Synthesis, X-ray crystal structure, and reactivity of Pd2(μ-dotpm)2 (dotpm = bis(di-ortho-tolylphosphino)methane)

Article abstract of DOI:10.1016/j.jorganchem.2009.10.010

Alkylation of PdCl₂(dotpm) (dotpm = bis(di-ortho-tolylphosphino)methane) with n-butyllithium produces the binuclear Pd(0) complex Pd₂(μ-dotpm)₂ and the elimination byproducts 1-butene, cis-2-butene, trans-2-butene, butane,

Full text of DOI:10.1016/j.jorganchem.2009.10.010

Journal of Organometallic Chemistry 695 (2010) 201–205
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis, X-ray crystal structure, and reactivity of Pd2(l-dotpm)2
(dotpm = bis(di-ortho-tolylphosphino)methane)
*
Eleazar Lumbreras Jr., Elizabeth M. Sisler, Quinetta D. Shelby
Department of Chemistry, 1110 West Belden Avenue, DePaul University, Chicago, IL 60614, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 13 July 2009
Received in revised form 9 October 2009
Accepted 9 October 2009
Available online 10 November 2009
Alkylation of PdCl2(dotpm) (dotpm = bis(di-ortho-tolylphosphino)methane) with n-butyllithium pro-
duces the binuclear Pd(0) complex Pd2( -dotpm)2 and the elimination byproducts 1-butene, cis-2-
butene, trans-2-butene, butane, and octane. The dibutyl complex, Pd(dotpm)(n-Bu)2, is presumed to be
the reaction intermediate. The crystal structure of Pd2( -dotpm)2 reveals that the methylene groups of
l
l
the bridging dotpm ligands are located on opposite sides of the Pd2P4 unit, forming an 8-membered ring
that is in an elongated chair conformation. The four phosphorus atoms are not coplanar, and the P1–P2–
P3–P4 ring has a torsion angle of 13.8°, which minimizes the spatial interactions among the o-tolyl rings.
The Pd–Pd bond distance is 2.8560(6) Å, which indicates that there is a weak ‘‘closed-shell” bonding
interaction between the d10–d10 metal centers. Each palladium atom has a nearly linear geometry, and
the eight methyl groups of the dotpm ligands shield the open coordination sites on the metal centers.
Four methyl groups shield the metal atoms above and below the Pd2P4 ring cavity, and four methyl
Keywords:
Palladium
Bis(di-ortho-tolylphosphino)methane
Binuclear
Bisphosphine
Reductive elimination
Crystal structure
groups block the open metal sites outside of the Pd2P4 ring. The Pd2(
l
-dotpm)2 complex readily under-
-CH2)( -dotpm)2.
goes oxidative addition of dichloromethane to form the rigid A-frame complex Pd2Cl2(
l
l
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
bis(diisopropylphosphino)methane) is obtained as a byproduct of
the catalytic reaction of 1,3-butadiene with ethyl methylacetoace-
Binuclear complexes Pd2(
contain two coordinatively unsaturated palladium(0) centers that
are potential catalysts for the activation of organic halides [1–3]
l
-P–P)2 are of interest because they
tate in the presence of Pd(
structure of Pd2( -dippm)2 has been obtained [13]. The complex
Pd2( -dippe)2 (dippe = 1,2-bis(diisopropylphosphino)ethane) has
g
2-1,3-butadiene)(dippm); the X-ray
l
l
and hydrosilanes [1,2,4]. Another attractive feature of Pd2(
l
-P–P)2
been implicated in several reactions [14–17], but it can be isolated
complexes is that there is a weak ‘‘closed-shell” bonding interaction
between the d10–d10 metal centers [5–11] that can potentially
promote a cooperative catalytic system in which the substrate is
bonded to and activated by both metal centers [5]. One conse-
quence of this binuclear system with open coordination sites and
in high yield from the reduction of Pd(dippe)(OAc)2 by hydrazine
[1]. Similarly, hydrazine reduces Pd(dcpe)Cl2 to yield Pd2(l-dcpe)2
[1] (dcpe = 1,2-bis(dicyclohexylphosphino)ethane); this complex
also forms from the photolysis of a Pd(dcpe) oxalate compound,
and its X-ray structure has been determined [2]. A recent report
enhanced reactivity is that Pd2(
l
-P–P)2 complexes are rare, and
showed that the mixed compound, Pd2(l-dippe)(l-dcpe), forms
they require sterically bulky or electron-rich substituents on the
bisphosphine ligands to help stabilize them.
