Thermally induced dual P-C bond cleavage routes from the imido-capped cluster (see abstract)

Article abstract of DOI:10.1016/j.jorganchem.2004.07.056

The imido-capped cluster Ru₃(CO)₉(μ₃ -CO)(μ₃-NPh) (1) reacts with the diphosphine ligand 4,5-bis (diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) to furnish both Ru₃(CO)₇(μ₃-CO)(μ₃ -NPh)(bpcd) (2) and Ru₃(CO)₅(μ₃-CO) (μ₃-NPh)(bpcd)₂ (3) as the major and minor products, respectively, under thermal and Me₃NO activation. The thermolysis of cluster 2 affords the new triruthenium compounds Ru₃(CO)₅(μ₂-CO)₂(μ ₃-NPh)(μ₂-PPh₂)[μ,η ¹,η¹-C=C(PPh₂)C(O)CH₂ C(O)] (4), Ru₃(CO)₆(μ₂-CO)(μ ₃-NPh)(μ-PhCO)[μ₂,η²,η ¹-PPhC=C(PPh₂)C(O)CH₂C(O)] (5), and Ru₃(CO)₉(μ₃-NPh)(μ₃ -PPh) (6). Compounds 2-6 have been fully characterized in solution, and the molecular structures of 2, and 4-6 have been determined. Cluster 2 exhibits a nido-NRu₃ core with a face-capping μ₃ -CO and a chelating bpcd ligand that occupies an equatorial and axial site. VT ³¹P NMR data indicate that the bpcd ligand in 2 undergoes a rocking motion between the equatorial and axial sites at the attached ruthenium center at elevated temperatures. Cluster 4 possesses a similar nido polyhedral core that is tethered by a bridging phosphido group and the 3e-donor moiety μ₂,η ².η¹-C=C(PPh₂)C(O)CH₂ C(O). The structure of 5 reveals a hypho architecture containing a single Ru-Ru bond and where the three ruthenium centers are bridged by imido and benzoyl moieties and the seven-electron donor ligand μ ₂,η²,η¹-PPhC=C(PPh₂) C(O)CH₂C(O), which results from the cleavage of one the P-Ph bonds of the original bpcd ligand. The 50e cluster 6 exhibits a nido polyhedral core consisting of three Ru(CO)₃ groups that are capped by a μ₃-imido and μ₃-phosphinidine unit. Cluster 6 represents the first structurally characterized example of a mixed PhN/PhP capped cluster belonging to the family of nido-Ru ₃(CO)₉(μ₃-EPh)₂ clusters. The pertinent structural highlights associated with these clusters are discussed, and the lack of reactivity of the capping imido group with the bpcd ligand in Ru₃(CO)₇(μ₃-CO) (μ₃-NPh)(bpcd) during thermolysis is contrasted with the related benzylidyne-capped cluster PhCCo₃(CO)₇ (bpcd).

Full text of DOI:10.1016/j.jorganchem.2004.07.056

Journal of Organometallic Chemistry 689 (2004) 3426–3437
www.elsevier.com/locate/jorganchem
Thermally induced dual P–C bond cleavage routes from the
imido-capped cluster Ru3(CO)7(l3-CO)(l3-NPh)(bpcd): synthesis,
spectroscopic properties, and X-ray diffraction structures of
Ru3(CO)7(l3-CO)(l3-NPh)(bpcd), Ru3(CO)5(l2-CO)2(l3-NPh)
(l2-PPh2)[l,g1,g1-C@C(PPh2)C(O)CH2C(O)], Ru3(CO)6(l2-CO)
(l3-NPh)(l-PhCO)[l2,g2,g1-PPhC@C(PPh2)C(O)CH2C(O)], and
Ru3(CO)9(l3-NPh)(l3-PPh)
*
Simon G. Bott , Huafeng Shen, Michael G. Richmond
*
Department of Chemistry, University of Houston, Houston, TX 77204, USA
Department of Chemistry, University of North Texas, P.O. Box 305070, Denton, TX 76203, USA
Received 7 July 2004; accepted 23 July 2004
Available online 11 September 2004
Abstract
The imido-capped cluster Ru3(CO)9(l3-CO)(l3-NPh) (1) reacts with the diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclo-
penten-1,3-dione (bpcd) to furnish both Ru3(CO)7(l3-CO)(l3-NPh)(bpcd) (2) and Ru3(CO)5(l3-CO)(l3-NPh)(bpcd)2 (3) as the
major and minor products, respectively, under thermal and Me3NO activation. The thermolysis of cluster 2 affords the new
triruthenium compounds Ru3(CO)5(l2-CO)2(l3-NPh)(l2-PPh2)[l,g1,g1-C@C(PPh2)C(O)CH2C(O)] (4), Ru3(CO)6(l2-CO)(l3-
NPh)(l-PhCO)[l2,g2,g1-PPhC@C(PPh2)C(O)CH2C(O)] (5), and Ru3(CO)9(l3-NPh)(l3-PPh) (6). Compounds 2–6 have been fully
characterized in solution, and the molecular structures of 2, and 4–6 have been determined. Cluster 2 exhibits a nido-NRu3 core
with a face-capping l3-CO and a chelating bpcd ligand that occupies an equatorial and axial site. VT 31P NMR data indicate that
the bpcd ligand in 2 undergoes a rocking motion between the equatorial and axial sites at the attached ruthenium center at elevated
temperatures. Cluster 4 possesses a similar nido polyhedral core that is tethered by a bridging phosphido group and the 3e-donor
moiety l2,g2,g1-C@C(PPh2)C(O)CH2C(O). The structure of 5 reveals a hypho architecture containing a single Ru–Ru bond and
where the three ruthenium centers are bridged by imido and benzoyl moieties and the seven-electron donor ligand l2,g2,g1-
PPhC@C(PPh2)C(O)CH2C(O), which results from the cleavage of one the P–Ph bonds of the original bpcd ligand. The 50e cluster
6 exhibits a nido polyhedral core consisting of three Ru(CO)3 groups that are capped by a l3-imido and l3-phosphinidine unit.
Cluster 6 represents the first structurally characterized example of a mixed PhN/PhP capped cluster belonging to the family of
nido-Ru3(CO)9(l3-EPh)2 clusters. The pertinent structural highlights associated with these clusters are discussed, and the lack of
reactivity of the capping imido group with the bpcd ligand in Ru3(CO)7(l3-CO)(l3-NPh)(bpcd) during thermolysis is contrasted
with the related benzylidyne-capped cluster PhCCo3(CO)7(bpcd).
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Metal clusters; P–C bond activation; Electrochemistry; Imido-capped clusters; Diphosphine ligand; Redox chemistry
*
Corresponding authors. Tel.: +713 743 2771/+940 565 3548; fax:
+940 565 4318.
E-mail addresses: sbott@uh.edu (S.G. Bott), cobalt@unt.edu
(M.G. Richmond).
