W2Cl4(NR2)2(PR′ 3)2 Molecules. 5. Preparation and Characterization of W2Cl4(NEt2)2(L-L) (L-L = dmpm, dmpe, dppe), W2Cl4(NBu2)2(L-L) (L-L = dmpm, dmpe), and W2Cl4(NHex2)2 (dmpm).

Article abstract of DOI:10.1021/ic961151z

The triply-bonded ditungsten complexes W₂Cl₄(NEt₂)₂(L-L) (L-L = dmpm, dmpe), W₂Cl₄(NBu₂)₂(L-L) (L-L = dmpm, dmpe), and W₂Cl₄(NHex₂)₂(dmpm) are formed in the reactions between W₂Cl₄(NR₂)₂(NHR₂) ₂ (R = Et, Bu, Hex = n-C₆H₁₃ and bis(dimethylphosphino)methane (dmpm) or bis(dimethylphosphino)ethane (dmpe). In each case, three isomeric forms have been detected in solution by ³¹P{¹H} NMR spectroscopy, and they are formulated as the trans,trans-, cis,trans-, and cis,cis-isomers. Complexes designated cis,trans have one P atom of the bridging diphosphine cis to the N atom on one W atom and another P atom trans to the N atom on the other W atom. The characterization of cis,trans-W₂Cl₄(NEt₂)₂(dmpm) ,(1). cis,cis-W₂Cl₄(NEt₂(dmpm) (2), cis,trans-W₂Cl₄(NBu₂)₂(dmpm) (3), cis,cis-W₂Cl₄(NBu₂)₂(dmpm) (4a, 4b), cis,cis-W₂Cl₄(NHex₂(dmpm) (5), cis,trans-W₂Cl₄(NEt₂)₂(dmpe) (6), and cis,trans-W₂Cl₄(NBu₂)₂(dmpe) (7) has been accomplished by X-ray crystallography. Pertinent crystal data are as follows: for 1, monoclinic space group C2/c, a = 33.210(3) ?, b = 8.725(4) ?, c = 17.052(4) ?, β= 100.44(1)°, Z = 8; for 2, monoclinic space group P2₁/c, a = 8.760(3) ?, b = 21.028(8) ?, c = 12.778(5) ?, β= 91.77(3)°, Z = 4; for 3, orthorhombic space group Pbca, a = 14.958(2) ?, b = 15.823(2) ?, c = 27.8014(9) ?, Z = 8; for 4a, C2/c, a = 18.011(4) ?, b = 17.221(4) ?, c = 21.264(6) ?, β= 103.33(2)°, Z = 8; for 4b (4a,b are polymorphic), Pbca, a = 14.772(2) ?, b = 17.188(1) ?, c = 25.370(3) ?, Z = 8; for 5, C2/c, a = 18.368(4) ?, b = 17.060(2) ?, c = 30.414(4) ?, β= 103.96(1)°, Z = 8; for 6, P2₁/c, a = 9.596(2) ?, b = 15.975(2) ?, c = 18.756(4) ?, β = 96.73(1)°, 2 = 4; for 7, monoclinic space group P2₁/n, a = 9.465(1) ?, b = 34.545(7) ?, c = 10.177(4) A, β= 97.220(1)°, Z = 4. Among them is one unprecedented type of geometrical isomer, namely, the cis,trans-isomers of W₂Cl₄P₂N₂ complexes. In order to structurally characterize a trans,trans-isomer for W₂Cl₄(NR₂)₂(L-L) molecules, a bis(diphenylphosphino)ethane (dppe) analogue, trans,trans-W₂Cl₄(NEt₂)₂(dppe) (8), has been prepared, and it crystallizes with a molecule of toluene, in the space group P2₁/n with a = 16.396(3) ?, b = 10.104(2) ?, c = 26.680(2) ?, β= 92.22(1)°, and Z = 4. Each of the compounds 1-8 has an essentially staggered W₂Cl₄P₂N₂ conformation with the W atoms bound by a triple bond. The W-W distances fall within the narrow range 2.314- 2.341 ?. All of them show significant torsion angles in the solid state.

Full text of DOI:10.1021/ic961151z

902
Inorg. Chem. 1997, 36, 902-912
W2Cl4(NR2)2(PR′3)2 Molecules. 5. Preparation and Characterization of W2Cl4(NEt2)2(L-L)
(L-L ) dmpm, dmpe, dppe), W2Cl4(NBu2)2(L-L) (L-L ) dmpm, dmpe), and
W2Cl4(NHex2)2(dmpm). First Complexes with Bridging Diphosphine Ligands in a
cis,trans-Stereochemistry
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 September 18, 1996X
The triply-bonded ditungsten complexes W2Cl4(NEt2)2(L-L) (L-L ) dmpm, dmpe), W2Cl4(NBu2)2(L-L) (L-L )
dmpm, dmpe), and W2Cl4(NHex2)2(dmpm) are formed in the reactions between W2Cl4(NR2)2(NHR2)2 (R ) Et,
Bu, Hex ) n-C6H13) and bis(dimethylphosphino)methane (dmpm) or bis(dimethylphosphino)ethane (dmpe). In
each case, three isomeric forms have been detected in solution by 31P{1H} NMR spectroscopy, and they are
formulated as the trans,trans-, cis,trans-, and cis,cis-isomers. Complexes designated cis,trans have one P atom
of the bridging diphosphine cis to the N atom on one W atom and another P atom trans to the N atom on the
other W atom. The characterization of cis,trans-W2Cl4(NEt2)2(dmpm) (1), cis,cis-W2Cl4(NEt2)2(dmpm) (2),
cis,trans-W2Cl4(NBu2)2(dmpm) (3), cis,cis-W2Cl4(NBu2)2(dmpm) (4a, 4b), cis,cis-W2Cl4(NHex2)2(dmpm) (5),
cis,trans-W2Cl4(NEt2)2(dmpe) (6), and cis,trans-W2Cl4(NBu2)2(dmpe) (7) has been accomplished by X-ray
crystallography. Pertinent crystal data are as follows: for 1, monoclinic space group C2/c, a ) 33.210(3) Å, b
) 8.725(4) Å, c ) 17.052(4) Å, â ) 100.44(1)°, Z ) 8; for 2, monoclinic space group P21/c, a ) 8.760(3) Å,
b ) 21.028(8) Å, c ) 12.778(5) Å, â ) 91.77(3)°, Z ) 4; for 3, orthorhombic space group Pbca, a ) 14.958(2)
Å, b ) 15.823(2) Å, c ) 27.8014(9) Å, Z ) 8; for 4a, C2/c, a ) 18.011(4) Å, b ) 17.221(4) Å, c ) 21.264(6)
Å, â ) 103.33(2)°, Z ) 8; for 4b (4a,b are polymorphic), Pbca, a ) 14.772(2) Å, b ) 17.188(1) Å, c ) 25.370(3)
Å, Z ) 8; for 5, C2/c, a ) 18.368(4) Å, b ) 17.060(2) Å, c ) 30.414(4) Å, â ) 103.96(1)°, Z ) 8; for 6, P21/c,
a ) 9.596(2) Å, b ) 15.975(2) Å, c ) 18.756(4) Å, â ) 96.73(1)°, Z ) 4; for 7, monoclinic space group P21/n,
a ) 9.465(1) Å, b ) 34.545(7) Å, c ) 10.177(4) Å, â ) 97.220(1)°, Z ) 4. Among them is one unprecedented
type of geometrical isomer, namely, the cis,trans-isomers of W2Cl4P2N2 complexes. In order to structurally
characterize a trans,trans-isomer for W2Cl4(NR2)2(L-L) molecules, a bis(diphenylphosphino)ethane (dppe) analogue,
trans,trans-W2Cl4(NEt2)2(dppe) (8), has been prepared, and it crystallizes with a molecule of toluene, in the space
group P21/n with a ) 16.396(3) Å, b ) 10.104(2) Å, c ) 26.680(2) Å, â ) 92.22(1)°, and Z ) 4. Each of the
compounds 1-8 has an essentially staggered W2Cl4P2N2 conformation with the W atoms bound by a triple bond.
The W-W distances fall within the narrow range 2.314-2.341 Å. All of them show significant torsion angles
in the solid state.
Introduction
four complexes of the unprecedented type II have now been
prepared and structurally characterized. The present work is
also an interesting extension of the earlier studies on W2Cl4-
(NHCMe3)2(L-L) and W2Cl4(NR2)2(PR′3)2 type compounds.
The recent syntheses of W2Cl4(NHCMe3)2(L-L) (L-L )
dmpm, dmpe, dppm, dppe)1 and W2Cl4(NR2)2(PR′3)2 (R ) Et,
Bu, Hex; R′3) Me3, Et2H)2 molecules sparked our interest for
the preparation of a new type of complex having the stoichi-
ometry W2Cl4(NR2)2(L-L), where L-L is a bidentate phosphine.
We therefore undertook studies of the reaction of W2Cl4(NR2)2-
(NHR2)2 with some diphosphine ligands.
There are six distinct geometric isomers for d3-d3 complexes
with a W2Cl4P2N2 core in a staggered geometry (where P2 is a
bridging diphosphine), as illustrated in Figure 1. They are
trans,trans- (I), two types of cis,trans- (II and III) and three
types of cis,cis- (IV-VI) isomers. None of these geometrical
isomers has ever been reported, though examples of cis,cis-
W2Cl4(NHCMe3)2(L-L) (L-L ) diphosphines) in a partly
eclipsed geometry1 and trans,trans- and cis,cis-W2Cl4(NHCMe3)2-
(PMe3)2 in a perfect eclipsed geometry3 are known in the
literature. One type I complex, three type IV complexes, and
Experimental Section
General Procedures. All manipulations were carried out under an
atmosphere of dinitrogen or argon. Standard Schlenk and vacuum line
techniques were used. Toluene, hexanes, and THF were purified by
distillation under N2 from potassium/sodium benzophenone ketyl.
