2-[(Diphenylphosphino)methyl]-6-methylpyridine (PN) coordination chemistry at triosmium clusters: Regiospecific ligand activation and DFT evaluation of the isomeric Os3 (CO)10 (PN) clusters

Article abstract of DOI:10.1016/j.jorganchem.2013.03.048

The reaction of 2-[(diphenylphosphino)methyl]-6-methylpyridine (PN) with Os₃(CO) _12-n(MeCN)_n [where n = 0 (1), 1 (2), 2 (3)] has been investigated. Os₃(CO)₁₂ reacts with PN in the presence of Me3NO to afford the clusters Os₃(CO) ₁₁(k¹-PN) (4) and 1,2-Os₃(CO)10(k1-PN)2 (5). X-ray diffraction analyses confirm the equatorial coordination of the phosphine(s) in 4 and 5, with the two phosphines in the latter cluster exhibiting a 1,2-trans orientation about the OseOs vector that contains the two ligands. Treatment of the MeCN-substituted cluster Os₃(CO) ₁₁(MeCN) and PN (1:1 ratio) in CH₂Cl2 gives clusters 4 and 5, in addition to HOs₃ (h1-Cl)(CO)₁₀( (k1-PN) (6) as a result of competitive activation of the reaction solvent. Cluster 6 contains 48-and the diffraction structure reveals the presence of axial chloride and equatorial phosphine ligands which are located on adjacent osmium atoms. The bridging hydride ligand in 6 spans the Cl,P-substituted OseOs vector. The reaction of Os₃(CO)10(MeCN)2 with PN furnishes 5, 6, and 1,1-Os ₃ (CO)₁₀( (k²-PN) (7) in yields that are dependent on the reagent stoichiometry and reaction solvent. The solid-state structure of 7 confirms the chelation of the PN ligand to a single osmium atom via the pyridine and phosphine moieties at axial and equatorial sites, respectively. The bonding in 7 relative to other possible stereoisomers has been explored by DFT calculations, and the diffraction structure is computed as the thermodynamically most stable form of this cluster. Cluster 4 is photosensitive and CO loss gives 7, in addition to the formation of the dihydride H ₂Os₃ (CO) ₈ [m-CH(NC₅H ₃)CH₂PPh₂] (8), whose origin derives from the double metalation of the C-6 methyl group of the PN ligand in 7. Photolysis of 7 yields 8 without detectable observation of the expected intermediate hydride HOs₃(CO)9[μ-CH₂(NC₅H₃) CH ₂PPh₂]. The PN ligand in 7 undergoes PeC bond activation in toluene at 110°C to afford the 50-cluster Os₃(CO) ₉ (μ-C₆H₄ )( μ-PPh) (9), which contains face-capping benzyne and phosphinidene moieties. The bonding between the benzyne moiety and the opened Os₃ frame in 9 has been examined computationally, and these data are discussed relative to s and p bonding contributions from the metalated aryl ring to the cluster polyhedron.

Full text of DOI:10.1016/j.jorganchem.2013.03.048

Journal of Organometallic Chemistry 744 (2013) 24e34
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
2-[(Diphenylphosphino)methyl]-6-methylpyridine (PN) coordination
chemistry at triosmium clusters: Regiospecific ligand activation and
DFT evaluation of the isomeric Os3(CO)10(PN) clusters
*
Chen-Hao Lin, Vladimir N. Nesterov, Michael G. Richmond
Department of Chemistry, University of North Texas, Denton, TX 76203, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of 2-[(diphenylphosphino)methyl]-6-methylpyridine (PN) with Os3(CO)12ꢀn(MeCN)n [where
Received 12 February 2013
Received in revised form
25 March 2013
n ¼ 0 (1), 1 (2), 2 (3)] has been investigated. Os3(CO)12 reacts with PN in the presence of Me3NO to afford
the clusters Os3(CO)11(k (k
1-PN) (4) and 1,2-Os3(CO)10 1-PN)2 (5). X-ray diffraction analyses confirm the
equatorial coordination of the phosphine(s) in 4 and 5, with the two phosphines in the latter cluster
exhibiting a 1,2-trans orientation about the OseOs vector that contains the two ligands. Treatment of the
MeCN-substituted cluster Os3(CO)11(MeCN) and PN (1:1 ratio) in CH2Cl2 gives clusters 4 and 5, in
Accepted 26 March 2013
This paper is dedicated to our colleague
Professor W.A. Herrmann on the occasion of
his 65th birthday. Herzlichen Glückwunsch
zum Geburtstag!
addition to HOs3(h (k
1-Cl)(CO)10 1-PN) (6) as a result of competitive activation of the reaction solvent.
Cluster 6 contains 48e and the diffraction structure reveals the presence of axial chloride and equatorial
phosphine ligands which are located on adjacent osmium atoms. The bridging hydride ligand in 6 spans
the Cl,P-substituted OseOs vector. The reaction of Os3(CO)10(MeCN)2 with PN furnishes 5, 6, and 1,1-
Os3(CO)10(k
2-PN) (7) in yields that are dependent on the reagent stoichiometry and reaction solvent.
Keywords:
Osmium clusters
Phosphinopyridine ligand
PeC and CeH bond activation
X-ray crystallography
DFT
The solid-state structure of 7 confirms the chelation of the PN ligand to a single osmium atom via the
pyridine and phosphine moieties at axial and equatorial sites, respectively. The bonding in 7 relative to
other possible stereoisomers has been explored by DFT calculations, and the diffraction structure is
computed as the thermodynamically most stable form of this cluster. Cluster 4 is photosensitive and CO
loss gives 7, in addition to the formation of the dihydride H2Os3(CO)8[
origin derives from the double metalation of the C-6 methyl group of the PN ligand in 7. Photolysis of 7
yields 8 without detectable observation of the expected intermediate hydride HOs3(CO)9[ -CH2(NC5H3)
CH2PPh2]. The PN ligand in 7 undergoes PeC bond activation in toluene at 110 ꢁC to afford the 50e cluster
Os3(CO)9( -C6H4)( -PPh) (9), which contains face-capping benzyne and phosphinidene moieties. The
bonding between the benzyne moiety and the opened Os3 frame in 9 has been examined computa-
m-CH(NC5H3)CH2PPh2] (8), whose
m
m
m
tionally, and these data are discussed relative to
ring to the cluster polyhedron.
s
and
p
bonding contributions from the metalated aryl
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
2-(diphenylphosphino)pyridine (dpppy) represents one of the
forerunners in this genre of bidentate ligands, and the ability of
dpppy to bind a single metal (chelate) and tether adjacent metals
(bridge) in polynuclear compounds is well documented. The
plethora of reactivity and structural reports underscores the early
popularity and importance of this particular compound as a ligand
[2]. The high rigidity and short bite angle in dpppy severely limit its
coordinative flexibility in reactions with metal clusters. And che-
lation of a single metal center in a polynuclear cluster by dpppy is
rare compared to the bridging of adjacent metal centers observed
in the majority of structurally characterized clusters containing this
ligand [3].
Bidentate compounds that contain both phosphorus and nitro-
gen donors have been extensively investigated as ligand auxiliaries
in a variety of important catalytic transformations [1]. Additional
interest in such hard-soft ligand combinations stems from their
potential hemilabile behavior and the inherent regio- and stereo-
chemical asymmetry that the two different pnictogen donors
impart to a transition metal(s) upon coordination. Of the many
different phosphorusenitrogen-based ligand systems known,
Increasing the flexibility of the backbone in dpppy through the
inclusion of one extra carbon spacer has been examined. Here
* Corresponding author. Tel.: þ1 940 565 3548.
E-mail address: cobalt@unt.edu (M.G. Richmond).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.03.048

C.-H. Lin et al. / Journal of Organometallic Chemistry 744 (2013) 24e34
25
researchers have investigated 2-(diphenylphosphinomethyl)pyri-
dine (dppmp) in order to study the effect that a saturated methy-
lene moiety imparts on the coordinative flexibility and chemical
reactivity vis-à-vis dpppy. Dppmp is easily synthesized from 2-
picoline and Ph2PCl (Eq. (1)), and numerous derivatives have
been prepared through modification of this protocol [4]. As a ligand
dppmp can function as both a chelating and bridging ligand with
mononuclear and simple dinuclear metal compounds. However, to
our knowledge no structurally characterized examples containing
dppmp-substituted polynuclear metals exist, and questions con-
cerning bonding preference and chemical stability of this ligand at
polynuclear metal clusters remain unanswered.
purchased from Cambridge Isotope Laboratories; the aromatic
solvent C6D6 was purified by bulb-to-bulb distillation from so-
dium/benzophenone ketyl while the CDCl3 was distilled in a
similar fashion from P2O5. The photolysis experiments were per-
formed at 366 nm (ꢂ20 nm) using GE blacklight bulbs or at
254 nm using a high-pressure mercury lamp (200 W) that was
configured to an Oriel 68805 universal power supply; the latter
photolyses were conducted in quartz NMR tubes that were
equipped with a J-Young valve. The combustion analyses were
performed by Atlantic Microlabs, Norcross, GA.
