Studies of a reluctant ligand. An X-ray crystallographic and NMR spectroscopic analysis of (OC)5W(η1-PPh2CH2PPh 2) and Its (OC)5W(μ-PPh2CH2PPh2)W(CO) 5 derivative

Article abstract of DOI:10.1021/om980288p

Tungsten pentacarbonyl complexes, (OC)₅W(η¹-PPh₂CH₂PPh ₂) (1) and (OC)₅W(μ-PPh₂CH₂PPh₂)W(CO) ₅ (2), have been synthesized from (OC)₅WNH₂Ph and Ph₂PCH₂PPh₂ in toluene, and their solid-state structures have been determined by single-crystal X-ray diffraction. The lone pair of electrons on the dangling phosphine in 1 is oriented toward the W(CO)₅ unit in the solid state, and ¹³C{¹H} and ³¹P{¹H} NMR data suggest that this conformation may also be dominant in solution. Phosphorus-phosphorus coupling in 1 (²J_PP = 106 Hz) is significantly larger than in any previously reported complex of Ph₂PCH₂PPh₂ and is highly dependent on changes in temperature and solvent. Also observed is an unprecedented long-range phosphorus-carbon coupling (⁴J_pc = 3.0 Hz) between the dangling phosphine and the equatorial carbonyl carbons of 1, which is attributed to a conformational and/or through-space enhancement. On the basis of the structural and spectral data, the reluctance of 1 to react with (OC)₅WNH₂Ph to give 2 is explained in terms of the substantial ligand conformation change required.

Full text of DOI:10.1021/om980288p

Organometallics 1998, 17, 4275-4281
4275
Stu d ies of a Relu cta n t Liga n d . An X-r a y
Cr ysta llogr a p h ic a n d NMR Sp ectr oscop ic An a lysis of
(OC)5W(η1-P P h 2CH2P P h 2) a n d Its
(OC)5W(µ-P P h 2CH2P P h 2)W(CO)5 Der iva tive
J ohn William Benson
Department of Chemistry, Rockford College, Rockford, Illinois 61108
Richard L. Keiter* and Ellen A. Keiter*
Department of Chemistry, Eastern Illinois University, Charleston, Illinois 61920
Arnold L. Rheingold* and Glenn P. A. Yap
Department of Chemistry, University of Delaware, Newark, Delaware 19716
Vera V. Mainz
Department of Chemistry, University of Illinois, Urbana, Illinois 61801
Received April 15, 1998
Tungsten pentacarbonyl complexes, (OC)5W(η1-PPh2CH2PPh2) (1) and (OC)5W(µ-
PPh2CH2PPh2)W(CO)5 (2), have been synthesized from (OC)5WNH2Ph and Ph2PCH2PPh2
in toluene, and their solid-state structures have been determined by single-crystal X-ray
diffraction. The lone pair of electrons on the dangling phosphine in 1 is oriented toward
the W(CO)5 unit in the solid state, and 13C{1H} and 31P{1H} NMR data suggest that this
conformation may also be dominant in solution. Phosphorus-phosphorus coupling in 1 (2J PP
) 106 Hz) is significantly larger than in any previously reported complex of Ph2PCH2PPh2
and is highly dependent on changes in temperature and solvent. Also observed is an
unprecedented long-range phosphorus-carbon coupling (4J PC ) 3.0 Hz) between the dangling
phosphine and the equatorial carbonyl carbons of 1, which is attributed to a conformational
and/or “through-space” enhancement. On the basis of the structural and spectral data, the
reluctance of 1 to react with (OC)5WNH2Ph to give 2 is explained in terms of the substantial
ligand conformation change required.
In tr od u ction
ethylene-bridged ligand, dppe (dppe ) Ph2PCH2CH2-
PPh2) in (OC)5M(η1-dppe) readily forms bimetallic com-
plexes at room temperature or below.7 The analogous
arsenic and antimony complexes, (OC)5M(η1-Ph2AsCH2-
Bis(diphenylphosphino)methane (dppm) is an impor-
tant and widely used ligand in homogeneous catalysis
and organometallic chemistry.1 Enormously flexible,
with P-C-P bond angles ranging from 92° to 133°, it
is able to accommodate a wide variety of structural
demands including those associated with chelation of a
single metal center and bridging two metal atoms. In
addition, a number of compounds exist in which dppm
is bound as a monodentate ligand.2 The first example
to be reported was (OC)5W(η1-dppm), 1,3 and its ap-
pearance was followed by a number of others, including
some that have been structurally characterized (Table
1).
Coordination of one end of dppm in 1 tends to reduce
the reactivity of the unbound end but not sufficiently
to prevent chelation,4 protonation,5 and quaternization.3
Nonetheless, early attempts to coordinate a second
M(CO)5 fragment to the free end of (OC)5M(η1-dppm)
(M ) Cr, Mo, W) were unsuccessful,3,6 even though the
(2) (a) Orth, S. D.; Terry, M. R.; Abboud, K. A.; Dodson, B.; McElwee-
White, L. Inorg. Chem. 1996, 35, 916. (b) Bo¨ttcher, H.-C.; Krug, A.;
Hartung, H. Polyhedron 1995, 14, 901. (c) Hsu, M.-A.; Yeh, W.-Y.; Peng,
S.-M.; Lee, G.-H. J . Chin. Chem. 1994, 41, 441. (d) Barral, M. C.;
J imenez-Aparicio, R.; Royer, E. C.; Saucedo, M. J .; Ubranos, F. A.;
Gutierrez-Puebla, E.; Ruiz-Valero, C. Inorg. Chim. Acta 1993, 209, 105.
(e) Douglas, G.; Manojlovic-Muir, L.; Muir, K. W.; J ennings, M. C.;
Lloyd, B. R.; Rashidi, M.; Schoettel, G.; Puddephatt, R. J . Organo-
metallics 1991, 10, 3927 (f) Scott, F.; Kruger, G. J .; Cronje, S.; Lombard,
A.; Raubenheimer, H. G.; Benn, R.; Rufinska, A. Organometallics 1990,
9, 1071. (g) Cano, M.; Campo, J . A.; Pe´rez-Garc´ıa, V.; Gutie´rrez-Puebla,
E.; Alvarez-Ibarra, C. J . Organomet. Chem. 1990, 382, 397. (h)
Cartwright, S.; Clucas, J . A.; Dawson, R. H.; Foster, D. F.; Harding,
M. M.; Smith, A. K. J . Organomet. Chem. 1990, 382, 397. (i) Riera, V.;
Ruiz, M. A.; Villafane, F.; Bois, C.; J eannin, Y. J . Organomet. Chem.
