POP-pincer osmium-polyhydrides: Head-to-head (Z)-dimerization of terminal alkynes

Article abstract of DOI:10.1021/ic400730a

A wide range of osmium-polyhydride complexes stabilized by the POP-pincer ligand xant(PⁱPr₂)₂ (9,9-dimethyl-4,5- bis(diisopropylphosphino)xanthene) have been synthesized through cis-OsCl ₂{κ-S-(DMSO)₄

Full text of DOI:10.1021/ic400730a

Article
pubs.acs.org/IC
POP-Pincer Osmium-Polyhydrides: Head-to-Head (Z)‑Dimerization
of Terminal Alkynes
Joaquín Alos, Tamara Bolano, Miguel A. Esteruelas,* Montserrat Olivan,
́
́
̃
Enrique Onate, and Marta Valencia
̃
́ ́ ́
Departamento de Química Inorganica, Instituto de Síntesis Química y Catalisis Homogenea, Universidad de Zaragoza − CSIC,
50009 Zaragoza, Spain
S
* Supporting Information
ABSTRACT: A wide range of osmium-polyhydride complexes stabilized by
the POP-pincer ligand xant(PiPr2)2 (9,9-dimethyl-4,5-bis(diisopropylphosphino)-
xanthene) have been synthesized through cis-OsCl2{κ-S-(DMSO)4}
(1, DMSO = dimethyl sulfoxide). Treatment of toluene solutions of this
adduct with the diphosphine, under reflux, leads to OsCl2{xant(PiPr2)2}-
(κ-S-DMSO) (2). The reaction of 2 with H2 in the presence of Et3N affords
OsH3Cl{xant(PiPr2)2} (3), which can be also prepared by addition of
xant(PiPr2)2 to toluene solutions of the unsaturated d4-trihydride OsH3Cl-
(PiPr3)2 (5). Complex 3 reductively eliminates H2 in toluene at 90 °C. In
the presence of dimethyl sulfoxide, the resulting monohydride is trapped by
the S-donor molecule to give OsHCl{xant(PiPr2)2}(κ-S-DMSO) (6). The
reaction of 2 with H2 is sensible to the Brønsted base. Thus, in contrast
to Et3N, NaH removes both chloride ligands and the hexahydride
OsH6{xant(PiPr2)2} (7), containing a κ2-P-binding diphosphine, is formed under 3 atm of hydrogen at 50 °C. Complex 7
releases a H2 molecule to yield the tetrahydride OsH4{xant(PiPr2)2} (8), which can be also prepared by reaction of OsH6(PiPr3)2
(9) with xant(PiPr2)2. Complex 8 reduces H+ to give, in addition to H2, the oxidized OsH4-species [OsH4(OTf){xant(PiPr2)2}]+
(10, OTf = trifluoromethanesulfonate). The redox process occurs in two stages via the OsH5-cation [OsH5{xant(PiPr2)2}]+ (11).
The metal oxidation state four can be recovered. The addition of acetonitrile to 10 leads to [OsH2(η2-H2)(CH3CN){xant-
(PiPr2)2}]2+ (12). The deprotonation of 12 yields the osmium(IV) trihydride [OsH3(CH3CN){xant(PiPr2)2}]+ (13), which is also
formed by addition of HOTf to the acetonitrile solutions of 8. The latter is further an efficient catalyst precursor for the head-to-
head (Z)-dimerization of phenylacetylene and tert-butylacetylene. During the activation process of the tetrahydride, the
t
bis(alkynyl)vinylidene derivatives Os(CCR)2(=CCHR){xant(PiPr2)2} (R = Ph (14), Bu (15)) are formed.
catalysis to promote some organic reactions.7 In addition,
INTRODUCTION
■
osmium-hydride complexes have been shown to facilitate
carbon−carbon and carbon−heteroatom coupling reactions,8
although it is difficult to rationalize the processes because the
products from the reactions of these compounds with unsaturated
organic molecules depend on the interactions within the OsHn
units,9 and further understanding of them is needed.
The chemistry of the osmium-pincer has been mainly focused
on a few PCP complexes reported by the groups of Gusev,10
Jia,11 and Milstein12 and PNP compounds described by the
groups of Caulton,13 Gusev,14 and Jia15 along with some CCC,16
CNC,17 CNN,18 CNO,19 and NNN20 derivatives. In the search
for more rigid and robust skeletons than our usual starting
fragment trans-Os(PiPr3)2,5b,21 three years ago we synthesized
the ligands 9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene
(xant(PiPr2)2) and 4,6-bis(diisopropylphosphino)dibenzofuran
(dbf(PiPr2)2), which were used to prepare the corresponding
osmium(III) complexes OsCl3(POP).22 Recently, we have
Pincer ligands develop marked abilities to stabilize less common
coordination polyhedra and unusual metal oxidation states due
to the disposition of their donor atoms. Consequently, they have
a tremendous impact on transition metal chemistry and are
viewed as an anchor for the future of the organometallics and
homogeneous catalysis.1 The most commonly encountered
linker groups in diphosphine type ligands consist of either a
metalated aryl group in anionic systems (PCP)2 or uncharged
pyridines (PNP)3 or neutral ethers (POP),4 whereas platinum
group metals occupy a prominent place among the metal
elements with the notable exception of osmium.1
The scarce development of the pincer-osmium chemistry is
probably due to the rooted belief that osmium is not useful
in catalysis because it is a reductant and prefers to be
coordinatively saturated and form redox isomers with greater
metal−carbon bond multiplicity.5 As a consequence of this
extended skepticism, not much effort to find starting materials
from OsCl3·H2O, similar adducts, or related salts has been
done.6 However, recent findings have proved that osmium can
be a promising alternative to the metals classically used in
Received: March 25, 2013
Published: April 26, 2013
© 2013 American Chemical Society
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shown an easy and direct access to diamagnetic osmium(II) and
osmium(IV) compounds with the dbf(PiPr2)2 ligand by using
cis-OsCl2{κ-S-(DMSO)4} as starting material. Furthermore, we
have proved that osmium is a promising alternative to
ruthenium for the direct synthesis of imines from alcohols and
amines, with liberation of molecular hydrogen.23 Now, we have
found the entry to diamagnetic xant(PiPr2)2 derivatives. In
addition, our interest in the interaction within the OsHn units
prompted us to prepare and to study OsHn{xant(PiPr2)2}
species and to test the feasibility of the Os{xant(PiPr2)2}
skeleton in the dimerization of aromatic and aliphatic alkynes.
This paper reveals two entries to diamagnetic osmium
complexes with the xant(PiPr2)2 ligand, describes the prep-
aration and nature of neutral and cationic OsHn{xant(PiPr2)2}
species with n = 1, 3, 4, 5, and 6, and demonstrates the capacity
of the tetrahydride OsH4{xant(PiPr2)2} for reducing H+ and
promoting the head-to-head (Z)-dimerization of terminal
alkynes.
Figure 1 shows a drawing of one of them. As expected for a
mer-coordination of the pincer, the Os{xant(PiPr2)2} skeleton is
RESULTS AND DISCUSSION
Figure 1. Molecular diagram of 2. Selected bond lengths (Å) and
angles (°): Os(1)−S(1) = 2.1812(18), 2.1727(17), Os(1)−O(1) =
2.247(4), 2.252(4), Os−P(1) = 2.3377(17), 2.3373(17), Os−P(2) =
2.3742(17), 2.3686(18), S(1)−O(2) = 1.483(5), 1.468(5); P(1)−
Os(1)−O(1) = 81.28(11), 81.17(12), P(2)−Os(1)−O(1) =
80.80(11), 80.62(12), P(1)−Os(1)−P(2) = 161.43(6), 161.84(6),
Cl(1)−Os(1)−Cl(2) = 171.95(8), 175.49(7), O(1)−Os(1)−S(1) =
174.06(1), 173.15(13).
■
Entries to the Os{xant(PiPr2)2} Chemistry. There are
relatively few examples in which Os(II)-DMSO species were
used as precursors in coordination chemistry, due probably
to the high affinity of osmium(II) for S-bonding.24 However,
Humphrey and co-workers proved in 1997 that the adduct
OsCl2(DMSO)4 is an useful starting material to prepare
OsCl2(chiral bidentate phosphine)2.25 In the light of this
precedent, and because the entry to complexes with the ligand
dbf(PiPr2)2 from 1 was a success,23 we decided to start exploring
similar entry procedures with xant(PiPr2)2. First, we were able
to significantly improve the synthetic method of Humphrey to
prepare OsCl2(DMSO)4. Thus, starting from OsCl3·H2O
instead of [NH4][OsCl6], we obtain cis-OsCl2{κ-S-(DMSO)4}
(1) in a selective and direct manner with a 73% yield, which
is approximately twice that previously reported. Complex 1 is
certainly a good precursor to prepare osmium complexes with
the ligand xant(PiPr2)2. Treatment of 2-propanol solutions of
the diphosphine xant(PiPr2)2 with 1.0 equiv of 1, under reflux
for 18 h, leads to OsCl2{xant(PiPr2)2}(κ-S-DMSO) (2), which is
isolated as an orange solid in 68% yield, according to Scheme 1.
T-shaped with the osmium atom situated in the common
vertex and P(1)−Os(1)−O(1), P(2)−Os(1)−O(1), and
P(1)−Os(1)−P(2) angles of 81.28(11)° and 81.17(12)°,
80.80(11)° and 80.62(12)°, and 161.43(6)° and 161.84(6)°,
respectively. Thus, the coordination geometry around the
metal center can be rationalized as a distorted octahedron with
trans chloride ligands (Cl(1)−Os(1)−Cl(2) = 171.95(8)° and
175.49(7)°) and the oxygen atom of the phosphine trans
disposed to the dimethyl sulfoxide group (O(1)−Os(1)−
S(1) = 174.06(1)° and 173.15(13)°). In agreement with the
S-bonding of the latter,27 the IR spectrum contains a ν(S−O)
band at 1085 cm−1, which is consistent with S(1)−O(2)
distances of 1.483(5) and 1.468(5) Å. The mutually trans
disposition of the chloride ligands is also evident in the 1H and
the 13C{1H} NMR spectra (CD2Cl2, r.t.), which show two signals
for the methyl groups of the phosphine isopropyl substituents
(δ1H, 1.36 and 1.31 ppm; δ13C, 21.9 and 21.0 ppm) and one
signal for the methyl substituents of the central heterocycle
(δ1H, 1.65 ppm; δ13C, 31.9 ppm). According to equivalent PiPr2
groups, the 31P{1H} NMR spectrum contains a singlet at 10.3 ppm.
Complex 2 reacts with molecular hydrogen in the presence
of a Brønsted base. Thus, the stirring of its toluene solutions in
the presence of 2.1 equiv of Et3N, under 3 atm of hydrogen, at
90 °C, for 60 h leads to the trihydride OsH3Cl{xant(PiPr2)2}
(3, in Scheme 1), which is isolated as a pale yellow solid in 57%
yield. Its formation can be rationalized according to Scheme 2.
The dissociation of the dimethyl sulfoxide group from the
osmium atom of 2 should afford the five-coordinate species A,
related to the well-known compound OsCl2(PPh3)3.28 Then,
intermediate A could coordinate a hydrogen molecule to give B.
