Ligand degradation and phosphorus scavenging in the reaction between 1,2-bis(diphenylphosphino)benzene (dppbz) and Ru6(μ6-C)(CO)17: Synthesis and X-ray structure of the edge-bridged square-pyramidal cluster HRu6(μ5-C)(μ3-P)(CO)14(dppbz)

Article abstract of DOI:10.1016/j.jorganchem.2006.12.036

Thermolysis or Me₃NO activation of the hexaruthenium cluster Ru₆(μ₆-C)(CO)₁₇ in the presence of the diphosphine ligand 1,2-bis(diphenylphosphino)benzene (dppbz) does not furnish the expected dppbz-substituted cluster Ru₆(μ₆-C)(CO)₁₅(dppbz) but rather HRu₆(μ₅-C)(μ₃-P)(CO)₁₄(dppbz), whose edge-bridged square-pyramidal structure has been established by X-ray crystallography. Accompanying the opening of the original closo Ru₆ polyhedron is the dephosphination of a second dppbz ligand through three rapid P-C bond cleavages, leading to the capture of the phosphorus atom as a face-capping phosphido ligand. This unprecedented reactivity between Ru₆(μ₆-C)(CO)₁₇ and the dppbz ligand is discussed relative to other diphosphine ligands.

Full text of DOI:10.1016/j.jorganchem.2006.12.036

Journal of Organometallic Chemistry 692 (2007) 1648–1652
www.elsevier.com/locate/jorganchem
Ligand degradation and phosphorus scavenging in the reaction between
1,2-bis(diphenylphosphino)benzene (dppbz) and Ru6(l6-C)(CO)17:
Synthesis and X-ray structure of the edge-bridged square-pyramidal
cluster HRu6(l5-C)(l3-P)(CO)14(dppbz)
a,
b
b,
*
William H. Watson *, Srikanth Kandala , Michael G. Richmond
a
Department of Chemistry, Texas Christian University, Fort Worth, TX 76129, USA
b
Department of Chemistry, University of North Texas, Denton, TX 76203, USA
Received 14 December 2006; received in revised form 15 December 2006; accepted 15 December 2006
Available online 10 January 2007
Abstract
Thermolysis or Me3NO activation of the hexaruthenium cluster Ru6(l6-C)(CO)17 in the presence of the diphosphine ligand 1,2-
bis(diphenylphosphino)benzene (dppbz) does not furnish the expected dppbz-substituted cluster Ru6(l6-C)(CO)15(dppbz) but rather
HRu6(l5-C)(l3-P)(CO)14(dppbz), whose edge-bridged square-pyramidal structure has been established by X-ray crystallography.
Accompanying the opening of the original closo Ru6 polyhedron is the dephosphination of a second dppbz ligand through three rapid
P–C bond cleavages, leading to the capture of the phosphorus atom as a face-capping phosphido ligand. This unprecedented reactivity
between Ru6(l6-C)(CO)17 and the dppbz ligand is discussed relative to other diphosphine ligands.
Ó 2006 Elsevier B.V. All rights reserved.
Keywords: Hexaruthenium cluster; Ligand substitution; Cluster expansion; P–C bond cleavage
1. Introduction
developed opening of the wing-tip ruthenium center relative
to the square-pyramidal base is arrested due to dppf coordi-
nation of the wing-tip and one of the non-hinged ruthenium
atoms within the square base of the molecular polyhedron.
The replacement of two CO groups in the octahedral clus-
ter Ru6(l6-C)(CO)17 by the ligands dppm, dppe, and dppp
proceeds readily under mild conditions and without compli-
cations to afford the corresponding diphosphine-bridged
clusters Ru6(l6-C)(CO)15(l-P-P) [1]. The substitution reac-
tion between Ru6(l6-C)(CO)17 and dppf follows a similar
path insomuch as the dppf ligand serves to bridge adjacent
ruthenium centers in the product Ru6(l6-C)(CO)15(l-dppf).
However, unlike the octahedral Ru6 structures exhibited by
the aforementioned Ru6(l6-C)(CO)15(l-P-P) derivatives, the
dppf ligand promotes a partial expansion of the closo Ru6
core to a ‘‘hinged’’ or edge-bridged square-pyramid Ru6
polyhedral motif, as shown in Eq. (1) [2]. A full or more
Fe
Ph2P
Ru
C
Ru
PPh2
Ru
Ru
Ru
Ru
Ru
Ru
dppf/heat
Ru
C
Ru
Ru
Ru
ð1Þ
The dppf-induced polyhedral opening attendant in the
formation of Ru6(l6-C)(CO)15(l-dppf) suggests that other
diphosphine ligands have the potential to function simi-
larly, which could in turn expose reactive ruthenium sites
*
Corresponding authors. Tel.: +1 817 257 7195 (W.H. Watson); Tel.:
+1 940 565 3548; fax: +1 940 565 4318 (M.G. Richmond).
