Pincer ligand coordination at a triosmium cluster: X-ray structures of 1,2-Os3(CO)10[4,6-bis(diphenylphosphinomethyl)-m-xylene] and 1,2-Os3(CO)10[1-diphenylphosphino-1-{(2,4-dimethyl-5-diphenylphosphinomethyl)phenyl}-propan-2-ol]

Article abstract of DOI:10.1016/j.jorganchem.2006.10.021

The reaction between the triosmium cluster 1,2-Os₃(CO)₁₀(MeCN)₂ and the diphosphine pincer ligand 4,6-bis(diphenylphosphinomethyl)-m-xylene (dppx) has been examined and found to yield the pincer-bridged cluster 1,2-Os₃(CO)₁₀(dppx) (2) as the major product, in addition to the pincer-bridged cluster 1,2-Os₃(CO)₁₀[1-diphenylphosphino-1-{(2,4-dimethyl-5-diphenylphosphinomethyl)phenyl}-propan-2-ol] (3) in trace amounts (<2% yield). Both cluster products have been isolated and their molecular structures determined by crystallographic analyses. The structural highlights of compounds 2 and 3, which represent the first examples of pincer-ligated metal clusters, are discussed. The origin of the functionalized diphosphine ligand in 3 is traced to the ethanol solvent that was used in the recrystallization of the dppx ligand.

Full text of DOI:10.1016/j.jorganchem.2006.10.021

Journal of Organometallic Chemistry 692 (2007) 1806–1811
www.elsevier.com/locate/jorganchem
Pincer ligand coordination at a triosmium cluster: X-ray structures
of 1,2-Os3(CO)10[4,6-bis(diphenylphosphinomethyl)-m-xylene]
and 1,2-Os3(CO)10[1-diphenylphosphino-1-
{(2,4-dimethyl-5-diphenylphosphinomethyl)phenyl}-propan-2-ol]
a,
b
b,
b,
*
Vladimir Nesterov *, Bhaskar Poola , Xiaoping Wang *, Michael G. Richmond
a
Department of Chemistry, New Mexico Highlands University, Las Vegas, NM 87701, United States
Department of Chemistry, University of North Texas, P.O. Box 305070, Denton, TX 76203-5070, United States
b
Received 23 August 2006; received in revised form 10 October 2006; accepted 10 October 2006
Available online 18 October 2006
Dedicated to Prof. Gulya Palyi for his lifetime contributions in organometallic chemistry on occasion of his 70th birthday.
Abstract
The reaction between the triosmium cluster 1,2-Os3(CO)10(MeCN)2 and the diphosphine pincer ligand 4,6-bis(diphenylphosphinom-
ethyl)-m-xylene (dppx) has been examined and found to yield the pincer-bridged cluster 1,2-Os3(CO)10(dppx) (2) as the major product, in
addition to the pincer-bridged cluster 1,2-Os3(CO)10[1-diphenylphosphino-1-{(2,4-dimethyl-5-diphenylphosphinomethyl)phenyl}-pro-
pan-2-ol] (3) in trace amounts (<2% yield). Both cluster products have been isolated and their molecular structures determined by crys-
tallographic analyses. The structural highlights of compounds 2 and 3, which represent the first examples of pincer-ligated metal clusters,
are discussed. The origin of the functionalized diphosphine ligand in 3 is traced to the ethanol solvent that was used in the recrystalli-
zation of the dppx ligand.
Ó 2006 Elsevier B.V. All rights reserved.
Keywords: Pincer ligands; Diphosphine ligands; Osmium clusters; Diphosphine ligand activation; Ligand substitution
1. Introduction
mercial benefits associated with the production of com-
modity chemicals using abundant but unreactive alkane/
arene feedstocks [2]. Truly impressive are the reports of cat-
alytic alkane dehydrogenation and the activation of ammo-
nia, as exemplified by the two reactions [3,4].
The last two decades have witnessed the synthesis of a
multitude of terdentate-coordinated organometallic com-
pounds based on PCP, NCN, and PNP pincer-ligand plat-
forms [1]. Literally scores of new pincer-ligated metal
compounds have been prepared and structurally character-
ized. The study of the reactivity exhibited by such pincer-
based complexes continues to receive attention with respect
to C–H and C–C bond activation due to the potential com-
O
O
(But)2P
Ir
P(But)2
(ref 3)
H
H
heat
*
Corresponding authors. Tel.: +1 505 454 3464; fax: +1 940 565 4318
NH3/RT
(V. Nesterov), tel.: +940 369 8489 (X. Wang), tel.: +940 565 3548 (M.G.