Dichloromethane was distilled under N2 from phosphorus pentoxide.
dmpm and dmpe were purchased from Strem Chemicals and used as
received. All dialkylamines and dppe were purchased from Aldrich,
Inc., and used without further purification. WCl4 was prepared by
refluxing WCl6 and W(CO)6 in chlorobenzene,4 and W2Cl6(THF)4 was
prepared according to the literature method using Na-Hg as the
reducing agent.5
Syntheses. (i) W2Cl4(NEt2)2(dmpm). An excess of dmpm (0.12
mL) was added by syringe to a stirred solution of W2Cl4(NEt2)2(NHEt2)2
X Abstract published in AdVance ACS Abstracts, February 1, 1997.
(1) Cotton, F. A.; Dikarev, E. V.; Wong, W. Y. Inorg. Chem. 1997, 36,
(3) (a) Bradley, D. C.; Hursthouse, M. B.; Powell, H. R. J. Chem. Soc.,
Dalton Trans. 1989, 1537. (b) Cotton, F. A.; Yao, Z. J. Cluster Sci.
80.
1994, 5, 11.
(2) Cotton, F. A.; Dikarev, E. V.; Nawar, N.; Wong, W. Y. Inorg. Chem.
1997, 36, 559.
(4) Schrock, R. R.; Sturgeoff, L. G.; Sharp, P. R. Inorg. Chem. 1983, 22,
2801.
S0020-1669(96)01151-2 CCC: $14.00 © 1997 American Chemical Society

W2Cl4(NR2)2(PR′3)2 Molecules
Inorganic Chemistry, Vol. 36, No. 5, 1997 903
(ii) W2Cl4(NBu2)2(dmpm). To the tetrahydrofuran solution (15 mL)
of W2Cl4(NBu2)2(NHBu2)2 (from 0.50 g WCl4)2 was added excess
dmpm (0.12 mL) via syringe, and the color of the solution became
dark-brown in a few minutes. As in (i), the 31P{1H} NMR spectrum
of this solution mixture again indicated that three distinct isomers of
W2Cl4(NBu2)2(dmpm) were present. The reaction mixture was stirred
for about 1 h, after which all the volatile components were removed
under vacuum. The dark red-brown residue was first extracted with
warm hexanes (10 mL), from which some tiny red crystals of 3 of
good X-ray quality (40 mg, 6%) were obtained by keeping the hexanes
extract in a freezer at ca. -15 °C for several days. No attempts were
made to optimize the yield of 3 in this reaction. The remaining residue
was then redissolved in hot toluene (15 mL), and isomeric hexanes
was carefully layered on this deep red solution. This layered mixture
was left undisturbed for 1 week, producing cis,cis-W2Cl4(NBu2)2(dmpm)
(4a,b) in two polymorphic forms with the overall yield of about 52%,
based on WCl4.
For the trans,trans-isomer, 31P{1H} NMR data (C6D6 + toluene +
1
2
THF, 19 °C, δ): -3.15 (s, JW-P ) 56 Hz, JP-P ) 12.2 Hz).
For 3, 31P{1H} NMR data (C6D6 + toluene + THF, 19 °C, δ): -1.06
2
2
(d, JP-P ) 101.4 Hz, trans-P), 1.56 (d, JP-P ) 101.4 Hz, cis-P).
For 4, IR data (cm-1): 1414 (w), 1296 (w), 1283 (w), 1261 (vs),
1171 (w), 1094 (vs, br), 1020 (vs, br), 957 (m), 940 (m), 901 (w), 872
(w), 853 (w), 801 (vs), 744 (w).
1H NMR data (C6D6, 24 °C, δ): 0.88-0.96 (m, 10H, distal CH3 +
NCH2(CH2)2CH3), 1.05-1.22 (m, 20H, proximal CH3 + PMe2
+
NCH2(CH2)2CH3), 1.67 (m, br, 4H, NCH2(CH2)2CH3), 1.90 (virtual t,
6H, PMe2), 2.18 (m, 2H, distal NCH2(CH2)2CH3), 2.72 (m, 2H, distal
NCH2(CH2)2CH3), 2.91 (t, J ) 10 Hz, 2H, PCH2P), 4.13 (m, 2H,
proximal NCH2(CH2)2CH3), 6.75 (m, 2H, proximal NCH2(CH2)2CH3).
31P{1H} NMR data (C6D6 + toluene + THF, 19 °C, δ): 4.73 (s,
Figure 1. The six possible geometrical isomers for W2Cl4(NR2)2(L-
L) molecules.
prepared by reaction of W2Cl6(THF)4 (from 0.50 g of WCl4) with
diethylamine in tetrahydrofuran (15 mL).2 The solution started to turn
dark-brown, and in situ monitoring by 31P{1H} NMR spectroscopy of
a sample of the mixture at the very beginning of the experiment (within
10 min) showed the presence of trans,trans- and cis,trans-isomers in
the approximate proportion 72:28, respectively, based on integrated
intensities of the 31P{1H} NMR spectral peaks at room temperature.
As time passed, three isomers corresponding to trans,trans-, cis,trans-
and cis,cis-stereochemistry appeared at the same time in the mixture.
After about 1 h of stirring, the solvent and other volatile components
were removed under vacuum. The residual solid was redissolved in
hot toluene (10 mL) to give a deep red solution, and 15 mL of hexanes
was layered on it. Bright red microcrystalline cis,cis-W2Cl4-
(NEt2)2(dmpm) (2) (0.35 g, 58% based on WCl4) and a tiny amount of
dark-red crystals of cis,trans-W2Cl4(NEt2)2(dmpm) (1) (24 mg, 4%)
were observed in the Schlenk tube after 1 day at room temperature.
Attempts to isolate and crystallize the trans,trans-isomer were unsuc-
cessful so far, and no attempts were made to optimize the yield of 1 in
this reaction. Single crystals of 2 were obtained by slow diffusion of
hexanes into a solution of 2 in dichloromethane at room temperature
for 2 days.
2
1JW-P ) 150 Hz, JP-P ) 74.9 Hz).
FAB/DIP (NBA, neat, m/z): 902 ([M]+), 866 ([M - Cl]+), 774 ([M
- NBu2]+), 738 ([M - 2Cl]+), 646 ([M - 2NBu2]+).
(iii) W2Cl4(NHex2)2(dmpm). The synthesis of W2Cl4(NHex2)2(dmpm)
followed a similar course to that for (i) and (ii). Upon addition of
dmpm to a solution of W2Cl4(NHex2)2(NHHex2)2 (from 0.50 g of WCl4)
in tetrahydrofuran (15 mL),2 the 31P{1H} NMR spectrum initially
revealed a mixture of trans,trans- and cis,cis-isomers in solution in
ratio of 76:24 after 10 min at room temperature. After 1 h of stirring,
all the volatile components of the slurry were removed under reduced
pressure. Initial hexanes extraction (15 mL) of the resulting residue
led to immediate crystallization of irregular orange-red microcrystals
of 5 at room temperature as identified by 31P{1H} NMR spectroscopy.
The residue was extracted with a minimum volume of toluene (10 mL),
and hexanes were layered on this solution. However, no crystals were
obtained in this way. A second crop of red crystals of 5 suitable for
X-ray diffraction studies was then obtained from the toluene/hexanes
solvent mixture at -15 °C after 1 week. The overall yield of 5 was
about 55%, based on starting WCl4. However, no crystals were yet
available for the other two isomers.
For the trans,trans-isomer, 31P{1H} NMR data (C6D6 + THF, 19
For the trans,trans-isomers, 31P{1H} NMR data (C6D6 + THF, 19
1
2
°C, δ): -1.74(s, JW-P ) 57 Hz, JP-P ) 13.0 Hz).
1
2
°C, δ): -2.00 (s, JW-P ) 57 Hz, JP-P ) 13.0 Hz).
For 1, 31P{1H} NMR data (C6D6 + THF, 19 °C, δ): -0.45 (d, 2JP-P
For the cis,trans-isomer, 31P{1H} NMR data (C6D6 + THF, 19 °C,
2
) 101.8 Hz, trans-P), 2.68 (d, JP-P ) 101.8 Hz, cis-P).
2
2
δ): -0.32 (d, JP-P ) 101.4 Hz, trans-P), 2.76 (d, JP-P ) 101.4 Hz,
cis-P).
For 5, IR data (cm-1): 1418 (w), 1296 (w), 1282 (w), 1260 (s),
1150 (w), 1092 (s, br), 1019 (s, br), 957 (m), 938 (m), 873 (w), 799
(vs).
For 2, IR data (cm-1): 1409 (w), 1366 (ms), 1354 (m), 1294 (w),
1284 (m), 1261 (s), 1185 (w), 1153 (w), 1144 (w), 1099 (s), 1080 (s),
1018 (s), 1007 (s), 950 (ms), 935 (s), 895 (vw), 879 (w), 873 (w), 845
(w), 803 (vs), 747 (w).
1H NMR data (CDCl3, 24 °C, δ): 0.98 (t, J ) 7.1 Hz, 6H, distal
CH3), 1.46 (t, J ) 7.1 Hz, 6H, proximal CH3), 1.49 (t, J ) 4.8 Hz, 6H,
PMe2), 2.23 (t + m, J ) 4.8 Hz, 8H, PMe2 + distal NCH2CH3), 2.74
(m, 2H, distal NCH2CH3), 3.70 (t, J ) 10.6 Hz, 2H, PCH2P), 4.37 (m,
2H, proximal NCH2CH3), 6.28 (m, 2H, proximal NCH2CH3).
31P{1H} NMR data (C6D6 + THF, 19 °C, δ): 5.86 (s, 1JW-P ) 150
1H NMR data (C6D6, 24 °C, δ): 0.76 (virtual t, 6H, distal CH3),
0.91 (m, 14H, proximal CH3 + NCH2(CH2)4CH3), 1.10(virtual t, J )
3.9 Hz, 6H, PMe2), 1.13-1.60 (m, br, 16H, NCH2(CH2)4CH3), 1.92
(virtual t, J ) 4.7 Hz, 6H, PMe2), 2.23 (m, 2H, distal NCH2(CH2)4CH3),
2.50 (m, 8H, NCH2(CH2)4CH3), 2.80 (m, 2H, distal NCH2(CH2)4CH3),
2.94 (t, J ) 10.5 Hz, 2H, PCH2P), 4.18 (m, 2H, proximal NCH2(CH2)4-
CH3), 6.75 (m, 2H, proximal NCH2(CH2)4CH3).