when Pd2( -dippe)2 and Pd2( -dcpe)2 are combined in solution;
the mixed compound has not been isolated [1]. There are two
l
l
Bisphosphine complexes Pd2(
a number of different reaction methods [1–3,12–18]. For example,
Pd2( -dppm)2 [3,12] (dppm = bis(diphenylphosphino)methane)
has not been isolated, but it is observed in situ from the dispropor-
tionation of Pd2ClMe( -dppm)2 [3], and it has been proposed as an
intermediate in the electrolysis of Pd2( -dppm)3 [12]. Most of the
other Pd2( -P–P)2 complexes are formed from mononuclear
palladium compounds. For example, Pd2( -dippm)2 (dippm =
l-P–P)2 have been synthesized by
examples of the reductive elimination of ethane from dimethylpal-
ladium species to form Pd2(
Pd(dcpm)Me2 (dcpm = bis(dicyclohexylphosphino)methane) gives
the dimer Pd2( -dcpm)2, which has been crystallographically char-
acterized [18]. In an analogous reaction, the complex Pd2(
l-P–P)2 complexes. Thermolysis of
l
l
l
l-
l
dtbpm)2 (dtbpm = bis(di-tert-butylphosphino)methane) forms in
high yield from the reaction of dtbpm with Pd(tmeda)Me2 in hot
benzene; the product is believed to form from the reductive elim-
ination of ethane via an unstable Pd(dtbpm)Me2 intermediate [18].
l
l
We now report a new procedure for the synthesis of a Pd2(l-P–P)2
complex that is the first example containing two substituted aryl
bisphosphine bridges. Our results demonstrate that sterically
* Corresponding author. Tel.: +1 773 325 7402; fax: +1 773 325 7421.
E-mail addresses: qshelby@depaul.edu, qshelby@condor.depaul.edu (Q.D. Shel-
bulky aryl groups stabilize the Pd2(l-P–P)2 complex.
by).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.10.010

202
E. Lumbreras Jr. et al. / Journal of Organometallic Chemistry 695 (2010) 201–205
solid n-BuLi, 31P signals belonging to 1 (d À2.8), free dotpm (d
2. Results and discussion
À43.1), and an unknown species (d À22.7) appear. Over time, the
resonance for complex 1 significantly predominates (88%) in solu-
tion followed by the signal for dotpm; the singlet for the unknown
species disappears completely. Similar changes were observed in
the corresponding 1H NMR spectra. Proton resonances for complex
1 increase in intensity while those for free dotpm gradually be-
The room-temperature reaction of PdCl2(dotpm) [19]
(doptm = bis(di-ortho-tolylphosphino)methane) with
lents of n-BuLi in diethyl ether yields red crystals of Pd2(
2
equiva-
-dot-
l
pm)2, 1 (Scheme 1). We believe that the reaction proceeds
through the dialkylated intermediate Pd(dotpm)(n-Bu)2, which
quickly undergoes reductive elimination to yield the dimer.
The X-ray crystal structure of 1 (Fig. 1) shows that both dotpm
ligands bridge the two palladium centers. The methylene groups
are located on opposite sides of the Pd2P4 unit, forming an 8-mem-
bered ring that is in an elongated chair conformation. The four
phosphorus atoms in 1 are not coplanar, and the P1–P2–P3–P4 ring
has a torsion angle of 13.8°. The slight twist from planarity mini-
mizes the spatial interactions among the o-tolyl rings. Notably,
all eight methyl substituents of the o-tolyl rings are oriented to-
ward the open sites of the coordinatively unsaturated Pd atoms.