Richmond).
E-mail addresses: vnesterov@nmhu.edu (V. Nesterov), xpwang@
unt.edu (X. Wang), cobalt@unt.edu (M.G. Richmond).
(ref 4)
(But)2P
Ir
P(But)2
(But)2P
Ir
P(But)2
NH2
-propylene
H
0022-328X/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.10.021

V. Nesterov et al. / Journal of Organometallic Chemistry 692 (2007) 1806–1811
1807
In comparison to the myriad pincer-ligated mononu-
clear complexes known, no examples exist, to our knowl-
edge, for the coordination of this genre of ligand to a
polynuclear entity. The coordination mode that would be
exhibited by such pincer ligands at a metal cluster is not
immediately obvious since the pincer could function as a
4e-bridging or chelating ligand via binding of the two phos-
phine or amine moieties in the case of the xylene-based pin-
cer ligands 1,3-(R2PCH2)2C6H4 and 1,3-(RNCH2)2C6H4.
Accompanying this P,P/N,N coordination uncertainty is
the possible promotion of aryl cyclometalation and the
generation of a meridionally tethered pincer ligand through
use of one of the metal–metal bonds. While it would be
premature to extol excessively any reactivity advantages
associated with the corresponding terdentate-derived poly-
nuclear systems, pincer-substituted metal clusters have the
potential to facilitate multisite substrate activation unlike
their mononuclear counterparts.
benzene. All reaction, IR, and NMR solvents were of
reagent grade and were either degassed with argon prior
to their use or distilled from a suitable drying agent and
stored in Schlenk vessels equipped with Teflon stopcocks
[10]. The combustion analysis was performed by Atlantic
Microlab, Norcross, GA.
The reported infrared spectral data were recorded on a
Nicolet 20 SXB FT-IR spectrometer in a 0.1 mm NaCl cell,
1
using PC control and OMNIC software. The H NMR
data were recorded at 200 MHz on a Varian Gemini-200
spectrometer, and the 31P NMR data were recorded at
121 MHz on a Varian 300-VXR spectrometer. The
reported 31P chemical shifts were acquired in the proton-
decoupled mode and referenced to external H3PO4 (85%),
taken to have d = 0. The ESI-APCI mass spectral data
for cluster 3 and the two diphosphine ligands were
obtained at the UC San Diego Mass Spectrometry Center.
We have recently initiated substitution studies with the
pincer ligand 4,6-bis(diphenylphosphinomethyl)-m-xylene
(dppx) with different metal clusters. Depending on the reac-
tion conditions and the nature of the starting cluster, our
preliminary data indicate that the dppx ligand can coordi-
nate one cluster unit at each phosphine group in an g1
fashion or act as a bridging ligand and bind adjacent metal
centers. For example, the reaction between dppx and the
tricobalt cluster PhCCo3(CO)9 gives the bis(cluster) com-
pound [PhCCo3(CO)8]2(dppx) while the use of the hexaru-
thenium cluster Ru6(l6-C)(CO)17 yields the bis(cluster)
compound [Ru6(l6-C)(CO)16]2(dppx) and the pincer-
bridged cluster Ru6(l6-C)(CO)15(dppx) [5]. Herein we pres-
ent our findings for the reaction of the dppx ligand with the
triosmium cluster 1,2-Os3(CO)10(MeCN)2. The replace-
ment of the two MeCN groups by the dppx ligand
furnishes the diphosphine-bridged cluster 1,2-Os3(CO)10-
(dppx) (2) as the predominant product, along with trace
amounts of the cluster compound 1,2-Os3(CO)10[1-diph-
enylphosphino-1-{(2,4-dimethyl-5-diphenylphosphinom-
ethyl)phenyl}-propan-2-ol] (3). The identities of both 2 and
3 have been established by X-ray analyses. Preliminary
NMR data from near-UV irradiation experiments with
cluster 2 confirm the facile activation of 2 and suggest
the formation of phosphido-bridged Os3 clusters.
