Ligand chelation, P-C bond cleavage, and phenyl-group transfer in the reaction between RCCo3(CO)9 and 1,8-bis(diphenylphosphino)naphthalene (dppn): Syntheses and X-ray diffraction structures of PhCCo3(CO)4(μ-CO)3(dppn) and PhCCo3(CO)8[η1-PPh(OH)C10H6P(O)Ph2]

Article abstract of DOI:10.1016/j.jorganchem.2006.10.052

The tricobalt cluster PhCCo₃(CO)₉ (1) undergoes facile ligand substitution with 1,8-bis(diphenylphosphino)naphthalene (dppn) under thermal and Me₃NO activation to afford the cluster compounds PhCCo₃(CO)₈[PPh₂(1-C₁₀H₇)] (2) and PhCCo₃(CO)₄(μ-CO)₃(dppn) (3). Whereas thermolysis of dppn with the methylidyne-capped cluster HCCo₃(CO)₉ (4) yields only HCCo₃(CO)₈[PPh₂(1-C₁₀H₇)] (5) and HCCo₃(CO)₄(μ-CO)₃(dppn) (6) as isolable products, the reaction between 4 and dppn in the presence of Me₃NO furnishes the latter two clusters in addition to the phenyl-capped cluster PhCCo₃(CO)₈[η¹-PPh(OH)C₁₀H₆P(O)Ph₂] (7). The clusters 2 and 5 represent simple substitution products based on the ligand diphenyl(1-naphthyl)phosphine, while clusters 3 and 6 each possess a chelating dppn ligand and three bridging CO groups in the solid state. Oxidation of the two phosphine moieties by Me₃NO and transfer of one of the phenyl groups from the dppn ligand to the methylidyne carbon moiety in cluster 4 produces the thermally unstable cluster 7. These clusters have been characterized in solution by IR and ³¹P NMR spectroscopies, and the solid-state structures of 3 and 7 established by X-ray crystallography.

Full text of DOI:10.1016/j.jorganchem.2006.10.052

Journal of Organometallic Chemistry 692 (2007) 968–975
www.elsevier.com/locate/jorganchem
Ligand chelation, P–C bond cleavage, and phenyl-group transfer
in the reaction between RCCo3(CO)9 and
1,8-bis(diphenylphosphino)naphthalene (dppn): Syntheses and
X-ray diffraction structures of PhCCo3(CO)4(l-CO)3(dppn) and
PhCCo3(CO)8[g1-PPh(OH)C10H6P(O)Ph2]
a,
b
b,
*
William H. Watson *, Srikanth Kandala , Michael G. Richmond
a
Department of Chemistry, Texas Christian University, Fort Worth, TX 76129, United States
b
Department of Chemistry, University of North Texas, Denton, TX 76203, United States
Received 30 September 2006; received in revised form 23 October 2006; accepted 23 October 2006
Available online 3 November 2006
Abstract
The tricobalt cluster PhCCo3(CO)9 (1) undergoes facile ligand substitution with 1,8-bis(diphenylphosphino)naphthalene (dppn) under
thermal and Me3NO activation to afford the cluster compounds PhCCo3(CO)8[PPh2(1-C10H7)] (2) and PhCCo3(CO)4(l-CO)3(dppn) (3).
Whereas thermolysis of dppn with the methylidyne-capped cluster HCCo3(CO)9 (4) yields only HCCo3(CO)8[PPh2(1-C10H7)] (5) and
HCCo3(CO)4(l-CO)3(dppn) (6) as isolable products, the reaction between 4 and dppn in the presence of Me3NO furnishes the latter
two clusters in addition to the phenyl-capped cluster PhCCo3(CO)8[g1-PPh(OH)C10H6P(O)Ph2] (7). The clusters 2 and 5 represent simple
substitution products based on the ligand diphenyl(1-naphthyl)phosphine, while clusters 3 and 6 each possess a chelating dppn ligand
and three bridging CO groups in the solid state. Oxidation of the two phosphine moieties by Me3NO and transfer of one of the phenyl
groups from the dppn ligand to the methylidyne carbon moiety in cluster 4 produces the thermally unstable cluster 7. These clusters have
been characterized in solution by IR and 31P NMR spectroscopies, and the solid-state structures of 3 and 7 established by X-ray
crystallography.
Ó 2006 Elsevier B.V. All rights reserved.
Keywords: Tricobalt clusters; Ligand substitution; Diphosphine ligand; P–C bond cleavage; Phenyl-group transfer
1. Introduction
has received relatively little attention. Early expectations
for dppn as a ligand were high due to the transannular
properties extant from the peri-disposed phosphorus atoms
associated with the naphthalene platform and new com-
pounds exhibiting novel physical properties were antici-
pated. While the reported mononuclear complexes
possessing a dppn ligand have not provided unusual prop-
The synthesis of the diphosphine ligand 1,8-bis(diph-
enylphosphino)naphthalene (dppn) was first reported in
1993 [1], but unlike the well-known and thoroughly studied
diphosphine ligands 1,1-bis(diphenylphosphino)methane
(dppm) and 1,2-bis(diphenylphosphino)ethane (dppe), the
coordination chemistry associated with the dppn ligand
´
erties vis-a-vis related dppe-substituted complexes [2–5],
coordination of dppn to the metal cluster compounds
Ru3(CO)12 and Os3(CO)12 is accompanied by facile degra-
dation of the diphosphine ligand via C–H and P–C bond
cleavages [6,7]. The only known cluster structure contain-
ing an intact dppn ligand is Ru3(CO)8(l-dppm)(dppn),
*
Corresponding authors. Tel.: +1 817 257 7195; fax: +1 940 565 4318
(W.H. Watson); Tel.: +1 940 565 3548 (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.2006.10.052

W.H. Watson et al. / Journal of Organometallic Chemistry 692 (2007) 968–975
969
which has been isolated in low yield from the thermolysis
2. Experimental
reaction involving Ru3(CO)10(l-dppm) and dppn [6].