Four methyl groups shield the metal atoms above and below the
Pd2P4 ring cavity, and four methyl groups block the open metal
sites outside of the Pd2P4 ring.
come minor signals in the NMR spectra. Interestingly, three proton
3
resonances appear at
d
1.00 (t, JHH = 7.3 Hz, CH3), 2.44 (s,
C6H4CH3), and 3.47 (t, 2JPH = 7.3 Hz, PCH2P), and they decrease with
the same relative magnitudes. The ratio of these three signals is
approximately 6:12:2, respectively, and they are associated with
another resonance at d 1.63 (m), which is partially obscured by
other reaction byproducts. Other proton signals belonging to the
intermediate could not be definitively identified because of the
presence of several overlapping signals in the 1–3 ppm range. In
repeated studies, the four proton signals belonging to the reaction
intermediate are observed only when the phosphorus signal at d
À22.7 is present in the corresponding 31P NMR spectrum. The neg-
ative 31P chemical shift value for the intermediate is indicative of a
chelating bisphosphinomethane ligand [21,22], and the relative
intensities of the proton resonances assigned to the intermediate
suggest that this species has one dotpm ligand for every two
methyl groups. We believe that the intermediate is the dialkylated
complex Pd(dotpm)(n-Bu)2. Other key resonances in the 1H NMR
The geometries of both Pd centers in 1 deviate slightly from lin-
earity (P3–Pd1–P1 173.56(3)° and P4–Pd2–P2 173.99(3)°), and the
two palladium atoms are drawn toward each other. The Pd1–Pd2
bond distance is 2.8560(6) Å, which is on the long end of the Pd–
Pd bond range (2.7611(5)–2.8582(6) Å) found for other Pd2(
P)2 complexes [2,13,18]. Although the Pd–Pd bond distance is too
long for a formal Pd–Pd -bond (2.53–2.77 Å) [20], 1 likely pos-
sesses weak d10–d10 Pd(0)–Pd(0) bonding interactions attributed
l-P–
r
to d–p mixing in the
Pd2(
r
-bonding orbital that are proposed in its
*
l
-P–P)2 analogues. The long wavelength dr ? pr electronic
absorption of 1 (kmax = 494 nm) is slightly lower in energy than re-
lated binuclear complexes (Pd2( -dippe)2, kmax = 455 nm [1];
Pd2( -dcpe)2, kmax = 456 nm [2]; Pd2( -dtbpm)2, kmax = 462 nm
[18]; Pd2( -dcpm)2, kmax = 480 nm [18]). The lower absorption en-
l
l
l
l
ergy for 1 is consistent with its relatively longer Pd–Pd bond
length.
The NMR spectra for 1 are consistent with a highly symmetrical
molecule. Its 31P{1H} NMR spectrum in tetrahydrofuran-d8 con-
tains only a sharp singlet at d À4.8. Its corresponding 1H NMR spec-
trum contains a singlet at d 2.48 for the eight methyl groups of the
o-tolyl rings. The methylene signal at d 3.33 is broad due to unre-
solved coupling to phosphorus. The four unique aromatic protons
on each o-tolyl ring resonate at d 6.87 (d), 6.94 (t), 7.09 (t), and
7.56 (broad d), where the latter resonance shows unresolved phos-
phorus coupling. The 13C NMR spectrum of 1 contains one methyl
resonance at d 23.3, a methylene resonance at d 32.4, and six aro-
matic resonances at d 126.1, 129.2, 131.7, 133.5, 137.0, and 142.6;
carbon–phosphorus coupling was not observed. Clearly, movement
of the P4 and o-tolyl rings in 1 is fast on the NMR time scale.
Fig. 1. Molecular structure of Pd2(l-dotpm)2 (1). View down the Pd2P4 ring cavity.
Thermal ellipsoids are represented by the 35% probability surfaces. Selected bond
lengths (Å) and angles (°): Pd1–Pd2 2.8560(6), Pd1–P1 2.2698(10), Pd1–P3
2.2615(10), Pd2–P2 2.2676(10), Pd2–P4 2.2643(10), P3–Pd1–P1 173.56(3), P4–
Pd2–P2 173.99(3), P1–C1–P2 115.46(18), P3–C30–P4 114.81(17), P1–Pd1–Pd2–P4
170.80(3), P3–Pd1–Pd2–P2 170.14(3).
2.1. NMR study of the synthesis of complex 1
The formation of 1 was monitored by NMR spectroscopy. When
an insoluble mixture of PdCl2(dotpm) in C6D6 is combined with
o-tolyl
o-tolyl
o-tolyl
o-tolyl
o-tolyl
o-tolyl
o-tolyl
P
Pd
P
P
Pd
P
(o-tolyl)2P
(o-tolyl)2P
P(o-tolyl)2
Pd Pd
P(o-tolyl)2
CH2
P
P
Cl
Pd
CH2Cl2
4 n-BuLi
2
Cl
Cl
Cl
o-tolyl
o-tolyl
o-tolyl
o-tolyl
o-tolyl
1
2
Scheme 1. Preparation and reaction of complex 1.

