectively, which are consistent with a formal WtW bond. The W-P and W-Cl distances are
similar in all of the complexes reported. The average W-N distance of 1.905(7) Å is indicative of a W-N
double bond having some N f W π character. No orientational disorder of the central ditungsten units was
observed. While strong N-H‚‚‚Cl hydrogen bonding is retained in these diphosphine complexes, each molecule
deviates from an eclipsed geometry with torsion angles involving the hydrogen-bonded N and Cl atoms being in
the range 12.8-22.0°. It is also noteworthy that all complexes are highly twisted and display exceptionally large
torsional angles for the bridging diphosphines across the WtW bond (1, 46.2°; 2, 59.9°; 3‚CH2Cl2, 43.6°; 4,
56.8°). As far as the stereochemistry of each molecule is concerned, the structure analyses reveal that the final
product in each case was the cis,cis isomer of W2Cl4(NHCMe3)2(L-L) with the P and N atoms mutually cis on
each W atom. In addition to the structural data for these complexes, IR, 31P{1H} and 1H NMR spectroscopy, and
mass spectrometry have been used to characterize the complexes.
by refluxing over appropriate reagents and freshly distilled under
dinitrogen immediately prior to use. tert-Butylamine, dppm, and dppe
were purchased from Aldrich, Inc., and used as received. WCl4, dmpm,
and dmpe were purchased from Strem Chemicals and used as received.
The compound W2Cl4(NHCMe3)2(NH2CMe3)2 was prepared according
to the published procedure using Na-Hg as the reducing agent.4
Syntheses. (i) cis,cis-W2Cl4(NHCMe3)2(dmpm) (1). W2Cl4-
(NHCMe3)2(NH2CMe3)2 (0.5 g, 0.62 mmol) was dissolved in hexanes
(10 mL), and dmpm (1 equiv) was added via syringe with constant
stirring. The color of the solution immediately changed from orange
to red, and a brown-red precipitate formed in a few minutes. Stirring
was continued for 1 h, after which the solvent, liberated tert-butylamine,
and any excess of dmpm were removed under vacuum. The resulting
residue was redissolved in a minimum volume of hot toluene to yield
a deep-orange solution after filtration through Celite. When hexanes
were carefully layered on this solution, red block-shaped crystals of
cis,cis-W2Cl4(NHCMe3)2(dmpm) (0.22 g, yield 45%) were obtained
after 2 days at room temperature.
Introduction
We have reported on the chemistry of the isomeric title
compounds W2Cl4(NHCMe3)2(PR3)2 with monodentate phos-
phines in parts 1 and 2.1 However, no examples of compounds
having the formula W2Cl4(NHR)2(L-L), where L-L is a bridging
bidentate phosphine, are known.2 Besides, relatively few data
6+
are available for W2
species with the formula W2Clx-
(NR2)6-x(L-L) containing bidentate phosphines L-L. To our
knowledge, only two complexes of this type have been prepared,
viz., W2Cl2(NMe2)4(dmpm) and W2Cl2(NMe2)4(dmpe), but no
structural characterization has been carried out.3 In this paper,
we report the first W2Cl4(NHCMe3)2(L-L)-type compounds with
bridging diphosphines L-L ) dmpm, dmpe, dppm, and dppe.
Each of these compounds has been characterized by IR, 31P-
{1H} and 1H NMR spectroscopy, mass spectrometry, and single-
crystal X-ray diffraction studies.
IR data (cm-1): 3226 (w), 1402 (w), 1301 (w), 1285 (w), 1261 (s),
1217 (w), 1202 (w), 1171 (w), 1094 (s, br), 1019 (s, br), 941 (m), 898
(vw), 863 (w), 801 (vs), 725 (vw), 707 (vw), 701 (vw).
Experimental Section
1H NMR data (benzene-d6, 24 °C, δ): 1.01 (s, 18H, CMe3), 1.21
(virtual triplet, J ) 5.6 Hz, 6H, PMe2), 2.08 (virtual triplet, J ) 5.6
General Procedures. All manipulations were carried out under an
atmosphere of dry argon or dinitrogen using standard Schlenk
techniques. Commercial grade solvents were dried and deoxygenated
Hz, 6H, PMe ), 2.19 (t, J ) 11.2 Hz, 2H, PCH2P), 12.80 (br, 2H,
2
NH).
X Abstract published in AdVance ACS Abstracts, December 15, 1996.
(1) (a) Cotton, F. A.; Yao, Z. J. Cluster Sci. 1994, 5, 11. (b) Chen, H.;
Cotton, F. A.; Yao, Z. Inorg. Chem. 1994, 33, 4255.
(2) Cotton, F. A.; Walton, R. A. Multiple Bonds between Metal Atoms,
2nd ed.; Oxford University Press: New York, 1993; see also references
therein.
1
31P{1H} NMR data (benzene-d6, 19 °C, δ): 10.29 (s, JW-P ) 150
2
Hz, JP-P ) 84.3 Hz).
FAB/DIP (DIP ) direct insertion probe) MS (NBA, m/z): 790
([M]+), 754 ([M - Cl]+).
(3) Ahmed, K. J.; Chisholm, M. H.; Folting, K.; Huffman, J. C. Inorg.