1990, 382, 407. (j) Bruce, M. I.; Cifuentes, M. P.; Grudny, K. R.; Liddell,
M. J .; Snow, M. R.; Tiekink, E. R. T. Aust. J . Chem. 1988, 41, 597. (k)
Kerschner, J . L.; Fanwick, P. E.; Rothwell, I. P. J . Am. Chem. Soc.
1988, 110, 8235. (l) Braunstein, P.; De Meric de Bellefon, C.; Lanfran-
chi, M.; Tiripicchio, A. Organometallics 1984, 3, 1772. (m) Olmstead,
M. M.; Lee, C.-L.; Balch, A. L. Inorg. Chem. 1982, 21, 2712. (n) Ball,
R. G.; Domazetis, G.; Dolphin, D.; J ames, B. R.; Trotter, J . Inorg. Chem.
1981, 20, 1556. (o) Drew, M. B. G.; Wolters, A. P.; Thomkins, I. B. J .
Chem. Soc., Dalton Trans. 1977, 974.
(1) (a) Puddephatt, R. J . Chem Soc. Rev. 1983, 12, 99. (b) Chaudret,
B.; Delavaux, B.; Poilblanc, R. Coord. Chem. Rev. 1988, 86, 191.
(3) (a) Keiter, R. L.; Shah, D. P. Inorg. Chem. 1972, 11, 191. (b)
Keiter, R. L.; Cary, L. W. J . Am. Chem. Soc. 1972, 94, 9232.
S0276-7333(98)00288-X CCC: $15.00 © 1998 American Chemical Society
Publication on Web 08/19/1998

4276 Organometallics, Vol. 17, No. 19, 1998
Benson et al.
2
Ta ble 1. Liga n d Tor sion An gles, P -C-P An gles, J P P Cou p lin g Con sta n ts, a n d Con figu r a tion Typ e for
Str u ctu r a lly Ch a r a cter ized Com p ou n d s Con ta in in g η1-d p p m
compound
torsion angle (deg)
P-C-P angle (deg)
2J PP (Hz)
conf. type
ref
dppm
74.3
26.5
20.3
88.8
42.0
38
152.0
167.3
170.3
106.2
111.5
112.6
116.3
110.6
114.0
117.3
117.2
118.9
125 (CD2Cl2)
106 (CDCl3)
75.7 (CDCl3)
73
46 (CD2Cl2)
40.0 (THF)
47.7 (THF)
54.7 (CD2Cl2)
21.5 (CDCl3)
I
I
I
I
I
I
II
II
II
25
W(CO)5(η1-dppm)
this work
Fe(CO)4(η1-dppm)
11
29
30
2f
2f
2h
2d
Mo2(η5-Cp)2(µ-CNBut)(η1-dppm)
Fe2(CO)5(u-PCy2)(u-PBut2)(η1-dppm)
Fe(η5-Cp)(η3-MeCS2)(η1-dppm)
Fe(η5-Cp)(η2-MeCS2)(η1-dppm)
Os3(CO)9(µ-dppm)(η1-dppm)
Ru(trans-quin)2(η1-dppm)2
quin ) 2-quinaldinate
Ru(TTP)(η1-dppm)2
178.6
118.7
30.2 (CDCl3)
II
2n
TTP ) tetraphenylphorphyrin
RuCl(PPh3)(η5-Cp)(η1-dppm)
Ru(η5-Cp)(η2-dppm)(η1-dppm)
fac-Mo(CO)3(η2-phen)(η1-dppm)
W(L)(OAr-2,6,6Ph2)(η1-dppm)
L ) (OC6H3Ph-η6-C6H5)
177
117
18.3 (CDCl3)
40.2 (CD2Cl2)
66.1
II
II
II
II
28
31
32
33
140.9
156.8
158.9
120.4
118.0
116.4
65
Pt4(µ-H)(µ-CO)2(µ-dppm)3(η1-dppm)+
(OC)5W(µ-dppm)W(CO)5
161.9
43.3
120.1
133.1
73
II
III
34
22.9 (CDCl3)
this work
AsPh2)8 and (OC)5M(η1-Ph2SbCH2SbPh2)9 (M ) Cr, Mo,
W) were isolated long ago, but their bimetallic deriva-
tives were also unknown until quite recently.9b The
reluctance of these monodentate complexes to function
as ligands toward a second M(CO)5 group was attributed
to unfavorable steric interactions between the four
phenyl groups and the two metal carbonyl fragments
that result because the methylene bridge provides a bite
angle that is too small to allow the necessary space
accommodations. This notion was supported by the fact
that while 1 reacts with MeI at room temperature to
give the quaternized product, [(OC)5W(η1-PPh2CH2PPh2-
Me]I, it does not react with the bulkier benzyl bromide.3
Furthermore, substituting the sterically less demanding
Fe(CO)4 for M(CO)5 allows formation of (OC)4Fe(µ-
dppm)Fe(CO)4,10 and (OC)4Fe(η1-dppm)11 has been shown
to combine with Mo(CO)5 to give (OC)5Mo(µ-dppm)Fe-
(CO)4.12
temperatures.13 Likewise, the dppm-bridged complex,
[{(η5-C5H5)Ru(1,10-phen)}2(µ-dppm)](PF6)2, forms in re-
fluxing ethanol, while only the monodentate complex
forms at room temperature.14
In this work we report an improved synthesis of 2,
X-ray structures of both 1 and 2, and 31P{1H} and 13C
NMR spectral data suggesting that solution and solid-
state conformations of dppm in complex 1 are very
similar. This information is used to explain the reluc-
tance of 1 to bind to a second W(CO)5 unit to form 2.
