Preparation of half-sandwich ethylene complexes of Osmium(II)

Article abstract of DOI:10.1016/j.jorganchem.2011.12.032

Ethylene complexes [OsCl(η⁶-p-cymene)(η²- CH₂CH₂)L]BPh₄ (1, 2) [L = P(OMe)₃, P(OEt)₃, PPh(OEt)₂, ^tBuNC) were prepared by allowing the dichloro compounds OsCl₂(η⁶-p-cymene)L to react with CH₂CH₂ in mild conditions (1 atm). Treatment of 1 with amine or hydrazine yielded [OsCl(p-tolyl-NH₂) (η⁶-p-cymene){PPh(OEt)₂}]BPh₄ (3) or [OsCl(η⁶-p-cymene)(CH₃NHNH₂){PPh(OEt) ₂}]BPh₄ (4) derivatives. The vinylidene cation [OsCl{CC(H)Ph}(η⁶-p-cymene){PPh(OEt)₂}]⁺ (5⁺) was also prepared from 1 and PhCCH. The complexes were characterized spectroscopically and by X-ray crystal structure determination of [OsCl(η⁶-p-cymene)(η²-CH₂CH ₂){P(OMe)₃}]BPh₄ (1a). The nature of the Os-ethylene bond was investigated from a computational point of view.

Full text of DOI:10.1016/j.jorganchem.2011.12.032

Journal of Organometallic Chemistry 702 (2012) 45e51
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Preparation of half-sandwich ethylene complexes of Osmium(II)
,
b
a
a
b
Gabriele Albertin a , Alberto Albinati , Stefano Antoniutti , Marco Bortoluzzi , Silvia Rizzato
*
a Dipartimento di Scienze Molecolari e Nanosistemi, Università Ca’ Foscari Venezia, Dorsoduro 2137, 30123 Venezia, Italy
b Dipartimento di Chimica Strutturale e Stereochimica Inorganica, Università degli Studi di Milano, Via Venezian 21, 20133 Milano, Italy
a r t i c l e i n f o
a b s t r a c t
Ethylene complexes [OsCl(h h
6-p-cymene)(
2-CH2]CH2)L]BPh4 (1, 2) [L ¼ P(OMe)3, P(OEt)3, PPh(OEt)2,
Article history:
tBuNC) were prepared by allowing the dichloro compounds OsCl2( 6-p-cymene)L to react with CH2]CH2
h
Received 3 November 2011
Received in revised form
15 December 2011
in mild conditions (1 atm). Treatment of 1 with amine or hydrazine yielded [OsCl(p-tolyl-NH2)(
cymene){PPh(OEt)2}]BPh4 (3) or [OsCl(
6-p-cymene)(CH3NHNH2){PPh(OEt)2}]BPh4 (4) derivatives. The
vinylidene cation [OsCl{]C]C(H)Ph}(
6-p-cymene){PPh(OEt)2}]þ (5D) was also prepared from 1 and
PhC^CH. The complexes were characterized spectroscopically and by X-ray crystal structure determi-
nation of [OsCl(
6-p-cymene)( 2-CH2]CH2){P(OMe)3}]BPh4 (1a). The nature of the Oseethylene bond
h
6-p-
h
h
Accepted 22 December 2011
Keywords:
Synthesis
Half-sandwich complexes
Ethylene ligand
h
h
was investigated from a computational point of view.
Ó 2012 Elsevier B.V. All rights reserved.
Phosphite and isocyanide ligands
Osmium(II)
1. Introduction
2. Experimental section
The coordination of an alkene to a transition metal fragment
occupies an important place in organometallic chemistry [1,2], not
only due to the significant changes in structure and chemical
reactivity that the alkene coordination to a central metal may
induce [3,4], but also due to the influence that the metal fragment
may have in its catalytic transformations [5]. A number of alkene
complexes have been prepared [1,3,4,6] for different central metals
with various types of ligands, in order to probe the most important
factors which influence the stability of the coordinated alkene and
its reactivity in stoichiometric and catalytic organic reactions.
However, the number of reported alkene complexes for the
metals of the iron triad is still limited, compared with other metal
triads [7] such as those of cobalt and nickel, and the known
ethylene complexes for osmium are still few [8].
2.1. General comments
All synthetic work was carried out in an appropriate atmosphere
(Ar, N2) using standard Schlenk techniques or an inert atmosphere
dry-box. Once isolated, the complexes were found to be relatively
stable in air, allowing their characterization; nonetheless they were
stored under nitrogen at ꢀ25 ꢁC. All solvents were dried over
appropriate drying agents, degassed on a vacuum line, and distilled
into vacuum-tight storage flasks. OsO4 was a Pressure Chemical Co.