2
Hz, JP-P ) 76.7 Hz).
FAB/DIP (NBA, CH2Cl2, m/z): 790 ([M]+), 755 ([M - Cl]+), 718
([M - 2Cl]+ or [M - NEt2]+), 681 ([M - 3Cl]+ or [M - Cl - NEt2]+).
31P{1H} NMR data (C6D6 + THF, 19 °C, δ): 5.74 (s, 1JW-P ) 149
2
Hz, JP-P ) 76.2 Hz).
FAB/DIP (NBA, neat, m/z): 1014 ([M]+), 978 ([M - Cl]+), 830
(5) (a) Chisholm, M. H.; Eichhorn, B. W.; Folting, K.; Huffman, J. C.;
Ontiveros, C. D.; Streib, W. E.; Van Der Sluys, W. G. Inorg. Chem.
1987, 26, 3182. (b) Sharp, P. R.; Schrock, R. R. J. Am. Chem. Soc.
1980, 102, 1430.
([M - NHex2]+), 794 ([M - Cl - NHex2]+).
(iv) W2Cl4(NEt2)2(dmpe). Similar procedures to those for (i) were
followed to prepare W2Cl4(NEt2)2(dmpe) using dmpe (0.13 mL, >1

904 Inorganic Chemistry, Vol. 36, No. 5, 1997
Cotton et al.
equiv) instead of dmpm. The reaction mixture immediately after mixing
of the reactants was shown by 31P{1H} NMR spectroscopy to contain
a mixture of trans,trans-, cis,trans-, and cis,cis-isomers in the ap-
proximate proportion 75:24:1. Stirring was continued for 1 h, after
which the solvent and other volatile components were removed in
Vacuo. The residue was then extracted with warm hexanes (20 mL),
and the bright red solution was concentrated and allowed to stand at
room temperature for 3-4 days to afford a first crop of red plate-
shaped crystals of trans,trans-W2Cl4(NEt2)2(dmpe) as identified by
31P{1H} NMR spectroscopy and mass spectrometry. A second crop
of red crystals was obtained by keeping the supernatant liquid at 0 °C
for 2 days. The overall yield was about 51%. In fact, X-ray data
collection has been carried out for these crystals four times and each
case led to an orthorhombic or tetragonal crystal system. However,
attempts to solve the structure have met with little success, probably
due to the occurrence of superlattices for the crystals. The remaining
residue was dissolved in toluene (10 mL) to give an orange-red solution.
Orange-red crystalline solids of 6 (0.11 g, 18%) were obtained upon
cooling a concentrated toluene solution to 0 °C for 2-3 days. Single
crystals of 6 were grown by slow diffusion of hexanes into a
dichloromethane solution of 6 at room temperature for 2 days, but slight
decomposition also took place to leave some brown precipitates.
Following toluene extraction, the remaining residue was further
dissolved in CH2Cl2. The 31P{1H} spectrum of this CH2Cl2 solution
shows a significant amount of cis,cis-W2Cl4(NEt2)2(dmpe), but this
complex readily undergoes oxidation in chlorinated solvents at ambient
temperature.
orange-red crystals of 7 (71 mg, 10%) formed in 2 days at room
temperature. Attempts to isolate the cis,cis-isomer are so far unsuc-
cessful.
For the trans,trans-isomer, IR data (cm-1): 1419 (s), 1363 (m), 1300
(ms), 1284 (ms), 1260 (w), 1225 (vw), 1156 (ms), 1115 (m), 1106
(m), 1074 (m), 1051 (vw), 1018 (m), 998 (ms), 952 (vs), 934 (vs), 916
(vs), 897 (s), 882 (w), 872 (vw), 844 (ms), 808 (w), 796 (m), 780 (w),
742 (s), 711 (s), 643 (s).
1H NMR data (C6D6, 24 °C, δ): 0.79 (d, J ) 6.8 Hz, 6H, PMe2),
0.82 (t, J ) 7.2 Hz, 6H, distal CH3), 1.07 (t, J ) 7.2 Hz, 6H, proximal
CH3), 1.23 (m, NCH2(CH2)4CH3 and part of CH2 protons of
Me2P(CH2)2PMe2), 1.67 (d, J ) 9.2 Hz, 6H, PMe2), 1.50-1.88 (m, br,
NCH2(CH2)4CH3), 2.04 (d, J ) 10.4 Hz, CH2 protons of Me2P(CH2)2-
PMe2), 2.57 (m, 2H, distal NCH2(CH2)4CH3), 3.10 (m, 2H, distal
NCH2(CH2)4CH3), 4.77 (m, 2H, proximal NCH2(CH2)4CH3), 5.98 (m,
2H, proximal NCH2(CH2)4CH3).
1
31P{1H} NMR data (C6D6, 19 °C, δ): 6.16 (s, JW-P ) 112 Hz,
3JP-P ) 23.0 Hz).
FAB/DIP (NBA, C6H6, m/z): 916 ([M]+), 881 ([M - Cl]+), 788
([M - NBu2]+), 751 ([M - Cl - NBu2]+), 716 ([M - 2Cl - NBu2]+),
661 ([M - 2NBu2]+).
For 7, IR data (cm-1): 1422 (vw), 1412 (vw), 1383 (m), 1303 (w),
1285 (w), 1261 (ms), 1160 (w), 1095 (s), 1020 (s), 947 (m), 934 (m),
918 (w), 900 (w), 875 (vw), 801 (s), 744 (w), 715 (w), 667 (vw), 643
(vw).
1H NMR data (CDCl3, 24 °C, δ): 0.83 (m), 0.93-1.27 (m), 1.36-
1.61 (m), 1.82 (d, J ) 8.8 Hz, 3H, PMe2), 1.97 (d, J ) 8.8 Hz, 3H,
PMe2), 2.08-2.99 (m, distal NCH2(CH2)4CH3), 4.59 (m, 1H, proximal
NCH2(CH2)4CH3), 4.90 (m, 1H, proximal NCH2(CH2)4CH3), 5.20 (m,
1H, proximal NCH2(CH2)4CH3), 5.89 (m, 1H, proximal NCH2(CH2)4CH3).
The same reaction has also been carried out using a pure crystalline
sample of cis,cis-W2Cl4(NEt2)2(NHEt2)2, and the results were essentially
the same.
For the trans,trans-isomer, IR data (cm-1): 1417 (w), 1356 (vw),
1300 (w), 1282 (w), 1261 (vs), 1185 (vw), 1148 (sh), 1095 (vs), 1019
(vs), 946 (m), 935 (w), 880 (m), 869 (sh), 799 (vs), 740 (vw), 668
(vw), 644 (vw).
1H NMR data (C6D6, 24 °C, δ): 0.78 (d, J ) 8.9 Hz, 6H, PMe2),
1.01 (m, 8H, distal CH3 + CH2 protons of Me2P(CH2)2PMe2), 1.48 (t,
J ) 7.1 Hz, 6H, proximal CH3), 1.67 (d, J ) 9.2 Hz, 6H, PMe2), 2.03
(d, J ) 9.2 Hz, 2H, CH2 protons of Me2P(CH2)2PMe2), 2.59 (m, 2H,
distal NCH2CH3), 2.92 (m, 2H, distal NCH2CH3), 4.66 (m, 2H, proximal
NCH2CH3), 5.87 (m, 2H, proximal NCH2CH3).
1
31P{1H} NMR data (C6D6, 19 °C, δ): 6.03 (d, JW-P ) 140 Hz,
3JP-P ) 32.7 Hz, trans-P), 9.34 (d, 1JW-P ) 293 Hz, 3JP-P ) 32.7 Hz,
cis-P).
FAB/DIP (NBA, neat, m/z): 916 ([M]+), 881 ([M - Cl]+), 788 ([M
- NBu2]+), 751 ([M - Cl - NBu2]+), 660 ([M - 2NBu2]+).
For the cis,cis-isomer, 31P{1H} NMR data (C6D6 + toluene, 19 °C,
1
3
δ): 10.74 (s, JW-P ) 303 Hz, JP-P ) 45.9 Hz).
(vi) trans,trans-W2Cl4(NEt2)2(dppe) (8). dppe (0.30 g, >1 equiv)
was dissolved in toluene (5 mL) and added via cannula to a solution
of W2Cl4(NEt2)2(NHEt2)2 prepared in situ from 0.50 g of WCl4 in
tetrahydrofuran (15 mL). The 31P{1H} NMR spectrum of the reaction
mixture indicated that compound 8 was the sole product (as identified
by X-ray diffraction) and no other isomers were observed even after 1
day stirring or heating. After 1 h, the solvent was removed under
vacuum and the residue extracted with hot toluene to afford a deep red
solution. An abundant crop of red needles of 8 of good X-ray quality
(0.41 g, 51% based on WCl4) was obtained by slow diffusion of hexanes
into the toluene solution at room temperature for 15 h. However,
compound 8 was readily oxidized (or disproportionated) in solutions
at room temperature to form a pink solution. We were able to identify
one of the decomposition products to be [WOCl(dppe)2]+ on the basis
of 31P{1H} NMR and UV-vis spectral data.6
1
31P{1H} NMR data (C6D6, 19 °C, δ): 6.14 (s, JW-P ) 112 Hz,
3JP-P ) 23.0 Hz).
FAB/DIP (NBA, C6H6, m/z): 804 ([M]+), 769 ([M - Cl]+), 733
([M - 2Cl]+ or [M - NEt2]+), 695 ([M - 3Cl]+ or [M - Cl - NEt2]+),
660 ([M - 2Cl - NEt2]+).