2.2. Instrumentation
The IR spectra were recorded on a Nicolet 6700 FT-IR spec-
trometer, and the 1H NMR spectra were recorded at 400 or
500 MHz on Varian VNMRS-400 and VNMRS-500 spectrometers,
respectively. The reported 1H assignments were corroborated
through the use of COSY, HMQC, HMBC, and NOESY pulse se-
quences. The 31P{1H} NMR spectra were recorded on the latter
spectrometer at 202 MHz and are referenced to external H3PO4
1. BuLi
2. Ph2PCl
PPh2
N
N
dppmp
(85%), whose chemical shift was set at
d
¼ 0. The ESI-APCI mass
(1)
spectrum was recorded at the UC San Diego mass spectrometry
facility in the positive ionization mode.
Given our interest in the fluxionality and reactivity of diphos-
phine and diimine ligands at Os3 clusters [5], we wished to examine
the reactivity of a suitable bidentate phosphorusenitrogen donor
with Os3(CO)12-n(MeCN)2 [n ¼ 0 (1), n ¼ 1 (2), 2 (3)]. A mixed
phosphorusenitrogen donor would allow us to study the syner-
gistic and regiochemical aspects related to the mode of ligand co-
ordination in the Os3 product(s) and bond activation of the mixed
ligand upon thermolysis and photolysis. While many potential
phosphorusenitrogen donor candidates for study exist, recent re-
ports on 2-[(diphenylphosphino)methyl]-6-methylpyridine (PN) as
a ligand with mononuclear ruthenium and rhodium compounds
stand out [6]. The resulting PN-substituted products were shown to
exhibit extremely high turnover numbers in the transfer hydroge-
nation of acetophenone by 2-propanol and the ROMP of norbor-
nene. Herein we report our results on the reaction of the mixed
pnictogen 2-[(diphenylphosphino)methyl]-6-methylpyridine (PN)
with a series of triomsium clusters. This particular PN compound
was chosen as a ligand for study because its coordination at an
intact metal cluster, which has not previously explored, would
allow us to probe for possible cluster-promoted regioselective bond
activation of the methyl and phenyl substituents in PN.
2.3. Synthesis of 4 and 5 from 1 and PN
To 0.10 g (0.11 mmol) of 1 in 50 mL of CH2Cl2 under argon was
added 32 mg (0.11 mmol) of PN, followed by 17 mg (0.22 mmol) of
Me3NO. The reaction solution was stirred overnight at room tem-
perature and then examined by TLC analysis (1:1 Et2O/hexane),
which revealed the presence of clusters 4 (Rf ¼ 0.48) and 5
(Rf ¼ 0.30), in addition to unreacted 1. The two products were
subsequently isolated by column chromatography over silica gel
using the aforementioned solvent system, after which both prod-
ucts were recrystallized from benzene/CH2Cl2 (4) and hexane/
CH2Cl2 (5). The spectroscopic data for all new products are sum-
marized in Table 1. Yield 4: 40% (52 mg). Anal. Calcd (found) for
C30H18NO11Os3P$3/4benzene: C, 33.70 (33.45); H, 1.83 (2.14). Yield
5: 30% (47 mg). Anal. Calcd (found) for C48H36N2O10Os3P2: C, 40.22
(40.14); H, 2.53 (2.57).
2.4. Synthesis of 4, 5, and 6 from 2 and PN
To a medium Schlenk tube under argon flush was added 0.15 g
(0.16 mmol) of 2 and 50 mL of CH2Cl2, followed by the addition of
48 mg (0.16 mmol) of PN. The solution was stirred for 1.5 h at room
temperature and then examined by TLC analysis using 1:1 Et2O/
hexane as the eluent. The presence of 4 (major) and 5 (minor) was
noted, along with a third slower moving spot at Rf ¼ 0.21 corre-
sponding to cluster 6. The three products were isolated by column
chromatography and recrystallized from hexane/CH2Cl2. The yield
for clusters 4 and 5 was 50% (95 mg) and 20% (47 mg), respectively.
Yield of 6: 15 mg (8%). Anal. Calcd (found) for C29H19ClNO10Os3P$1/
2hexane: C, 31.43 (31.98); H, 2.13 (2.28). Repeating this reaction
using toluene as the solvent furnished only 4 (50%) and 5 (25%).
2. Experimental section
2.1. Materials and equipment
Os3(CO)12 (1) was synthesized from OsO4 and CO in a Parr
Series 4560 autoclave (450 mL capacity) [7], and the parent
cluster was used as the starting material for the preparation of
Os3(CO)11(MeCN) (2), and Os3(CO)10(MeCN)2 (3) [8]. The 2-
[(diphenylphosphino)methyl]-6-methylpyridine (PN) employed in
our studies was prepared from 2,6-lutidine and Ph2PCl according
to the procedure of Lugan and Lavigne [6c]. OsO4 was purchased
from Electron Microscopy Sciences, and the organic chemicals
Me3NO$xH2O, Ph2PCl, 2,6-lutidine, and BuLi (2.5 M in hexanes)
were obtained from Aldrich Chemical Co. With the exception of
the Me3NO$xH2O that was azeotropically dried using benzene
solvent, all other starting reagents were used as received. The
reaction solvents were obtained from an Innovative Technology
(IT) solvent purification system or were distilled under argon from
a suitable drying agent prior to use [9]. All NMR solvents were
2.5. Reaction of 3 with PN
2.5.1. Reaction of 3 and PN in toluene
To 0.10 g (0.11 mmol) of 3 in 25 mL of toluene was added
dropwise, through the use of a syringe pump, 31 mg (0.11 mmol) of
PN dissolved in 5 mL of toluene. The reaction mixture was stirred at
room temperature for 2 h, after which time TLC examination (7:3
Et2O/hexane) revealed the presence of starting cluster, 5, and 7
(major product) as the only mobile materials. Attempts to purify 7

26
C.-H. Lin et al. / Journal of Organometallic Chemistry 744 (2013) 24e34
Table 1
Spectroscopic data for the clusters 4e9.a
Cluster
IR, cmꢀ1
1H NMR,
d
31P NMR,
d
2
4
2106 (m), 2053 (s), 2034 (m),
2017 (vs), 1996 (m), 1986 (m),
1777 (sh, m)
2.35 (3H, s, Me), 4.13 (2H, d, CH2, JPeH ¼ 11 Hz),
ꢀ4.93
3
6.04 (1H, d, py H3, JHeH ¼ 7.5 Hz),
3
6.88 (1H, d, py H5, JHeH ¼ 7.5 Hz),
3
7.15 (1H, t, py H4, JHeH ¼ 7.5 Hz),
7.35e7.48 (10 H, m, aryl)
5b
2084 (m), 2027 (s), 2011 (sh, m),
1997 (vs), 1964 (b, m)
2.31 (6H, s, Me), 4.08 (4H, broad, CH2),
6.05 (2H, broad singlet, py, H3),
ꢀ10.13, ꢀ6.59,
ꢀ5.24
3
6.83 (2H, d, py H5, JHeH ¼ 7.5 Hz),
3
7.09 (2H, t, py H4, JHeH ¼ 7.5 Hz),
7.35 (6 H, broad, aryl), 7.45 (4 H, broad, aryl)
2
6
2114 (m), 2078 (s), 2063 (s),
2030 (vs), 2020 (sh, s), 1976 (b, m)
ꢀ16.11 (1H, d, hydride, JPeH ¼ 11 Hz),
ꢀ6.36
2.38 (3H, s, Me), 4.39 (2H, m, CH2),
3
6.22 (1H, d, py H3, JHeH ¼ 8 Hz),
3
7.95 (1H, d, py H5, JHeH ¼ 8 Hz),
3
7.25 (1H, t, py H4, JHeH ¼ 8 Hz),
7.45e7.62 (10 H, m, aryl)
7
2087 (m), 2044 (sh, m), 2037 (s),
2000 (b, vs), 1987 (sh, s), 1970 (sh),
1950 (b, m), 1928 (sh, w), 1906 (sh)
3.11 (3H, s, Me),
22.57
2
4.47 (1H, dd, CH2, JPeH ¼ 16 Hz, 2JHeH ¼ 8 Hz),
5.21 (1H, t, CH2, JPeH ¼ 8 Hz, 2JHeH ¼ 8 Hz),
2
3
6.98 (4H, m, aryl), 7.33 (1H, d, py, JHeH ¼ 8 Hz),
3
7.52 (2H, m, aryl), 7.55 (1H, d, py, JHeH ¼ 8 Hz),
3
7.60 (1H, t, py H4, JHeH ¼ 8 Hz),
7.78 (4H, m, aryl)
8c
2087 (s), 2044 (s), 2005 (vs),
1987 (m), 1953 (m)
ꢀ14.21 (1H, s, hydride),
20.62
2
ꢀ13.14 (1H, d, hydride, JPeH ¼ 9 Hz),
2
2
2.70 (1H, dd, CH2, JHeH ¼ 16 Hz, JPeH ¼ 5.2 Hz),
2
2
3.50 (1H, dd, CH2, JHeH ¼ 16 Hz, JPeH ¼ 12.8 Hz),
5.49 (1H, s, benzylidene CH),
3
5.94 (1H, d, py H3, JHeH ¼ 7.6 Hz),
3
6.24 (1H, d, py H5, JHeH ¼ 7.6 Hz),
3
6.61 (1H, t, py H4, JHeH ¼ 7.6 Hz),
6.83e7.05 (8H, m, aryl), 7.47e7.53 (2H, m, aryl)
7.09 (2H, m, benzyne),
9
2065 (vs), 2042 (s), 2007 (s),
221.45
1990 (m), 1968 (sh, w), 1942 (sh, w)
7.41 (3H, m, PPh aryl),
7.60 (4H, m, PPh aryl and benzyne)
a
All IR spectra were recorded in CH2Cl2 and the NMR spectra recorded in CDCl3 at room temperature, unless otherwise noted.
