Synthesis and characterization of molybdenum and tungsten complexes containing tris(diphenylphosphino)methane (tdppm)

Article abstract of DOI:10.1016/j.inoche.2012.01.030

Reaction of tris(diphenylphosphino)methane, (Ph₂P)₃CH (tdppm) with 1 equivalent of M(CO)₃(EtCN)₃ (M = Mo 1a, M = W 1b) affords [Mo{η²-(Ph₂P)₃CH}(CO) ₃(EtCN)] 2a and [W{η²-(Ph₂P) ₃CH}(CO)₃(EtCN)] 2b, respectively. Single crystal structure determinations were performed for complexes 2a and 2b. Both structures adopt a distorted octahedral geometry about Mo and W atoms, with one CO and EtCN group occupying an axial position, while the phosphine ligand and two CO ligands occupy the equatorial positions. To our knowledge this is the first structurally-characterized W complex containing the tdppm ligand.

Full text of DOI:10.1016/j.inoche.2012.01.030

Inorganic Chemistry Communications 18 (2012) 110–112
Contents lists available at SciVerse ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Synthesis and characterization of molybdenum and tungsten complexes containing
tris(diphenylphosphino)methane (tdppm)
Agnes Mrutu a, Wilson N. William a, Richard A. Kemp a,b,
⁎
a
Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, NM 87131, USA
b
Advanced Materials Laboratory, Sandia National Laboratories, Albuquerque, NM 87106, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Reaction of tris(diphenylphosphino)methane, (Ph2P)3CH (tdppm) with 1 equivalent of M(CO)3(EtCN)3
(M=Mo 1a, M=W 1b) affords [Mo{η2-(Ph2P)3CH}(CO)3(EtCN)] 2a and [W{η2-(Ph2P)3CH}(CO)3(EtCN)]
2b, respectively. Single crystal structure determinations were performed for complexes 2a and 2b. Both
structures adopt a distorted octahedral geometry about Mo and W atoms, with one CO and EtCN group occu-
pying an axial position, while the phosphine ligand and two CO ligands occupy the equatorial positions. To
our knowledge this is the first structurally-characterized W complex containing the tdppm ligand.
© 2012 Elsevier B.V. All rights reserved.
Received 5 November 2011
Accepted 22 January 2012
Available online 31 January 2012
Keywords:
Molybdenum
Tungsten
Tris(diphenylphosphino)methane
X-ray crystallography
One of the primary goals of synthetic organometallic or coordina-
tion chemists is to control the interactions between metals and li-
gands. Towards this end, over the years chemists have prepared
ligands with a wide range of features designed to achieve their partic-
ular purposes. As a common example, ligands have been carefully
crafted with precise steric features designed to control reactivity at
a metal site. As another generalized example, ligands have been syn-
thesized that are multidentate in order to again control reactivity at
the metal site, or perhaps to force two metals to interact. The varieties
of ligands and ligand–metal interactions that are possible appear to
be virtually unlimited. In this submission we report on some new
synthetic Mo and W chemistry of a known multidentate ligand, tris(-
diphenylphosphino)methane, (Ph2P)3CH, or tdppm [1,2]. It has been
well-documented in the organometallic literature, as well as in the
Cambridge Structural Database (CSD) [3], that this tridentate tdppm
ligand can act in various manners towards transition metals, coordi-
nating as either a bridging [4,5], bridging–chelating [6–10], chelating
[11–15], or simply as a monodentate ligand [12]. In particular, there
has been historical interest in using the three P atoms of tdppm as a
“capping” ligand for metals. We also note that the structure of the
tdppm ligand itself has also been reported [16].
