Complexation and metallation of the multifunctional [Ph2P(o-C6H4)CH=N(CH2)2(0-C5H4N)] ligand on triosmium carbonyl clusters

Article abstract of DOI:10.1039/a910260o

Reaction of the phosphine-imine-pyridine containing ligand Ph2P(o-C6H4)CH=N(CH2)2(o-C5H4N) (abbreviated to PNN) with [Os3(CO)lo(NCMe)2] at ambient temperature affords {Os3(CO),0[r|2-Ph2P(o-C6H4)CH=N(CH2)2(o-C5H4N)]} 1. Thermolysis of 1 in refluxing toluene leads to CO dissociation to give {Os3(CO)9[u-ri3-Ph2P(o-C6H4)CH=N(CH2)2(o-C5H4N)]} 2, and C-H activation of the PNN ligand to give {(n-H)Os3(CO)8[u3-r|4-Ph2P(0-C6H4)CH=NCH2CH(o-C5H4N)]} 3 and {(u-H)Os3(CO)8[u-r|4-Ph2P(o-C6H4)C=N(CH2)2(o-C5H4N)]} 4. In contrast, copyrolysis of [Os3(CO),2] with PNN in a sealed tube results in 2,3 and the diosmium phosphido complex {Os2(CO)5(u-PPh2)[u-ti3-Ph2P(o-C6H4)C=N(CH2)2(0-C5H4N)]} 5. The structures of 1,3,4 and 5 have been determined by an X-ray diffraction study. Compounds 3 and 4 are isomers with the methylene and the imine C-H bonds of the PNN ligand being activated by the Os} cluster, respectively. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/a910260o

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Complexation and metallation of the multifunctional
[Ph P(o-C H )CH᎐N(CH ) (o-C H N)] ligand on
᎐
2
6
4
2 2
5
4
triosmium carbonyl clusters
Wen-Yann Yeh,*a Ching-Chao Yang,a Shie-Ming Peng*b and Gene-Hsiang Leeb
a Department of Chemistry, National Sun Yat-Sen University, Kaohsiung, Taiwan 804
b Department of Chemistry, National Taiwan University, Taipei, Taiwan 106
Received 22nd December 1999, Accepted 15th March 2000
Published on the Web 27th April 2000
Reaction of the phosphine–imine–pyridine containing ligand Ph P(o-C H )CH᎐N(CH ) (o-C H N) (abbreviated
᎐
2
6
4
2
2
5
4
to PNN) with [Os (CO) (NCMe) ] at ambient temperature affords {Os (CO) [η2-Ph P(o-C H )CH᎐N(CH ) -
᎐
3
10
2
3
10
2
6
4
2 2
(o-C5H4N)]} 1. Thermolysis of 1 in refluxing toluene leads to CO dissociation to give {Os3(CO)9[µ-η3-Ph2P(o-C6H4)-
CH᎐N(CH ) (o-C H N)]} 2, and C–H activation of the PNN ligand to give {(µ-H)Os (CO) [µ -η4-Ph P(o-C H )-
᎐
᎐
2
2
5
4
3
8
3
2
6
4
CH᎐NCH CH(o-C H N)]} 3 and {(µ-H)Os (CO) [µ-η4-Ph P(o-C H )C᎐N(CH ) (o-C H N)]} 4. In contrast, co-
᎐
2
5
4
3
8
2
6
4
2
2
5
4
pyrolysis of [Os3(CO)12] with PNN in a sealed tube results in 2, 3 and the diosmium phosphido complex {Os2(CO)5-
(µ-PPh )[µ-η3-Ph P(o-C H )C᎐N(CH ) (o-C H N)]} 5. The structures of 1, 3, 4 and 5 have been determined by an
᎐
2
2
6
4
2
2
5
4
X-ray diffraction study. Compounds 3 and 4 are isomers with the methylene and the imine C–H bonds of the PNN
ligand being activated by the Os3 cluster, respectively.
mass spectrometer with 3-nitrobenzyl alcohol as the matrix.
Introduction
Elemental analyses were performed at the National Science
Council Regional Instrumentation Center at National Chen-
Kung University, Tainan, Taiwan.
The ability of a metal atom (or ion) to organize a flexible
multifunctional ligand around its coordination sphere has led
to the design of several catalytic systems and intramolecularly
organized recognition sites.1 The Ph P(o-C H )CH᎐N(CH ) -
᎐
2
6
4
2 2
Reaction of [Os3(CO)10(NCMe)2] with PNN
(o-C5H4N) molecule (abbreviated to PNN), which contains a
phosphine, an imine and a pyridyl electron-donating group, was
previously prepared by Lavery and Nelson from the Schiff’s
An oven-dried, 50 cm3 Schlenk flask, equipped with a magnetic
stir bar, was evacuated and refilled with dinitrogen three times.
