Reactivity study of cyclopentadienyl osmium(II) bisphosphine azido complexes with activated alkynes and nitriles: Isolation of osmium triazolato and tetrazolato complexes by 1,3-dipolar addition

Article abstract of DOI:10.1016/j.ica.2007.10.016

The cyclopentadienyl osmium(II) complexes [(η⁵-C₅H₅)Os(PPh₃)₂X] [X = Br (1), CH₃CN (2)] reacts with sodium azide (NaN₃) to yield the corresponding azido complex [(η⁵-C

Full text of DOI:10.1016/j.ica.2007.10.016

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Inorganica Chimica Acta 361 (2008) 2025–2031
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Reactivity study of cyclopentadienyl osmium(II) bisphosphine
azido complexes with activated alkynes and nitriles: Isolation of osmium
triazolato and tetrazolato complexes by 1,3-dipolar addition
a
b
a,
*
K. Pachhunga , Patrick J. Carroll , Kollipara Mohan Rao
a
Department of Chemistry, North-Eastern Hill University, Shillong 793022, Meghalaya, India
Department of Chemistry, University of Pennsylvania, 3301 Spruce Street, Philadelphia, PA 19104-6323, USA
b
Received 24 August 2007; accepted 15 October 2007
Available online 22 October 2007
Abstract
The cyclopentadienyl osmium(II) complexes [(g5-C5H5)Os(PPh3)2X] [X = Br (1), CH3CN (2)] reacts with sodium azide (NaN3) to
yield the corresponding azido complex [(g5-C5H5)Os(PPh3)2N3] (3). This undergoes [3+2] dipolar cycloaddition reaction with activated
alkynes like dimethyl and diethyl acetylenedicarboxylate to yield triazolato complexes [(g5-C5H5)Os(PPh3)2{N3C2(CO2R)2}] [R = –
CH2CH3 (4) and –CH3 (5)]. The complex 3 also reacts with nitriles such as tetracyanoethylene (TCE), fumaronitrile and p-nitrobenzo-
nitrile to yield complexes of the type [(g5-C5H5)Os(PPh3)2{N4C2(CN)@C(CN)2}] (6), [(g5-C5H5)Os(PPh3)2{N3C2HCN}] (7) and
[(g5-C5H5)Os(PPh3)2{N4C(C6H4–p-NO2)}] (8). These complexes were fully characterized on the basis of microanalyses, FT-IR and
NMR spectroscopic data. The molecular structure of the representative complex [(g5-C5H5)Os(PPh3)2{N3C2(CO2CH2CH3)2}] (4) was
determined by single crystal X-ray analysis.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Osmium complexes; Cyclopentadienyl; Dialkylacetylenedicarboxylate; Fumaronitrile; Tetracyanoethylene; p-Nitrobenzonitrile
1. Introduction
((g5-C5H5)OsL3)+ compounds in comparison with the
related cyclopentadienyl ruthenium complexes [5]. Our
interest arises due to their catalytic potential in organic
reactions, in particular, the synthesis of heterocyclic com-
pounds [6]. Tetrazoles are important not only as precursors
to a variety of nitrogen heterocycles [7] but also in their
diverse applications in the pharmaceutical [8] and explosive
industries [9] as well as corrosion inhibitors [10]. The pres-
ence of a coordinated azide in certain metal complexes has
been reported to react with electron-poor nitriles [11] and
isonitriles [12] under relatively mild conditions to produce
metal–nitrogen and metal–carbon bonded tetrazoles,
respectively. Similar reactions with alkynes produce triazo-
lates, whereas alkenes react very slowly and mostly afford
an impure product [13]. Similarly, it has been reported that
azido complexes react with carbon disulfides to produce
thiothiatriazolates [14]. A number of azido complexes have
been found to react with organic isothiocyanates and alkyl
The r-donor and p-acceptor abilities of the cyclopenta-
dienyl ligands stabilize transition metal complexes in low
and high oxidation states. The half-sandwich cyclopenta-
dienyl ruthenium and osmium biphosphine complexes,
viz., [(g5-C5H5)Ru(PPh3)2Cl] and [(g5-C5H5)Os(PPh3)2Br]
(1), have generated a great deal of interest for the last
few decades due to their high reactivity [1] and catalytic
activity [2]. However, the chemistry of [(g5-C5H5)Os-
(PPh3)2Br] (1) is less well-researched compared to the anal-
ogous ruthenium complexes [3]. This could be due to lack
of a convenient osmium synthetic precursor [4] or due to
the higher kinetic stability of the cyclopentadienyl osmium
*
Corresponding author. Tel.: +91 364 272 2620; fax: +91 364 2550486.
