Synthesis of [{Os3(CO)10(Μ2-H)}2{Μ2,Μ2-NC6H4C6H4N}] and [{Os3(CO)9(Μ2-H)PPh3}2{Μ2,Μ2-NC6H4C6H4N}]: Carbon-carbon bond formation promoted by organorhodium species

Article abstract of DOI:10.1016/j.ica.2005.12.046

Synthesis and characterization of linked cluster [{Os₃(CO)₁₀(μ₂-H)}₂{μ ₂,μ₂-NC₆H₄C₆H₄N}] (1) from the reaction of [Os₃Rh(μ-H)₃(CO)₁₂] with aniline in the presence of an excess amount of 4-vinyl phenol in refluxing heptane is reported. A similar reaction with [Os₃(CO)₁₀(NCMe)₂] as starting material gave a known compound, [Os₃(CO)₁₀(μ₂-H)(μ₂-HN C₆H₅)] (2). The treatment of complexes 1 and 2 with Wilkinson's catalyst in refluxing heptane respectively, yielded [{Os₃(CO)₉(μ₂-H)PPh₃}₂{μ₂,μ₂-NC₆H₄C ₆H₄N}] (3). An interesting and unexpected C-C coupling of phenyl-amido ligands was observed in complexes 1 and 3, which is believed to be catalysed by the organometallic rhodium species. The newly synthesized compounds 1 and 3 were fully characterized by IR, ¹H NMR spectroscopy, mass spectroscopy, elemental analysis, and X-ray crystallography. Both structures 1 and 3 comprise two triangles of osmium atoms. The two triangular osmium metal cores are linked by a bi-amido ligand via the two nitrogen atoms N(1) and N(1)* and N(1) and N(2), at their equatorial sites. The electronic absorption spectra of complexes 1, 2, and 3 display both low energy absorption, dπ (Os) → π* (amido) metal-to-ligand charge-transfer (MLCT) transition, and π → π* intra-ligand electronic transitions of the amido and bi-amido ligands.

Full text of DOI:10.1016/j.ica.2005.12.046

Inorganica Chimica Acta 359 (2006) 3632–3638
www.elsevier.com/locate/ica
Synthesis of [{Os3(CO)10(l2-H)}2{l2,l2-NC6H4C6H4N}]
and [{Os3(CO)9(l2-H)PPh3}2{l2,l2-NC6H4C6H4N}]:
Carbon–carbon bond formation promoted by organorhodium species
*
Jasmine Po-Kwan Lau, Wing-Tak Wong
Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, China
Received 31 October 2005; received in revised form 1 December 2005; accepted 1 December 2005
Available online 17 February 2006
Dedicated to D.M.P. Mingos.
Abstract
Synthesis and characterization of linked cluster [{Os3(CO)10(l2-H)}2{l2,l2-NC6H4C6H4N}] (1) from the reaction of [Os3Rh(l-
H)3(CO)12] with aniline in the presence of an excess amount of 4-vinyl phenol in refluxing heptane is reported. A similar reaction with
[Os3(CO)10(NCMe)2] as starting material gave a known compound, [Os3(CO)10(l2-H)(l2-HNC6H5)] (2). The treatment of complexes 1
and 2 with Wilkinson’s catalyst in refluxing heptane respectively, yielded [{Os3(CO)9(l2-H)PPh3}2{l2,l2-NC6H4C6H4N}] (3). An inter-
esting and unexpected C–C coupling of phenyl-amido ligands was observed in complexes 1 and 3, which is believed to be catalysed by the
organometallic rhodium species. The newly synthesized compounds 1 and 3 were fully characterized by IR, 1H NMR spectroscopy, mass
spectroscopy, elemental analysis, and X-ray crystallography. Both structures 1 and 3 comprise two triangles of osmium atoms. The two
triangular osmium metal cores are linked by a bi-amido ligand via the two nitrogen atoms N(1) and N(1)* and N(1) and N(2), at their
equatorial sites. The electronic absorption spectra of complexes 1, 2, and 3 display both low energy absorption, dp (Os) ! p* (amido)
metal-to-ligand charge-transfer (MLCT) transition, and p ! p* intra-ligand electronic transitions of the amido and bi-amido ligands.
Ó 2005 Elsevier B.V. All rights reserved.