The stopper was briefly removed and [Os3(CO)10(NCMe)2] (205
mg, 0.22 mmol) and PNN (96 mg, 0.24 mmol) were added
against a dinitrogen flow. Freshly distilled dichloromethane (20
cm3) was then introduced by means of a cannula through the
septum stopper. The mixture was stirred at ambient temper-
ature for 1 h, resulting in a color change from pale yellow to
orange-red. The volatile materials were removed under vacuum,
and the residue was subjected to TLC with dichloromethane–n-
hexane (1:1, v/v) as eluant. The major orange band afforded
base condensation of Ph P(o-C H )C(᎐O)H and H N(CH ) -
᎐
2
6
4
2
2 2
(o-C5H4N).2 Due to its flexible structure, PNN can act either as
a monodentate phosphine, a bidentate phosphine–imine or a
tridentate P–N–N ligand. A few PNN complexes of Pd(0),
Pd(), Pt() and Group VI metals are known.3 However, the
coordination chemistry of PNN with metal clusters has
received little attention, though the related poly(pyridyl) cluster
complexes were recently described by Wang and co-workers.4
Arising from our interest in the systematic chemistry of organic
substrates bound to transition-metal clusters,5 this paper shows
the results of an investigation of PNN reacting with [Os3-
(CO)12] and [Os3(CO)10(NCMe)2].
{Os (CO) [η2-Ph P(o-C H )CH᎐N(CH ) (o-C H N)]} 1 (137
᎐
3
10
2
6
4
2
2
5
4
mg, 0.11 mmol, 50%) (Found: C, 34.65; H, 1.98; N, 2.18.
C36H23N2O10POs3 requires C, 34.72; H, 1.86; N, 2.25%): IR
(CH2Cl2, cmϪ1) ν(CO) 2092m, 2040s, 2000vs, 1980s, 1960 (sh)
and 1912w; mass spectrum (FAB) m/z 1250 (Mϩ, 192Os) and
1250 Ϫ 28n (n = 1–10); 1H NMR (C6D6, 20 ЊC) δ 8.34 (d,
Experimental
JP–H = 5 Hz, CH᎐N), 7.87–6.50 (m, 18H, C H , C H N), 4.96
General methods
᎐
6
4
5
4
(m, 1H), 4.54 (m, 1H), 2.62 (m, 1H) and 2.23 (m, 1H, CH2).
All manipulations were carried out under an atmosphere
of purified dinitrogen with standard Schlenk techniques.6
[Os3(CO)12]7 and [Os3(CO)10(NCMe)2]8 were prepared by liter-
31P{1H} NMR (C6D6, 20 ЊC) δ 15.62 (s).
Thermolysis of 1
ature methods. Ph P(o-C H )CH᎐N(CH ) (o-C H N) was syn-
᎐
2
6
4
2
2
5
4
thesized from condensation of Ph P(o-C H )C(᎐O)H and
An oven-dried, 50 cm3 two-necked Schlenk flask was equipped
with a magnetic stir bar. One neck was stopped and the other
neck had a reflux condenser connected to an oil bubbler. A
solution of 1 (123 mg, 0.099 mmol) in dry toluene (6 cm3) was
introduced into the flask, heated to reflux under dinitrogen for
2 h and cooled to ambient temperature, forming an orange-
yellow solution and a brown-red precipitate. The solid was
filtered off and recrystallized from dichloromethane–n-hexane
᎐
2
6
4
NH2(CH2)2(o-C5H4N) (Aldrich) as described in the literature.2
Solvents were dried over appropriate reagents under dinitrogen
and distilled immediately before use.9 Preparative thin-layer
chromatographic (TLC) plates were prepared from silica gel
(Merck). Infrared spectra were recorded with a 0.1 mm path
CaF2 solution cell on a Hitachi I-2001 IR spectrometer. 1H and
31P NMR spectra were obtained on a Varian VXR-300 spec-
trometer at 300 and 121.4 MHz, respectively and referenced to
SiMe4 and 85% aqueous H3PO4. Fast-atom-bombardment
(FAB) mass spectra were recorded by using a VG Blotch-5022
to afford {(µ-H)Os (CO) [µ -η4-Ph P(o-C H )CH᎐NCH CH-
᎐
3
8
3
2
6
4
2
(o-C5H4N)]} 3 (61 mg, 0.051 mmol, 52%). The filtrate was
dried under vacuum and the residue was subjected to TLC with
DOI: 10.1039/a910260o
J. Chem. Soc., Dalton Trans., 2000, 1649–1654
This journal is © The Royal Society of Chemistry 2000
1649

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Table 1 Crystallographic data for compounds 1, 3–5
1
3
4
5
Formula
Crystal solvent
M
Crystal system
Space group
a/Å
b/Å
c/Å
C36H23N2O10Os3P
C34H23N2O8Os3P
C34H23N2O8Os3P
0.5 n-hexane
1231.19
C43H32N2O5Os2P2
1245.13
Triclinic
1188.11
Triclinic
1099.05
Orthorhombic
Pbcn
18.8768(3)
21.023(2)
20.026(4)
Triclinic
¯
¯
¯
P1
P1
P1
10.979(1)
12.592(2)
14.214(3)
80.23(2)
72.02(2)
79.29(1)
1823.2(5)
293(2)
10.0659(1)
13.4957(1)
13.6217(1)
66.709(1)
84.669(1)
85.686(1)
1690.81(2)
295(2)
9.5720(1)
10.6385(2)
20.2534(2)
79.228(1)
88.699(1)
68.027(1)
1876.39(4)
295(2)
α/Њ
β/Њ
γ/Њ
U/Å3
T/K
7901(2)
295(2)
Z
2
2
2
8
µ/mm–1
R1, wR2
10.531
0.0353, 0.0929
11.345
0.0313, 0.0544
10.227
0.0310, 0.0729
6.555
0.0358, 0.0570
dichloromethane–n-hexane (1:1, v/v) as eluant. Isolation of the
material forming the fourth yellow band gave {(µ-H)Os3(CO)8-
cmϪ1) ν(CO) 2048s, 1976s, 1952m and 1930m; mass spectrum
(FAB) m/z 1102 (Mϩ, 192Os) and 1102 Ϫ 28n (n = 1–5); 1H
NMR (CD2Cl2, 20 ЊC) δ 8.49–6.61 (m, 28H, C6H4, C5H4N),
4.07 (m, 1H), 3.32 (m, 1H), 2.90 (m, 1H) and 2.45 (m, 1H,
CH2); 31P{1H} NMR (CD2Cl2, 20 ЊC) δ 80.97 (d, JP–P = 15 Hz,
µ-PPh2) and 31.60 (d, JP–P = 15 Hz, PNN).