Exp er im en ta l Section
Gen er a l Com m en ts. All reactions were performed in a
nitrogen atmosphere using standard Schlenk apparatus. Tolu-
ene was dried over CaH2 and distilled at ambient pressure.
All other solvents were of reagent grade and used without
further purification. Other materials were prepared as previ-
ously described: (OC)5W(NH2Ph),3,15 (OC)5W(η1-dppm),3 and
(OC)5W(η1-dppe).3 Solution FT-IR spectra were obtained on a
Nicolet 20-DBX spectrometer. Room-temperature 31P{1H}
NMR (referenced to an external standard of 85% H3PO4) and
13C{1H} NMR (referenced to TMS) spectra were obtained on a
General Electric QE-300 NMR spectrometer. Variable-tem-
perature 31P{1H} NMR spectra were performed at Spectral
Data Services, Champaign, IL, using a Nicolet NT-400 spec-
trometer. Phosphorus decoupled C-13 spectra were obtained
with a Varian Unity Inova 500 MHz spectrometer.
Early unsuccessful efforts to synthesize (OC)5W(µ-
dppm)W(CO)5, 2, were performed at near room temper-
ature to minimize chelation of 1.3,6 More recently, it
has been shown that 2 does in fact form from (OC)5W-
(NCMe) and dppm if reactions are carried out at higher
(4) (a) Cheung, K. K.; Lai, T. F.; Mok, K. S. J . Chem. Soc. (A) 1971,
1644. (b) Grim, S. O.; Briggs, W. L.; Barth, R. C.; Tolman, C. A.; J esson,
J . P. Inorg. Chem. 1974, 13, 1095. (c) Grim, S. O.; Mitchell, J . D. Inorg.
Chem. 1977, 16, 1770.
Syn th esis of (OC)5W(µ-d p p m )W(CO)5 (2). Meth od A.
A toluene solution (25 mL) of (OC)5W(η1-dppm) (0.150 g, 0.212
mmol) and (OC)5W(NH2Ph) (0.113 g, 0.271 mmol) was stirred
at 60 °C for 16 h. The dark solution was cooled to room
temperature and filtered to give a greenish yellow solution and
a black precipitate. The solvent was removed from the filtrate
under vacuum, and the resulting solid was chromatographed
on neutral, deactivated16 alumina using 3:1 hexanes/CH2Cl2
as the eluent. The first yellow band collected was identified
as the product, 2, by its 31P{1H} NMR spectrum.13a The solvent
was removed under vacuum; the resulting solid was recrystal-
lized from CH2Cl2/CH3OH (1:10) to give 0.191 g (87%). 1H
(5) Rottink, M. K.; Angelici, R. J . Inorg. Chem. 1993, 32, 2421.
(6) (a) Hor, T. S. A. J . Organomet. Chem. 1987, 319, 213. (b) Chan,
H. S. O.; Hor, T. S. A.; Chiam, C. S. M.; Chong, T. C. J . Therm. Anal.
1987, 32, 1115. (c) Alyea, E. C.; Ferguson, G.; Fisher, K. J .; Gossage,
R. A.; J ennings, M. C. Polyhedron 1990, 9, 2393.
(7) (a) Keiter, R. L.; Kaiser, S. L.; Hansen, N. P.; Brodack, J . W.;
Cary, L. W. Inorg. Chem. 1981, 20, 283. (b) Dickson, C.-A.; McFarlane,
A. W.; Coville, N. J . Inorg. Chim. Acta 1989, 158, 205. (c) Connor, J .
A.; Day, J . P.; J ones, E. M.; McEwen, G. K. J . Chem. Soc. 1973, 347.
(d) Keiter, R. L.; Fasig, K. M.; Cary, L. W. Inorg. Chem. 1975, 14, 201.
(e) Keiter, R. L.; Benedik, J . E., J r.; Cary, L. W. Inorg. Nucl. Chem.
Lett. 1977, 13, 455.
(8) Colton, R.; Rix, C. J . Aust. J . Chem. 1971, 24, 2461.
(9) (a) Fukumoto, T.; Matsumura, Y.; Okawara, R. J . Organomet.
Chem. 1972, 37, 113. (b) Hill, A. M.; Homes, N. J .; Genge, A. R. R.;
Levason, W.; Webster, M.; Rutschow, S. J . Chem. Soc., Dalton Trans.
1998, 825.
(10) Wegner, P. A.; Evans, L. F.; Haddock, J . Inorg. Chem. 1975,
14, 192.
(13) (a) Benson, J . W.; Keiter, E. A.; Keiter, R. L. J . Organomet.
Chem. 1995, 495, 77. (b) O¨ zer, Z.; O¨ zkar, S.; Pamuk, H. O¨ . Z.
Naturforsch. B 1993, 48b, 37.
(11) (a) Keiter, R. L.; Rheingold, A. L.; Hamerski, J . J .; Castle, C. K
Inorg. Chem. 1983, 2, 1635. (b) Dias Rodrigues, A. M. G.; Lechat, J .
R.; Francisco, R. H. P. Acta Crystallogr. 1992, C48, 159.
(12) J acobsen, G. B.; Shaw, B. L.; Thornton-Pett, M. J . Chem. Soc.,
Dalton Trans. 1987, 1509.
(14) Albers, M. O.; Liles, D. C.; Robinson, D. J .; Singleton, E. J .
Organomet. Chem. 1987, 323, C39.
(15) Angelici, R. J .; Malone, M. D. Inorg. Chem. 1967, 6, 1731.
(16) Neutral alumina, Brockman Activity I, 150 mesh (Aldrich), was
degassed for 24 h under vacuum and deactivated with 5% (w/w) water.