Chem. 1985, 24, 4039.
(4) Bradley, D. C.; Errington, R. J.; Hursthouse, M. B.; Short, R. L. J.
Chem. Soc., Dalton Trans. 1986, 1305.
S0020-1669(96)00906-8 CCC: $14.00 © 1997 American Chemical Society

Characterization of cis,cis-W2Cl4(NHCMe3)2(L-L)
Inorganic Chemistry, Vol. 36, No. 1, 1997 81
Table 1. Crystallographic Data for cis,cis-W2Cl4(NHCMe3)2(dmpm) (1), cis,cis-W2Cl4(NHCMe3)2(dmpe) (2),
cis,cis-W2Cl4(NHCMe3)2(dppm)‚CH2Cl2 (3‚CH2Cl2), and cis,cis-W2Cl4(NHCMe3)2(dppe) (4)
1
2
3
4
formula
fw
W2Cl4P2C13H34N2
789.86
W2Cl4P2C14H36N2
803.89
W2Cl6P2C34H44N2
1123.05
W2Cl4P2C34H44N2
1052.15
space group (No.)
P21/n (14)
13.807(1)
11.835(2)
15.348(1)
109.19(2)
2368.6(5)
4
2.215
10.292
Mo KR (0.710 73)
-150
P21/n (14)
14.144(2)
11.991(1)
15.662(2)
109.50(1)
2503.9(5)
4
2.132
21.877
Cu KR (1.541 84)
20
P21/c (14)
18.777(6)
10.273(2)
21.082(3)
94.11(6)
4056(2)
4
1.839
6.168
Mo KR (0.710 73)
-60
P21/n (14)
11.938(1)
18.583(3)
17.606(2)
106.54(6)
3744.1(8)
4
1.867
6.537
Mo KR (0.710 73)
-60
a, Å
b, Å
c, Å
â, deg
V, Å3
Z
F
calc, g/cm3
µ, mm-1
radiation (λ, Å)
temp, °C
transm. factors
R1a, R2b [I > 2σ(I)]
R1a, R2b (all data)
0.9953-0.4896
0.032, 0.083
0.039, 0.088
1.0000-0.4952
0.034, 0.088
0.042, 0.095
0.300-0.197
0.042, 0.091
0.056, 0.098
none
0.050, 0.117
0.062, 0.127
2
2
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) [∑[w(Fo - Fc2) ]/∑[w(Fo )2]]1/2
.
(ii) cis,cis-W2Cl4(NHCMe3)2(dmpe) (2). The synthesis of com-
pound 2 followed a similar course to that of 1. Upon adding dmpe,
the color of the solution changed from orange to dark-red. After 1 h
of stirring, all the volatile components of the mixture were removed
under reduced pressure. Initial hexanes extraction (15 mL) of the
resulting residue afforded a bright-red solution, which was shown by
31P{1H} NMR at room temperature to contain a complicated mixture
of products which as yet remains uncharacterized. The residue was
then extracted with a minimum volume of toluene (10 mL), and the
deep-red solution was allowed to stand at room temperature for a week
to afford a first crop of red crystals. A second crop of crystals was
obtained by keeping the filtrate in a freezer at -15 °C for 2 days. The
overall yield was about 39%.
washed with hexanes (3 × 5 mL), and dried in Vacuo. The solid
compound was recrystallized at room temperature by slow diffusion
of hexanes into a CH2Cl2 solution for 1 day to yield orange plates of
cis,cis-W2Cl4(NHCMe3)2(dppe). A second batch of compound 4 was
obtained by cooling the toluene filtrate to 0 °C to give an overall yield
of about 39%.
IR data (cm-1): 3157 (m), 3055 (w), 1435 (s), 1365 (m), 1325 (w),
1306 (vw), 1261 (m), 1202 (s), 1173 (vw), 1161 (vw), 1093 (s), 1024
(m), 955 (w), 915 (vw), 864 (m), 816 (ms), 799 (ms), 749 (m), 741
(m), 711 (w), 694 (s), 668 (w).
1H NMR data (CD2Cl2, 24 °C, δ): 1.07 (s, 18H, CMe3), 2.08 (br,
2H, P(CH2)2P), 3.63 (br, 2H, P(CH2)2P), 7.11-7.98 (m, 20H, Ph), 12.76
(br, 2H, NH).
IR data (cm-1): 3203 (m), 1413 (w), 1367 (m), 1361 (m), 1324
(w), 1300 (vw), 1283 (w), 1261 (w), 1218 (w), 1202 (m), 1170 (vw),
1161 (vw), 1092 (m, br), 1022 (w), 949 (s), 921 (m), 870 (w), 844
(w), 798 (m), 793 (m), 745 (w), 728 (w), 709 (w).
2
31P{1H} NMR data (1/3benzene-d6 + /3CH2Cl2, 19 °C, δ): 33.85
1
3
(s, JW-P ) 279 Hz, JP-P ) 21.1 Hz).
FAB/DIP MS (NBA, m/z): 1052 ([M]+), 1017 ([M - Cl]+).