E-mail addresses: w.watson@tcu.edu (W.H. Watson), cobalt@unt.edu
(M.G. Richmond).
0022-328X/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.12.036

W.H. Watson et al. / Journal of Organometallic Chemistry 692 (2007) 1648–1652
1649
within an intact molecular cluster capable of participation
in unusual catalytic cycles. Given the general paucity of
reactions involving Ru6(l6-C)(CO)17 and diphosphine
ligands [1–3], we have initiated substitution studies between
the parent Ru6 cluster and the unsaturated diphosphine
ligands 4,6-bis(diphenylphosphinomethyl)-m-xylene (dppx),
1,2-bis(diphenylphosphino)benzene (dppbz), and (Z)-1,2-
bis(diphenylphosphino)ethylene (dppen). Our interest in
such ligands stems, in part, from the coordinative flexibility
exhibited by these and related diphosphines at metal cluster
compounds in terms of nondissocative isomerization behav-
ior [4]. In comparison to the extensive literature examples
that exist for dppm-, dppe-, and dppf-substituted polynu-
clear compounds, metal clusters containing a dppx or
dppbz ligand are essentially nonexistent. The synthesis
and structural characterization of the double homometallic
cluster [Ru6(l6-C)(CO)16]2(dppx) and its thermal conver-
sion to the pincer-bridged cluster Ru6(l6-C)(CO)15(dppx)
have recently been reported by us [5]. Herein we present
our data on the reaction between Ru6(l6-C)(CO)17 and
the diphosphine ligand dppbz to give HRu6(l5-C)(l3-P)-
(CO)14(dppbz). The chelation of one dppbz ligand to a sin-
gle ruthenium atom and the facile decomposition of an
additional dppbz ligand to furnish the observed capping
phosphido moiety in the product are discussed.
room temperature for 1 h and then examined by TLC using
CH2Cl2/hexane (1:1) as the eluent. A small, fast moving
spot belonging to the starting cluster (Rf = 0.90; estimated
at ca. 20%) and one large spot (Rf = 0.50) corresponding
to HRu6(l5-C)(l3-P)(CO)14(dppbz) were observed, in addi-
tion to some black material that remained irreversibly
bound at the origin of the plate. The solvent was concen-
trated and the desired product separated by column chro-
matography over silica gel using the aforementioned
mobile phase. The crude sample was recrystallized from
CH2Cl2/hexane to afford X-ray quality crystals of
HRu6(l5-C)(l3-P)(CO)14(dppbz) in 40% yield (55 mg). An
acceptable combustion sample was obtained from a sample
of HRu6(l5-C)(l3-P)(CO)14(dppbz) that was recrystallized
from C6H6/hexane. IR (CH2Cl2): m(CO) 2079 (s), 2044
(vs), 2018 (s) cmꢀ1 1H NMR (C6D6): d 6.60–7.50 (m,
.
24H), ꢀ21.55 (s, bridging hydride). 31P NMR (CD2Cl2): d
76.51 (s, 2P, dppbz), 68.30 (s, l3-P moiety). Anal. Calc.
(found) for C45H25O14P3Ru6 Æ C6H6: C, 39.09 (39.02); H,
1.99 (2.27).
2.3. Thermolysis of Ru6(l6C)(CO)17 in the presence of
dppbz
This reaction was carried out in a Schlenk tube employ-
ing 50 mg (0.045 mmol) of Ru6(l6-C)(CO)17, 23 mg
(0.052 mmol) of dppbz, and 20 mL of 1,2-dichloroethane
(DCE). The solution was heated at 45 °C overnight and
then checked by TLC analysis, which revealed the presence
2. Experimental
2.1. General methods
The Ru6(l6-C)(CO)17 cluster used in these studies was
synthesized from Ru3(CO)12 and ethylene using a 450 mL
Parr Series 4560 bench-top mini reactor [6], while the latter
cluster was prepared from hydrated RuCl3 and CO using a
1l Parr Series 4000 rocking autoclave [7]. The chemicals
dppbz and Me3NO Æ nH2O were purchased from Aldrich
Chemical Co. The Me3NO Æ nH2O was dried by azeotropic
distillation from benzene and the anhydrous Me3NO was
stored in a Schlenk tube under argon. All reaction, IR,
and NMR solvents were of reagent grade and were distilled
from a suitable drying agent and stored in Schlenk vessels
equipped with Teflon stopcocks [8]. The combustion anal-
ysis 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,
using PC control and OMNIC software. The 1H
(200 MHz) and 31P{1H} (162 MHz) spectra were recorded
on Varian Gemini-200 and Bruker AVANCE DRX-400
spectrometers, respectively.