0022-328X/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.07.056

S.G. Bott et al. / Journal of Organometallic Chemistry 689 (2004) 3426–3437
3427
1. Introduction
extend our studies to a structurally similar bpcd-substi-
tuted cluster containing a different organic capping lig-
and. Here the coordination of bpcd to Ru3(CO)10(l3-
NPh) was expected to afford the new cluster Ru3
(CO)8(l3-NPh)(bpcd), from which we could explore
the reactivity of (1) the diphosphine ligand at a non-co-
balt containing cluster and (2) the propensity of the imi-
do ligand to participate in a reductive coupling reaction
with the transient Ru–C(dione) moiety, should P–C
bond cleavage be observed in a manner analogous to
that of the tricobalt cluster RCCo3(CO)7(bpcd).
The chemistry of imido-capped clusters has been
extensively explored over the last several years due to
their manifold importance in organometallic transfor-
mations and substrate functionalization reactions [1].
For example, unequivocal evidence from myriad studies
involving the reductive carbonylation of aryl nitro com-
pounds in the presence of M3(CO)12 (where M = Fe,
Ru) reveals that the formation of imido-capped clusters
M3(CO)10(l3-NR) are a prerequisite for productive
catalysis [2]. The imido groups in such systems serve
as a crucial platform for the ultimate release of carba-
mates, isocyanates, amides, and oximes, in addition to
complex heterocycles depending upon the reaction con-
ditions [3]. Several excellent mechanistic studies have
greatly contributed to our overall understanding involv-
ing the initial reduction of the nitro group to an imido
moiety at a polynuclear cluster [c,4]. These studies have
also substantiated the acceleratory effect that halide and
alkoxide additives have had on the reduction of the nitro
group in organic compounds, along with the importance
of single-electron transfer in the activation of the nitro
Ph
Ph
C
O
C
thermolysis
or hυ
Co
Co
Ph2
P
PPh2
Co
Co
O
O
Co
P
PPh2
Ph2
Co
O
ð1Þ
Herein we report our results on the reaction between
Ru3(CO)10(l3-NPh) and bpcd to furnish the new cluster
compounds 2–6. The solution spectroscopic data and
structural features of these products are discussed.
moiety by the anionic cluster [Fe3(CO)11]2ꢀ
.
The chemistry of the l3-imido ligand in Ru3
(CO)10(l3-NPh) has also been studied with respect to al-
kyne insertion and coupling reactivity, with binuclear
metallapyrrolidone compounds having been isolated
and structurally characterized [5]. The same cluster also
functions as a building block for the construction of
higher-nuclearity mixed-metal clusters via face capping
and polyhedral expansion sequences [6].
2. Experimental
2.1. General methods
Nitrosobenzene and Me3NO Æ 2H2O were purchased
from Aldrich Chemical Co., with the former chemical
used as received while the latter was dried by azeotropic
distillation from benzene. The bpcd ligand used in these
studies was synthesized from 4,5-dichloro-4-cyclopen-
ten-1,3-dione and Ph2PTMS according to the known
procedure [12], while the Ru3(CO)12 used in the prepara-
tion of Ru3(CO)9(l3-CO)(l3-NPh) [13] was prepared
from hydrated RuCl3 using the carbonylation procedure
of Bruce [14]. All reaction, NMR, and electrochemistry
solvents were distilled under argon from a suitable dry-
ing agent and stored in Schlenk storage vessels [15]. The
tetra-n-butylammonium perchlorate electrolyte (TBAP)
was purchased from Johnson Matthey Electronics and
recrystallized from ethyl acetate/hexane (1:1), followed
by drying for at least 48 h under high vacuum. All C
and H analyses were performed by Altantic Microlab,
Norcross, GA.
Our interest in Ru3(CO)10(l3-NPh) has focused on
the molecular dynamics associated with ligand fluxional-
ity and bonding considerations between the Ru3 frame
and the ancillary ligands [7], in addition to the ligand
substitution behavior exhibited by Ru3(CO)10(l3-NPh)
in the presence of PPh3 under thermal, reagent assisted,
and ETC activation [8]. Prior to our latter report, the
only other published work with a phosphine-substituted
derivative of Ru3(CO)10(l3-NPh) involved Ru3
(CO)8(l3-NPh)(dppm). Here the synthesis and fragmen-
tation of Ru3(CO)8(dppm)(l3-NPh) in the presence of
alkynes were investigated [9]. Given this dearth of ligand
substitution chemistry in Ru3(CO)10(l3-NPh), coupled
with our desire to further our studies with other lig-
and-capped tetrahedral clusters with the redox-active
diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclo-
penten-1,3-dione (bpcd) [10,11], we have investigated
the reaction between Ru3(CO)10(l3-NPh) and bpcd.
The propensity of this ligand to undergo facile P–C
bond cleavage in the alkylidyne-capped clusters
RCCo3(CO)7(bpcd) has been unequivocally demon-
strated by us, as depicted in Eq. (1). However, given that
the majority of our research has relied on clusters that
possessed a capping alkylidyne ligand, we wished to
The reported infrared data were recorded on a Nico-
let 20 SXB FT-IR spectrometer in 0.1 mm NaCl cells,
using PC control and OMNIC software. The 1H
NMR spectra were recorded at 200 MHz on a Varian
Gemini-200 spectrometer, and the 31P NMR spectra
were recorded at 121 MHz on a Varian 300-VXR spec-
trometer. The reported 31P chemical shifts are referenced

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S.G. Bott et al. / Journal of Organometallic Chemistry 689 (2004) 3426–3437
to external H3PO4 (85%), taken to have d = 0.0. Here
positive chemical shifts are to low field of the external
standard. The cyclic voltammetry studies were carried
out on a PAR Model 273 potentiostat/glavanostat under
argon in airtight cells, as previously described [16].
not extensively investigated as a preparative route to
cluster 2.
2.3. Thermolysis of Ru3(CO)7(l3-CO)(l3-NPh)(bpcd)
To 0.35 g (0.32 mmol) of Ru3(CO)7(l3-CO)(l3-
NPh)(bpcd) in a large Schlenk tube was added 50 mL
of 1,2-dichloroethane. The vessel was sealed and then
heated for 5.0 h at ca. 70 °C. At this point TLC analysis
of the reaction solution using CH2Cl2 revealed the com-
plete consumption of the starting cluster and the pres-
ence of three new products, in addition to a tiny
amount of material that remained at the origin. Column
chromatography over neutral alumina using petroleum
ether as the eluent gave a yellow band that corresponded
to Ru3(CO)9(l3-NPh)(l3-PPh) (6). Changing the eluent
to CH2Cl2/petroleum ether (1:1) next afforded the
brown-colored cluster Ru3(CO)5(l2-CO)2(l3-NPh)
2.2. Synthesis of Ru3(CO)7(l3-CO)(l3-NPh)(bpcd)
(2) and Ru3(CO)5(l3-CO)(l3-NPh)(bpcd)2 (3)
2.2.1. Me3NO activation
To 0.30 g (0.45 mmol) of Ru3(CO)9(l3-CO)(l3-NPh)
and 0.21 g (0.45 mmol) of bpcd in 50 mL of CH2Cl2 in a
Schlenk tube was added 67 mg (0.90 mmol) of Me3NO.
The solution was stirred for 2.0 h at room temperature
and examined by TLC analysis, which revealed the pres-
ence of a small amount of unreacted 1, along with two
slower moving spots that corresponded to clusters 2
and 3. Ru3(CO)7(l3-CO)(l3-NPh)(bpcd) was subse-
quently isolated by column chromatography over silica
gel using CH2Cl2/petroleum ether (1:1), with Ru3
(CO)5(l3-CO)(l3-NPh)(bpcd)2 being eluted from the
column upon changing the solvent system to CH2Cl2.