31P NMR spectrum recorded at 333 K in CDCl3.
NMR spectra recorded in C6D6.
b
c
by column chromatography were accompanied by excessive
product, which was subsequently purified by recrystallization from
hexane/CH2Cl2 to give 7 as a yellow solid in 45% yield (66 mg). ESI-
MS: m/z 1165.53 [M þ Na]þ, and ions for the loss of 1e3 CO
molecules.
decomposition with isolated yields <5%. Cluster 5 was the major
species isolated by chromatography, and the yield of 5 after
recrystallization was 46 mg (30% yield). Repeating the reaction with
a twofold excess of PN relative to 3 did not significantly increase the
yield of the chelate cluster 7. Here 5 (61 mg; 40%) was again isolated
as the major after chromatography, followed by recrystallization.
2.7. Synthesis of 8 from the photochemical activation of 7
To a 5 mm NMR tube equipped with a J-Young valve was added
50 mg (0.044 mmol) of 7 and 0.7 mL of C6D6. The tube was sealed
and the contents were evacuated by three freezeepumpethaw
degas cycles, after which the NMR tube was irradiated at 366 nm.
The progress of the reaction was monitored by NMR spectroscopy,
with complete consumption of the starting cluster and formation of
8 achieved after several days. The solvent was removed and the
crude product taken up in hexane and placed in the freezer at 5 ꢁC
in order to induce crystallization. 8 was isolated as a yellow solid in
90% yield (48 mg). Anal. Calcd (found) for C27H18NO8Os3P$hexane:
C, 33.79 (34.00); H, 2.73 (2.91).
2.5.2. Reaction of 3 and PN in CH2Cl2
This experiment was carried out exactly as described above (1:1
stoichiometry) except for the use of CH2Cl2 as the reaction solvent.
The reaction solution was examined after 1 h by TLC, to reveal the
presence of the PN-substituted clusters 5 (25%), 6 (40%), and 7 (5%),
and the known cluster HOs3(m-Cl)(CO)10 (10%) [10]; the identity of
the latter cluster was confirmed by TLC and 1H NMR comparisons
against an independently prepared sample of this cluster.
Increasing the PN amount twofold relative to 3 afforded the
disubstituted cluster 5 (40%), 6 (5%), and a trace amount of 7.
2.6. Preparation of 7 from 4 and Me3NO
2.8. Synthesis of 9 from the thermolysis of 7
To 0.15 g (0.13 mmol) of 4 in a medium Schlenk tube was added
50 mL of toluene via cannula, followed by the addition of 12 mg
(0.16 mmol) of Me3NO. The vessel was sealed and the solution was
stirred overnight at room temperature. TLC examination of the
reaction solution the following day confirmed the presence of 7 as
the principal product, in addition to a small amount of material that
remained at the origin of the TLC plate. The IR spectrum of the
solution before purification was in concert with the desired
The thermolysis reaction was carried out in a heavy-walled
Carius tube that was charged with 0.10 g (0.088 mmol) of 7 and
25 mL of toluene. After the reaction solution was deoxygenated by
three freezeepumpethaw degas cycles, the Carius tube was sealed
and heated at 110 ꢁC for 48 h. TLC analysis (1:1 Et2O/hexane) of the
cooled reaction solution confirmed the loss of 7 and the presence of
fast moving yellow spot at Rf ¼ 0.71, which was subsequently
identified as 9. Some decomposition was observed in this reaction,

C.-H. Lin et al. / Journal of Organometallic Chemistry 744 (2013) 24e34
27
on the basis of a small amount of material that remained the origin
of the TLC plate. The desired product was purified by column
chromatography over silica gel, followed by recrystallization from
heptane/benzene, to give 9 in 70% yield (62 mg). Anal. Calcd (found)
for C21H9O9Os3P$heptane: C, 30.52 (30.94); H, 2.09 (2.26).
2.9. X-ray crystallographic data
Single crystals of 4e7 and 9 were grown by slowly evaporating
the CH2Cl2 solvent from hexane/CH2Cl2 solutions containing each
cluster at 5 ꢁC. All X-ray diffraction examinations were carried out
using a Bruker SMART APEX2 CCD-based X-ray diffractometer
equipped with a low-temperature cryostat (Oxford Instruments)
ꢀ
and a Mo-target X-ray tube (
l
¼ 0.71073 A). With the exception of 6,
whose X-ray data were collected at room temperature, the X-ray
data for the other clusters werecollected at 100(2) K. Data collection,
indexing, and initial cell refinements were carried out using APEX2
[11], with the frame integrations and final cell refinements carried
out using SAINT [12]. An absorption correction was applied to each
system using the program SADABS [13], and all non-hydrogen atoms
were refined anisotropically. The bridging hydride in 6 was located
during refinement and refined isotropically, while all remaining
hydrogen atoms in all of the other structures were placed in ideal-
ized positions and were refined using a riding model. The highly
disordered molecule of CH2Cl2 extant in 7 was treated using the
PLATON/SQUEEZE program [14]; this treatment gave an electron
count in the unit cell of 32 electrons/cell that is close to the required
value for one CH2Cl2 molecule (42 electrons/cell). The reported
structures were solved and refined using the SHELXTL program
package software [15]. Refinement details and structural parame-
ters for these structures are summarized in Table 2.
Fig. 1. Thermal ellipsoid plot of the molecular structure of 4 at the 50% probability
level. Selected bond distances (A) and angles (deg) for the diffraction structure: Os(1)e
ꢀ
Os(2)
¼
2.8801(2), Os(1)eOs(3)
¼
2.8907(2), Os(2)eOs(3)
¼
2.9150(2), Os(2)e
P(1) ¼ 2.345(1), P(1)eOs(2)eOs(1) ¼ 165.87(3), P(1)eOs(2)eOs(3) ¼ 106.84(2), C(5)e
Os(2)eP(1) ¼ 89.2(1), C(6)eOs(2)eP(1) ¼ 89.8(1), C(7)eOs(2)eP(1) ¼ 99.0(1).
exchange functional (B3) [17], combined with the correlation
functional of Lee, Yang and Parr (LYP) [18]. The Os atoms were
described by StuttgarteDresden effective core potentials (ecp) and
an SDD basis set, while a 6-31G(d’) basis set was employed for the
remaining atoms.
2.10. Computational methodology and modeling details
All reported geometries correspond to fully optimized ground-
state structures based on positive eigenvalues obtained from the
analytical Hessian. The computed frequencies were used to make
zero-point and thermal corrections to the electronic energies; the
reported enthalpies are quoted in kcal/mol relative to the
The reported calculations were performed with the hybrid DFT
functional B3LYP, as implemented by the Gaussian 09 program
package [16]. This functional utilizes the Becke three-parameter
Table 2
X-ray crystallographic data and processing parameters for the clusters 4e7, and 9.
Compound
4
5
6
7
9
CCDC entry no.
