Preparation of half-sandwich osmium complexes by deprotonation of aromatic and pro-aromatic acids with a hexahydride bronsted base

Article abstract of DOI:10.1021/om200371r

Figure Persented: Half-sandwich osmium(II) and osmium(IV) complexes have been prepared by reaction of the hexahydride complex OsH₆(P ⁱPr₃)₂ (1) with phenol, pyrrole, and methylcyclopentadienes. The reaction with phenol initially leads to OsH ₃(OPh)(PⁱPr₃)₂ (2). In toluene, 2 undergoes reductive elimination of phenol, which tautomerizes to give OsH ₂(η⁴-2,4-cyclohexadien-1-one)(PⁱPr ₃)₂ (3). The equilibrium mixture of 2 and 3 evolves into OsH(η⁵-PhO)(PⁱPr₃)₂ (4) with loss of molecular hydrogen. The addition of HBF₄ to diethyl ether solutions of 4 leads to [OsH(η⁶-PhOH)(PⁱPr ₃)₂]BF₄ (6). The reaction of 1 with pyrrole gives OsH(η⁵-C₄H₄N)(PⁱPr ₃)₂ (7), which by addition of HBF₄ affords [OsH₂(η⁵-C₄H₄N)(P ⁱPr₃)₂]BF₄ (8). Similarly, treatment of 1 with methylcyclopentadiene leads to OsH(η⁵-C ₅H₄Me)(PⁱPr₃)₂ (9), which reacts with HBF₄ to give [OsH₂(η⁵-C ₅H₄Me)(PⁱPr₃)₂]BF ₄ (10). Treatment of toluene solutions of 1 with tetramethylcyclopentadiene gives a mixture of the trihydride OsH ₃(η⁵-C₅HMe₄)(P ⁱPr₃) (11; 56%) and the dihydride-tolyl derivatives OsH₂(m-tolyl)( η⁵-C₅HMe₄)(P ⁱPr₃) (12; 14%) and OsH₂(p-tolyl)( η⁵-C₅HMe₄)(PⁱPr₃) (13; 30%). However in n-octane the trihydride 11 is formed in 85% yield. In contrast to tetramethylcyclopentadiene, pentamethylcyclopentadiene reacts with 1 in toluene to give selectively the trihydride OsH₃(η ⁵-C₅Me₅)(PⁱPr₃) (14). Complexes 2 and 7 have been characterized by X-ray diffraction analysis.

Full text of DOI:10.1021/om200371r

ARTICLE
pubs.acs.org/Organometallics
Preparation of Half-Sandwich Osmium Complexes by
Deprotonation of Aromatic and Pro-aromatic Acids with
a Hexahydride Brønsted Base
Miguel A. Esteruelas,* Jorge García-Raboso, and Montserrat Olivꢀan
Departamento de Química InorgꢀanicaÀInstituto de Síntesis Química y Catꢀalisis Homogꢀenea (ISQCH),
Universidad de ZaragozaÀCSIC, 50009 Zaragoza, Spain
S Supporting Information
b
ABSTRACT: Half-sandwich osmium(II) and osmium(IV) com-
plexes have been prepared by reaction of the hexahydride complex
OsH6(PiPr3)2 (1) with phenol, pyrrole, and methylcyclopentadienes.
The reaction with phenol initially leads to OsH3(OPh)(PiPr3)2 (2).