phosphorus ligands has also been developed for coordination to
both mono- and multi-metallic complexes (illustrative examples in-
cluding tdppm are shown in Fig. 1). Herein, we report the synthesis
and characterization of Group 6 (Mo and W) metal complexes con-
taining the tdppm ligand that possess the general formula [M{η2-
(Ph2P)3CH}(CO)3(EtCN)] where M=Mo 2a, and W 2b. Interestingly,
complexes of tdppm with various transition metals have been struc-
turally characterized as noted above; however, crystallographically-
characterized tdppm complexes containing two of the most common
Group 6 metals – Mo and W – are rare (Mo) or non-existent (W). In
the rare cases of Mo, tdppm has only been used to bridge a Mo\Mo
quadruple bond [17], and to serve as a bridging ligand to Mo and Au
in a series of heterometallic compounds [18]. A search of the CSD
(version 5.32, November 2011 update) indicates that there are no di-
rectly bound tdppm-W complexes that have been structurally charac-
terized. Surprisingly, the starting tdppm-Mo complexes prior to Au
complexation have also not been structurally-characterized. In this
paper we help fill the void in the solid-state characterization of
these complexes and also utilize a Group 6 starting reagent –
M(CO)3(EtCN)3 – that leaves a weakly-coordinated EtCN moiety on
the complex that is available for further substitution chemistry.
As outlined in Scheme 1, reaction of M(CO)3(EtCN)3 (M=Mo 1a,
W 1b) with tdppm ligand in a 1:1 molar ratio in proprionitrile/
dichloromethane or toluene resulted in the formation of complexes
[Mo{η2-(Ph2P)3CH}(CO)3(EtCN)] 2a and [W{η2-(Ph2P)3CH}(CO)3(-
EtCN)] 2b in 65% and 70% yields, respectively [19]. In order to speed
up each reaction, brief sonication of the reaction mixtures occurred
during which time precipitates were formed. After sonication, each
reaction mixture was stirred at room temperature for an additional
12 h. The precipitates were removed by filtration and washed with
In an electronic sense, there are numerous examples of chelating
di-phosphorus ligands that are capable of donating lone pairs of elec-
trons to a single metal atom in a σ- rather than π-fashion. As well, the
σ-donor ligative behavior of various tri, tetra-, or higher chelating
⁎
Corresponding author at: Department of Chemistry and Chemical Biology, University
of New Mexico, Albuquerque, NM 87131, USA. Tel.: +1 505 2727609; fax: +1 505
2727336.
E-mail address: rakemp@unm.edu (R.A. Kemp).
1387-7003/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2012.01.030

A. Mrutu et al. / Inorganic Chemistry Communications 18 (2012) 110–112
111
R2P
P
R
PR2
R2P
PR2
R2P
PR2
H
C
R2P
PR2
R2P
PR2
PR2
R2P
PR2
tdppm, R = Ph
Fig. 1. Examples of multidentate phosphines (R = alkyl, aryl), including tdppm.
Fig. 2. Molecular structure of 2a with thermal ellipsoids projected at 50% level. Hydro-
gen atoms have been omitted for clarity. Selected bond distances (Å) and angles (°):
Mo1\C1 1.977(2), Mo1\C2 1.946(3), Mo1\N1 2.201(3), Mo1\P1 2.4962(6);
P1\Mo1\P2 67.24(3), C1\Mo1\C2 87.46(10), N1\Mo1\C2 178.57(11), C1\Mo1\P1
99.47(7), N1\Mo1\P1 88.51(6), C10\P1\C4 100.16(10), C10\P1\Mo1122.76(7).
Scheme 1. Preparation of tdppm complexes of Mo and W.
Single crystal X-ray analyses [21,22] of 2a and 2b definitively indi-
cated that the tdppm ligand had coordinated to the metal in a biden-
tate fashion for both complexes, leaving one phosphine arm free [23].