For 6, IR data (cm-1): 1494 (w), 1418 (m), 1354 (m), 1300 (m),
1284 (m), 1261 (w), 1183 (w), 1158 (vw), 1144 (w), 1097 (m), 1066
(w), 1038 (w), 1023 (vw), 1000 (ms), 947 (vs), 931 (s), 894 (w), 883
(m), 841 (w), 797 (s), 744 (m), 733 (ms), 714 (ms), 696 (w), 644 (m).
1H NMR data (CDCl3, 24 °C, δ): 1.05-1.23 (m), 1.31-1.54 (m),
1.82 (d, J ) 9.4 Hz, 3H, PMe2), 1.97 (d, J ) 9.4 Hz, 3H, PMe2), 2.30-
3.08 (m, br, distal NCH2CH3), 4.77 (m, 1H, proximal NCH2CH3), 5.03
(m, 1H, proximal NCH2CH3), 5.26 (m, 1H, proximal NCH2CH3), 5.92
(m, 1H, proximal NCH2CH3).
IR data (cm-1): 3061 (w), 3043 (w), 1495 (m), 1484 (m), 1433 (s),
1407 (w), 1356 (m), 1299 (vw), 1287 (vw), 1261 (m), 1186 (m), 1160
(w), 1149 (w), 1100 (s), 1090 (m), 1075 (w), 1064 (w), 1038 (w), 1027
(w), 1002 (m), 920 (vw), 879 (w), 862 (m), 835 (w), 800 (s), 750 (s),
744 (s), 740 (s), 735 (s), 705 (s), 693 (s), 677 (m), 668 (w).
1H NMR data (C6D6, 24 °C, δ): 0.87 (t, J ) 7.0 Hz, 6H, distal
CH3), 1.50 (t, J ) 7.0 Hz, 6H, proximal CH3), 2.33 (virtual t, J ) 9.8
Hz, 2H, P(CH2)2P), 2.37 (m, 2H, distal NCH2CH3), 2.74 (m, 2H, distal
NCH2CH3), 3.17 (virtual t, J ) 9.8 Hz, 2H, P(CH2)2P), 4.78 (m, 2H,
proximal NCH2CH3), 6.01 (m, 2H, proximal NCH2CH3), 6.75-7.36
1
31P{1H} NMR data (C6D6, 19 °C, δ): 5.58 (d, JW-P ) 141 Hz,
3JP-P ) 32.5 Hz, trans-P), 8.92 (d, 1JW-P ) 292 Hz, 3JP-P ) 32.5 Hz).
FAB/DIP (NBA, neat, m/z): 804 ([M]+), 769 ([M-Cl]+), 733 ([M
- 2Cl]+ or [M - NEt2]+), 695 ([M - 3Cl]+ or [M - Cl - NEt2]+).
For the cis,cis-isomer, 31P{1H} NMR data (C6D6 + toluene, 19 °C,
1
3
δ): 10.42 (s, JW-P ) 303 Hz, JP-P ) 47.5 Hz).
(m, 20H, Ph).
(v) W2Cl4(NBu2)2(dmpe). Compound W2Cl4(NBu2)2(dmpe) was
prepared in a similar manner as W2Cl4(NEt2)2(dmpe) using W2Cl4-
(NBu2)2(NHBu2)2 as the starting material instead. Upon the addition
of dmpe (0.13 mL) and with similar work-up procedures using
extraction into hexanes (20 mL), an abundant crop of red crystals of
trans,trans-W2Cl4(NBu2)2(dmpe) (0.40 g, 57%) was obtained by cooling
a concentrated hexanes solution to ca. 0 °C for 1 week. As for the
analogous trans,trans-W2Cl4(NEt2)2(dmpe) complex, no structure solu-
tion has yet been available for these crystals. When hexanes were
layered on the toluene extract of the remaining residue, plate-shaped
1
31P{1H} NMR data (C6D6 + CH2Cl2, 19 °C, δ): 9.47 (s, JW-P
)
3
80 Hz, JP-P ) 12.8 Hz).
FAB/DIP (NBA, neat, m/z): 1051 ([M]+), 1016 ([M - Cl]+), 980
([M - 2Cl]+ or [M - NEt2]+), 945 ([M - 3Cl]+ or [M - Cl - NEt2]+).
Physical Measurements. The IR spectra were recorded on a Perkin-
Elmer 16PC FT-IR spectrophotometer as Nujol mulls between KBr
plates. 1H NMR spectral measurements were performed on a Varian
(6) Chiu, K. W.; Lyons, D.; Wilkinson, G. Polyhedron 1983, 2, 803.

W2Cl4(NR2)2(PR′3)2 Molecules
Inorganic Chemistry, Vol. 36, No. 5, 1997 905
XL-200 spectrometer operating at 200 MHz. 1H NMR chemical shifts
are referenced to the residual proton impurity in the deuterated solvent.
The 31P{1H} NMR data (81 MHz) were obtained at room temperature
on a Varian XL-200 broad band spectrometer with the chemical shift
values referenced externally and are reported relative to 85% H3PO4/
D2O. The FAB/DIP (DIP ) direct insertion probe) 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 either by dissolving neat solid compound in m-
nitrobenzyl alcohol (NBA) matrix or mixing a solution of the compound
in CH2Cl2 or C6H6 with an 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.
X-ray Crystallographic Procedures. Single crystals of compounds
1-8 were obtained as described in the Experimental Section. Geo-
metric and intensity data were collected on the following diffractome-
ters: Rigaku AFC7R (1), Rigaku AFC5R (2 and 8‚C7H8), Enraf-Nonius
CAD-4S (5‚C7H8 and 6‚CH2Cl2), and Enraf-Nonius FAST (3, 4a,b,
7). Detailed procedures have previously been described.1,2 For the
crystals on the CAD-4S and Rigaku diffractometers, unit cells were
determined by using search, center, index, and least-squares routines.
The Laue classes and lattice dimensions were verified by axial
oscillation photography. The intensity data were corrected for Lorentz
and polarization effects and for decay where necessary. Empirical
absorption corrections based on a series of Ψ scans were also applied.7
For the crystals on the FAST diffractometer, a preliminary data
collection was first carried out to afford all parameters and an orientation
matrix. Fifty reflections were used in cell indexing and 250 reflections
in cell refinement. Axial images were used to confirm the Laue group
and cell dimensions. All calculations were performed on a DEC 3000-
800 AXP workstation. The coordinates of W atoms for all structures
were determined by direct methods as programmed in SHELXS-868
or SHELXTL.9 The positions of the remaining non-hydrogen atoms
were located using subsequent sets of least-squares refinement cycles
followed by difference Fourier syntheses using the SHELXL-93
structure refinement program.10 These positions were initially refined
with isotropic displacement parameters and then with anisotropic
displacement parameters to convergence. Except for compounds 1 and
6‚CH2Cl2, hydrogen atoms were included in the structure factor
calculations at idealized positions in each model and were allowed to
ride on the neighboring carbon atoms. Crystallographic data and
refinement results for 1-8 are summarized in Table 1. Tables 2 and
4 list the selected bond distances and angles for the cis,trans- and cis,cis-
isomers, respectively. Tables 3 and 5 tabulate the important torsional
angles about the W-W axis for 1-7. The important molecular
parameters for 8 are presented in Table 6. Tables of positional and
isotropic parameters, 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,trans-W2Cl4(NEt2)2(dmpm) (1). A dark-red crystal with the
approximate dimensions of 0.50 × 0.10 × 0.10 mm was mounted and
sealed inside a Lindemann capillary. The unit cell constants were
determined from 25 reflections in the range 12 < 2θ < 17°. Data
collection was carried out with an ω-2θ scan motion in the range 4 <
2θ < 48°. There was no observable decay during the data collection.
Systematic absences narrowed the choice of space groups to C2/c and
Cc. The centrosymmetric space group, C2/c, was selected for initial
(7) (a) North, A. C. T.; Phillips, D. C.; Mathews, F. S. Acta Crystallogr.,
Sect. A 1968, A24, 351. (b) TEXSAN: Crystal Structure Analysis
Package, Molecular Structure Corp., Houston, TX, 1985 and 1992.
(8) Sheldrick, G. M. In Crystallographic Computing 3; Sheldrick, G. M.,
Kruger, C., Goddard, R., Eds.; Oxford University Press: Oxford, U.K.,
1985; p 175.
(9) SHELXTL V. 5, Siemens Industrial Automation Inc., 1994.
(10) Sheldrick, G. M. In Crystallographic Computing 6; Flack, H. D.,
Parkanyi, L., Simon, K., Eds.; Oxford University Press: Oxford, U.K.,
1993, p 111.

906 Inorganic Chemistry, Vol. 36, No. 5, 1997
Cotton et al.
refinement, and this choice proved satisfactory. Hydrogen atoms were
located from difference Fourier maps and were refined. The largest
remaining peak in the final difference Fourier map was 0.74 e/Å3.
cis,cis-W2Cl4(NEt2)2(dmpm) (2). A red crystal with dimensions
of 0.35 × 0.15 × 0.10 mm was mounted on the top of a glass fiber
with epoxy cement. Centering, indexing, and a least-squares calculation
on the 25 reflections with 58 < 2θ < 78 ° (Cu KR radiation) gave a
monoclinic crystal system. The intensity data were gathered by the
ω-2θ scan method in the range 8 < 2θ < 120°. No crystal decay
was observed. The space group P21/c was assigned from systematic
absences. The largest peak in the difference Fourier map was 2.76
e/Å3, lying 1.28 Å from W atom.
cis,trans-W2Cl4(NBu2)2(dmpm) (3). A tiny red block of dimensions
0.18 × 0.13 × 0.13 mm was mounted with silicone grease on the tip
of a quartz fiber and immediately placed in a stream of cold nitrogen
at -60 °C. The intensity data were collected with an area detector for
4 < 2θ < 50°. The data were corrected for Lorentz and polarization
effects by the MADNES program.11 Systematic absences in the data
uniquely determined the space group to be Pbca. The data were
corrected for absorption anisotropy effects using a local adaptation of
the program SORTAV.12 All the non-hydrogen atoms were refined
anisotropically. The final difference Fourier map showed no significant
peaks other than those located in the vicinity of the W atoms.
cis,cis-W2Cl4(NBu2)2(dmpm) (4a,b). Crystals of 4a,b obtained by
slow diffusion of hexanes into the CH2Cl2 solution were separated under
a microscope on the basis of the different shapes of the crystals (red-
brown blocks for 4a and red needles for 4b). For 4a, a red-brown
block-shaped crystal of dimensions 0.13 × 0.08 × 0.05 mm was
selected and mounted on the end of a quartz fiber with grease. Data
collection was carried out in the range 4 < 2θ < 50°. The space group
C2/c was chosen and confirmed by successful solution and refinement
of the structure. Direct methods led to the location of the positions of
W(1) and W(2) of two crystallographically independent molecules. The
rest of the structure was developed in a series of alternating difference
Fourier maps and least-squares refinements. No absorption corrections
were applied. Anisotropic displacement parameters were used for all
the non-hydrogen atoms. The final difference map contained several
small “ghost” peaks in close proximity to the heavy atoms, but no effort
was made to correct for this problem.