Keywords: Carbon–carbon bond formation; Rhodium compound; Osmium cluster; X-ray crystal structures
1. Introduction
workers reported the carbon-centered coupling of two
propadiene molecules with a ruthenium complex resulted
into ½Cpꢀ2Ru2ðg3 : g3-C6H8ÞCl4ꢁ [4]. Other studies have
revealed that the C–C coupling of arenes by cationic Pt(II)
complexes into biaryls is also possible. The Pt–biaryl com-
plexes can then be oxidatively cleaved to generate free biar-
yls, which offers a new perspective for the synthesis of
organic compounds [1]. In addition to these organometallic
complexes, a great deal of work has also been devoted to
the use of the rhodium complexes [5–7]. The C–C coupling
reaction of olefins and diphenyldiazomethane catalysed by
cationic rhodium(I) complexes has been previously
reported by Werner and co-workers [8].
The chemistry of the transition-metal-catalysed coupling
of various reagents to generate new carbon–carbon bonds
is currently a field of great interest [1–3]. Organometallic
compounds may be regarded as model compounds for
intermediates in the catalytic processes. Over the years,
new C–C bond formations that are derived from different
organic ligands catalysed by a wide range of transition
metal complexes have been reported. Organoruthenium,
iron, and platinum are good candidates for the promotion
of the carbon–carbon bond formation. Girolami and co-
In the context of our studies on the reaction of
[Os3Rh(l-H)3(CO)12] with aniline, we have been able to
isolate a linked bis-triosmium metal clusters in which the
*
Corresponding author. Fax: +852 25472933/28571586.
E-mail address: wtwong@hkucc.hku.hk (W.-T. Wong).
0020-1693/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2005.12.046

J.Po-Kwan Lau, W.-T. Wong / Inorganica Chimica Acta 359 (2006) 3632–3638
3633
metal triangles are bridged by a biphenyl-amido ligand
[{Os3(CO)10(l2-H)}2{l2,l2-NC6H4C6H4N}] (1). To our
knowledge, biphenyl-amido containing cluster complex is
very rare. Gunnoe reported an aryl-coupled binuclear
compound by the oxidation of the Ru(II) amido complexes
gen atmosphere for 2 h. The solution gradually turned
from yellow to yellow brown with some brown oily prod-
uct. The solution was then filtered and the volume was
reduced to 5 cm3 in vacuo. Purification was accomplished
by TLC using hexane–CH2Cl2 (3:1 v/v) as an eluent to
yield complex 1 as a major purple red compound in a
43% yield (75.35 mg, 0.04 mmol). Two other uncharacter-
ized yellow bands in very low yields were observed. Ele-
mental Anal. Calc. for C32H10N2O20Os6: C, 20.40; H,
0.54; N, 1.49. Found: C, 20.55; H, 0.60, N, 1.50%. The
IR spectrum was [m(CO), cmꢃ1, CH2Cl2]: 2110vs, 2077vs,
2054s, 2033w, 2014 br. MS (FAB +ve) m/z: 1883 [M]+,
TpRuL2(NHPh),
(Tp = Hydridotris(pyrazolylborate);
L = CO, PMe3, or P(OMe)3) [9]. Herein, we report the syn-
thesis of [{Os3(CO)10(l2-H)}2{l2,l2-NC6H4C6H4N}] (1)
and [Os3(CO)10(l2-H)(l2-HNC6H5)] (2) from the reaction
of [Os3Rh(l-H)3(CO)12] and [Os3(CO)10(NCMe)2] with
aniline respectively, and the reactivity of both complexes
1 and 2 with Wilkinson’s catalyst. Studies on the cleavage
of the Os-bi-phenyl amido complexes to generate free
biphenyl diamine are underway.
1
observed 914 [M/2ꢃCO]+. The H NMR study at 298 K
comprised two sets of signals 1a and 1b at a ratio of
approximately 2:1 and showed the presence of two isomers,
1a: d 7.92 (m, 4H, aryl H), d 7.54 (m, 4H, aryl H), d ꢃ19.65
(s, 2H, Os–H) 1b: d 7.44 (m, 4H, aryl H), d 6.71 (m, 4H,
aryl H), d ꢃ10.41 (s, 2H, Os–H). Single crystals of 1 that
were suitable for X-ray studies were obtained by the gas-
phase diffusion of hexane into CH2Cl2 solution.
2. Experimental
2.1. General procedures
All of the reactions and manipulations were carried out
under nitrogen using Schlenk techniques unless otherwise
stated. The glassware was pre-dried in an oven (ꢂ120 °C)
before use. The reactions were monitored by both IR spec-
troscopy and analytical thin-layer chromatography (Merck
Kieselgel 60 F254), and the products were separated by
thin-layer chromatography on plates that are coated with
silica (Merck Kieselgel 60 F254). Dichloromethane (Ajax,
AR) was distilled over calcium hydride. n-Hexane (Ajax,
AR) was purified by distillation in the presence of
sodium-benzophenone. All of the other solvents were of
analytical grade and were freed from oxygen by degassing
and saturating with nitrogen atmosphere before use.