Table 1
Crystal data and structure refinement details for HRu6(l5-C)(l3-
P)(CO)14(dppbz)
CCDC entry no.
Crystal system
Space group
622,560
Monoclinic
P21/c
˚
a (A)
13.334(2)
17.446(2)
21.050(2)
94.026(2)
4884.7(9)
C45H25P3O14Ru6
1487.97
4
˚
b (A)
˚
c (A)
b °
V (A )
3
˚
Molecular formula
fw
Formula units per cell (Z)
Dcalcd (Mg/m3)
2.023
0.71073
1.970
˚
k (Mo Ka) (A)
Absorption coefficient (mmꢀ1
Rmerge
)
0.1064
Absorption correction
Absorption correction factor
Total reflections
SADABS
0.8481/0.6499
41940
Independent reflections
Data/res/parameters
11594
11594/0/614
0.0552
0.0965
0.884
2.2. Me3NO activation of Ru6(l6C)(CO)17 in the presence
of dppbz
a
R1 [I P 2r(I)]
b
wR2 (all data)
GOF on F2
Dq(max), Dq(min) (e/A )
3
To a 250 mL Schlenk flask under argon was added 0.10 g
(0.091 mmol) of Ru6(l6-C)(CO)17, 43 mg (0.096 mmol) of
dppbz, and 14 mg (0.19 mmol) of Me3NO, followed by
20 mL of CH2Cl2 via syringe. The solution was stirred at
˚
0.996, ꢀ0.786
P
P
a
R1 = iFoj ꢀ jFci/ jFoj.
n
h
i.
h
io
1=2
P
P
2
2
b
R2 ¼
wðF 2o ꢀ F 2c Þ
wðF 2oÞ
.

1650
W.H. Watson et al. / Journal of Organometallic Chemistry 692 (2007) 1648–1652
Table 2
versible binding to the chromatographic support. Doubling
of the amount of dppbz relative to the starting cluster and
using 2.0 equiv. Me3NO led only to a modest increase in
HRu6(l5-C)(l3-P)(CO)14(dppbz) (ca. 55%), while reactions
employing 1 equiv. of Me3NO and a 1:1 mixture of cluster
and ligand gave the title cluster in reduced yields on the
order of 25–30%. Thermolysis of Ru6(l6-C)(CO)17 and
dppbz (1:1) in CH2Cl2, 1,2-dichloroethane, or toluene sol-
vents over the temperature range of 40–55 °C proceeded
similarly with only HRu6(l5-C)(l3-P)(CO)14(dppbz)
observed by TLC. The product, whose structure is shown
below, was isolated by column chromatography over silica
gel as a relatively air-stable solid.
˚
Selected bond distances (A) and angles (°) for HRu6(l5-C)(l3-
P)(CO)14(dppbz)
Bond distances
Ru(1)–P(2)
Ru(1)–P(3)
Ru(1)–Ru(3)
Ru(2)–Ru(3)
Ru(2)–Ru(5)
Ru(3)–Ru(6)
Ru(4)–Ru(6)
Ru(5)–Ru(6)
2.280(2)
2.300(2)
Ru(1)–P(1)
Ru(1)–Ru(2)
Ru(2)–P(3)
Ru(2)–Ru(6)
Ru(3)–P(3)
Ru(3)–Ru(4)
Ru(4)–Ru(5)
C(1)–C(2)
2.284(2)
2.8557(9)
2.349(2)
2.8200(9)
2.342(2)
2.885(1)
2.902(1)
1.39(1)
2.8620(9)
2.6703(9)
2.8540(9)
2.8127(9)
2.8096(9)
2.8252(9)
Bond angles
P(2)–Ru(1)–P(1)
P(2)-Ru(1)-P(3)
C(1)–P(1)–Ru(1)
Ru(1)–P(3)–Ru(3)
Ru(3)–P(3)–Ru(2)
O(4)–C(34)–Ru(2)
82.61(7)
97.13(7)
108.1(3)
76.12(6)
69.40(6)
162.9(7)
C(31)–Ru(1)–P(3)
P(1)–Ru(1)–P(3)
C(2)–P(2)–Ru(1)
Ru(1)–P(3)–Ru(2)
O(2)–C(32)–Ru(3)
161.6(2)
100.59(7)
107.5(2)
75.78(6)
166.3(7)
Ru
Ru
H
Ru
C
of unreacted Ru6(l6-C)(CO)17 and HRu6(l5-C)(l3-P)-
(CO)14(dppbz). The dppbz-substituted cluster was isolated
by column chromatography as described above in 44%
yield (30 mg).