Cryst system
Space group
889198
Triclinic
P ꢀ1
889199
Triclinic
P ꢀ1
889197
Triclinic
P ꢀ1
889196
Triclinic
P ꢀ1
889200
Monoclinic
P21/c
14.625(1)
15.557(1)
20.488(2)
ꢀ
a, A
11.3969(5)
11.5122(5)
14.1471(6)
72.425(1)
73.549(1)
67.277(1)
1602.6(1)
C30H18NO11Os3P
1170.02
12.191(2)
13.746(2)
16.615(3)
66.871(2)
88.256(2)
63.791(2)
2262.5(7)
C48H36N2O10Os3P2
1433.33
11.344(1)
16.286(2)
19.029(2)
111.754(1)
98.109(1)
90.048(1)
3227.0(6)
C29H19ClNO10Os3P
1178.47
10.1087(7)
10.3833(7)
16.678(1)
73.747(1)
73.368(1)
80.865(1)
1604.4(2)
C29H18NO10Os3P$1/2CH2Cl2
1184.48
ꢀ
b, A
ꢀ
c, A
a
, deg
, deg
b
95.111(1)
g
, deg
3
ꢀ
V, A
4642.7(6)
C21H9O9Os3P
1006.85
Mol formula
Fw
Formula units per cell (Z)
2
2
4
2
8
Dcalcd (Mg/m3)
2.425
0.71073
11.973
2.104
0.71073
8.536
2.426
0.71073
11.971
2.452
0.71073
12.040
2.881
0.71073
16.499
ꢀ
l
m
(Mo K
a
), A
)
(mmꢀ1
Absorption correction
Semiempirical from
equivalents
0.4055/0.1857
14616
Semiempirical from
equivalents
0.7374/0.2553
27622
Semiempirical from
equivalents
0.4671/0.3073
39299
Semiempirical from
equivalents
0.4241/0.1969
18912
Semiempirical from
equivalents
0.4585/0.1983
46956
Abs corr factor
Total reflections
Independent reflections
Data/res/parameters
6971
6971/0/410
0.0223
0.0556
1.037
9958
9958/0/588
0.0159
0.0376
1.001
14177
14177/0/821
0.0345
0.0863
1.022
6993
6993/0/398
0.0238
0.0730
1.009
9890
9890/0/613
0.0231
0.0495
1.015
R1a [I ꢃ 2
s(I)]
wR2b (all data)
GOF on F2
Dr(max), Dr(min) (e/A )
3
ꢀ
1.228, ꢀ1.288
1.241/ꢀ0.842
2.823/ꢀ0.775
1.351/ꢀ1.507
2.813/ꢀ2.195
P
P
a
R1 ¼ jjFoj ꢀ jFcjj= jFoj0;
P
P
R1 ¼ f ½wðFo2 ꢀ Fc2Þ2ꢄ= ½wðFo2Þ2ꢄg1=2
b

28
C.-H. Lin et al. / Journal of Organometallic Chemistry 744 (2013) 24e34
Fig. 2. Thermal ellipsoid plot of the molecular structure of 5 at the 50% probability
ꢀ
level. Selected bond distances (A) and angles (deg) for the diffraction structure: Os(1)e
Os(3)
¼
2.9230(4), Os(1)eOs(2)
¼
2.9266(4), Os(2)eOs(3)
¼
2.8914(5), Os(2)e
P(2) ¼ 2.3454(7), Os(3)eP(1) ¼ 2.3473(7), P(2)eOs(2)eOs(3) ¼ 161.02(2), P(2)eOs(2)e
Os(1) ¼ 103.57(2), P(1)eOs(3)eOs(2) ¼ 164.24(2), P(1)eOs(3)eOs(1) ¼ 105.42(2).
Fig. 3. Thermal ellipsoid plot of the molecular structure of 6 at the 50% probability
ꢀ
level. Selected bond distances (A) and angles (deg) for the diffraction structure: Os(1)e
Os(2)
H(1) ¼ 1.79(9), Os(3)eH(1) ¼ 1.89(9), Os(1)eP(1) ¼ 2.363(2), Os(3)eCl(1) ¼ 2.472(2),
P(1)eOs(1)eOs(2) 167.44(4), P(1)eOs(1)eOs(3) 109.60(4), C(8)eOs(3)e
Cl(1) ¼ 174.7(2), C(9)eOs(3)eCl(1) ¼ 83.9(2), C(9)eOs(3)eOs(1) ¼ 115.5(2).
¼
2.8989(4), Os(1)eOs(3)
¼
3.0274(5), Os(2)eOs(3)
¼
2.8758(4), Os(1)e
specified standard. The natural charges and Wiberg indices were
computed using Weinhold’s natural bond orbital (NBO) program
[19,20]. The geometry-optimized structures presented here have
been drawn with the JIMP2 molecular visualization and manipu-
lation program [21].
¼
¼
spectral data reported for a diverse group of phosphine-substituted
Os3 clusters [23]. The 31P NMR spectrum recorded for 5 at room
temperature revealed the presence of three broad singlets, whose
integration confirmed the existence of a 1:1 mixture of stereoiso-
mers based on 5. This ratio remained unchanged when the 31P NMR
spectrum was recorded at 333 K. While specific 31P assignments
cannot be made based on these data, the two stereoisomers are
attributed to the 1,2-Os3(CO)10(PN)2 clusters, where the ancillary
PN ligands are attached to adjacent osmium centers at equatorial
sites that differ only by the PeOseOseP dihedral angle [24]. Leong
and Liu have observed this exact phenomenon in the case of 1,2-
Os3(CO)10(PPh3)2 [25].
3. Results and discussion
3.1. Reaction of Os3(CO)12 (1) with PN
Treatment of a CH2Cl2 solution containing equimolar amounts of
1 and PN with a measured excess of the oxidative-decarbonylation
reagent Me3NO [22] furnishes the PN-substituted clusters 4 and 5.
Both 4 and 5 were obtained as reaction products independent of the
stoichiometry of 1:Me3NO employed, and we had to settle on the
separation of the binary mixture in order to isolate pure samples of
each cluster. Repeating this reaction with an increased PN:1 ratio
led to the predictable gain in 5 at the expense of 4. Both PN-
substituted clusters were isolated by column chromatography
over silica gel and characterized in solution by IR and NMR spec-
troscopies. Eq. (2) summarizes this reaction that yields 4 and 5.
The crystal structures of 4 and 5 were established by X-ray
crystallography, and the solid-state structures for 4 and 5 are
shown in Figs. 1 and 2, respectively. Here the coordination of the
phosphorus group to the cluster, as opposed to the pyridyl moiety,
Os
Os
Os
PN + Me3NO
NP
(2)
Os
Os
Os
Os
Os
Os
RT
PN
PN
1
4
5
The pertinent spectral data for 4 and 5, as well as the other new
products, are reported in Table 1; the (CO) frequencies for the
terminal carbonyl groups and the NMR data are consistent with the
is confirmed in each case. The mean OseOs bond distance in 4
(2.8953 A) and 5 (2.914 A) fall within acceptable ranges found for
the OseOs distances in the other Os3(CO)12ꢀnPn clusters (where
ꢀ
ꢀ
y

C.-H. Lin et al. / Journal of Organometallic Chemistry 744 (2013) 24e34
29
Table 3
n ¼ 1, 2) [23,25,26]. To our knowledge 4 and 5 represent the first
structurally characterized metal clusters containing a coordinated
PN ligand(s) [27]. The remaining bond distances and angles in 4 and
5 are unremarkable and require no comment.
ꢀ
Selected X-ray diffraction and DFT bond distances (A) and angles (deg) in 7 (A1) and
9 (C1).
X-ray
DFT
7 (A1)
Bond distances
Os(1)eOs(2)
Os(1)eOs(3)
Os(2)eOs(3)
Os(3)eN(1)
3.2. Reaction of Os3(CO)11(MeCN) (2) with PN
2.8853(3)
2.8959(3)
2.9131(3)
2.291(4)
2.298(1)
2.9877
2.9920
3.0243
2.422
The reaction of the labile cluster 2 with PN was next examined.