(USA) product, used as received. Phosphines PPh(OEt)2 and
PPh2OEt were prepared by the method of Rabinowitz and Pellon
[10], and P(OMe)3 and P(OEt)3 were Aldrich products, purified by
distillation under nitrogen. Isocyanides RNC (R
¼
p-tolyl,
p-methoxy) were obtained by the method of Ziehn [11], and tBuNC
was an Aldrich product used as received. Other reagents were
purchased from commercial sources in the highest available purity
and used as received. Infrared spectra were recorded on a Per-
kineElmer Spectrum-One FT-IR spectrophotometer. NMR spectra
(1H, 13C, 31P) were obtained on AVANCE 300 Bruker spectrometer at
temperatures between ꢀ90 and þ30 ꢁC, unless otherwise stated. 1H
and 13C spectra are referred to internal tetramethylsilane and 31P
{1H} ones to 85% H3PO4 with downfield shifts considered positive.
COSY, NOESY, HMQC and HMBC NMR experiments were performed
with standard programs. The iNMR software package [12] was used
to treat NMR data. The conductivity of 10ꢀ3 mol dmꢀ3 solutions of
the complexes in CH3NO2 at 25 ꢁC was measured on a Radiometer
We have a long-standing interest in the chemistry of arene
complexes [9] of the iron triad and, during our studies on the
reactivity of p-cymene complexes of osmium, we found that
ethylene may coordinate to the metal fragment [OsCl(h
6-p-cym-
ene)L]þ (L ¼ phosphite) in very mild conditions.
We report here the results of these studies, including the
synthesis and characterization of ethylene complexes of osmium
stabilized by the p-cymene ligand.
* Corresponding author. Fax: þ39 041 234 8917.
E-mail address: albertin@unive.it (G. Albertin).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.12.032

46
G. Albertin et al. / Journal of Organometallic Chemistry 702 (2012) 45e51
CDM 83. Elemental analyses were determined in the Microanalyt-
ical Laboratory of the Dipartimento di Scienze Farmaceutiche,
University of Padova (Italy).
1c: 1H NMR (CD2Cl2, 25 ꢁC)
d: 7.85e6.86 (m, 25 H, Ph), ABCDX, dA
5.52, dB 5.62, dC 5.07, dD 5.66, JAB ¼ 5.9, JAC ¼ 0.6, JAD ¼ 1.0, JAx ¼ 0.6,
JBC ¼ 1.0, JBD ¼ 0.6, JBx ¼ 1.7, JCD ¼ 5.9, JCx ¼ 1.6, JDx ¼ 1.5 (4 H, Ph p-
cym), EFGHX spin syst (X ¼ 31P), dE
¼
dG 4.24, dF
¼
dH 3.11,
JEG ¼ JFH ¼ 9.5, JEH ¼ JFG ¼ 9.2, JEF ¼ JGH ¼ 0.6, JEx ¼ JGx ¼ 3.8,
JFx ¼ JHx ¼ 2.1 (4 H, CH2 ethylene), 4.04 (m, 4 H, CH2 phos), 2.28 (m,
1 H, CH iPr), 1.68 (s, 3 H, CH3 p-cym), 1.39 (JHH ¼ 7.0), 1.33 (JHH ¼ 7.0)
(t, 6 H, CH3 phos), 1.09 (JHH ¼ 6.7), 1.07 (JHH ¼ 6.6) (d, 6 H, CH3 iPr).
2.2. Synthesis of complexes
Complexes [OsCl(
m
-Cl)(
h
6-p-cymene)]2, OsCl2(
h
6-p-cymene)L
[L ¼ P(OMe)3, P(OEt)3, PPh(OEt)2] and OsCl2(
h
6-p-cymene)(CNR)
31P{1H} NMR (CD2Cl2, 25 ꢁC) : 84.2 (s). 13C{1H} NMR (CD2Cl2, 25 ꢁC)
d
(R ¼ tBu, p-tolyl) were prepared following the methods previously
d
: 165e122 (m, Ph), 116.24 (d, JCP ¼ 1.8, C1 p-cym), 104.06 (s, C4),
reported [9d,13].
91.65 (d, JCP ¼ 2.3, C5), 90.37 (d, JCP ¼ 3.7, C3), 86.57 (d, JCP ¼ 5.8, C6),
81.22 (d, JCP ¼ 5.2, C2), 66.96, 66.93, 66.26 (d, JCP ¼ 11.0, CH2 phos),
i
6-p-cymene)(
h
2-CH2]CH2)L]BPh4 (1) [P ¼ P(OMe)3 (a),
51.00 (d, JCP ¼ 1.5, CH2 ethylene), 30.74 (s, CH Pr), 21.95, 21.50 (s,
2.3. [OsCl(
P(OEt)3 (b), PPh(OEt)2 (c)]
h
CH3 iPr), 17.31 (s, CH3 p-cym), 16.31 (JCP ¼ 6.7), 16.22 (JCP ¼ 6.6) (d,
CH3 phos). LM ¼ 53.5
U
ꢀ1 molꢀ1 cm2. C46H53BClO2OsP (905.38): C
61.02, H 5.90, Cl, 3.92; found C 59.84, H 6.02, Cl 3.70%.
In a 25-mL three-necked round-bottomed flask were placed
a solid sample of the appropriate complex OsCl2(
6-p-cymene)L
h
2.4. [OsCl(
h
6-p-cymene)( 2-CH2]CH2)(CNtBu)]BPh4 (2)
h
(0.38 mmol), an excess of NaBPh4 (0.77 mmol, 0.26 g), and 4 mL of
ethanol. The resulting mixture was stirred under an ethylene
atmosphere (1 atm) at room temperature for 24 h. The yellow solid
which separated out was filtered and crystallized under ethylene
from CH2Cl2 and ethanol; yield ꢂ90%.