In toluene, 2 undergoes reductive elimination of phenol, which
tautomerizes to give OsH2(η4-2,4-cyclohexadien-1-one)(PiPr3)2
(3). The equilibrium mixture of 2 and 3 evolves into OsH(η5-
PhO)(PiPr3)2 (4) with loss of molecular hydrogen. The addition of
HBF4 to diethyl ether solutions of 4 leads to [OsH(η6-PhOH)-
(PiPr3)2]BF4 (6). The reaction of 1 with pyrrole gives OsH(η5-
C4H4N)(PiPr3)2 (7), which by addition of HBF4 affords [OsH2(η5-
C4H4N)(PiPr3)2]BF4 (8). Similarly, treatment of 1 with methylcy-
clopentadiene leads to OsH(η5-C5H4Me)(PiPr3)2 (9), which reacts
with HBF4 to give [OsH2(η5-C5H4Me)(PiPr3)2]BF4 (10). Treatment of toluene solutions of 1 with tetramethylcyclopentadiene
gives a mixture of the trihydride OsH3(η5-C5HMe4)(PiPr3) (11; 56%) and the dihydride-tolyl derivatives OsH2(m-tolyl)(η5-
C5HMe4)(PiPr3) (12; 14%) and OsH2(p-tolyl)(η5-C5HMe4)(PiPr3) (13; 30%). However in n-octane the trihydride 11 is formed
in 85% yield. In contrast to tetramethylcyclopentadiene, pentamethylcyclopentadiene reacts with 1 in toluene to give selectively the
trihydride OsH3(η5-C5Me5)(PiPr3) (14). Complexes 2 and 7 have been characterized by X-ray diffraction analysis.
’ INTRODUCTION
Transition-metal hydride compounds, as η5-half-sandwich
complexes, play a central role in modern organometallic and
inorganic chemistries.6 The hydride ligand is viewed as one of the
best anchors to secure unsaturated organic molecules in transition-
metal compounds. As a consequence of this property, osmium
hydride complexes have generated a wide range of organome-
tallic functional groups,3d,7 which facilitate some carbonÀcarbon
coupling reactions and the formation of organic fragments with a
rich chemistry.8 Our interest in complexes that promote the
functionalization of organic molecules2,9 prompted us to search
for new general methods to prepare half-sandwich osmium hydride
complexes, including those containing a heteroaromatic ring.
The saturated d2 hexahydride complex OsH6(PiPr3)2 activates
CÀH bonds of a broad number of organic molecules10 and, by
protonation with weak Brønsted acids, releases molecular hydro-
gen to afford d4-osmium hydride species, which contain the
corresponding conjugated Brønsted base as a ligand.11 Because
phenol, pyrrole, and cyclopentadienes are weak Brønsted acids of con-
jugated aromatic Brønsted bases, which can be η5-coordinated,
we have investigated the reactivity of OsH6(PiPr3)2 with these
η5-Half-sandwich complexes are one of the cornerstones of
transition-metal chemistry. Those of the iron triad have played
a fundamental role in the development of the organometallic
area and homogeneous catalysis. A number of half-sandwich
ruthenium compounds have been shown to be versatile catalysts
or reaction intermediates for relevant organic transformations.1 In
contrast to ruthenium, osmium chemistry is still underdeveloped.
However, recent findings have proved that osmium is a promising
alternative to ruthenium catalysts,2 and since stoichiometric osmium
chemistry seems to be more rich than that of ruthenium,3 an
increasing interest in η5-half-sandwich osmium complexes begins to
be perceptible.
The methods of general use to prepare η5-half-sandwich
osmium complexes are limited to the synthesis of species with
cyclopentadienyl and related five-membered hydrocarbon rings.
They are furthermore very scarce. We have reported that the
treatment of OsH2Cl2(PiPr3)2 or OsH3Cl(PiPr3)2 with the
corresponding hydrocarbon derivative of an s- or p-block ele-
ment allows obtaining OsÀPiPr3 compounds,3c,4 whereas Jia and
co-workers have shown that reactions of OsH3Cl(PPh3)3 with
cyclopentadienes and monosubstituted fulvenes afford Os-PPh3
derivatives.5
Received: May 4, 2011
Published: June 29, 2011
r
2011 American Chemical Society
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|

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Scheme 1
Brønsted acids, in order to prepare half-sandwich osmium
hydride complexes in a general manner.
This paper describes a general method to prepare half-
sandwich osmium hydride complexes and shows the influence
of the η5-ligand on the stoichiometry of the formed species and
the protonation of the latter.