Both products were recrystallized from CH2Cl2/hexane
(1:1) to afford the analytical sample of each product
and single crystals of Ru3(CO)7(l3-CO)(l3-NPh)(bpcd)
suitable for X-ray diffraction analysis. Yield of brown
2: 0.35 g (72%). IR (CH2Cl2): m(CO) 2074 (s), 2048
(vs), 2003 (vs), 1944 (m), 1749 (w, symm dione carbo-
nyl), 1718 (m, antisymm dione carbonyl), 1674 (m, br,
(l2-PPh2)[l,g1,g1-C@C(PPh2)C(O)CH2C(O)],
while
pure CH2Cl2 finally furnished a red band belonging
to Ru3(CO)6(l2-CO)(l3-NPh)(l-PhCO)[l2,g2,g1-PPhC@
C(PPh2)C(O)CH2C(O)]. Recrystallization of Ru3
(CO)9(l3-NPh)(l3-PPh) from hexane at ꢀ5 °C gave sin-
gle crystals suitable for X-ray crystallography and ana-
lytical pure Ru3(CO)9(l3-NPh)(l3-PPh). The analytical
sample and crystals for X-ray diffraction analysis of clus-
ters 4 and 5 were obtained from CH2 Cl2/methanol (1:1)
at ꢀ10 °C. Yield of 4: 95 mg (28%). IR (CH2Cl2): m(CO)
2063 (s), 2043 (s), 2005 (vs), 1939 (w), 1865 (w), 1725 (w,
symm dione carbonyl), 1694 (m, antisymm dione carbo-
l3-CO) cmꢀ1 31P NMR (CDCl3, 222 K): d 57.84 (s),
.
44.92 (s). 1H NMR (CDCl3): d 6.67–7.60 (m, 25 H, aryl),
3.28 (s, 2H, CH2). Anal. Calc. (found) for C43H27NO10-
P2Ru3: C, 47.70 (47.51); H, 2.51 (2.64). Yield of green 3:
42 mg (6%). IR (CH2Cl2): m(CO) 2034 (w), 2015 (vs),
1959 (vs), 1746 (m, symm dione carbonyl), 1715 (m,
nyl) cmꢀ1
.
31P NMR (CDCl3, 298 K): d 165.92 (d, JP–
1
P = 87 Hz), 0.80 (d, JP–P = 87 Hz). H NMR (CDCl3):
d 6.46–7.50 (m, 25 H, aryl), 2.78 (b, 2H, CH2). Anal.
Calc. (found) for C42H27NO9P2Ru3: C, 47.82 (48.39);
H, 2.58 (2.86). Yield of 5: 0.17 g (48%). IR (CH2Cl2):
m(CO) 2063 (sh), 2051 (vs), 2036 (s), 1996 (s), 1914 (w),
1715 (w, symm dione carbonyl), 1668 (m, antisymm
antisymm dione carbonyl), 1639 (m, br, l3-CO) cmꢀ1
.
31P NMR (CDCl3, 212 K): d 50.49 (d, JP–P = 14 Hz),
49.18 (dd, JP–P = 52, 14 Hz), 16.62 (d, JP–P = 52 Hz),
dione carbonyl) cmꢀ1 31P NMR (CDCl3, 298 K): d
.
1
0.89 (t, JP–P = 52 Hz). H NMR (CDCl3): d 6.53–8.15
66.82 (d, JP–P = 17 Hz), ꢀ4.19 (d, JP–P = 17 Hz). 1H
NMR (CDCl3): d 6.47–8.27 (m, 25 H, aryl), 3.14 (AB
quartet, 2H, CH2). Anal. Calc. (found) for C43H27NO10-
P2Ru3: C, 47.40 (48.34); H, 2.51 (3.04). Yield of 6: 38 mg
(16%). IR (hexane): m(CO) 2091 (w), 2070 (vs), 2045 (vs),
(m, 45 H, aryl), 3.22 (AB quartet, 2H, CH2), 3.16 (AB
quartet, 2H, CH2). Anal. Calc. (found) for
C70H49O10NP4Ru3 Æ hexane: C, 57.82 (58.47); H, 3.99
(4.31)%.
2022 (vs), 1999 (vs) cmꢀ1 31P NMR (CDCl3): d 269.66.
.
2.2.2. Thermal activation
1H NMR (CDCl3): d 6.70–7.60 (m, 10 H, aryl). Anal.
Calc. (found) for C21H10NO9PRu3: C, 33.43 (34.65); H,
1.34 (1.82)%.
Heating 0.30 g (0.45 mmol) of Ru3(CO)9(l3-CO)(l3-
NPh) and 0.21 g (0.45 mmol) of bpcd together in 50
mL of 1,2-dichloroethane at ca. 75–80 °C in a Schlenk
tube over a 0.5–1.0 h period initially produces clusters
2 and 3 as the major and minor products, respectively.
However, all thermolysis reactions were accompanied
by the formation of clusters 4–6 (vide infra), even at
early reaction times, with clusters 4–6 becoming the
predominant products as heating was continued. Gi-
ven the significant band overlap of all five product
clusters on silica gel, this thermolysis reaction was
2.4. X-ray crystallography
Table 1 contains the X-ray data and processing param-
eters for the compounds 2 and 4–6. Selected crystals of 2
and 4–6 suitable for X-ray diffraction analysis were grown
as described above and were each sealed inside a
Lindemann capillary, followed by mounting on an
Enraf-Nonius CAD-4 diffractometer. After the cell

S.G. Bott et al. / Journal of Organometallic Chemistry 689 (2004) 3426–3437
3429
Table 1
X-ray crystallographic data and processing parameters for the triruthenium compounds 2 and 4–6
Compound
2
4
5
6
CCDC entry no
Space group
23990
239901
239902
239720
ꢀ
Monoclinic, P21/c
19.909(2)
11.847(1)
Monoclinic, P21/n
11.9071(8)
16.5367(9)
20.920(1)
Monoclinic, P21/n
9.6690(7)
36.247(4)
Triclinic, P1
10.0505(5)
10.1915(8)
12.4045(9)
86.156(6)
87.520(5)
81.429(5)
1252.9(2)
˚
a (A)
˚
b (A)
˚
c (A)
20.547(3)
11.560(1)
a (°)
b (°)
c (°)
113.47(1)
100.496(5)
92.808(7)
3
˚
V (A )
4445.3(9)
C43H27NO10P2Ru3
1082.85
4
4050.3(4)
C42H27NO9P2Ru3
1054.84
4
4046.6(6)
C43H27NO10P2 Ru3
1082.85
4
Mol. formula
fw
C21H10NO9PRu3
754.50
2
Formula units per cell (Z)
Dcalc (g/cm3)
1.618
1.730
1.777
2.000
0.71073
19.0
˚
k(Mo Ka) (A)
0.71073
11.11
0.037
0.71073
12.16
0.023
0.71073
12.21
0.031
Absorption coefficient (cmꢀ1
Rmerge
)
Abs. corr. factor
Total reflections
0.76–1.25
5661
3680
0.91–1.12
5457
2869
0.88–1.09
2858
1377
0.86–1.25
3056
2780
Independent reflections
Data/res/parameters
3680/0/412
0.0458
0.0534
2869/0/304
0.0370
0.0403
1377/0/252
0.0423
0.0479
2780/0/316
0.0249
0.0285
R
Rw
GOF
Weights
1.16
[0.04F2 + (rF)2]ꢀ1
0.67
[0.04F2 + (rF)2]ꢀ1
0.53
[0.04F2 + (rF)2]ꢀ1
1.41
[0.04F2 + (rF)2]ꢀ1
constants were obtained for all four samples, intensity
data in the range of 2° 6 2h 6 44° (clusters 2, 4, and 6)
and 2° 6 2h 6 ° (cluster 5) were collected at 298 K and
were corrected for Lorentz, polarization, and absorption
(DIFABS). Cluster 2 was solved by using Multan, while
clusters 4 and 5 were solved by using standard Patterson
techniques, which revealed the positions of the ruthenium
and phosphorus atoms. The structure of cluster 6 was
established by using SIR. In the case of 2, all non-hydro-
gen atoms were located with difference Fourier maps and
full-matrix least-squares refinement and were refined
anisotropically with the exception of the phenyl carbon
atoms. Except for the carbon atoms in 4, all non-hydro-
gen atoms in 4 were refined anisotropically, and refine-
ment of cluster 5 followed similar data reduction
procedures, with only the ruthenium atoms receiving
anisotropic treatment. All non-hydrogen atoms in 6 were
refined with anisotropically. Refinement on 2 converged
at R = 0.0458 and Rw = 0.0534 for 3680 unique reflections
with I > 3r(I), while for 4 refinement converged at
R = 0.0370 and Rw = 0.0403 for 2869 unique reflections
with I > 3r(I). The refinementfor 5 and 6 afforded conver-
gence values of R = 0.0423 and Rw = 0.0479 for 1377 un-
ique reflections with I > 3r(I) and R = 0.0249 and
Rw = 0.0285 for 2780 unique reflections with I > 3r(I),
respectively.