[µ-η4-Ph P(o-C H )C᎐N(CH ) (o-C H N)]}
4 (5 mg, 4%).
᎐
2
6
4
2
2
5
4
Isolation of the material forming the seventh pale yellow
band afforded {Os (CO) [µ-η3-Ph P(o-C H )CH᎐N(CH ) -
᎐
3
9
2
6
4
2 2
(o-C5H4N)]} 2 (5 mg, 4%). The remaining several minor bands
(<1%) were not characterized.
Thermolysis of 2
Compound 2 (Found: C, 34.80; H, 1.87; N, 2.22. C35H23-
N2O9POs3 requires C, 34.54; H, 1.90; N, 2.30%): IR (CH2Cl2,
cmϪ1) ν(CO) 2088s, 2048vs, 2000vs, 1990 (sh), 1972 (sh), 1964
(sh) and 1942m; mass spectrum (FAB) m/z 1222 (Mϩ, 192Os)
A solution of 2 (15 mg) in toluene (5 cm3) was heated to reflux
under dinitrogen for 12 h. The reaction was monitored inter-
mittently by IR and TLC. Unreacted 2 (52%) and compound
4 (12%) were obtained after separation by TLC, while no
evidence supported the formation of compound 3.
1
and 1250 Ϫ 28n (n = 1–9); H NMR (CD2Cl2, 20 ЊC) δ 8.44 (d,
JP–H = 5 Hz, CH᎐N), 7.95–7.10 (m, 18H, C H , C H N), 4.23
᎐
6
4
5
4
(m, 1H), 3.46 (m, 1H), 2.95 (m, 1H) and 1.29 (m, 1H, CH2);
31P{1H} NMR (CD2Cl2, 20 ЊC) δ 35.25 (s).
Thermolysis of 3 and 4
Compound 3 (Found: C, 34.35; H, 2.03; N, 2.16. C34H23-
N2O8POs3 requires C, 34.34; H, 1.95; N, 2.36%): IR (CH2Cl2,
cmϪ1) ν(CO) 2060s, 2008vs, 1988s, 1970w, 1954m, 1944s and
1916w; mass spectrum (FAB) m/z 1194 (Mϩ, 192Os) and
1194 Ϫ 28n (n = 1–8); 1H NMR (CD2Cl2, 20 ЊC) δ 8.54 (d,
Typically, 10 mg of 3 (or 4) was dissolved in 5 cm3 of dry
toluene and heated to reflux under dinitrogen for 5 h, showing
no reaction as evidenced by IR and TLC. This indicates that
compounds 3 and 4 are not interconvertible.
JP–H = 5 Hz, CH᎐N), 7.61–6.45 (m, 18H, C H , C H N), 5.08
᎐
6
4
5
4
Structure determination for 1 and 5
(m, 1H), 4.09 (m, 1H), 3.56 (m, 1H, CH2) and Ϫ10.35 (d,
JP–H = 15 Hz, Os–H); 31P{1H} NMR (CD2Cl2, 20 ЊC) δ 3.56 (s).