E-mail address: mohanrao59@hotmail.com (K.M. Rao).
0020-1693/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2007.10.016

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K. Pachhunga et al. / Inorganica Chimica Acta 361 (2008) 2025–2031
thiocyanates to give tetrazolinethionates and 5-(thi-
oalkyl)tetrazolates, respectively [15].
acetone, besides being stable in solution. The IR spectrum
of the complex exhibits a strong band at 2037 cmꢀ1 due to
the terminal azido group. The 31P NMR spectrum of the
complex 3 displays a singlet at d 1.15 corresponding to
the triphenylphosphine groups. The 1H NMR spectrum
of the complex 3 displays a singlet resonance at d 4.47
assigned to the protons of cyclopentadienyl group. The
cyclopentadienyl protons appears down field compared to
the starting complex (d 4.31), presumably due to the
increased steric factor on the metal centre of the complex
(3). The spectrum also displays a multiplet in the range
of d 7.82–7.01, corresponding to the protons of the triphen-
ylphosphine groups.
Cyclopentadienyl ruthenium triazolato and tetrazolato
complexes have been recently reported [16]. We recently
reported triazolato complexes of the type [(g6-arene)R-
u(LL){N3C2(CO2R)2}] and [(g5-indenyl)Ru(LL){N3C2-
(CO2R)2}] (LL = b-diketonates, dppe, dppm) which result
from the reaction of [(g6-arene)Ru(l-N3)(LL)] and [(g5-
indenyl)Ru(LL)(N3)], respectively, with various substituted
acetylenes [17]. The study revealed two important observa-
tions, viz., (i) g5-indenyl ruthenium(II) complexes contain-
ing bulky triphenylphosphine ligands did not undergo
1,3-cycloaddition, and (ii) the ethoxy substituted complex
exclusively produces the isomer with the metal bonded to
the terminal nitrogen atom (N1) of the triazolato ring.
To understand the role of steric factors in 1,3-dipolar
cycloaddition reactions, we carried out the reaction
between activated alkynes/nitriles and the cyclopentadienyl
osmium azido complex [(g5-C5H5)Os(PPh3)2N3] (3), which
constitutes the work presented here.
2.2. Reaction of complex 3 with diethylacetylenedi-
carboxylate
The azido complex [(g5-C5H5)Os(PPh3)2N3] (3) is trea-
ted with excess of diethylacetylenedicarboxylate in dichlo-
romethane and stirred at room temperature for 15 h,
resulting in a light yellow solid compound 4 in good yield.
The formation of the complex was readily confirmed by the
disappearance of the characteristic azide peak and the sub-
sequent appearance of sharp peaks at 1735 and 1439 cmꢀ1
corresponding to the characteristic stretching frequency of
C@O and N@N, respectively. The formation of the com-
plex is supported by the single crystal X-ray analysis. The
proton NMR spectrum shows a quartet at d 3.23, a triplet
at d 1.94, and a singlet at d 4.51 indicating the ten ethoxy
protons and the five cyclopentadienyl protons. It has been
reported that the triazole anion could be coordinate to a
metal centre through either its N(1) or N(2) nitrogen atoms
[18]. Evidence obtained till date indicates that both the
2. Results and discussion
2.1. Preparation of azido complex [(g5-C5H5)Os
(PPh3)2N3]
Treatment of the complexes [(g5-C5H5)Os(PPh3)2Br] (1)
and [(g5-C5H5)Os(PPh3)2CH3CN]BF4 (2) with an excess of
sodium azide (NaN3) in ethanol under refluxing conditions
for 5 h affords a pale yellow product of cyclopentadienyl
osmium azido complex [(g5-C5H5)Os(PPh3)2N3] (3) in
good yield (Scheme 1). The azido complex 3 is air-stable
and soluble in polar solvents such as CH2Cl2, CHCl3 and
R'
N
N
CH2Cl2
R
Os
N
L1
Ph3P
PPh3
N
N
CN
N
CH 2Cl2
L2
Os
N
NC
H
CN
Ph3P
PPh3
NaN3
Os
Br
Os
N=N=N
PPh3
EtOH
N
N
Ph3P
P
Ph3
PPh3
CH2Cl2
L3
CN
N
Os
Ph3P
L1 = diethylacetylenedicarboxylate = R, R' = CO2Et (4)
= dimethylacetylenedicarboxylate = R, R' = CO2Me (5)
L2 = tetracyanoethylene (6)
PPh3
L3 = fumaronitrile (7)
L4 = p-nitrobenzonitrile (8)
N
N
N
CH2Cl2
L4
Os
N
NO2
Ph3P
PPh3
Scheme 1.