In a 25-mL three-necked round-bottomed flask were placed
0.20 g (0.41 mmol) of OsCl2(
6-p-cymene)(CNtBu), an excess of
h
NaBPh4 (0.82 mmol, 0.28 g) and 4 mL of ethanol. The resulting
mixture was stirred under an ethylene atmosphere (1 atm) at room
temperature for 30 h. A yellow solid separated out which was
filtered and crystallized under ethylene from CH2Cl2 and ethanol;
1a: 1H NMR (CD2Cl2, 25 ꢁC)
d (see Chart 1): 7.40e6.87 (m, 20 H,
BPh4), ABCDX spin syst (X ¼ 31P), dA 5.77, dB 5.21, dC 5.87, dD 5.73,
JAB ¼ 6.2, JAC ¼ 0.8, JAD ¼ 1.2, JAx ¼ 0.1, JBC ¼ 1.2, JBD ¼ 0.8, JBx ¼ 1.0,
JCD ¼ 6.2, JCx ¼ 1.6, JDx ¼ 1.2 (4 H, Ph p-cym), EFGHX spin syst
yield ꢂ80%. IR (KBr) nCN: 2191 (s) cmꢀ1. 1H NMR (CD2Cl2, ꢀ30 ꢁC)
d:
(X ¼ 31P), dE
¼
dG 4.15, dF
¼ dH 3.15, JEG ¼ JFH ¼ 9.7, JEH ¼ JFG ¼ 9.0,
7.85e6.86 (m, 20 H, BPh4), ABCD, dA 5.05, dB 5.15, dC 5.49, dD 5.09,
JAB ¼ 6.0, JAC ¼ 0.7, JAD ¼ 1.2, JBC ¼ 1.2, JBD ¼ 0.7, JCD ¼ 6.0 (4 H, Ph p-
JEF ¼ JGH ¼ 0.6, JEx ¼ JGx ¼ 4.4, JFx ¼ JHx ¼ 1.9 Hz (4 H, CH2 ethylene),
cym), EFGH spin syst (X ¼ 31P), dE
¼
dG 4.04, dF
¼
dH 3.47,
i
3.87 (d, 9 H, JHP ¼ 11.0, CH3 phos), 2.43 (m, 1 H, JHH ¼ 6.9, CH Pr),
1.20 (d, 3 H, JHH ¼ 7.0, CH3 p-cym), 1.15 (d, 6 H, JHH ¼ 6.9, CH3 iPr)
JEG ¼ JFH ¼ 17.6, JEH ¼ JFG ¼ 9.6, JEF ¼ JGH ¼ 0.6 (4 H, CH2 ethylene),
2.41 (m, 1 H, CH iPr), 1.54 (s, 9 H, CH3 tBu), 1.31 (s, 3 H, CH3 p-cym),
1.15 (JHH ¼ 6.9), 1.14 (JHH ¼ 6.8) (d, 6 H, CH3 iPr). 13C{1H} NMR
ppm. 31P{1H} NMR (CD2Cl2, 25 ꢁC) : 60.4 (s). 13C{1H} NMR (CD2Cl2,
d
25 ꢁC)
d
: 165e122 (m, BPh4), 116.96 (d, JCP ¼ 2.8, C1 p-cym), 106.24
(CD2Cl2, 25 ꢁC)
d: 165e122 (m, BPh4), 111.24 (s, C1 p-cym), 105.73 (s,
(d, JCP ¼ 1.0, C4), 91.30 (d, JCP ¼ 4.2, C5), 90.01 (d, JCP ¼ 2.1, C3), 88.61
(d, JCP ¼ 1.3, C6), 88.11 (d, JCP ¼ 3.0, C2), 56.77 (d, JCP ¼ 9.5, CH3
C4), 89.39 (s, C5), 88.47 (s, C3), 88.24 (s, C6), 86.32 (s, C2), 60.17 (s,
C]N), 57.91 (s, CH2 ethylene), 31.56 (s, CH iPr), 31.23 (s, CMe3 tBu),
30.29 (s, CH3 tBu), 22.00, 21.91 (s, CH3 iPr), 18.08 (s, CH3 p-cym).
i
phos), 50.02 (d, JCP ¼ 3.6, CH2 ethylene), 31.07 (s, CH Pr), 22.02,
21.67 (s, CH3 iPr), 17.98 (s, CH3 p-cym). LM ¼ 56.2 Uꢀ1 molꢀ1 cm2.
C39H47BClO3OsP (831.26): C 56.35, H, 5.70, Cl 4.26; found C 56.11, H
5.81, Cl 4.08%.
LM ¼ 55.1
U
ꢀ1 molꢀ1 cm2. C41H47BClNOs (790.31): C 62.31, H 5.99,
N 1.77, Cl 4.49; found C 62.13, H 6.10, N 1.68, Cl 4.71%.