Physical Measurements. The IR spectra were recorded on a Perkin-
Elmer 16PC FT-IR spectrophotometer as Nujol mulls between KBr
plates. 1H NMR studies (200 MHz) were performed on a Varian XL-
200 spectrometer using CD2Cl2 or benzene-d6, and the chemical shifts
were referenced to SiMe4 (δ ) 0). The 31P{1H} NMR data (81 MHz)
were obtained at room temperature in 10 mm NMR tubes on a Varian
XL-200 broad band spectrometer with the chemical shift values
referenced externally and were reported relative to 85% H3PO4/D2O.
The FAB/DIP mass spectra were acquired using a VG Analytical 70S
high-resolution, double-focusing, sectored (EB) mass spectrometer. The
instrument is equipped with a VG 11/250J data system that allowed
computer control of the instrument, data recording, and data processing.
Samples for analysis were prepared by dissolving neat solid compound
in m-nitrobenzylalcohol (NBA) matrix on the direct insertion probe
tip. The probe was then inserted into the instrument through a vacuum
interlock and the sample bombarded with 8 keV xenon primary particles
from an Ion Tech FAB gun operating at an emission current of 2 mA.
Positive secondary ions were extracted and accelerated to 6 keV and
then mass analyzed.
1H NMR data (CD2Cl2, 24 °C, δ): 1.22 (s, 18H, CMe3), 1.46 (d, J
) 8.4 Hz, P(CH2)2P), 1.56 (br, 6H, PMe2), 2.11 (d, J ) 10.2 Hz,
P(CH2)2P), 2.60 (br, 6H, PMe2), 12.21(br, 2H, NH).
1
31P{1H} NMR data (CDCl3, 19 °C, δ): 13.74 (s, JW-P ) 305 Hz,
3JP-P ) 31.4 Hz).
FAB/DIP MS (NBA, m/z): 804 ([M]+), 767 ([M - Cl]+), 732 ([M
- 2Cl]+), 659 ([M - 2NHCMe3]+).
(iii) cis,cis-W2Cl4(NHCMe3)2(dppm) (3). Dppm (0.24 g, 0.62
mmol) was dissolved in toluene (10 mL) and added via cannula to a
solution of W2Cl4(NHCMe3)2(NH2CMe3)2 (0.5 g, 0.62 mmol) in hexanes
(10 mL). The color started to turn dark-red, and after about 1 h of
stirring, the solvent and other volatile components were removed under
vacuum. The residual dark-red solid was redissolved in hot toluene
(10 mL) to give a deep-red solution. An initial attempt to grow single
crystals by layering hexanes on the toluene extract failed. However,
bright-red block-shaped crystals of 3 of good X-ray quality (0.27 g,
42%) were obtained in 2 days by layering hexanes over a CH2Cl2
solution of 3 at room temperature.
IR data (cm-1): 3202 (w), 3178 (w), 3039 (w), 1485 (m), 1434 (s),
1365 (ms), 1324 (w), 1310 (vw), 1281 (w), 1261 (m), 1200 (s), 1171
(w), 1156 (w), 1146 (w), 1091 (s), 1025 (m), 954 (w), 916 (w), 802
(ms), 791 (ms), 741 (ms), 728 (ms), 694 (s).
X-ray Crystallographic Procedures. Single crystals of 1-4 were
obtained as described above in the Experimental Section. Routine unit
cell identification and intensity data collection procedures were followed
utilizing the options specified in Table 1 and the general procedures
previously described.5 Crystal quality was first checked by means of
a rotation photograph. In all cases, lattice dimensions and Laue
symmetry were checked using axial photographs. All calculations were
performed on a DEC 3000-800 AXP workstation. The coordinates of
the tungsten atoms for all of the structures were found in direct-methods
E maps using the structure solution program in SHELXTL.6 The
1H NMR data (CD2Cl2, 24 °C, δ): 1.18 (s, 18H, CMe ), 5.01 (t, J
3
) 10.6 Hz, 2H, PCH2P), 7.09-8.03 (m, 20H, Ph), 12.95 (br, 2H, NH).
2
31P{1H} NMR data (1/3benzene-d6 + /3CH2Cl2, 19 °C, δ): 36.45
1
2
(s, JW-P ) 140 Hz, JP-P ) 76.3 Hz).
FAB/DIP MS (NBA, m/z): 1038 ([M]+), 1003 ([M - Cl]+), 967
([M - 2Cl]+), 931 ([M - 3Cl]+).
(iv) cis,cis-W2Cl4(NHCMe3)2(dppe) (4). W2Cl4(NHCMe3)2(NH2-
CMe3)2 (0.5 g, 0.62 mmol) was dissolved in hexanes (10 mL), and
dppe (0.25 g, 0.62 mmol) in toluene (10 mL) was transferred by cannula
with stirring of the solution. The color of the reaction mixture changed
to red, and after about 15 min, a red-brown solid started to precipitate.
(5) (a) Bino, A.; Cotton, F. A.; Fanwick, P. E. Inorg. Chem. 1979, 18,
3558. (b) Cotton. F. A.; Frenz, B. A.; Deganello, G.; Shaver, A. J.
Organomet. Chem. 1973, 227. (c) Bryan, J. C.; Cotton, F. A.; Daniels,
L. M.; Haefner, S. C.; Sattelberger, A. P. Inorg. Chem. 1995, 34, 1875.
(6) SHELXTL, Version 5; Siemens Industrial Automation, Inc., 1994.