K. Pachhunga et al. / Inorganica Chimica Acta 361 (2008) 2025–2031
2027
N(1)- and N(2)-bonded isomers are formed simultaneously.
2
3
NO
2
In our case, the N(2) bound isomer is produced exclusively.
The 1H NMR spectrum also displays a multiplet in the aro-
matic region due to the phenyl groups of the triphenylphos-
phine ligands.
N
N
1
Os
4
N
N
Ph P
3
PPh
3
Fig. 1. Triazolato complex [(g5-C5H5)Os(PPh3)2N4C(C6H4–p-NO2)] (8)
with numbering scheme.
2.3. Reaction of complex 3 with dimethylacetylen-
edicarboxylate
of the triazole group, besides a singlet resonance at d 4.05
attributed to the protons of the cyclopentadienyl ligand.
The 31P NMR resonance of this complex appears at d
1.25 indicating the two triphenylphosphine groups are in
the similar environment. The complex is soluble in polar
solvents such as acetone, chloroform, methanol and is also
air-stable. The cycloaddition reaction of fumaronitrile to
coordinated azide can take place via the C@C or C„N
bond. In addition, the reaction of the coordinated azide
ligand in the Ni(II) complex with CH2@CHCN gave a tria-
zolinato complex [18]. A pathway via direct cyclization of
HC„CCN with azide resulting in the formation of triazo-
late has been reported [20]. The formation of this complex
can also be readily confirmed by the disappearance of the
azide peak at 2037 cmꢀ1, and the simultaneous appearance
of the peak for the C„N group.
Treatment of the complex 3 with excess of dimethyl-
acetylenedicarboxylate in dichloromethane at room
temperature for 15 h affords the 4,5-bis(methoxycarbonyl)-
1,2,3-triazolato complex 5 in good yield. The infrared spec-
trum shows sharp peaks at 1735 and 1439 cmꢀ1 which are
assigned to the stretching frequencies of the C@O and
N@N ligands present in the complex. The proton NMR
spectrum displays a singlet at d 3.06 and d 4.51 corresponds
to the methoxy and cyclopentadienyl protons. The 31P
NMR signal of the complex 5 appears at d 1.19 which is
comparable to the starting complex 3. The complex is sol-
uble in polar solvents but insoluble in non-polar solvents,
and is air-stable.
2.4. Reaction of complex 3 with tetracyanoethylene (TCE)
The azido complex 3 was reacted with excess of tetracy-
anoethylene in dichloromethane at room temperature. The
reaction mixture turned deep green in colour after 1 h.
Continued stirring up to 36 h ensured complete reaction.
2.6. Reaction of complex 3 with p-nitrobenzonitrile
Treatment of complex 3 with a fivefold excess of p-nitro-
benzonitrile at room temperature for one week gave a deep
green complex [(g5-C5H5)Os(PPh3)2{N4C(C6H4–p-NO2)}]
(8), in good yield. The formation of the complex is evident
from the appearance of a –NO2 peak at 1475 cmꢀ1 and the
This
afforded
the
tetrazolato
complex
[(g5-
C5H5)Os(PPh3)2N4C{C(CN)C(CN)2}] (6) in good yield.
The infrared spectrum exhibits sharp peaks at 2227 and
1430 cmꢀ1 assigned to the stretching frequencies of C„N
and N@N groups, in good agreement with the reported
1
disappearance of the terminal azide peak. The H NMR
1
spectrum shows a singlet peak at d 4.82, assigned to the
protons of cyclopentadienyl ligand, appearing very down
field compared to the starting complex (d 4.47). The p-
nitrobenzonitrile ligand exhibits two doublets at d 9.3
and d 8.2 which correspond to the 1,2 and 3,4 protons of
the benzyl group (Fig. 1).