The starting materials [Os3Rh(l-H)3(CO)12] [10], [Os3(l-
2.1.2. Synthesis of [Os3(CO)10(l2-H)(l2-HNC6H5)] (2)
To
a
solution of [Os3(CO)10(NCMe)2] (100 mg,
0.11 mmol) in heptane (50 ml), one equivalent of aniline
(10.2 mg, 0.11 mmol) was added. The yellow solution was
allowed to heat under reflux for 2 h until the reaction mix-
ture changed gradually to brown. The solvent was then
removed in vacuo and redissolved in CH2Cl2 (3 cm3). Puri-
fication by TLC using n-hexane–CH2Cl2 (3:1 v/v) as an elu-
ent gave a lilac compound 2 in a 40% yield (41.45 mg,
0.04 mmol) together with two uncharacterized light purple
bands. Elemental Anal. Calc. for C16H6NO10Os3: C, 20.38;
H, 0.64; N, 1.49. Found: C, 20.45; H, 0.66; N, 1.50%. The
IR spectrum was [m(CO), cmꢃ1, CH2Cl2]: 2113vs, 2074vs,
2062vs, 2026vs, 2012vs, 1981m. MS (FAB +ve) m/z: 943
[M]+; observed: 915 [MꢃCO]+. The 1H NMR study at
298 K, d 7.46 (t, 2H, aryl H), d 6.97 (s, 1H, aryl H), d
6.71 (d, 2H, aryl H), 3.43 (s, 1H, NH), d ꢃ10.47 (s, 1H,
Os–H). No single crystals of 2 that were suitable for X-
ray studies were obtained.
H)2(CO)10]
[11],
[Os3(CO)10(NCMe)2]
[12],
and
[{Rh(CO)2Cl}2] [13] were prepared according to literature
procedures. All of the chemicals, unless otherwise stated,
were purchased commercially and used as received. Infra-
red spectra were recorded on a Bio-Rad FTS-165 IR spec-
1
trometer, using 0.5 mm CaF2 solution cells. H NMR was
obtained on a Bruker DPX400 spectrometer using CD2Cl2
and referenced to SiMe4 (d = 0). Positive ionization fast
atom bombardment (FAB) mass spectra were recorded
on a Finnigan MAT 95 mass spectrometer, using 3-nitrob-
enzyl alcohol as the matrix solvent. GC–MS spectra were
obtained on a GCD series II gas chromatograph electron
ionization detector. UV–Vis electronic absorption spectra
were obtained from a microprocessor-controlled HP
8450P array spectrophotometer using a quartz cell with a
path length of 1 cm. Elemental analyses were performed
by the Department of Chemistry, City University of Hong
Kong.
2.1.3. Synthesis of [{Os3(CO)9(l2-H)PPh3}2{l2,l2-
NC6H4C6H4N}] (3)
Both compounds 1 (100 mg, 0.05 mmol) and 2 (100 mg,
0.11 mmol) with an excess amount of Wilkinson’s catalyst
respectively, were stirred overnight in refluxing heptane
(50 cm3) for 24 h. Both the solutions turned from orange
red to light brown. The solvent was then removed in vacuo
to give a brown solid material, which was redissolved in 2–
3 cm3 of dichloromethane. The residue was chromato-
graphed on TLC using n-hexane–CH2Cl2 (3:1 v/v) as an
eluent to give a blue complex 3 as the major product.
The reaction of both compounds 1 and 2 yielded 40% of
complex 3, that is (48.2 mg, 0.02 mmol) and (96.4 mg,
0.04 mmol), respectively. Elemental Anal. Calc. for
C68H40N2Os6O18P2: C, 34.37; H, 1.70; N, 1.18. Found: C,
34.50, H, 1.65; N, 1.20%. The IR spectrum was [m(CO),
2.1.1. Synthesis of [{Os3(CO)10(l2-H)}2{l2,l2-
NC6H4C6H4N}] (1)
[Os3Rh(l-H)3(CO)12] (100 mg, 0.10 mmol) and aniline
(9.2 mg, 0.10 mmol) with an excess amount of 4-vinylphe-
nol were stirred in refluxing heptane (50 cm3) under a nitro-

3634
J.Po-Kwan Lau, W.-T. Wong / Inorganica Chimica Acta 359 (2006) 3632–3638
cmꢃ1, CH2Cl2]: 2083s, 2048s, 2006vs. MS (FAB +ve) m/z:
2409 [M]+; observed: 2353 [Mꢃ2CO]+. The 1H NMR
study at 298 K comprised two sets of signals 3a and 3b at
a ratio of approximately 1:1, and showed the presence of
two isomers in the range of d 6.45–7.60 (m, 16H, aryl H),
d 7.20–7.45 (m, 60H, PPh3), and d ꢃ14.05 to ꢃ14.15 (m,
4H, Os–H). Single crystals of 3 that were suitable for X-
ray studies were obtained by the vapour diffusion of octane
into CH2Cl2 solution.