Subsequent heterolytic activation of the coordinated hydrogen
molecule29 should release HCl, which could be trapped by Et3N,
generating C. Thus, the addition of a new hydrogen molecule to
C should lead to 3.
Scheme 1
Complex 2 was characterized by X-ray diffraction analysis.
The structure has two chemically equivalent but crystallo-
graphically independent molecules in the asymmetric unit.26
The sequence of reactions shown in Scheme 1 is a three-step
procedure, which allows us to obtain 3 in 28% yield with regard
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xant(PiPr2)2 ligand is a relatively rapid process, which is per-
formed in toluene under reflux and affords 3 in an isolated yield
of 68% after 4 h.
Scheme 2
Complex 3 was also characterized by X-ray diffraction analysis.
Figure 2a shows a view of the molecule. The Os{xant(PiPr2)2}
skeleton is T-shaped with the metal situated in the common
vertex, as in 2. The P(1)−Os−O(1), P(2)−Os−O(1), P(1)−
Os−P(2) angles of 82.65(5)°, 82.71(5)°, and 162.90(2)° agree
well with the related parameters of 2. The coordination geometry
around the metal center can be rationalized as a distorted
pentagonal bipyramid, with the hydride and chloride ligands
lying in the perpendicular plane to the P−Os−P direction along
with the oxygen atom of the phosphine, which is situated
between the chloride and the hydride H(03) (O(1)−Os−
Cl(1) = 80.15(6)°, O(1)−Os−H(03) = 85.6(12)°). The DFT
optimized structure (Figure 2b) confirms the trihydride character
of the OsH3 unit. The H(01)−H(02) and H(02)−H(03)
separations are 1.616 and 1.618 Å, respectively. In accordance
with the presence of the hydride ligands, the 1H NMR spectrum
in dichloromethane-d2, at room temperature, shows at
−13.17 ppm a triplet with a H−P coupling constant of 11.0 Hz.
This is consistent with the operation of two thermally activated
site exchange processes within the OsH3 unit, in agreement with
the behavior of other d4-OsH3XY(PiPr3)2 complexes.31 Decreasing
the temperature of the sample leads to a broadening of the
resonance. Between 243 and 233 K, decoalescence occurs and two
signals, centered at −12.98 and −13.38 ppm, in a 1:2 intensity
ratio are observed. Although at lower temperatures than 233 K
the resonance at higher field displays broad, the expected second
decoalescence is not reached even at 183 K. According to the
trihydride character of the complex, a 400 MHz T1(min) value of
104 3 ms was found for both signals at 233 K. In contrast to the
1H NMR spectrum, the 31P{1H} NMR spectrum is temperature
invariant, showing a singlet at 50.6 ppm in agreement with the
equivalence of the PiPr2 groups.
to OsCl3·H2O. In order to increase the obtained amount of
trihydride, we designed a new sequence of reactions (Scheme 3).
Scheme 3
This alternative method, which uses the unsaturated six-
coordinate d4-hydride derivatives OsH2Cl2(PiPr3)2 (4) and
OsH3Cl(PiPr3)2 (5) as intermediate species, leads to 3 in 55%
yield with regard to OsCl3·3H2O, although it is also a three-step
procedure. Complex 4 is a well-known compound that is
obtained in 80% yield by reaction of OsCl3·3H2O with PiPr3 in
2-propanol under reflux.6d Its transformation into 5, by reaction
with molecular hydrogen in the presence of Et3N,30 has been
improved reaching almost quantitative yield (for more details
see the Experimental Section). The substitution of PiPr3 by
The position of the chloride ligand determines the nature of
the OsH3 unit. Thus, interestingly, DFT calculations reveal the
existence of a trans-chloride-oxygen isomer (3a), 20.1 kcal·mol−1
(ΔG, 1 atm, 298.15 K) less stable than 3, which is a hydride-
dihydrogen species. Figure 3 gives a view of DFT optimized
structure of this compound. The coordinated hydrogen molecule
lies trans to the hydride ligand and is disposed almost parallel to
Figure 2. (a) Molecular diagram of 3. Selected bond lengths (Å) and angles (°): Os−O(1) = 2.224(2), Os−Cl(1) = 2.4840(11), Os−P(1) =
2.2906(12), Os−P(2) = 2.2933(11); P(1)−Os−O(1) = 82.65(5), P(2)−Os−O(1) = 82.71(5), P(1)−Os−P(2) = 162.90(2), O(1)−Os−Cl(1) =
80.15(6). (b) DFT optimized structure of 3. Selected bond lengths (Å) and angles (°): Os−O(1) = 2.286, Os−Cl(1) = 2.524, Os−P(1) = 2.319,
Os−P(2) = 2.319; P(1)−Os−O(1) = 81.9, P(2)−Os−O(1) = 81.9, P(1)−Os−P(2) = 162.9, O(1)−Os−Cl(1) = 76.6.
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Scheme 4
Figure 3. DFT optimized structure of 3a. Selected bond lengths (Å)
and angles (°): Os−O(1) = 2.243, Os−Cl(1) = 2.443, Os−P(1) =
2.307, Os−P(2) = 2.307; P(1)−Os−O(1) = 82.0, P(2)−Os−O(1) =
82.0, P(1)−Os−P(2) = 157.2.
the P−Os−P direction with the hydrogen atoms separated by
0.856 Å.
Complex 3 reductively eliminates a hydrogen molecule in
toluene at 90 °C. In the presence of dimethyl sulfoxide, the
resulting unsaturated d6-monohydride species is trapped by the
S-donor solvent to afford OsHCl{xant(PiPr2)2}(κ-S-DMSO)
(6), which is isolated as a white solid in 80% yield, according to
eq 1. The S-bonding of the dimethyl sulfoxide group is strongly
supported by IR, which shows a ν(S−O) band at 1072 cm−1 in
agreement with 2. As expected for the presence of a hydride
ligand, the 1H NMR spectrum (CD2Cl2, r.t.) contains at
−18.77 ppm a triplet with a H−P coupling constant of
19.8 Hz, whereas the 31P{1H} NMR spectrum shows a singlet
at 35.4 ppm that is split into a doublet under off resonance
conditions.
1
Figure 4. H NMR spectrum of 7 (400 MHz, CD2Cl2, r.t.) with the
integrated intensity of each signal. ★ Resonances corresponding to the
complex OsH4{xant(PiPr2)2}.
the complex, a 400 MHz T1(min) value of 113 3 ms was found
at 228 K for this resonance.
OsH6{xant(PiPr2)2} and OsH4{xant(PiPr2)2}. The reaction
of 2 with molecular hydrogen is sensible to the Brønsted base
used and to the experimental conditions. In contrast to Et3N
in toluene, sodium hydride in tetrahydrofuran removes both
chloride ligands and, furthermore, a hydrogen molecule displaces
the oxygen atom of the diphosphine, which becomes a κ2-P-
binding. Thus, the stirring of the tetrahydrofuran solutions of 2
in the presence of 10 equiv of the superbase, under 3 atm of
hydrogen, at 50 °C, for 48 h leads to the hexahydride derivative
OsH6{xant(PiPr2)2} (7), which is isolated as a pale yellow solid
in 50% yield according to Scheme 4. A briefer method implies
the treatment of tetrahydrofuran solutions of 2 with 20 equiv
of LiAlH4, at 80 °C, for 3 h. By this procedure, complex 7 is
obtained in 37% yield.
Figure 5 shows the DFT optimized structure of 7. In agree-
ment with other OsH6-species6d,32 and related eight-coordinate
osmium-polyhydrides,33 the coordination geometry around
the metal center can be rationalized as being derived from a
distorted dodecahedron, which is defined by two intersecting
BAAB orthogonal (84.11°) trapezoidal planes.34 One of them
contains the atoms H(01), H(03), H(05), and P(1) (maximum
deviation 0.183 Å for H(03)) with a H(01)−Os−P(1) angle
of 149.8°, whereas the second one contains the atoms P(2),
H(06), H(02), and H(04) (maximum deviation 0.180 Å for
H(02)) with a P(2)−Os−H(04) angle of 146.4°. The P(1)−
Os−P(2) bite angle of the diphosphine of 105.4° is consistent
with those reported for other complexes containing κ2-P-
bonding xantphos type ligands.35 As expected for the classical
polyhydride character of this species, the separations between
the hydride ligands are longer than 1.686 Å (H(04)−H(02)
and H(03)−H(01)).
The κ2-P-binding coordination mode of the diphosphine is
strongly supported by the 1H NMR spectrum of the compound
in dichloromethane-d2, at room temperature (Figure 4), which
shows two double of doublets at 1.13 and 1.07 ppm for the
methyl groups of the phosphine isopropyl substituents. In the
high field region of the spectrum, the hydride ligands give
rise to a singlet at −10.08 ppm, which displays an integrated
intensity of 6. According to the classical polyhydride nature of
Complex 7 is stable under hydrogen atmosphere at temp-
eratures below 293 K. In methanol, under argon atmosphere,
it slowly loses a hydrogen molecule, and the diphosphine
coordinates the oxygen atom to the metal center. Thus, the
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the complex was confirmed by the DFT optimized structure
(Figure 6b), which yields H−H separations longer than 1.683 Å
(H(02)−H(03)).
The 31P{1H} and 1H NMR spectra of 8 in dichloromethane-
d2 are consistent with the structure shown in Figure 6. In
agreement with equivalent PiPr2 groups, the 31P{1H} NMR
spectrum contains a singlet at 66.3 ppm, which remains invariant
between 293 and 193 K. In contrast to the 31P{1H} NMR
1
spectrum, the H NMR spectrum is temperature dependent. As
expected for two inequivalent hydride positions, two broad
resonances centered at −3.14 and at −16.63 ppm are observed in
the high field region of the spectrum at 183 K. Between 193 and
203 K, coalescence takes place. According to the classical
polyhydride character of the complex, at 213 K, a 400 MHz
Figure 5. (a) DFT optimized structure of 7. Selected bond lengths (Å)
and angles (°): Os−P(1) = 2.448, Os−P(2) = 2.446; P(1)−Os−P(2) =
105.4. (b) View of the two intersecting BAAB orthogonal trapezoidal
planes.
T1(min) value of 179
3 ms was found for the resulting
resonance. The behavior of the hydride resonances with the
temperature indicates that in dichloromethane-d2, the hydride
ligands H(01) and H(02) (or H(04) and H(03)) undergo
stirring of methanol solutions of 7 at room temperature for
six days gives rise to the quantitative precipitation of the
tetrahydride derivative OsH4{xant(PiPr2)2} (8, in Scheme 4), as
a white solid in 30% yield with regard to OsCl3·3H2O. Complex
8 can be prepared through a briefer method by using the
dihydride 4. The latter is initially transformed into the hexa-
hydride OsH6(PiPr3)2 (9), which is isolated in 60% yield, after
reaction with a toluene suspension of NaBH4 and some drops
of methanol.6d,36 Subsequent treatment of a toluene solution
of 9 with 1.1 equiv of the diphosphine affords 8 in a 20% yield
with regard to OsCl3·3H2O, after 12 h under reflux.
a thermally activated position exchange. A ΔG‡ value of
203
8.1 kcal·mol−1 was estimated for the process.