Our groups have had a long-term interest in the study of
the rigid, unsaturated diphosphine ligands (Z)-Ph2PCH
@CHPPh2, 2,3-bis(diphenylphosphino)maleic anhydride
(bma) and 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-
dione (bpcd) with numerous metal cluster compounds [8].
Reaction of these ligands with the tricobalt clusters
RCCo3(CO)9 gives the corresponding products RCCo3-
(CO)7(P–P) (where P–P = diphosphine ligand). In the case
2.1. General methods
The starting clusters PhCCCo3(CO)9 and HCCo3(CO)9
were prepared from Co2(CO)8 [9], while the ligand dppn
was synthesized by employing either 1,8-dibromonaphtha-
lene or 1-bromonaphthalene as starting materials accord-
ing to the published procedures [1,10,11]. The
1-naphthyldiphenylphosphine ligand used in the indepen-
dent preparation of clusters 2 and 5 was synthesized from
1-bromonaphthalene and chlorodiphenylphosphine [12].
With the exception of Co2(CO)8, which was purchased
from Strem Chemicals, the other chemicals used in these
studies 1,8-diaminonaphthalene, 1-bromonaphthalene,
chlo rodiphenylphosphine, bromoform, and Me3NO Æ
2H2O were all obtained from Aldrich Chemical Co. The
latter reagent was dried by azeotropic distillation from ben-
zene, after which it was stored under argon. All reaction
and NMR solvents were distilled under argon from a suit-
able drying agent and stored in Schlenk storage vessels [13].
All preparative chromatographic separations were done by
column chromatography under atmospheric conditions
without any special precautions. The combustion analyses
were performed by Atlantic Microlab, Norcross, GA.
The reported ESI-APCI (positive ionization mode) and
FAB mass spectral data of cluster 7 were recorded at the
UC San Diego Mass Spectrometry Center, with 3-nitrob-
enzyl alcohol employed as the sample matrix in the acqui-
sition of the FAB mass spectrum.
of
the
cluster
compound
PhCCo3(CO)7[(Z)-
Ph2PCH@CHPPh2], the diphosphine ligand functions as a
bridging ligand that stabilizes the cluster against fragmenta-
tion relative to the bma- and bpcd-substituted derivatives.
Moreover, the cluster compounds PhCCo3(CO)7(bma) and
PhCCo3(CO)7(bpcd) display reversible chelate-to-bridge
fluxionality of the diphosphine ligand at ambient tempera-
ture, in addition to exhibiting facile cluster/ligand activation
that involves the cleavage of a Ph2P–C(ring) bond, followed
by the reductive coupling of the transient Co–C(ring) moiety
and the benzylidyne capping ligand. Scheme 1 summarizes
this chemistry for PhCCo3(CO)7(bpcd).
Wishing to extend our substitution studies in the tetra-
hedrane clusters RCCo3(CO)9 with different diphosphine
ligands, we have examined the reactivity of dppn with the
clusters PhCCo3(CO)9 (1) and HCCo3(CO)9 (4). Herein we
present our results on the thermolysis and Me3NO-activated
reactions of clusters 1 and 4 in the presence of dppn to afford
the dppn-chelated clusters 3 and 6 as the major products.
The minor products isolated from these reactions include
PhCCo3(CO)8[PPh2(1-C10H7)] (2), HCCo3(CO)8[PPh2(1-
C10H7)] (5), and PhCCo3(CO)8[g1-PPh(OH)C10H6P(O)Ph2]
(7), all of which provide evidence for the fragmentation of
the dppn during the course of the reaction.
All reported infrared data were recorded on a Nicolet 20
SXB FT-IR spectrometer in 0.1 mm amalgamated NaCl
cells, using PC control and OMNIC software, while the
31P NMR spectra were recorded on a Varian 300-VXR
O
Ph
R
C
C
O
Ph2
P
Co
Co
PPh2
Co
O
Co
R
PPh2
Co
P
Co
R = Ph
C
Ph2
O
Co
heat
bpcd/heat
Co
Co
(R = H, Ph)
O
Ph
P
R = H
R
C
Ph2
P
O
O
Co
Co
Co
P
Co
Ph2
Co
PPh2
O
Co
Scheme 1.

970
W.H. Watson et al. / Journal of Organometallic Chemistry 692 (2007) 968–975
spectrometer at 121 MHz. The 31P NMR data were
acquired in the proton-decoupled mode and are reported
relative to external H3PO4, taken to have d = 0.
C48H31Co3O7P2 Æ CH2Cl2 Æ 1/2C6H6: C, 54.84 (54.95); H,
3.40 (3.94).