E. Lumbreras Jr. et al. / Journal of Organometallic Chemistry 695 (2010) 201–205
203
spectra provide evidence for the formation of alkenes (1-butene,
complex, 1, or in its unsubstituted dppm analogue, Pd2Cl2(
l-
cis-2-butene, and trans-2-butene) and alkanes (butane and octane)
during the reaction process. The NMR data suggests that 1-butene
isomerizes to the more stable 2-butene compounds, and the for-
mation of octane in the reaction solution was confirmed by GC/
MS techniques. The ratio of alkenes to alkanes varies somewhat
in repeated studies (1.0:1.3–1.0:1.9, respectively), however, the
concentration of alkanes is always higher than the concentration
of alkenes. The generation of free dihydrogen was not evident from
the 1H NMR spectra. Variable-temperature NMR studies conducted
in toluene-d8 show that the intermediate and free dotpm are pres-
ent at À40 °C and that complex 1 is formed above 0 °C. Other phos-
phorus-containing species were not detected in the 31P NMR
spectra, and 1H signals for dihydrogen and Pd hydride species were
not observed. It is possible that, in the synthesis of 1, the mononu-
clear dibutyl complex Pd(dotpm)(n-Bu)2 forms initially, then rap-
idly undergoes b-hydride elimination of alkene and/or reductive
coupling of alkane, forming the bridged dimer. Notably, the ther-
CH2)( -dppm)2 [3,24].
l
2.3. Steric effects
We further examined the spatial effects of the aromatic substit-
uents in the ligand and found that PdCl2(dppm) [13,25,26] reacts
with 2 equivalents of n-BuLi in diethyl ether to give orange-red
crystals of the known binuclear complex Pd2(l-dppm)3 (Scheme
2) [27–29]. Obviously, the dipalladium(0) structure can accommo-
date three bridging dppm ligands but only two bridging dotpm li-
gands, because the o-tolyl groups are more sterically demanding.
The NMR study on the reaction between PdCl2(dppm) and n-
BuLi showed that after 5 min at room temperature, Pd2(
is the only phosphorus-containing species present in solution. Var-
iable-temperature NMR spectra show that Pd2( -dppm)3 and free
dppm are present at À40 °C. Dihydrogen was detected in solution
(d 4.46) however, signals for Pd hydride species were not observed.
Resonances corresponding to a dibutyl reaction intermediate were
not observed in any of the NMR spectra, although two similar stud-
ies reported the presence of the dimethyl complex Pd(dppm)Me2
l-dppm)3
l
mal decomposition of the dinuclear dibutyl complex, [Pd2Bu2(
l-
Br)( -dppm)2]PF6, was reported to give 1-butene and 2-butene
l
as the only elimination products [23]. A report showed that both
dimethyl complexes Pd(dcpm)Me2 and Pd(dtbpm)Me2 undergo
as the intermediate for the formation of Pd2(l-dppm)3 [19,30].
Apparently, the reaction involving dppm occurs faster than the
dotpm reaction, and free dppm is not observed because three li-
reductive elimination of ethane to yield the dimers Pd2(
l-dcpm)2
and Pd2( -dtbpm)2, respectively [18]. Apparently, our synthetic
l
route to 1 also proceeds via reductive elimination processes.
gands are required to form Pd2(
responding to alkene and alkane byproducts suggest that both 1
and Pd2( -dppm)3 form through the same reaction mechanism.
l-dppm)3. Proton resonances cor-
2.2. Reactivity of complex 1
l
Complex 1 is stable in most organic solvents. Crystals of 1 and
its pink-red powder obtained when the reaction solution is too
concentrated are not very soluble in fresh diethyl ether; 1 is
slightly soluble in pentane but very soluble in tetrahydrofuran,
benzene, and toluene. Interestingly, complex 1 readily adds dichlo-
2.4. Conclusions
In summary, this study shows that PdCl2(dotpm) reacts with n-
BuLi to form Pd2(l-dotpm)2 and the elimination byproducts 1-bu-
tene, cis-2-butene, trans-2-butene, butane, and octane. Presum-
ably, the dibutyl complex, Pd(dotpm)(n-Bu)2, is the reaction
intermediate. This reaction method is a new route for the synthesis
of a zerovalent dipalladium bisphosphine complex. The complex
romethane to form the new methylene-bridged complex Pd2Cl2(
CH2)( -dotpm)2, 2 (Scheme 1). A similar result was reported for
the dppm analogue of 1; Pd2( -dppm)2, generated in situ, reacts
easily with dichloromethane to give Pd2Cl2( -CH2)( -dppm)2 [3].