2.2. Synthesis of 1,2-Os3(CO)10(dppx) and
1,2-Os3(CO)10[1-diphenylphosphino-1-{(2,4-dimethyl-5-
diphenylphosphinomethyl)phenyl}-propan-2-ol]
To 0.30 g (0.32 mmol) of 1,2-Os3(CO)10(MeCN)2 in
40 mL of CH2Cl2 under argon was added 0.16 g
(0.32 mmol) of dppx. The reaction solution was stirred at
room temperature and monitored by TLC using a 1:1 mix-
ture of CH2Cl2/hexane as the eluent, which confirmed the
complete consumption of the starting cluster after 2 h
and the presence of one spot corresponding to cluster 2
(Rf = 0.65) and a trace amount of a slower moving spot
for cluster 3 (Rf = 0.10). The solvent was concentrated
under vacuum and subjected to column chromatography
over silica gel using CH2Cl2/hexane (3:7). Cluster 2 was
obtained as an air-stable yellow solid that was recrystal-
lized from CH2Cl2/hexane in 79% yield (0.34 g). Cluster
2: IR (CH2Cl2): m(CO) 2088 (s), 2051 (m), 2023 (s), 2004
1
(vs), 1969 (m), 1949 (m) cmꢀ1. H NMR (CDCl3): d 1.67
(s, 6H, Me), 3.57 (d, 4H, benzylic, JP–H = 11 Hz), 6.61 (s,
1H, aryl), 7.20–7.65 (m, 20H, aryl), 7.80 (s, 1H, aryl). 31P
(CDCl3): d ꢀ0.76 (s). Anal. Calc. (found) for C44H32Os3-
O10P2 Æ CH2Cl2: C, 37.58 (37.46); H, 2.38 (2.36). Cluster
3: IR (CH2Cl2): m(CO) 2078 (s), 2063 (s), 2051 (s), 2027
(vs), 2009 (vs), 1997 (vs), 1970 (sh) cmꢀ1 1H NMR
.
(CDCl3): d 1.90 (s, 3H, Me), 2.02 (b, 3H, Me), 2.15 (s,
3H, Me), 3.35–3.65 (b, 4H, benzylic hydrogens and
CH(OH) methine hydrogen), 6.58 (s, 1H, aryl), 7.10–7.80
(bm, 21H, aryl). ESI-APCI MS (m/z): 1399.55 [3+H]+.
2. Experimental
2.1. General
High-pressure carbonylation of OsO4 afforded
Os3(CO)12 [6], which was then used in the synthesis of
the labile cluster 1,2-Os3(CO)10(MeCN)2 [7]. The pincer
ligand dppx was synthesized according to the published
procedure using 1,3-bis(chloromethyl)-4,6-dimethylben-
zene and Ph2PLi [8,9] and initially purified by recrystalliza-
tion from EtOH. The chemicals Me3NO Æ nH2O and
m-xylene were purchased from Aldrich Chemical Co., with
the former chemical dried by azeotropic distillation from
2.3. X-ray diffraction structure for clusters 2 and 3
Single crystals of clusters 2 and 3 suitable for X-ray crys-
tallography were grown from a CH2Cl2 solution containing
each cluster that had been layered with hexane. The X-ray
data for 2 Æ CH2Cl2 (NMHU) and 3 (UNT) were collected
on APEX II CCD-based diffractometers at 295 K and
100 K, respectively. The frames were integrated with the
available SAINT [11] and APEX2 [12] software packages using

1808
V. Nesterov et al. / Journal of Organometallic Chemistry 692 (2007) 1806–1811
Table 2
a narrow-frame algorithm, and each structure was solved
and refined using the SHELXTL program package [13]. The
molecular structures were checked using PLATON [14], and
all non-hydrogen atoms were refined anisotropically. All
hydrogen atoms were assigned calculated positions and
allowed to ride on the attached heavy atom. The refinement
for 2 converged at R = 0.0747 and Rw = 0.1746 for 11005
˚
Selected bond distances (A) and angles (°) for clusters 2 and 3
Bond distances
Cluster 2
Cluster 3
Os(1)–Os(2)
Os(2)–Os(3)
Os(1)–Os(3)
Os(1)–P(1)
Os(2)–P(2)
P(1)ꢁ ꢁ ꢁP(2)
2.9743(9)
2.898(1)
2.8862(9)
2.356(4)
2.348(4)
5.530(8)
Os(1)–Os(2)
Os(2)–Os(3)
Os(1)–Os(3)
Os(1)–P(1)
Os(2)–P(2)
P(1)ꢁ ꢁ ꢁP(2)
2.9802(3)
2.8962(3)
2.8789(3)
2.359(1)
2.368(2)
5.539(2)
independent reflection with I > 2r(I) and for
3 at
R = 0.0296 and Rw = 0.0566 for 8664 independent reflection
with I > 2r(I). Tables 1 and 2 summarize the pertinent X-ray
data.