P
Ru
Ru
Ph2P
Ru
PPh2
2.4. X-ray structural data
The X-ray data for HRu6(l5-C)(l3-P)(CO)14(dppbz)
were collected on a Bruker SMARTä 1000 CCD-based dif-
fractometer at 233 K. The frames were integrated with
the available SAINT software package using a narrow-frame
algorithm [9], and the structure solved and refined using the
SHELXTL program package [10]. The molecular structure
was checked by using PLATON [11], and all nonhydrogen
atoms refined anisotropically. All carbon-bound hydrogen
atoms were assigned calculated positions and allowed to
ride on the attached heavy atom, unless otherwise noted.
The bridging hydride that is assumed to span the Ru(4)–
Ru(5) vector was not located during refinement. The refine-
ment for HRu6(l5-C)(l3-P)(CO)14(dppbz) converged at
R = 0.0552 and Rw = 0.0965 for 11,594 independent reflec-
tion with I > 2r(I). Tables 1 and 2 summarize the pertinent
X-ray data.
HRu6(l5-C)(l3-P)(CO)14(dppbz) was initially charac-
terized in solution by spectroscopic methods. The IR
spectrum recorded in CH2Cl2 revealed only terminal car-
bonyl bands at 2079 (s), 2044 (vs), and 2018 (s) cmꢀ1, and
the 1H NMR recorded in C6D6 exhibited an aromatic
multiplet at d 6.60–7.50 for the dppbz ligand and a
high-field bridging hydride at d ꢀ21.55. The chemical
shift for the hydride in HRu6(l5-C)(l3-P)(CO)14(dppbz)
1
parallels those H NMR data for the hydride ligands in
the pentaruthenium clusters HRu5(l5-C)(CO)14(SiEt3)
and HRu5(l5-C)(CO)15(SiEt3) [12]. To determine whether
the bridging hydride is derived from the dppbz ligand or
the reaction solvent, we investigated the reaction between
Ru6(l6-C)(CO)17, dppbz, and Me3NO in CDCl3. 1H
NMR analysis of the crude reaction mixture displayed a
hydride resonance at d ꢀ18.90 that allows us to rule
out solvent participation in the formation of HRu6-
(l5-C)(l3-P)(CO)14(dppbz). The presence of different
phosphorus groups in HRu6(l5-C)(l3-P)-(CO)14(dppbz)
was verified by 31P NMR spectroscopy, with the two
31P singlets recorded at d 76.51 and 68.30 ascribed to a
chelating dppbz ligand and a face-capping l3-phosphido
moiety, respectively.
The unequivocal identity and the structural composi-
tion of HRu6(l5-C)(l3-P)(CO)14(dppbz) were established
by X-ray crystallography. Fig. 1 shows the thermal ellip-
soid plot of HRu6(l5-C)(l3-P)(CO)14(dppbz). The title
cluster consists of a square-pyramidal Ru5 core that is
edged-bridged by the sixth ruthenium atom and whose
polyhedral structure is in keeping with its 88-electron
count and structural trends exhibited by other condensed
3. Results and discussion
Our initial reaction between Ru6(l6-C)(CO)17 and
dppbz was carried out at room temperature. No reaction
was observed when equimolar amounts of the reagents
were stirred over a 24 h period. The addition of the oxida-
tive-decarbonylation reagent Me3NO (2 equiv.) to the solu-
tion led to the rapid consumption of most of the starting
cluster (>70–75%) and formation of the hexaruthenium
cluster HRu6(l5-C)(l3-P)(CO)14(dppbz) as the sole mobile
product by TLC analysis. The reaction is also accompanied
by cluster decomposition based on the presence of an
unknown black solid at the origin of the TLC plate, whose
in-depth characterization was not pursued due to its irre-

W.H. Watson et al. / Journal of Organometallic Chemistry 692 (2007) 1648–1652
1651
Fig. 1. Thermal ellipsoid plot of HRu6(l5-C)(l3-P)(CO)14(dppbz) at the 50% probability level.
polynuclear clusters [13,14]. The Ru–Ru bond distances
C(45) atom is situated in the basal plane of the square
pyramid as in Ru5(l5-C)(CO)15 [17]. The remaining dis-
tances and angles require no comment.