Studies of a Reluctant Ligand
Organometallics, Vol. 17, No. 19, 1998 4277
Ta ble 2. Cr ysta l Da ta for (OC)5WP P h 2CH2P P h 2 (1) a n d [(OC)5WP P h 2]2CH2(2)
1
2
formula
fw
temp, K
wavelength, Å
cryst syst
space group
a, Å
R, deg
b, Å
C
30H22O5P2W
C35H22O10P2W2
1032.17
296(2)
0.71073
monoclinic
P21/c
17.494(8)
90
10.332(4)
93.67(4)
19.796(9)
90
708.27
296(2)
0.71073
monoclinic
Pc
8.798(2)
90
13.936(3)
96.54(3)
11.266(2)
90
â, deg
c, Å
γ, deg
vol, Å3; Z
1372.3(5); 2
1.714
4364
3571(3); 4
1.920
6583
density (calcd), Mg/m3
abs coeff, mm-1
F(000)
962
1960
cryst size, mm
cryst color
θ range for data collection, deg
limiting indices
no. of rflns collected
no. of indep rflns
0.40 × 0.30 × 0.20
0.40 × 0.12 × 0.10
colorless
colorless
2.33-30.07
-12 e h e 12, 0 e k e 19, -1 e l e 15
4589
4589
2.06-27.57
-22 e h e 22, 0 e k e 13, 0 e l e 25
8437
8193
(Rint ) 0.0000)
(Rint ) 0.0314)
refinement meth
full-matrix least-squares on F2
no. of data/restraints/parameters
4585/15/409
1.034
8193/0/442
1.152
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
R1 ) 0.0589, wR2 ) 0.1384
R1 ) 0.0637, wR2 ) 0.1444
0.02(6)
8766(395)
4.865 and -1.882
R1 ) 0.0386, wR2 ) 0.0646
R1 ) 0.0794, wR2 ) 0.0672
absolute structure parameter
extinction coeff
largest diff peak and hole, e Å-3
1.075 and -1.672
NMR (CDCl3): δ 7.4-7.1 (m, Ph), 4.05 (t, 2J PH ) 5.0 Hz, CH2).
contribute to poor refinement, we discovered the presence of
a minor contribution (ca. 8%) from a racemic twin. With the
inclusion of these contributions, R(F) dropped to 5.9% and the
largest peak on the difference map was now 2.5 e Å-3. For 2,
all non-hydrogen atoms were also refined anisotropically. In
both cases, hydrogen atoms were included in idealized contri-
butions. All software, including routines for dealing with
twinning, is contained in SHELXTL.17
2
13C{1H} (CDCl3): δ 199.2 (t, | J CP + 4J CP| ) 23.2 Hz, trans CO),
2
197.0 (t, | J CP + 4J CP| ) 5.9 Hz, 1J CW ) 119.6 Hz, cis CO), 133.2
1
2
(five-line pattern, | J CP + 3J CP| ) 41.9 Hz, ipso), 132.1 (t, | J CP
+ 4J CP| ) 11.7, ortho), 130.4 (s, para), 128.6 (t, | J CP + 5J CP| )
3
1
9.7 Hz, meta), 37.2 (t, J CP ) 5.0 Hz, CH2). A second, bright
yellow band eluted and was identified by its IR spectrum as
unreacted (OC)5W(NH2Ph).
Con for m a tion a l An a lysis of η1-d p p m Liga n d s. Torsion
angles (M-P-P-lone pair) for complexes containing η1-dppm
ligands were determined using CS Chem 3D Pro, version 3.5
(CambridgeSoft Corporation). Literature values for atomic
coordinates were used to reconstruct the dppm framework
including the metal atom. The position of the lone pair on
the unbound P atom was determined by placing a single atom
(A) in an idealized position, such that all three lone pair-P-C
angles were equal. Values for torsional angles are listed in
Table 1.
Meth od B. A toluene solution (20 mL) of (OC)5W(NH2Ph)
(0.601 g, 1.44 mmol) and dppm (0.269 g, 0.700 mmol) was
heated to 60 °C for 19 h. The resulting solution was worked
up as above to give 0.428 g of 2 (58%).
13C{1H} NMR of (OC)5W(η1-d p p m ) (1). (CD2Cl2): δ 200.1
(d, 2J CP ) 22.0 Hz, trans CO), 197.6 (dd, 2J CP ) 6.9 Hz, 4J CP
)
1
1
3.0 Hz, cis CO), 136.0 (d, J CP ) 40.7 Hz, ipso), 135.9 (d, J CP
2
) 41.1 Hz, ipso), 132.7 (d, J CP ) 21.1 Hz, ortho), 132.2 (d,
3
2J CP ) 11.7 Hz, ortho), 128.4 (d, J CP ) 2.9 Hz, meta), 128.3
3
4
(d, J CP ) 5.3 Hz, meta), 130.2 (d, J CP ) 1.7 Hz, para), 128.7
1
(s, para), 33.7 (dd, J CP ) 30.3, 22.1 Hz, CH2).
13C{1H} NMR of (OC)5W(η1-d p p e) (3). (CDCl3): δ 199.1
Resu lts a n d Discu ssion
2
2
1
(d, J CP ) 21.5 Hz, trans CO), 196.7 (d, J CP ) 7.1 Hz, J CW
)
1
Syn th esis a n d Ch a r a cter iza tion of 2. Compound
2 was synthesized either from a 2:1 ratio of (OC)5W-
(NH2Ph) and dppm or from a 1:1 ratio of 1 and (OC)5W-
(NH2Ph) in toluene at 60 °C.
126.4 Hz, cis CO), 137.2 (d, J CP ) 13.5 Hz, ipso), 135.5 (d,
1J CP ) 40.1 Hz, ipso), 132.5 (d, J CP ) 18.5 Hz, ortho), 131.9
2
2
(d, J CP ) 11.0 Hz, ortho), 130.3 (s, para), 128.7 (m, Ph), 29.4
(dd, 1J CP ) 23.2, 2J CP ) 18.9 Hz, CH2CH2), 22.2 (d, 1J CP ) 16.1
Hz, CH2CH2).
Str u ctu r e Deter m in a tion of (OC)5W(η1-d p p m ) (1) a n d
(OC)5W(µ-d p p m )W(CO)5 (2). Crystals of 1 and 2 were grown
in a CH2Cl2/hexanes solution at -18 °C. Data collection and
parameters are listed in Table 2. Preliminary photographic
evidence showed that both 1 and 2 were monoclinic. System-
atic absences in the diffraction data indicated that 1 belonged
to either of the space groups Pc or P2/c. Since 1 does not
possess 2-fold symmetry, the noncentrosymmetric alternative,
Pc, was used for refinement. Empirical corrections for absorp-
tion were applied for both data sets. Initially, the refinement
process for 1 for an all anisotropic model converged at R(F) )
13.4% with several large (>10 e Å-3) unassigned peaks near
the W atom. In an exploration of the many factors that can
2(OC)5W(NH2Ph) + dppm f
(OC)5W(µ-dppm)W(CO)5
+ 2PhNH2 (1)
2
1
(OC) W(NH Ph) +
f
(OC)5W(η -dppm)
5
2
1
(OC)5W(µ-dppm)W(CO)5
+ PhNH2 (2)
2
(17) Sheldrick, G. SHELXTL, ver 5.01, Program Libraries, Siemans
XRD: Madison, WI.