Unlike the tri-bridged complex Pd2( -dppm)3 [24], the dimers
Pd2( -dppm)2 and 1 are highly reactive toward C–Cl oxidative
l-
l
l
l
l
Pd2(
l
-dotpm)2 quickly undergoes oxidative addition of dichloro-
-CH2)( -dotpm)2.
-dotpm)2 are
l
methane to form the A-frame complex, Pd2Cl2(
Additional studies on the reactivity of Pd2(
l
l
l
l
addition because their Pd(0) centers are more coordinatively
unsaturated.
underway.
The room temperature 1H NMR spectrum of 2 contains broad
resonances throughout. The Pd–CH2–Pd protons resonate at d
1.64 (br s). Two resonances at d 1.94 (br s) and 2.32 (br s) corre-
spond to the inequivalent methyl substituents of the o-tolyl rings
that occupy opposite sides of the Pd2P4 plane. The two inequivalent
methylene protons of dotpm resonate at d 3.05 (br s) and 3.78 (br
s). The aromatic region of the 1H NMR spectrum of 2 contains
broad multiplets at d 6.96–7.32. The room temperature 31P NMR
spectrum of 2 contains two very broad resonances at d 17.7 and
23.1. Complex 2 decomposes slowly in solution even at low tem-
peratures, therefore, meaningful 1H NMR data at low temperature
were not obtained. However, at À68 °C, the 31P NMR spectrum of 2
3. Experimental
3.1. General methods
All operations were performed under nitrogen in a drybox or by
using Schlenk and cannula methods. Diethyl ether and dichloro-
methane were distilled immediately before use from sodium ben-
zophenone or calcium hydride, respectively. The compounds
PdCl2(dppm) [12] and dotpm [19] were prepared according to lit-
erature methods. The chemicals palladium(II) dichloride, n-butyl-
lithium, and dichloromethane-d2 were purchased from Aldrich
and used as received. Benzene-d6 (Aldrich) was distilled from so-
dium benzophenone. Tetrahydrofuran-d8 (Aldrich) was dried over
alumina before use. IR spectra were recorded on a Nicolet Avatar
360 Fourier transform infrared spectrometer as Nujol mulls
3
contains two major signals at d 14.9 (d of d, JPP = 54, 15 Hz) and
3
18.2 (d of d, JPP = 54, 15 Hz).
The A-frame complex 2 has two potential mirror planes, one
along the Cl–Pd–Pd–Cl plane and another that bisects the three
methylene carbon atoms. As noted previously for the crystal struc-
ture of 1, steric crowding of the o-tolyl groups is minimized by a P4
twist angle of 13.8°. We expect that complex 2 also possesses a dis-
torted P4 plane because steric congestion around its two Pd centers
is increased significantly by the bridging methylene and terminal
chlorine atoms bonded to the two metal centers. The NMR spectra
of 2 at room temperature indicate that twisting of the Pd2P4 plane
and rotation or twisting of the aromatic rings are more hindered in
the A-frame structure than in its coordinatively unsaturated parent
Ph Ph
P
P
P
Cl
Cl
6 n-BuLi
Pd
Pd
Pd
P
P
P
3
P
P
Ph Ph
Pd2(µ-dppm)3
Scheme 2. Preparation of complex Pd2( -dppm)3.
l

204
E. Lumbreras Jr. et al. / Journal of Organometallic Chemistry 695 (2010) 201–205
2
2
between KBr salt plates. The NMR data were recorded on a Bruker
Avance 300 spectrometer with the following frequencies and refer-
ences: 300 MHz (1H, residual solvent), 75 MHz (13C, residual sol-
vent), or 121 MHz (31P, external H3PO4). The low temperature
NMR data were recorded on a Varian U400 spectrometer at
161 MHz (31P) at the University of Illinois at Urbana-Champaign.
Chemical shifts are reported in ppm (positive shifts to high fre-
quency) and coupling constants in hertz. All spectra were recorded
at ꢀ20 °C except where indicated. UV–Vis data were obtained on a
Varian Cary 100 UV–Visible spectrophotometer. GC/MS spectra
were recorded on an HP-6890 instrument equipped with an Agi-
lent Technologies 5975 Mass Selective Detector. Low resolution
electrospray (ESI) mass spectra were obtained at the University
of Illinois at Urbana-Champaign. Elemental analyses were per-
formed by Intertek (Whitehouse, NJ).