For 4b, a red needle with dimensions of 0.50 × 0.08 × 0.05 mm
was mounted on the tip of a quartz fiber with grease and kept at -60
°C throughout the experiment. The intensity data were collected for 4
< 2θ < 50°. Systematic absences in the data led to the space group
Pbca. Direct methods revealed the location of two W atoms of a
dinuclear unit. The use of alternating difference Fourier maps and least-
squares refinements gave the positions of all the remaining non-
hydrogen atoms. The program SORTAV was used to correct for
absorption. All non-hydrogen atoms were refined anisotropically. The
final difference map was essentially featureless, the largest peaks being
associated with the W atoms.
cis,cis-W2Cl4(NHex2)2(dmpm) (5). A red block-shaped crystal with
dimensions of 0.35 × 0.23 × 0.18 mm was selected and fixed on the
tip of a quartz fiber with grease at -100 °C in the diffractometer.
Indexing based on 24 reflections resulted in a monoclinic cell and the
cell parameters were further refined in the range 27 < 2θ < 31°. The
intensity data were gathered by the ω-θ scan technique for 4 < 2θ <
46°. No significant decay was found during the data collection. 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 toluene molecules,
and there were eight C7H8 molecules per unit cell. After the heavy
atoms had been refined anisotropically, it became apparent that all four
hexyl chains of both independent molecules were disordered. This
disorder was modeled by constraining the displacement parameters to
be equal and restraining the chemically equivalent bonds to be
approximately equal. Also, the site occupany factors were allowed to
vary but were constrained so that the sum equaled to 1. The resulting
model yielded reasonable bond distances and angles. All the nondis-
ordered non-hydrogen atoms were then refined anisotropically. The
final difference electron density map had no significant features other
than several small peaks close to W atoms.
cis,trans-W2Cl4(NEt2)2(dmpe) (6). A red block-shaped crystal
having dimensions of 0.50 × 0.35 × 0.28 mm was mounted on the
top of a quartz fiber with grease. A monoclinic cell was obtained based
on the 25 reflections with 2θ values 36-40°. The intensities of all
reflections with 2θ values in the range 4-54° were measured by the
ω-θ scan technique. The space group P21/c was identified uniquely
from the systematic absences in the data. After all the non-hydrogen
atoms of the whole dinuclear complex had been located, the difference
Fourier map still had three significant peaks which appeared to be a
CH2Cl2 solvent molecule. The non-hydrogen atoms in both molecules
were refined anisotropically. Hydrogen atoms were then included and
refined. This model was refined to convergence and the final difference
electron density map revealed only one peak above 1 e/Å3, lying 1.10
Å from W(1).
cis,trans-W2Cl4(NBu2)2(dmpe) (7). An orange-red crystal of di-
mensions 0.30 × 0.15 × 0.10 mm was carefully selected and mounted
on the top of a quartz fiber. The intensity data were measured in the
range 4 < 2θ < 43°. The space group P21/n was determined based on
the systematic absences. Absorption corrections based on the SORTAV
program were applied. The largest remaining peak in the final
difference map was 0.83 e/Å3, located 1.25 Å from W atom.
trans,trans-W2Cl4(NEt2)2(dppe) (8). A red needle-shaped crystal
with dimensions of 0.80 × 0.10 × 0.10 mm was glued on the tip of a
glass fiber with epoxy cement. Compound 8 crystallized in the
monoclinic crystal system based on the 25 reflections with 2θ ranging
from 28 to 35° (Cu KR radiation). An ω-2θ scan method was used
to collect the intensity data for 6 < 2θ < 115°. A significant decay in
intensity was observed during the entire period of data collection, and
an appropriate decay correction was applied. Systematic absences
uniquely determined the space group as P21/n. The difference Fourier
map showed several peaks that could be assigned to be solvent
molecules. These peaks were modeled as toluene molecules. In each
C7H8 molecule, all carbon atoms were found to be disordered over two
sites. All the non-hydrogen atoms, except the carbon atoms for the
toluene solvent molecule, were refined with anisotropic displacement
parameters. A final difference Fourier map revealed that the highest
remaining peak of electron density (0.72 e/Å3) was located near W(1).
Results and Discussion
Synthesis, Solubility and Stability. The preparation of
triply-bonded complexes W2Cl4(NR2)2(L-L) (R ) Et, L-L )
dmpm, dmpe, dppe; R ) Bu, L-L ) dmpm, dmpe; R ) Hex,
L-L ) dmpm) proceeds straightforwardly via reaction of
W2Cl4(NR2)2(NHR2)2 (R ) Et, Bu, Hex) with 1 equiv of the
appropriate bidentate phosphines at room temperature. Reac-
tions involving dmpm or dmpe readily afford products in three
isomeric forms, trans,trans-, cis,trans-, and cis,cis-W2Cl4(NR2)2(L-
L) (R ) Et, Bu, Hex; L-L ) dmpm, dmpe) with proportions
depending on the reaction time as well as the diphosphines and
dialkylamido groups used (Scheme 1). When W2Cl4(NR2)2-
(NHR2)2 (R ) Et, Bu, Hex) and dmpm are allowed to react in
tetrahydrofuran or toluene, the major products are trans,trans-
W2Cl4(NR2)2(dmpm) (R ) Et, Bu, Hex) initially. However,
attempts to isolate this type of isomer are not yet successful.
According to 31P{1H} NMR spectroscopic studies of the reaction
mixture, the concentration of the trans,trans-isomer in each case
gradually decreased with time while the amount of the other
two isomers continuously built up. In each case, all the
trans,trans-isomer eventually disappeared, and thus, the failure,
so far, to isolate the pure trans,trans-isomer can be understood.
When the mixture was allowed to stand at room temperature,
only the cis,cis-isomer, as identified by 31P{1H} NMR spec-
troscopy, remained at the end. We believe that the trans,trans-
isomer of the type W2Cl4(NR2)2(dmpm) (R ) Et, Bu, Hex) is
(11) 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 in: Messerschmitt, A.; Pflugrath, J. J. Appl. Crystallogr. 1987,
20, 306.
(12) Blessing, R. H.; Acta Crystallogr., Sect. A 1995, A51, 33.

W2Cl4(NR2)2(PR′3)2 Molecules
Inorganic Chemistry, Vol. 36, No. 5, 1997 907
Scheme 1
the kinetic product. The trans,trans-isomer slowly isomerizes
in solution to form first the cis,trans-isomer and finally the
thermodynamically favored cis,cis-isomer. Moreover, a sample
of cis,cis-isomer was left in CH2Cl2 for 1 week and showed no
indication of isomerization back to either cis,trans- or trans,
trans-isomer. In the case of dmpe, the trans,trans-isomers again
seem to be the kinetically favored products in each case.
However, they are much more thermodynamically stable than
their dmpm counterparts and can be easily isolated by extracting
the products into hexanes. On the other hand, the reaction of
W2Cl4(NEt2)2(NHEt2)2 with another diphosphine ligand having
two carbon atoms linking the phosphorus atoms, namely, dppe,
forms purely the trans,trans-isomer 8 in 51% yield. When a
pure sample of 8 in solution was monitored by 31P{1H} NMR
spectroscopy at room temperature, no evidence of isomerization
to any other isomers was observed which, at first sight, means
that the isomerization barrier might be too high for intercon-
version at ambient temperature (i.e. kinetically stabilized).
Attempts were then made to heat the sample solution up to 80
°C, but the spectrum remained more or less the same. Hence,
compound 8 is both the kinetically and thermodynamically
favored isomer in this case.
The trans,trans-isomers of W2Cl4(NR2)2(dmpe) (R ) Et, Bu)
are very soluble in hexanes. The rest of the compounds exhibit
fair solubility in toluene and benzene and higher solubility in
CH2Cl2. All the compounds appear to be air stable for short
periods of time in the solid state. In solution, they slowly
decompose upon exposure to air. This was evidenced by the
observation of a significant amount of [WOCl(dppe)2]+ in the
31P{1H} NMR spectrum of 8.
Spectroscopic Properties. All complexes of W2Cl4(NR2)2(L-
L) reported here exhibit parent molecular ion peaks M+ in their
mass spectra, and many W2-containing fragment ions were
observed. Losses of chlorine ligands and amido groups are
competitive processes during fragmentation. For all the com-
pounds except 6 and 7, the most abundant fragment ion is
[W2Cl4(NR2)(L-L)]+ in each case. In contrast, the fragment
ions [W2Cl3(NR2)2(dmpe)]+ (R ) Et, Bu) appear as the most
intense peaks in the mass spectra of 6 and 7. It is interesting
to note that fission of the metal-metal bond is not facile for
this kind of complex under the experimental conditions.