Compound 4 (Found: C, 34.25; H, 2.34; N, 2.58. C34H23-
N2O8POs3 requires C, 34.34; H, 1.95; N, 2.36%): IR (CH2Cl2,
cmϪ1) ν(CO) 2068s, 1986vs, 1974 (sh), 1956w, 1932w and
1912m; mass spectrum (FAB) m/z 1194 (Mϩ, 192Os) and
A crystal of 1 (ca. 0.45 × 0.40 × 0.40 mm) and 5 (ca. 0.40 ×
0.25 × 0.10 mm) were each mounted in a thin-walled glass
capillary and aligned on the Nonius CAD-4 diffractometer
with graphite-monochromated Mo-Kα radiation (λ = 0.7107
Å). All data were corrected for Lorentz and polarization effects
and for the effects of absorption. The structure was solved by
direct methods and refined by full-matrix least-squares cycles on
F2 on the basis of 5180 observed reflections (I > 2σ(I)) for 1 and
4243 observed reflections for 5. The non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were included but not
refined. All calculations were performed using the SHELXTL
package.10a A summary of relevant crystallographic data is
provided in Table 1.
1
1194 Ϫ 28n (n = 1–8); H NMR (C6D6, 20 ЊC) δ 7.61–5.60 (m,
18H, C6H4, C5H4N), 3.47 (m, 1H), 3.16 (m, 1H), 3.05 (m, 1H),
1.72 (m, 1H, CH2) and Ϫ13.23 (d, JP–H = 7 Hz, Os–H); 31P{1H}
NMR (C6D6, 20 ЊC) δ 31.15 (s).
Pyrolysis of [Os3(CO)12] with PNN
[Os3(CO)12] (100 mg, 0.11 mmol) and PNN (100 mg, 0.25
mmol) were ground, mixed and sealed in Pyrex glass tubing
under vacuum (0.01 Torr). The tube was placed in a silicon oil
bath at 120 ЊC for 40 min and then at 160 ЊC for 30 min. The
tube was removed from the bath, cooled to room temper-
ature and opened in air. The brown residue was dissolved in
dichloromethane, applied to a preparative TLC plate and eluted
with dichloromethane–n-hexane (1:1, v/v). The unreacted
[Os3(CO)12] (35 mg, 35%) was recovered from the first yellow
band. Compound 3 (30 mg, 23%) was obtained from the
ninth band. Compound 2 (5 mg, 4%) was obtained from the
tenth band. Isolation of the material forming the eleventh pale
Structure determination for 3 and 4
A crystal of 3 (ca. 0.20 × 0.12 × 0.03 mm) and 4 (ca. 0.35 ×
0.13 × 0.08 mm) were each mounted in a thin-walled glass capil-
lary and aligned on the Siemens SMART-CCD diffractometer
with graphite-monochromated Mo-Kα radiation (λ = 0.71073
Å). 20361 reflections were measured and 6888 reflections
(Rint = 0.0461) were unique for 3, while 23505 reflections were
measured and 7633 reflections (Rint = 0.0341) were unique for 4.
Sadabs absorption corrections10b were made for 3 (Tmin
=
yellow band gave {Os (CO) (µ-PPh )[µ-η3-Ph P(o-C H )C᎐N-
0.2931, Tmax = 0.4921) and 4 (Tmin = 0.1440, Tmax = 0.2627).
The structures were solved by direct methods and refined by
full-matrix least-squares on F2. The program used was the
SHELXTL package.10a The data collection and refinement
parameters are collected in Table 1.
᎐
2
5
2
2
6
4
(CH2)2(o-C5H4N)]} 5 (21 mg, 0.019 mmol, 17%). The remaining
minor bands were not characterized.
Compound 5 (Found: C, 46.89; H, 3.17; N, 2.71. C43H32-
N2O5P2Os2 requires C, 46.99; H, 2.93; N, 2.55%): IR (CH2Cl2,
1650
J. Chem. Soc., Dalton Trans., 2000, 1649–1654

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Scheme 1
CCDC reference number 186/1901.
(1)
See http://www.rsc.org/suppdata/dt/a9/a910260o/ for crystal-
lographic files in .cif format.
Results and discussion
Reactions
Treating [Os3(CO)10(NCMe)2] with equimolar amounts of
PNN at room temperature results in the facile substitution
of the labile acetonitrile ligands by the phosphine and imine
groups of PNN to generate {Os3(CO)10[η2-Ph2P(o-C6H4)-
CH᎐N(CH ) (o-C H N)]}
1 in 50% yield. Compound 1
᎐
2
2
5
4
remains intact to 80 ЊC, while in refluxing toluene (110 ЊC) it
decomposes to generate several products. After separation by
TLC, three major complexes are purified for characteriz-
(1)). For the latter reaction, formation of 5 is likely to involve
coordination and rearrangement of two PNN ligands accom-
panied by cluster fragmentation from Os3 to Os2 under harsh
conditions.
ation, namely {Os (CO) [µ-η3-Ph P(o-C H )CH᎐N(CH ) -
᎐
3
9
2
6
4
2 2
(o-C H N)]} 2 (4%), {(µ-H)Os (CO) [µ -η4-Ph P(o-C H )CH᎐
᎐
5
4
3
8
3
2
6
4
NCH2CH(o-C5H4N)]}
Ph P(o-C H )C᎐N(CH ) (o-C H N)]} 4 (4%). Thermolysis of 1
3
(52%) and {(µ-H)Os3(CO)8[µ-η4-
Characterization of new compounds
᎐
2
6
4
2
2
5
4
in the presence of PNN gives the same products. A mechanistic
study was taken to trace the origins of 3 and 4, such that
heating pure 2 in refluxing toluene led to 4 but not to 3, and
thermolysis of 3 (or 4) at 110 ЊC did not generate 4 (or 3). The
results, summarized in Scheme 1, imply that compounds 3
and 4 are formed via separate routes, and compound 2 is the
precursor of 4.