sonable chemical structure was found. Therefore, no
modeling was made for the residue electron density
observed. The calculations were performed on a Silicon
Graphics computer using teXsan [16] crystallographic
software package.
3. Results and discussion
Treatment of [Os3Rh(l-H)3(CO)12] with 1 equivalent of
aniline in the presence of an excess amount of 4-vinylphe-
nol in heptane (50 cm3) under reflux for 2 h yielded a
purple red product [{Os3(CO)10(l2-H)}2{l2,l2-NC6H4C6-
H4N}] (1) in a 43% yield and two other uncharacterized
yellow bands in very low yields upon TLC separation on
silica, see Scheme 1. The IR spectra of cluster 1 gave peaks
in the range of 2014–2110 cmꢃ1, which indicates the pres-
2.1.4. Crystallography
All pertinent crystallographic data and other experi-
mental details are summarized in Table 5. Crystals suit-
able for X-ray analyses were glued on glass fibres with
epoxy resin or sealed in a 0.3 mm glass capillary. Inten-
sity data were collected at an ambient temperature on
a Bruker AXS SMART CCD diffractometer equipped
with graphite-monochromated Mo Ka radiation (k =
1
ence of terminal bonded carbonyl ligands only. The H
NMR spectrum of compound 1 in CD2Cl2 at room temper-
ature comprises two sets of signals at a relative ratio of 2:1
in the aromatic and hydride regions where the two sets of
signals have a similar coupling pattern, which indicates
that two isomers are present in solution. The presence of
the isomers may be due to the hindered rotation about
the C–C bond that links the two tri-osmium cluster units,
˚
0.71073 A). All structures were solved by direct methods
(SHELX97) [14] and expanded by Fourier-difference
technique (DIRDIF99) [15]. All metal atoms were aniso-
tropically refined in 1, and the rest were refined isotrop-
ically. All metal, nitrogen and phosphorous atoms with
some carbon atoms were refined anisotropically in 3,
except C(8) and the carbon atoms of the bi-amido phe-
nyl ligands were refined isotropically. The hydrogen
atoms were generated in their ideal position and were
included in the structure factor calculations using the rid-
ing mode, but were not refined for all of the structures.
The metal-hydrido atoms were placed in their ideal posi-
tion, but were not refined. Due to the highly disordered
nature of the solvent molecule in compound 3, the car-
bon and hydrogen atoms of the octane molecule were
only refined with their xyz position, and a long C–C
bond distance and a bad angle were observed. Some res-
idue peaks in the final differences Fourier map were also
observed in 3, which may be due to the presence of
another highly disorder solvent moiety, several attempts
were made to model the solvent molecule, but an unrea-
1
see Scheme 2. The H NMR spectra at 298 K of both of
the isomers consists of two aromatic signals, 1a: d 7.92, d
7.54; 1b: d 7.44, d 6.71, and one hydride signal, 1a: d
ꢃ19.65 and 1b: d ꢃ10.41, which confirms the presence of
the biphenyl-amido ligand and the metal hydride. The posi-
tive FAB mass spectrum of 1 exhibits an envelope that is
centered at m/z = 914, which suggests the cleavage of the
bi-amido ligand at the C–C bond, leading to the formation
of 2 {Os3(CO)10(l2-H)(l2-NC6H4)} units with a stepwise
loss of carbonyl ligands (see Table 1). To establish the
molecular structure of 1, an X-ray analysis was carried
out on a purple red crystal that was obtained by the slow
evaporation of n-hexane into CH2Cl2 solution below
ꢃ5 °C over a period of a few days. The structure is shown
in Fig. 1, together with the atomic labeling scheme, selected
Os
Os
(i)
Os
H
H
Os
[Os3Rh(μ-H)3(CO)12
]
N
N
Os
Os
1
Os
PPh3
H
Os
(iii)
Os
H
N
N
Os
Os
PPh3
Os
HN
Os
(ii)
Os
H
[Os3(CO)10(NCMe)2]
Os
3
2
Scheme 1. Reagent and conditions: (i) aniline, 4-vinylphenol, heptane, reflux; (ii) aniline, heptane, reflux; (iii) Wilkinson’s catalyst, heptane, reflux.