The 1H NMR spectra of all the available compounds clearly
show that substitution of both dialkylamino groups by the
Figure 2. 31P{1H} NMR spectra of (a) trans,trans-W2Cl4(NEt2)2(dppe)
in C6D6/CH2Cl2, (b) cis,trans-W2Cl4(NEt2)2(dmpe) in C6D6 and (c)
cis,cis-W2Cl4(NHex2)2(dmpm) in C6D6, at room temperature.
appropriate bidentate phosphines took place. At room temper-
ature, compounds 2, 6, and 8 display well-separated proximal
and distal NEt resonances akin to those reported for W2Cl4-
(NR2)2(PR′3)2 molecules.2 It is noteworthy that, for 6 with a
cis,trans-stereochemistry, each set of proximal and distal NEt
signals is further split into another set due to the different
chemical environment caused by the phosphorus atoms cis and
trans to the NEt2 groups. This makes the interpretation of the
corresponding spectrum more difficult. For those compounds
with NBu2 and NHex2 groups, proximal and distal resonances
were also observed for the CH2CH3 groups. The spectra were,
however, complicated by the signals arising from diphosphine
ligands and other methylene protons. Because of the low
stability of 1 and 3 in all common organic solvents, it was
impossible to obtain decent NMR spectra of these two com-
pounds.
The identities of the three isomeric types of dinuclear complex
observed in this study are readily established by their distinctive
31P{1H} NMR spectra. Figure 2a-c provides representative
31P{1H} NMR spectra for each of the isomers studied. As
expected for ABX (PP183W) systems in cis- and trans-
W2Cl4(NHCMe3)2(PR3)2 molecules,13 both cis,cis- and trans,
trans-isomers consist of strong central singlets flanked by weak
satellites due to 31P-183W coupling. In each case, approximate
P-P coupling constants may be deduced from the satellite
doublets. The spectra of cis,trans-W2Cl4(NR2)2(L-L) molecules
are of particular interest as they provide a unique opportunity
to examine the characteristics of diphosphines on dinuclear
complexes in such an unprecedented bonding mode. The full
(13) Chen, H.; Cotton, F. A.; Yao, Z. Inorg. Chem. 1994, 33, 4255.

908 Inorganic Chemistry, Vol. 36, No. 5, 1997
Cotton et al.
Figure 4. Perspective drawing of cis,trans-W2Cl4(NEt2)2(dmpm) (1).
Atoms are represented by thermal ellipsoids at the 40% probability
level. Carbon atoms are shown as spheres of arbitrary radii.
Figure 3. 31P{1H} NMR spectra of W2Cl4(NHex2)2(dmpm) at various
time intervals in C6D6/THF, showing the interconversion among the
three distinct isomers at room temperature.
proton-decoupled 31P NMR spectrum of 6, shown in Figure 2b,
consists of a set of two intense doublets centered at 5.58 and
8.92 ppm. The upfield and downfield resonances are tentatively
assigned to the phosphorus atom cis and trans to NBu2 groups,
respectively. The assignments were made on the basis of 31P-
183W coupling observed in the spectrum. A notable feature in
this spectrum is the prominence of the set of 183W satellites
and its complexity, relative to those of the cis,cis- and
trans,trans-isomers. The magnitude of the 1JW-P(cis) coupling
(292 Hz) is significantly larger than that for the trans phosphorus
atom (141 Hz), as one might expect.13 It can be seen clearly
that the four intense signals in Figure 2b do not have equal
intensities, the so-called “roof effect”. To obtain such a coupling
scheme, it is necessary to consider an AB system when 183W
coupling is ignored. As defined in Figure 2b, the chemical shifts
for each P atom are given by νcis ) νz +∆ν/2 and νtrans ) νz -
∆ν/2, where ∆ν ) (|(f1 - f4)(f2 - f3)|)1/2 Hz and f1, f2, f3, and
f4 are the resonance frequencies of the four lines of the AB
spectrum.14 Such an AB system thus gives rise to the observed
doublet of doublets with νcis at 8.92 ppm, νtrans at 5.58 ppm
and 3JP-P ) 32.5 Hz. However, due to the poor quality of the
low-intensity portion of the spectrum, the values of the coupling
Figure 5. Perspective drawing of cis,trans-W2Cl4(NBu2)2(dmpm) (3).
Atoms are represented by thermal ellipsoids at the 40% probability
level. Carbon atoms are shown as spheres of arbitrary radii.
constants determined should only be regarded as approximate.
Also, a noteworthy feature is that the JW-P and JP-P values for
each particular type of isomer are relatively insensitive to the
variation of the amido ligands for a given diphosphine used.
As mentioned in the foregoing section, preliminary results
indicate that the relative concentrations of the three isomers of
W2Cl4(NR2)2(dmpm) in solution are dependent on the reaction
time. The results of a run for W2Cl4(NHex2)2(dmpm) in which
the trans,trans-compound was converted to a cis,trans/cis,cis-
mixture in C6D6/THF at room temperature at various times are
shown in Figure 3. It can be seen that the conversion was
completed in 4 days, leaving only the cis,cis-isomer in the
mixture. Although the exact mechanism for this isomerization
is obscure, the reaction is completely reproducible.
Structure and Bonding. The W2Cl4(NR2)2(L-L) compounds
1-8 reported here have been characterized by X-ray crystal-
(14) Friebolin, H. Basic One- and Two-Dimensional NMR Spectroscopy,
2nd ed.; VCH: New York, 1993.

W2Cl4(NR2)2(PR′3)2 Molecules
Inorganic Chemistry, Vol. 36, No. 5, 1997 909
Table 2. Selected Bond Distances (Å) and Angles (deg) for cis,
trans-W2Cl4(NEt2)2(dmpm) (1), cis,trans-W2Cl4(NBu2)2(dmpm) (3),
cis,trans-W2Cl4(NEt2)2(dmpe) (6), and cis,trans-W2Cl4(NBu2)2-
(dmpe) (7)
1
3
6
7
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)
2.3259(5) 2.3261(6) 2.3136(4) 2.3182(8)
2.510(2)
2.654(2)
1.905(6)
1.915(7)
2.397(2)
2.360(2)
2.437(2)
2.375(2)
2.522(3)
2.611(3)
1.90(1)
1.929(9)
2.399(3)
2.365(3)
2.427(3)
2.368(3)
2.518(1)
2.588(1)
1.916(4)
1.936(4)
2.387(1)
2.370(1)
2.433(1)
2.369(1)
2.525(3)
2.596(4)
1.910(9)
1.95(1)
2.391(3)
2.362(3)
2.440(3)
2.374(3)
P(1)-W(1)-N(1)
88.3(2)
89.9(3)
88.4(1)
155.57(4) 155.0(1)
89.0(3)
P(1)-W(1)-Cl(1) 159.11(8) 158.4(1)
P(1)-W(1)-Cl(2) 77.83(8)
N(1)-W(1)-Cl(1) 97.0(2)
N(1)-W(1)-Cl(2) 143.1(2)
Cl(1)-W(1)-Cl(2) 86.02(8)
W(2)-W(1)-P(1) 92.67(5)
W(2)-W(1)-N(1) 106.6(2)
77.7(1)
96.6(3)
143.7(3)
85.1(1)
92.11(7)
104.7(3)
77.73(4)
97.5(1)
143.4(1)
83.62(4)
97.49(3)
103.8(1)
77.3(1)
96.7(3)
144.6(3)
84.2(1)
97.83(8)
103.2(3)
W(2)-W(1)-Cl(1) 105.00(6) 106.0(8)
103.99(3) 104.48(9)
W(2)-W(1)-Cl(2) 108.05(6) 109.62(7) 111.41(3) 110.77(8)
P(2)-W(2)-N(2)
161.9(2)
161.8(3)
79.5(1)
81.5(1)
95.5(3)
92.4(3)
156.8(1)
79.59(4)
79.24(4)
95.7(1)
92.5(1)
144.01(5) 142.8(1)
157.1(3)
78.6(1)
79.3(1)
95.8(3)
93.1(3)
Figure 6. Perspective drawing of cis,trans-W2Cl4(NEt2)2(dmpe) (6).
Atoms are represented by thermal ellipsoids at the 40% probability
level. Carbon atoms are shown as spheres of arbitrary radii.
P(2)-W(2)-Cl(3) 80.26(8)
P(2)-W(2)-Cl(4) 81.71(8)
N(2)-W(2)-Cl(3) 94.1(2)
N(2)-W(2)-Cl(4) 93.4(2)
Cl(3)-W(2)-Cl(4) 143.76(8) 141.8(1)
W(1)-W(2)-P(2) 91.74(5)
W(1)-W(2)-N(2) 106.3(2)
92.12(6)
105.9(3)
97.63(3)
105.3(1)
97.97(8)
104.8(3)
W(1)-W(2)-Cl(3) 110.66(6) 110.84(8) 109.97(3) 109.79(8)
W(1)-W(2)-Cl(4) 101.04(6) 102.67(7) 101.45(4) 102.62(9)
Table 3. Selected Torsion Angles (deg) for cis,trans-W2Cl4-
(NEt2)2(dmpm) (1), cis,trans-W2Cl4(NBu2)2(dmpm) (3), cis,trans-
W2Cl4(NEt2)2(dmpe) (6), and cis,trans-W2Cl4(NBu2)2(dmpe) (7)
1
3
6
7
P(1)-W(1)-W(2)-P(2)
P(1)-W(1)-W(2)-Cl(3)
N(1)-W(1)-W(2)-N(2)
-37.67(7) -38.3(1) -43.71(4) -43.2(1)
42.57(8) 41.3(1) 37.94(4) 37.4(1)
54.4(3)
53.3(4) 49.8(2)
48.5(4)
N(1)-W(1)-W(2)-Cl(3) -46.5(2) -49.1(3) -52.3(1) -53.4(3)
Cl(1)-W(1)-W(2)-N(2) -47.8(2) -48.2(3) -51.7(1) -52.1(3)
Cl(1)-W(1)-W(2)-Cl(4) 49.18(8) 48.1(1) 44.04(5) 44.6(1)
Cl(2)-W(1)-W(2)-P(2)
40.40(8) 39.4(1) 36.00(4) 36.1(1)
Cl(2)-W(1)-W(2)-Cl(4) -41.50(8) -42.4(1) -44.50(4) -44.6(1)
molecules indicated that the bridging ligands do not cause any
special shortness on the observed metal-metal bond lengths in
these d3-d3 dinuclear compounds. The mean value of W-N
distances (1.92 Å) in all molecules is within the range anticipated
for such bonds. The specific characteristics of each complex
and the relationships between them will be explored in the
following paragraphs.