À68 °C): d 14.9 (d of d, JPP = 54, 15 Hz), 18.2 (d of d, JPP = 54,
15 Hz). mass spectrum (ESI): m/z 1143, 100% [M+ÀCl].
3.5. Tris[
l-bis(diphenylphosphino)methane]dipalladium(0),
Pd2( -dppm)3
l
To a pale yellow suspension of PdCl2dppm (0.30 g, 0.53 mmol)
in diethyl ether (20 mL) was added n-BuLi (0.73 mL of a 1.6 M solu-
tion in hexanes, 1.17 mmol). The resulting dark red mixture was
stirred for 2 h and filtered twice through Celite. The solution was
allowed to sit at room temperature to afford orange-red crystals
of Pd2(l-dppm)3. Yield: 0.086 g (35%). Mp: 151 °C (dec.) Anal Calc.
for C75H66P6Pd2: C, 65.94; H, 4.87. Found: C, 62.94; H, 4.62%. 1H
3
NMR (thf-d8): d 3.04 (br s, 6H, PCH2P), 6.79 (t, JHH = 7.5 Hz, 24H,
3
3
m-C6H5), 6.96 (t, JHH = 7.2 Hz, 12H, p-C6H5), 7.24 (d, JHH = 6.9 Hz,
24H, o-C6H5). 13C{1H} NMR (thf-d8): d 29.6 (s, PCH2P), 127.0 (s, p-
C6H5), 127.2 (s, m-C6H5), 132.3 (s, o-C6H5), 142.5 (m, i-C6H5).
31P{1H} NMR (thf-d8): d 13.0 (s).
3.2. Dichlorobis[di-(2-methylphenyl)phosphino]methane-
palladium(II), PdCl2(dotpm) [19]
A solid mixture of dotpm (0.655 g, 1.49 mmol) and PdCl2
(0.26 g, 1.47 mmol) was suspended in 50% ethanol (25 mL) and
concentrated HCl (25 mL). The mixture was refluxed for 16 h, and
a yellow solid precipitated from solution. The solution was filtered.
The yellow solid was washed with H2O (2 Â 25 mL) and ethanol
(2 Â 25 mL) then dried under vacuum. Yield: 0.804 g (89%). Anal
Calc. for C29H30Cl2P2Pd: C, 56.38; H, 4.89; P, 10.03. Found: C,
56.50; H, 4.88; P, 9.24%. 1H NMR (CDCl3): d 2.31 (s, 12H,
3.6. NMR experiments on the formation of 1 and Pd2(l-dppm)3
Room temperature: For the synthesis of 1, n-BuLi (0.038 mL of a
1.6 M solution in hexanes, 0.06 mmol) was added to an NMR tube
in the glovebox, and the solvent was removed under vacuum leav-
ing a white residue. The dichloride complex, PdCl2(dotpm), (17 mg,
0.028 mmol) was mixed with C6D6 (0.3 mL) in a vial, and the yel-
low slurry was transferred to the NMR tube. The NMR tube was
placed in the NMR probe and the progression of the reaction was
monitored by 1H and 31P{1H} NMR spectroscopy. After the reaction
was complete, the mixture was opened to air and octane was
eluted from silica gel using hexanes. The same procedure was used
2
C6H4CH3), 4.31 (t, JPH = 9.9 Hz, 2H, PCH2P), 7.21–7.27 (m, 8H,
C6H4CH3), 7.44 (t, 4H, 3JHH = 7.4 Hz, C6H4CH3), 8.00 (virtual quartet,
J = 8.5 Hz, 7.7 Hz, 4H, C6H4CH3). 31P NMR (CDCl3) d À51.4 (s). IR
(cmÀ1) 3050 (w), 2954 (s), 2913 (s), 2838 (s), 2003 (w), 1737 (w),
1709 (w), 1634 (w), 1586 (m), 1562 (m), 1453 (s), 1374 (m),
1357 (m), 1282 (m), 1197 (m), 1166 (w), 1135 (m), 1100 (m),
1067 (m), 1032 (w), 806 (s), 762 (s), 738 (s).
for the synthesis of Pd2(l-dppm)3, with n-BuLi (0.037 mL of a
1.6 M solution in hexanes, 0.06 mmol) and PdCl2(dppm), (15 mg,
0.027 mmol). Variable temperature: n-BuLi was added to an NMR
tube in the glovebox, and the solvent was removed under vacuum.