1b: 1H NMR (CD2Cl2, 25 ꢁC)
d: 7.35e6.90 (m, 20 H, BPh4), ABCDX,
2.5. [OsCl(p-tolyl-NH2)(
h
6-p-cymene){PPh(OEt)2}]BPh4 (3) and
6-p-cymene)(CH3NHNH2){PPh(OEt)2}]BPh4 (4)
dA 5.77, dB 5.18, dC 5.87, dD 5.69, JAB ¼ 6.0, JAC ¼ 0.5, JAD ¼ 1.3, JAx ¼ 0.7,
[OsCl(
h
JBC ¼ 1.3, JBD ¼ 0.5, JBx ¼ 0.4, JCD ¼ 6.0, JCx ¼ 0.8, JDx ¼ 0.3 (4 H, Ph p-
cym), EFGHX spin syst (X ¼ 31P), dE
¼
dG 4.15, dF
¼
dH 3.14,
To a solution of [OsCl(
h
6-p-cymene)( 2-CH2]CH2){PPh(OEt)2}]
h
JEG ¼ JFH ¼ 11.2, JEH ¼ JFG ¼ 9.1, JEF ¼ JGH ¼ 0.6, JEx ¼ JGx ¼ 4.4,
JFx ¼ JHx ¼ 1.9 (m, 4 H, CH2 ethylene), 4.06 (m, 6 H, CH2 phos), 2.46
BPh4 (100 mg, 0.11 mmol) in CH2Cl2 (10 mL) was added an excess of
p-toluidine (0.33 mmol, 35 mg), in one case, or an excess of
i
(m, 1 H, JHH ¼ 7.0, CH Pr), 1.90 (s, 3 H, CH3 p-cym), 1.33 (td, 9 H,
methylhydrazine (0.33 mmol, 18
mL) in the other. The reaction
JHH ¼ 7.0, JHH ¼ 0.46, CH3 phos), 1.20 (JHH ¼ 6.9), 1.17 (JHH ¼ 6.9) (d,
6 H, CH3 iPr). 31P{1H} NMR (CD2Cl2, 25 ꢁC) : 55.49 (s). 13C{1H} NMR
d
mixture was stirred at room temperature for 2 h. The solvent was
removed under reduced pressure to give an oil, which was treated
with ethanol (3 mL) containing an excess of NaBPh4 (0.22 mmol,
75 mg). A yellow solid slowly separated out, which was filtered and
crystallised from CH2Cl2 and ethanol; yield ꢂ80%.
(CD2Cl2, 25 ꢁC)
d
: 165-122 (m, BPh4), 117.13 (d, JCP ¼ 2.8, C1 p-cym),
105.32 (s, C4), 91.46 (d, JCP ¼ 4.2, C5), 90.48 (d, JCP ¼ 2.2, C3), 88.55
(d, JCP ¼ 1.3, C6), 88.06 (d, JCP ¼ 6.7, C2), 66.14 (d, JCP ¼ 9.9, CH2
i
phos), 49.77 (d, JCP ¼ 3.4, CH2 ethylene), 30.98 (s, CH Pr), 21.96,
3: LM ¼ 52.8 Uꢀ1 molꢀ1 cm2. C51H58BClNO2OsP (984.48): C
62.22, H 5.94, N 1.42, Cl 3.60; found C 62.08, H 6.08, N 1.55, Cl 3.42%.
4: LM ¼ 54.1 Uꢀ1 molꢀ1 cm2. C45H55BClN2O2OsP (923.40): C
58.53, H 6.00, N 3.03, Cl 3.84; found C 58.71, H 5.87, N 3.15, Cl 3.64%.
IR and NMR data were exactly the same of the related complexes
previously prepared [9d,30].
21.69 (s, CH3 iPr), 17.82 (s, CH3 p-cym), 16.29 (d, JCP ¼ 6.4, CH3 phos).
LM ¼ 52.8 Uꢀ1 molꢀ1 cm2. C42H53BClO3OsP (873.34): C 57.76, H
6.12, Cl 4.06; found C 57.55, H 6.02, Cl 4.29%.
HB
C4
HA
C1
HE
HF
C3
C5
C2
C6
CH3
H
C
C
2.6. [OsCl{]C]C(H)Ph}(h
6-p-cymene){PPh(OEt)2}]þCF3SOꢀ3 (5)
H3C
C
[Os]
CH3
An excess of phenylacetylene (0.33 mmol, 37
mL) was added to
a solution of [OsCl(
h
6-p-cymene)( 2-CH2]CH2){PPh(OEt)2}]BPh4
h
HH
HG
HC
HD
(100 mg, 0.11 mmol) in CH2Cl2 (7 mL) and the reaction mixture was
stirred at room temperature for 3 h. The solvent was removed
under reduced pressure to give an oil, which was characterised as
Chart 1. Labeling scheme of the p-cymene and ethylene ligands used for the NMR
study.

G. Albertin et al. / Journal of Organometallic Chemistry 702 (2012) 45e51
47
such. 1H and 13C NMR data were exactly the same of the related
complex previously prepared [9b].