Cluster 2 reacts rapidly with one equivalent of PN in CH2Cl2 at room
temperature, to afford cluster 4 as the major product (50%); accom-
panying the reaction are clusters 5 and 6 in 20 and 8% yields,
respectively. The 1H NMR spectrum of 6 shows the expected number
of resonances for the coordinated PN ligand, in addition to a high-field
Os(3)eP(1)
Bond angles
2.371
C(9)eOs(3)eC(10)
C(9)eOs(3)eN(1)
C(10)eOs(3)eN(1)
C(9)eOs(3)eP(1)
C(10)eOs(3)eP(1)
N(1)eOs(3)eP(1)
C(10)eOs(3)eOs(1)
N(1)eOs(3)eOs(1)
P(1)eOs(3)eOs(1)
N(1)eOs(3)eOs(2)
P(1)eOs(3)eOs(2)
9 (C1)
Bond distances
Os(1)/Os(2)
Os(1)eOs(3)
Os(2)eOs(3)
Os(1)eP(1)
Os(2)eP(1)
Os(3)eP(1)
Os(1)eC(10)
Os(1)/C(11)
Os(2)eC(15)
Os(3)eC(10)
C(10)eC(15)
C(10)eC(11)
85.9(2)
170.9(2)
87.3(2)
96.8(2)
100.7(2)
78.4(1)
107.3(2)
102.8(1)
152.00(3)
93.9(1)
87.5
170.3
87.5
96.3
102.0
76.5
103.7
102.5
154.28
95.8
doublet (1H) at
d
ꢀ16.11, which supports the presence of a bridging
hydride ligand. The structure of 6, which exists in the unit cell as two
independent molecules, was subsequently determined by X-ray
diffraction analysis. No significant differences exist between the two
structures, and the ORTEP plot of the molecular structure of one of the
two molecules of 6 is shownin Fig. 3, where the coordination of the PN
ligand, one terminal chloride, and a bridging hydride are confirmed.
The bridging hydride in each molecule of 6 was located during data
reduction and refined isotropically in the analysis. Assuming that the
chloride and hydride ligands both function as one-electron donors,
cluster 6 is best viewed as electron precise with an electron count of
48e. The PN and chloride ligands are situated at equatorial and axial
positions at the Os(1) and Os(3) atoms, respectively, while the hydride
ligand H(1) is of the edge-bridging variety, spanning the Os(1)eOs(3)
92.45(3)
94.80
3.9899(4)
2.7880(3)
2.9292(3)
2.339(1)
2.306(1)
2.420(1)
2.308(5)
2.922(5)
2.120(5)
2.182(5)
1.424(8)
1.427(7)
1.366(8)
1.385(8)
1.393(8)
1.389(8)
4.0683
2.8698
3.0283
2.379
2.359
2.477
2.371
3.056
2.150
2.240
1.440
1.431
1.391
1.402
1.399
1.405
ꢀ
vector. The OseOs bond distances range from 2.8758(4) A [Os(2)e
ꢀ
Os(3)] to 3.0274(5) A [Os(1)eOs(3)], with the longest of the three Ose
Os bond distances associated with the hydride-bridged metalemetal
bond [28].
In comparison to the numerous Os3 clusters that possess an edge-
bridging chloride ligand, the presence of a terminal chloride ligand
remains a rarity. Apart from 6, other structurally characterized tri-
C(11)eC(12)
C(12)eC(13)
C(13)eC(14)
C(14)eC(15)
osmium clusters having a terminal chloride ligand include H2Os3(h1
-
Bond angles
Cl)(CO)8[m3-C(4-methylquinol-8-yl)], HOs3(
h
1-Cl)(CO)10(CNPr), and
Os(1)eOs(3)eOs(2)
Os(1)eP(1)eOs(2)
P(1)eOs(2)eC(15)
P(1)eOs(3)eC(10)
P(1)eOs(1)eC(10)
Os(1)eC(10)eOs(3)
C(10)eC(15)eOs(2)
88.478(9)
118.42(6)
80.7(1)
77.5(1)
76.8(1)
87.180
118.33
81.9
77.5
77.0
H2Os3( -NH2) [29]. The presence of the terminal chloride
h
1-Cl)(CO)9(
m
ligand in 6 must derive from the CH2Cl2 solvent, and this was easily
verified by repeating the reaction with toluene as the solvent; use of
toluene gave only 4 and 5. The point at which CH2Cl2 undergoes
activation remains unclear, but pure samples of 4 and 5 kept under an
argon atmosphere show no evidence for reactionwith CH2Cl2. Finally,
the introductionof a chlorideligand(s)intothecoordinationsphereof
different clusters is known to occur in thermolysis and photolysis
reactions that have been conducted in the presence of a chlorinated
solvent [29c,30]. In some of these paradigms, a free-radical chain
process is unquestionably operative but it isunlikely the only route by
which the halide is incorporated into the final product.
76.7(2)
111.7(4)
76.9
113.6
situation; cluster 7 could be isolated free of accompanying by-
products using 4 as the starting reagent (vide infra). Finally, the
effect of doubling the concentration of PN to 3 was examined in
CH2Cl2, and here the amount of 5 increased but not that of 7.
Of further interest in this last reaction is the significant diminution
in the yields of 6 and HOs3(m-Cl)(CO)10, which was observed in
3.3. Synthesis of 7 and DFT evaluation of the bridged and chelated
trace amounts by TLC analysis. Clearly a complex relationship
exists between the initial concentrations of 3 and PN and the two
cluster products derived from the activation of the halogenated
solvent.
stereoisomers
The reaction between 3 and PN is rapid, and the product dis-
tribution is dependent on the reaction solvent and reagent stoi-
chiometry. Treatment of an equimolar mixture of reagents in
CH2Cl2 furnishes the PN-containing products 5 (25%), 6 (40%), and 7
The reaction between 3 and PN in toluene yields 5 and 7 as the
principal substitution products. Using a 1:1 reagent stoichiometry
gives 5 and 7 in 30 and 40% yields (TLC). The crude yield of 7 was
maximized at 60% when a 1:2 ratio of 3:PN was employed, and
multiple recrystallizations eventually furnished 7 in yields <20%.
We were able to synthesize 7 in higher yield from 4 and Me3NO, as
outlined in Eq. (3). This particular protocol furnished 7 with mini-
mal side-products and in yields >80% when 4 was treated with a
slight excess of Me3NO in toluene. Pure 7 could be obtained by
simply washing the crude product with multiple portions of hexane
or recrystallization from hexane/CH2Cl2.
(5%), in addition to the known cluster HOs3(m-Cl)(CO)10 (10%),
whose identity was established through TLC and spectroscopic
comparisons against an independently prepared sample of this
cluster [10a]. The yields of these products are estimates based on
TLC analysis of the crude mixture. Cluster 7 is unstable on common
chromatographic supports and attempts to isolate 7 by column
chromatography were met with extensive and unacceptable ma-
terial loss. Performing the chromatographic separation under an
inert atmosphere and at low temperature did not improve the

30
C.-H. Lin et al. / Journal of Organometallic Chemistry 744 (2013) 24e34
structure, as verified by a comparison of the selected bond dis-
tances and angles (experiment versus theory) in Table 3.
N
The stability of the chelated PN ligand in 7 relative to other
possible PN coordination modes was investigated computation-
ally by DFT [35]. Fig. 5 shows the energy ordering of several
different isomeric chelated and bridged clusters based on 7. The
dissimilar pnictogen atoms in PN lead to a greater number of
possible coordination modes for the PN ligand when regio- and
stereochemical aspects are considered relative to symmetrical
bidentate PP and NN ligands. Species A1 is the thermodynami-
cally most stable form of this cluster, a feature that reconciles
theory with the experimentally determined solid-state structure.
The equatorially bridged species A2 lies 6.6 kcal/mol higher in
enthalpy than A1, while the equatorially chelated species A3,
which represents a commonly observed coordination motif for
rigid diphosphines having a two-carbon backbone [5a,d], is
computed to be higher in enthalpy than A1 by 8.0 kcal/mol.
The effect of the PN coordination mode on the charge distribution
and bond indices in A1eA7 was explored by NBO analysis. Table 4
shows the natural charges and Wiberg indices for selected atoms
in the isomeric clusters. All of the osmium atoms exhibit a negative
charge and the pyridyl-substituted osmiums are the least electron
rich of the metal centers. The nitrogen atoms all carry a negative
charge and the charge density is relatively unaffected by the site of
coordination in the cluster. The phosphorus atoms all display a
positivecharge, with thecomputedcharges rangingfrom 1.37 to 1.24.
The clusters having an axial phosphine are expected to experience
less efficient overlap between the Os and P centers, which in turn
manifests itself in a lower positive charge on the pnictogen center as
opposed to their equatorial counterparts. The Wiberg bond indices,
which serve as a measure of bond strength, are more or less uniform
within the different bond groups. The computed indices for the Ose
Os, OseP, and OseN vectors are consistent with the accepted single-
bond designation for these groups.