These structures represent rare examples of structurally character-
ized, tdppm complexes of Group 6 metals that do not contain any ad-
ditional metals. As well, each contains a residual EtCN ligand that is
more labile than the CO ligand. Complex 2a crystallizes in the ortho-
rhombic crystal system, space group Pnma, and contains a mirror
plane of symmetry bisecting through P(2), C(3), C(22)-C(24) and
Mo(1). As depicted in Fig. 2 complex 2a adopts a distorted octahedral
geometry in the solid-state. This distortion is mostly attributed to the
restricted bite angle of the chelating phosphine [P1-Mo1-P1 is
67.24(3)°]. The bite angle for complex 2a is comparable to those
found for the molybdenum complexes containing chelated phosphine
ligands [18,23,24]. However, this bite angle is smaller than that
reported by Beckett and co-workers [25] for the square-planar com-
plex [Pt{PPh2)2CHPPh2}2][BF4]2. Briefly, the structure consists three
CO ligands with Mo\C1 and Mo\C2 bond distances of 1.977(2) Å
and 1.946(3) Å, respectively. The Mo\C bond distances for 2a are
within the range of values for molybdenum carbonyl complexes
reported in the literature [26–28]. The bond lengths Mo1\P1 and
Mo1\N1 are 2.4962(6) Å and 2.201(3) Å, respectively. Both of
these values comparable favorably to other reported values for Mo
complexes in the literature [12–15]. One of the CO ligands and the
EtCN group is trans to each other and occupies axial positions, while
the chelating phosphine ligand and two CO ligands occupy the four
remaining equatorial positions. The EtCN ligand is located in the coor-
dination position to allow for the mirror plane symmetry found the
molecule.
diethyl ether and dried. Analytically-pure crystals of 2a and 2b were
grown at room temperature from a concentrated solution of each
complex in dichloromethane.
Complex 2a was fully characterized by a combination of 1H, 13C,
and 31P NMR spectroscopies, elemental analysis, IR, and single crystal
X-ray diffraction. Elemental analysis of complex 2a is consistent with
the calculated values for the proposed structure. The 1H NMR analysis
of 2a revealed a triplet at 1.02 ppm and a quartet at 1.32 ppm with
3JH − H =7.5 Hz, consistent with the \CH2CH3 group. As well, a singlet
observed at 4.75 ppm can be assigned to the hydrogen that is at-
tached to the tertiary carbon of tdppm ligand. The 13C NMR spectrum
of 2a in CD2Cl2 revealed peaks that are consistent with \C6H6,
\CH2CH3, and \CN groups; however, the chemical shift correspond-
ing to the \CO group was not observed. The inability to see this peak
is not surprising and may be due to low signal-to-noise in the absence
of 13C-labeled carbonyls. At ambient temperature, the 31P NMR spec-
trum of 2a in CD2Cl2 exhibits a doublet at 24.2 ppm and a triplet at
2
−23.0 ppm with JP − P =23 Hz, indicating two different phosphorus
environments. This suggests that phosphorus atoms of the ligand are
bound to the metal in a bidentate fashion with one free phosphine
arm. The υCO frequencies for 2a are observed at 1890 cm−1 and
1770 cm−1, very similar to those observed by Chatt and co-workers
[20] and Fernandez and co-workers [18] for related complexes utiliz-
ing Group 6 hexacarbonyls as the starting reagents.
As with 2a, 2b was also fully characterized by a combination of 1H,
and 31P NMR spectroscopy, elemental analysis, IR and X-ray crystal-
lography. 13C NMR data were not obtained because of the poorer sol-
ubility of complex 2b. In the 1H NMR spectrum the characteristic
singlet observed at 5.60 ppm is found and can be assigned to the hy-
drogen that is attached to the tertiary carbon of tdppm ligand. Similar-
ly to complex 2a, 31P NMR analysis of complex 2b in CD3OCD3 exhibits
Similarly to 2a, the W atom in 2b is coordinated by three carbonyl
groups, EtCN, and the two phosphorus groups from the tdppm ligand;
hence, it adopts a distorted octahedral geometry in the solid state
(Fig. 3). Analysis shows that 2b is isostructural to 2a and crystallizes
in the orthorhombic crystal system, space group Pnma. Similar to
2a, complex 2b also contains a mirror plane of symmetry bisecting
through P2, C2, O2, EtCN, and W1. The restricted bite angle of the
phosphine, P1-W1-P1 of 67.23(5)° is comparable with those reported
in the literature for tungsten compounds containing the related li-
gand bis(diphenylphosphino)methane, (Ph2P)2CH2 [20]. The chelate
ring formed by W, P(1), C(3), and P(1) in complex 2b is nearly planar.