(l3-NPh)(bpcd)2 were carried out with the original pro-
gram developed by Hoffmann and Lipscomb [17], as
modified by Mealli and Proserpio [18], using the pro-
gram contained weighted Hijꢀs. The input Z-matrix for
the model cluster Ru3(CO)7(l3-CO)(l3-NHh)(H4-bpcd)
possessing a chelating diphosphine ligand was con-
structed from the X-ray fractional coordinates of Ru3
(CO)7(l3-CO)(l3-NPh)(bpcd). All phenyl groups were
replaced by a hydrogen, with the N–H and P–H bond
˚
distances assigned lengths of 1.01 and 1.41 A, respec-
tively [19]. The bridged isomer of Ru3(CO)7-
(l3-CO)(l3-NH)(H4-bpcd), which was confined to Cs
symmetry, and the bis-ligand substituted cluster Ru3
(CO)5(l3-CO)(l3-NH)(H4-bpcd)2 were both constructed
with bond distances and angles appropriate for this
genre of cluster.
3. Results and discussion
3.1. Synthesis of Ru3(CO)7(l3-CO)(l3-NPh)(bpcd)
and Ru3(CO)5(l3-CO)(l3-NPh)(bpcd)2 and X-ray dif-
fraction structure of Ru3(CO)7(l3-CO)(l3-NPh)(bpcd)
Treatment of an equimolar mixture of Ru3(CO)9(l3-
CO)(l3-NPh) (1) and bpcd in CH2Cl2 with two equiv.
of Me3NO at room temperature led to a rapid reaction
and the formation of two products, as assessed by TLC
analysis. Both of these products were subsequently iso-
lated by chromatography and characterized in solution
as Ru3(CO)7(l3-CO)(l3-NPh)(bpcd) (2, major) and
2.5. Extended Hu¨ckel MO calculations
The extended Huckel calculations on the Ru
¨
(CO)7(l3-CO)(l3-NPh)(bpcd) and Ru3(CO)5(l3-CO)
3

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S.G. Bott et al. / Journal of Organometallic Chemistry 689 (2004) 3426–3437
Ru3(CO)5(l3-CO)(l3-NPh)(bpcd)2 (3, minor). The room
temperature 31P NMR spectrum of 2 revealed a single,
broad resonance at d 50.00 indicative of a fluxional bpcd
ligand. As the coordination mode of the ancillary phos-
phine ligand in 2 could not be assigned with certainty
under these conditions, we examined the 31P NMR spec-
trum of 2 at 222 K. Dropping the temperature gave a
pair of equal intensity 31P resonances at d 44.92 and
57.84, which immediately rules out a bridging bpcd lig-
and and supports a chelating bpcd ligand that is bound
to a ruthenium center via an axial and equatorial site.
The fluxional behavior exhibited by the bpcd ligand pre-
sumably involves the rocking of the two 31P centers be-
tween the axial and equatorial positions as shown below
in Eq. (2) [20]. The chelation of the bpcd ligand and the
overall molecular structure of 2 was established by
X-ray crystallography. Fig. 1 shows the ORTEP dia-
gram of Ru3(CO)7(l3-CO)(l3-NPh)(bpcd), with selected
bond distances and angles reported in Table 2. The over-
all structure of 2 is unchanged form the parent cluster 1,
insomuch that it contains 48 valence electrons and a
nido-Ru3N core [21]. The coordination of the bpcd lig-
and to the axial and one of the two equatorial sites at
Ru(1) is in excellent agreement with the limiting 31P
NMR data for cluster 2 and stands in contrast to the
cluster Ru3(CO)7(l3-CO)(l3-NPh)(dppm) that contains
a bridging dppm ligand. To our knowledge, the latter
dppm-substituted cluster and 2 represent the only struc-
turally characterized Ru3(CO)7(l3-CO) (l3-NPh)(P–P)
clusters to date. The mean Ru–Ru and Ru–N bond dis-
Ru3(CO)7(l3-CO)(l3-NPh)P2 (where P2 = dppm, PPh3)
[8,9a,22], confirming the absence of any significant per-
turbation on the cluster core by the bpcd ligand.
Ph
N
Ph
N
Ph2
P
O
Ph2
P
O
Ru
Ru
P
P
O
Ph2
Ph2
C
O
C
O
O
cluster 2
ð2Þ
The minor product from the reaction was assigned to
that of the bis-phosphine cluster Ru3(CO)5(l3-CO)(l3-
NPh)(bpcd)2, on the basis of solution IR and NMR
data. Our attempts to grow single crystals of 3 suitable
for X-ray analysis were not successful. The l3-CO group
at 1639 cmꢀ1 in 3 has shifted 35 cmꢀ1 to lower energy
relative to 2 consistent with the introduction of a second
bpcd ligand, while the 1H NMR appearance of two
methylene groups as AB quartets at d 3.16 and 3.22
clearly support the presence of two inequivalent dione
moieties in 3. The room temperature 31P NMR spec-
trum of 3 revealed three broad resonances at d 50, 16,
and 0 in ca. a 2:1:1 integral ratio. When the same spec-
trum was recorded at 212 K four sharp resonances each
integrating for one phosphorus were observed at 50.49
(d), 49.18 (dd), 16.62 (d), and 0.89 (t). On the basis of
nuclear shielding arguments and the paradigm of cluster
2, the two downfield resonances may be confidently as-
signed to the chelating bpcd ligand, with the remaining
two higher field resonances belonging to the bridging
bpcd group [23]. The structure of Ru3(CO)5(l3-
CO)(l3-NPh)(bpcd)2 that is consistent with the 31P
assignments is depicted below.