Heating PNN and [Os3(CO)12] in refluxing toluene for 6 h
affords 2, 3 and 4 in low yields, while co-pyrolysis of PNN with
[Os3(CO)12] in a sealed tube results in 2, 3 and a diosmium
phosphido complex {Os2(CO)5(µ-PPh2)[µ-η3-Ph2P(o-C6H4)-
Compounds 1–5 form air-stable crystalline solids which have
been characterized by elemental analyses (C, H, and N), mass,
IR and NMR. The FAB mass spectra of these complexes dis-
play their molecular ion peaks and fragments resulting from
successive loss of CO ligands. The isotopic distribution of the
envelope surrounding the molecular ion matches that calcu-
lated for each compound.
1
The H NMR spectrum of free PNN in CDCl3 presents a
doublet resonance at δ 9.01 (JP–H = 5 Hz) for the CH᎐N proton
᎐
and two 2H triplets at δ 3.93 and 3.04 (JH–H = 7 Hz) for the
(CH2)2 protons, while its 31P{1H} NMR spectrum shows a sing-
let at δ Ϫ13.08 for the phosphine group. Upon coordination to
C᎐N(CH ) (o-C H N)]} 5 (17%) as the major products (eqn.
᎐
2
2
5
4
J. Chem. Soc., Dalton Trans., 2000, 1649–1654
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the osmium carbonyl clusters, the phosphine 31P resonances are
shifted downfield to δ 3.56–35.25, and the imine CH᎐N proton
᎐
resonances are shifted upfield to ca. δ 8.4. Furthermore, the
(CH2)2 proton resonances are split into four 1H multiplets
(except in 3) in the range δ 4.9–1.3, indicating asymmetric
coordination of the PNN ligands on the clusters to result in
diastereotopic methylene groups.
The molecular ion peaks of 1 and 2 at m/z 1250 and 1222
suggest an [Os3(CO)10(PNN)] and an [Os3(CO)9(PNN)] form-
1
ula, respectively. On the basis of the H and 31P NMR data,
the PNN ligand of 1 likely forms a phosphine–imine chelate
and of 2 donates its P,N,N set to result in a total of 48 valence
electrons for the clusters.11 The IR absorptions in the carbonyl
region for 1 and 2 are shifted to lower energy compared with
[Os3(CO)12], consistent with the stronger net donor capability
of the PNN compared with CO.12
Compounds 3 and 4 form brown-red and yellow crystals,
respectively. Their mass spectra present identical molecular ion
peaks at m/z 1194, which is 28 less than that of 2 to imply a
formal [Os3(CO)8(PNN)] formula. The 1H NMR spectrum of 3
Fig. 1 ORTEP17 drawing of 1. Thermal ellipsoids are drawn at the
shows a doublet at δ 8.54 for the CH᎐N proton, three 1H multi-
᎐
30% probability level.
plets at δ 5.08, 4.09 and 3.56 for the methylene protons, and a
doublet at δ Ϫ10.35 for the hydride resonance. In contrast, the
1H NMR spectrum of 4 shows four 1H multiplets in the range
δ 3.47–1.72 for the methylene protons and a hydride resonance
Table 2 Selected bond distances (Å) and bond angles (Њ) for 1
Os(1)–Os(2)
Os(2)–Os(3)
Os(1)–P(1)
N(1)–C(18)
2.9232(8)
2.8933(7)
2.308(2)
Os(1)–Os(3)
Os(1)–N(1)
N(1)–C(17)
2.8829(6)
2.204(7)
1.283(10)
at δ Ϫ13.23, while the CH᎐N resonance is absent. It appears
᎐
that compounds 3 and 4 are configurational isomers with the
methylene and the imine C–H bonds of the PNN ligand being
activated by the Os3 cluster. An X-ray diffraction study was
thus conducted to elucidate the exact way in which the ligands
are bound to the cluster in 3 and 4.
The mass spectrum of 5 shows the parent ion at m/z 1102
plus ions corresponding to the successive loss of 5 carbonyls.
The isotopic distribution surrounding the molecular ion peak
matches an Os2 composition. The 1H NMR spectrum indicates
1.491(10)
Os(1)–Os(2)–Os(3)
Os(2)–Os(1)–Os(3)
C(17)–N(1)–C(18)
59.42(2)
59.77(2)
112.8(7)
Os(1)–Os(3)–Os(2)
N(1)–Os(1)–P(1)
C(16)–C(17)–N(1)
60.80(2)
81.3(2)
128.4(8)
Å, while the imine group takes up an axial position with
Os(1)–N(1) = 2.204(7) Å. The P(1), C(11), C(16) and C(17)
atoms are coplanar to within 0.01 Å, and the dihedral angle
between this plane and the P(1)–Os(1)–N(1) plane is 50.42Њ.
the presence of PNN but without the CH᎐N proton resonance.