1
Stirring was continued for /2 h, after which the solid was filtered,

82 Inorganic Chemistry, Vol. 36, No. 1, 1997
Cotton et al.
Table 2. Selected Bond Distances (Å) and Angles (deg) for
cis,cis-W2Cl4(NHCMe3)2(dmpm) (1),
cis,cis-W2Cl4(NHCMe3)2(dmpe) (2), cis,cis-W2Cl4(NHCMe3)2(dppm)
(3), and cis,cis-W2Cl4(NHCMe3)2(dppe) (4)
give R ) 0.032 (for 3763 reflections with I > 2σ(I)) and R ) 0.039
(for all 4160 data). The largest peak in the final difference Fourier
map was 2.16 e/Å3, located in the vicinity of the W atoms.
cis,cis-W2Cl4(NHCMe3)2(dmpe) (2). A red rhomboidal crystal with
dimensions of 0.25 × 0.18 × 0.13 mm was mounted on the top of a
glass fiber with epoxy resin. Diffraction data were collected at 20 °C
on a Rigaku AFC5R diffractometer using Cu KR radiation, and
reflections suitable for indexing were found using the automatic search
routine. A least-squares analysis of the setting angles of 25 reflections
with 46° < 2θ < 68° provided accurate unit cell parameters (Table 1).
Three standard reflections were measured during data collection and
displayed no systematic variation in intensity. A total of 3897
reflections in the range 7° < 2θ < 120° were collected using the ω-2θ
scan technique. Empirical absorption corrections based on ψ scans of
six reflections were applied to the data set using the TEXSAN software
package.9 The space group was assigned as P21/n from the systematic
absences in the data. Final least-squares refinement of 225 parameters
resulted in R ) 0.034 (for 3316 reflections with I > 2σ(I)) and R )
0.042 (for all 3722 data). The final difference map was essentially
featureless, the largest peaks being associated with the W atoms.
1
2
3
4
W(1)-W(2)
W(1)-P(1)
W(2)-P(2)
W(1)-N(1)
W(2)-N(2)
W(1)-Cl(1)
W(2)-Cl(4)
W(1)-Cl(2)
W(2)-Cl(3)
2.3247(4) 2.3274(5) 2.328(1)
2.3452(5)
2.555(2)
2.525(2)
1.908(7)
1.912(7)
2.387(2)
2.407(2)
2.410(2)
2.404(3)
2.508(2)
2.501(2)
1.896(6)
1.911(6)
2.392(2)
2.379(2)
2.445(2)
2.431(2)
2.521(2)
2.528(3)
1.899(7)
1.898(7)
2.404(2)
2.390(2)
2.425(2)
2.418(2)
2.542(2)
2.538(2)
1.895(6)
1.905(5)
2.381(2)
2.396(2)
2.424(2)
2.400(2)
P(1)-W(1)-N(1)
95.9(2)
90.9(2)
98.0(2)
98.5(2)
P(1)-W(1)-Cl(1) 160.85(6) 164.03(8) 158.44(6) 159.84(8)
P(1)-W(1)-Cl(2) 77.29(6)
N(1)-W(1)-Cl(1) 98.8(2)
N(1)-W(1)-Cl(2) 140.9(2)
Cl(1)-W(1)-Cl(2) 83.56(6)
W(2)-W(1)-P(1) 89.77(5)
W(2)-W(1)-N(1) 100.7(2)
W(2)-W(1)-Cl(1) 99.52(5)
81.15(8)
97.1(2)
141.2(2)
84.00(9)
92.54(6)
101.5(2)
99.36(6)
75.61(5)
98.5(2)
146.1(2)
82.94(6)
91.62(4)
99.6(2)
76.24(8)
95.5(2)
140.7(2)
83.74(9)
94.14(7)
99.8(2)
cis,cis-W2Cl4(NHCMe3)2(dppm) (3). A block-shaped red crystal
with dimensions of 0.53 × 0.25 × 0.20 mm was mounted on the tip of
a quartz fiber with grease and quickly placed in the cold stream at
-60 °C of the low temperature controller model FR 558-S. Intensity
data were collected on an Enraf-Nonius FAST automated diffractometer
with an area detector for 5° < 2θ < 50° using Mo KR radiation. The
general procedures have been fully described elsewhere.5c A prelimi-
nary data collection was first carried out to afford all parameters and
an orientation matrix. Fifty reflections were used in indexing and 250
reflections with 18° < 2θ < 42° in cell refinement. Systematic
absences uniquely determined the space group as P21/c. The data were
corrected for Lorentz and polarization effects by the MADNES
program.10 Reflection profiles were fitted, and values of F2 and σ(F2)
for each reflection were obtained by the program PROCOR, which
uses a fitting algorithm developed by Kabsch.11 The reflection data
file was reformatted by the program for use with the SHELXL-93
structure refinement software package. The data were corrected for
absorption anisotropy effects by an empirical method based on the
difference in observed intensities of symmetry and/or azimuth rotation
equivalent reflections, and all equivalent reflections merged, using a
local adaptation of the program SORTAV.12 After isotropic refinement
of all atoms of the dinuclear complex, the difference Fourier map
showed several peaks that could be ascribed to solvent molecules. These
peaks were modeled as CH2Cl2 solvent molecules, and the crystal
contains four dichloromethane molecules in the unit cell. In each
CH2Cl2 molecule, both Cl atoms were found to be disordered at three
positions each. Full refinement of 437 parameters led to residuals of
R ) 0.042 (for 5165 reflections with I > 2σ(I)) and R ) 0.056 (for all
6130 data). The final difference Fourier map revealed only one peak
above 1 e/Å3, lying 0.87 Å from W(2).