˚
tances of 2.753 and 2.047 A, respectively, are unremark-
able in comparison to the parent cluster and
Ph
N
Ph2
P
Ph2P
O
Ru
O
Ph2P
P
Ph2
C
O
O
O
cluster 3
3.2. Thermolysis reactivity of Ru3(CO)7(l3-CO)(l3-
NPh)(bpcd) and X-ray diffraction structures of clusters
4–6
The thermolysis of Ru3(CO)9(l3-CO)(l3-NPh) with
bpcd in 1,2-dichloroethane at ca. 75 °C was also investi-
gated and found to furnish cluster 2 as the major prod-
uct, along with four additional products as judged by
TLC analysis, one of which corresponded to cluster 3.
Prolonged reaction times led to the gradual diminution
Fig. 1. ORTEP drawing of Ru3(CO)7(l3-CO)(l3-NPh)(bpcd) (2)
showing the thermal ellipsoids at the 50% probability level.

S.G. Bott et al. / Journal of Organometallic Chemistry 689 (2004) 3426–3437
3431
Table 2
Selected bond distances (A) and angles (deg) in the triruthenium compounds 2, and 4–6
a
˚
Ru3(CO)7(l3-CO)(l3-NPh)(bpcd) (2)
Bond distances
Ru(1)–Ru(2)
Ru(2)–Ru(3)
Ru(1)–P(2)
Ru(1)–C(2)
Ru(2)–C(2)
Ru(3)–C(2)
2.753(1)
2.726(1)
2.334(2)
2.06(1)
2.19(1)
2.24(1)
Ru(1)–Ru(3)
Ru(1)–P(1)
2.779(1)
2.333(3)
2.053(9)
2.040(7)
2.048(8)
1.34(2)
Ru(1)–N(16)
Ru(2)–N(16)
Ru(3)–N(16)
C(11)–C(15)
Bond angles
P(1)–Ru(1)–P(2)
P(1)–Ru(1)–C(1)
P(2)–Ru(1)–N(16)
N(16)–Ru(1)–C(2)
P(2)–Ru(1)–C(2)
Ru(1)–N(16)–Ru(3)
84.6(1)
83.5(4)
103.6(2)
84.0(4)
141.0(3)
85.3(3)
P(1)–Ru(1)–N(16)
P(1)–Ru(1)–C(2)
N(16)–Ru(1)–C(1)
P(2)–Ru(1)–C(1)
Ru(1)–N(16)–Ru(2)
Ru(2)–N(16)–Ru(3)
171.0(2)
87.2(4)
100.1(4)
90.2(3)
84.5(3)
83.7(3)
Ru3(CO)5(l2-CO)2(l3-NPh)(l2-PPh2)[l,g1,g1-C@C(PPh2)C(O)CH2C(O)] (4)
Bond distances
Ru(1)–Ru(2)
Ru(2)–Ru(3)
Ru(1)–P(2)
Ru(1)–N(16)
Ru(3)–N(16)
C(11)–C(15)
Ru(3)–C(2)
Ru(3)–C(4)
2.694(1)
2.848(1)
2.335(3)
2.109(8)
2.026(7)
1.35(1)
Ru(1)–Ru(3)
Ru(1)–P(1)
Ru(2)–P(2)
Ru(2)–N(16)
Ru(3)–C(15)
Ru(1)–C(2)
Ru(2)–C(4)
2.774(1)
2.358(3)
2.360(3)
2.108(7)
2.032(9)
1.90(1)
2.473(9)
2.458(9)
1.99(1)
Bond angles
P(1)–Ru(1)–P(2)
P(2)–Ru(1)–N(16)
Ru(3)–Ru(1)–P(1)
Ru(1)–P(2)–Ru(2)
Ru(2)–C(4)–O(4)
Ru(3)–C(4)–O(4)
135.1(1)
78.4(2)
P(1)–Ru(1)–N(16)
P(2)–Ru(2)–N(16)
Ru(2)–Ru(3)–C(15)
Ru(1)–C(2)–O(2)
Ru(3)–C(2)–O(2)
97.0(2)
77.8(2)
89.69(7)
70.03(7)
153.5(9)
127.4(9)
142.8(3)
158.0(9)
124.2(9)
Ru3(CO)5(l2-CO)2(l3-NPh)(l-PhCO)[l2,g2,g1-PPhC@C(PPh)2C(O)CH2C(O)] (5)
Bond distances
Ru(2)–Ru(3)
Ru(1)–P(2)
Ru(1)–O(23)
Ru(2)–P(2)
Ru(2)–C(6)
Ru(3)–N(16)
Ru(3)–C(11)
2.839(3)
2.355(6)
2.16(1)
2.377(6)
2.32(3)
2.16(2)
2.26(2)
Ru(1)–P(1)
2.301(6)
2.17(1)
2.97(1)
2.06(1)
1.98(2)
1.95(3)
2.21(2)
Ru(1)–N(16)
Ru(1)–C(24)
Ru(2)–N(16)
Ru(2)–C(24)
Ru(3)–C(6)
Ru(3)–C(15)
Bond angles
P(1)–Ru(1)–P(2)
P(2)–Ru(1)–N(16)
N(16)–Ru(1)–O(23)
P(2)–Ru(2)–C(24)
N(16)–Ru(3)–C(11)
C(11)–Ru(3)–C(15)
Ru(1)–N(16)–Ru(2)
Ru(2)–C(6)–Ru(3)
Ru(3)–C(6)–O(6)
87.4(2)
73.0(4)
84.1(5)
83.3(6)
90.0(6)
38.5(7)
101.1(6)
82.9(9)
150(2)
P(1)–Ru(1)–O(23)
P(2)–Ru(1)–O(23)
Ru(3)–Ru(2)–C(24)
N(16)–Ru(2)–C(24)
N(16)–Ru(3)–C(15)
Ru(1)–P(2)–Ru(2)
Ru(1)–N(16)–Ru(3)
Ru(2)–C(6)–O(6)
168.1(4)
82.4(4)
137.6(5)
91.9(7)
89.1(7)
87.4(2)
118.2(7)
126(2)
Ru3(CO)9(l3-NPh)(l3-PPh) (6)
Bond distances
Ru(1)–Ru(2)
2.7591(6)
2.293(2)
2.393(2)
2.302(1)
Ru(2)–Ru(3)
Ru(1)–N
Ru(2)–N
2.7687(6)
2.129(4)
2.125(4)
2.118(4)
Ru(1)–P
Ru(2)–P
Ru(3)–P
Ru(3)–N
(continued on next page)

3432
S.G. Bott et al. / Journal of Organometallic Chemistry 689 (2004) 3426–3437
Table 2 (continued)
Bond angles
P–Ru(1)–N
P–Ru(2)–N
Ru(1)–P–Ru(2)
Ru(2)–P–Ru(3)
Ru(1)–N–Ru(3)
a
71.4(1)
69.5(1)
Ru(1)–Ru(2)–Ru(3)
P–Ru(3)–N
79.51(2)
71.4(1)
72.11(5)
72.24(5)
112.7(2)
Ru(1)–P–Ru(3)
Ru(1)–N–Ru(2)
Ru(2)–N–Ru(3)
100.59(6)
80.9(1)
81.5(2)
Numbers in parentheses are estimated standard deviations in the least significant digits.