Hydrogen Evolution. The H2 molecule is a promising
energy carrier to replace hydrocarbons due to its cleanness. The
hydrogen evolution reaction, which implies the reduction of
H+, is the cathodic half reaction in the water splitting process.
The tetrahydride complex 8 is a strong reductor, which is
able to promote the reduction of H+ (eq 2), in spite of the
Complex 8 has been characterized by X-ray diffraction
analysis. The structure has four chemically equivalent but cry-
stallographically independent molecules in the asymmetric unit.
Figure 6a shows a drawing of one of them. The Os{xant(PiPr2)2}
skeleton is T-shaped with the metal situated in the common
vertex, as in 2 and 3. The P(1)−Os(1)−O(1), P(2)−Os(1)−
O(1), and P(1)−Os(1)−P(2) angles of 82.00(9), 81.84(9),
82.29(9), and 81.99(9)°, 82.68(9), 82.21(9), 82.57(9), and
81.89(9)°, and 164.53(5), 164.05(5), 164.74(5), and 163.87(5)°,
respectively, are consistent with the related parameters of 2
and 3. Thus, the coordination geometry around the metal center
can be rationalized as a distorted pentagonal bipyramid with the
hydride ligands lying in the perpendicular plane to the P−Os−P
direction along with the oxygen atom of the phosphine, which is
situated between H(01) and H(04). The tetrahydride nature of
high oxidative state of the metal center. Thus, the addition of
4.0 equiv of triflic acid (HOTf) to its dichloromethane-d2
solutions gives molecular hydrogen and the oxidized OsH4-
species [OsH4(OTf){xant(PiPr2)2}]+ (10). The presence of
four hydrogen atoms bonded to the metal center is strongly
supported by the H NMR spectrum of the resulting solution,
which shows a triplet (JH−P = 4.0 Hz) at −11.62 ppm with an
integrated intensity of 4. This resonance exhibits a 400 MHz
1
Figure 6. (a) Molecular diagram of 8. Selected bond lengths (Å) and angles (°): Os(1)−O(1) = 2.222(3), 2.237(3), 2.213(3), and 2.230(4), Os−P(1) =
2.2721(15), 2.2693(14), 2.2693(13), and 2.2692(15), Os−P(2) = 2.2662(15), 2.2719(14), 2.2764(13), and 2.2684(15); P(1)−Os(1)−O(1) = 82.00(9),
81.84(9), 82.29(9), and 81.99(9), P(2)−Os(1)−O(1) = 82.68(9), 82.21(9), 82.57(9), and 81.89(9), P(1)−Os(1)−P(2) = 164.53(5), 164.05(5),
164.74(5), and 163.87(5). (b) DFT optimized structure of 8. Selected bond lengths (Å) and angles (°): Os(1)−O(1) = 2.285, Os−P(1) = 2.296, Os−
P(2) = 2.296; P(1)−Os(1)−O(1) = 82.0, P(2)−Os(1)−O(1) = 82.0, P(1)−Os(1)−P(2) = 163.7.
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T1(min) value of 73 3 ms at 243 K. Between 203 and 193 K,
decoalescence occurs and at 183 K two broad signals centered at
−9.78 and −13.53 ppm, with a 1:1 intensity ratio, are observed.
The 31P{1H} NMR spectrum shows a singlet at 65.9 ppm.
Figure 7 shows the DFT optimized structure of 10. In agree-
ment with the spectroscopic features, two groups of equivalent
interactions in the OsH5 unit. The 31P{1H} NMR spectrum
shows a singlet at 60.7 ppm. DFT calculations reveal that there
are three structures differing by 3.0 kcal·mol−1 (ΔG, 1 atm,
298.15 K): the hydride-elongated dihydrogen−dihydrogen
conformers 11a and 11b and the trihydride-elongated
dihydrogen 11c. Figure 8 shows views of their DFT optimized
structures. The main difference between 11a and 11b is the con-
formation of the central six-membered ring of the phosphine,
which is planar in the first of them and boat in the second
one. Conformer 11a is 2.8 kcal·mol−1 more stable than 11b. In
both compounds, the dihydrogen ligand is disposed almost
parallel to the P−Os−P direction, with similar H(04)−H(05)
bond lengths of 0.873 (11a) and 0.870 (11b) Å, whereas the
elongated dihydrogen ligand H(02)−H(03) lies in the
perpendicular plane along with the hydride H(01) and the
oxygen atom of the phosphine. The H(01)−H(02) and H(02)−
H(03) separations are 1.739 and 1.398 Å (11a) and 1.693 and
1.455 Å (11b). The disposition of the hydrogen atoms of the
OsH5 unit in 11c is similar to those of 11a and 11b with the
H(04)−H(05) bond completely added and the hydrogen
atoms H(04) and H(05) separated by 1.762 Å. The separations
between H(01) and H(02) and between H(02) and H(03) of
1.886 and 1.473 Å, respectively, are longer than in 11a and 11b.
These results can be rationalized by means of the fast equilibria
shown in Scheme 5.
Figure 7. DFT optimized structure of the cation of 10. Selected bond
lengths (Å) and angles (°): Os−O(1) = 2.289, Os−O(2) = 2.166,
Os−P(1) = 2.390, Os−P(2) = 2.388; P(1)−Os−O(1) = 80.5, P(2)−
Os−O(1) = 80.6, P(1)−Os−P(2) = 160.3.
The metal oxidation state four can be recovered (Scheme 6).
The addition of 1.0 equiv of acetonitrile to the dichloro-
methane-d2 solutions of 10 produces the replacement of the
coordinated trifluoromethanesulfonate anion by the N-donor
ligand to afford [OsH4(CH3CN){xant(PiPr2)2}]2+ (12), which
exhibits a broad resonance at −11.45 ppm, with an integral
hydrogen atoms (H(01) and H(02), and H(03) and H(04))
bonded to the metal center are shown. Thus, as expected for an
eight-coordinate osmium polyhydride, the ligands around the
metal center form a distorted dodecahedron, which is defined
by the intersecting P(1), H(04), H(03), and P(2) and O(1),
H(01), H(02), and O(2) orthogonal (89.96°) trapezoidal
planes. The separation between H(03) and H(04) is 1.545 Å,
while H(01) and H(02) form an elongated dihydrogen ligand
of 1.25 Å. Some reported osmium skeletons stabilizing
dihydride-elongated dihydrogen OsH4-species are [Os(η5-
C5H5)(PR3)]+ (R = Me,37 H38), [Os(TACN)(PiPr3)]2+
(TACN = 1,4,7-triazacyclononane), and [Os(TACD)(PiPr3)]2+
(TACD = 1,4,7-triazacyclodecane).39 However, [OsTp(PiPr3)]+
(Tp = hydridotris(pyrazolyl)borate)40 and [Os(BAEA)-
(PiPr3)]2+ (BAEA = bis(2-aminoethyl)amine)39 metal fragments
favor the formation of bis(dihydrogen) derivatives. In this
context, it should be mentioned that OsH4 species are very
sensitive to the L−M−L angles. Small changes in these angles
can invert the relative energies of the metal orbitals interacting
with those of the dihydrogens.39,40
1
intensity of 4, in the H NMR spectrum. This resonance has a
short 400 MHz T1(min) value of 22 2 ms at 243 K, indicating
a significant increase of the nonclassical interactions in the
OsH4 unit with regard to 10; i.e., the substitution of the
trifluoromethanesulfonate anion by the acetonitrile molecule
causes the intramolecular reduction of the metal center.
Decoalescence occurs between 243 and 233 K and at lower temp-
eratures than the latter two signals at −11.29 and −11.82 ppm,
with a 1:1 intensity ratio observed. The 31P{1H} NMR spectrum
shows a singlet at 56.7 ppm that is temperature invariant between
293 and 183 K. In accordance with these spectroscopic features,
the DFT optimized structure of 12 (Figure 9) supports a
dihydride−dihydrogen nature. The dihydrogen ligand is situated
in the perpendicular plane to the P−Os−P direction with the
hydrogen atoms separated by 0.898 Å, while the hydride ligands
lie in the trapezoidal plane containing the phosphorus atoms with
the hydrogens separated by 1.475 Å. The addition of 1.0 equiv
of Et3N to the dichloromethane-d2 solutions of 12 causes its
deprotonation and the formation of the osmium(IV) trihydride
13. The reaction is reversible, and the addition of 1.0 equiv of
HOTf to the dichloromethane-d2 solutions of 13 regenerates 12.
Complex 13 is the result of the replacement of a hydride
ligand of 8 by an acetonitrile molecule. The substitution can
be carried out in one-pot synthesis by addition of 4.0 equiv of
HOTf to the acetonitrile solutions of 8. By this procedure,
the OTf salt of 13 is isolated as a yellow solid in 63% yield.
Figure 10a gives a view of the X-ray structure of the cation of 13.
The distribution of ligands around the metal center is similar to
those of 3 and 8 with the acetonitrile molecule occupying the
position of the chloride ligand of 3 or the hydride H(04) of
8 and P(1)−Os−O(1), P(2)−Os−O(1), and P(1)−Os−P(2)
angles of 82.40(8)°, 82.07(8)°, and 162.29(4)°, respectively.
The redox reaction shown in eq 2 occurs in two stages (eqs 3
and 4). Initially, complex 8 adds a proton to afford
[OsH5{xant(PiPr2)2}]+ (11), which reacts with HOTf to give
molecular hydrogen and 10.
OsH4{xant(PiPr ) } + H+ → [OsH5{xant(PiPr ) }]+
2 2
2 2
(3)
8
11
+
[OsH5{xant(PiPr ) }] + H+ + OTf−
2 2
11
+
→ [OsH4(OTf){xant(PiPr2)2}] + H2
(4)
10
1
The most noticeable signal in the H NMR spectrum of 11
is a triplet (JH−P = 5.2 Hz) at −7.71 ppm, which displays
an integrated intensity of 5. This resonance does not reach
decoalescence even at 183 K and has a short 400 MHz T1(min)
value of 20
3 ms at 193 K, which indicates nonclassical
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Figure 8. DFT optimized structure of the cations of 11a, 11b, and 11c. Selected bond lengths (Å) and angles (°): Os−O(1) = 2.230 (11a), 2.256
(11b), and 2.240 (11c), Os−P(1) = 2.351 (11a), 2.349 (11b), and 2.372 (11c), Os−P(2) = 2.350 (11a), 2.349 (11b), and 2.372 (11c); P(1)−Os-
O(1) = 82.1 (11a), 82.8 (11b), and 82.6 (11c), P(2)−Os−O(1) = 82.2 (11a), 82.8 (11b), and 82.6 (11c), P(1)−Os−P(2) = 159.7 (11a), 160.4
(11b), and 148.0 (11c).
Scheme 5
Scheme 6
Figure 9. DFT optimized structure of the cation of 12. Selected bond
lengths (Å) and angles (°): Os−N(1) = 2.056, Os−O(1) = 2.298,
Os−P(1) = 2.409, Os−P(2) = 2.409; P(1)−Os−O(1) = 80.2, P(2)−
Os−O(1) = 80.2, P(1)−Os−P(2) = 159.1.