2.5. Me3NO activation of HCCo3(CO)9 (4) in the presence
of dppn
2.2. Thermolysis of PhCCo3(CO)9 (1) with dppn
50 mg (0.096 mmol) of PhCCo3(CO)9 and 52 mg
(0.10 mmol) of dppn were charged to a small Schlenk tube,
followed by 20 mL of 1,2-dichloroethane (DCE) via syr-
inge. The vessel was sealed and the reaction solution heated
overnight at 50 °C. TLC examination of the cooled reac-
tion solution using a 1:4 mixture of CH2Cl2/hexane
revealed the presence of two new spots belonging to clus-
ters 2 (Rf = 0.70) and 3 (Rf = 0.55), along with some unre-
acted cluster 1. The solvent was removed under vacuum
and the residue subsequently purified by column chroma-
tography over silica gel using the aforementioned solvent
system. Both product clusters were recrystallized from
CH2Cl2 and hexane. Cluster 2: 7.5 mg (10% yield). IR
To a Schlenk tube was added 0.10 g (0.22 mmol) of clus-
ter 4, 0.12 g (0.24 mmol) of dppn, and 36 mg (0.47 mmol)
of Me3NO, after which 20 mL of CH2Cl2 was syringed into
the flask. The reaction was stirred for 1 h at room temper-
ature and then examined by TLC using CH2Cl2/hexane
(1:3), which revealed the presence of two spots correspond-
ing to clusters 5 and 6 along with a slower moving spot
(Rf = 0.30) attributed to cluster 7. These products were
subsequently isolated by careful chromatography. Yield
of 5: 10% (17 mg). Yield of 6: 35% (70 mg). Yield of 7:
10% (21 mg). IR (CH2Cl2): m(CO) 2075 (s), 2032 (vs),
2018 (vs), 2010 (sh) cmꢀ1 31P NMR (CDCl3): d 130.49
.
(s), 39.62 (s). FAB-MS (m/z): 743 [7]+. ESI-APCI MS
(m/z): 958.95 [7+H2O+H]+ and 974.96 [7+MeOH+H]+.
(CH2Cl2): m(CO) 2078 (s), 2042 (vs), 2021 (vs) cmꢀ1 31P
.
NMR (CDCl3): d 31.80. Cluster 3: 32 mg (35% yield). IR
(CH2Cl2): m(CO) 2052 (s), 2017 (vs), 1988 (vs), 1862 (m),
2.6. X-ray crystallographic data
1827 (m) cmꢀ1 31P NMR (CDCl3): d 40.18 (s), 35.12 (s),
.
30.54 (s). Anal. Calc. (found) for C48H31Co3O7P2 Æ CH2Cl2:
C, 56.40 (56.28); H, 3.19 (3.46).
Crystals of clusters 3 and 7 suitable for X-ray diffraction
analysis were grown from a CH2Cl2 solution containing
each cluster that had been layered with hexane. Tables 1
and 2 provide the X-ray data and processing parameters
and selected bond distances and angles, respectively, for
compounds 3 and 7. The reported X-ray data were col-
2.3. Me3NO activation of PhCCo3(CO)9 (1) in the presence
of dppn
To a 250-mL Schlenk flask under argon flush was added
0.10 g (0.19 mmol) of PhCCo3(CO)9, 0.11 g (0.21 mmol) of
dppn, and 20 mL of CH2Cl2. Stirring was initiated and
31 mg (0.41 mmol) of Me3NO was next added in one por-
tion to the reaction and stirring continued for 1 h, after
which the progress of the reaction was checked by TLC
analysis. The presence of clusters 2 and 3 were confirmed
and then isolated as described above. Yield of cluster 2:
23 mg (15%). Yield of cluster 3: 74 mg (40%).
Table 1
X-ray crystallographic data and processing parameters for the clusters 3
and 7
Compound
3
7
CCDC entry no.
Crystal system
Space group
619643
Monoclinic
P21/n
11.296(1)
19.146(3)
19.345(3)
102.384(2)
4086.5(9)
619644
Monoclinic
P21/c
8.990(1)
35.591(5)
12.928(2)
103.182(3)
4028(1)
˚
a (A)
˚
b (A)
˚
c (A)
2.4. Thermolysis of HCCo3(CO)9 (4) with dppn
b (°)
3
˚
V (A )
The thermolysis reaction was carried similarly as that
described for cluster 1. Here 50 mg (0.11 mmol) of
HCCo3(CO)9, 61 mg (0.12 mmol) of dppn, and 20 mL of
CH2Cl2 were employed. The reaction was heated at 45 °C
overnight, allowed to cool to room temperature, and then
examined by TLC analysis using CH2Cl2/hexane (1:3).
The presence of the monophosphine-substituted cluster 5
(Rf = 0.75) and the dppn-chelated cluster 6 (Rf = 0.55)
were the sole observed products. These clusters were iso-
lated by column chromatography over silica gel and recrys-
tallized from CH2Cl2 and benzene. Yield of 5: 10%
(8.5 mg). IR (CH2Cl2): m(CO) 2081 (s), 2038 (vs), 2022
Molecular formula
Formula weight
Formula units per cell (Z)
Dcalc (Mg/m3)
C
958.46
4
1.558
0.71073
1.336
48H31Co3O7P2
C43H27Co3O10P2
942.38
4
1.554
0.71073
1.359
˚
k (Mo Ka) (A)
Absorption coefficient (mmꢀ1
Maximum/minimum
transmission
)
0.5150/0.4161
0.8462/0.7258
Total reflections
Independent reflections
Data/restraint/parameters
R
34270
9507
9507/0/541
0.0475
0.0870
0.870
[0.04F2 + (rF)2]ꢀ1 [0.04F2 + (rF)2]ꢀ1
Empirical Empirical
0.561 and ꢀ0.349 0.419 and ꢀ0.335
24042
5767
5767/0/528
0.0406
0.0749
0.889
Rw
GOF on F2
Weights
(vs) cmꢀ1
yield (31 mg). IR (CH2Cl2): m(CO) 2055 (s), 2021 (vs),
1993 (vs), 1858 (m), 1824 (m) cmꢀ1 31P NMR (CDCl3):
d 44.80 (s), 35.00 (s), 30.05 (s). Anal. Calc. (found) for
.