᎐
The 31P{1H} NMR spectrum reveals two doublet signals at
δ 31.60 and 80.97 (JP–P = 15 Hz) in about equal intensities. The
former 31P resonance, assigned to a phosphine group, is com-
patible with that of 4, while the latter resonance falls in the
range measured for a bridging phosphido (µ-PPh2) moiety.13
The spectroscopic data suggest an [Os2(CO)5(PNN–H)(PPh2)]
formula for 5. Owing to the absence of diagnostic spectral
features to reveal the structure of 5, an single-crystal X-ray
diffraction study was performed.
The C(17)–N(1) distance of 1.28(1) Å retains a C᎐N double
᎐
bond character, while the C(18)–N(1) single bond distance is
1.49(1) Å.
Crystal structure of 3
An ORTEP diagram of 3 is shown in Fig. 2. Selected bond
distances and bond angles are collected in Table 3. The tri-
metallic parts are based on a triangular array of osmium atoms
in which the Os(1)–Os(2) distance of 3.0229(3) Å is significantly
longer than the other two intermetallic distances, i.e. Os(1)–
Os(3) = 2.8085(4) Å and Os(2)–Os(3) = 2.8535(4) Å. The Os(2),
Os(1) and Os(3) atoms are each associated with two, three and
three terminal carbonyl ligands. The Os–CO distances range
from 1.863(7) Å through 1.924(8) Å, and the Os–C–O angles
are in the range 175.1(7)–178.4(8)Њ. The equatorial carbonyl
C(1), C(2), C(5) and C(7) atoms lie approximately on the tri-
osmium plane and the C(8) atom is bent towards the pyridyl
group with a Os(1)–Os(2)–Os(3)–C(8) torsion angle of 34.22Њ.
The hydride atom was not located, but the distribution of
carbonyl groups indicates that it probably binds the Os(3) atom
(or bridges the Os(3)–Os(2) edge) to provide an 18-electron
configuration for each Os atom.
The PNN ligand bridges the three Os atoms. The phosphine
and imine groups chelate the Os(2) atom with the distances
P(1)–Os(2) = 2.324(2) Å, N(2)–Os(2) = 2.159(5) Å and a bite
angle P(1)–Os(2)–N(2) = 88.4(1)Њ. The pyridyl group replaces
an axial carbonyl of Os(1) with the distance N(1)–Os(1) =
2.195(5) Å and the angles N(1)–Os(1)–C(3) = 176.0(3)Њ, N(1)–
Os(1)–Os(2) = 95.5(1)Њ and N(1)–Os(1)–Os(3) = 85.5(1)Њ. The
methylene C(14) atom is metallated on the Os(3) atom. The
Os(3)–C(14) length of 2.204(6) Å is characteristic of an Os–
C(sp3) σ bond.
Crystal structure of 1
An ORTEP diagram of 1 is shown in Fig. 1. Selected bond
distances and bond angles are collected in Table 2. There are
no abnormally short intermolecular contacts. The molecule is
formally derived from [Os3(CO)12], but with two carbonyls
being replaced by the phosphine and imine groups of PNN.
The osmium–osmium bonds show substantial variation, with
Os(1)–Os(2) = 2.9232(8) Å, Os(1)–Os(3) = 2.8829(6) Å and
Os(2)–Os(3) = 2.8933(7) Å, which are longer than the values
found in the parent compound [Os3(CO)12] (Os–Os(av)
=
2.877(3) Å).14
The carbonyl ligands are terminally bonded to the Os3 cluster
with the Os–C–O angles in the range 172.7(8)–179.5(9)Њ. The
Os(2) and Os(3) atoms are each linked to four carbonyl ligands
with the Os–CO lengths ranging from 1.88(1) Å to 1.95(1) Å,
while two carbonyls are associated with the Os(1) atom showing
a shorter Os–CO bond length of 1.85(1) Å. This can be attrib-
uted to enhancement of the Os(1)←CO back-donation by the
stronger net electron-donating phosphine and imine groups.