2
a doublet at 2.1 ppm and a triplet at −23.1 ppm with JP − P =25 Hz,
indicating again that the two phosphorus atoms are bound to the
metal in a bidentate fashion. Elemental analysis for 2b was consistent
with the calculated values for %N and %H; however, a slight difference
in %C between experimental and calculated was observed. IR analysis
for complex 2b indicated strong υCO absorbances at 1930 cm−1 and
1785 cm−1, again similar to those reported by Chatt and co-workers
[20].

112
A. Mrutu et al. / Inorganic Chemistry Communications 18 (2012) 110–112
be obtained from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data to this
article can be found online at doi:10.1016/j.inoche.2012.01.030.
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Fig. 3. Molecular structure of 2b with thermal ellipsoids projected at 50% level. Hydro-
gen atoms have been omitted for clarity. Selected bond distances (A) and angles (°):
W1\C1 1.971(5), W1\C2 1.952(7), W1\N1 2.179(6) , W1\P1 2.4866(10); C2\W1\C1
88.17(18), C2\W1\N1 178.8(2), C1\W1\N1 91.04(17), C1\W1\P1 99.07(13),
P1\W1\P1 67.23(5), C13\P1\W1 118.94(14), C7\P1\W1 122.51(13).
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[29]. Aditionally, the W1\P1 and W1\N1 bond lengths are
2.4866(10) Å and 2.179(6) Å, respectively. The W\P bond distance
found in complex 2b is slightly shorter than the values observed in
other tungsten complexes [24,29,30].
In summary, we have prepared and fully-characterized rare Mo
and W metal complexes that contain tdppm ligand acting as a tradi-
tional bidentate ligand. The coordination mode observed in com-
plexes 2a and 2b by X-ray crystallography confirms that the tdppm
ligand acts as a chelating ligand to Group 6 metals, with three CO's
and one EtCN ligand filling out the distorted octahedral coordination
sphere. The present work has helped fill the void in solid-state char-
acterization of directly bound tdppm-W and Mo complexes. Impor-
[19] Preparation of 2a: the tpddm (Ph2P)3CH ligand (0.30 g, 0.52 mmol) was added to
a 100 ml Schlenk flask containing 10 ml of toluene in an inert atmosphere. This
was followed by dropwise addition of 1a (0.18 g, 0.52 mmol) dissolved in 10 ml
of propionitrile. The solution was sonicated for 5 min and then allowed to stir
for additional 12 h. The precipitate formed was separated from the solution
using a fine filter frit. The solid was washed with diethyl ether (10 ml×3) then
dried under vacuum. The yield of 2a was 0.30 g [65% isolated, crystalline product