31P NMR (CDCl3): d 44.50. Yield of 6: 30%
Absorption correction
Largest difference in peak and
.
3
˚
hole (e/A )

W.H. Watson et al. / Journal of Organometallic Chemistry 692 (2007) 968–975
971
Table 2
cluster products, as confirmed by TLC analysis of the reac-
tion solution. The same product distribution was also
observed when cluster 1 and dppn were allowed to react
in the presence of the oxidative-decarbonylation reagent
Me3NO. Both methods of cluster activation afforded a
black solid that remained at the origin of the TLC plate
and whose identity is attributed to some type of cluster-
related decomposition product(s). The characterization of
this origin material was not pursued since it remained irre-
versibly bound to the chromatographic support under all
conditions. Both 2 and 3 were subsequently isolated by col-
umn chromatography and characterized in solution by IR
and 31P NMR spectroscopies, and the solid-state structure
of the latter product determined by X-ray diffraction anal-
ysis. Both products appear to be stable in the solid state for
a period of months, with solutions of both clusters that
have been exposed to the atmosphere exhibiting noticeable
decomposition after several hours. Eq. (1) depicts the two
products isolated from the reaction between cluster 1 and
dppn
˚
Selected bond distances (A) and angles (°) for clusters 3 and 7
Cluster 3
Bond distances
Co(1)–Co(2)
Co(2)–Co(3)
Co(1)–P(2)
Co(1)–C(41)
Co(3)–C(41)
Co(1)–C(43)
Co(2)–C(46)
Co(3)–C(46)
2.5308(6)
2.3989(6)
2.1998(9)
1.960(3)
1.950(3)
1.912(3)
2.022(3)
1.901(3)
Co(1)–Co(3)
P(1)ꢁ ꢁ ꢁP(2)
Co(1)–P(1)
Co(2)–C(41)
Co(1)–C(42)
Co(2)–C(43)
Co(3)–C(42)
2.5202(6)
3.112(1)
2.2544(9)
1.915(3)
1.826(3)
2.029(3)
2.197(3)
Bond angles
P(2)–Co(1)–P(1)
P(1)–Co(1)–C(41)
P(1)–Co(1)–Co(3)
P(1)–Co(1)–Co(2)
O(1)–C(42)–Co(3)
O(2)–C(43)–Co(1)
Co(1)–C(43)–Co(2)
O(5)–C(46)–Co(2)
88.62(3)
169.82(9)
120.43(3)
126.31(3)
126.0(2)
149.2(3)
79.9(2)
P(2)–Co(1)–C(41)
P(2)–Co(1)–Co(3)
P(2)–Co(1)–Co(2)
O(1)–C(42)–Co(1)
Co(1)–C(42)–Co(3)
O(2)–C(43)–Co(2)
O(5)–C(46)–Co(3)
Co(2)–C(46)–Co(3)
101.47(9)
144.63(3)
123.80(3)
156.7(3)
77.0(1)
130.9(2)
145.6(3)
75.3(1)
139.0(3)
Cluster 7
Bond distances
Co(1)–Co(2)
Co(2)–Co(3)
P(1)ꢁ ꢁ ꢁP(2)
Co(1)–C(29)
Co(3)–C(29)
P(1)–C(1)
P(2)–O(2)
P(2)–C(11)
O(1)–H(1)
2.474(1)
2.478(1)
3.771(3)
1.917(5)
1.936(5)
1.849(5)
1.499(4)
1.802(6)
1.10(7)
Co(1)–Co(3)
Co(1)–P(1)
O(1)ꢁ ꢁ ꢁO(2)
Co(2)–C(29)
P(1)–O(1)
P(1)–C(23)
P(2)–C(9)
P(2)–C(17)
H(1)ꢁ ꢁ ꢁO(2)
2.473(1)
2.221(2)
2.481(5)
1.901(5)
1.592(4)
1.816(5)
1.836(6)
1.818(6)
1.39(7)
Ph
C
Co
dppn
Co
Co
cluster 1
Ph
C
Ph
C
Bond angles
Ph2P
Co
P(1)–Co(1)–Co(3)
O(1)–P(1)–Co(1)
C(1)–P(1)–Co(1)
O(2)–P(2)–C(17)
O(1)–H(1)ꢁ ꢁ ꢁO(2)
158.30(6)
109.4(2)
118.3(2)
107.2(3)
175(7)
P(1)–Co(1)–Co(3)
C(23)–P(1)–Co(1)
O(2)–P(2)–C(11)
O(2)–P(2)–C(9)
98.23(5)
108.2(2)
113.4(2)
116.3(2)
Ph2
P
Co
P
Co
Co
Ph2
Co
Co
cluster 3
cluster 2
lected on a Bruker SMARTä 1000 CCD-based diffractom-
eter at 213 K. The frames were integrated with the avail-
ð1Þ
able SAINT software package using
a
narrow-frame
The IR spectrum of 2 in CH2Cl2 displays the signature
pattern of a monosubstituted RCCo3(CO)8P cluster (where
P = phosphine ligand) based on terminal m(CO) bands 2078
(s), 2042 (vs), and 2021 (vs) cmꢀ1 [17], while the broad sin-
glet observed at d 31.80 in the 31P NMR spectrum of 2
agrees nicely with the 31P chemical data reported for other
RCCo3(CO)8P clusters [17c]. Given the facile fragmentation
and activation of the dppn ligand reported during the ther-
molysis with the cluster compounds M3(CO)12 (where
M = Ru, Os) by Bruce and co-workers [6,7], two logical
possibilities existed for cluster 2. Here the dppn ligand could
undergo a formal transformation to the monodentate phos-
phine ligands PPh3 or PPh2(1-naphthyl) [18]. Control exper-
iments between the parent cluster 1 and the ligands PPh3
and PPh2(1-naphthyl) were carried out and the correspond-
ing PhCCo3(CO)8P clusters isolated and characterized by
IR and 31P spectroscopies and TLC analyses. The IR data
for 2 in hexane best matched that of independently prepared
PhCCo3(CO)8[PPh2(1-naphthyl)], also recorded in hexane.