The PNN ligand chelates the Os(1) atom with the bite angle
N(1)–Os(1)–P(1) = 81.3(2)Њ. The pyridyl group is pendent and
pointed away from the cluster. The bulky phosphine group is in
the more opened equatorial position with Os(1)–P(1) = 2.308(2)
1652
J. Chem. Soc., Dalton Trans., 2000, 1649–1654

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Table 3 Selected bond distances (Å) and bond angles (Њ) for 3
Table 4 Selected bond distances (Å) and bond angles (Њ) for 4
Os(1)–Os(2)
Os(2)–Os(3)
Os(2)–N(2)
Os(3)–C(14)
N(2)–C(15)
3.0229(3)
2.8535(4)
2.159(5)
2.204(6)
1.482(7)
Os(1)–Os(3)
Os(1)–N(1)
Os(2)–P(1)
N(2)–C(16)
2.8085(4)
2.195(5)
2.324(2)
1.279(7)
Os(1)–Os(2)
Os(2)–Os(3)
Os(1)–N(1)
Os(2)–C(16)
N(2)–C(15)
2.9772(3)
2.8701(4)
2.166(5)
2.100(6)
1.475(9)
Os(1)–Os(3)
Os(1)–N(2)
Os(2)–P(1)
N(2)–C(16)
C(16)–C(17)
2.8319(4)
2.130(5)
2.317(2)
1.294(8)
1.485(9)
Os(1)–Os(2)–Os(3)
Os(2)–Os(1)–Os(3)
N(1)–Os(1)–Os(3)
N(2)–Os(2)–Os(3)
P(1)–Os(2)–Os(1)
C(14)–Os(3)–Os(1)
C(13)–C(14)–C(15)
57.011(9)
58.456(9)
85.5(1)
86.8(1)
112.08(4)
84.0(2)
Os(1)–Os(3)–Os(2)
N(1)–Os(1)–Os(2)
N(2)–Os(2)–Os(1)
N(2)–Os(2)–P(1)
P(1)–Os(2)–Os(3)
C(14)–Os(3)–Os(2)
C(16)–N(2)–C(15)
64.533(9)
95.5(1)
89.2(1)
88.4(1)
168.11(4)
82.5(2)
Os(1)–Os(2)–Os(3)
Os(2)–Os(1)–Os(3)
N(1)–Os(1)–Os(3)
N(2)–Os(1)–Os(3)
P(1)–Os(2)–Os(1)
C(16)–N(2)–C(15)
57.900(9)
59.154(9)
168.5(1)
93.1(1)
116.90(4)
123.6(5)
Os(1)–Os(3)–Os(2)
N(1)–Os(1)–Os(2)
N(2)–Os(1)–Os(2)
N(2)–Os(1)–N(1)
P(1)–Os(2)–Os(3)
N(2)–C(16)–C(17)
62.947(9)
109.4(1)
67.3(1)
80.1(2)
166.77(4)
123.8(6)
107.7(5)
115.6(5)
Fig. 2 ORTEP drawing of 3. Thermal ellipsoids are drawn at the 30%
probability level.
Fig. 3 ORTEP drawing of 4. Thermal ellipsoids are drawn at the 30%
probability level.
Crystal structure of 4
distances and bond angles are collected in Table 5. This com-
plex consists of Os(CO)2 and Os(CO)3 units connected by a
three-electron-donating diphenylphosphido group and a five-
electron-donating metallated PNN ligand, resulting in a total
of 34 valence electrons. This electron count requires one metal–
metal bond to provide an 18-electron configuration on each
osmium atom, in agreement with the observed Os(1)–Os(2)
distance (2.7944(6) Å). In addition, on the basis of the angles
subtended, the coordination about both Os(1) and Os(2) atoms
can be described as distorted octahedral.
The phosphido group bridges the two osmium atoms about
equally, being 2.367(2) Å to Os(1) and 2.355(2) Å to Os(2). The
Os(1) and Os(2) atoms are each associated with two and three
terminal carbonyl ligands, with the Os–C distances ranging
from 1.87(1) to 1.92(1) Å and the Os–CO angles in the range
176.2(8)–179.3(8)Њ. The PNN ligand is connected to Os(1)
through the phosphine P(1) atom (2.302(2) Å) and the imine
C(12) atom (2.099(7) Å), and to Os(2) through the imine N(1)
atom (2.129(6) Å). The Os(1), Os(2), N(1) and C(12) atoms are
planar to within 0.05 Å, and the Os(1), P(1), C(6), C(11) and
C(12) atoms are to within 0.1 Å, giving a dihedral angle of
13.11Њ between the two planes. Presumably, this coplanar
An ORTEP diagram of 4 is shown in Fig. 3. Selected bond
distances and bond angles are collected in Table 4. The mole-
cule consists of a triangular array of osmium atoms in which
the individual bond lengths are Os(1)–Os(2) = 2.9772(3) Å,
Os(1)–Os(3) = 2.8319(4) Å and Os(2)–Os(3) = 2.8701(4) Å. The
hydride ligand was not located directly, but the lengthened
Os(1)–Os(2) distance and the orientation of carbonyls indicates
that it likely bridges the Os(1)–Os(2) edge. The Os(1) and Os(2)
atoms are each linked to two terminal carbonyl ligands, and
Os(3) has four. The Os–C–O angles are in the range 175.1(7)–
179.4(7)Њ. The Os–CO distances are diverse, ranging from
1.858(7) Å to 1.956(8) Å.