(BS1), which is a combination of the 6e31G(d,p) basis set with the
LANL2DZ effective core basis set. The atoms between hydrogen and
argon are described with the 6e31G(d,p) basis set, and the heavier
atoms are modeled with the LANL2DZ basis set [21]. Further
refining was carried out with the hybrid DFT B3PW91 functional
2.7. X-ray structure determination
[22] in combination with a polarized triple-z quality basis set (BS2)
Air stable, yellow crystals of 1a, suitable for X-ray diffraction,
were obtained by crystallization from CH2Cl2 and ethanol. A crystal
of 1a was mounted on a Bruker APEXII CCD diffractometer equip-
ped with a CCD detector and cooled, using a cold nitrogen stream,
to 120(2) K for the data collection. The space group was determined
from the systematic absences and confirmed by the successful
refinement, while the cell constants were refined, at the end of the
data collection with the data reduction software SAINT [14]. The
experimental conditions for the data collections, crystallographic
and other relevant data are listed in Table 1 and in the Supporting
Information. Collected intensities were corrected for Lorentz and
polarization factors [14] and empirically for absorption using the
SADABS program [15].
The structure was solved by direct and Fourier methods and
refined by full matrix least squares [16], minimizing the function
[Sw(Fo2ꢀ(1/k)F2c)2] and using anisotropic displacement parameters
for all atoms, except the hydrogens.
The contribution of the hydrogen atoms, in their calculated
positions, was included in the refinement using a riding model
(B(H) ¼ aB(Cbonded)(Å2), a ¼ 1.5 for the the methyl groups and
a ¼ 1.2 for the others); the H atoms of the ethylene moiety were
refined with their B’s treated as above. Refining Flack’s parameter
tested the handedness of the structure [17].
composed by the 6e311G(d,p) basis set on the light atoms and the
LANL2TZ(f) basis set on the metal center [23]. “Restricted”
formalism was applied in all calculations and the stationary points
were characterized as true minima by IR simulation. Atomic
charges were derived from Mulliken population analysis. Energy
differences (
metal fragments and free ligands were calculated on the basis of
equation:
E ¼ E(complex) ꢀ E(metal fragment) ꢀ E(olefin). Results
DE) between the complexes and the corresponding
D
were corrected for zero-point vibrational energy and the basis set
superposition error [24]. [Os]eolefin dissociation energy was also
studied for each complex by a series of restricted single-point
energy calculations at fixed [Os]eolefin lengths longer than those
of equilibrium, up to 9 Å. Dissociation energy (ED) was calculated on
the basis of equation: ED ¼ EN ꢀ Eeq, where Eeq is equilibrium
energy and EN was obtained by fitting the computed energy values
(E) and the Meolefin distances (r) according to the following
equation: E ¼ EN ꢀ AeꢀBr, where EN, A and B are the parameters to
be optimized.
DFT EDF2 calculations were carried out with Spartan 08 [25] on
a x86-64 workstation based on an Intel Core I7 940 processor.
Gaussian 09 was used for the calculations based on the B3PW91
functional [26]. DFT B3PW91 calculations were performed at
CINECA (Centro Italiano di Supercalcolo, Bologna, Italy) on an IBM
P6-575 workstation equipped with 64-bit IBM Power6 processors.
No extinction correction was deemed necessary. Upon conver-
gence the final Fourier difference map showed no significant peaks.
All calculations and plotting were carried out with the PC
version of SHELX-97 [16], WINGX [18], ORTEP [18] and Mercury
programs [19].
3. Results and discussion
Ethylene reacts in mild conditions (1 atm, room temperature)
h
6-p-cymene)L in the presence of
2.8. Theoretical calculations
with dichloro complexes OsCl2(
NaBPh4 to give h -
h
2-ethylene derivatives [OsCl( 6-p-cymene)(h2
The computational geometry optimization of the complexes
was carried out by the hybrid DFT EDF2 method [20] without
symmetry constraints, in combination with the LACVP** basis set
CH2]CH2)L]BPh4 (1), which were isolated as yellow solids and
characterized (Scheme 1).
Important for successful synthesis was the presence of the salt
NaBPh4, which probably favors substitution of the chloride ligand
in the starting complexes, thus allowing derivatives 1 to be ob-
tained in good yields.
Table 1
Studies of the reaction of dichloro complexes OsCl2(h
6-p-cym-
Experimental data for the X-ray diffraction study of compound 1a.
ene)L with CH2]CH2 showed that only phosphines with small cone
Formula
Fw
Data coll. T, K
Cryst syst.