’ RESULTS AND DISCUSSION
1. Reactions with Phenol. Treatment of toluene solutions
of the hexahydride complex OsH6(PiPr3)2 (1) with 3.0 equiv of
phenol for 5 h, under reflux, leads to a mixture of OsH3(OPh)-
(PiPr3)2 (2), OsH2(η4-2,4-cyclohexadien-1-one)(PiPr3)2 (3), and
OsH(η5-PhO)(PiPr3)2 (4), in a 1.3:1:4.3 molar ratio. The forma-
tion of the mixture can be rationalized according to Scheme 1.
Osmium polyhydrides are Brønsted bases that show a marked
tendency to deprotonate alcohols to afford alkoxy species, which
evolve by β-hydrogen elimination into ketone derivatives12 or via
aldehyde intermediates into carbonyl compounds.2b,9c,13 Phenol
is a particularly acidic alcohol having no geminal hydrogen atoms.
Thus, the abstraction of its OH-hydrogen by one of the hydride
ligands of 1 generates molecular hydrogen and a phenoxy species,
which releases a second hydrogen molecule to give 2. The latter
can be prepared as a brown solid in 96% yield, by stirring of a
tetrahydrofuran solution of the trihydride OsH3Cl(PiPr3)2 (5) in
the presence of 6.0 equiv of sodium phenoxide, for 20 min, at
room temperature.
Complex 2 has been characterized by X-ray diffraction anal-
ysis. Figure 1 shows a view of the molecular geometry. The
structure has essentially C2v symmetry with trans phosphines
(P(1)ÀOsÀP(2) = 176.15(5)°) and the oxygen atom of the
phenoxy group, the metal center, and the hydride ligands lying in
the plane perpendicular to the PÀOsÀP direction. The most
noticeable feature of the complex are the H(01)ÀOsÀH(02)
and H(02)ÀOsÀH(03) angles of 58.1(5)° and 62.1(15)°,
respectively, which markedly deviate from 90°. It is well known
that the octahedral geometry is not favorable for heavy metal d4
complexes, which prefer to be diamagnetic.11a,12c,14 These com-
plexes therefore undergo a distortion that destabilizes one orbital
from the t2g set and simultaneously stabilizes some occupied
orbitals. The distortion is typical for OsH3X(PR3)2 complexes
and partially cancels the electron deficiency at the metal, which
receives additional electron density from the hydrides via stron-
ger σ-bonds and from one lone pair of X via a π-bond.14e In
agreement with the latter, the OsÀO distance of 2.027(3) Å is
Figure 1. Molecular diagram of complex 2. Selected bond lengths (Å)
and angles (deg): OsÀP(1) = 2.3370(14), OsÀP(2) = 2.3311(14),
OsÀO = 2.027(3), H(01)ÀH(02) = 1.53(1), H(02)ÀH(03) = 1.63(4);
P(1)ÀOsÀP(2) = 176.15(5), OsÀOÀC(1) = 134.9(3), H(01)ÀOsÀ
H(02) = 58.1(5), H(02)ÀOsÀH(03) = 62.1(15).
consistent with some multiple character for the OsÀO bond.15
The π-donation from the oxygen atom into the metal is also
supported by the OsÀOÀC(1) angle of 134.9(3)°, which is
certainly greater than thatexpected from a pyramidal oxygen atom.
Fast rotation around the OsÀO bond gives rise to a single
time-averaged 31P{1H} NMR signal at 53.2 ppm, between 298
and 183 K. The hydride ligands display at À18.60 ppm a triplet
1
with a HÀP coupling constant of 11.4 Hz in the H NMR
spectrum, in toluene-d8, at room temperature. Lowering the
sample temperature produces a broadening of the resonance.
However, decoalescence is not observed at 183 K. A variable-
temperature 300 MHz T1 study between 273 and 183 K gave a
T1(min) value of 133 ( 1 ms at 203 K, which is consistent with the
trihydride character of the complex.