The imine C(16)–H bond of the PNN ligand has been acti-
vated by the Os(2) atom. In contrast to 1 and 3, the imine and
pyridyl groups chelate the Os(1) atom with a bite angle N(1)–
Os(1)–N(2) = 80.1(2)Њ. The C(16)–N(2) bond is parallel to the
Os(1)–Os(2) edge, forming a σ bond to Os(2) (2.100(6) Å) and a
dative bond to Os(1) (2.130(5) Å). The dihedral angle between
the triosmium plane and the Os(1)–Os(2)–C(16)–N(2) plane is
71.73Њ. The C(16)–Os(2) distance of 2.100(6) Å is between those
measured for Os–C σ bonds (such as C(14)–Os(3) = 2.204(6) Å
in 3) and Os᎐C double bonds (2.04–2.07 Å) in some carbene
feature results in delocalization of the C᎐N π electrons, such
that the C(12)–N(1) length (1.326(9) Å) is 0.03 Å longer than
the value measured for 4.
᎐
᎐
systems,15 suggesting a partial double bond feature. The
phosphine P(1) and pyridine N(1) atoms are in the equatorial
positions to bind Os(2) (2.317(2) Å) and Os(1) (2.166(5) Å),
respectively. However, the torsional angles P(1)–Os(2)–Os(1)–
Os(3) = 166.01Њ, N(1)–Os(1)–Os(2)–Os(3) = 178.40Њ and N(1)–
Os(1)–Os(2)–P(1) = 12.39Њ indicate that the P(1) atom is bent
away from the Os3 plane.
Probable reaction mechanism
It is apparent that compound 2 is formed from substitution of
a CO ligand by the pendent pyridyl group of 1, and compounds
3 and 4 arise from C–H activation of the PNN ligand on the
Os3 cluster together with CO loss.
Crystal structure of 5
Compound 1 is thermally stable to 80 ЊC in either solid or
An ORTEP diagram of 5 is shown in Fig. 4. Selected bond
solution state. At higher temperatures, however, decarbonyl-
J. Chem. Soc., Dalton Trans., 2000, 1649–1654
1653

View Article Online
Table 5 Selected bond distances (Å) and bond angles (Њ) for 5
In summary, activation of the methylene and imine C–H
bonds presented herein is unique because it is orthometallation
of the phenyl and pyridyl groups which commonly occurs in
related cluster reactions.16 Our observations illustrate that pri-
marily geometrical factors control the structure of the products
formed rather than the electron donor ability of the various
donor groups in this potentially tetradentate ligand.
Os(1)–Os(2)
Os(1)–P(2)
Os(2)–P(2)
N(1)–C(12)
C(12)–C(11)
2.7944(6)
2.367(2)
2.355(2)
1.326(9)
1.48(1)
Os(1)–P(1)
Os(1)–C(12)
Os(2)–N(1)
N(1)–C(13)
2.302(2)
2.099(7)
2.129(6)
1.466(8)
P(1)–Os(1)–Os(2)
P(1)–Os(1)–C(12)
P(2)–Os(1)–C(12)
P(2)–Os(2)–Os(1)
N(1)–Os(2)–Os(1)
N(1)–C(12)–C(11)
147.33(6)
80.8(2)
83.4(2)
53.92(6)
69.8(2)
126.9(7)
P(1)–Os(1)–P(2)
P(2)–Os(1)–Os(2)
C(12)–Os(1)–Os(2)
P(2)–Os(2)–N(1)
Os(1)–P(2)–Os(2)
C(12)–N(1)–C(13)
111.70(8)
53.52(5)
69.3(2)
80.3(2)
72.56(6)
127.0(6)
Acknowledgements
We are grateful for support of this work by the National
Science Council of Taiwan.
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Fig. 4 ORTEP drawing of 5. Thermal ellipsoids are drawn at the 30%
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ation might occur to generate an unsaturated species [Os3(CO)9-
(η2-PNN)], which is followed by coordination of the pendent
pyridyl group to generate [Os3(CO)9(η3-PNN)]. Since heating 1
in the presence of free PNN gives the same results, the reaction
is presumably governed by the chelate effect. Two configur-
ational isomers 2 and 2Ј can be drawn to account for [Os3-
(CO)9(η3-PNN)]. The structure of 2Ј is related to 1 with a P–N
chelate, while of 2 the imine group has moved to the adjacent
Os atom to form a N–N chelate. Compound 2Ј is likely to be the
kinetic product, which then undergoes ligand migration to give
2 or C–H activation to lead to 3. It is probable the different
arrangements of PNN ligands constrain the pyridyl α-CH2
moiety of 2Ј and the imine H–C bond of 2 close to the cluster
framework, and the subsequent C–H activation reactions of
which afford 3 and 4, respectively. Apparently, compound 3 is
more stable (less strained) than 4 and should be dominant, in
agreement with the observed product distribution. However,
since compound 2Ј is not isolated, an alternative route via initial
C–H activation of 1 followed by CO/pyridyl substitution to
generate 3 cannot be excluded.
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On the other hand, two PNN molecules might be added into
the cluster in the co-pyrolysis of Os3(CO)12 and PNN, and sub-
sequent cluster fragmentation from Os3 to Os2 accompanied by
elimination of a PhCH᎐N(CH ) (C H N) species under harsh
᎐
2
2
5
4
conditions could lead to 5, though no mechanistic information
is available at this stage.
1654
J. Chem. Soc., Dalton Trans., 2000, 1649–1654