J.Po-Kwan Lau, W.-T. Wong / Inorganica Chimica Acta 359 (2006) 3632–3638
3635
Table 2
Selected bond distances (A) and angles (°) for cluster 1
˚
Os
Os
Os
Os
Os(1)–Os(2)
2.846(3)
2.07(3)
2.06(4)
1.45(6)
1.36(6)
1.47(5)
1.36(6)
60.41(6)
60.43(6)
Os(1)–Os(3)
Os(2)–Os(3)
N(1)–C(11)
C(11)–C(16)
C(13)–C(14)
C(14)–C(15)
2.810(2)
2.846(3)
1.26(5)
1.45(6)
1.45(6)
1.37(1)
Os(1)–N(1)
Os(3)–N(1)
C(11)–C(12)
C(12)–C(13)
C(14)–C(15)
C(15)–C(16)
Os(2)–Os(1)–Os(3)
Os(2)–Os(3)–Os(1)
N
H
N
H
Os
Os
1a
Os(3)–Os(2)–Os(1)
Os(3)–N(1)–Os(1)
59.16(6)
85(1)
˚
N–C bond lies between 1.29(3) and 1.38(5) A. Within the
molecule, N(1), C(11), C(12), C(13), C(14), C(15), and
C(16) form a plane that is almost perpendicular to the
osmium triangle of Os(1), Os(2), and Os(3) with a dihedral
angle of 68.13°. The hydride ligand was not located directly
in the analysis, but the bending of the equatorial carbonyl
groups C(3) O(3) and C(8) O(8) away from the Os(1)–Os(3)
edge suggests that it lies in the plane of the imido ligand
that bridges across the Os(1)–Os(3) edge. To gain insight
into the mechanism by which the bi-amido ligand is
formed, we treated [Os3(CO)10(NCMe)2] with aniline in
refluxing heptane for 2 h to compare with the former reac-
tion product. The analysis shows that no coupling of the
amido ligands has occurred, and the known cluster,
[Os3(CO)10(l2-H)(l2-HNC6H5)] (2), is obtained instead
[20]. This suggests that the rhodium metal in the cluster
[Os3Rh(l-H)3(CO)12] plays an important role in the forma-
tion of the C–C bond in [{Os3(CO)10(l2-H)}2{l2,l2-NC6-
H4C6H4N}] (1). There are some examples of rhodium-
catalysed coupling reactions [2,6,7]. In addition to rhodium
metal, organoruthenium and platinum have been shown to
be able to promote C–H bond activations and C–C bond
formation between other unsaturated hydrocarbons [1,4].
Treatment of the two products [{Os3(CO)10(l2-H)}2-
{l2,l2-NC6H4C6H4N}] (1) and [Os3(CO)10(l2-H) (l2-HN-
C6H5)] (2) with an excess amount of Wilkinson’s catalyst
in refluxing heptane respectively, gave the same blue com-
plex [{Os3(CO)9(l2-H)PPh3}2{l2,l2-NC6H4C6-H4N}] (3)
in roughly 40% yield upon TLC separation on silica, see
Scheme 1. The compound 3 was characterized by spectro-
scopic and crystallographic techniques. The IR, 1H
NMR, and mass spectroscopy data for the new complex
is fully consistent with those of solid-state structures (see
Os
Os
Os
H
N
N
H
Os
Os
Os
1b
Scheme 2. A possible isomerisation process of [{Os3(CO)10(l2-H)}2{l2,l2-
NC6H4C6H4N}] (1).
bond distances and angles of cluster 1 are presented in
Table 2 and the relevant structural parameters are listed
in Table 5. The structure of 1 comprises two triangles of
osmium atoms with 10 terminal carbonyl groups each.