The phenyl protons of the PPh3 group appear in the aro-
matic region. Moreover, only a slight shift (d 1.19) in the
31P NMR was observed in comparison to the starting com-
plex (d 1.15). The complex is a deep green solid, soluble in
polar solvents such as acetone, dichloromethane, chloro-
form and methanol and is air-stable.
values [17]. The H NMR spectrum shows a singlet at d
4.05 for the cyclopentadienyl protons, where the up field
chemical shift here is due to increased electron density on
the metal centre. Multiplets observed at the aromatic
region correspond to the protons of the triphenylphosphine
ligands. The 31P NMR spectrum of this complex displays a
singlet at d 1.26. The formation of complex 6 is also con-
formed by the disappearance of the terminal azide peak
(observed at 2037 cmꢀ1) and by the appearance of the
stretching frequency of C„N groups. In general, most tet-
razoles are prepared from the corresponding nitriles by
reaction with sodium azide and ammonium chloride [19].
3. Crystal structure
2.5. Reaction of complex 3 with fumaronitrile
Crystal structure determination of the compound [(g5-
C5H5)Os(PPh3)2{N3C2(CO2C2H5)}] (4) has been carried
out. Details of the crystallographic data collection param-
eters are summarized in Table 1. The ORTEP diagram of
the complex along with the atom labelling scheme is shown
in Figs. 2a and 2b. The diagram Fig. 2b exhibits a clear
view of the molecule since the phenyl groups of the triphen-
ylphosphine are not included. In this complex, the osmium
Treatment of complex 3 with excess of fumaronitrile
at room temperature afforded a chocolate coloured
4-cyano-1,2,3-triazolato complex [(g5-C5H5)Os(PPh3)2-
{N3C2HCN}] (7) in good yield. The infrared spectrum of
the complex shows sharp peaks at 2221 and 1433 cmꢀ1
assignable to the stretching frequency of the C„N and
N@N groups. The 1H NMR spectrum displays a character-
istic singlet resonance at d 7.1 assigned to the –CH proton

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K. Pachhunga et al. / Inorganica Chimica Acta 361 (2008) 2025–2031
Table 1
Summary of structure determination for [(g5-C5H5)Os(PPh3)2-
N3C2(CO2C2H5)2] (4)
Empirical formula
C49H45N3P2O4Os
Formula weight
992.02
Temperature (K)
143
Crystal system, space group
Unit cell dimensions
monoclinic, P21/n (no. 14)
˚
a (A)
12.4947(7)
24.8362(13)
13.7755(8)
99.558(2)
˚
b (A)
˚
c (A)
b (ꢁ)
Volume (A )
3
˚
4215.5(4)
l
Z
31.50 cmꢀ1
4
Dcalc (g/cm3)
Radiation A
1.563
˚
Mo Ka (k = 0.71069)
1992
F(000)
Fig. 2b. ORTEP diagram of complex 4 with 30% probability thermal
Crystal size (mm3)
hkl collected
0.35 · 0.20 · 0.18
ꢀ15 6 h 6 16,
ꢀ26 6 k 6 32,
ꢀ17 6 l 6 17
21130
ellipsoids displayed without the phosphine phenyl groups and H atoms
˚
being omitted for clarity. Selected bond lengths (A) and angles (ꢁ): Os(1)–
P(1) 2.3232(7), Os(1)–P(2) 2.3263(6), N(1)–N(2) 1.302(3), N(2)–N(3)
1.343(3), N(1)–Os(1) 2.078(3), N(3)–C(1) 1.343(3), N(1)–C(2) 1.346(3),
Os(1)–N(2) 2.110(2), C(1)–C(3) 1.502(4), C(2)–C(6) 1.478(3), Os(1)–Cp
centroid 1.66, N(2)–N(1)–C(2) 105.0(2), N(1)–N(2)–N(3) 114.9(2), N(3)–
N(2)–Os(1) 118.20(14), N(1)–N(2)–Os(1) 126.7(2), N(2)–N(3)–C(1)
104.8(2), N(2)–Os(1)–P(1) 87.11(6), N(2)–Os(1)–P(2) 92.19(5), P(1)–
Os(1)–P(2) 102.77(2).