Space group (no.)
a, Å
b, Å
C39H47BClO3OsP
831.20
120(2)
Orthorhombic
Pna21 (33)
27.002(2)
12.6690(7)
10.2909(6)
3520.4(3)
4
angles, such as P(OMe)3, P(OEt)3 and PPh(OEt)2, allow the ethylene
to be coordinated to the metal center of the fragment [OsCl(h
6-p-
cymene)L]þ. Instead, with bulkier phosphines such as PPh2OEt,
PPh3 or PiPr3 no formation of alkene complex 1 was observed. The
important role of steric factors in determining the coordination of
alkene to the p-cymene fragment was further confirmed by react-
c, Å
V, Å3
ing propylene CH3CH]CH2 with OsCl2(
h
6-p-cymene)L which, at
Z
1 atm, did not yield any
h
2-alkene derivative. Even with the less
r(calcd), g cmꢀ3
1.568
37.80
m
, cmꢀ1
bulky phosphite P(OMe)3, coordination of the propylene was not
observed in any studied conditions; this negative result suggests
that only ethylene, in mild conditions, can bind to the metal center
Radiation
MoKa (graphite monochrom.,
l
¼ 0.71073 Å)
q
range, deg
1.78 ꢃ
q
ꢃ 29.46
No. independent data
9179
No. obs. Refctl. (no)
8565
2
[jFoj2 > 2.0
s
(jFj )]
+
No. of param. refined (nv)
R (obsd reflns)a
R2w (obsd reflns)b
GOFc
427
CH2=CH2, 1 atm
EtOH, NaBPh4
0.0207
0.0458
1.023
Os
Os
BPh4
L
L
Cl
Cl
Cl
P
P
a
b
c
R ¼ ðjFo ꢀ ð1=kÞFejÞ= jFoj.
1
P
P
R2w ¼ f ½wðFo2 ꢀ ð1=kÞFc2Þ2ꢄ= wjF02j2ꢄg1=2
.
P
GOF ¼ ½ wðFo2 ꢀ ð1=kÞFc2Þ2=ðno ꢀ nvÞꢄ1=2
.
Scheme 1. L ¼ P(OMe)3 (a), P(OEt)3 (b), PPh(OEt)2 (c).

48
G. Albertin et al. / Journal of Organometallic Chemistry 702 (2012) 45e51
of a p-cymene fragment [OsCl(h
6-p-cymene)L]þ, containing small
cone-angle phosphines.
As isocyanides, RNC, are also ligands with little steric hindrance
and -acceptor ability quite comparable with those of phosphites,
we reacted isocyanide complex OsCl2(
6-p-cymene)(RNC) with
ethylene in the presence of NaBPh4 and did observed the formation
of ethylene derivative [OsCl(
6-p-cymene)( 2-CH2]CH2)(RNC)]
BPh4 (2), as shown in Scheme 2.
p
h
h
h
However, a pure solid sample could only be obtained with tert-
butyl isocyanide, and only an oil was separated with p-tolylNC. In
this case too, propylene CH3CH]CH2 did not react even with iso-
cyanide precursors OsCl2(
complex was obtained.
h
6-p-cymene)(RNC) and no alkene
We have also reacted with CH2]CH2 the p-cymene complexes
OsCl2(
6-p-cymene)L containing carbonyl or pyrazole as support-
ing ligands, but did not observe any formation of
2-ethylene
h
h
complexes. Therefore, it seems that only with phosphite having
small cone angle or with tert-butyl isocyanide can the p-cymene
fragment “OsCl(h
6-p-cymene)L” bind only the smallest of alkenes,
under mild conditions.
Ethylene complexes 1 and 2 were isolated as yellow solids stable
in air and in solution of polar organic solvents, where they behave
as 1:1 electrolytes [27]. Elemental analyses and spectroscopic data
(IR and 1H, 31P, 13C NMR) support this formulation, which was
confirmed by the X-ray crystal structure determination of complex
Fig. 1. Molecular structure of [OsCl(h h
6-p-cymene)( 2-CH2]CH2){P(OMe)3}]þ (1aþ).
Thermal ellipsoids are drawn at 50% probability. Relevant bond lengths (Å) and angles
(deg): OseCl 2.3962(7), OseP 2.2864(7), OseC11 2.231(3), OseC21 2.265(3), C11eC21
1.373(5), OseC1 2.318(3), OseC2 2.289(2), OseC3 2.220(3), OseC4 2.278(3), OseC5
2.226(3), OseC6 2.222(3), C1eC2 1.398(4), C2eC3 1.441(4), C3eC4 1.413(4), C4eC5
1.428(4), C5eC6 1.406(5), PeOseCl 85.89(3), P-Os-Cb 93.9(2), Cl-Os-Cb 84.2(2) (Cb is
the midpoint of the C]C bond).
[OsCl(
The immediate coordination sphere of the Os atom consists of
the
6-p-cymene ring, the P and Cl atoms and the 2-C2H4 ligand,
h h
6-p-cymene)( 2-CH2]CH2){P(OMe)3}]BPh4 (1a) (Fig. 1).
h
h
resulting in a three-legged piano-stool coordination. The ethylene
ligand is asymmetrically bonded to the Os center (OseC 2.231(3) Å
and 2.265(3) Å respectively); these distances are quite long and fall
in the upper range of those reported for other Os complexes con-
taining a coordinated double bond (in the range 2.16e2.25 Å)
[8c,i,j,28] and are comparable with those found in the octahedral
[OsH(C2H4)2(PMe2Ph)3]þ [8c] complex where the C2H4 moiety is
trans to a hydride ligand (2.235(6) and 2.247(6) Å respectively). We
note, however, that in those three-legged piano-stool structures
where only one “h2eC2H4” moiety is coordinated to the metal
center [8j,28c] the OseC separations are usually shorter (in the
range 2.08e2.21 Å).