The two triangular osmium metal core are linked by a bi-
amido ligand which is formed via the coupling of the
˚
C(14)–C(14*) bond, 1.37 A, which is short enough to have
multiple bond character. Complex 1 sits on a crystallo-
graphic center of symmetry at the mid point of the
C(14)–C(14*) bond. The bi-amido ligand symmetrically
bridges Os(1)–Os(3) and Os(1)*–Os(3)* of the triosmium
metal clusters via the two nitrogen atoms N(1) and
N(1)*, respectively. The bi-amido moiety in this complex
˚
contains a C@N double bond (1.26(5) A), which is not
commonly observed. Similar geometric bridging arrange-
ments have been found in [Os3(CO)10{l-N(H)(C5H3NBr)}-
{l-N(C10H13NO)}] [17], [Os3(l-H)(CO)10(l-N@C(H)CF3)]
[18], and [Os3(l-H)(CO)10(l-N@C(H)Et)] [19], in which the
Table 1
Spectroscopic data for compounds 1–3
Cluster IR spectraa m(CO)/cmꢃ1
Mass spectrab m/z 1H NMR spectrac d, J/Hz
1
2110vs, 2077vs, 2054s, 2033w, 2014br
914 [M/2ꢃCO]+
At 298 K for 1a: d 7.92 (m, 4H, aryl H), d 7.54 (m, 4H, aryl H), d
ꢃ19.65 (s, 2H, Os–H) 1b: d 7.44 (m, 4H, aryl H), d 6.71 (m, 4H, aryl H),
d ꢃ10.41 (s, 2H, Os–H)
2
3
2113vs, 2074vs, 2062vs, 2026vs, 2012vs, 1981m 915 [MꢃCO]+
At 298 K, d 7.46 (t, 2H, aryl H), d 6.97 (s, 1H, aryl H), d 6.71 (d, 2H,
aryl H), d 3.43 (s, 1H, NH), d ꢃ10.47 (s, 1H, Os–H)
2083s, 2048s, 2006vs
2353 [Mꢃ2CO]+
At 298 K for 3a and 3b: d 6.45–7.60 (m, 16H, aryl H), d 7.20–7.45 (m,
60H, PPh3), and d ꢃ14.05 to ꢃ14.15 (m, 4H, Os–H)
a
b
c
Recorded in CH2Cl2 unless otherwise stated.
Positive FAB MS; the calculated values are in parentheses.
Recorded in CDCl2 for 1–3.

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J.Po-Kwan Lau, W.-T. Wong / Inorganica Chimica Acta 359 (2006) 3632–3638
O(5)
C(5)
O(7)
C(7)
O(2)
C(4)
O(1)*
C(1)
O(4)
C(2)
O(9)
O(10)*
C(6)
O(3)*
Os(2)
Os(1)
C(3)*
C(16)
C(15)*
C(12)*
C(16)*
O(6)
C(15)
C(9)
Os(1)*
C(10)
C(14)*
C(14)
C(11)*
O(3)
C(3)
O(8)*
C(8)*
N(1)
C(11)
C(1)
C(13)
N(1)*
Os(3)*
Os(3)
C(12)
C(13)*
C(8)
O(8)
O(6)*
O(1)
C(6)*
C(7)*
Os(2)*
C(4)*
C(5)*
O(5)*
C(9)*
C(10)
O(10)
O(4)*
O(9)*
O(7)*
Fig. 1. The molecular structure of [{Os3(CO)10(l2-H)}2{l2,l2-NC6H4C6H4N}] (1) with the atom numbering scheme.
Table 1). Only terminal carbonyls were observed in the IR
region (mCO 2200–1600) for the complex in solution. The
FAB mass spectra of cluster 3 showed the corresponding
parent molecular ion peak at m/z 2353 (calc. 2409), which
reveals the loss of two CO units. The 1H NMR spectrum of
compound 3 in CD2Cl2 at room temperature comprises
two sets of signals at a relative ratio of 1:1 in the aromatic
and hydride regions, and shows the presence of two iso-
mers in the range of d 6.45–7.60 (m, 16H, aryl H), d
7.20–7.45 (m, 60H, PPh3), and d ꢃ14.05 to ꢃ14.15 (m,
4H, Os–H). It is suggested that the presence of the two
isomers in solution is due to a similar C–C bond rotation
process proposed for 1. To elucidate the structure of cluster
3, an X-ray analysis was carried out on a blue crystal that
was grown by the slow evaporation of an octane/CH2Cl2
solution at ꢃ5 °C over a period of a few days. The molec-
ular structure of [{Os3(CO)9(l2-H)PPh3}2{l2,l2-NC6H4C6-
H4N}] (3) is shown in Fig. 2, and the associated bond
lengths and interbond angles are presented in Table 3.