The DFT optimized structure (Figure 10b) confirms the tri-
hydride character of the cation and reveals that replacement of
the hydride by acetonitrile does not produce any significant
change in the nature of the OsH3 unit. Thus, the H(01)−H(02)
and H(02)−H(03) separations of 1.552 and 1.606 Å agree well
with those of 3 and 8.
The position of the acetonitrile molecule also determines the
nature of the OsH3 unit in this case. Similarly to 3, complex 13
has a hydride−dihydrogen tautomer (13a) with the acetonitrile
ligand trans to the oxygen atom of the phosphine. This species
is 10.7 kcal·mol−1 (ΔG, 1 atm, 298.15 K) less stable than 13.
Figure 11 shows a view of its DFT optimized structure. The
hydrogen molecule is disposed almost parallel to the P−Os−P
direction with the hydrogen atoms separated by 0.859 Å. In this
context, it should be noted that the difference in stability bet-
ween 13 and 13a is significantly smaller than between 3 and 3a.
This appears to be a consequence of the lower donor power of
the acetonitrile molecule with regard to the chloride anion and
the positive charge of 13a.41
Acetonitrile favors the dihydrogen form with regard to the
chloride anion. Hydride site exchange processes in OsIVH3
derivatives implies Os−H stretching, H−H shortening, and
subsequent rotation of the resulting dihydrogen ligand.42 So,
lower activation barriers for the hydride site exchanges should
be expected in 13 than in 3. In fact, the 1H NMR spectrum of 13
in dichloromethane-d2, at room temperature, shows a hydride
resonance at −12.58 ppm, which appears as a triplet with a H−P
coupling constant of 10.5 Hz. In contrast to 3, although lowering
the sample temperature leads to a broadening of the signal,
decoalescence is not reached even at 183 K. It should be also
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Figure 10. (a) Molecular diagram of the cation of 13. Selected bond lengths (Å) and angles (°): Os−N(1) = 2.120(4), Os−O(1) = 2.212(3), Os−
P(1) = 2.3001(11), Os−P(2) = 2.3072(12); P(1)−Os(1)−O(1) = 82.40(8), P(2)−Os(1)−O(1) = 82.07(8), P(1)−Os(1)−P(2) = 162.29(4). (b)
DFT optimized structure of the cation of 13. Selected bond lengths (Å) and angles (°): Os−N(1) = 2.147, Os−O(1) = 2.280, Os−P(1) = 2.336,
Os−P(2) = 2.338; P(1)−Os(1)−O(1) = 82.1, P(2)−Os(1)−O(1) = 82.4, P(1)−Os(1)−P(2) = 159.4.
of phenylacetylene to give a mixture of (Z)-PhCCCHCHPh
and (E)-PhCCCHCHPh in a 5:2 molar ratio.47 In contrast
to the latter and 8, in the presence of diethylamine, the known
5b
complex OsHCl(CO)(PiPr3)2 promotes the formation of
butatrienes, RCHCCCHR, which are stable under the
t
Figure 11. DFT optimized structure of the cation of 13a. Selected
reaction conditions when R = Bu and Cy. For R = Ph, the
bond lengths (Å) and angles (°): Os−N(1) = 1.964, Os−O(1) =
butatriene polymerizes to −[CH(Ph)CCCH(Ph)]n−, while
2.227, Os−P(1) = 2.340, Os−P(2) = 2.340; P(1)−Os−O(1) = 81.8,
for R = Me3Si the butatriene isomerizes into the enyne (Z)-
P(2)−Os−O(1) = 81.8, P(1)−Os−P(2) = 158.2.
Me3SiCCCHCHSiMe3.48 In addition, it should be noted
that the behavior of 8 is also in contrast to those of (PNP)Rh43a
and (PCP)Ir43b pincer-ligated species, which promote the
mentioned that, in agreement with closer hydride ligands in 13
than in 3, a shorter 400 MHz T1(min) value of 88 2 ms was
found for this resonance at 193 K. The equivalent PiPr2 groups
display a singlet at 49.0 ppm in the 31P{1H} NMR spectrum.
Head-to-Head (Z)-Dimerization of Phenylacetylene
and tert-Butylacetylene Promoted by 8. Transition-
metal-catalyzed dimerizations of terminal alkynes are attractive
atom-economical C−C bond forming reactions, which afford
products containing structural units in natural products and
materials.43 In most cases, mixtures of regio (head-to-head vs
head-to-tail) and stereo (E/Z-head-to-head) isomers have been
obtained. From a mechanistic point of view, it has been
proposed that the (Z)-isomer is generated by intramolecular
addition of an alkynyl ligand to the α-carbon atom of a metal-
bond vinylidene ligand, while the (E)-isomer results from the
insertion of a π-bond alkyne into an alkenyl−metal bond.44
The regio- and stereoselective head-to-head (Z)-dimerization
is of special interest, since the resulting (Z)-enynes are key units
found in a variety of natural occurring anticancer antibiotics.45
However, it has been hardly achieved.46 The tetrahydride
complex 8 is an efficient catalyst precursor for the regio- and
stereoselective head-to-head (Z)-dimerization of phenylacety-
lene and tert-butylacetylene. In toluene-d8 at 110 °C, the enynes
(Z)-PhCCCHCHPh and (Z)-tBuCCCHCHtBu are
formed in 94% and 90% yield with a turnover frequency at 50%
conversion (TOF50%) of 100 and 30 h−1, respectively (eq 5).
This fact is noticeable, because the osmium catalysts for the
alkyne dimerization are extremely rare. The hydride-vinylidene
OsH(κ2-O2CCH3)(=CCHPh)(PiPr3)2 catalyzes the dimerization
formation of (E)-enynes.
Complex 8 is transformed into the bis(alkynyl)vinylidene
derivatives Os(CCR)2(=CCHR) {xant(PiPr2)2} (R = Ph
t
(14), Bu (15)), along with 2 equiv of the corresponding
olefin and one hydrogen molecule, under catalytic conditions
before the first turnover (eq 6). These species were detected
during the catalysis by 1H and 31P{1H} NMR spectroscopy and
prepared as analytically pure yellow solids in 79% (14) and 87%
(15) yield at Schlenk scale, by means of the treatment of
toluene solutions of 8 with 10 equiv of alkyne at 110 °C, for 2 h.
The bis(alkynyl)vinylidene formulation is strongly supported
by the 1H and the 13C{1H} NMR spectra of the obtained solids.
1
In the H NMR spectra, the most noticeable signals are the
characteristic CβH-resonances of the vinylidene ligands which
appear at 3.04 ppm (14) and at 1.05 ppm (15). Furthermore,
the spectra reveal a high symmetry in these molecules. Thus,
they show two doublets of virtual triplets at 1.61 and 1.51 ppm
for 14 and at 1.70 and 1.66 ppm for 15, corresponding to the
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methyl groups of the phosphine isopropyl substituents, and a
singlet at 1.28 ppm (14) and at 1.30 ppm (15), due to the
methyl substituent of the central heterocycle of the phosphine,
which are consistent with the mutually trans disposition of the
alkynyl groups and indicate a low activation barrier for the
rotation of the vinylidene ligand in agreement with that observed
in previous cases.49 In the 13C{1H} NMR spectra, the Cα and Cβ
resonances of the vinylidene ligands are observed at 300.1 and
106.4 ppm for 14 and at 290.8 and 112.9 ppm for 15, whereas
the Cα and Cβ signals of the alkynyl groups appear at 109.5 and
129.3 ppm (14) and at 91.6 and 124.0 ppm (15). The 31P{1H}
NMR spectra show singlets at 14.4 (14) and at 11.6 ppm (15),
in agreement with equivalent PiPr2 groups.
being able to promote the reduction of H+, in dichloromethane,
at room temperature. The process takes place in two stages via
a cationic OsH5-species. The metal oxidation state four can be
recovered by treatment of the resulting oxidized OsH4-species
with 1 equiv of acetonitrile and subsequently with 1 equiv of
triethylamine. Complex OsH4{xant(PiPr2)2} is also an efficient
catalyst precursor for the head-to-head (Z)-dimerization of
terminal alkynes. Thus, the enynes (Z)-RCCCHCHR (R =
t
Ph, Bu) are formed in a regio- and stereoselective manner in
high yields and good TOF50% in the presence of this compound.
The catalysis takes place through the bis(alkynyl)vinylidene
derivatives Os(CCR)2(CCHR){xant(PiPr2)2}, which are
formed during the activation process of the tetrahydride and
have been isolated and fully characterized.
In conclusion, we have found two entries to obtain Os{xant-
(PiPr2)2} complexes, in particular polyhydride derivatives,
which are allowing us to discover interesting properties of
some compounds of this type as the capacity for reducing
H+ and for promoting the head-to-head (Z)-dimerization of
terminal alkynes.
The formation of 14 and 15 is consistent with a head-to-head
(Z)-dimerization of the alkynes, which can be rationalized
according to Scheme 7. The migratory insertion of the vinyli-
Scheme 7
EXPERIMENTAL SECTION
■
All reactions were carried out with rigorous exclusion of air using
Schlenk-tube techniques. 2-Propanol, methanol, acetonitrile, acetone,
and dimethyl sulfoxide (DMSO) were dried and distilled under argon.
Other solvents were obtained oxygen- and water-free from an MBraun
solvent purification apparatus. NMR spectra were recorded on a Varian
Gemini 2000, a Bruker ARX 300 MHz, a Bruker Avance 300 MHz, a
Bruker Avance 400 MHz, or a Bruker Avance 500 MHz instrument.
Chemical shifts (expressed in parts per million) are referenced to
residual solvent peaks (1H, 1H{31P}, 13C{1H}) or external 85% H3PO4
(31P{1H}), or external CFCl3 (19F). Coupling constants J and N (N =
J(PH) + J(P’H) for 1H and N = J(PC) + J(P’C) for 13C{1H}) are given
in hertz. Attenuated total reflection infrared spectra (ATR-IR) of
solid samples were run on a Perkin-Elmer Spectrum 100 FT-IR
spectrometer. C, H, and N analyses were carried out in a Perkin-Elmer
2400 CHNS/O analyzer. High-resolution electrospray mass spectra
(HRMS) were acquired using a MicroTOF-Q hybrid quadrupole time-
of-flight spectrometer (Bruker Daltonics, Bremen, Germany). Phenyl-
acetylene, tert-butylacetylene, and triethylamine (Et3N) were purchased
from commercial sources and vacuum distilled. All other reagents
were purchased from commercial sources and used as received.
dene ligand into one of the Os-alkynyl bonds could afford the
butenynyl intermediates D. The displacement of the coordi-
nated carbon−carbon triple bond of the butenynyl ligand by
an alkyne molecule should lead to E, which could release
the (Z)-enyne to give F. The coordination of a new alkyne
molecule to F should regenerate 14 or 15.
9,9-Dimethyl-4,5-bis(diisopropylphosphino)xanthene (xant(PiPr2)2)22
6d,36
and OsH6(PiPr3)2
were prepared according to the published
methods. An improved method for the preparation of cis-OsCl2{κ-S-
(DMSO)4} is included.