The C]C separation at 1.373(5) Å falls in the range reported in
the literature (1.36e1.44 Å) [8c,i,j,28,29] and is shorter than the
average value of 1.392 Å expected for a coordinated unsubstituted
ethylene fragment [29]. We note that these distances are consistent
with a weakly bonded ligand in keeping with the reactivity of this
complex and the results of the DFTcalculations reported below. The
C2H4 ligand makes an angle of 58.1(2)ꢁ with the mean-plane
defined by atoms P, Cl and the mid-point of the C]C bond. The
p-cymene ligand is distorted upon coordination to the Os atom, as
shown by the significantly different metal-carbon separations (in
the range 2.22e2.32 Å) and by small, but significant, deviations
from planarity of the aromatic ring (max. deviation from the least-
squares plane defined by atom C1eC6, þ0.04 Å, with atoms C3 and
C6 closer to the Os). The CeC bonds in the p-cymene ring are also
different (see caption to Fig. 1) and the shortest CeC (1.398(4) Å)
involves the atom (C1) with the longest separation from the metal
center. OseP and OseCl distances are unexceptional.
The position of BPh4ꢀanions with respect to cations is informa-
tive and this is shown in Fig. 2. There are short contacts between
the BPh4ꢀ anion and the cationic osmium complex in the range
2.3e2.8 Å, the other packing distances being longer than 3.0 Å. We
note that the anion is placed away from the ethylene ligand and
close to the phosphite methoxy groups. NOESY NMR experiments
(showing a correlation between the methoxy hydrogen atoms of
P(OMe)3 and the phenyl protons of BPhꢀ4 ) indicate that similar
arrangements of the anions also occur in solution. There are no
short intermolecular contacts involving the ethylene ligands.
At room temperature, beside the signals of p-cymene and
phosphite ligands and the BPhꢀ4 anion, the 1H NMR spectra of
phosphine complexes [OsCl(h h
6-p-cymene)( 2-CH2]CH2)L]BPh4
+
CH2=CH2, 1 atm
EtOH, NaBPh4
Os
Os
RNC
Cl
RNC
Cl
Cl
2
Scheme 2. R ¼ tBu.
Fig. 2. Space filling model of [OsCl(h h
6-p-cymene)( 2-CH2]CH2)L]BPh4.

G. Albertin et al. / Journal of Organometallic Chemistry 702 (2012) 45e51
49
(1) show two multiplets at 4.24e4.14 and 3.15e3.11 ppm, attrib-
3.1. DFT calculations
uted to the protons of the coordinate ethylene. Lowering the
sample temperature caused a variation in the spectra but, even
at ꢀ90 ꢁC, ethylene peaks were still broadened, suggesting that
rotation of CH2]CH2 is still present at this temperature. The
multiplicity of signals is due to the presence of a chiral center in the
molecule, which makes the protons of ethylene two-by-two dia-
stereotopic, thus appearing at different values of chemical shift and
coupled with the phosphorus of the phosphine. The pattern may be
simulated by an ABCDX model (X ¼ 31P) with the parameters re-
ported in Experimental section and the good fit between experi-
mental and calculated spectra strongly support the proposed
attributions. The 31P NMR spectra of 1 appear as sharp singlets,
whereas the 13C spectra, show the characteristic signals of sup-
porting ligands and display a singlet at 51.00e49.77 ppm, which
was correlated, in a HMQC experiment, with the two ethylene
Theoretical studies were carried out on ethylene and propylene
complexes [OsCl(
6-p-cymene)( 2-CH2]CH2){P(OMe)3}]þ (OsP-
ethylene), [OsCl(
6-p-cymene)( 2-CH2]CHCH3){P(OMe)3}]þ (OsP-
propylene), [OsCl( (OsC-
6-p-cymene)( 2-CH2]CH2)(CNtBu)]þ
ethylene)and[OsCl(
6-p-cymene)( 2-CH2]CHCH3)(CNtBu)]þ (OsC-
h
h
h
h
h
h
h
h
propylene). Tables S2 and S3 list a selection of computed bond
lengths and, in the case of OsP-ethylene, a comparison with
data from the X-ray structure determination of 1a is made. Both
computational approaches used (EDF2/BS1 and B3PW91/BS2)
gave comparable bond lengths. Fig. 3 shows the ground-state
optimized geometry of OsP-ethylene. The overall match
between X-ray and calculated geometry is good, the main
differences being the relative orientation of the p-cymene ligand
and a few dihedral angles in P(OMe)3, which are probably due
to interactions between complex and counterion (see above).
The calculated values for some bond lengths, such as the olefin
C]C (C11eC21), OseCl and OseP, are slightly overestimated. In
particular, both EDF2/BS1 and B3PW91/BS2 calculations predict
the length of the olefin C]C bond about 2% higher than the
experimental value.