of 2 with the concomitant increase in the three new
clusters Ru3(CO)5(l2-CO)2(l3-NPh)(l2-PPh2)[l,g1,g1-
C@C(PPh2)C(O)CH2C(O)] (4), Ru3(CO)6(l2-CO)(l3-
NPh)(l-PhCO)[l2,g2,g1-PPhC@C(PPh2)C(O)CH2C(O)]
(5), and Ru3(CO)9(l3-NPh)(l3-PPh) (6), whose struc-
tures are depicted below. The source of these new
clusters 4–6 was presumed to be that of Ru3(CO)7(l3-
CO)(l3-NPh)(bpcd), and this fact was easily verified
by carrying out control experiments involving cluster
2. Heating pure samples of 2 at ca. 70 °C do indeed pro-
duce the clusters 4–6. The thermal chemistry of Ru3
(CO)5(l3-CO)(l3-NPh)(bpcd)2 was not investigated gi-
ven the low yields that accompanied the formation of
cluster 3. Compounds 4–6 were isolated by careful col-
umn chromatography over silica gel and were found to
be relatively stable provided that excessive exposure to
oxygen was avoided.
quences have precedence and have been demonstrated
by us in a variety of dinuclear and polynuclear systems
[10,11,24]. The 31P NMR spectrum of 4 confirmed the
latter bpcd ligand activation possibility since a bridging
phosphido moiety was found at d 165.92, whose down-
field location indicates that this phosphido ligand spans
a Ru–Ru bond [25]. The remaining phosphorus group
still attached to the dione ring appears at d 0.80. These
two resonances are coupled and appear as a pair of dou-
2
blets having a J value of 87 Hz. While the 31P NMR
data for 4 corroborate the cleavage of one of the two
distinctive P–C bonds inherent in the bpcd ligand [i.e.,
P–Ph vs. P–C(dione)], the unambiguous identity of 4
was ascertained by X-ray crystallography. The ORTEP
diagram of 4 is shown in Fig. 2, where the phosphido lig-
and that bridges the Ru(1)–Ru(2) vector proves
the course of bpcd activation as involving that of
Ph
Ph
N
O
P
PPh2
Ru
Ru
O
PPh2
Ph
O
PPh2
O
N
Ph
O
5
4
Ph
N
Ru
P
Ph
6
The IR spectrum for 4 in CH2Cl2 displayed three
prominent terminal m(CO) bands at 2063 (s), 2043 (s),
and 2005 (vs) cmꢀ1, in addition to two weak semibridg-
ing carbonyl stretching bands at 1939 and 1865 cmꢀ1
.
The two vibrationally coupled dione m(CO) bands were
observed at 1725 and 1694 cmꢀ1. This ca. 20 cmꢀ1 shift
to lower energy in the dione CO groups signals the acti-
vation of the bpcd ligand either through P–C bond scis-
sion or complexation of the alkene p bond of the dione
ring to one of the ruthenium centers. Both reaction se-
Fig. 2. ORTEP drawing of Ru3(CO)5(l2-CO)2(l3-NPh)(l2-
PPh2)[l,g1,g1-C@C(PPh2)C(O)CH2C(O)] (4) showing the thermal
ellipsoids at the 50% probability level.

S.G. Bott et al. / Journal of Organometallic Chemistry 689 (2004) 3426–3437
3433
P–C(dione) bond cleavage. Cluster 4 is electron precise
and contains 48 valence electrons, and the nido polyhe-
dral structure is unchanged from that of Ru3(CO)9(l3-
CO)(l3-NPh) and cluster 2. The Ru–Ru bond distances
range from 2.694(1) A [Ru(1)–Ru(2)] to 2.848(1) A
˚
[Ru(2)–Ru(3)] and display a mean distance of 2.772 A,
which agrees with their single-bond designation [26].
The three-electron donor ligand l2,g2,g1-C@C(PPh2)
C(O)CH2C(O) bridges the Ru(1)–Ru(3) bond via a
while the remaining resonance is ascribed to a phosph-
ido moiety. Besides the ambiguity associated with the
aforementioned P–C bond cleavage scenarios, the chem-
ical shift of the phosphido group in 5 presented an addi-
tional problem since it is found in a region where this
linkage may bridge a Ru–Ru bond as well as span two
non-bonded ruthenium centers. The generally recog-
nized trend in 31P chemical shifts is that phosphido
groups that bridge a metal–metal bond appear over
the range of d 50–300, while the same group, if it spans
two non-bonded metals, is found at higher field from d
ꢀ300 to 50 [21,28]. Accordingly, the composition and
ligand arrangement in 5 was resolved by X-ray analysis.
The ORTEP diagram of 5 is shown in Fig. 3, where it is
seen that the phosphido moiety derives via the scission
of one of the P–Ph groups of the bpcd ligand. The loss
of two ruthenium–ruthenium bonds in 5 relative to
either the parent cluster 1 or precursor cluster 2 follows
from its 52-valence electron count and is understood
within the tenets of polyhedral skeletal electron pair
(PSEP) theory. Here cluster 5 may by viewed as a
four-vertex hypho cluster that possesses 8 SEP and
whose polyhedral shape may be traced back to the par-
ent four-vertex nido cluster 1 before the formal associa-
tion of two additional SEP. The Ru(2)–Ru(3) bond
distance of 2.839(3) is similar to the Ru–Ru distances
found in clusters 2 and 4, and other polynuclear ruthe-
nium clusters. The Ru(1)ꢁ ꢁ ꢁRu(2) and Ru(1)ꢁ ꢁ ꢁRu(3)
˚
˚
˚
Ru(3)–C(15) r bond of 2.032(9) A and a Ru(1)–P(1) da-
˚
tive bond of 2.358(3) A. Of the seven CO groups in 4,
the Ru(1)–C(2)–O(2) and Ru(2)–C(4)–O(4) linkages
are clearly semibridging in nature based on the observed
angles of 158.0(9)° and 153.5(9)°, respectively [27]. The
presence of these semibridging CO groups in cluster 4
facilitates electron delocalization away from the elec-
tron-rich P-substituted ruthenium centers Ru(1) and
Ru(2) and towards the Ru(3) center. The carbocyclic
portion of the dione ring is nearly coplanar with the
three ruthenium atoms based on the ca. 16° dihedral an-
gle found for these groups of atoms.