99.11(6)
97.73(8)
W(2)-W(1)-Cl(2) 117.55(5) 116.61(6) 113.67(6) 119.31(6)
P(2)-W(2)-N(2)
94.8(2)
91.4(2)
79.76(9)
98.5(2)
76.86(5)
93.0(2)
81.65(7)
P(2)-W(2)-Cl(3) 76.16(7)
P(2)-W(2)-Cl(4) 159.65(7) 162.63(8) 160.73(6) 161.97(8)
N(2)-W(2)-Cl(3) 143.2(2)
N(2)-W(2)-Cl(4) 100.0(2)
Cl(3)-W(2)-Cl(4) 83.64(7)
W(1)-W(2)-P(2) 90.30(5)
W(1)-W(2)-N(2) 99.4(2)
142.8(2)
97.7(2)
84.12(9)
93.52(6)
99.6(2)
146.5(2)
95.2(2)
84.21(6)
90.51(4)
99.4(2)
143.9(2)
94.6(2)
82.55(8)
95.10(5)
100.9(2)
W(1)-W(2)-Cl(3) 115.98(5) 116.80(6) 113.74(6) 115.01(7)
W(1)-W(2)-Cl(4) 100.91(5) 99.52(6) 100.51(5) 99.43(7)
positions of the remaining non-hydrogen atoms were located using
subsequent sets of least-squares refinement cycles followed by differ-
ence Fourier syntheses employing the SHELXL-93 structure refinement
program.7 These positions were initially refined with isotropic
displacement parameters and then with anisotropic displacement
parameters to convergence. In each model, hydrogen atoms were
introduced in idealized positions for the calculation of structure factors,
and the entire model was refined to convergence. Important crystal-
lographic details pertinent to individual compounds are presented in
the following paragraphs. Table 2 lists the selected bond distances
and angles for each of the structures. Table 3 tabulates the torsional
angles along the WtW bond in each structure. Tables of atomic
coordinates and anisotropic displacement parameters as well as complete
tables of bond distances and angles and coordinates of hydrogen atoms
are available as Supporting Information.
cis,cis-W2Cl4(NHCMe3)2(dmpm) (1). A red block-shaped crystal
with the approximate dimensions of 0.45 × 0.35 × 0.30 mm was
attached to the end of a quartz fiber with grease and immediately placed
in a cold stream of nitrogen (-150 °C). Intensity data were collected
on an Enraf-Nonius CAD-4S diffractometer equipped with graphite-
monochromated Mo KR radiation. The unit cell constants were
determined from the geometrical parameters of 25 well-centered
reflections in the range 21° < 2θ < 28°. The unit cell constants and
axial photographs were consistent with a monoclinic lattice. Data
collection was carried out with an ω-2θ scan motion in the range 4°
< 2θ < 50°. Three standard reflections measured every 1 h revealed
negligible decay. Correction for Lorentz, polarization, and absorption
effects were applied. The latter correction was based on azimuthal
scans of three reflections with the Eulerian angle ø near 90°. The
computations were done with Enraf-Nonius SDP software.8 From the
systematic absences in the data, the space group was uniquely
determined to be P21/n. A total of 208 parameters were varied in the
final anisotropic refinement for all atoms except hydrogen atoms, to
cis,cis-W2Cl4(NHCMe3)2(dppe) (4). An orange platelike crystal
having dimensions of 0.40 × 0.13 × 0.05 mm was coated with grease
and mounted on the tip of a quartz fiber. The data collection procedures
at -60 °C on an Enraf-Nonius FAST diffractometer using Mo KR
radiation were essentially the same as those for the crystal of 3. Fifty
reflections were employed in cell indexing and 250 reflections in cell
refinement. Axial images were used to confirm the Laue group and
cell dimensions. No absorption correction was applied. Crystals of 4
conformed to the space group P21/n based on the systematic absences
in the data. Final anisotropic refinement of 403 parameters resulted
in R ) 0.050 (for 5689 reflections with I > 2σ(I)) and R ) 0.062 (for
all 6666 data). The final difference map contained several small “ghost”
(9) TEXSAN-TEXRAY, Structure Analysis Package; Molecular Structure
Corp., 1985.
(10) Pflugrath, J.; Messerschmitt, A. MADNES, Munich Area Detector (New
EEC) System, version EEC 11/9/89; with enhancements by Enraf-
Nonius Corp.: Delft, The Netherlands. A description of MADNES
appears: Messerschmitt, A.; Pflugrath, J. J. Appl. Crystallogr. 1987,
20, 306.
(7) Sheldrick, G. M. Crystallographic Computing 6; Flack, H. D.,
Parkanyi, L., Simon, K., Eds.; Oxford University Press: Oxford, 1993;
p 111.