Compounds 1, 3, 6‚CH2Cl2, and 7. Crystals of compounds
1 and 3 conform to the monoclinic space group C2/c and
orthorhombic space group Pbca, respectively, with eight
molecules per unit cell for each complex. Compounds 6 and 7
crystallize in the monoclinic space groups P21/c and P21/n,
respectively, with four molecules per unit cell. The structure
of 6 contains a molecule of CH2Cl2. Perspective views of the
structures of 1, 3, 6 and 7 are depicted in Figures 4-7. The
core structures of all the compounds are very similar, and each
molecule is chiral. The ligand arrangement found in these
complexes belongs to the type II isomer (Figure 1) and has not
previously been reported for other triply-bonded dinuclear
complexes. It provides the first examples of a W2Cl4P2N2 type
molecule in which one WCl2PN unit has a cis arrangement while
the other WCl2PN unit has a trans arrangement. Hence, the
two phosphorus atoms are non-equivalent in the molecule. In
Figure 7. Perspective drawing of cis,trans-W2Cl4(NBu2)2(dmpe) (7).
Atoms are represented by thermal ellipsoids at the 40% probability
level. Carbon atoms are shown as spheres of arbitrary radii.
lography. The molecules possess a common W26+ unit having
eight ligated atoms and geometries based on a W2Cl4P2N2 core.
Each W atom in the molecule is approximately square planar
with two Cl, one P, and one N atoms coordinated to it. The
two pseudoplanar WCl2PN units united by a W-W triple bond
are staggered with respect to each other and the central
(WtW)6+ unit is spanned by a bridging diphosphine. An
interesting difference between various isomeric compounds lies
in the way the two phosphorus atoms of the diphosphine are
bonded to the W atoms with respect to the amido groups. In
no case was any disorder problem of the W2 units in the crystals
encountered. The W-W bond distances span the narrow range
of 2.314-2.341 Å and fall within the range of the bond distances
established for the WtW bond with a σ2π4 ground-state
electronic configuration.15 Comparison between W2Cl4(NR2)2-
2
(PR′3)2 and W2Cl4(NR2)2(L-L) (L-L ) bidentate phosphines)

910 Inorganic Chemistry, Vol. 36, No. 5, 1997
Cotton et al.
Figure 8. Views of the central part of (a, left) cis,trans-W2Cl4(NEt2)2(dmpm) (1), (b, center) cis,cis-W2Cl4(NEt2)2(dmpm) (2), and (c, right) trans,trans-
W2Cl4(NEt2)2(dppe) (8) directly down W-W axis. Ethyl groups, methyl groups, and phenyl rings are omitted for clarity.
Table 4. Selected Bond Distances (Å) and Angles (deg) for cis,cis-
W2Cl4(NEt2)2(dmpm) (2), cis,cis-W2Cl4(NBu2)2(dmpm) (4a,b) and
cis,cis-W2Cl4(NHex2)2(dmpm) (5)
2
4aa
4b
5a
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)
2.332(1)
2.506(3)
2.526(3)
1.918(9)
1.92(1)
2.375(4)
2.391(3)
2.432(3)
2.417(3)
2.341(1) 2.3396(6) 2.340(1)
2.515(5) 2.512(2)
2.529(3)
2.519(3)
1.91(1)
1.93(2)
1.918(8)
1.904(9)
2.406(4) 2.406(3)
2.407(3)
2.411(5) 2.421(3)
2.412(3)
2.399(3)
2.414(3)
P(1)-W(1)-N(1)
P(1)-W(1)-Cl(1)
P(1)-W(1)-Cl(2)
87.3(3)
158.9(1)
77.7(1)
90.3(4)
159.7(2) 159.3(1)
79.2(2)
92.8(4)
143.9(4) 143.4(3)
86.7(2)
92.5(1)
104.4(4) 103.7(2)
88.4(2)
88.3(3)
161.4(1)
79.6(1)
95.0(3)
142.5(3)
87.0(1)
92.25(8)
103.7(3)
79.34(9)
94.5(2)
N(1)-W(1)-Cl(1) 97.5(3)
N(1)-W(1)-Cl(2) 142.9(3)
Cl(1)-W(1)-Cl(2) 86.4(1)
Figure 9. Perspective drawing of cis,cis-W2Cl4(NEt2)2(dmpm) (2).
Atoms are represented by thermal ellipsoids at the 40% probability
level. Carbon atoms are shown as spheres of arbitrary radii.
86.4(1)
92.23(7)
W(2)-W(1)-P(1)
93.15(8)
W(2)-W(1)-N(1) 104.7(3)
difference between W(1)-P(1) and W(2)-P(2) distances in
these four molecules ranges from 0.07 to 0.14 Å (Table 2). This
lengthening of the W-P bond distances is primarily attributed
to the stronger trans influence of NR2 groups compared to
phosphine and chlorine ligands. Another striking structural
feature of these molecules is the twisted configuration. Figure
8a shows a view of the inner part of a molecule of 1 looking
down the W-W bond. This molecule displays a twisted
configuration for the central portion with the torsional angle
P(1)-W(1)-W(2)-P(2) being 37.7° (Table 3). The corre-
sponding torsional angles for 3, 6, and 7 are 38.3, 43.7, and
43.2°, respectively.
W(2)-W(1)-Cl(1) 105.4(1)
106.3(1) 106.91(7) 104.67(8)
W(2)-W(1)-Cl(2) 109.75(9) 110.5(1) 111.04(7) 112.05(9)
P(2)-W(2)-N(2)
P(2)-W(2)-Cl(3)
P(2)-W(2)-Cl(4)
89.8(3)
80.4(1)
162.0(1)
89.0(2)
79.88(9)
161.8(1)
143.2(3)
94.2(2)
N(2)-W(2)-Cl(3) 142.4(3)
N(2)-W(2)-Cl(4) 93.9(3)
Cl(3)-W(2)-Cl(4) 86.0(1)
87.0(1)
W(1)-W(2)-P(2)
91.41(8)
92.29(7)
104.5(3)
110.81(7)
104.21(7)
W(1)-W(2)-N(2) 103.6(3)
W(1)-W(2)-Cl(3) 112.75(9)
W(1)-W(2)-Cl(4) 104.8(1)
a
Distances and angles are the averages for the two independent
molecules of the asymmetric unit.
Compounds 2, 4a, 4b, and 5‚C7H8. Compound 2 crystal-
lizes in the space group P21/c with four molecules per unit cell.
Compounds 4a and 5 both conform to the space group C2/c
with two independent molecules in the asymmetric unit each.
W(1) and W(1A) atoms form one dinuclear unit, and W(2) and
W(2A) atoms form the other molecule. In total, there are eight
W2Cl4(NR2)2(dmpm) molecules in the unit cell in each case.
The crystals of 5 contain eight toluene solvent molecules in
the unit cell. Compound 4b, a polymorph of 4a, crystallizes in
the orthorhombic space group Pbca with eight W(1)-W(2)
dinuclear units per unit cell. The molecular structures of 2,
4a, and 5 are shown in Figures 9-11, respectively.
each case, it is clear that the W(1)-Cl(1) distance is shorter
than the W(1)-Cl(2) distance (average ∆(W-Cl) ) 0.04 Å)
(Table 2). This is, no doubt, a manifestation of the trans
influence which has been observed in many other systems16
including W2Cl4(NHCMe3)2(L-L) (L-L ) diphosphines)1 and
W2Cl4(NR2)2(PR′3)2.2 On the other hand, the W(2)-Cl(3) and
W(2)-Cl(4) distances are comparable to each other. One
notable feature is an increase in the W(2)-P(2) distance relative
to that observed in the cis,cis-counterparts (Vide infra), and the
(15) Cotton, F. A.; Walton, R. A. Multiple Bonds between Metal Atoms,
2nd ed.; Oxford University Press: New York, 1993; see also references
therein.
(16) (a) Cotton, F. A.; Felthouse, T. R. Inorg. Chem. 1981, 20, 3880. (b)
Cotton, F. A.; Extine, M. W.; Felthouse, T. R.; Kolthammer, B. W.
S.; Lay, D. G. J. Am. Chem. Soc. 1981, 103, 4040.
The core structure of each molecule has only C2 symmetry,
and each molecule is chiral. In each case, the central W2Cl4P2N2
core unit has essentially the same structure with the two chlorine
atoms in a cis position in each WCl2PN unit and it is similar to

W2Cl4(NR2)2(PR′3)2 Molecules
Inorganic Chemistry, Vol. 36, No. 5, 1997 911
Table 5. Selected Torsion Angles (deg) for cis,cis-W2Cl4(NEt2)2(dmpm) (2), cis,cis-W2Cl4(NBu2)2(dmpm) (4a,b), and
cis,cis-W2Cl4(NHex2)2(dmpm) (5)
2
4b
4aa
5a
P(1)-W(1)-W(2)-P(2)
P(1)-W(1)-W(2)-Cl(3)
N(1)-W(1)-W(2)-Cl(3)
N(1)-W(1)-W(2)-Cl(4)
Cl(1)-W(1)-W(2)-N(2)
Cl(1)-W(1)-W(2)-Cl(4)
Cl(2)-W(1)-W(2)-P(2)
Cl(2)-W(1)-W(2)-N(2)
-36.9(1)
43.2(1)
-44.8(3)
47.0(3)
42.6(3)
-55.2(1)
41.1(1)
-49.0(3)
-37.33(9)
42.7(1)
-46.2(2)
46.0(2)
45.2(3)
-53.1(1)
42.1(1)
-47.4(3)
P(1)-W(1)-W(1A)-P(1A)
P(1)-W(1)-W(1A)-Cl(2A)
N(1)-W(1)-W(1A)-Cl(2A)
N(1)-W(1)-W(1A)-Cl(1A)
Cl(1)-W(1)-W(1A)-N(1A)
Cl(1)-W(1)-W(1A)-Cl(1A)
Cl(2)-W(1)-W(1A)-P(1A)
Cl(2)-W(1)-W(1A)-N(1A)
-36.3(2)
43.1(2)
-47.8(5)
44.7(5)
44.7(5)
-52.6(2)
43.1(2)
-47.8(5)
-37.3(2)
42.4(1)
-46.3(3)
46.3(3)
46.3(3)
-52.7(2)
42.4(1)
-46.3(3)
a Torsion angles are the averages for the two independent molecules of the asymmetric unit.