4278 Organometallics, Vol. 17, No. 19, 1998
Benson et al.
the W-P bond (which would give rise to two doublets
rather than a doublet of doublets) was also considered.
The infrared spectrum of 1, however, is consistent with
(1)
C4v symmetry (overlapping E and A1 modes at 1938
(2)
cm-1; A1 mode at 2071 cm-1, B1 mode at 1981 cm-1
)
and within experimental error identical to that of 3 in
both CHCl3 and CCl4. The possibility of restricted
rotation, which might cause only a slight perturbation
in the IR spectrum, could not be completely eliminated
on the basis of the IR data alone. Additional support
was provided by 13C{31P} spectra in which the coordi-
nated and dangling phosphorus nuclei were independ-
ently decoupled from carbon. The result for each was
a doublet for the equatorial CO signal, proving that the
dangling phosphorus is indeed coupled to the cis car-
bonyl carbons. In view of the general observation that
coupling is more effective through a trans configuration
F igu r e 1. 13C{1H} NMR spectrum of the carbonyl region
of (OC)5W(η1-dppm) (1).
The IR and 31P{1H} NMR spectra are in agreement with
previous assignments,13a and characterization of 2 is
now complete with the addition of 1H and 13C{1H} NMR
spectra and single-crystal X-ray diffraction. The prepa-
ration of 2 from (OC)5W(NCMe) as described previously13a
is limited because (OC)4W(η2-dppm) forms in addition
to 2 as a significant side product. Using aniline as a
leaving group instead of acetonitrile, however, es-
sentially eliminates the competing chelation reaction
and increases the yield of 2 to 87%. The formation of
(OC)4W(η2-dppm) from (OC)5W(NCMe) apparently oc-
curs because the acetonitrile complex18 disproportion-
ates to give W(CO)6 and (OC)4W(NCMe)2, which can
then react with dppm and undergo chelation. The
disproportionation reaction is not known to occur for
(OC)5W(NH2Ph).
2
than through a cis arrangement (e.g., J PC trans is
2
greater than 3 times J PC cis), it is noteworthy that no
long-range coupling is observed between the dangling
phosphorus atom and the trans carbonyl carbon. These
observations led us to speculate about the possibility of
the uncoordinated phosphorus group interacting directly
with the equatorial carbonyl group. The crystal struc-
ture of 1, presented in the next section, shows that the
dangling phosphorus is tilted toward the cis carbonyl
plane, bisecting the C(3)-W-C(4) angle and giving a
phosphorus-carbon separation [3.5 Å] equal to the
approximate sum of the van der Waals radii for C (1.70
Å) and P (1.85 Å).22 Evidence is presented suggesting
that this molecular arrangement also exists in solution.
However, neither 13C{1H} NMR nor IR spectra support
a localized interaction between the dangling phos-
phorus group and an individual equatorial carbonyl
carbon. A nonlocalized van der Waals interaction in
which the dangling phosphorus group of 1 is precessing
about the plane of the equatorial carbonyl groups is
consistent with the spectral data. The observed long-
range coupling may arise from a particularly favor-
able conformational arrangement of the dppm ligand
or from a through-space interaction or a combination
of both.23
The CO region of the 13C{1H} NMR spectrum of 2
consists of a set of downfield peaks assigned to the 13CO
group trans to the coordinated phosphorus atom and a
set of upfield signals arising from cis 13CO groups. An
AA’X pattern is apparent in these signals as well as for
those in the phenyl region of the spectrum.19,20 Both
the trans and cis 13CO signals should appear as five-
line patterns, but the two outer lines of each are not
sufficiently intense to be observed. For the former the
separation of the two lines flanking the center line
2
corresponds to | J CP + 4J CP| ) 23.2 Hz, quite consistent
with trans couplings observed in 1 (2J C-P ) 22.0 Hz)
2
and 3 (2J CP ) 21.5 Hz); for the latter | J C-P + 4J C-P| )
5.9 Hz and is similar to the cis coupling in 3 (2J C-P
7.1 Hz).
)
Complex 1 shows a cis carbonyl spectral pattern that
is quite unexpected21 (Figure 1). Here we see an
Str u ctu r es of 1 a n d 2. The structures of 1 and 2
are shown in Figures 2 and 3, respectively, and selected
bond distances and angles for both compounds are given
in Table 3. Each tungsten atom is coordinated to five
carbonyl ligands and one phosphine in approximate C4v
symmetry; the P-W-C axis angles are 175.1(8)° in 1
and 179.4(2)° and 178.8(3)° in 2. Slight tilting of this
axis has been observed previously in LM(CO)5 com-
plexes and attributed to dissimilar orientations of
substituents on phosphorus relative to the equatorial
carbonyl groups; that is, one R group lies between while
4
apparent doublet of doublets (2J C-P ) 6.3 Hz; J C-P
)
3.0 Hz) for which there is no precedent in the LM(CO)5
literature. The possibility of endo and exo isomers was
considered as an explanation for the four-line pattern
but ruled out because other signals in the 13C{1H} and
31P{1H} NMR spectra were entirely consistent with one
conformation. The possibility of two sets of nonequiva-
lent CO groups resulting from restricted rotation about
(18) (a) Strohmeier, W.; Schonauer, G. Chem. Ber. 1961, 94, 1346.
(b) Dobson, G. R.; Amr El Sayed, M. F.; Stolz, I. W.; Sheline, R. K.
Inorg. Chem. 1962, 1, 526.
(19) Bovey, F. A. Nuclear Magnetic Resonance Spectroscopy, 2nd ed.;
Academic Press: New York, 1988.