Bond angles
P(1)–Os(1)–Os(3)
P(2)–Os(2)–Os(3)
C(9)–P(1)–Os(1)
C(22)–P(2)–Os(2)
C(2)–C(9)–P(1)
C(6)–C(22)–P(2)
177.7(1)
P(1)–Os(1)–Os(3)
P(2)–Os(2)–Os(3)
C(11)–P(1)–Os(1)
C(20)–P(2)–Os(2)
C(12)–C(11)–P(1)
C(14)–C(20)–P(2)
175.79(4)
173.45(9)
119.6(5)
121.9(5)
113(1)
176.76(4)
120.0(2)
128.5(2)
111.5(4)
116.8(4)
3. Results and discussion
3.1. Synthesis and molecular structures for clusters 2 and 3
120(1)
Treatment of 1,2-Os3(CO)10(MeCN)2 with an equimolar
amount of dppx in CH2Cl2 at room temperature leads to a
rapid substitution reaction and formation of cluster 2 as
the predominant product, as assessed by TLC analysis.
Besides 2, TLC also revealed the presence of a slow moving
yellow spot that suggested the formation of another
osmium containing product. Both cluster products were
subsequently isolated by column chromatography over sil-
ica gel as air-stable solids. The structures for these two clus-
ters are
Os
Os
Os
Os
Os
Os
Table 1
PPh2
Ph2P
Ph2P
PPh2
OH
X-ray crystallographic data and processing parameters for clusters 2 and 3
Compound
2
3
CCDC entry number
Crystal system
Space group
616548
Triclinic
616547
Triclinic
cluster 2
cluster 3
ꢀ
ꢀ
P1
P1
˚
a (A)
10.183(3)
12.424(3)
19.616(4)
82.388(6)
80.807(4)
73.278(4)
2336.4(1)
12.6828(6)
13.0300(6)
15.3073(8)
93.362(1)
103.088(1)
114.539(1)
2207.9(2)
˚
b (A)
˚
The major product corresponds to the dppx-bridged
cluster 2, which was isolated in 79% yield and characterized
in solution by IR and NMR spectroscopies, elemental anal-
ysis, and X-ray crystallography. The 1H NMR spectrum of
2 displays resonances at d 1.67 and 3.57 for the pairwise
equivalent methyl and benzylic hydrogens, respectively,
with the aromatic hydrogens of the Ph2P moieties appear-
ing as a multiplet from d 7.20 to 7.65. The two singlets that
integrate for 1H each at d 6.61 and 7.80 are readily assigned
to the unique aryl hydrogens on the xylene platform. These
data confirm that cyclometalation of the dppx ligand has
not occurred. The high-field 31P singlet recorded at d
ꢀ0.76 for 2 is in accord with the proposed structure and
the NMR data reported by us for other diphosphine-
bridged Os3 clusters [15]. The molecular structure for 2 is
shown in Fig. 1. Cluster 2 contains 48-valence electrons
and is electronically saturated, with the bridging of the
Os(1) and Os(2) centers by the dppx ligand structurally
confirmed. The Os–Os bond distances range from
c (A)
a (°)
b (°)
c (°)
3
˚
V (A )
Molecular formula
Formula weight
Formula units per cell (Z)
Dcalcd (Mg/m3)
C44H32O10Os3P2 Æ CH2Cl2 C46H36O11Os3P2
1438.16
2
2.044
0.71073
8.375
1397.29
2
2.102
0.71073
8.744
˚
k (Mo Ka) (A)
Absorption coefficient
(mmꢀ1
)
Rmerge
Absorption correction,
max/min
0.0496
0.0388
Multi-scan,
0.8504/0.4880
23211
11005
11005/1/561
0.0747
Multi-scan,
0.5796/0.2611
18941
8664
8664/0/562
0.0296
0.0566
1.015
1.873, ꢀ1.188
Total reflections
Independent reflections
Data/res/parameters
aR
bRw
0.1746
0.998
cGoodness-of-fit on F2
Largest difference in peak 2.801, ꢀ1.257
3
˚
and hole (e/A )
˚
˚
2.8862(9) A [Os(1)–Os(3)] to 2.9743(9) A [Os(1)–Os(2)],
with a mean distance of 2.9195 A that is consistent with
those distances found in simple triosmium clusters and
related diphosphine-bridged Os3(CO)10(P–P) clusters
P
P
a
R ¼ kF o j ꢀ j F ck= j F o j.