The small but observable frequency differences in the
algorithm [14], and the structures were solved and refined
using the SHELXTL program package [15]. The molecular
structures for both cluster compounds were checked using
PLATON [16], and solved by direct methods with all nonhy-
drogen atoms refined anisotropically. All carbon-bound
hydrogen atoms were assigned calculated positions and
allowed to ride on the attached heavy atom, unless other-
wise noted. The hydrogen atom H(1) in 7 was located in
a difference map, and it was allowed to refine isotropically.
3. Results and discussion
3.1. Reaction of PhCCo3(CO)9 with dppn and molecular
structure of 3
The benzylidyne-capped cluster PhCCo3(CO)9 (1) reacts
with the diphosphine ligand dppn readily at 50 °C in 1,2-
dichloroethane to afford PhCCo3(CO)8[PPh2(1-C10H7)]
(2) and PhCCo3(CO)4(l-CO)3(dppn) (3) as the principal

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W.H. Watson et al. / Journal of Organometallic Chemistry 692 (2007) 968–975
high-energy m(CO) band in these clusters serve as a very sen-
sitive indicator as to the amount and nature of the ancillary
phosphine ligand associated with the cluster [19]. Moreover,
TLC analysis (eluent: CH2Cl2/hexane 1:4) revealed that of
the two independently prepared clusters PhCCo3-
(CO)8(PPh3) and PhCCo3(CO)8[PPh2(1-naphthyl)], the
former cluster exhibited a slightly larger Rf value (0.72) in
comparison to PhCCo3(CO)8[PPh2(1-naphthyl)], whose Rf
value (0.70) exactly matched that of cluster 2 isolated from
the reaction. That the ancillary phosphine ligand in 2
derives from diphenyl(1-naphthyl)phosphine and not PPh3
is in good agreement with those data reported by Bruce
and co-workers for the formation of Os3(CO)11[PPh2(1-
naphthyl)] from dppn and Os3(CO)12 [7].
The IR spectrum for 3 exhibited prominent terminal car-
bonyl stretching bands at 2052 (s), 2017 (vs), and 1988 (vs)
cmꢀ1, along with bridging m(CO) bands at 1862 (m) and
1827 (m) cmꢀ1. The room temperature 31P NMR spectrum
displayed three singlets at d 40.18, 35.12, and 30.54 that
may be ascribed to the two dppn chelating isomers shown
to the right. Here the latter two high-field singlets are
assigned to the inequivalent phosphine groups in the triply
bridged l2-CO isomer on the left-hand side of the equilib-
rium. The more intense 31P resonance at d 40.18 is consis-
tent with the all terminal carbonyl isomer of
PhCCo(CO)7(dppn) that contains an equatorially disposed
dppn ligand. Integration of these resonances yields a Keq
value of ca. 1.5 in favor of the all-terminal carbonyl isomer
[20,21]. Another possibility for the all-terminal carbonyl
isomer of PhCCo(CO)7(dppn) involves a dppn ligand that
is chelated to a single cobalt atom at the axial and one of
the two equatorial sites (not shown). In this particular iso-
mer one expects two different 31P resonances in the absence
of a rapid rocking motion that would equilibrate the two
phosphine moieties, giving rise to a weighted-average 31P
resonance. Examples of homo- and heterometallic tetra-
hedrane clusters exhibiting such diphosphine-ligand fluxio-
nality have been published by our groups [22].
Ph
C
Ph
C
Ph2P
Co
Ph2P
Co
Keq = 1.5
P
P
Co
Co
Ph2
Ph2
Co
Co
The thermal ellipsoid plot shown in the left-hand side
of Fig. 1 confirms the chelation of the dppn ligand to the
cluster polyhedron in 3, along with the presence of three
l2-CO groups. Cluster 3 contains 48-valence electrons
and may be considered electron precise [23]. The triangu-
lar array of cobalt atoms is best described by an isosceles
triangle, where the two longer, pairwise equivalent
Co(1)–Co(3) and Co(1)–Co(2) bonds display a mean
˚
length of 2.526(5) A, with the Co(2)–Co(3) vector of
˚
˚
2.3989(6) A shorter by ca. 0.13 A. The observed Co–Co
bond-length trends in cluster 3 are in keeping with a
dppn-induced perturbation that manifests itself in the
elongation of the metal–metal bonds associated with
the cobalt atom tethered to the chelating dppn ligand.