(22) (a) Huheey, J . E.; Keiter, E. A.; Keiter, R. L. Inorganic
Chemistry, 4th ed.; HarperCollins: New York, 1993. (b) Bondi, A. J .
Phys. Chem. 1964, 68, 441.
(20) (a) Verstuyft, A. W.; Nelson, J . H.; Cary, L W. Inorg. Chem.
1976, 15, 732. (b) Hersh, W. H. J . Chem. Educ. 1997, 74, 1485. (c)
King, R. B.; Cloyd, J . C., J r. J . Chem. Soc., Perkin Trans. 1975, 938.
(21) (a) Nelson, J . H. Coord. Chem. Rev. 1995, 139, 245. (b) Bancroft,
G. M.; Dignard-Bailey, L.; Puddephatt, R. J . Inorg. Chem. 1986, 25,
3675. (c) Buchner, W.; Schenk, W. Inorg. Chem. 1984, 23, 132. (d)
Bodner, G. M.; May, M. P.; McKinney, L. E. Inorg. Chem. 1980, 19,
1951. (e) Inubushi, Y.; Huy, N. H. T.; Mathey, F. Chem. Commun. 1996,
1903. (f) Streubel, R.; Kusenberg, A.; J eske, J .; J ones, P. G. Angew.
Chem. 1994, 33, 2427. (g) Hung, J .-T.; Chang, P.; Fronczek, F. R.;
Watkins, S. F.; Lammertsma, K. Organometallics 1993, 12, 1401.
(23) (a) Holmes, R. R.; Prasha, T. K.; Pastor, S. D. In Phosphorus-
31 NMR Spectral Properties in Compound Characterization and
Structural Analysis; Quin, L. D., Verkade, J . G., Eds.; VCH: New York,
1994. (b) Mathey, F.; Mercier, F.; Nief, F.; Fischer, J .; Mitschler, A. J .
Am. Chem. Soc. 1982, 104, 2077. (c) Pastor, S. D.; Shum, S. P.; DeBellis,
A. D.; Burke, L. P.; Rodebaugh, R. K.; Clarke, F. H.; Rihs, G. Inorg.
Chem. 1996, 35, 949. (d) Szalontai, G.; Bakos, J .; Toth, I.; Heil, B.
Magn. Reson. Chem. 1987, 25, 761. (e) Gu¨nther, H. NMR Spectroscopy,
2nd ed.; J ohn Wiley: New York, 1995; p 129.

Studies of a Reluctant Ligand
Organometallics, Vol. 17, No. 19, 1998 4279
Ta ble 3. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for (OC)5W(η1-d p p m ) (1) a n d
(OC)5W(µ-d p p m )W(CO)5 (2)
1
2
2
Distances
W(1)-P(1)
W(1)-C(1)
W(1)-C(2)
W(1)-C(3)
W(1)-C(4)
W(1)-C(5)
C(1)-O(1)
C(2)-O(2)
C(3)-O(3)
C(4)-C(4)
C(5)-C(5)
P(1)-C(26)
P(1)-C(50)
P(1)-C(16)
P(2)-C(36)
P(2)-C(46)
P(2)-C(50)
2.516(5) 2.536(2) W(2)-P(2)
2.026(8) 2.029(11) W(2)-C(6)
2.025(8) 2.083(9) W(2)-C(7)
2.023(8) 2.084(10) W(2)-C(8)
2.028(9) 2.037(9) W(2)-C(9)
2.019(8) 2.031(10) W(2)-C(10)
1.152(9) 1.127(11) C(6)-O(6)
1.148(9) 1.104(10) C(7)-O(7)
1.147(8) 1.124(10) C(8)-O(8)
1.155(9) 1.123(9) C(9)-O(9)
1.142(8) 1.125(10) C(10)-O(10)
1.83(3) 1.829(8)
2.540(2)
2.056(9)
2.078(9)
2.071(9)
2.043(9)
2.045(10)
1.138(9)
1.120(10)
1.125(8)
1.121(9)
1.119(10)
1.85(2) 1.856(8)
1.82(2) 1.830(9)
1.86(3) 1.822(8)
1.83(2) 1.846(8)
1.84(2) 1.858(7)
F igu r e 2. Molecular structure of (OC)5W(η1-dppm) (1).
Angles
P(1)-C(50)-P(2) 111.5(11) 133.1(4)
O(1)-C(1)-W(1) 170(4)
O(2)-C(2)-W(1) 169(3)
O(3)-C(3)-W(1) 177(2)
O(4)-C(4)-W(1) 166(2)
O(5)-C(5)-W(1) 170(4)
175.6(9) O(6)-C(6)-W(2) 178.8(9)
179.1(9) O(7)-C(7)-W(2) 176.4(9)
179.1(9) O(8)-C(8)-W(2) 176.7(8)
179.1(8) O(9)-C(9)-W(2) 176.9(8)
177.5(10) O(10)-C(10)-W(2) 179.2(10)
87.9(14) 88.6(4) C(6)-W(2)-C(7) 93.1(4)
C(1)-W(1)-C(2)
C(1)-W(1)-C(3)
C(1)-W(1)-C(4)
C(1)-W(1)-C(5)
C(2)-W(1)-C(3)
C(2)-W(1)-C(4)
C(2)-W(1)-C(5)
C(3)-W(1)-C(4)
C(3)-W(1)-C(5)
C(4)-W(1)-C(5)
C(1)-W(1)-P(1)
C(2)-W(1)-P(1)
C(3)-W(1)-P(1)
C(4)-W(1)-P(1)
C(5)-W(1)-P(1)
174(2)
177.0(3) C(6)-W(2)-C(8)
176.3(4)
90.8(3)
98.5(14) 90.8(4) C(6)-W(2)-C(9)
86.1(14) 85.7(4) C(6)-W(2)-C(10) 89.6(4)
86.5(9) 89.2(4) C(7)-W(2)-C(8)
173.5(9) 179.1(3) C(7)-W(2)-C(9)
89.9(4)
174.4(3)
94.5(11) 89.7(4) C(7)-W(2)-C(10) 87.3(4)
87.1(9) 91.5(4) C(8)-W(2)-C(9) 86.4(3)
86.1(14) 92.3(3) C(8)-W(2)-C(10) 92.7(3)
87.1(12) 90.8(4) C(9)-W(2)-C(10) 88.6(4)
90.4(9) 94.7(3) C(6)-W(2)-P(2)
88.9(7) 89.8(3) C(7)-W(2)-P(2)
89.8(7) 87.3(2) C(8)-W(2)-P(2)
90.0(9) 89.7(2) C(9)-W(2)-P(2)
88.9(3)
92.0(3)
88.8(2)
92.2(2)
175.1(8) 179.4(2) C(10)-W(2)-P(2) 178.8(3)
F igu r e 3. Molecular structure of (OC)5W(µ-dppm)W(CO)5
(2).