The OseC(ethylene) and the C]C (ethylene) bond lengths are
almost unaffected by substitution of the ancillary ligand P(OMe)3
with CNtBu. The olefin C]C double bond is only slightly weakened
(w5%) by coordination to the metal fragments, matching reactivity
and structural results. In addition, the OseC(olefin) and C]C
(olefin) bond lengths are similar in the ethylene and propylene
complexes for both metal fragments. Replacement of the ancillary
ligand and the olefin do not greatly influence the Oseolefin inter-
action, as shown by the energy values for dissociation of the alkene
molecule from Os complexes (ED) and energy differences between
the complexes and the corresponding metal fragments and free
proton multiplets at 4.24e3.10 ppm and attributed to
carbon resonances, matching the proposed formulation.
The IR spectrum of isocyanide complex [OsCl(
6-p-cymene)(h2
h
2-CH2]CH2
h
-
CH2]CH2)(CNtBu)]BPh4 (2) shows a strong band at 2191 cmꢀ1 due
to nCN of the isocyanide ligand. The 1H NMR spectrum confirms the
presence of the tBuNC group, showing a singlet at 1.54 ppm of the
protons of the tBu substituents. The spectrum also contains
two multiplets of the ethylene hydrogen atoms (at 4.04 and
3.47 ppm respectively). The 13C NMR spectrum confirms the
presence of the
h a singlet at
2-CH2]CH2 ligand, showing
57.91 ppm, which was correlated, in a HMQC experiment, with the
proton multiplets at 4.04 and 3.47 ppm and attributed to ethylene
carbon resonances. The spectrum also shows the characteristic
signals of p-cymene and the two singlets at 60.17 and 31.23 ppm of
the tBu substituent of the isocyanide ligand, matching the
proposed formulation.
Reactivity studies on ethylene complexes 1 and 2 with nucleo-
philic reagents were also carried out, to test whether reactions on
coordinate alkene would occur. Unfortunately, results only showed
olefins (DE) (see Table S4). All examined complexes have similar ED
substitution of the
h
2-CH2]CH2 ligand by amine or hydrazine,
affording related p-cymene derivatives 3 and 4 (Scheme 3).
The relative lability of the coordinate ethylene was also
confirmed by the reaction with PhC^CH, which afforded vinyli-
dene cations [OsCl{]C]C(H)Ph}(
h
6-p-cymene)L]þ (5) through an
initial substitution of
h
2-CH2]CH2 with alkyne, which tauto-
merizes on the metal center, yielding the final vinylidene species 5.
Although complexes 3e5 are known [9b,d,30], the use of ethylene
complexes 1 and 2 as precursors is an easy new method for their
preparation.
+
p-tolyl-NH2
Os
L
NH2-p-tolyl
Cl
3
+
+
MeNHNH2
PhC CH
Os
Os
L
L
NH2NHMe
+
Cl
Cl
4
Os
L
C
Ph
Cl
5
C
H
Fig. 3. Equilibrium geometry of OsPeethylene (B3PW91/BS2). Hydrogen atoms
omitted for clarity. Selected bond lengths (Å): C]C (olefin) 1.402; OseC(olefin) 2.235,
2.214; OseC(cymene) 2.288, 2.221, 2.193, 2.247, 2.243, 2.348; OseP 2.314; OseCl 2.403.
Scheme 3. L ¼ P(OMe)3, P(OEt)3, PPh(OEt)2, tBuNC.

50
G. Albertin et al. / Journal of Organometallic Chemistry 702 (2012) 45e51
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DE values show weak
variations when the ancillary or alkene ligands are changed and are
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h
6-p-cymene)
{P(OMe)3}]þ and [OsCl( 6-p-cymene)(CNtBu)]þ. The Mulliken
h
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In this paper we report the preparation of ethylene complexes of
osmium stabilised by the p-cymene ligand. The facile substitution
of the h
2-CH2]CH2 ligand allowed new half-sandwich derivatives
to be obtained. The structural parameters and the nature of the
Oseethylene bond in the ethylene complexes are also discussed.
(k) S. Bajo, M.A. Esteruelas, A.M. López, E. Oñate, Organometallics 30 (2011)
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[9] (a) G. Albertin, S. Antoniutti, J. Castro, Organometallics 30 (2011) 1914e1919;
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(c) G. Albertin, S. Antoniutti, J. Castro, S. García-Fontán, Eur. J. Inorg. Chem.
(2011) 510e520;
Acknowledgments
(d) G. Albertin, S. Antoniutti, J. Castro, S. Paganelli, J. Organomet. Chem. 695
(2010) 2142e2152;
(e) G. Albertin, S. Antoniutti, J. Castro, J. Organomet. Chem. 695 (2010)
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(f) G. Albertin, S. Antoniutti, J. Castro, Eur. J. Inorg. Chem. (2009) 5352e5357;
(g) G. Albertin, S. Antoniutti, F. Callegaro, J. Castro, Organometallics 28 (2009)
4475e4479.
The authors wish to thank MIUR (PRIN2009) for financial
support and CINECA Award N. HP10CI3CHF (2010) for making
available high-performance computing resources and support.
Thanks also go to Mrs. Daniela Baldan, from the Università Ca’
Foscari Venezia (Italy), for technical assistance.
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