PPh2
Os
Os
Os
Me3NO/RT
-CO2
Os
Os
Os
PN
4
7
(3)
7 was characterized in solution by IR and NMR spectroscopies. Of
note in the 1H NMR spectrum is the diastereotopic nature of the
methylene hydrogens associated with the 2-(diphenylphosphino)
methyl moiety. These hydrogens appear as separate resonances at
d
4.47 and d 5.21 and display doublet of doublets and triplet splitting
patterns, respectively. The coordination mode adopted by the PN
ligand in 7 was unequivocally established by X-ray diffraction anal-
ysis. Selected bond distances and angles are reported in Table 3, and
Fig. 4 (left-hand side) shows the thermal ellipsoid plot of the mo-
lecular structure of 7, where chelation of the PN ligand at axial (N)
and equatorial (P) sites at the Os(3) center is confirmed. As
mentioned earlier, 7 is the first structurally characterized metal
cluster that contains the compound PN as a bidentate ligand. The
axial versus equatorial coordination of the pyridyl moiety in 7 is in
keeping with the stereochemical preference of such ligands in tri-
metallic clusters [31]. The metallic core consists of a triangular array
of osmium atoms where the OseOs bond distances range from
ꢀ
ꢀ
2.8853(3) A [Os(1)eOs(2)] to 2.9131(3) A [Os(2)eOs(3)]. The Os(3)e
N(1) [2.291(4) A] and Os(3)eP(1) [2.298(1) A] bond distances are
consistent with those OseN(pyridyl) and OseP distances found in
ꢀ
ꢀ
the dpppy-substituted osmium clusters Os3(CO)10
(m-dpppy) [32],
H4Os4(CO)10 -dpppy) [33], and HOs3(CO)9( -PhPpy) [34]. The ten
(m
m
carbonyl groups are all linear in nature and do not exhibit any un-
usual distances and angles. The bonding in 7 was also explored by
DFT, and the geometry-optimized structure of A1 is displayed
alongside the X-ray diffraction structure of 7 in Fig. 4. The optimized
structure of A1 shows a good correspondence with the solid-state
3.4. Photochemical activation of 4 and 7 to give 8
Optical excitation of 4 or 7, using either near-UV of UV light,
leads to loss of CO and formation of the dihydride cluster 8 (Eq.
Fig. 4. Thermal ellipsoid plot of the molecular structure of 7 at the 50% probability level (left) and the optimized B3LYP structure of A1 (right).

C.-H. Lin et al. / Journal of Organometallic Chemistry 744 (2013) 24e34
31
Fig. 5. Ground-state enthalpy ordering of the isomeric clusters Os3(CO)10(PN). All enthalpy values are in kcal/mol relative to species A1.
(4)), whose origin derives from the double metalation of the 6-Me
group associated with the PN ligand. Photochemically promoted
CeH bond activation of chelated bidentate ligands in Os3 clusters
is common [36], and the mechanism responsible for CeH bond
activation of the methyl group in related nitrogen-based ligands
coordinated to Os3 clusters has been investigated [5,37]. That 4
undergoes an initial loss of CO, followed by chelation of the
we attribute to the low quantum efficiency for CO loss as opposed
to dynamics stemming from the activation of the CeH bonds. For
those reactions that were monitored by NMR spectroscopy, no
evidence was seen for the expected intermediate hydride
HOs3(CO)9[m-CH2(NC5H3)CH2PPh2], which once formed must un-
dergo rapid conversion to the dihydride. 8 was isolated by column
chromatography, and the 1H NMR spectrum revealed the pres-
pendant
k
1-PN ligand to give 7, was confirmed in those reactions
ence of a pair of high-field hydrides at
d
ꢀ14.31 and ꢀ13.14 and a
that were monitored by NMR spectroscopy. Loss of two additional
molecules of CO in 7 ultimately furnishes 8. Prolonged irradiation
is required to drive these reactions to completion, behavior that
benzylidene (CH) singlet at 5.49, all of which derive from the
d
original 6-Me group in 7. As found in 7, the methylene hydrogens
belonging to the 2-(diphenylphosphino)methyl moiety in 8 are
Table 4
Selected natural charges and Wiberg bond indices for the isomeric clusters Os3(CO)10(PN) (A1eA7).a
Os2
Os2
Os2
Os2
Os2
Os2
Os2
P
N
P
P
N
N
N
P
P
Os1
Os3
Os1
Os3
Os1
Os3
Os1
Os3
Os1
Os3
Os1
Os3
Os1
Os3
N
P
N
N
P
1,1-Nax,Peq
1,2-Neq,Peq
1,1-Neq,Peq
1,1-Neq,Pax
1,2-Nax,Pax
1,2-Nax,Peq
1,2-Neq,Pax
A1
A2
A3
A4
A5
A6
A7
Atomic charge
Os1
Os2
Os3
P
ꢀ1.39
ꢀ1.41
ꢀ0.94
1.33
ꢀ0.99
ꢀ1.31
ꢀ1.44
1.37
ꢀ1.37
ꢀ1.35
ꢀ1.04
1.37
ꢀ1.40
ꢀ1.34
ꢀ0.89
1.24
ꢀ0.72
ꢀ1.43
ꢀ1.43
1.31
ꢀ0.86
ꢀ1.38
ꢀ1.46
1.37
ꢀ0.97
ꢀ1.34
ꢀ1.35
1.29
N
ꢀ0.42
ꢀ0.39
ꢀ0.38
ꢀ0.40
ꢀ0.45
ꢀ0.43
ꢀ0.39
Wiberg index
Os1eOs2
Os1eOs3
Os2eOs3
OseP
0.43
0.48
0.46
0.76
0.40
0.53
0.44
0.45
0.80
0.43
0.42
0.41
0.51
0.81
0.45
0.41
0.42
0.53
0.68
0.42
0.49
0.37
0.41
0.74
0.23
0.44
0.50
0.45
0.80
0.32
0.55
0.44
0.40
0.74
0.43
OseN
a
Atom orientation and numbering scheme for the Os3 clusters depicted above. Only the Os, P, and N atoms and selected CO ligands are shown.

32
C.-H. Lin et al. / Journal of Organometallic Chemistry 744 (2013) 24e34
Table 5
diastereotopic, and they appear as two separate doublet of dou-
Selected natural charges and Wiberg bond indices for the clusters H2Os3(CO)8[m-
blets at
d
2.70 and 3.50.
CH(NC5H3)CH2PPh2] (B1) and Os3(CO)9(
m
-C6H4)(
m
-PPh) (C1).a
C4 C3
H
C2
C5
C6
C1
N
C1
N
N
Os1
Os3
H2
PPh2
Os
PPh2
H
Os3
Os
PPh2
H
B1
C1
H1
Os2
Os1
h
Os2
Os
Os
P
Os
Os
H
8
-2CO
Ph
7
(4)
B1
C1
We were able to obtain two preliminary X-ray diffraction
structures of 8 that confirmed the activation of the 6-Me group,
but the crystals were of poor quality and twinned. Attempts to
grow high quality crystals of 8 that were not twinned failed, and
the convergence values for those crystals that did furnish a
diffraction structure were unacceptably high (>13%) and accom-
panied by disordered solvent and phenyl groups. Accordingly, we
resorted to DFT calculations to establish the bonding of the PN
residue to the Os3 frame and the locus of the hydrides ligands in 8.
The geometry-optimized structure of the dihydride cluster B1 is
shown below. The hydrides bridge adjacent OseOs edges, with
one located in the plane of the metals and the other situated
below the metallic frame opposite the face-capping PN ligand. The
computed charges and Wiberg indices for B1 are summarized in
Table 5. These data are consistent with the computational results
reported by us for related phosphine-substituted Os3 clusters [38].
The double metalation found in the conversion of A1 / B1 þ CO
(2 equivs) is endergonic by 2.3 kcal/mol, and the principal driving
Atomic charge
Os1
Os2
Os3
P
N
C1
C6
H1
ꢀ1.21
ꢀ1.08
ꢀ1.19
1.33
ꢀ1.15
ꢀ1.30
ꢀ1.30
0.95
ꢀ0.41
ꢀ0.42
ꢀ0.21
ꢀ0.01
0.14
0.09
H2
Wiberg index
Os1eOs2
Os1eOs3
Os2eOs3
Os1eP
Os2eP
Os3eP
OseN
Os1eC1
Os3eC1
Os2eC6
C1eC6
C1eC2
C2eC3
C3eC4
C4eC5
C5eC6
Os1eH1
Os3eH1
Os1eH2
Os2eH2
0.24
0.29
0.49
0.04
0.40
0.34
0.85
0.88
0.63
0.75
0.50
0.69
0.69
0.43
0.61
0.75
1.25
1.26
1.47
1.39
1.43
1.41
force is the entropic release of the CO molecules. The computed DS
value is 68.8 eu, which translates to 34.4 eu per CO, and is in
excellent agreement with the ortho-metalation thermodynamics
computed for the conversion of HOs3(CO)8(
k m-SC6H4Me-
2-bcpd)(
4) to H2Os3(CO)7( -SC6H3Me-4) [38a].
k
2-bcpd)(
m
0.40
0.37
0.41
0.38
a
Atom orientation and numbering scheme for the Os3 clusters depicted above.
lower yields. The IR and NMR properties of 9 closely match those
spectroscopic data reported for Os3(CO)9(m-C6H4)(m-PR) (where
R ¼ Me, Et) [39,40]. Particularly diagnostic is the low-field 31P
resonance at
d 221.45, which signals the transformation of the
original phosphine moiety to a phosphinidene ligand.