The analysis reveals that the structure of cluster 3 is very
similar to that of complex 1, which contains two triangular
osmium metal cores, [Os(1)–Os(2), 2.825(1); Os(2)–Os(3),
2.859(1); Os(1)–Os(3), 2.850(1); Os(4)–Os(5), 2.822(1);
Os(5)–Os(6), 2.847(1) and Os(4)–Os(6), 2.849(1)], that are
linked by a C–C (C(60)–C(61), 1.41(2)) coupled bi-amido
ligand that bridges the Os(1)–DOs(2) and Os(4)–Os(5)
edges through N(1) and N(2) at the equatorial sites. It only
differs in the terminal ligands, in which one of the terminal
carbonyl groups is replaced by a PPh3 ligand. Both of the
C–N bond in the bi-amido moiety are double bond
˚
(1.35(2) A), which compares well with similar systems
[17–19]. The two phenyl ring in 3 are found to be co-planar
to each other with a small dihedral angle of 3.465°. Hence,
the atoms N(1), C(55), C(56), C(57), C(58), C(59), C(60)
C(22)
C(23)
C(21)
C(24)
O(1)
O(17)
O(16)
C(19)
C(26)
C(27)
C(16)
C(35)
C(17)
C(25)
C(36)
P(1)
Os(3)
C(28)
O(10)
Os(6)
C(10)
C(34)
C(29)
C(18)
C(31)
C(32)
Os(2)
C(30)
C(2)
C(66)
C(65)
C(59)
C(61)
C(62)
C(58)
N(2)
C(64)
C(33)
O(18)
Os(1)
O(3)
Os(4)
O(4)
C(4)
O(11)
C(12)
C(11)
C(14)
N(1)
C(3)
C(55)
O(13)
C(60)
C(63)
C(13)
Os(5)
C(5)
O(5)
C(57)
O(9)
C(56)
C(9)
Os(3)
O(14)
O(12)
C(54)
C(49)
P(2)
C(53)
C(52)
C(8)
O(8)
C(37)
C(42)
C(6)
O(6)
C(48)
C(43)
C(7)
O(7)
C(50)
C(41)
C(40)
C(51)
C(47)
C(46)
C(38)
C(44)
C(39)
C(45)
Fig. 2. The molecular structure of [{Os3(CO)9(l2-H)PPh3}2{l2,l2-NC6H4C6H4N}] (3) with the atom numbering scheme.

J.Po-Kwan Lau, W.-T. Wong / Inorganica Chimica Acta 359 (2006) 3632–3638
3637
Table 5
Table 3
Selected bond distances (A) and angles (°) for cluster 3
˚
Crystallographic data and data collection parameters for complexes 1 and
3
Os(1)–Os(2)
Os(1)–N(1)
Os(2)–N(1)
Os(4)–Os(6)
Os(5)–Os(6)
N(1)–C(55)
C(55)–C(56)
C(56)–C(57)
C(58)–C(59)
C(60)–C(61)
C(61)–C(66)
C(65)–C(66)
Os(2)–Os(1)–Os(3)
Os(2)–Os(3)–Os(1)
Os(6)–Os(5)–Os(4)
Os(2)–N(1)–Os(1)
2.825(9)
2.08(2)
2.04(1)
2.849(1)
2.847(1)
1.35(2)
1.42(3)
1.38(2)
1.34(3)
1.41(2)
1.42(2)
1.37(3)
60.49(3)
59.31(3)
60.32(3)
86.7(5)
Os(1)–Os(3)
Os(2)–Os(3)
Os(4)–Os(5)
Os(4)–N(2)
Os(5)–N(2)
N(2)–C(64)
C(55)–C(58)
C(57)–C(60)
C(59)–C(60)
C(61)–C(62)
C(64)–C(65)
2.850(1)
2.859(1)
2.822(1)
2.04(1)
2.04(2)
1.35(2)
1.45(2)
1.39(2)
1.48(3)
1.46(3)
1.42(3)
Compound
1
3
Empirical formula
Formula weight
Crystal system
Space group
Os6C32H10N2O20 Os6C68H40N2O18P2
1883.63
monoclinic
P21/n (#14)
7.361(2)
30.711(7)
9.356(2)
90
100.28(1)
90
2081.1(9)
2
3.006
1664
183.12
298
13223
4820
2409.31
triclinic
P1 (#2)
ꢀ
˚
a (A)
11.007(3)
18.114(6)
20.762(7)
75.00(1)
75.22(1)
87.13(1)
3865.6(21)
2
2.070
2226
99.21
298
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
Os(3)–Os(1)–Os(1)
Os(5)–Os(4)–Os(6)
Os(5)–Os(6)–Os(4)
Os(5)–N(2)–Os(4)
60.19(3)
60.27(3)
59.40(3)
87.6(5)
3
˚
V (A )
Z value
Dcalc (g cmꢃ3
F(000)
)
C(61), C(62), C(63), C(64), C(65), C(66), and N(2) can be
regarded as a plane and makes an angle of 69.00(1)° and
67.65(3)° with the osmium triangles, Os(1), Os(2) and
Os(3) and Os(4), Os(5) and Os(6), respectively. The plane
is nearly co-planar with one of the phenyl rings of each
of the PPh3 units, i.e., C(25) to C(30) and C(49) to C(54),
respectively, with dihedral angles of only 9.55(2)° and
9.82(2)°. The hydride ligand was not located directly in
the analysis, but both the bridged and unbridged Os-Os
bonds in cluster 3 show only a little variation in bond dis-
tance, and therefore the two hydrido ligands are located
according to the bending of the equatorial carbonyl groups
C(2) O(2) and C(4) O(4) away from the Os(1)–Os(2) edge,
and C(11) O(11) and C(14) O(14) bending away from the
Os(4)–Os(5) edge. The coupling of the two coordinated
amido ligands {NC6H5} in 2 that leads to [{Os3(CO)9(l2-
H)PPh3}2l2,l2-NC6H4C6H4N}] (3) is observed, which fur-
ther suggests the function of organorhodium species in pro-
moting C–H bond activation and C–C bond formation
between the amido ligands.