˚
˚
range from 2.6703(9) A [Ru(2)–Ru(3)] to 2.902(1) A
˚
[Ru(4)–Ru(5)] and exhibit a mean distance of 2.830 A that
is in agreement with those Ru–Ru distances found in
other carbide-containing Ru5 and Ru6 clusters [1,11,15].
Although the bridging hydride was not located during
refinement, it has been assigned to the long basal
Ru(4)–Ru(5) vector. This hydride location gives rise to a
mirror plane of symmetry that bisects the square pyrami-
dal core, the l3-P moiety, and the dppbz-substituted
Ru(1) center of the cluster, leading to a single 31P reso-
nance for the dppbz ligand in agreement with the 31P
NMR data. The Ru–P distances associated with the
face-capping phosphido moiety reveal an average distance
of 2.330 A that is 0.043 A longer than the mean distance
from the Ru–P bonds from the dppbz ligand. The pres-
ence of the l3-P and chelating diphosphine moieties in
HRu6(l5-C)(l3-P)(CO)14(dppbz) is unexampled in car-
bido-substituted polynuclear ruthenium clusters. A check
of the Cambridge Structural Database for dppbz-substi-
tuted clusters reveals Ir4(CO)10(dppbz) as the only entry.
Here the chelating dppbz ligand was formed from an
ortho phosphorylation of the PPh3 ligands in Ir4(CO)10-
(PPh3)2 [16]. The Ru(3)–C(32)–O(2) and Ru(2)–C(34)–
O(4) carbonyls are weakly semibridging based on bond
angles of 166.3(7)° and 162.9(7)°, respectively, and bent
slightly towards the Ru(1) center. Finally, the carbide
Documented examples of phosphine ligand activation in
clusters derived from Ru6(l6-C)(CO)17 are scarce. The
phosphine ligands in Ru6(l6-C)(CO)15(PhPMe2)2 have
been shown to undergo both P–C and C–H bond cleavage
on treatment with Me3NO at room temperature to produce
Ru6(l6-C)(CO)13(l-PMe2)(l3-g3-Me2PC6H4) and Ru6-
(l6-C)(CO)14(PhPMe2)(l-g2-MePhPCH2)(l-H) [18]. The
data from this latter report and our present study support
the existence of low-energy manifolds for the deleterious
fragmentation of a coordinated phosphine ligand(s) in this
genre of cluster. The sequence of events leading to
HRu6(l5-C)(l3-P)(CO)14(dppbz) is unknown at this time,
and attempts to isolate the presumed intermediate
Ru6(l6-C)(CO)15(dppbz) have not been successful. The fac-
ile degradation of the dppbz ligand found here stands in
sharp contrast to those results obtained in the reaction of
the unsaturated diphosphine ligand dppen with Ru6(l6-
C)(CO)17 conducted under identical conditions [19]. Here
the dppen ligand acts as a face-capping 6e donor through
the use of the two phosphine moieties and the alkene p
bond to furnish the cluster compounds Ru6(l6-C)(CO)14-
(l-dppen) and Ru5(l5-C)(CO)12(l-dppen) shown below.
No evidence for the degradation of the dppen ligand was
observed.
˚
˚

1652
W.H. Watson et al. / Journal of Organometallic Chemistry 692 (2007) 1648–1652
[3] The reaction between Ru6(l6-C)(CO)17 and the multidentate2,20-
bis(diphenylphosphino)-4,40-bipyridine affords the corresponding
P,N-bridged cluster: I.O. Koshevoy, M. Haukka, T.A. Pakkanen,
S.P. Tunik, P. Vainiotalo, Organometallics 24 (2005) 3516.
[4] (a) K. Yang, J.M. Smith, S.G. Bott, M.G. Richmond, Organomet-
allics 12 (1993) 4779;
PPh2
PPh2
Ru
C
Ru
C
PPh2
PPh2
Ru
Ru
Ru
Ru
Ru
Ru
Ru
Ru
(b) S.G. Bott, K. Yang, M.G. Richmond, J. Organomet. Chem. 690
(2005) 3067;
(c) W.H. Watson, G. Wu, M.G. Richmond, Organometallics 24
(2005) 5431;
W.H. Watson, G. Wu, M.G. Richmond, Organometallics 25 (2006)
930;
(d) W.H. Watson, B. Poola, M.G. Richmond, J. Organomet. Chem.