Figure 10. Perspective drawing of cis,cis-W2Cl4(NBu2)2(dmpm) (4a).
Atoms are represented by thermal ellipsoids at the 40% probability
level. Carbon atoms are shown as spheres of arbitrary radii.
Figure 12. Perspective drawing of trans,trans-W2Cl4(NEt2)2(dppe) (8).
Atoms are represented by thermal ellipsoids at the 40% probability
level. Carbon atoms are shown as spheres of arbitrary radii. Phenyl
rings are not labeled for clarity.
Table 6. Selected Bond Distances (Å) and Angles (deg) and
Torsion Angles (deg) for trans,trans-W2Cl4(NEt2)2(dppe) (8)
W(1)-W(2)
W(2)-P(2)
W(2)-N(2)
W(2)-Cl(4)
W(2)-Cl(3)
2.3178(6)
2.676(2)
1.906(7)
2.372(2)
2.357(3)
W(1)-P(1)
W(1)-N(1)
W(1)-Cl(1)
W(1)-Cl(2)
2.659(3)
1.910(7)
2.378(2)
2.360(2)
P(1)-W(1)-N(1)
P(1)-W(1)-Cl(2)
N(1)-W(1)-Cl(2)
W(2)-W(1)-P(1)
W(2)-W(1)-Cl(1)
P(2)-W(2)-N(2)
P(2)-W(2)-Cl(4)
N(2)-W(2)-Cl(4)
W(1)-W(2)-P(2)
W(1)-W(2)-Cl(3)
150.8(2)
82.19(8)
97.4(2)
103.71(5)
104.67(6)
158.7(3)
76.49(8)
91.1(3)
P(1)-W(1)-Cl(1)
N(1)-W(1)-Cl(1)
Cl(1)-W(1)-Cl(2)
W(2)-W(1)-N(1)
W(2)-W(1)-Cl(2)
P(2)-W(2)-Cl(3)
N(2)-W(2)-Cl(3)
Cl(3)-W(2)-Cl(4)
W(1)-W(2)-N(2)
W(1)-W(2)-Cl(4)
75.33(8)
91.1(2)
147.17(9)
104.7(2)
103.69(7)
85.19(8)
94.6(3)
141.74(9)
104.3(2)
108.21(7)
Figure 11. Perspective drawing of cis,cis-W2Cl4(NHex2)2(dmpm) (5).
Only the major orientation of the hexyl chains is shown. Atoms are
represented by thermal ellipsoids at the 40% probability level. Carbon
atoms are shown as spheres of arbitrary radii.
96.08(5)
106.89(8)
that observed in W2Cl4(NR2)2(PR′3)2 molecules with mono-
phosphines. A comparison of 2 with 1 reveals several changes
in geometry and subtle changes in the molecular parameters.
The geometric changes are obvious in the drawings shown in
Figures 8a,b. This variation in geometry does not result in a
significant change in the W-W bond length (0.006 Å) but does
cause significant changes in W-P and W-Cl distances (Tables
2 and 4). The changes in W-P and W-Cl distances reflect
the nature of the atoms that are trans to the P or Cl atom. The
W(2)-P(2) bond distances differ by ca. 0.13 Å for 1 and 2.
Both W(2)-Cl(3) and W(2)-Cl(4) distances are also ap-
proximately 0.04 Å longer in 2 than in 1 due to the influence
of the atoms trans to the atoms in question. The structural
characterization of 4a,b and 5 revealed little that is exceptional
compared to 2. The internal parameters for the W2Cl4P2N2 cores
of these four complexes (Table 4) are, not surprisingly, very
similar and, together with the previously reported W2Cl4P2N2
cores of W2Cl4(NR2)2(PR′3)2 molecules, form an interesting
P(1)-W(1)-W(2)-P(2) -38.48(7) P(1)-W(1)-W(2)-Cl(4) 39.26(8)
N(1)-W(1)-W(2)-N(2) -51.5(4) N(1)-W(1)-W(2)-Cl(3) 48.0(2)
Cl(1)-W(1)-W(2)-P(2) 39.66(8) Cl(1)-W(1)-W(2)-Cl(3) -47.14(9)
Cl(2)-W(1)-W(2)-N(2) 50.1(3) Cl(2)-W(1)-W(2)-Cl(4) -45.88(9)
group of d3-d3 ditungsten compounds in a cis,cis-stereochem-
istry. The most obvious difference between them is the
significant change in the torsional angles P-W-W′-P′ by
switching from monophosphines to diphosphines. The com-
plexes studied here with bridging diphosphines show torsional
angles P-W-W′-P′ in the small range 36.3-37.3° (Table 5),
while the corresponding values for W2Cl4(NR2)2(PR′3)2 mol-
ecules lie in the range 126.7-138.0°.
Compound 8. Crystals of 8 conform to the monoclinic space
group P21/n with four molecules per unit cell. There are also
four toluene solvent molecules in the unit cell. Figure 12
displays a perspective drawing of the molecule in its entirety,
and Figure 8c shows a view of the central portion down W-W

912 Inorganic Chemistry, Vol. 36, No. 5, 1997
Cotton et al.
cis,trans-compounds are of particular interest because these are
the first examples of metal-metal-bonded complexes with such
a stereochemistry.
In all the systems studied here, when the diphosphine ligands
substitute NHR2 of W2Cl4(NR2)2(NHR2)2, it is believed that the
kinetic products are the trans,trans-isomers, as evidenced by
31P{1H} NMR spectra. However, we are still unsure of the exact
mechanism for the formation of other isomers in this kind of
reactions and a detailed explanation for this observation cannot
be given at this time. Apparently, there should be some driving
force, either kinetic or thermodynamic, that controls the fractions
of each isomer in the product mixture. Detailed studies of the
isomerization processes have to be pursued so as to determine
what factors such as time, solvent, types of diphosphine used,
or reaction conditions influence the processes and whether they
are reversible.
On the other hand, out of the six possible geometrial isomers
shown in Figure 1, only three of them (I, II, and IV) have been
observed in all cases, irrespective of the bridging diphosphines
and dialkylamido groups used. Presumably, a plausible expla-
nation for this is the unfavorable interaction as a a consequence
of steric repulsions between the PMe3 and NR2 groups in types
III, V, and VI. It can be seen clearly that, for complexes of
types I, II, and IV, there is no close contact between the N and
P atoms in each case. This phenomenon can be further
substantiated by the observation of only one type of isomer in
the monophosphine system.2 As illustrated in Figure 13, there
are twelve isomeric possibilities in W2Cl4(NR2)2(PR′3)2 mol-
ecules with a staggered rotational geometry. Previous studies
by us showed that 31P{1H} NMR spectroscopy indicated the
absence of any tran,trans- or cis,trans-isomer in the reaction
mixture.2 It is evident from Figure 13 that all of the conforma-
tions except the known cis,cis-isomer (the one in brackets)
exhibit highly unfavorable steric interactions between adjacent
P atoms or between adjacent N and P atoms. The unique isomer
thus formed is the one in which steric interactions between the
bulky phosphine ligands or between PR′3 and NR2 groups are
minimized. It is also noteworthy that close contact between
two NR2 moieties does not contribute much in determining the
observed configurations of the molecules in question.
Figure 13. Schematic diagrams showing the 12 isomeric possibilities
of W2Cl4(NR2)2(PR′3)2 molecules with a staggered conformation.
axis. Although orientational disorder of the W2 unit has
frequently been observed in trans-W2Cl4(NHCMe3)2(PMe3)2
molecules,3 no indication of such a disorder can be observed in
this structure. Compared with the previous structures 1 and 2
in Figure 8a,b, the obvious difference is that both phosphorus
atoms are now arranged in trans positions to the two NEt2
groups. The W-W bond distance of 2.3178(6) Å (Table 6) is
characteristic of a W-W triple bond. The average W-Cl and
W-P bond distances are 2.367(3) and 2.668(3) Å, respectively.
The W-P distance is comparable to the corresponding distances
observed in the trans WCl2PN unit of all cis,trans-isomers
mentioned above. Presumably, the trans influence order NEt2
> PPh2R accounts for the significant lengthening of the W-P
distance in this case. The projection along the W-W axis, as
shown in Figure 8c, shows the torsional angle P(1)-W(1)-
W(2)-P(2) as 38.5° (Table 6).
Acknowledgment. We are grateful to the National Science
Foundation for financial support. We also thank the Department
of Chemistry, The University of Hong Kong, for providing the
diffractometer facilities for the X-ray data collection of com-
pound 1 during the leave of absence of W.-Y.W. in Hong Kong.
Concluding Remarks
The preparation of W2Cl4(NR2)2(L-L) (L-L ) bidentate
phosphines) molecules by reaction of the W2Cl4(NR2)2(NHR2)2
type intermediate complex with a stoichiometric amount of L-L
is reported here. For L-L ) dmpm and dmpe, 31P{1H} NMR
spectroscopic evidence suggests that three distinct isomeric
species exist in solution, and they are the trans,trans-, cis,trans-,
and cis,cis-isomers. The structural characterization of the
Supporting Information Available: Nine X-ray crystallographic
files, in CIF format, are available. Access information is given on any
current masthead page.
IC961151Z