Number of reflections measured
Number of unique reflections
(Rint = 0.0193)
9051
7407
Number of observed reflections (F > 4r)
Completeness to 2h (%)
Data/restraints/parameters
Goodness-of-fit on F2
535
5.08–54.98
535
0.914
R1 [I > 2r(I)], wR2
R1, R2 (all data)
Largest difference in peak and hole (e A
R1 = 0.0214, wR2 = 0.0387
R1 = 0.0286, wR2 = 0.0404
pentadienyl ligand occupies three facial coordination sites.
The remaining coordination sites are occupied by the P
atoms of the triphenylphosphines and an N-atom of the
coordinated triazolato group. The complex 4 adopts the
well-known piano stool geometry with the P and N atoms
forming the legs. The planar five-membered triazolato ring
is coordinated to Os via N(2). The N(1)–N(2) and N(2)–
N(3) bond distances are 1.331(4) A and 1.343(3) A, respec-
tively, comparable to the values reported for its ruthenium
analogues [17]. The Os–P(1) and Os–P(2) bond lengths are
ꢀ3
˚
)
+1.579 and ꢀ0.923
P
P
P
P
2
2
1=2
R1 ¼ kF oj ꢀ jF ck= jF oj; wR2 ¼ f wðF 2o ꢀ F c2Þ = wðF o2Þ g
.
P
2
1=2
GOF ¼ f wðF 2o ꢀ F 2c Þ =ðn ꢀ pÞg where n = the number of reflections
and p = the number of parameters refined.
atom is p-bonded to the cyclopentadienyl group in g5-fash-
ion, with the distance between the osmium atom and the
centroid of the cyclopentadienyl being 1.66 A (similar to
the ruthenium analogues). The geometry around the
osmium atom is a distorted octahedral assuming the cyclo-
˚
˚
˚
˚
˚
2.323 A and 2.326 A, respectively, slightly longer than the
˚
average Os–P distance of 2.293 A [21].
Fig. 2a. ORTEP diagram of complex 4 with 30% probability thermal ellipsoids displayed and H atoms being omitted for clarity.

K. Pachhunga et al. / Inorganica Chimica Acta 361 (2008) 2025–2031
2029
4. Experimental
solvent was evaporated under reduced pressure to ca. 5 ml.
To this solution was added 30 ml of hexane, whereupon the
compound precipitated out as a light yellow solid. The
solid compound was collected by centrifuge, washed with
hexane (2 · 20 ml) and dried under vacuum to yield the
N(2)-bound triazole complex [(g5-C5H5)Os(PPh3)2N3C2-
(CO2C2H5)2] (4).
All solvents were dried in appropriate drying agents and
distilled prior to use [22]. Osmium tetroxide (Arora
Matthey Ltd.), dimethyl acetylenedicarboxylate, diethyl
acetylenedicarboxylate, tetracyanoethylene, fumaronitrile
(Aldrich) and p-nitrobenzonitrile (Acros) were used as
received. NMR spectra were recorded on AMX-400 MHz
spectrometer at 400.13 MHz (1H), 100.61 MHz (13C) and
161.97 MHz (31P) with SiMe4 or 85% H3PO4 as references.
Coupling constants were given in Hertz. Infrared spectra
were recorded as KBr pellets on a Perkin–Elmer Model
983 spectrometer. Elemental analyses were carried out at
the Sophisticated Analytical Instrumentation Facility,
NEHU, Shillong, using a Perkin–Elmer 2400 CHN/S ana-
lyzer. The precursor complexes [(g5-C5H5)Os(PPh3)2Br]
(1) and [(g5- C5H5)Os(PPh3)2CH3CN][PF6] (2) were pre-
pared by following a literature method [21].
Yield: 85 mg, 62.69%. Elemental Anal. Calc. for
C49H45N3P2O4Os: C, 59.3; H, 4.5; N, 4.2. Found: C,
59.9; H, 4.1; N, 4.8%. IR (KBr, cmꢀ1): 1735 (mC@O), 1439
1
(mN@N), 1245 (mC–O). H NMR (CDCl3, d): 7.45–7.03 (m,
30H; Ph); 4.51 (s, 5H, C5H5); 3.23 (q, 2H, –OCH2CH3);
1.94 (t, 3H, OCH2CH3). 31P {1H} NMR (CDCl3, d): 1.15
(s).