These Co–Co bond distances are well within the range
of those distances reported for the parent cluster 1 and
related RCCo3(CO)9ꢀnPn clusters [24]. The Co(1)–P(1)
˚
˚
[2.2544(9) A] and Co(1)–P(2) [2.1998(9) A] distances and
88.62(3)° bite angle exhibited by the P(1)–Co(1)–P(2)
atoms are in excellent agreement with those values
reported in Ru3(CO)8(l-dppm)(dppn), which represents
the only other structurally characterized cluster contain-
ing an intact chelating dppn ligand.6 The three bridging
CO groups exhibit highly asymmetric Co–C bond dis-
˚
tances, ranging from 1.826(3) A [Co(1)–C(42)] to
2.029(3) A [Co(2)–C(43)] but well within the boundaries
found for those distances in other carbonyl-bridged
derivatives [17a,19,25]. The remaining distances and
angles are unremarkable and require no comment.
˚
Fig. 1. Thermal ellipsoid plots of the tricobalt clusters 3 (left) and 7 (right) showing the thermal ellipsoids at the 50% probability level.

W.H. Watson et al. / Journal of Organometallic Chemistry 692 (2007) 968–975
973
3.2. Thermolysis of HCCo3(CO)9 with dppn and formation
of clusters 5 and 6
structural highlights associated with 7 include (1) the
replacement of the carbyne hydrogen atom in 4 by a phenyl
group from the dppn ligand and (2) oxidation of the phos-
phine groups of the dppn ligand to hydroxyl phosphine
and phosphine oxide moieties, as shown in the below pic-
ture of cluster 7 [26,27].
Thermolysis of HCCo3(CO)9 (4) with a slight excess of
dppn at 45 °C leads to CO displacement and formation
the clusters HCCo3(CO)8[PPh2(1-C10H7)] (5) and HCCo3-
(CO)4(l-CO)3(dppn) (6) in yields comparable to those
found in the reactions between cluster 1 and dppn. Both
new products were isolated and spectroscopically charac-
terized in solution and by comparison to an independently
prepared sample in the case of cluster 5 (vide supra for 2).
The IR spectral data for the methylidyne-capped clusters 5
and 6 parallel those data already described for the benzyli-
dyne-substituted derivatives 2 and 3, with only a slight
exception found in the 31P NMR spectrum of the dppn-
chelated cluster 6. Here three 31P resonances were observed
at d 44.80 (s), 35.00 (s), and 30.05 (s), with the all-terminal
carbonyl isomer of HCCo3(CO)7(dppn) (d 44.80) present in
solution as the major species (ca. 95%). Subtle steric effects
involving the capping carbyne R group and the ancillary
dppn ligand are presumably at play and control the
amount of the all-terminal carbonyl isomer in solution.
The preparation of other derivatives are planned in order
to more fully probe the effect of the R-capping group on
the isomeric equilibrium in RCCo3(CO)7(dppn).
Ph
O
OH
C
PPh2
Co
P
Ph
Co
Co
cluster 7
˚
The mean Co–Co bond distance of 2.475(2) A in 7 is
unremarkable compared to those distances reported in
the nonacarbonyl clusters RCCo3(CO)9 and simple-substi-
tuted Co3 derivatives [19,24,25]. The coordination of the
two-electron hydroxyl phosphine moiety P(1) to the cluster
core is supported by conventional electron-counting rules,
similarity of the IR spectrum of 7 relative to other RCCo3
(CO)8P clusters [17], and an observed Co(1)–P(1) bond
˚
length of 2.221(2) A, all of which support the existence of
a cobalt–phosphorus single bond [28]. The P(1)–O(1)
3.3. Reaction of HCCo3(CO)9 with dppn using Me3NO and
molecular structure of 7
˚
˚
[1.592(4) A] and P(2)–O(2) [1.499(4) A] distances are in
accord with P–O and P@O bond character, respectively,
and those distances found in other oxidized phosphine
compounds [29]. The H(1) atom is covalently bound to
Treatment of cluster 4 and a slight excess of dppn with
Me3NO led to an immediate reaction and the formation
of three products when the reaction solution was moni-
tored by TLC using CH2Cl2/hexane (1:3). The two faster
moving spots were readily assigned to clusters 5 and 6,
while the slower moving compound 7 (Rf = 0.30) repre-
sented a compound not observed in the thermolysis reac-
tion of 4 and dppn. All products were separated by
column chromatography over silica gel, after which 7 was
appropriately characterized in solution by IR and 31P
NMR spectroscopies, mass spectrometry, and X-ray dif-
fraction analysis. 7 was isolated in low yield as an air-sen-
sitive solid having limited thermal stability.
The IR spectrum of compound 7 displayed terminal car-
bonyl stretching bands at 2075 (s), 2032 (vs), 2018 (vs), and
2010 (sh) cmꢀ1, signaling the presence of a monosubsti-
tuted RCCo3(CO)8P cluster. The possibility of HCCo3-
(CO)8(g1-dppn) representing 7 was immediately eliminated
from contention based on 31P NMR spectroscopy and
mass spectrometry. The 31P NMR spectrum of 7 exhibited
a pair of inequivalent singlets d 130.49 and 39.62 that indi-
cated the presence of distinctly different phosphine moieties
from the coordination of an activated dppn ligand. Both
FAB and ESI mass spectral data for 7 revealed parent
peaks whose mass was in excess of the simple g1-dppn
derivative. The unequivocal molecular structure for 7 was
determined by X-ray diffraction analysis. The thermal ellip-
soid plot of 7 is shown in Fig. 1 (right-hand side). The
˚
O(1) based on a 1.10(7) A bond length found for the
O(1)–H(1) vector and is hydrogen bonded, albeit asymmet-
˚
rically, to O(2) based on the 1.39(7) A bond distance found
for the H(1)ꢁ ꢁ ꢁO(2) atoms. This intramolecular hydrogen
bond is essential linear, displaying a bond angle of
175(7)° for the O(1)–H(1)ꢁ ꢁ ꢁO(2) linkage [30]. The remain-
ing distances and angles in 7 are unremarkable.