Phenol normally exists in solution as an enol. However, when
it is coordinated to a transition metal, its dienone tautomers can
become energetically competitive. Thus, several transition-metal
cyclohexadien-1-one derivatives have been isolated and chara-
cterized.16 Complex 2 is unstable in solution. At room tempera-
ture, it undergoes reductive elimination of phenol, which tauto-
merizes into 2,4-cyclohexadien-1-one to afford after 48 h a 93:7
mixture of 2 and 3. Free phenol stabilizes the coordinated
dienone form as a consequence of the formation of O HÀO
3 3 3
hydrogen bonds between the OH-hydrogen atom and the
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ARTICLE
Figure 2. Partial view of the 1HÀ C HMBC NMR spectrum of 3.
13
carbonyl group. Thus, in the presence of 3.0 equiv of phenol the
amount of dienone derivative increases to 67%, whereas in the
presence of 6.0 equiv 90% of 3 is formed.
1
The 31P{1H} and H NMR spectra of 3 suggest that the
dienone rotates around an OsÀdienone axis, in agreement with
that previously observed for the related compound OsH2(η4-1,3-
cyclohexadiene)(PiPr3)2.17 Thus, at room temperature, the 31P-
{1H} NMR spectrum contains a singlet at 31.5 ppm for the
inequivalent phosphine groups, whereas the 1H NMR spectrum
shows at À13.40 ppm a triplet with a HÀP coupling constant of
30.8 Hz, for the inequivalent hydride ligands. As expected for the
rigid structure proposed in Scheme 1, at 193 K, the 31P{1H}
NMR spectrum contains an AB spin system centered at 33.6
ppm and defined by Δν = 930 Hz and JAÀB = 661.0 Hz, while the
1H NMR spectrum shows two hydride resonances at À12.8 and
À15.7 ppm. Assuming an entropy of activation close to 0, a ΔHq
Figure 3. Partial viewof the1H NMR spectra of OsH(η5-PhO)(PiPr3)2
xPhOH as a function of the amount of phenol in the benzene-d6 solution.
3
as the amount of phenol in the solution increases, while the
resonance due to protons 3 and 5 is shifted toward higher field.
Interestingly, the value of Δδ (δ3,5 À δ2,6) changes from 0.08
to À0.19 as the amount of phenol in the solution increases from
1 to 5 equiv. However, an increase of 5 to 10 in the number
of equivalents of phenol only produces a change from À0.19
to À0.21 in the value of Δδ. In agreement with the formation
of a five-solvated phenol species the treatment of toluene
solutions of 1 with 6.0 equiv of phenol for 5 h under reflux leads
value of about 9 kcal molÀ1 can be estimated as the rotation
3
barrier, on the basis of a coalescence temperature of 203 K. In the
low-field region of the 1H NMR spectrum, the inequivalent CH2-
hydrogen atoms of the dienone display resonances at 4.30 and
3.09 ppm, which show cross signals with the carbonyl resonance
to OsH(η5-PhO)(PiPr3)2 5PhOH, which is isolated as a brown
3
oil in 93% yield, according to eq 1. The hydrogen bonds certainly
weaken the CÀO double bond of the dienylone ligand. In
agreement with other η5-dienylone compounds18 the CO reso-
nance in the 13C{1H} NMR spectrum appears at 161.4 ppm, shifted
by about 50 ppm toward higher field with regard to that of 3.
13
at 201.2 ppm in the 1HÀ C HMBC NMR spectrum (Figure 2).
The equilibrium mixtures of 2 and 3 lose molecular hydrogen
in toluene to afford the η5-dienylone derivative 4, which reacts
with HBF4 OEt2 to give the η6-phenyl compound [OsH(η6-
3
PhOH)(PiPr3)2]BF4 (6), as a result of the protonation of the
carbonyl group. The protonation is reversible. Treatment of
tetrahydrofuran solutions of 6 with 1.1 equiv of KtBuO regen-
erates 4 in almost quantitative yield. Characteristic spectroscopic
data of 4 are a singlet at 15.4 ppm in the 31P{1H} NMR spectrum
and a triplet (JHÀP = 33.5 Hz) at À14.20 ppm, due to the hydride
ligand, in the 1H NMR spectrum.