(8) Structure Determination Package, Enraf-Nonius, Delft, The Nether-
lands, 1979.
(11) (a) Kabsch, W. J. Appl. Crystallogr. 1988, 21, 67; (b) 1988, 21, 916.
(12) Blessing, R. H. Acta Crystallogr. 1995, A51, 33.

Characterization of cis,cis-W2Cl4(NHCMe3)2(L-L)
Inorganic Chemistry, Vol. 36, No. 1, 1997 83
Table 3. Torsion Angles (deg) about the W-W Axis for cis,cis-W2Cl4(NHCMe3)2(dmpm) (1), cis,cis-W2Cl4(NHCMe3)2(dmpe) (2),
cis,cis-W2Cl4(NHCMe3)2(dppm) (3), and cis,cis-W2Cl4(NHCMe3)2(dppe) (4)
1
2
3
4
P(1)-W(1)-W(2)-P(2)
P(1)-W(1)-W(2)-N(2)
P(1)-W(1)-W(2)-Cl(3)
P(1)-W(1)-W(2)-Cl(4)
N(1)-W(1)-W(2)-P(2)
N(1)-W(1)-W(2)-N(2)
N(1)-W(1)-W(2)-Cl(3)
N(1)-W(1)-W(2)-Cl(4)
Cl(1)-W(1)-W(2)-P(2)
Cl(1)-W(1)-W(2)-N(2)
Cl(1)-W(1)-W(2)-Cl(3)
Cl(1)-W(1)-W(2)-Cl(4)
Cl(2)-W(1)-W(2)-P(2)
Cl(2)-W(1)-W(2)-N(2)
Cl(2)-W(1)-W(2)-Cl(3)
Cl(2)-W(1)-W(2)-Cl(4)
46.22(7)
141.1(2)
-28.50(7)
-116.69(7)
142.2(2)
59.93(8)
151.9(2)
-20.4(1)
-108.56(9)
151.3(2)
43.63(5)
142.4(2)
-32.22(6)
-120.47(6)
142.1(2)
56.82(7)
150.9(2)
-26.33(8)
-112.46(8)
156.1(2)
-122.9(3)
-116.7(3)
-119.2(2)
-109.8(3)
67.4(2)
71.0(2)
66.2(2)
73.0(2)
-20.8(2)
-116.95(7)
-22.0(2)
168.32(7)
80.13(7)
-29.29(7)
65.6(2)
-17.1(2)
-109.39(8)
-17.4(2)
170.3(1)
82.12(9)
-21.45(9)
70.5(2)
-22.0(2)
-117.60(6)
-18.9(2)
166.55(6)
78.31(7)
-31.36(6)
67.4(2)
-13.1(2)
-106.85(8)
-12.8(2)
169.99(8)
83.86(9)
-19.72(8)
74.4(2)
-104.01(7)
167.80(7)
-101.8(1)
170.07(9)
-107.21(6)
164.54(6)
-102.87(9)
171.00(9)
Scheme 1
Table 4. Comparison of 31P{1H} NMR Data for Complexes 1-4
and their Corresponding Free Ligands, Measured under Identical
Conditions
peaks in close proximity to the heavy atoms, but no effort was made
to correct for this problem.
Results and Discussion
δ
∆δ, ppm
Synthesis. All cis,cis-W2Cl4(NHCMe3)2(L-L) (L-L ) dmpm,
dmpe, dppm, dppe) compounds reported herein are formed
straightforwardly from the reaction of W2Cl4(NHCMe3)2(NH2-
CMe3)2 with 1 equiv of the appropriate bidentate phosphine
ligands (L-L) at ambient temperature (Scheme 1). These
products are obtainable in yields of 39-45%. Compounds 1-4
are readily soluble in CH2Cl2 and slightly soluble in toluene
and benzene. However, they are insoluble in hexanes. In the
solid state, all the compounds may be handled in air for short
periods of time. In solution, they decompose within 5 min of
exposure to air to form brown solutions. We were able to
identify one of the decomposition products to be the mono-
nuclear W(IV) species [WOCl(dmpe)2]+ 13 and [WOCl(d-
ppe)2]+ 14 for 2 and 4, respectively, on the basis of 31P{1H}
NMR and UV spectral data.
W2Cl4(NHCMe3)2(dmpm) (1) 10.29 (C6D6)
65.91
dmpm
-55.62 (C6D6)
13.74 (CDCl3)
W2Cl4(NHCMe3)2(dmpe) (2)
60.84
59.42
46.76
dmpe
-47.10 (CDCl3)
W2Cl4(NHCMe3)2(dppm) (3)
dppm
W2Cl4(NHCMe3)2(dppe) (4)
dppe
36.45 (C6D6/CH2Cl2)
-22.97 (C6D6/CH2Cl2)
33.85 (C6D6/CH2Cl2)
-12.91 (C6D6/CH2Cl2)
data for the complexes 1-4 and their corresponding free ligands.
The diphosphine ligands were found to experience significant
downfield shifts in the 31P{1H} NMR signals upon coordination
to the dinuclear W26+ unit. The largest chemical shift difference
is about 65.9 ppm. This reflects the electron-withdrawing
capability of the ditungsten units in these complexes. In all
cases, only those molecules with one 183W nucleus can cause
observable satellites. In addition, the satellites in compounds
1-4 are further split into doublets which, for an ABX spin
system, PP183W, here, will be proportional to JA-B (i.e., JP-P).