Synthesis of cis-OsCl2{κ-S-(DMSO)4} (1). A solution of
OsCl3·3H2O (2.00 g, 5.70 mmol) in DMSO (8 mL) was heated
under reflux for 15 min. Then, SnCl2 (1.62 g, 8.56 mmol) was added
and the mixture was heated until a color change from very dark brown
to pale amber was observed. The solvent was removed in vacuo
and acetone (2 mL) was added to afford a white solid, which was
washed with a 1:5 mixture of acetone/diethyl ether (3 × 6 mL).
Dichloromethane (40 mL) was added and the suspension was filtered
through Celite to remove the tin salts. The filtrate was concentrated to
ca. 1 mL, and acetone (2 mL) was added to afford a white precipitate,
which was washed with a 1:5 mixture of acetone/diethyl ether
(2 × 6 mL) and diethyl ether (2 × 3 mL) and dried in vacuo. Yield:
CONCLUDING REMARKS
■
This work shows two different entries to the chemistry of
osmium polyhydrides containing the POP-pincer ligand xant-
(PiPr2)2, starting from the commercially available OsCl3·3H2O.
One route uses the adduct cis-OsCl2{κ-S-(DMSO)4} as inter-
mediate species and allows one to prepare a wide range of
OsHn{xant(PiPr2)2} complexes including n = 1, 3, 4, 5, and 6.
The other one has been designed to specifically prepare the
compounds OsH3Cl{xant(PiPr2)2} and OsH4{xant(PiPr2)2},
employs the dihydride OsH2Cl2(PiPr3)2 as key intermediate,
affords similar or better yields, and is more direct. Some of
these polyhydrides are hydrogen reservoirs losing molecular
hydrogen under mild conditions. An example is the noticeable
hexahydride complex OsH6{xant(PiPr2)2}, which releases H2 in
methanol at room temperature to afford OsH4{xant(PiPr2)2}.
This osmium(IV) tetrahydride has a strong reducing power
1
2.40 g (73%). H NMR (400 MHz, CD2Cl2, 293 K): δ 3.51 (s, 6H,
CH3), 3.48 (s, 6H, CH3), 3.35 (s, 6H, CH3), 2.73 (s, 6H, CH3).
Synthesis of OsCl2{xant(PiPr2)2}(κ-S-DMSO) (2). Complex 1
(0.400 g, 0.700 mmol) was added to a solution of xant(PiPr2)2 (0.309 g,
0.700 mmol) in 2-propanol (15 mL), and the resulting suspension was
heated under reflux for 18 h. Color changed from white to orange with
appearance of an orange precipitate when the mixture was cooled to
room temperature. After the solvent was removed, the solid was washed
with acetone (3 × 2 mL) and diethyl ether (3 × 3 mL) and dried
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in vacuo. Yield: 0.370 g (68%). Anal. Calcd. for C29H46Cl2O2OsP2S: C,
44.55; H, 5.93; S: 4.10. Found: C, 44.03; H, 5.65; S: 3.46. HRMS
(electrospray, m/z): calcd. for C27H40Cl2OOsP2 [M − DMSO + H]+:
705.1600, found: 705.1487. IR (cm−1): ν(O−C) 1184 (s); ν(OS)
1085 (s). 1H NMR (400 MHz, CD2Cl2, 293 K): δ 7.58 (dd, JH−H = 7.6,
JH−H = 1.4, 2H, CHarom), 7.52 (vtdd, JH−H = 7.6, JH−H = 1.4, N = 3.8,
2H, CHarom), 7.32 (t, JH−H = 7.6, 2H, CHarom), 3.77 (s, 6H, SO(CH3)2),
3.24 (m, 4H, PCH(CH3)2), 1.65 (s, 6H, CH3), 1.36 (dvt, JH−H = 7.2,
N = 15.2, 12H, PCH(CH3)2), 1.31 (dvt, JH−H = 7.2, N = 13.6, 12H,
PCH(CH3)2). 13C{1H}-APT NMR (100.63 MHz, CD2Cl2, 293 K): δ
157.4 (vt, N = 12.6, Carom), 132.5 (vt, N = 5.6, Carom), 132.3 (s,
CHarom), 128.4 (s, CHarom), 125.7 (vt, N = 31, Cipso), 125.2 (vt, N = 5.2,
CHarom), 52.5 (s, SO(CH3)2), 34.5 (s, C(CH3)2), 31.9 (s, C(CH3)2),
27.4 (vt, N = 25.7, PCH(CH3)2), 21.9 and 21.0 (both s, PCH(CH3)2).
31P{1H} NMR (161.69 MHz, CD2Cl2, 293 K): δ 10.3 (s).
S, 4.29. Found: C, 47.00; H, 6.30; S, 4.24. HRMS (electrospray, m/z):
calcd. for C29H47O2OsP2S [M − Cl]+: 713.2380, found: 713.2459.
IR (cm−1): ν(Os−H) 2119, ν(O−C) 1194 (s); ν(OS) 1072 (s). 1H
NMR (400 MHz, CD2Cl2, 293 K): δ 7.60 (m, 2H, CHarom), 7.47 (dd,
JH−H = 7.7, JH−H = 1.2, CHarom), 7.27 (t, JH−H = 7.7, 2H, CHarom), 3.64
(s, 6H, SO(CH3)2), 3.11 (m, 2H, PCH(CH3)2), 2.67 (m, 2H,
PCH(CH3)2), 1.74 (s, 3H, CH3), 1.43 (s, 3H, CH3), 1.40 (dvt, JH−H
=
6.8, N = 20.4, 6H, PCH(CH3)2), 1.37 (dvt, JH−H = 7.2, N = 16, 6H,
PCH(CH3)2), 1.33 (dvt, JH−H = 7.2, N = 16, 6H, PCH(CH3)2), 1.00
(dvt, JH−H = 6.8, N = 14, 6H, PCH(CH3)2), −18.77 (t, JP−H = 19.8,
1H, OsH). 13C{1H}-APT NMR (100.63 MHz, CD2Cl2, 293 K): δ
158.8 (vt, N = 12.8, Carom), 132.6 (vt, N = 6, Carom), 130.1 (s, CHarom),
127.4 (s, CHarom), 126.5 (vt, N = 28.8, Cipso), 125.6 (vt, JC−P = 4.7,
CHarom), 57.8 (s, SO(CH3)2), 34.5 (s, C(CH3)2) 33.7 (s, C(CH3)2),
30.4 (vt, N = 19.1, PCH(CH3)2), 28.9 (vt, N = 34.8, PCH(CH3)2),
27.9 (s, C(CH3)2), 20.1 and 19.8 (both s, PCH(CH3)2), 19.4 (vt, N =
4.4, PCH(CH3)2), 19.1 (s, PCH(CH3)2). 31P{1H} NMR (161.69
MHz, CD2Cl2, 293 K): δ 35.4 (s).
Synthesis of OsH3Cl{xant(PiPr2)2} (3). Method a: A Fisher-Porter
bottle was charged with a mixture of OsCl2{xant(PiPr2)2}(κ-S-DMSO)
(2) (0.200 g, 0.256 mmol) and Et3N (75 μL, 0.537 mmol) in toluene
(25 mL). The bottle was pressurized to 3 atm of H2, and the mixture
was stirred at 90 °C, for 60 h changing the color from orange to pale
yellow. After being cooled to room temperature, the mixture was
filtered and volatiles were removed in vacuo. Addition of pentane to
the residue afforded a pale yellow solid, which was washed with
pentane (3 × 3 mL) and dried in vacuo. Yield: 0.098 g (57%). Method
b: A solution of OsH3Cl(PiPr3)2 (5) (0.600 g, 1.093 mmol) in toluene
(7 mL) was added to a solution of xant(PiPr2)2 (0.532 g, 1.202 mmol)
in toluene (5 mL), and the resulting mixture was heated to reflux for
4 h. After being cooled to room temperature, the solvent was
concentrated to ca. 2 mL and pentane was added to afford a yellow
precipitate, which was dried to dryness, and washed with methanol
(2 × 1 mL). After the solvent was removed, pentane was added to
afford a yellow solid, which was washed with pentane (3 × 5 mL) and
dried in vacuo. Yield: 0.497 g (68%). Anal. Calcd. for C27H43ClOOsP2:
C, 48.31; H, 6.46. Found: C, 48.26; H, 6.26. HRMS (electrospray,
m/z): calcd. for C27H43OOsP2 [M − Cl]+: 637.2400, found: 637.2419.
Synthesis of OsH6{xant(PiPr2)2} (7). Method a: A Fisher-Porter
bottle was charged with OsCl2{xant(PiPr2)2}(κ-S-DMSO) (2) (0.200 g,
0.256 mmol), NaH (0.065 g, 2.700 mmol), and tetrahydrofuran (20 mL).
The bottle was pressurized to 3 atm of H2, and the mixture was stirred at
50 °C, for 48 h. During this time, the color of the mixture changed from
orange to pale yellow. After the mixture was cooled to room temperature,
it was filtered through Celite, and the resulting yellow solution obtained
was dried in vacuo. Toluene (10 mL) was added to the residue, and the
suspension was filtered through Celite and taken to dryness. Addition of
pentane to the residue afforded a pale yellow solid that was washed with
pentane and dried in vacuo. Yield: 0.080 g (46%). Method b: A solution
of OsCl2{xant(PiPr2)2}(κ-S-DMSO) (2) (0.100 g, 0.128 mmol) in
tetrahydrofuran (10 mL) was treated with LiAlH4 (0.124 g, 2.560 mmol).
The mixture was heated under reflux for 3 h. After the mixture was
cooled to room temperature, it was filtered through Celite, and the
resulting yellow solution obtained was dried in vacuo. Toluene (10 mL)
was added to the residue, and the suspension was filtered and taken to
dryness. Addition of pentane to the residue afforded a pale yellow solid
that was washed with pentane and dried in vacuo. Yield: 0.030 g (37%).
HRMS (electrospray, m/z): calcd. for C27H43OOsP2 [M − 3H]+:
637.2400, found: 637.2509. IR (cm−1): ν(Os−H) 2082, ν(O−C) 1185
1
IR (cm−1): ν(Os−H) 2106 (w), 1995 (w); ν(C−O) 1182 (m). H
NMR (400 MHz, CD2Cl2, 293 K): δ 7.53 (dd, JH−H = 7.4, JH−H = 1.6,
2H, CHarom), 7.51 (m, 2H, CHarom), 7.29 (t, JH−H = 7.4, 2H, CHarom),
2.70 (m, 2H, PCH(CH3)2), 2.27 (m, 2H, PCH(CH3)2), 1.84 (s, 3H,
CH3), 1.47 (dvt, JH−H = 7.2, N = 14.4, 6H, PCH(CH3)2), 1.46 (s, 3H,
CH3), 1.36 (dvt, JH−H = 7.4, N = 15.8, 6H, PCH(CH3)2), 1.18 (dvt,
JH−H = 7.4, N = 16.2, 6H, PCH(CH3)2), 0.72 (dvt, JH−H = 7.2, N =
1
(s). H NMR (400 MHz, CD2Cl2, 293 K): δ 7.46 (d, JH−H = 8.0,
CHarom), 7.26 (m, 2H, CHarom), 7.15 (t, JH−H = 8.0, 2H, CHarom), 2.36
(m, 4H, PCH(CH3)2), 1.57 (s, 6H, CH3), 1.13 (dd, JP−H = 12.0, JH−H
=
1
14.8, 6H, PCH(CH3)2), −13.17 (t, JH−P = 11.0, 3H, OsH). H{31P}
8.0, 12H, PCH(CH3)2), 1.07 (dd, JP−H = 16.0, JH−H = 8.0, 12H,
PCH(CH3)2), −10.08 (s, 6H, OsH). 13C{1H}-APT NMR (100.63 MHz,
CD2Cl2, 293 K): δ 157.1 (dd, JP−H = 3.0, Carom), 135.8 (dd, JP−H = 1.5,
Carom), 129.0 and 125.7 (both s, CHarom), 122.5 (dd, JP−H = 2.0, CHarom),
122.2 (dd, JP−H = 35.2, JP−H = 5.0, Cipso), 36.6 (s, C(CH3)2), 28.8 (dd,
JP−H = 34.2, JP−H = 3.0, PCH(CH3)2), 27.3 (s, C(CH3)2), 19.7 (s,
PCH(CH3)2), 18.7 (s, PCH(CH3)2). 31P{1H} NMR (161.69 MHz,
CD2Cl2, 293 K): δ 4.2 (s). T1(min) (ms, OsH, 400 MHz, CD2Cl2, 228 K):
113 3 (−10.06 ppm).