3.4. Reactivity studies using clusters 3 and 6
The thermal stability of the dppn-chelated clusters 3 and
6 was next explored given our interest on the decomposi-
tion pathways attendant in clusters containing a diphos-
phine ligand [8,20,31]. Heating solutions of 3 in CH2Cl2
or toluene overnight at 55 °C lead to the decomposition
of the starting cluster, as assessed by TLC analysis. Here
the formation of a black colored material that was irrevers-
ibly bound at the origin of the TLC plate was found. Mon-
itoring the same reaction by IR spectroscopy revealed only
a slow loss of the carbonyl bands associated with 3. Ther-
molysis of cluster 6 under identical conditions affords two
new compounds when monitored by TLC. However,
attempts to isolate these highly air- and thermally-sensitive
products for more thorough characterization were met
with very limited success. We were able to record the 31P
NMR spectrum before decomposition intervened and

974
W.H. Watson et al. / Journal of Organometallic Chemistry 692 (2007) 968–975
found two sets of 31P resonances at d 35.30 and 35.73 and d
74.57 and 75.25 that are ascribed to phosphine and phos-
phido moieties, respectively [32]. While the nature of the
phosphido moieties cannot be absolutely ascertained at this
juncture, cleavage of P–Ph and P–C(naphthyl) bonds in the
dppn ligand is fully consistent with the dppn-degradation
manifolds promoted by the group 8 clusters Ru3(CO)12
and Os3(CO)12 [6,7].
(b) V.W.-W. Yam, C.-K. Li, C.-L. Chan, K.-K. Cheung, Inorg.
Chem. 40 (2001) 7054.
[5] A. Karacar, M. Freytag, H. Tho¨nnessen, J. Omelanczuk, P.G. Jones,
R. Bartsch, R. Schmutzler, Z. Anorg. Allg. Chem. 626 (2000) 2361.
[6] M.I. Bruce, P.A. Humphrey, S. Okucu, R. Schmutzler, B.W. Skelton,
A.H. White, Inorg. Chim. Acta 357 (2004) 1805.
[7] M.I. Bruce, P.A. Humphrey, R. Schmutzler, B.W. Skelton, A.H.
White, J. Organomet. Chem. 689 (2004) 2415.
[8] (a) K. Yang, S.G. Bott, M.G. Richmond, J. Organomet. Chem. 454
(1993) 273;
(b) K. Yang, J.M. Smith, S.G. Bott, M.G. Richmond, Organomet-
allics 12 (1993) 4779;
4. Conclusions
(c) S.G. Bott, H. Shen, R.A. Senter, M.G. Richmond, Organomet-
allics 22 (2003) 1953;
(d) S.G. Bott, K. Yang, M.G. Richmond, J. Organomet. Chem. 691
(2006) 3771.
The reaction of the tricobalt clusters PhCCo3(CO)9 (1)
and HCCo3(CO)9 (4) with the diphosphine ligand dppn
has been investigated. Evidence is presented for both the
facile fragmentation of the dppn ligand (clusters 2, 5, and
7) and chelation of the ligand to the cluster frame (clusters
3 and 6). In the case of cluster 7, it is clear that the detri-
mental oxidation of the dppn ligand by Me3NO and trans-
fer of one of the phenyl groups from the dppn ligand to the
cluster complicate and lower the yields of the substitution
reaction. Our data on the reactivity of dppn with clusters
1 and 4 are in agreement with those observations of Bruce
and co-workers and underscore the inability of the dppn
ligand to serve as a stabilizing ligand for multimetallic
[9] M.O. Nestle, J.E. Hallgren, D. Seyferth, Inorg. Synth. 20 (1980) 226.
[10] D. Seyferth, S.C. Vick, J. Organomet. Chem. 141 (1977) 173.
[11] A. Karacar, H. Tho¨nnessen, P.G. Jones, R. Bartsch, R. Schmutzler,
Heteroat. Chem. 8 (1997) 539.
[12] K. Issleib, H. Volker, Chem. Ber. 94 (1961) 392.
[13] D.F. Shriver, The Manipulation of Air-Sensitive Compounds,
McGraw-Hill, New York, 1969.
[14] SAINT Version 6.02, Bruker Analytical X-ray Systems, Inc. Copyright
1997–1999.
[15] SHELXTL Version 5.1, Bruker Analytical X-ray Systems, Inc. Copy-
right 1998.
[16] A.L. Spek, PLATON – A Multipurpose Crystallographic Tool, Utrecht
University, Utrecht, The Netherlands, 2001.
´
polyhedra vis-a-vis diphosphine ligands such as dppe and
[17] (a) T.W. Matheson, B.H. Robinson, W.S. Tham, J. Chem. Soc. A
(1971) 1457;
(Z)-Ph2PCH@CHPPh2.
(b) A. Cartner, R.G. Cunningham, B.H. Robinson, J. Organomet.
Chem. 92 (1975) 49;
(c) A.J. Downard, B.H. Robinson, J. Simpson, Organometallics 5
(1986) 1122.
5. Supplementary material
CCDC 619643 and 619644 contain the supplementary
crystallographic data for 3 and 7. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@
ccdc.cam.ac.uk.
[18] No mechanistic pathway is implied here. At this juncture it is
unknown whether the dppn first coordinates to cluster 1 prior to its
transformation to give cluster 2 or if free PPh2(1-naphthyl) undergoes
reaction with 1 directly to furnish 2.