˚
n
o
o
1=2
P
P
2
2
b
Rw
¼
½wðF 2o ꢀF c2Þ ꢂ= ½wðF 2oÞ ꢂ
, where w = 1/jr2(F2) + (aP)2 +
bPj and P ¼ ½2F 2c þ MaxðF 2o; 0Þꢂ=3.
n
1=2
P
˚
2
c
½wðF 2o ꢀ F 2c Þ ꢂ=ðn ꢀ pÞ
, where n is the number of reflec-
[14,16]. The internuclear P(1)ꢁ ꢁ ꢁP(2) distance is 5.530(8) A
GOF ¼
tions and p is the total number of parameters refined.
and the two equatorially disposed phosphine moieties are

V. Nesterov et al. / Journal of Organometallic Chemistry 692 (2007) 1806–1811
1809
Fig. 1. Thermal ellipsoid plots of 1,2-Os3(CO)10(dppx) (left: 2; 30% probability level) and 1,2-Os3(CO)10[1-diphenylphosphino-1-{(2,4-dimethyl-5-
diphenylphosphinomethyl)phenyl}-propan-2-ol] (right: 3; 50% probability level). With the exception of the H(11) atom in the latter structure, all hydrogen
atoms have been omitted for clarity.
situated essentially trans to the non-bridged Os–Os bonds
based on the observed bond angles of 177.7(1)° and
173.45(9)° for the P(1)–Os(1)–Os(3) and P(2)–Os(2)–Os(3)
linkages, respectively. The nine-membered ring formed by
the coordination of the dppx ligand to the Os(1)–Os(2) vec-
tor core exhibits a ‘‘terraced’’ motif with the planes defined
by the xylene ring and trimetallic plane representing adja-
cent terrace steps.
dence for the presence of dppx0 in the recystallized sample
of the diphosphine ligand was also provided by electrospray
mass spectrometry in the positive ionization mode. A sam-
ple of the diphosphine ligand in MeOH solvent exhibited
m/z peaks at 535.25 and 557.27 for [dppx+MeOH+H]+
and [dppx+MeOH+Na]+ in excellent agreement with the
calculated m/z values of 535.60 and 557.22, respectively.
Moreover, the small m/z value recorded at 601.17 provided
proof for the presence of the functionalized ligand 1-diph-
enylphosphino-1-{(2,4-dimethyl-5-diphenylphosphinom-
ethyl)phenyl}-propan-2-ol in the dppx ligand sample based
on the calculated m/z value of 601.24 for [dppx0+
MeOH+Na]+. Both analytical techniques indicate that the
dppx0 ligand was present from the start and carried along
in the reaction with cluster 1. Finally, independent thermol-
ysis of dppx in EtOH solvent gives the functionalized ligand
dppx0 in low yields, as judged by NMR analysis (Eq. 1). The
details associated with this unexpected reaction and its gen-
erality are under study and will be published in due course.
Suffice it to say, the inert behavior that is generally ascribed
to this genre of pincer ligand needs to be viewed with cau-
tion given the mild conditions under which dppx reacts with
EtOH.
The slower moving spot obtained from the chromato-
graphic separation was characterized in solution by IR
1
and H NMR spectroscopies and ESI mass spectrometry.
These data were consistent with the formation of an Os3
cluster containing a dppx-derived ligand. The unequivo-
cally identity of this minor product was subsequently estab-
lished by X-ray diffraction analysis. The structure for
cluster 3 is given in the right-hand portion of Fig. 1. Of sur-
prise to us was the ‘‘HOCHCH3’’ appendage at the ben-
zylic C(20) center in 3. The coordination of the
functionalized dppx ligand (also referred to as dppx0 for
convenience) to the Os3 frame in 3 is analogous to that
already described for cluster 2. The diphosphine-bridged
˚
Os(1)–Os(2) bond is slightly longer (ca. 0.093 A) than the
non-bridged Os–Os bonds, whose mean length is
˚
2.8876 A. The internuclear P(1)ꢁ ꢁ ꢁP(2) distance of
Ph2P
Ph2P
PPh2
PPh2
˚
5.539(2) A agrees well with that distance found in cluster 2.