The P–C bond cleavage that accompanies the forma-
tion of cluster 4 is similar to that exhibited by the
isolobal
tricobalt
cluster
PhCCo3(CO)7(bpcd)
[11a,11c], except that the putative r-bound intermediate
PhCCo3(CO)6[l-g1,r-C@C(PPh2)C(O)CH2C(O)](l2-
PPh2), which is the first product from P–C(dione) bond
scission, undergoes a fast reductive C–C bond coupling
of the Co–C(dione) moiety with one of the Co–C(car-
byne) bonds to produce Co3(CO)6[l2-g2,g1-C(Ph)C@
C(PPh2) C(O)CH2C(O)](l2-PPh2). Cluster 4 showed no
evidence for the analogous reductive coupling between
the Ru–C(dione) and the Ru–N groups, as illustrated
in Eq. (3). The negligible coupling reactivity of these lat-
ter two bonds in 4 in comparison to the related tricobalt
intermediate most likely derives from the greater kinetic
stability commonly found for second- and third-row
metals versus first-row derivatives.
˚
distances of 3.269(3) and 3.711(3) A clearly preclude
any bonding interactions between these metal centers.
The l2,g2,g1-PPhC@C(PPh2)C(O)CH2C(O) ligand
Ph
N
O
Ph
N
PPh2
Ru
O
Ru
Ru
PPh2
Ru
Ph2
P
P
O
Ph2
O
ð3Þ
The IR spectrum of 5 exhibited low-energy dione
m(CO) bands at 1715 and 1668 cmꢀ1 analogous to those
of cluster 4 and signaled the activation of the ancillary
bpcd ligand by the cluster. The 31P NMR spectrum of
5 consisted of two doublets at d 66.82 and ꢀ4.19 and
provides critical information as to the nature of the
two different phosphorus groups. The high-field reso-
nance is assigned to that of the PPh2(dione) ligand,
Fig.
3. ORTEP
drawing
of
Ru3(CO)6(l2-CO)(l3-NPh)(l-
PhCO)[l2,g2,g1-PPhC@C(PPh2)C(O)CH2C(O)] (5) showing the ther-
mal ellipsoids at the 50% probability level.

3434
S.G. Bott et al. / Journal of Organometallic Chemistry 689 (2004) 3426–3437
functions as a 7e donor ligand and is attached to the
three ruthenium atoms in a fashion analogous to that
found by us in the tricobalt cluster Co3(CO)7[l2,g2,g1-
PPhC@C(PPh2)C(O)OC(O)] [11a]. The transient Ru–
Ph bond that follows from the P–Ph bond cleavage
undergoes rapid carbonylation to furnish the observed
benzoyl moiety that tethers the non-bonded Ru(2) and
Ru(1) centers. The benzoyl unit is r-bound through
M3(CO)9(EPh)2 (where M = Fe, Ru, Os; E = N, P)
clusters, whose M3E2 polyhedra exhibit a nido frame-
work given their 50e count. While the mixed phosphin-
idine-imido cluster Fe3(CO)9(l3-NPh)(l3-PPh) has been
prepared and structurally characterized [31], the corre-
sponding mixed-capped Ru3 analogue has not been re-
ported to our knowledge. The three Ru–P and Ru–N
˚
bonds display a mean distance of 2.329 and 2.124 A,
˚
the carbonyl carbon atom C(24) to Ru(2) [1.98(2) A]
˚
and the oxygen atom O(23) to Ru(1) [2.16(1) A] in a
respectively, and are not significantly different from
the values reported for the homo-capped species Ru3-
(CO)9(NPh)2 [32] and related l3-PPh capped clusters
[33]. The remaining bond distances and angles are unex-
ceptional and require no comment.
fashion typified by other open triruthenium clusters con-
taining an acyl bridging ligand [29]. The semibridging
CO group that spans the Ru(2)–Ru(3) bond is confirmed
by the non-linear Ru(2)–C(6)–O(6) and Ru(3)–C(6)–
O(6) bond angles of 126(2)° and 150(2)°, respectively.
The mixed phosphinidine-imido capped cluster Ru3
(CO)9(l3-NPh)(l3-PPh) was also produced in minor
amounts from the thermolysis of 2. The IR spectrum
of 6 exhibited terminal carbonyl stretching bands and
no evidence for the presence of the bpcd ligand or a
dione-derived moiety. The 31P NMR spectrum of 6
exhibited a single resonance at d 269.66 that is suggestive
of a capping-phosphinidine group and agrees closely to
the value of d 239 that has been reported for the Ru3
(CO)9(PPh)2 [30]. The molecular structure of 6, which
is depicted in Fig. 4, consists of a bicapped-Ru3(CO)9
cluster that is structurally similar to the well-known
bis(imido)- and bis(phosphinidine)-capped family of
3.3. Cyclic voltammetry and MO data
Due to the ability of an intact bpcd ligand to function
as an electron reservoir, we have explored the redox
properties of clusters 2 and 3 by cyclic voltammetry at
a platinum electrode in CH2Cl2 containing 0.1 M tet-
ra-n-butylammonium perchlorate (TBAP) as the sup-
porting electrolyte. We have previously shown that the
parent cluster 1 undergoes an irreversible reduction at
Ecp ¼ ꢀ1:47 V through an ECE path where the rapid
loss of CO from the transient radical anion
[Ru3(CO)10(NPh)]ꢀꢀ is followed by a second electron
accession
to
furnish
the
reactive
dianion
[Ru3(CO)9(NPh)]2ꢀ [8]. The CV of 2 (not shown) over
the potential range of ꢀ1.4 to 1.0 V at a scan rate of
0.1 V/s revealed the expected bpcd-based reduction wave
at ꢀ0.88 V, along with an irreversible oxidation wave at
Eap ¼ 0:61 V. Although not examined in detail, the oxi-
dation remained irreversible up to a scan rate of 1.0 V/s.
The orbital composition of the 0/1ꢀ redox couple was
confirmed by carrying out extended Huckel MO calcula-
¨
tions on the compound Ru3(CO)7(l3-CO)(l3-NH)(H4-
bpcd [34].) The LUMO of the model cluster occurs at
10.43 eV and resides on the chelating H4-bpcd ligand
and is best viewed as a w4-type molecular orbital that
is confined to the p system of the cyclopenten-1,3-dione
moiety in total agreement with the MO data published
on mono- and polynuclear compounds containing either
a bpcd or bma ligand [16,24a,35].
The coordination two bpcd ligands to the triruthe-
nium frame of 3 presented us the opportunity to explore
the extent, if any, of the electron delocalization between
the two ligand reduction sites (chelate and bridge). If the
p* systems of these ancillary diphosphines were exten-
sively coupled, a mixed-valence compound of either
Class II or III might result [36]. The CV of 3 exhibits
two reversible one-electron reductions at E1/2 = ꢀ0.93
and ꢀ1.04 V, as depicted in Fig. 5. Scanning the same
sample from 0.0 V out to 1.0 V and back to the resting
potential of 0.0 V revealed the presence of an irreversible
oxidation wave at Eap ¼ 0:36 V. The oxidation wave in 3
Fig. 4. ORTEP drawing of Ru3(CO)9(l3-NPh)(l3-PPh) (6) showing
the thermal ellipsoids at the 50% probability level.

S.G. Bott et al. / Journal of Organometallic Chemistry 689 (2004) 3426–3437
3435
Proof that the first reduction is regioselective and
takes place at the bridging diphosphine as opposed to
the chelating diphosphine ligand derives from extended
4
2
Huckel MO calculations on the model cluster com-
¨
pound Ru3(CO)5(l3-CO)(l3-NH)(H4-bpcd)2 that con-
tains both a chelating and bridging H4-bpcd ligand.