[19] B.R. Penfield, B.H. Robinson, Acc. Chem. Res. 6 (1973) 73.
[20] For related isomerization behavior of a diphosphine ligand in this
genre of cluster, see: S.G. Bott, H. Shen, M.G. Richmond, Struct.
Chem. 12 (2001) 225.
[21] See also G.H. Worth, B.H. Robinson, J. Simpson, Organometallics
11 (1992) 3863.
Acknowledgments
[22] (a) S.G. Bott, H. Shen, M.G. Richmond, J. Organomet. Chem. 689
(2004) 3426;
(b) W.H. Watson, S. Kandala, M.G. Richmond, J. Chem. Crystal-
logr. 35 (2005) 157;
(c) W.H. Watson, S.G. Bodige, K. Ejsmont, J. Liu, M.G. Richmond,
J. Organomet. Chem. 691 (2006) 3609.
Financial support from the Robert A. Welch Founda-
tion (Grant Nos. P-0074 to W.H.W. and B-1093 to
M.G.R) is appreciated, and Dr. Yongxuan Su (UCSD) is
thanked for recording the FAB and ESI mass spectra of
cluster 7.
[23] D.M.P. Mingos, D.J. Wales, Introduction to Cluster Chemistry,
Prentice-Hall, Englewood Cliffs, NJ, 1990.
[24] (a) S.B. Colbran, B.H. Robinson, J. Simpson, Acta Crystallogr.,
Sect. C 42 (1986) 972;
(b) M. Ahlgre´n, T.T. Pakkanen, I. Tahvanainen, J. Organomet.
Chem. 323 (1987) 91;
References
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Chem. 458 (1993) C3.
(d) M.-J. Don, M.G. Richmond, W.H. Watson, M. Krawiec, R.P.
Kashyap, J. Organomet. Chem. 418 (1991) 231;
(e) P.W. Sutton, L.F. Dahl, J. Am. Chem. Soc. 89 (1967) 261;
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[2] S.L. James, A.G. Orpen, P.G. Pringle, J. Organomet. Chem. 525
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[3] V.W.-W. Yam, C.-L. Chan, S.W.-K. Choi, K.M.-C. Wong, E.C.-C.
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Commun. (2000) 53.
[4] (a) Related to the work in Ref. [3] are the reports of unsupported
AuII–AuII compounds possessing chelating dppn ligands, see: V.W.-
W. Yam, S.W.-K. Choi, K.-K. Cheung, Chem. Commun. (1996)
1173;
[25] (a) M.-J. Don, M.G. Richmond, W.H. Watson, R.P. Kashyap, Acta
Crystallogr., Sect. C 47 (1991) 20;
(b) W.H. Watson, A. Nagl, S. Huang, M.G. Richmond, J. Organo-
met. Chem. 445 (1993) 163.

W.H. Watson et al. / Journal of Organometallic Chemistry 692 (2007) 968–975
975
[26] (a) For reports dealing with the reactivity of carbyne-centered radicals
in trimetallic clusters, see: D. Seyferth, J.E. Hallgren, J. Organomet.
Chem. 49 (1973) C41;
cluster 7, see: I.A. Razak, A. Usman, H.-K. Fun, B.M. Yamin,
N.A.M. Kassim, Acta Crystallogr., Sect. C 58 (2002) 225;
(b) B.D. Ellis, C.L.B. Macdonald, Inorg. Chem. 43 (2004) 5981;
(c) B. Walther, H. Hartung, M. Maschmeier, U. Baumeister, B.
Messbauer, Z. Anorg. Allg. Chem. 566 (1988) 121.
[31] W.H. Watson, G. Wu, M.G. Richmond, Organometallics 24 (2005)
5431;
(b) D.S. Strickland, S.R. Wilson, J.R. Shapley, Organometallics 7
(1988) 1674;
(c) N. Hadj-Bagheri, D.S. Strickland, S.R. Wilson, J.R. Shapley, J.
Organomet. Chem. 410 (1991) 231.
[27] With the identity of 7 established by X-ray crystallography, the
unambiguous assignment of the 31P NMR resonances at d 130.49 and
39.62 in 7 to the hydroxy phosphine [P(1)] and phosphine oxide [P(2)]
moieties, respectively, is ascertained.
[28] A.G. Orpen, L. Brammer, F.K. Allen, O. Kennard, D.G. Watson,
R. Taylor, J. Chem. Soc., Dalton Trans. (1989) S1.
[29] (a) L.-B. Han, N. Choi, M. Tanka, Organometallics 15 (1996) 3259;
Organometallics 25 (2006) 930.
[32] (a) The pair of low-field 31P resonances observed may be
confidently assigned to phosphido moieties based on their large
nuclear deshielding relative to the 31P resonances of the dppn
ligand in the starting cluster 6. See: P.E. Garrou, Chem. Rev. 81
(1981) 229;
(b) A.J. Carty, S.A. MacLaughlin, D. Nucciarone, in: J.G.
Verkade, L.D. Quin (Eds.), Phosphorus-31 NMR Spectros-
copy in Stereochemical Analysis: Organic Compounds and
Metal Complexes, VCH Publishers, New York, 1987 (Chapter
16).
´
(b) R. Torres-Lubian, M.J. Rosales-Hoz, A.M. Arif, R.D. Ernst,
A.M. Paz-Sandoval, J. Organomet. Chem. 585 (1999) 68.
[30] (a) For other examples containing hydrogen-bonding in hydroxy-
phosphine and phosphine-oxide compounds akin to that found in