The dichloride complex, PdCl2(P–P) was added to the NMR tube,
which was cooled to À78 °C before toluene-d8 (0.6 mL) was in-
jected. The NMR sample was vigorously shaken immediately be-
fore it was inserted into the NMR probe, which was pre-cooled
to À40 °C. The progression of the reaction was monitored by 1H
and 31P{1H} NMR spectroscopy, and the NMR probe was warmed
in 10 °C increments. Data were collected approximately 5 min after
the desired temperature had been reached.
3.3. Bis[l-bis(di-(2-methylphenyl)phosphino)methane]-
dipalladium(0), Pd2(l-dotpm)2 (1)
To a yellow suspension of PdCl2(dotpm) (0.264 g, 0.43 mmol) in
diethyl ether (20 mL) was added n-BuLi (0.59 mL of a 1.6 M solu-
tion in hexanes, 0.94 mmol) over 30 s. The resulting bright red
mixture was stirred for 2 h then filtered twice through Celite.
The solution was allowed to sit at room temperature to afford
red crystals of 1. Yield: 0.091 g (39%). Mp: 150 °C (dec.). UV–Vis
(toluene): kmax = 494 nm. Anal Calc. for C58H60P4Pd2: C, 63.69; H,
5.53. Found: C, 63.71; H, 5.92%. 1H NMR (thf-d8): d 2.48 (s, 24H,
Complex 1: 1H NMR (C6D6): d 2.68 (s, 24H, C6H4CH3), 3.30 (t,
2JPH = 3.4 Hz, 4H, PCH2P), 6.80–6.98 (m, C6H4CH3), 7.53 (d,
3JHH = 5.8 Hz, 8H, C6H4CH3). 31P{1H} NMR (C6D6): d À2.8 (s).
3
3
C6H4CH3), 3.33 (br s, 4H, PCH2P), 6.87 (d, JHH = 7.2 Hz, 8H,
Pd(dotpm)(n-Bu)2: 1H NMR (C6D6): d 1.00 (t, JHH = 7.3 Hz, 6H,
C6H4CH3), 6.94 (t, 3JHH = 7.4 Hz, 8H, C6H4CH3), 7.09 (t, 3JHH = 7.2 Hz,
8H, C6H4CH3), 7.56 (br d, 3JHH = 6.8 Hz, 8H, C6H4CH3). 13C{1H} NMR
(thf-d8): d 23.3 (s, C6H4CH3), 32.4 (s, PCH2P), 126.1 (s, C6H4CH3)
129.2 (s, C6H4CH3), 131.7 (s, C6H4CH3), 133.5 (s, C6H4CH3), 137.0
(s, i-CP of C6H4CH3), 142.6 (s, i-CCH3 of C6H4CH3). 31P{1H} NMR
(thf-d8): d À4.8 (s).
CH3), 1.63 (m), 2.44 (s, 12H, C6H4CH3), 3.47 (t, JPH = 7.3 Hz, 2H,
2
PCH2P). 31P{1H} NMR (C6D6): d À22.7 (s).
dotpm: 1H NMR (C6D6): d 2.30 (s, 12H, C6H4CH3), 7.35 (d,
3JHH = 5.9 Hz, 4H, C6H4CH3). Other signals were hidden by signals
due to 1. 31P{1H} NMR (C6D6): d À43.1 (s).
1-Butene: 1H NMR (C6D6): d 1.92 (m, 2H, CH2), 4.94 (d,
3
3JHH = 10.2 Hz, 1H, CH@CH2), 4.99 (d, JHH = 17.2 Hz, 1H, CH@CH2),
3.4. Dichloro(
methane] dipalladium(II), Pd2Cl2(
l
-methylene)bis[
l
-bis(di-(2-methylphenyl)phosphino)-
-CH2)( -dotpm)2 (2)
5.79 (m, 1H, CH@CH2). Its methyl signal was obscured by those due
l
l
to other byproducts.