4.3. Synthesis of [(g5-C5H5)Os(PPh3)2 {N3C2(CO2
CH3)2}] (5)
This complex was prepared in a similar manner to that
for complex 4, except that dimethylacetylenedicarboxylate
[C2(CO2Me)2] was used instead of [C2(CO2C2H5)2], yield-
ing a light yellow complex (5).
Yield: 85 mg, 64.52%. Elemental Anal. Calc. for
C47H41N3P2O4Os: C, 58.6; H, 4.3; N, 4.4. Found: C,
58.1; H, 4.8; N, 4.2%. IR (KBr, cmꢀ1): 1735 (mC@O), 1439
(mN@N). 1H NMR (CDCl3, d): 7.45–7.03 (m, 30H, Ph);
4.51 (s, 5H, C5H5); 3.06 (s, 3H, OCH3). 13C {1H} NMR
(CDCl3, d): 162.9 (CO2); 135.2{C(CO2CH3)}; 133.8 (Ph);
82.81 (C5H5); 51.4 (OCH3). 31P {1H} NMR (CDCl3, d):
1.19 (s).
4.1. Synthesis of complex [(g5-C5H5)Os(PPh3)2N3] (3)
Two routes were used to prepare this complex:
(Caution: Reactions with azide salts and their complexes
should be carried out with extreme care)
Route (a): A solution of [(g5-C5H5)Os(PPh3)2Br] (1)
(100 mg, 0.12 mmol) and NaN3 (50 mg, 0.75 mmol) in eth-
anol (30 ml) was refluxed for ca. 5 h. During the period of
reaction, the colour of the solution progressively changed
from pale yellow to orange. The solution was concentrated
to ca. 5 ml and left at room temperature overnight; a pale
green crystalline compound was deposited on the beaker.
The crystalline compound was collected and washed with
cold ethanol (3 · 10 ml) and air dried.
4.4. Synthesis of [(g5- C5H5)Os(PPh3)2N4C{C(CN)
C(CN)2}] (6)
Route (b):
A
mixture of [(g5-C5H5)Os(PPh3)2-
(CH3CN)][PF6] (2) (100 mg, 0.10 mmol) and NaN3
(20 mg, 0.31 mmol) in ethanol (30 ml) was refluxed for
ca. 3 h. The solvent was removed under reduced pressure;
the solid residue extracted with dichloromethane and then
filtered to remove sodium chloride and excess sodium
azide. The filtrate upon concentration to ca. 5 ml and addi-
tion of excess hexane gave a pale green crystalline solid (3),
which was washed with cold ethanol (3 · 10 ml).
Dichloromethane (20 ml) was added to a round-bot-
tomed flask charged with complex 3 (100 mg, 0.12 mmol)
and tetracyanoethylene (0.60 mmol). The reaction mixture
was stirred at room temperature for ca. 36 h. The solvent
was evaporated under reduced pressure to ca. 5 ml. To
the solution was added 20 ml of n-hexane, whereupon a
deep blue compound was precipitated. The precipitate
was filtered, washed with n-hexane (2 · 10 ml) and dried
under vacuum to yield [(g5-C5H5)Os(PPh3)2{N4C{C(CN)-
C(CN)2}] (6).
Yield: 72 mg, 84.61%. Elemental Anal. Calc. for
C41H35P2N3Os: C, 59.2; H, 4.2; N, 5.1. Found: C, 59.75;
1
H, 4.87; N, 5.64%. H NMR (CDCl3, d): 7.82–7.01 (m,
Yield: 83 mg, 64.0%. Elemental Anal. Calc. for
C47H35N7P2Os: C, 59.4; H, 3.7; N, 10.3. Found: C, 58.9;
H, 3.2; N, 9.8%. IR (KBr, cmꢀ1): 2227, 2183 (s, mC„N),
30H, Ph); 4.47 (s, 5H, C5H5). 13C {1H} NMR (CDCl3,
d): 133.5–127.6 (Ph), 79.7 (C5H5). 31P {1H} NMR (CDCl3,
d): 1.15.
1
1430 (s, mN@N). H NMR (CDCl3, d): 7.73–6.96 (m, 30H,
Ph); 4.05 (s, 5H, C5H5). 13C {1H} NMR (CDCl3, d):
154.2 {C(CN)2}, 139.4 {C(CN)}, 132.1–126.4 (Ph), 125.3
(C@N), 112. 6, 110.4, 108.5 (CN), 81.4 (s, C5H5). 31P
{1H} NMR (CDCl3, d): 1.26 (s).