EtOH/heat
OH
Since we had recrystallized the dppx ligand from EtOH
[17], it seemed reasonable to assume that the recrystalliza-
tion solvent was activated by the diphosphine ligand. This
premise was subsequently verified by NMR and mass spec-
tral analyses of the recrystallized dppx ligand. The 1H NMR
spectrum of the ‘‘purified’’ ligand revealed resonances for
the dppx ligand in agreement with the data reported by Mil-
stein and coworkers that accounted for >95% of the mate-
rial [8]. Further careful inspection of the 1H NMR spectrum
revealed broadened baselines about the methyl and benzylic
singlets belonging to the dppx ligand, along with a broad-
ened AB quartet at d 3.50, which in hindsight would be in
agreement with the diastereotopic hydrogens at the non-
activated benzylic site on the dppx0 ligand. Unequivocal evi-
ð1Þ
dppx
dppx'
3.2. Activation of the dppx ligand in cluster 2
Due to our long-term interest in the study of the degra-
dation pathways available to cluster-bound diphosphine
ligands [14,18], we have carried out preliminary studies
on the photochemical and thermal stability of cluster 2.
Irradiation of sealed NMR tubes of 2 in C6D6 with
366 nm light leads to the complete consumption of 2 over
the course of several days and the formation of two new

1810
V. Nesterov et al. / Journal of Organometallic Chemistry 692 (2007) 1806–1811
species based on the appearance of 31P NMR resonances at
d 16.90, 18.72, 36.70, and 38.36. The H NMR spectrum
(#616547) have been deposited with the Cambridge Crys-
tallographic Data Center, CCDC 260091 contain the sup-
plementary crystallographic data for this paper. These
data can be obtained free of charge via http://www.ccdc.
cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit
@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.jorganchem.2006.10.021.
1
also exhibits two sets of singlets at d 1.45, 2.15 and 1.74,
2.40 for the xylene-based methyl groups in support of the
formation of two major products. Careful inspection of
the high-field region of the NMR spectrum confirms the
absence of metal hydride resonances, which in turn rules
out an ortho-metalation reaction involving the different
aromatic rings and supports to the formation of phosph-
ido-bridged osmium clusters.
Samples of 2 in C6D6 in sealed NMR tubes were found to
be stable at temperatures up to 75 °C for a period of several
days (<5% conversion). However, thermolysis at 100 °C led
to the slow consumption of cluster 2 and the formation of
three new hydride-bridged clusters based on the presence
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=
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allics 22 (2003) 47.
The substitution reaction of the well-known pincer
ligand dppx with 1,2-Os3(CO)10(MeCN)2 has been investi-
gated. The two acetonitrile ligands in 1 are replaced by the
dppx ligand to afford the diphosphine-bridged cluster 1,2-
Os3(CO)10(dppx) as the major product. We have also
succeeded in isolating and characterizing the cluster
compound
1,2-Os3(CO)10[1-diphenylphosphino-1-{(2,4-
dimethyl-5-diphenylphosphinomethyl)phenyl}-propan-2-ol].
The origin of this new dppx-derived ligand in cluster 3 has
been traced to the EtOH solvent that was used in the
recrystallization of the dppx ligand. The generality associ-
ated the unexpected reaction between the dppx ligand
and EtOH is currently under investigation. It is hoped that
our fortuitous uncovering of this latter reaction may serve
as an entry point into the synthesis of more exotic diphos-
phine ligands based on dppx.
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McGraw-Hill, New York, 1969.
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1999, Madison, WI.
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Acknowledgments
Organometallics 25 (2006) 930.
[16] (a) V.M. Hansen, A.K. Ma, K. Biradha, R. Pomeroy, M.J.
Zaworotko, Organometallics 17 (1998) 5267;
Financial support from the Robert A. Welch Founda-
tion (Grant B-1093-MGR) is much appreciated, and the
NSF/DMR (Grant 0420863-VN) is thanked for the pur-
chase of the single-crystal X-ray diffractometer. Dr. Yon-
gxuan Su (UCSD) is thanked for recording the mass
spectral data on cluster 3 and the dppx/dppx0 sample.
(b) M.R. Churchill, B.G. DeBoer, Inorg. Chem. 16 (1977) 878;
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solid triarylphosphines involves recrystallization from EtOH. For
Appendix A. Supplementary material
X-ray crystallographic files, in CIF format, for the struc-
ture determination of both clusters 2 (#616548) and 3

V. Nesterov et al. / Journal of Organometallic Chemistry 692 (2007) 1806–1811
1811
example, see: V.D. Bianco, S. Doronzo, Inorg. Synth. 18 (1978) 169;
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¨
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