NMR (400 MHz, CD2Cl2, 223 K, high field region): δ −12.98 (br, 2H,
OsH), −13.38 (br, 1H, OsH). 13C{1H}-APT NMR (100.63 MHz,
CD2Cl2, 293 K): δ 158.2 (vt, N = 13.7, Carom), 132.2 (vt, N = 5.7,
Carom), 131.2 (s, CHarom), 129.6 (vt, N = 27, Cipso), 128.0 (s, CHarom),
125.7 (vt, N = 4.8, CHarom), 35.6 (s, C(CH3)2), 34.8 (s, C(CH3)2),
27.9 (s, C(CH3)2), 27.8 (vt, N = 23.5, PCH(CH3)2), 26.4 (vt, N =
31.8, PCH(CH3)2), 22.8 (vt, N = 4.6, PCH(CH3)2), 20.7 (vt, N = 10.0,
PCH(CH3)2), 20.3 (s, PCH(CH3)2), 19.4 (vt, N = 2.8, PCH(CH3)2).
31P{1H} NMR (161.69 MHz, C6D6, 293 K): δ 50.6 (s). T1(min) (ms,
Synthesis of OsH4{xant(PiPr2)2} (8). Method a: A methanol
solution of OsH6{xant(PiPr2)2} (7) (0.080 g, 0.125 mmol) was stirred
at room temperature for 6 days to afford a white precipitate which
was isolated by decantation from the mother liquor, washed with
cold methanol (2 × 2 mL) and dried in vacuo. Yield: 0.070 g (88%).
Method b: A solution of OsH6(PiPr3)2 (9) (0.600 g, 1.162 mmol) in
toluene (10 mL) was added to a solution of xant(PiPr2)2 (0.566 g,
1.278 mmol) in toluene (5 mL), and the mixture was heated to reflux
for 12 h. After being cooled to room temperature, the solvent was
concentrated to ca. 2 mL. Addition of methanol led to a white solid
which was washed with methanol (2 × 2 mL) and dried under vacuo.
Yield: 0.290 g (39%). Anal. Calcd. for C27H44OOsP2: C, 50.93; H,
6.96. Found: C, 50.68; H, 6.92. HRMS (electrospray, m/z): calcd. for
C27H43OOsP2 [M − H]+: 637.2400, found: 637.2444. IR (cm−1):
ν(Os−H) 2128 (w); ν(C−O) 1188 (m). 1H NMR (500 MHz,
OsH, 400 MHz, CD2Cl2, 233 K): 104 3 (−12.98 ppm); 104
3
(−13.38 ppm).
Synthesis of OsH3Cl(PiPr3)2 (5). In a Schlenk flask equipped
with a Teflon stopcock, a brown suspension of OsH2Cl2(PiPr3)2 (4)
(1 g, 1.712 mmol) in toluene (15 mL) was added Et3N (1 mL,
7.170 mmol). The Ar atmosphere was displaced with H2 and stirred
for 4 h. During this time, the color of the mixture changed from brown
to light brown. It was filtered through Celite, the light brown solution
obtained was concentrated to dryness, and a brown solid was obtained.
Yield: 0.870 g (92%). NMR spectroscopic data agree with those
reported previously for this complex.30a
Synthesis of OsHCl{xant(PiPr2)2}(κ-S-DMSO) (6). A solution
of OsH3Cl{xant(PiPr2)2} (3) (0.022 g, 0.030 mmol) in toluene-d8
(0.5 mL) was treated with 0.250 mL of DMSO. The mixture was
heated at 90 °C, for 16 h. After being cooled to room temperature,
volatiles were removed in vacuo, and the resulting white solid
was washed with diethyl ether (3 × 3 mL) and dried in vacuo. Yield:
0.020 g (80%). Anal. Calcd. for C29H47ClO2OsP2S: C, 46.60; H, 6.34;
CD2Cl2, 293 K): δ 7.47 (m, 2H, CHarom), 7.38 (dd, JH−H = 7.5, JH−H
=
2.5, CHarom), 7.20 (t, JH−H = 7.5, 2H, CHarom), 2.12 (m, 4H,
PCH(CH3)2), 1.58 (s, 6H, CH3), 1.19 (dvt, JH−H = 5.0, N = 15.0, 12H,
PCH(CH3)2), 0.89 (dvt, JH−H = 5.0, N = 15.0, 12H, PCH(CH3)2),
6208
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Inorganic Chemistry
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1
1
−9.53 (t, JP−H = 12.5, 4H, OsH). H{31P} NMR (300 MHz, CD2Cl2,
183 K, high field region): δ −3.14 (br, 2H, OsH), −16.63 (br, 2H,
OsH). 13C{1H}-APT NMR (125.8 MHz, CD2Cl2, 293 K): δ 158.6 (vt,
N = 13.8, Carom), 131.3 (vt, N = 25.2, Cipso), 131.1 (vt, N = 5.0, Carom),
130.3 and 127.9 (both s, CHarom), 125.5 (vt, N = 5.0, CHarom), 34.3 (s,
C(CH3)2), 33.1 (s, C(CH3)2), 28.6 (vt, N = 28.9, PCH(CH3)2), 21.3
(vt, N = 10.1, PCH(CH3)2), 19.9 (s, PCH(CH3)2). 31P{1H} NMR
(202.5 MHz, CD2Cl2, 293 K): δ 66.3 (s). T1(min) (ms, OsH, 400 MHz,
CD2Cl2, 213 K): 179 3 (−9.54 ppm).
spectroscopies. H NMR (300 MHz, CD2Cl2, 293 K): δ 7.89 (dd,
JH−H = 7.5, JH−H = 3, 2H, CHarom), 7.69 (m, 2H, CHarom), 7.64 (t,
JH−H = 7.5, 2H, CHarom), 3.02 (m, 2H, PCH(CH3)2), 2.94 (m, 2H,
PCH(CH3)2), 2.50 (s, 3H, CH3CN), 1.84 (s, 3H, CH3), 1.65 (s, 3H,
CH3), 1.47 (dvt, JH−H = 6.0, N = 18.0, 6H, PCH(CH3)2), 1.39
(dvt, JH−H = 6.0, N = 18.0, 6H, PCH(CH3)2), 1.32 (dvt, JH−H = 6.0,
N = 18.0, 6H, PCH(CH3)2), 0.96 (dvt, JH−H = 6.0, N = 18.0, 6H,
PCH(CH3)2), −11.45 (br, 4H, OsH). 1H{31P} NMR (300 MHz,
CD2Cl2, 223 K, high field region): δ −11.29 (br, 2H, OsH), −11.82
(br, 2H, OsH). 13C{1H}-APT NMR plus HMBC (75.47 MHz,
CD2Cl2, 233 K): δ 156.8 (vt, N = 12.1, Carom), 133.1 (vt, N = 7.5,
Carom), 132.9 (s, CHarom), 131.5 (s, CHarom), 128.7 (s, CN), 128.6 (vt,
N = 4.5, CHarom), 116.4 (vt, N = 20.4, Cipso), 34.4 (s, C(CH3)2), 34.2
(s, C(CH3)2), 29.3 (s, C(CH3)2), 26.7 (vt, N = 30.9, PCH(CH3)2),
25.0 (vt, N = 31.7, PCH(CH3)2), 19.8, 19.1, 18.1, and 17.6 (all s,
PCH(CH3)2), 4.3 (s, CH3CN). 31P{1H} NMR (121.5 MHz, CD2Cl2,
293 K): δ 56.7 (s). T1(min) (ms, OsH, 400 MHz, CD2Cl2, 243 K):
22 2 (−11.65 ppm).
Formation of [OsH2(H···H)(OTf){xant(PiPr2)2}]+ (10). A screw-
top NMR tube containing a solution of OsH4{xant(PiPr2)2} (8)
(0.015 g, 0.023 mmol) in 0.5 mL of dichloromethane-d2 was treated
with HOTf (8 μL, 0.092 mmol). The immediate and quantitative
conversion of 8 to a new species was observed by H and 31P{1H}
1
NMR spectroscopies. All our attempts of isolation of the formed
species were unsuccessful resulting in complex mixtures of unidentified
products. HRMS (electrospray, m/z): calcd. for C27H43OOsP2 [M −
CF3SO3]+: 637.2400, found: 637.2494. H NMR (400 MHz, CD2Cl2,
1
Synthesis of [OsH3(NCCH3){xant(PiPr2)2}]OTf (13). Method a: A
screw-top NMR tube containing a solution of OsH4{xant(PiPr2)2} (8)
(0.030 g, 0.047 mmol) in 0.5 mL of dichloromethane-d2 was treated
with HOTf (16.7 μL, 0.188 mmol). After addition of acetonitrile
(2.5 μL, 0.047 mmol), the color of the mixture changed from pale
yellow to light brown. Addition of Et3N (6.6 μL, 0.047 mmol) afforded
a yellow solution. The immediate and quantitative conversion of 8 to a
293 K): δ 7.88 (dd, JH−H = 7.6, JH−H = 1.5, 2H, CHarom), 7.69 (m, 2H,
CHarom), 7.63 (t, JH−H = 7.6, 2H, CHarom), 3.05 (m, 4H, PCH(CH3)2),
1.99 (s, 3H, CH3), 1.51 (dvt, JH−H = 7.5, N = 14.8, 6H, PCH(CH3)2),
1.50 (s, 3H, CH3), 1.42 (dvt, JH−H = 6.9, N = 16.4, 6H, PCH(CH3)2),
1.38 (dvt, JH−H = 7.5, N = 16.4, 6H, PCH(CH3)2), 0.87 (dvt, JH−H
=
6.9, N = 18.0, 6H, PCH(CH3)2), −11.62 (t, JP−H = 4.0, 4H, OsH).