Our MO calculations revealed that the LUMO, which
occurs at ꢀ10.47 eV, in Ru3(CO)5(l3-CO)(l3-NH)(H4-
bpcd)2 corresponded to the p* system associated with
the bridging H4-bpcd ligand, with the analogous lig-
and-based p* system of the chelating diphosphine
moiety being found only slightly higher in energy at
ꢀ10.34 eV. While the accuracy of these calculations
might lead one to question our conclusion concerning
the site of the first electron accession, we note that in
the case of the isomeric dicobalt compounds Co2(-
CO)4(l-PhCCPh) (bma), the bridged diphosphine was
found to undergo reduction at slightly more positive
potential than the chelated isomer [40]. Additional
examples of compounds containing two different bpcd
coordination modes will allow us to validate the gener-
ality of bridging versus chelating ligand reduction
trends. Since the MO data show no significant orbital
overlap between the p* systems of both ligands, the par-
ticipation of a mixed-valence intermediate upon the for-
mation of the first radical anion may be eliminated from
consideration. That this is correct is further corrobo-
rated by the calculated comproportionation constant
(Kc) of 72, which clearly places cluster 3 in the Robin–
Day scheme of a class I compound (Kc < 100). Here
the two individual and distinct bpcd reduction sites ex-
hibit minimal electronic communication.
0
-2
0.0
0.4
0.8
1.2
1.6
E(V)
Fig. 5. Cathodic scan cyclic voltammogram of Ru3(CO)5(l3-CO)(l3-
NPh)(bpcd)2 ca. 10ꢀ3 M in CH2Cl2 containing 0.1 M TBAP at 0.1 V/s
at room temperature.
remained irreversible up to a scan rate of 1.0 V/s and
was not examined further.
The observation of two reduction waves in 3 gives
rise to two likely scenarios, namely two individual
one-electron reductions at each bpcd ligand or the
sequential reduction of one bpcd ligand to the corre-
sponding dianion. The DE1/2 magnitude of 0.11 V for
the two reductions leads us to favor the former redox
scheme. Our contention is indirectly supported by the
CV behavior of free bpcd in CH2Cl2 containing 0.1 M
TBAP, where the 0/1ꢀ redox couple is observed at
ꢀ1.10 V when the sample is scanned from 0.0 V out to
ꢀ1.5 V [37,38]. Here the absence of an observable reduc-
tion of the bpcd radical anion to [bpcd]2ꢀ at a potential
close to the radical anion (<0.4 V) implies that the sec-
ond electron transfer to an already reduced bpcd ring
is not operative for 3ꢀꢀ. When the bpcd ligand does un-
dergo a net 2eꢀ reduction, as it does in the sulfido-
capped cluster SFeCo2(CO)7(bpcd), the 0/1ꢀ and 1ꢀ/2ꢀ
redox couples are separated by 0.65 V [39]. Accordingly,
we assign the two one-electron reduction waves in 3 to
the site-localized reduction of each bpcd ligand in 3, as
depicted below.
4. Conclusions
CO substitution in Ru3(CO)9(l3-CO)(l3-NPh) with
the diphosphine ligand bpcd has been studied and found
to give initially the mono- and bis-substituted clusters
Ru3(CO)9ꢀx(l3-CO)(l3-NPh)(bpcd)n (x = 2, n = 1; x = 4,
n = 2). The thermal degradation of Ru3(CO)7(l3-CO)-
(l3-NPh)(bpcd) has been explored and found to proceed
via both P–Ph and P–C(dione) bond activation routes.
The resulting thermolysis products were isolated and
fully characterized in solution and by X-ray crystallog-
raphy. No evidence for the reductive coupling of the
transient Ru–Ph or Ru–C(dione) moieties with the cap-
ping imido ligand was observed. The redox properties of
Ru3(CO)7(l3-CO)(l3-NPh)(bpcd) and Ru3(CO)5(l3-CO)-
(l3-NPh)(bpcd)2 were examined by cyclic voltammetry
and MO calculations, which confirm the electron reduc-
tion sites being fully localized on the ancillary bpcd
ligand(s). In the case of the latter cluster, the addition
of the first electron during the reduction is shown to oc-
cur exclusively at the bridging bpcd ligand and not the
chelating ligand. The calculated comproportionation
Ph
N
Ph2
P
-
+e
Ph2P
O
Ru
3
O
Ph2P
P
Ph2
C
O
O
O
ð4Þ
Ph
N
Ph2
P
-
+e
Ph2P
O
Ru
O
Ph2P
P
Ph2
C
O
O
O

3436
S.G. Bott et al. / Journal of Organometallic Chemistry 689 (2004) 3426–3437
[8] H. Shen, R.A. Senter, S.G. Bott, M.G. Richmond, Inorg. Chim.
Acta 247 (1996) 161.
constant reveals the both bpcd moieties function as
independent and distinct electron sites.
[9] (a) M. Pizzotti, F. Porta, S. Cenini, F. Demartin, J. Organomet.
Chem. 356 (1988) 105;
(b) M. Pizzotti, S. Cenini, C. Crotti, F. Demartin, J. Organomet.
Chem. 375 (1989) 123.
5. Supporting information
[10] (a) S.G. Bott, H. Shen, M.G. Richmond, Struct. Chem. 12 (2001)
225;
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic
Data Center, CCDC No. 23990 for 2; 239901 for 4;
239902 for 5; and 239720 for 6. Copies of this informa-
tion may be obtained free of charge from the Director,
CCDC, 12 Union Road, Cambridge, CB2 1EZ UK
[fax: +44(1223)336-033; e-mail: deposit@ccdc.ac.uk or
http://www:ccdc.cam.ac.uk].
(b) S.G. Bott, K. Yang, J.C. Wang, M.G. Richmond, Inorg.
Chem. 39 (2000) 6051.
[11] (a) For related bma-substituted compounds and ligand-cluster
reactivity, see: C.-G. Xia, K. Yang, S.G. Bott, M.G. Richmond,
Organometallics 15 (1996) 4480;
(b) S.G. Bott, K. Yang, K.A. Talafuse, M.G. Richmond,
Organometallics 22 (2003) 1383;
(c) K. Yang, J.M. Smith, S.G. Bott, M.G. Richmond, Organo-
metallics 12 (1993) 4779.
[12] (a) D. Fenske, H. Becher, Chem. Ber. 107 (1974) 117;
(b) D. Fenske, Chem. Ber. 112 (1979) 363.
[13] J.A. Smieja, W.L. Gladfelter, Inorg. Chem. 25 (1986) 2667.
[14] M.I. Bruce, C.M. Jensen, N.L. Jones, Inorg. Synth. 26 (1989) 259.
[15] D.F. Shriver, The Manipulation of Air-Sensitive Compounds,
McGraw-Hill, New York, 1969.
Acknowledgement
Financial support from the Robert A. Welch Foun-
dation (B-1093-MGR) is greatly appreciated.
[16] K. Yang, S.G. Bott, M.G. Richmond, Organometallics 14 (1995)
2387.
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