4.2. Synthesis of [(g5-C5H5)Os(PPh3)2
{N3C2(CO2C2H5)2}] (4)
General
procedure:
Diethylacetylenedicarboxylate
(175 mg, 1.23 mmol) and dichloromethane (20 ml) were
added to a round-bottomed flask charged with the appro-
priate azido complex (3) (100 mg, 0.12 mmol). The reaction
mixture was stirred at room temperature for ca. 15 h. The
4.5. Synthesis of [(g5-C5H5)Os(PPh3)2N3C2HCN] (7)
A mixture of azido complex [(g5-C5H5)Os(PPh3)2N3] (3)
(100 mg, 0.12 mmol) and fumaronitrile [C2H2(CN)2]

2030
K. Pachhunga et al. / Inorganica Chimica Acta 361 (2008) 2025–2031
(0.60 mmol) was stirred at room temperature for 36 h in
dichloromethane (20 ml). The solution was then concen-
trated to ca. 5 ml. To this solution was added 30 ml of n-
pentane, whereupon the compound precipitated as a deep
green solid. The solid compound was centrifuged, collected
and washed with n-pentane (2 · 10 ml) to yield the complex
[(g5-C5H5)Os(PPh3)2N3C2HCN] (7) which was further
dried under vacuum.
5.08 6 2h 6 54.98ꢁ, ꢀ15 6 h 6 16, ꢀ26 6 k 6 32, ꢀ17 6 l
6 17 yielding 9051 unique reflections (Rint = 0.0193). The
intensity data were corrected for Lorentz and polarization
effects and for absorption using REQAB [23] (minimum
and maximum transmission 0.836, 1.000). The structure
was solved by direct methods (SIR97) [25]. Refinement
was by a full-matrix least squares method based on F2
using SHELXL-97 [26]. All reflections were used during
refinement (F2’s that were experimentally negative were
replaced by F2 = 0). The weighting scheme used was
w ¼ 1=½r2ðF o2Þ þ 0:0112P2 þ 0:0000Pꢁ where P ¼ ðF 2oþ
2F 2cÞ=3. Non-hydrogen atoms were refined anisotropically
and hydrogen atoms were refined using a ‘‘riding’’ model.
Refinement converged to R1 = 0.0214 and wR2 = 0.0387
for 7407 reflections for which F > 4r(F) and R1 = 0.0286,
wR2 = 0.0404 and GOF = 0.914 for all 9051 unique, non-
zero reflections and 535 variables. The maximum D/r in
the final cycle of least squares was 0.003 and the two most
prominent peaks in the final difference Fourier were +1.579
Yield: 86 mg; 72.1%. Elemental Anal. Calc. for
C4H36N4P2Os: C, 60.5; H, 4.1; N, 6.4. Found: C, 59.5;
H, 4.1; N, 8.7%. IR (KBr, cmꢀ1): 2221 (s, mC@N), 1433 (s,
1
m
N@N). H NMR (CDCl3, d): 7.50–7.13 (m, 30H, Ph); 7.1
(s, 1H, CH); 4.05 (s, 5H, C5H5). 13C {1H} NMR (CDCl3,
d): 137.2 {C(CN)}, 136.02 (CH); 132.1–126.4 ({1H} Ph),
113.8 (CN); 82.8 (s, C5H5). 31P {1H} NMR (CDCl3, d):
1.25 (s).
4.6. Synthesis of [(g5-C5H5)Os(PPh3)2N4C(C6H4–p-
NO2)] (8)
3
˚
and ꢀ0.923 e/A . Crystallographic details are summarized
A mixture of azido complex [(g5-C5H5)Os(PPh3)2N3] (3)
(100 mg, 0.12 mmol) and para-nitrobenzonitrile (NO2–
C6H4–C„N) (0.60 mmol) in dichloromethane (20 ml) was
stirred at room temperature for one week, and the solution
concentrated to ca. 5 ml. To this solution was added 30 ml
of n-pentane, when the compound precipitated as a deep
green solid. The solid compound was centrifuged, collected
and washed with n-pentane (2 · 20 ml) to yield the complex
[(g5-C5H5)Os(PPh3)2N4C(C6H4-p-NO2)] (16) which was
dried under vacuum.
in Table 1. Figs. 2a and 2b were drawn with an ORTEP-
II [27] representation of the molecule with 30 % probability
thermal ellipsoids displayed.