C(26)-P(1)-C(50) 102.4(11) 107.6(3)
C(26)-P(1)-C(16) 104.2(10) 104.9(4)
C(16)-P(1)-(C(50) 104.5(10) 104.5(4)
C(46)-P(2)-C(50) 101.4(10) 106.6(3)
C(46)-P(2)-C(36) 101.4(9) 102.9(4)
C(36)-P(2)-C(50) 102.2(10) 108.7(4)
C(26)-P(1)-W(1) 119.2(7) 119.3(3) C(36)-P(2)-W(2) 116.2(3)
C(50)-P(1)-W(1) 113.2(8) 108.6(2) C(50)-P(2)-W(2) 108.3(2)
C(16)-P(1)-W(1) 111.8(7) 110.9(3) C(46)-P(2)-W(2) 113.7(3)
the other two nearly eclipse the carbonyls.24 The W-P
bond distance in 1 is 2.516(5) Å, identical to that found
in (OC)5WPMe3, 2.516(2) Å,24b even though dppm is
generally viewed as more sterically demanding than
PMe3. The W-P bond distances in 2 are 2.536(2) and
2.540(2) Å, very similar to the W-P bond distance in
(OC)5WPPh3, 2.545(1) Å,24c and not unexpected.
An unusual structural feature of 1 is the deviation
from linearity in the equatorial O-C-W bond angles
(166-170°). The torsional angle of dppm in 1 is 26.5°,
which directs the dangling phosphorus lone pair toward
C(4)-O(4). The W-C(4)-O(4) bond angle is 166(2)°
with O(4) directed away from the phosphorus lone pair,
which raises the possibility that the absence of linearity
is due to some interaction between CO and the dangling
phosphorus group.
Ch a r t 1
The structure of the free dppm ligand is known,25
allowing for comparison of conformational changes in
the dppm ligand when one end (1) or both ends (2) are
coordinated to W(CO)5. Three possible conformations
are shown in Chart 1. As a free ligand, dppm adopts
conformation I, an orientation that minimizes steric
interactions between the phenyl rings. The lone pairs
of electrons are staggered, each on opposite sides of the
plane formed by P(1), C(50), and P(2); the computed
torsion angle between the two lone pairs is 74.3°.
Coordination of one W(CO)5 unit to dppm changes the
conformation of the dppm ligand only slightly. The
(24) (a) Lee, K. J .; Brown, T. L. Inorg. Chem. 1992, 31, 289. (b)
Cotton, F. A.; Darensbourg, D. J .; Kolthammer, B. W. S. Inorg. Chem.
1981, 20, 4440. (c) Aroney, M. J .; Buys, I. E.; Davies, M. S.; Hamby, T.
W. J . Chem. Soc., Dalton Trans. 1994, 2827.
(25) Schmidbauer, H. Inorg. Chim. Acta 1988, 147, 150.

4280 Organometallics, Vol. 17, No. 19, 1998
Benson et al.
2
Ta ble 4. Va r ia tion of J P P (Hz) w ith Tem p er a tu r e
in (OC)5W(η1-d p p m ) (1)
dppm ligand still adopts conformation I with the lone
pair of electrons on the free phosphine end directed
toward W(CO)5. This seems to be a more stable ar-
rangement than configuration II, which would direct the
phenyl rings on the uncoordinated end toward the bulky
W(CO)5 group. The P(1)-C(50)-P(2) angle of 111.5(11)°
is greater than the value of 106.2(3)° in the free ligand
but is more acute than typically found in η1-dppm
complexes (see Table 1).
2J PP (C6D5CD3)
temp (°C)
2J PP (C6D5CD3)
temp (°C)
122.4
121.0
119.0
116.6
-50
-30
-10
10
114.1
111.7
110.6
30
50
70
2
Ta ble 5. Va r ia tion of J P P (Hz) w ith Solven t in
(OC)5W(η1-d p p m ) (1)
Addition of a second W(CO)5 to give 2 results in a
dramatic alteration of the dppm conformation. The
ligand now adopts conformation III (Chart 1), giving a
severely crowded arrangement for the four phenyl rings.
The crowding is relieved in several ways. First, the
P(1)-C(50)-P(2) bond angle increases to 133.1(4)°, an
increase of over 21° from 1. Extreme P-C-P angles
have been observed previously in [Ir2(η5-C5Me5)2(µ-
dppm)] (127.2°)26 and [Ru2(η5-C5H5)2(1,10-phenanthro-
line)2(µ-dppm)]2+ (133.1°).14 Second, the tungsten atoms
are on opposite sides of the P-C-P plane; the torsion
angle of 43.3° allows for staggering of the Ph groups.
Third, the W-P bond lengths in 2 are somewhat longer
than in 1, which may provide some added steric benefit.
(The P(1)-C(50) and P(2)-C(50) bond distances in 2 are
not lengthened over those found in 1 or in the free
ligand.) Fourth, the C-P-C bond angles in 2 are larger
than those in the free ligand as well as those associated
with the coordinated phosphorus in 1.
solvent
2J PP (∼20 °C)
solvent
2J PP (∼20 °C)
(CD3)2CO
THF-d8
C6D5(CD3)
119.1
116.0
114.7
C6D6
CD2Cl2
CDCl3
114.7
109.4
106.2
in solution, some correlations are apparent. Type I
complexes tend to have smaller P-C-P bond angles
(110.6-116.3°) than type II complexes (116.4-120.1°).