N
PPh2
Os
Os
Os
heat
Os
Os
Os
-CO
3.5. Thermal decomposition of the PN ligand in 7 to give 9
P
7
9
Ph
Thermolysis of cluster 7 in toluene at 110 ꢁC furnishes 9 (Eq. (5)),
whose formation is accompanied by loss of the pyridyl moiety and
activation of the Ph2P group. Of all of the clusters reported here, 9 is
by far the most stable, and it was isolated by chromatography in
70% yield. Thermolysis of 4 in toluene affords 9, albeit in slightly
(5)
9 was structurally characterized by X-ray crystallography, and
Fig. 6 shows one of the two independent molecules of 9 found in

C.-H. Lin et al. / Journal of Organometallic Chemistry 744 (2013) 24e34
33
Fig. 6. Thermal ellipsoid plot of the molecular structure of 9 at the 50% probability level (left) and the optimized B3LYP structure of C1 (right).
the unit cell; the thermal ellipsoid plot of the molecular structure
confirms the activation of the PN ligand and the capping of the two
Os3 faces by benzyne and phenylphosphinidene moieties. 9 con-
tains 50e, assuming that the face-capping ligands each function as
component that arises from the overlap of the Os(1) and C(1) atoms
reveals a Wiberg index of 0.43. The overlap between the C(6) atom
and the Os(1) and Os(3) centers is negligible based on bond indices
of 0.06.
4e donors, and is structurally similar to Os3(CO)9(m-C6H4)(m-PR)
[39]. The dihedral angle formed by the planes defined by the
benzyne carbons and osmium metals is ca. 73ꢁ, and the organic
fragment is tipped toward the metallic plane in order to facilitate
4. Conclusions
The ability of 2-[(diphenylphosphino)methyl]-6-methylpyridine
(PN) to serve as a ligand in the osmium clusters based on
Os3(CO)12ꢀn(MeCN)n has been investigated. Bidentate coordination
of PN is demonstrated in the case of 7, whose X-raystructure reveals a
chelated PN ligand having axial pyridyl and equatorial phosphine
moieties. The energies of alternative stereoisomers based on 7 have
been computed by electronic structure calculations, and the solid-
state structure has been confirmed as the ground-state minimum.
7 is thermally and photochemically sensitive, and the decomposition
products 8 and 9 have been isolated and shown to derive from a
combinationofCeH andPeC bondcleavages. Thereaction ofPNwith
other metal clusters is under investigation, and our results will be
published in due course.
the transfer of
p electron density to Os(1) center. The Os(2)eC(15)
and Os(3)eC(10) vectors exhibit distances of 2.120(5) and 2.182(5)
ꢀ
A, bond lengths that are best reconciled as OseC
s bonds. The
ꢀ
longer Os(1)eC(10) bond distance [2.308(5) A] compares well to
that distance reported in the EtP- and MeP-capped clusters
Os3(CO)9(m-C6H4)(m-PR) [39]. The internuclear distance between
ꢀ
the Os(1) and Os(2) atoms is 3.9899(4) A and this exceeds the van
der Waals radii for the two osmium atoms, preventing any signif-
icant orbital overlap between these two metals [41]. The observed
bond distances and angles associated phosphinidene moiety and
the nine terminal carbonyl ligands are unremarkable and require
no comment.
The asymmetric coordination of the benzyne moiety to the
osmium atoms in Os3(CO)9(
discussion with respect to the
m
-C6H4)(
m
-PR) has been the subject of
contributions from the
Acknowledgments
s
and
p
organic fragment to the Os3 core [39,40]. On the basis of crystal-
lographic and VT NMR data, Deeming and coworkers have pre-
sented compelling evidence for a benzyne bonding model that
Financial support from the Robert A. Welch Foundation (Grant B-
1093-MGR) is greatly appreciated. NSF support of the NMR and
computational facilities at UNT through grants CHE-0840518
and CHE-0741936 is acknowledged. We wish to thank Prof.
Michael B. Hall (TAMU) for providing us a copy of his JIMP2 program,
which was used to prepare the geometry-optimized structures re-
ported here.
involves one
is best viewed as originating from a benzyne molecular orbital of
suitable symmetry with the wingtip osmium that is not -bound
p and two s components [39b]. The former interaction
p
s
to the C6H4 ring. In order to better address this bonding conundrum
in 9, we have performed DFT calculations on 9 and have computed
the atomic charges and Wiberg indices. The B3LYP-optimized
structure of C1 is shown alongside the structure of 9 in Fig. 6.
Good visual agreement exists between the pair of structures in the
Figure, and the bond distances and angles in Table 3 track reason-
ably well. The Wiberg indices computed for C1 reinforce the
Appendix A. Supplementary material
CCDC 889198, 889199, 889197, 889196, and 889200 contain the
supplementary crystallographic data for this paper. These data may
be obtained free of charge from The Cambridge Crystallographic Data
Centre via http://www.ccdc.cam.ac.uk/data_request/cif. Atomic co-
ordinates of the DFT data reported here are available from MGR upon
request.
bonding model advocated by Deeming. The stronger OseC
are assigned to the Os(3)eC(1) and Os(2)eC(6) vectors, which
display a bond index of 0.61 and 0.75, respectively. The weaker
s bonds
p

34
C.-H. Lin et al. / Journal of Organometallic Chemistry 744 (2013) 24e34
[23] (a) M.I. Bruce, M.J. Liddell, C.A. Hughes, B.W. Skelton, A.H. White,
References
J. Organomet. Chem. 347 (1988) 157;
(b) V.M. Hansen, A.K. Ma, K. Biradha, R.K. Pomeroy, M.J. Zaworotko, Organo-
metallics 17 (1998) 5267;
(c) K. Biradha, V.M. Hansen, W.K. Leong, R.K. Pomeroy, M.J. Zaworotko,
J. Cluster Sci. 11 (2000) 285.
[1] (a) K.N. Gavrilov, A.I. Polosukhin, Russ. Chem. Rev. 69 (2000) 661;
(b) G. Müller, M. Klinga, P. Osswald, M. Leskelä, B. Rieger, Z. Naturforsch. 57b
(2002) 803;
(c) A. Kermagoret, F. Tomicki, P. Braunstein, Dalton Trans. (2008) 2945;
(d) S. Maggini, Coord. Chem. Rev. 253 (2009) 1793;
(e) L. Fanfoni, A. Meduri, E. Zangrando, S. Castillon, F. Felluga, B. Milani,
Molecules 16 (2011) 1804.(f) P. Nareddy, L. Mantilli, L. Guénée, C. Mazet,
Angew. Chem. Int. Ed. 51 (2012) 3826.
[24] Of the three stereoisomeric possibilities for diequatorial-substituted
1,2-Os3(CO)10P2 clusters, DFT calculations (unpublished work) confirm that
the below species represent the two most stable conformations for the
disposition of the monodentate phosphine ligands about the cluster
polyhedron:
[2] (a) J.P. Farr, M.M. Olmstead, A.L. Balch, J. Am. Chem. Soc. 102 (1980) 6654;
(b) K. Kurtev, D. Ribola, R.A. Jones, D.J. Cole-Hamilton, G. Wilkinson, Dalton
Trans. (1980) 55;
Os
Os
(c) Z.-Z. Zhang, H. Cheng, S.-M. Kuang, Y.-Q. Zhou, Z.-X. Liu, J.-K. Zhang, H.-
G. Wang, J. Organomet. Chem. 516 (1996) 1.(d) R. Gobetto, C.G. Arena,
D. Drommi, F. Farone, Inorg. Chim. Acta 248 (1996) 257;
(e) Z.Z. Zhang, H. Cheng, Coord. Chem. Rev. 147 (1996) 1;
(f) A.J. Deeming, M.B. Smith, Dalton Trans. (1993) 3383.
P
P
P
Os
Os
Os
Os
[3] For a report on a Ru2 compound that contains a chelating dpppy ligand, see:
Y. Yamamoto, Y. Miyabe, K. Itoh, Eur. J. Inorg. Chem. (2004) 3651.
[4] (a) W.J. Knebel, R.J. Angelici, Inorg. Chim. Acta 7 (1973) 713;
(b) W.J. Knebel, R.J. Angelici, Inorg. Chem. 13 (1974) 632;
(c) M. Alvarez, N. Lugan, R. Mathieu, Dalton Trans. (1994) 2755;
(d) H.-F. Lang, P.E. Fanwick, R.A. Walton, Inorg. Chim. Acta 328 (2002) 232;
(e) F. Hung-Low, K.K. Klausmeyer, Inorg. Chim. Acta 361 (2008) 1298.