1H{31P} NMR (300 MHz, CD2Cl2, 183 K, high field region): δ −9.78
(br, 2H, OsH), −13.53 (br, 2H, OsH). 13C{1H} NMR (75.47 MHz,
CD2Cl2, 293 K): δ 159.0 (vt, N = 12.1, Carom), 134.5 (vt, N = 6.8,
Carom), 132.7 (s, CHarom), 131.5 (s, CHarom), 129.5 (vt, N = 7.5,
CHarom), 118.1 (vt, N = 20.4, Cipso), 117.5 (q, JC−F = 317.2, CF3SO3),
35.2 (s, C(CH3)2), 30.2 (s, C(CH3)2), 28.4 (vt, N = 29.4,
PCH(CH3)2), 26.9 (s, C(CH3)2), 24.6 (vt, N = 36.2, PCH(CH3)2),
20.1 (s, PCH(CH3)2), 20.0 (vt, N = 4.5, PCH(CH3)2), 19.6 and 17.9
(both s, PCH(CH3)2). 31P{1H} NMR (121.5 MHz, CD2Cl2, 293 K):
δ 65.9 (s). 19F NMR (282.3 MHz, CD2Cl2, 293 K): δ −77.7 (s,
new species was observed by H and 31P{1H} NMR spectroscopies.
1
Method b: A white suspension of OsH4{xant(PiPr2)2} (8) (0.100 g,
0.157 mmol) in acetonitrile (2 mL) was treated with HOTf (55.6 μL,
0.628 mmol). Immediately, a clear solution was obtained. Addition of
diethyl ether (3 mL) afforded a yellow precipitate, which was washed
with diethyl ether (2 × 2 mL) and dried in vacuo. Yield: 0.082 g (63%).
Anal. Calcd. for C30H46F3NO4OsP2S: C, 43.63; H, 5.61; N, 1.70; S,
3.88. Found: C, 43.51; H, 5.55; N, 1.66; S, 3.80. HRMS (electrospray,
m/z): calcd. for C27H43OOsP2 [M − CH3CN]+: 637.2400, found:
637.2400. IR (cm−1): ν(CN) 2147 (w); ν(Os−H) 1920 (w); ν(O−
CF3SO3). T1(min) (ms, OsH, 400 MHz, CD2Cl2, 243 K): 73
(−11.69 ppm).
3
C) 1097 (s). 1H NMR (300 MHz, CD2Cl2, 293 K): δ 7.65 (dd, JH−H
6.8, JH−H = 1.5, 2H, CHarom), 7.53 (m, 2H, CHarom), 7.42 (t, JH−H
=
=
Formation of [OsH5{xant(PiPr2)2}]+ (11). A screw-top NMR tube
containing a solution of OsH4{xant(PiPr2)2} (8) (0.015 g, 0.023 mmol)
in 0.5 mL of dichloromethane-d2 was treated with HOTf (4 μL,
0.047 mmol). The immediate and quantitative conversion of 8 to a new
species was observed by 1H and 31P{1H} NMR spectroscopies. All our
attempts of isolation of the formed species were unsuccessful, always
resulting in complex mixtures of unidentified products. HRMS
(electrospray, m/z): calcd. for C27H43OOsP2 [M − 2H]+: 637.2400,
found: 637.2475. 1H NMR (500 MHz, CD2Cl2, 293 K): δ 7.64
(d, JH−H = 8.8, 2H, CHarom), 7.57 (m, 2H, CHarom), 7.47 (t, JH−H = 8.8,
2H, CHarom), 2.56 (m, 4H, PCH(CH3)2), 1.61 (s, 3H, CH3), 1.27 (s,
3H, CH3), 1.27 (dvt, JH−H = 5, N = 20, 12H, PCH(CH3)2), 0.95 (dvt,
JH−H = 7.5, N = 17.5, 12H, PCH(CH3)2), −7.71 (t, JH−P = 5.2, 5H,
OsH). 13C{1H} NMR (125.8 MHz, CD2Cl2, 293 K): δ 159.4 (vt, N =
10.1, Carom), 133.5 (vt, N = 5.0, Carom), 130.7 (s, CHarom), 130.4 (s,
CHarom), 128.3 (vt, N = 6.3, CHarom), 123.1 (vt, N = 40.3, Cipso), 31.1
(s, C(CH3)2), 30.1 (s, C(CH3)2), 28.5 (vt, N = 34.0, PCH(CH3)2),
20.8 (vt, N = 6.3, PCH(CH3)2), 19.1 (s, PCH(CH3)2). 31P{1H} NMR
(202.5 MHz, CD2Cl2, 293 K): δ 60.7 (s). T1(min) (ms, OsH, 400 MHz,
CD2Cl2, 195 K): 20 3 (−7.72 ppm).
6.8, 2H, CHarom), 2.49 (m, 2H, PCH(CH3)2), 2.33 (s, 3H, CH3CN),
1.90 (m, 2H, PCH(CH3)2), 1.88 (s, 3H, CH3), 1.45 (s, 3H, CH3), 1.38
(dvt, JH−H = 7.5, N = 16.5, 6H, PCH(CH3)2), 1.17 (dvt, JH−H = 6, N =
18, 6H, PCH(CH3)2), 1.08 (dvt, JH−H = 7.5, N = 16.5, 6H,
PCH(CH3)2), 0.76 (dvt, JH−H = 6.0, N = 15.0, 6H, PCH(CH3)2),
−12.58 (t, JH−P = 10.5, 3H, OsH). 13C{1H}-APT NMR plus HMBC
(75.47 MHz, CD2Cl2, 293 K): δ 159.7 (vt, N = 12.8, Carom), 133.6 (vt,
N = 6.0, Carom), 131.6 (s, CHarom), 129.9 (s, CHarom), 129.1 (s, CN),
128.1 (q, JC−F = 320.7, CF3SO3), 127.8 (vt, N = 5.3, CHarom), 126.9
(vt, N = 27.9, Cipso), 35.8 (s, C(CH3)2), 35.6 (s, C(CH3)2), 29.8 (vt,
N = 24.9, PCH(CH3)2), 27.9 (vt, N = 34.7, PCH(CH3)2), 27.6 (s,
C(CH3)2), 21.6 (s, PCH(CH3)2), 21.1 (vt, N = 8.0, PCH(CH3)2), 20.5
(vt, N = 6.0, PCH(CH3)2), 20.3 (s, PCH(CH3)2), 4.5 (s, CH3CN).
31P{1H} NMR (121.5 MHz, CD2Cl2, 293 K): δ 49.0 (s). 19F NMR
(282.3 MHz, CD2Cl2, 293 K): δ −78.0 (s, CF3SO3). T1(min) (ms, OsH,
400 MHz, CD2Cl2, 193 K): 88 2 (−12.50 ppm).
Synthesis of Os(CCPh)2(=CCHPh){xant(PiPr2)2} (14). In a
Schlenk flask equipped with a Teflon stopcock, a toluene solution of 8
(0.060 g, 0.094 mmol) was treated with phenylacetylene (103 μL,
0.942 mmol) and heated for 2 h at 110 °C. During this time the color
of the solution changed from colorless to yellow. After being cooled
to room temperature, the solvent was concentrated to ca. 1 mL, and
methanol (2 mL) was added resulting in the formation of a yellow
solid, which was washed with methanol (3 × 2 mL) and dried in vacuo.
Yield: 0.070 g (79%). Anal. Calcd. for C51H56OOsP2·CH3OH: C,
64.44; H, 6.24. Found: C, 64.18; H, 6.12. HRMS (electrospray, m/z):
calcd. for C51H57OOsP2 [M + H]+: 939.3498, found: 939.3526. IR
(cm−1): ν(CC) 2093 (s); ν(=CC) 1622 (s); ν(O−C) 1177 (m).
1H NMR (300 MHz, C6D6, 293 K): δ 7.75 (d, JH−H = 8.2, 2H, Ph),
7.37 (t, JH−H = 8.2, 2H, Ph), 7.19 (m, 2H, CHarom−xant(PiPr2)2),
7.15 (m, 1H, Ph), 7.08−6.78 (m, 14H, Ph and CHarom−xant(PiPr2)2),
3.22 (m, 4H, PCH(CH3)2), 3.04 (t, JP−H = 3.0, 1H, =CCH), 1.62
(dvt, JH−H = 6.0, N = 15.0, 12H, PCH(CH3)2), 1.51 (dvt, JH−H = 6.0,
Formation of [OsH2(η2-H2)(NCCH3){xant(PiPr2)2}]2+ (12). Meth-
od a: To a screw-top NMR tube charged with a solution of 8 (0.030 g,
0.047 mmol) in dichloromethane-d2 (0.5 mL) was added HOTf
(16.7 μL, 0.188 mmol). After addition of acetonitrile (2.46 μL,
0.047 mmol) the color of the mixture changed from pale yellow to
light brown. The immediate and quantitative conversion of 8 to a new
species was observed by H and 31P{1H} NMR spectroscopies. All
1
our attempts of isolation of the formed species were unsuccessful,
always resulting in complex mixtures of unidentified products. Method
b: To a screw-top NMR tube charged with a solution of 13 (0.022 g,
0.026 mmol) in dichloromethane-d2 (0.5 mL) was added HOTf
(2.3 μL, 0.026 mmol). Immediately the color of the mixture changed
from yellow to light brown. The immediate and quantitative conver-
sion of 13 to a new species was observed by H and 31P{1H} NMR
1
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Inorganic Chemistry
Article
N = 15.0, 12H, PCH(CH3)2), 1.28 (s, 6H, CH3). 13C{1H}-APT NMR
groups of POP ligands were observed disordered in two positions and
refined with isotropic thermal parameters and restrained geometry.
Crystal Data for 2. C29H46Cl2O2OsP2S·1/2(C4H10O) MW 818.82,
needle, yellow (0.16 × 0.04 × 0.02), monoclinic, space group P21/n, a:
18.775(2) Å, b: 13.0623(18) Å, c: 27.771(4) Å, β: 94.263(5)°, V =
6792.1(15) Å3, Z = 8, Z′ = 2, Dcalc: 1.601 g cm−3, F(000): 3304, T =
100(2) K, μ 4.096 mm−1. 42941 measured reflections (2θ: 3−58°,
ω scans 0.3°), 15626 unique (Rint = 0.0601); min./max. transm. factors
0.603/0.862. Final agreement factors were R1 = 0.0443 (10404
observed reflections, I > 2σ(I)) and wR2 = 0.0987, data/restraints/
parameters 15626/38/738; GOF = 1.057. Largest peak and hole:
2.056 and −1.015 e/Å3.
plus HSQC and HMBC (75.5 MHz, C6D6, 293 K): δ 300.1 (t, JC−P
=
9.1, Os=CC), 155.5 (vt, N = 11.3, Carom−xant(PiPr2)2), 133.7 (s,
CHarom−xant(PiPr2)2), 133.0 (t, JC−P = 2.3, Cipso), 131.9 (vt, N = 5.3,
Carom−xant(PiPr2)2), 130.7 (s, CHarom), 129.3 (t, JC−P = 1.1, CC),
129.0 (s, CHarom−xant(PiPr2)2), 128.3 (s, CHarom), 128.1 (s, CHarom),
127.7 (Cipso−xant(PiPr2)2, this resonance is masked by the resonance
of C6D6), 125.2 (s, CHarom), 124.7 (s, CHarom), 124.5 (vt, N = 5.3,
CHarom−xant(PiPr2)2), 122.9 (s, CHarom), 120.3 (s, Cipso), 109.5 (t,
JC−P = 12.1, CC), 106.4 (t, JC−P = 3.4, OsCC), 34.3 (s,
C(CH3)2), 33.1 (s, C(CH3)2), 27.9 (vt, N = 27.9, PCH(CH3)2), 21.8
and 20.0 (both s, PCH(CH3)2). 31P{1H} NMR (121.5 MHz, C6D6,
293 K): δ 14.4 (s).
Crystal Data for 3. C27H43ClOOsP2, MW 671.20, prism, colorless
(0.16 × 0.14 × 0.12), monoclinic, space group C2/c, a: 35.13(2) Å, b:
12.148(7) Å, c: 14.516(8) Å, β: 111.788(6)°, V = 5752(6) Å3, Z = 8,
Z′ = 1, Dcalc: 1.550 g cm−3, F(000): 2688, T = 100(2) K, μ 4.655
mm−1. 34295 measured reflections (2θ: 3−58°, ω scans 0.3°), 6929
unique (Rint = 0.0334); min./max. transm. factors 0.702/0.862. Final
agreement factors were R1 = 0.0222 (5879 observed reflections, I >
2σ(I)) and wR2 = 0.0569; data/restraints/parameters 6929/0/311;
GOF = 1.042. Largest peak and hole: 0.347 and −1.000 e/Å3.