3
cis-2-Butene: 1H NMR (C6D6): d 1.50 (d, JHH = 4.9 Hz, 6H, CH3),
Red crystals of complex 1 (15 mg, 0.014 mmol) were dissolved
in CH2Cl2 (0.25 mL) and mixed for 45 min. The protiated solvent
was removed under vacuum, and the orange-yellow residue was
washed with pentane (3 Â 0.5 mL) and dried under vacuum
(14 mg, 87%). This compound was used without further purifica-
tion. 1H NMR (CD2Cl2): d 1.64 (br s, 2H, PdCH2Pd), 1.94 (br s,
12H, C6H4CH3), 2.32 (br s, 12H, C6H4CH3), 3.05 (br s, 2H, PCH2P),
3.78 (br s, 2H, PCH2P), 6.96–7.32 (m, 32H, C6H4CH3). 31P{1H}
NMR (CD2Cl2): d 17.7 (br s), 23.1 (br s). 31P{1H} NMR (CD2Cl2,
5.47 (m, 2H, @CH).
3
trans-2-Butene: 1H NMR (C6D6): d 1.56 (d, JHH = 4.7 Hz, 6H,
CH3), 5.38 (m, 2H, @CH).
Butane: 1H NMR (C6D6): d 0.85 (t, CH3), 1.23 (m, CH2).
Octane: 1H NMR (C6D6): d 0.88 (t, CH3), 1.25 (br s, CH2). GC/MS:
m/z 114 (M+).
Pd2(l
-dppm)3: 1H NMR (C6D6): d 3.17 (s, 6H, PCH2P), 6.77–7.11
(m, 36H, C6H5), 7.44 (d, JHH = 7.1 Hz, 24H, o-C6H5). 31P{1H} NMR
3
(C6D6): d 15.6 (s).

E. Lumbreras Jr. et al. / Journal of Organometallic Chemistry 695 (2010) 201–205
205
Table 1
temperature NMR data; her assistance is greatly appreciated.
Crystallography was performed by Dr. Danielle L. Gray at the
George L. Clark X-Ray Facility in School of Chemical Sciences at
the University of Illinois at Urbana-Champaign; the Materials
Chemistry Laboratory was supported in part by grants from the
NSF (Grants CHE 95-03145 and CHE 03-43032).
Crystal data and structural parameters for Pd2(
l
-dotpm)2 (1).
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system, space group
Unit cell dimensions
a (Å)
C58H60P4Pd2
1093.74
193(2)
0.71073
Triclinic, P1
ꢀ
12.750(3)
13.354(3)
Appendix A. Supplementary data
b (Å)
c (Å)
16.634(4)
70.673(4)
82.640(4)
67.249(4)
2464.6(10)
2
1.474
0.898
CCDC 749906 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif. Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/j.jorganchem.
2009.10.010.
a
(ꢁ)
b (ꢁ)
(ꢁ)
c
Volume (Å3)
Z
qcalc (g cmÀ3
)
Absorption coefficient (mmÀ1
F(0 0 0)
)
1120
Crystal size (mm)
h Range for data collection ꢁ()
Index ranges
Reflections collected, unique
Refinement method
Completeness to h (ꢁ)
Data, restraints, parameters
Goodness-of-fit on F2
0.100 Â 0.180 Â 0.190
References
1.73–25.39
À15 h 15, À15 k 16, À20 l 20
25218, 9009 [Rint = 0.0391]
Full-matrix least-squares on F2
25.39, 99.4
9009, 38, 585
0.960
R1 = 0.0362, wR2 = 0.0905
R1 = 0.0597, wR2 = 0.0980
1.444 and À0.530
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A single crystal of Pd2(l-dotpm)2 (1) grown from a diethy ether
solution was mounted using Parantone-N oil (Exxon), and data
were collected with a Siemens Platform/CCD diffractometer using
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ment parameters are listed in Table 1. The structure was solved
using direct methods and refined with SHELXTL. A structural model
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H1B was restrained to prevent close interactions between atoms.
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We thank the National Science Foundation (Grant CHE-
0548107) and DePaul University for support of this work. The
NSF (Grant DUE-0310624) is also acknowledged for a grant that
provided partial support for the purchase of the departmental
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