[5] (a) W.H. Watson, G. Wu, M.G. Richmond, Organometallics 24 (2005) 5431, 25
(2006) 903;
P
[25] W.K. Leong, Y. Liu, J. Organomet. Chem. 584 (1999) 174.
[26] M.I. Bruce, M.J. Lindell, C.A. Hughes, J.M. Patrick, B.W. Skelton, A.H. White,
J. Organomet. Chem. 347 (1988) 181.
[27] A recent check of the Cambridge Structural Database, CSD version 5.33 shows
no polynuclear examples with PN as an ancillary ligand.
[28] For discussions on the hydride-induced lengthening of metal-metal bonds in
polynuclear clusters, see: (a) D.M.P. Mingos, D.J. Wales, Introduction to Cluster
Chemistry, Prentice Hall, Englewood Cliffs, NJ, 1990;
(b) R.G. Teller, R. Bau, Struct. Bonding (Berlin) 41 (1981) 1.
[29] (a) M.I. Hyder, S.E. Kabir, M.A. Miah, M.A. Mottalib, K.M.A. Malik, J. Bangladesh
Acad. Sci. 27 (2003) 175;
(b) B. Poola, C.J. Carrano, M.G. Richmond, Organometallics 27 (2008) 3018;
(c) C.J. Carrano, X. Wang, B. Poola, C.B. Powell, M.G. Richmond, J. Chem.
Crystallogr. 39 (2009) 820;
(d) X. Zhang, S. Kandala, L. Yang, W.H. Watson, X. Wang, D.A. Hrovat,
W.T. Borden, M.G. Richmond, Organometallics 30 (2011) 1253.
[6] (a) H. Yang, M. Alvarez-Gressier, N. Lugan, R. Mathieu, Organometallics 16
(1997) 1401;
(b) M.-L. Chung, F.-Y. Lee, L.-C. Lin, C.-J. Su, M.-Y. Chen, Y.-S. Wen, H.-M. Gau,
K.-L. Lu, J. Cluster Sci. 9 (1998) 445;
(c) Y. Li, W.-T. Wong, Z.-Y. Lin, Organometallics 22 (2003) 1029.
[30] For some reports on this particular phenomenon, see: (a) S.E. Kabir,
M.A. Rahman, M.N. Uddin, N. Begum, Indian J. Chem. 47A (2008) 657;
(b) W.H. Watson, S.-H. Huang, M.G. Richmond, J. Chem. Crystallogr. 37
(2007) 479;
(b) H. Yang, N. Lugan, R. Mathieu, Organometallics 16 (1997) 2089;
(c) E. Mothes, S. Sentets, M.A. Luquin, R. Mathieu, N. Lugan, G. Lavigne, Or-
ganometallics 27 (2008) 1193.
[7] S.R. Drake, P.A. Loveday, Inorg. Synth. 28 (1990) 230.
[8] J.N. Nicholls, M.D. Vargas, Inorg. Synth. 26 (1989) 289.
[9] D.F. Shriver, The Manipulation of Air-sensitive Compounds, McGraw-Hill,
New York, 1969.
[10] (a) A.J. Deeming, S. Hasso, J. Organomet. Chem. 114 (1976) 313;
(b) M.R. Churchill, R.A. Lashewycz, Inorg. Chem. 18 (1979) 1926.
[11] Bruker APEX2, Bruker Advanced Analytical X-ray Systems, Inc. Copyright
2007, Madison, WI.
(c) W.H. Watson, B. Poola, M.G. Richmond, J. Organomet. Chem. 691 (2006)
5567;
(d) C.E. Cooke, M.C. Jennings, M.J. Katz, R.K. Pomeroy, J.A.C. Clyburne, Or-
ganometallics 27 (2008) 5777;
(e) S.H. Huang, W.H. Watson, C.J. Carrano, X. Wang, M.G. Richmond, Or-
ganometallics 29 (2010) 61.
[31] N. Lugan, G. Lavigne, J.-J. Bonnet, Inorg. Chem. 26 (1987) 585 (and references
therein).
[12] Bruker Saint, Bruker Advanced Analytical X-ray Systems, Inc. Copyright 2007,
Madison, WI.
[32] A.J. Deeming, M.B. Smith, Chem. Commun. (1993) 844.
[33] Y.-Y. Choi, W.-T. Wong, J. Organomet. Chem. 573 (1999) 189.
[34] V.I. Ponomarenko, T.S. Pilyugina, V.D. Khripun, E.V. Grachova, S.P. Tunik,
M. Haukka, T.A. Pakkanen, J. Organomet. Chem. 691 (2006) 111.
[35] We have only considered those coordination modes for the PN ligand deemed
geometrically reasonable. For example, we did not investigate the diaxial
coordination of PN at a single metal and the trans diaxial bridging of adjacent
metal centers.
[36] S. Kandala, L. Yang, C.F. Campana, V. Nesterov, X. Wang, M.G. Richmond,
Polyhedron 29 (2010) 2814 (and references therein).
[37] (a) J.A. Cabeza, I. da Silva, I. Río, L. Martínez-Méndez, D. Miguel, V.I. Riera,
Angew. Chem. Int. Ed. 43 (2004) 3464;
(b) J.A. Cabeza, I. Río, L. Martínez-Méndez, D. Miguel, Chem. Eur. J. 12 (2006)
1529;
(c) J.A. Cabeza, M. Damonte, P. García-Álvarez, Organometallics 30 (2011) 2371.
[38] (a) L. Yang, V.N. Nesterov, X. Wang, M.G. Richmond, J. Cluster Sci. 23
(2012) 685;
[13] Bruker SADABS, Bruker Advanced Analytical X-ray Systems, Inc. Copyright
2007, Madison, WI.
[14] A.L. Spek, PLATON e a Multipurpose Crystallographic Tool, Utrecht University,
Utrecht, The Netherlands, 2006.
[15] G.M. Sheldrick, SHELXTL, Bruker Advanced Analytical X-ray Systems, Inc.
Copyright 2008, Madison, WI
[16] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,
G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato,
X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, M. Hada,
M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, T. Vreven, J.A. Montgomery Jr., J.E. Peralta, F. Ogliaro,
M. Bearpark, J.J. Heyd, E. Brothers, K.N. Kudin, V.N. Staroverov, R. Kobayashi,
J. Normand, K. Raghavachari, A. Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi,
M. Cossi, N. Rega, J.M. Millam, M. Klene, J.E. Knox, J.B. Cross, V. Bakken, C. Adamo,
J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi,
C. Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth,
P. Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, O. Farkas, J.B. Foresman,
J.V. Ortiz, J. Cioslowski, D.J. Fox, Gaussian 09, Revision A.02, Gaussian, Inc,
Wallingford CT, 2009.
(b) S. Ghosh, G. Hogarth, S.E. Kabir, A.K. Raha, M.G. Richmond, J.C. Sarker,
J. Cluster Sci. 23 (2012) 781;
(c) D.A. Hrovat, E. Nordlander, M.G. Richmond, Organometallics 31 (2012)
6608.
[17] A.D. Becke, J. Chem. Phys. 98 (1993) 5648.
[18] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785.
[19] A.E. Reed, L.A. Curtiss, F. Weinhold, Chem. Rev. 88 (1988) 899.
[20] K.B. Wiberg, Tetrahedron 24 (1968) 1083.
[21] (a) JIMP2, version 0.091, a free program for the visualization and manipula-
tion of molecules: M.B. Hall, R.F. Fenske Inorg. Chem. 11 (1972) 768;
(b) J. Manson, C.E. Webster, M.B. Hall, Texas A&M University, College Station,
TX, 2006: http://www.chem.tamu.edu/jimp2/index.html.
[22] (a) U. Koelle, J. Organomet. Chem. 133 (1977) 53;
[39] (a) S.C. Brown, J. Evans, L.E. Smart, Chem. Commun. (1980) 1021;
(b) A.J. Deeming, J.E. Marshall, D. Nuel, G. O’Brien, N.I. Powell, J. Organomet.
Chem. 384 (1990) 347.
[40] For related Os3 clusters containing an asymmetrically bound benzyne moiety,
see: (a) B.F.G. Johnson, J. Lewis, A.D. Massey, D. Braga, F. Grepioni,
J. Organomet. Chem. 369 (1989) C43;
(b) W.R. Cullen, S.J. Rettig, T.-C. Zheng, Organometallics 11 (1992) 928.
[41] A. Bondi, J. Phys. Chem. 68 (1964) 441.
(b) M.O. Albers, N.J. Coville, Coord. Chem. Rev. 53 (1984) 227.