6. Concluding remarks
This study describes the 1,3-dipolar addition of com-
plexes of [(g5-C5H5)Os(PPh3)2N3] with activated alkynes
and nitriles to generate cyclopentadienyl osmium triazolato
and tetrazolato complexes. These were formed in spite of
the complexes having bulky triphenylphosphine groups.
In contrast, the analogous ruthenium complexes [(g5-
C5H5)Ru(PPh3)2(N3)] and [(g5-indenyl) Ru(PPh3)2(N3)]
do not undergo such type of addition reactions. This could
be due to bulkiness of the triphenylphosphine group, or
due to the larger size of the osmium atom. Unlike the p-
cymene ruthenium triazolato complexes, the central nitro-
gen atom of the triazolato ring is bonded to the osmium
metal in these complexes. These reactions indicate that size
of the central atom plays a very important role in 1,3-dipolar
cycloaddition reactions. Further theoretical study is required
to substantiate these results. Another fascinating point is
that, in contrast to the ruthenium complexes, less crowded
complexes of the type [(g5-C5H5)Os(dppe)N3] and
[(g5-C5H5)Os(dppm)N3] do not undergo cycloaddition
reactions with diethylacetylenedicarboxylate and dimethyl-
acetylenedicarboxylate (investigation under process).
Yield: 75 mg, 71.0%. Elemental Anal. Calc. for
C48H39N5O2P2Os: C, 59.4; H, 4.0; N, 7.2. Found: C,
58.9; H, 4.7; N, 7.9%. IR (KBr, cmꢀ1): 1475 ðmNO Þ, 1430
2
(mN@N). 1H NMR (CDCl3, d): 4.82 (s, 5H, C5H5); 7.0–
7.56 (m, 30H, Ph); 8.3 (d, JH–H = 5.92 Hz, 1H); 9.3 (d,
JH–H = 5.6 Hz, 1H). 13C {1H} NMR (CDCl3, d): 36.02
(CH); 132.1–126.4 (Ph); 82.0 (C5H5). 31P {1H} NMR
(CDCl3, d): 1.19 (s).
5. Single crystal X-ray structures analyses
Crystals suitable for X-ray diffraction study was grown
by slow diffusion of diethylether into dichloromethane
solution of the complex 4. X-ray intensity data were col-
lected on a Rigaku Mercury CCD area detector employing
graphite-monochromated Mo Ka radiation (a = 0.71069
˚
A) at a temperature of 143 K. Preliminary indexing was
performed from a series of twelve 0.5ꢁ rotation images with
exposures of 30 s. A total of 410 rotation images were col-
lected with a crystal-to-detector distance of 35 mm, a 2a
swing angle of ꢀ12ꢁ, rotation widths of 0.5ꢁ and exposures
of 20 s. Rotation images were processed using Crystal
Clear [23] producing a listing of unaveraged F2 and a(F2)
values which were then passed to the crystal structure
[24] program package for further processing and struc-
ture solution on a Dell Pentium III computer. A total
of 21130 reflections were measured over the ranges
Acknowledgements
K.M.R. acknowledges the Department of Science and
Technology, New Delhi (Sanction Order No. SR/S1/IC-
11/2004) for financial support. We also thank Mırıam Per-
´
`
´
`
ez, Servi RMN Universitat Autonoma de Barcelona 08193
Bellaterra, Barcelona for providing the NMR facility.
Thanks are due to Prof. R.H. Duncan Lyngdoh for help
in preparing the manuscript.

K. Pachhunga et al. / Inorganica Chimica Acta 361 (2008) 2025–2031
2031
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Appendix A. Supplementary material
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[15] P.H. Kreutzer, J.C. Weis, H. Bock, J. Erbe, W. Beck, Chem. Ber. 116
(1983) 2691.
CCDC 649330 contains the supplementary crystallo-
graphic data for 4. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif. Supplementary
data associated with this article can be found, in the online
version, at doi:10.1016/j.ica.2007.10.016.
[16] Chao-Wan Chang, Gene-Hsiang Lee, Organometallics 22 (2003)
3107.
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