Clearly, for all the cis,cis isomers reported here, the P-P
coupling constants are large enough to give a resolved splitting
of the satellites. In each case, approximate P-P coupling
constants may be obtained from the spectra. For compounds 2
Spectroscopic Properties. All the complexes 1-4 show
absorption bands in the IR spectra above 3000 cm-1 due to
ν(N-H). The FAB/DIP mass spectra of compounds 1-4 all
exhibit small molecular ion peaks and comparatively more
intense peaks attributable to [M - Cl]+.
1
Compounds W2Cl4(NHCMe3)2(L-L) show H NMR spectra
1
consistent with the presence of a C2 symmetry axis and are fully
consistent with the solid state structures (Vide infra). The
and 4, the JW-P values (305 Hz for 2, 279 Hz for 4) are
comparable to those reported for cis-W2Cl4(NHCMe3)2(PR3)2
1
(R3 ) Me3, Et3, Prn , Me2Ph).1b It is noteworthy that for
alkylamide N-protons are evident in the H NMR spectra of
3
1-4 and appear as broad signals in the range 12.21-12.95 ppm.
On the other hand, the 31P{1H} NMR spectra of all the
compounds 1-4 consist of strong central singlets flanked by
weak satellites due to 183W-31P coupling (183W is 14.3%
complexes 1 and 3 containing dmpm and dppm ligands, the
1JW-P values are only 150 and 140 Hz, respectively. However,
JP-P values are considerably larger because they are 2JP-P rather
3
than JP-P couplings.
1
abundant with S ) /2). Table 4 compares the 31P{1H} NMR
Molecular Structures. Crystal structures of cis,cis-W2Cl4-
(NHCMe3)2(L-L) (L-L ) dmpm (1), dmpe (2), dppm (3), dppe
(4)) are very similar. They all crystallize in the centrosym-
metricmonoclinic space group P21/n (P21/c for 3‚CH 2Cl 2) with
four molecules (comprising two pairs of enantiomeric molecules)
(13) Cotton, F. A.; Llusar, R. Acta Crystallogr. 1988, C44, 952.
(14) (a) Levason, W.; McAuliffe, C. A.; McCullough, F. P., Jr. Inorg. Chem.
1977, 16, 2911. (b) Cotton, F. A.; Mandal, S. K. Eur. J. Solid State
Inorg. Chem. 1991, 28, 775.

84 Inorganic Chemistry, Vol. 36, No. 1, 1997
Cotton et al.
Figure 3. Perspective drawing of cis,cis-W2Cl4(NHCMe3)2(dppm) (3).
Thermal ellipsoids are shown at the 40% probability level. Carbon
atoms are shown as spheres of arbitrary radii and are not labeled for
clarity.
Figure 1. Perspective drawing of cis,cis-W2Cl4(NHCMe3)2(dmpm) (1).
Thermal ellipsoids are shown at the 40% probability level. Carbon
atoms are shown as spheres of arbitrary radii. Two hydrogen bonds
N-H‚‚‚Cl are shown as dashed lines.
Figure 4. Perspective drawing of cis,cis-W2Cl4(NHCMe3)2(dppe) (4).
Thermal ellipsoids are shown at the 40% probability level. Carbon
atoms are shown as spheres of arbitrary radii and are not labeled for
clarity.
Figure 2. Perspective drawing of cis,cis-W2Cl4(NHCMe3)2(dmpe) (2).
Thermal ellipsoids are shown at the 40% probability level. Carbon
atoms are shown as spheres of arbitrary radii.
W-Cl distances are statistically significant, suggesting a
stronger structural trans influence of NHCMe3 than that of the
phosphine toward the chlorine atoms. The average W-N bond
distances of 1.899(7)-1.910(7) Å for all complexes are normal
W-NH(R) bond distances of formal bond order 2. One of the
most notable features for all the compounds is the twisted
configuration of the molecules. Figure 5 illustrates this
significant structural aspect for compound 1, namely that the
torsion angle P(1)-W(1)-W(2)-P(2) is exceptionally large
(46.2°). The corresponding angle for 3 is 43.6°. However, both
2 and 4 exhibit an even larger conformational twist (Figure 6b)
than 1 and 3 (59.9 and 56.8°, respectively), which match well
with the longer P-P separation in their structures.
per unit cell for each complex. Perspective drawings of one
molecule of 1-4 are depicted in Figures 1-4, respectively. The
central portions of each structure consisting of the set of eight
ligands are the same, and each has only C2 symmetry with the
2-fold axis perpendicularly bisecting the WtW bond. Each
molecule is therefore chiral. The W-W bond distances in all
of them (1, 2.3247(4) Å; 2, 2.3274(5) Å; 3, 2.328(1) Å; 4,
2.3452(5) Å) (Table 2) fall within the range of the bond
distances established for the W-W triple bond with a σ2π4
configuration.2 The subtle lengthening in 4 probably reflects
steric interaction across the WtW bond. Each W atom in the
molecules is approximately square planar with the two chlorine
atoms in a cis arrangement in each WCl2NP fragment, and the
central (WtW)6+ unit is spanned by a bridging diphosphine.