l (Mo Ka) (cmꢃ1
)
Temperature (K)
Reflection collected
Unique reflection
Observed reflection [I > 2.00r(I)] 2185
Final R, Rw 0.055, 0.086
24443
16843
12076
0.055, 0.066
and bi-amido ligands that are attached to the tri-osmium
metal clusters. Similar absorption bands were found for
the corresponding untreated aniline and free biphenyl-
4,40-diamine (H2NC6H4C6H4NH2) ligand.
4. Conclusions
In this work, we demonstrate the coupling of two phenyl
amido units {NC6H5} into a biphenyl amido ligand via the
formation of a C–C bond in the two newly formed com-
plexes [{Os3(CO)10(l2-H)}2{l2,l2-NC6H4C6H4N}] (1) and
[{Os3(CO)9(l2-H)PPh3}2{l2,l2-NC6H4C6H4N}] (3) (see
Table 5). We could not establish the mechanistic details
for the coupling reactions, but we have found the key ele-
ment in the reaction that is responsible for the promotion
of the C–C bond formation. The rhodium metal in either
the starting material which is [Os3Rh(l-H)3(CO)12] for
compound 1 or the Wilkinson’s catalyst in catalyzing clus-
ter 2 is believed to play a very important role in the catalytic
reaction. No formation of bi-phenyl amido ligands was
observed without the present of the Rh metal. These com-
plexes display intense purple and blue colours, and show
both low and high energy absorption peaks in the electronic
absorption spectra, which are assigned as the dp (Os) ! p*
(amido) MLCT transition and the p ! p* intra-ligand elec-
tronic transitions of the amido and bi-amido ligands.
3.1. Electronic absorption spectra
The UV–Vis spectral data for complexes 1–3 in CH2Cl2
are summarized in Table 4. The absorptions in the lower
energy region (ca. 402–547 nm) are attributed to electronic
transitions that arise from the dp (Os) ! p* (amido) MLCT
transition, and are similar to those observed in a triosmium
metal cluster that contains an azo ligand at ca. 516 nm with
an extinction coefficient of 7217 dm3 molꢃ1 cmꢃ1 [21]. In
addition to the low energy absorption, the absorptions in
the higher energy region (ca. 264–334 nm) are assigned to
the p ! p* intra-ligand electronic transitions of the amido
Table 4
Electronic absorption data for compounds 1–3
Acknowledgements
Cluster
Electronic absorption kmax/nm (e/dm3 molꢃ1 cmꢃ1 a
)
We gratefully acknowledge the financial support of the
Hong Kong Research Grants Council and the University
of Hong Kong. J.P.K. Lau acknowledges the receipt of a
postgraduate studentship (2002–2005), a Hung Hing Ying
1
2
3
a
318 (3103), 547 (1028)
334 (1606), 546 (324)
264 (15822), 402 (833)
In CH2Cl2 at 298 K.

3638
J.Po-Kwan Lau, W.-T. Wong / Inorganica Chimica Acta 359 (2006) 3632–3638
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Appendix A. Supplementary data
Crystallographic data (excluding structure factors) for
the structures reported in this paper have been depo-
sited with the Cambridge Crystallographic Data Centre
(CCDC) as supplementary publication no. CCDC287374–
CCDC287375. Copies of the data can be obtained free of
charge on application to CCDC, 12 Union Road, Cam-
bridge CB2 1EZ, UK (fax: (+44) 1223 336 033; e-mail:
deposit@ccdc.cam.ac.uk). Supplementary data associated
with this article can be found, in the online version, at
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