691 (2006) 4676.
Ru
Ru6(μ6-C)(CO)14(μ-dppen)
Ru5(μ5-C)(CO)12(μ-dppen)
[5] W.H. Watson, B. Poola, M.G. Richmond, J. Chem. Crystallogr.,
(2007), in press.
[6] J.N. Nicholls, M.D. Vargas, Inorg. Synth. 26 (1989) 281.
[7] M.I. Bruce, C.M. Jensen, N.L. Jones, Inorg. Synth. 26 (1989) 259.
[8] D.F. Shriver, The Manipulation of Air-Sensitive Compounds,
McGraw-Hill, New York, 1969.
[9] Saint Version 6.02, Bruker Analytical X-ray Systems, Inc. Copyright,
1997–1999.
[10] SHELXTL Version 5.1, Bruker Analytical X-ray Systems, Inc. Copy-
right, 1998.
[11] A.L. Spek, PLATON – A Multipurpose Crystallographic Tool, Utrecht
University, Utrecht, The Netherlands, 2001.
[12] R.D. Adams, B. Captain, W. Fu, Organometallics 19 (2000) 3670.
[13] (a) For the theoretical justification of the adopted molecular
polyhedron, see: D.M.P. Mingos, Acc. Chem. Res. 17 (1984) 311;
(b) B.K. Teo, Inorg. Chem. 23 (1984) 1251, 1257;
(c) D.M.P. Mingos, D.J. Wales, Introduction to Cluster Chemistry,
Prentice-Hall, Englewood Cliffs, NJ, 1990.
4. Conclusions
The coordination and fragmentation of dppbz ligands at
Ru6(l6-C)(CO)17 furnishes the edge-bridged square-pyra-
midal cluster HRu6(l5-C)(l3-P)(CO)14(dppbz). The
remarkably mild conditions leading to the dephosphination
of one of the dppbz ligands and the ensuing formation of
the l3-P moiety are unprecedented in transition-metal clus-
ter chemistry. The substitution chemistry of the dppbz
ligand with metal clusters of varying nuclearity is currently
being investigated in order to establish the generality of the
diphosphine reactivity reported here.
[14] (a) For related hexametallic edge-bridged square-pyramidal struc-
tures, see: R.D. Adams, L.-W. Yang, J. Am. Chem. Soc. 104 (1982)
4115;
5. Supplementary material
CCDC 260091 contains the supplementary crystallo-
(b) R.D. Adams, J.E. Babin, M. Tasi, T.A. Wolfe, J. Am. Chem.
Soc. 110 (1988) 7093;
graphic
data
for
HRu6(l5-C)(l3-P)(CO)14(dppbz)
(#622560). 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.
(c) R.D. Adams, J.E. Babin, M. Tasi, T.A. Wolfe, New J. Chem. 12
(1988) 481;
(d) R.D. Adams, W. Wu, Organometallics 12 (1993) 1238, 1248;
(e) J.W.-S. Hui, W.-T. Wong, J. Chem. Soc., Dalton Trans. (1996)
2887;
(f) T. Chihara, T. Tase, H. Ogawa, Y. Wakatsuki, Chem. Commun.
(1999) 279;
(g) R.D. Adams, B. Captain, W. Fu, P.J. Pellechia, M.D. Smith,
Inorg. Chem. 42 (2003) 2094;
Acknowledgements
(h) R.D. Adams, B. Captain, L. Zhu, Organometallics 24 (2005)
2419.
[15] (a) P.J. Dyson, B.F.G. Johnson, J. Lewis, M. Martinelli, D. Braga,
F. Grepioni, J. Am. Chem. Soc. 115 (1993) 9062;
(b) A.J. Blake, J.L. Haggitt, B.F.G. Johnson, S. Parsons, J. Chem.
Soc., Dalton Trans. (1997) 991;
Financial support from the Robert A. Welch Founda-
tion (Grants P-0074-WHW and B-1093-MGR) is appreci-
ated. We also wish to thank Prof. Michael Lattman
(SMU) for assistance with the 31P NMR spectrum.
(c) D. Braga, F. Grepioni, L. Scaccianoce, B.F.G. Johnson, J. Chem.
Soc., Dalton Trans. (1998) 1321;
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