The average W-P bond distances for 1 and 2 (1, 2.505(2) Å;
2, 2.525(3) Å) are shorter than those observed in 3 and 4
(2.540(2) Å in both cases). This difference is presumably due
to the increased basicity and smaller size of dmpm and dmpe
relative to dppm and dppe. On the other hand, the P-W-N
angles are not as large in 3 and 4 as those in 1 and 2 as one
would predict from the corresponding ligand sizes. The average
W-Cl distances, trans to P, fall in the range 2.386(2)-2.397-
(2) Å for 1-4, while the mean W-Cl distances, trans to N, are
within 2.407(2)-2.438(2) Å (Table 2). These differences in
Only two crystal structures of the cis isomers of W2Cl4-
(NHCMe3)2(PR3)2 with monodentate phosphines (R3 ) Me3,
Me2Ph) are known to date.1a,15 The bond lengths and angles in
the central dimetal units of these two complexes are very close
to those reported herein for compounds 1-4. In all these cis
isomers, no disorder of the W2 units in the crystals was observed,
although this was frequently the case for trans-W2Cl4(NHCMe3)2-
(PR3)2 (R3 ) Me3, Et3, Prn , Me2Ph),1a which has been addressed
3
to the higher molecular symmetry for trans isomers than that
for cis isomers. The relationship between monodentate phos-
phine compounds and the title compounds 1-4 could be easily
(15) Bradley, D. C.; Hursthouse, M. B.; Powell, H. R. J. Chem. Soc., Dalton
Trans. 1989, 1537.

Characterization of cis,cis-W2Cl4(NHCMe3)2(L-L)
Inorganic Chemistry, Vol. 36, No. 1, 1997 85
Figure 5. View of the central part of molecule 1 directly down the
W(1)-W(2) axis. Methyl and tert-butyl groups are omitted for clarity.
visualized in Figure 6, which illustrates the central portion of
the molecule down the WtW axis in each case. It was noted
before1a,4,15 that a very important condition for the stability of
W2Cl4(NHCMe3)2(PR3)2 complexes is the intramolecular hy-
drogen bonding N-H‚‚‚Cl across the WtW bond with the
average Cl-W-W-N torsion angles being 15.5° (PR3
)
PMe3)1a and 15.9° (PR3 ) PMe2Ph)15 for the cis isomers
(Figure 6a). For those two cases, the P-W-W-P angles are
97.3 and 97.8° for PMe3 and PMe2Ph, respectively, while these
angles are getting smaller in the diphosphine compounds (Figure
6b), leading to a “rotation” of the whole set of ligands (P(2),
Cl(3), Cl(4), and N(2)) as compared to the monophosphine
counterpart shown in Figure 6a. But the average magnitudes
of all corresponding torsion angles for the hydrogen-bonded Cl
and N atoms across the W-W vector (-21.4(1), -17.3(2),
-20.5(3), -13.0(4)°) still allow the mean N-H‚‚‚Cl distances
to remain within the normal range 2.45-2.58 Å.
Figure 6. Comparison of the central portions of cis-W2Cl4(NHCMe3)2-
(PMe3)2 (a) and molecule 2 (b) directly down the W(1)-W(2) axis.
Methyl and tert-butyl groups are omitted for clarity. Hydrogen bonding
is shown as dashed lines.
studies of the reaction mixture at the beginning of the experiment
suggest that substitution reactions probably take place one by
one at each W atom, and we believe that the key initial step in
Scheme 1 involves the coordination of one PR2 group of the
diphosphine to one W atom, leaving the other PR2 moiety free.
However, no definite proof is yet available. As time passes,
the 31P{1H} NMR spectra become complex and additional peaks
(including those arising from the cis,cis isomer) appear, due
presumably to exchange or dissociation processes. There is still
much that is not clear about the kinetic and thermodynamic
aspects of these reactions. Work relating to this is currently
under way.
Concluding Remarks
Molecules of the general type W2Cl4(NHCMe3)2(L-L), where
L-L is a diphosphine, are easily accessible by the reaction of
W2Cl4(NHCMe3)2(NH2CMe3)2 with a stoichiometric amount of
L-L. The successful isolation of the dppm and dppe derivatives,
viz., W2Cl4(NHCMe3)2(dppm) (3) and W2Cl4(NHCMe3)2(dppe)
(4), is particularly interesting since according to an earlier report
it was not possible to prepare the triphenylphosphine or
(diphenylphosphino)ethane substitution products in this way.15
These results attest to the stability of the diphosphine as a
bridging ligand in the formation of complexes having the
stoichiometry W2Cl4(NHCMe3)2(L-L), regardless of the steric
bulk of the phenyl groups.
Acknowledgment. We thank the National Science Founda-
tion for support.
Supporting Information Available: Four X-ray crystallographic
files, in CIF format, are available. Access information is given on
any current masthead page.
It must be noted that in all four systems studied here, only
the cis,cis isomer of W2Cl4(NHCMe3)2(L-L) was obtained from
trans,trans-W2Cl4(NHCMe3)2(NH2CMe3)2, which is presumably
the thermodynamically stable product. In situ 31P{1H} NMR
IC960906Z