Crystal Data for 8. C27H44OOsP2, MW 636.76, irregular block,
colorless (0.24 × 0.08 × 0.06), orthorhombic, space group Pbca, a:
22.5833(14) Å, b: 21.4733(14) Å, c: 45.431(3) Å, V = 22031(2) Å3,
Z = 32, Z′ = 4, Dcalc: 1.536 g cm−3, F(000): 10240, T = 100(2) K, μ
4.763 mm−1. 195878 measured reflections (2θ: 3−58°, ω scans 0.3°),
26702 unique (Rint = 0.1007); min./max. transm. factors 0.527/0.862.
Final agreement factors were R1 = 0.0377 (17287 observed reflections,
I > 2σ(I)) and wR2 = 0.0750; data/restraints/parameters 26702/20/
1206; GOF = 1.0202. Largest peak and hole: 2.340 and −1.860 e/Å3.
Crystal Data for 13. C29H46NO3OsP2 × CF3OS, MW 825.88,
irregular block, colorless (0.30 × 0.04 × 0.03), monoclinic, space
group P21/n, a: 12.7693(8) Å, b: 22.3242(15) Å, c: 12.9072(9) Å, β:
112.1100(10)°, V = 3408.8(4) Å3, Z = 4, Z′ = 1, Dcalc: 1.609 g cm−3,
F(000): 1656, T = 150(2) K, μ 3.946 mm−1. 27839 measured
reflections (2θ: 3−58°, ω scans 0.3°), 7993 unique (Rint = 0.0410);
min./max. transm. factors 0.600/0.862. Final agreement factors were
R1 = 0.0360 (6637 observed reflections, I > 2σ(I)) and wR2 = 0.0778;
data/restraints/parameters 7993/3/399; GOF = 1.060. Largest peak
and hole: 1.221 and −0.655 e/Å3.
Synthesis of Os(CCtBu)2(=CCHtBu){xant(PiPr2)2} (15). In a
Schlenk flask equipped with a Teflon stopcock, a toluene solution of 8
(0.060 g, 0.094 mmol) was treated with tert-butylacetylene (116 μL,
0.942 mmol) and heated for 6 h at 110 °C. During this time the color
of the mixture changed from colorless to pale brown. After being
cooled to room temperature, the solvent was concentrated to ca. 1 mL,
and methanol (2 mL) was added resulting in the formation of a yellow
precipitate, which was washed with methanol (3 × 2 mL) and dried in
vacuo. Yield: 0.072 g (87%). Anal. Calcd. for C45H68OOsP2·CH3OH:
C, 60.76; H, 7.98. Found: C, 60.66; H, 7.94. HRMS (electrospray,
m/z): calcd. for C45H70OOsP2 [M + 2H]+: 881.4593, found: 881.4804.
IR (cm−1): ν(CC) 2091 (s); ν(=CC) 1645 (s); ν(O−C) 1181
(m). 1H NMR (300 MHz, C6D6, 293 K): δ 7.37 (m, 2H, CHarom), 7.07
(dd, JH−H = 7.5, JH−H = 1.5, 2H, CHarom), 6.90 (t, JH−H = 7.5, 2H,
CHarom), 3.44 (m, 4H, PCH(CH3)2), 1.70 (dvt, JH−H = 7.5, N = 13.5,
12H, PCH(CH3)2), 1.66 (dvt, JH−H = 7.5, N = 13.5, 12H,
PCH(CH3)2), 1.41 (s, 9H, =CCC(CH3)3), 1.30 (s, 6H, CH3),
1.05 (t, JH−P = 3, 1H, =CCH), 0.96 (s, 18H, CCC(CH3)3).
13C{1H}-APT NMR plus HSQC and HMBC (75.5 MHz, C6D6, 293
K): δ 290.8 (t, JC−P = 9.4, Os=CC), 156.7 (vt, N = 10.6, Carom),
132.6 (s, CHarom), 132.4 (vt, N = 5.3, Carom), 129.8 (vt, N = 32.5,
Cipso), 126.9 (s, CHarom), 124.1 (vt, N = 5.3, CHarom), 124.0 (s, CC),
112.9 (t, JC−P = 3.8, OsCC), 91.6 (t, JC−P = 12.1, CC), 34.6 (s,
C(CH3)2), 33.8 (s, =CCC(CH3)3), 32.7 (s, CCC(CH3)3), 31.1
(s, C(CH3)2), 29.2 (s, CCC(CH3)3), 28.4 (vt, N = 26.4,
PCH(CH3)2), 28.0 (s, =CCC(CH3)3), 22.6 and 20.6 (both s,
PCH(CH3)2). 31P{1H} NMR (121.5 MHz, C6D6, 293 K): δ 11.6 (s).
General Procedure of Dimerization of Terminal Alkynes to
(Z)−RCHCHCCR (R = Ph or R = tBu) Catalyzed by
OsH4{xant(PiPr2)2}. A screwtop NMR tube charged with a solution
Computational Details. The theoretical calculations were carried
out on the model complexes by optimizing the structure at the m06-
DFT52 levels with the Gaussian 09 program.53 The basis sets used
were LANL2DZ basis and pseudopotentials for Os, and 631G(d,p) for
the rest of atoms. The geometries were fully optimized, and sub-
sequent analytical frequency analyses were carried out to confirm the
nature of each stationary point.
For the calculations of Gibbs free energies, we used the standard
ideal gas-rigid rotor-harmonic oscillator approximation. All the Gibbs
energies collected in the text are calculated in a vacuum at 298.15 K
and 1 atm.54
t
of terminal alkyne (HCCR, R = Ph or Bu, 0.800 mmol) and
OsH4{xant(PiPr2)2} (0.005 g, 0.008 mmol) in toluene-d8 (0.5 mL)
was placed into a thermostatic bath at 110 °C, and the reaction
1
was monitored by H NMR spectroscopy, using dioxane (0.007 mL,
0.080 mmol) as internal standard. After the completion of the reaction
(3.75 h for phenylacetylene and 7.80 h for tert-butylacetylene), solvent
was removed and pentane was added to the crude product. The
solution was filtrated through silica gel and analyzed by 1H and
13C{1H} NMR spectroscopies (see Supporting Information).
All discussed relative energies in this paper are referred to as
ΔGvacuum, in order to better explain the experimental observations.
Structural Analysis of Complex 2, 3, 8, and 13. Crystals of 2
were obtained from saturated solutions in diethyl ether. Crystals of 3
and 13 were obtained by slow diffusion of pentane into solutions of
the complexes in THF. Crystals of 8 were obtained by slow diffusion
of methanol into solutions of the complex in toluene. X-ray data
were collected on a Bruker Smart APEX diffractometer equipped
with a normal focus, and 2.4 kW sealed tube source (Mo radiation,
λ = 0.71073 Å). Data were collected over the complete sphere, and
corrected for absorption by using a multiscan method applied with
the SADABS program.50 The structures were solved by the direct
methods. Refinement of complexes was performed by full-matrix least-
squares on F2 with SHELXL97,51 including isotropic and subsequently
anisotropic displacement parameters for nondisordered atoms. Hydride
ligands were located in the Fourier difference maps and refined
with restrained geometry (Os−H 1.59(5) Å). In 2 1/2 molecules of
disordered diethyl ether were observed in the asymmetric unit. This
molecule was refined with restrained geometry. In 8 some isopropyl
ASSOCIATED CONTENT
■
S
* Supporting Information
Text giving the completed ref 53, computational details, tables
giving optimized coordinates and energies of all optimized
complexes, a CIF giving crystallographic data for compounds 2,
1
3, 8, and 13, the H and 13C{1H} NMR data for (Z)-RCH
t
1
CHCCR (R = Ph, Bu), and the H and 31P{1H} NMR
spectra for complexes 7, 10, 11, and 12. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: maester@unizar.es.
6210
dx.doi.org/10.1021/ic400730a | Inorg. Chem. 2013, 52, 6199−6213

Inorganic Chemistry
Article
30, 6166. (h) Dallanegra, R.; Chaplin, A. B.; Weller, A. S.
Organometallics 2012, 31, 2720.
(5) (a) Caulton, K. G. J. Organomet. Chem. 2001, 617−618, 56.
(b) Esteruelas, M. A.; Oro, L. A. Adv. Organomet. Chem. 2001, 47, 1.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
(c) Esteruelas, M. A.; Lop
́
ez, A. M. Organometallics 2005, 24, 3584.
ez, A. M.; Olivan, M. Coord. Chem. Rev.
■
(d) Esteruelas, M. A.; Lop
́
́
Financial support from the Spanish MINECO (Projects
CTQ2011-23459 and Consolider Ingenio 2010 (CSD2007-
00006)), the DGA (E35) and the European Social Fund (FSE)
is acknowledged. T.B. thanks Spanish MINECO for funding
through the Juan de la Cierva programme. J.A. acknowledges
support via a predoctoral fellowship from the DGA. We thank
2007, 251, 795. (e) Bolano, T.; Esteruelas, M. A.; Onate, E. J.
̃
̃
Organomet. Chem. 2011, 696, 3911.
(6) For relevant osmium starting materials see: (a) Vaska, L.;
DiLuzio, J. W. J. Am. Chem. Soc. 1961, 83, 1262. (b) Esteruelas, M. A.;
Werner, H. J. Organomet. Chem. 1986, 303, 221. (c) Werner, H.;
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Esteruelas, M. A.; Lahoz, F. J.; Lopez, J. A.; Meyer, U.; Oro, L. A.;
́
Werner, H. Inorg. Chem. 1991, 30, 288. (e) Dickinson, P. W.;
Girolami, G. S. Inorg. Chem. 2006, 45, 5215. (f) Esteruelas, M. A.;
the Centro de Supercomputacion de Galicia (CESGA) for
generous allocation of computational resources.
́
García-Yebra, C.; Olivan, M.; Onate, E. Inorg. Chem. 2006, 45, 10162.
(g) Gross, C. L.; Brumaghim, J. L.; Girolami, G. S. Organometallics
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