At the same time the coupling constants for type I
complexes (40-106 Hz) tend to be larger than for type
II complexes (18.3-73 Hz). These observations lead us
to conclude that there is a tendency for the conformation
observed in the solid state to persist in solution. In
2
particular, complex 1 has the largest J PP of all dppm
complexes and one that is similar to that of the free
ligand; both the free ligand and 1 have type I solid-state
structures. Molecular models suggest that P(2) in 1 is
tilted toward the equatorial plane as a forced conse-
quence of the steric demands of the W(CO)5 and four
phenyl groups. The uncoordinated phosphine of (OC)4Fe-
(η1-dppm) also points toward the CO groups in the solid
state, but the Fe(CO)4 moiety is less sterically demand-
ing than W(CO)5 and the dppm conformation may not
be as fixed, leading to a smaller phosphorus-phospho-
rus coupling11b in solution. A solution structure for 1
that is consistent with all evidence is one in which the
dangling phosphine precesses around the equatorial
carbonyl plane, delocalized with respect to the four
carbonyl groups but experiencing a van der Waals
interaction.
Based on the solid-state structures of 1 and 2 and the
evidence that these structures persist in solution, the
dppm ligand must undergo a significant conformational
change in order to coordinate to a second W(CO)5 group.
The failure of 1 to react with (OC)5W(NH2Ph) at room
temperature at measurable rates can be attributed to
the substantial energy required to provide a sufficient
population of structures with conformations favorable
to reaction.
Solu tion Con for m a tion of d p p m in 1 a n d Its
Rela tion sh ip to Rea ctivity. It has been observed
that the magnitude of 2J PP depends on temperature, the
electronegativities of substituents bound to phosphorus,
the oxidation state of phosphorus, and the phosphorus
coordination number. It is also affected by the confor-
mation.27 When lone pairs of electrons of uncoordinated
diphosphines are separated by an amine or methylene
group and oriented toward each other (conformation I,
2
Chart 1), the value of J PP tends to be significantly
higher than when they are oriented away from each
other (conformations II and III, Chart 1). Compounds
containing η1-dppm for which X-ray structures have
2
been determined and for which solution J PP values are
known are found in Table 1, along with torsion and
P-C-P angles. Although one would not expect struc-
tures in the solid state to necessarily correspond to those
(26) Keim, W.; Kraneburg, P.; Dahmen, G.; Deckers, G.; Englert,
U.; Linn, K.; Spaniol, T. P.; Raabe, G.; Kru¨ger, C. Organometallics
1994, 13, 3085.
2
(27) (a) Bookham, J . L.; McFarlane, W.; Thornton-Pett, M. J . Chem.
Soc., Dalton Trans. 1992, 2353. (b) Keat, R.; Manojlovic-Muir, L.; Muir,
K. W.; Rycroft, D. S. J . Chem. Soc., Dalton Trans. 1981, 2192. (c) Cross,
R. J .; Green, T. H.; Keat, R. J . Chem. Soc., Dalton Trans. 1976, 1424.
(d) Brookham, J . L.; Conti, F.; McFarlane, C. E.; McFarlane, W.;
Thornton-Pett, M. J . Chem. Soc., Dalton Trans. 1994, 1791. (e)
Colquhoun, I. J .; McFarlane, W. J . Chem. Soc., Dalton Trans. 1982,
1915.
(28) Bruce, M. I.; Humphrey, M. G.; Patrick, J . M.; White, A. H.
Aust. J . Chem. 1983, 36, 2065.
(29) Riera, V.; Ruiz, M. A.; Villafan˜e, F.; Bois, C.; J eannin, Y. J .
Organomet. Chem. 1990, 382, 407.
The sensitivity of J PP to conformational changes
suggested that it might depend on temperature and
solvent. Values of 2J PP for 1 in deuterated toluene were
determined from -50 to 70 °C and found to decrease
from 122.4 to 110.6 Hz as the temperature was in-
creased (Table 4). This can be attributed to a steady
decrease in the population of complexes having confor-
mation I as the temperature increases. A significant
2
solvent dependence is also observed with J PP varying
over about 13 Hz (Table 5); higher values of J PP tend
(30) Bottcher, H.-C.; Krug, A.; Hartung, H. Polyhedron 1995, 14,
901.
2
to occur in solvents with greater donor numbers.
Con clu sion s. The dppm-bridged complex, 2, does
not form from 1 at room temperature but does form at
elevated temperatures. An explanation, derived from
the crystal structures of the two complexes and their
31P and 13C spectra, is the dramatic conformational
change in the dppm ligand that accompanies the reac-
(31) Bruce, M. I.; Cifuentes, M. P.; Grundy, K. R.; Liddell, M. J .;
Snow, M. R.; Tiekink, E. R. T. Aust. J . Chem. 1988, 41, 597.
(32) Cano, M.; Campo, J . A.; Pe´rez-Garc´ıa, V.; Gutie´rrez-Puebla, E.;
Alvarez-Ibarra, C. J . Organomet. Chem. 1990, 382, 397.
(33) Kerschner, J . L.; Fanwick, P. E.; Rothwell, I. P. J . Am. Chem.
Soc. 1988, 110, 8235.
(34) Douglas, G.; Manojlovic-Muir, L.; Muir, K.; Michael C.; J en-
nings, M. C.; Lloyd, B.; Mehda R.; Schoettel, G.; Puddephatt, R. J .
Organometallics 1991, 10, 3927.

Studies of a Reluctant Ligand
Organometallics, Vol. 17, No. 19, 1998 4281
tion. Supporting evidence for the solution conformation
of 1 includes phosphorus-phosphorus coupling that is
the largest yet observed in a complex of dppm and long-
range coupling between the uncoordinated phosphine
and the equatorial carbonyl carbons, an unprecedented
observation.
National Science Foundation (CHE-9708342 and CHE
8851619) for support of this work and for the purchase
of a General Electric QE300 NMR spectrometer.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data, positional and thermal parameters, and bond distances
and angles for complexes 1 and 2 (14 pages). Ordering
information is given on any current masthead page.
Ackn owledgm en t. We thank the Camille and Henry
Dreyfus Foundation for a Scholar/Fellow grant, and the
OM980288P