based on Mo(CO)3(EtCN)3]. Analytically pure crystals of 2a were obtained by re-
crystallization from CH2Cl2. Complex 2a decomposed at 188 °C. 1H NMR (CD2Cl2,
3
300 MHz, ppm): 6.43–7.76 (m, Ar-H, 30H), 4.75 (s, CH, 1H), 1.32 (q, JH − H
=
7.5 Hz, CH2, 2H), 1.03 (t, JH − H =7.5 Hz, CH3, 3H). 13C{1H} NMR (CD2Cl2,
3
75 MHz, ppm): 175.2, 154.3, 129.5, 124.9, 59.3, 58.6, 58.1. 31P{1H} NMR (CD2Cl2,
2
2
121.49 MHz, ppm): 24.2 (d, JP − P =23 Hz), −23.0 (t, JP − P =23 Hz). Anal.
Calcd: C 64.27, H 4.52, N 1.74. Found: C 64.25, H 4.37, N 1.39. IR: υCO =1930,
1785 cm−1. Compound 2b was prepared similarly in 70% yield. 2b decomposed
at 180 °C. 1H NMR (CD3COCD3, 300 MHz, ppm): 6.8–7.9 (m, Ar-H, 30H), 5.60 (s,
CH, 1H), 2.57 (q, JH − H =6.6 Hz, CH2, 2H), 1.13 (t, JH − H =6.6 Hz, CH3, 3H). 31P
3
3
{1H} NMR (CD3COCD3, 121.49 MHz, ppm): 2.1 (d, 2JP−P=25 Hz), −23.1 (t, 2JP−P
25 Hz). Anal. Calcd: C 57.80, H 4.07, N 1.57. Found: C 56.84, H 4.19, N 1.25. IR:
CO =1890, 1770 cm−1
=
tantly, using
a Group 6 starting material M(CO)3(EtCN)3 that
υ
.
eventually results in a weakly coordinated EtCN group remaining on
the complex, clearly has an advantage over M(CO)6-derived com-
plexes in that further substitution chemistry is facilitated.
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[22] Diffraction data were obtained on a Bruker X8 ApexII κ-axis diffractometer with
graphite-monochromated Mo-Kα radiation (λ=0.71073 Å) and a CCD camera.
The intensity data were corrected for Lorentz and polarization effects. The struc-
ture was solved using direct methods and refined by full-matrix least-squares
methods on F2. All hydrogens were added in idealized positions and not allowed
to vary. Crystal structure analysis for 2a: C43H36MoNO3P3, Fw 803.63, orthorhom-
bic, Pnma, a=16.5384(3) Å, b=20.6593(4) Å, c=11.3661(2)Å, α=β=γ=90˚,
V=3883.48(12) Å3, Z=4, F(000)=1648.0, T=188(2) K, green rods, 0.25×
0.07×0.07 mm3, μ=0.501 mm−1, Dx=1.374 g/cm3, 2θ-range 0.998 to 30.56°,
independent reflections 84431, wR (all data) 0.0885, R1[I>2(I)] 0.0753. Crystal
Acknowlegments
For financial support of this project we acknowledge the American
Chemical Society–Petroleum Research Fund via a grant to RAK
(48822-ND3). The Bruker X-ray diffractometer was purchased via a
National Science Foundation CRIF:MU award to the University of
New Mexico (CHE04-43580), and the NMR spectrometers were
upgraded via grants from the NSF (CHE08-40523 and CHE09-
46690). We also thank Dr. Eileen Duesler of UNM for assistance
structure analysis for 2b:
a=16.4570(5), b=20.7161(6),
V=3859.0(2) Å3, Z=4, F(000)=1776.0, T=188(2) K, yellow planks,
0.25×0.02×0.02 mm3, μ=3.158 mm−1 Dx=1.534 g/cm3, 2θ-range 0.998 to
C43H35WNO3P3, Fw 891.49, orthorhombic, Pnma,
c=11.3192(4) Å, α=β=γ=90°,
,
28.360°, independent reflections 4929, wR (all data) 0.0734, R1[I>2(I)] 0.0618.
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with X-ray data analysis. Sandia is
a multiprogram laboratory
operated by Sandia Corporation, a Lockheed Martin Company, for
the United States Department of Energy under Contract No. DE-
AC04-94AL85000.
Appendix A. Supplementary data
[30] W.A. Schenk, K. Nielsen, N.I. Burzlaff, M. Hagel, Inorg. Chem. 41 (2002)
1079–1085.
The structural data for 2a and 2b have been deposited as CCDC
851857 and 851858. These data are available free of charge and can