The solvation of the oxygen atom of the carbonyl group with
free phenol significantly improves the stability of 4. Phenol is less
volatile than tert-butanol, and its hydrogen bonds with the
dienylone ligand are stable under vacuum. Thus, in contrast to
the oil resulting from the deprotonation of 6 with KtBuO, which
is extremely unstable in benzene-d6 at room temperature once we
obtained accurate spectroscopic data, the oil generated from the
deprotonation with NaPhO can be handled without much
difficulty. The oxygen atom seems to have the size to form
a first solvation sphere with five phenol molecules. Figure 3
The phenol complex 6 was isolated as a white solid in 71%
yield. At room temperature the 31P{1H} NMR spectrum in
dichloromethane-d2 shows a singlet at 13.7 ppm, whereas the 1H
NMR spectrum contains at À12.95 ppm a triplet with a HÀP
coupling constant of 36.6 Hz due to the hydride ligand. These
spectroscopic data agree well with those reported for the com-
plexes [OsH(η6-C6H5R)(PiPr3)2]BF4 (R = CH3, H, F).19
Characteristic features of 6 are also a broad singlet at 8.21
1
shows the H NMR resonances of the hydrogen atoms of the
η5-coordinated ligand of the OsH(η5-PhO)(PiPr3)2 xPhOH
ppm, corresponding to the OH-proton, in the H NMR spec-
1
3
adducts, resulting from the sequential addition of phenol to the
trum and a singlet at 137.1 ppm due to the COH-carbon atom in
the 13C{1H} NMR spectrum. The latter appears shifted by about
24 ppm toward higher field with regard to the CO resonance of
the phenol-solvated dienylone adduct.
benzene-d6 solutions of the oil formed by deprotonation of 6
with NaPhO (OsH(η5-PhO)(PiPr3)2 PhOH). The resonances
3
corresponding to the protons 2, 6, and 4 move to lower field
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Scheme 2
Scheme 3
in Figure 4. The 31P{1H} NMR spectrum contains a singlet at
1
27.7 ppm. In the H NMR spectrum, the most noticeable
resonances are those corresponding to the hydride and pyrrolide
ligands. The first of them gives rise to a triplet (JHÀP = 29.8 Hz)
at À18.88 ppm, whereas the second one displays two signals at
5.88 and 4.85 ppm. In the 13C{1H} NMR spectrum, the pyrrolide
resonances are observed at 98.7 and 72.5 ppm as triplets with
CÀP coupling constants of 1.5 and 2.6 Hz, respectively. These
spectroscopic date agree well with those reported for the
ruthenium complex RuH(η5-C4NH4)(PCy3)2.22
One should expect that the pyrrolide nitrogen atom of 7, like
the dienylone oxygen atom of 4, is a strong basic center, since
only two of its three unshared electrons are needed for the aro-
matic sextet. However, in contrast to 4, the addition of 1.0 equiv
of HBF4 to diethyl ether solutions of 7 produces the protonation
of the osmium atom, revealing a strong electron donor power of
the η5-pyrrolide group. The oxidized product [OsH2(η5-C4NH4)-
(PiPr3)2]BF4 (8) is isolated as a white solid in 83% yield.
The 31P{1H} NMR spectrum of 8 in dichloromethane-d2
Figure 4. Molecular diagram of complex 7. Selected bond lengths (Å)
and angles (deg): OsÀP(1) = 2.2970(17), OsÀP(2) = 2.2867(17),
C(1)ÀC(2) = 1.396(11), C(2)ÀC(3) = 1.412(11), C(3)ÀC(4) =
1.404(11), NÀC(1) = 1.390(10), NÀC(4) = 1.384(10); P(1)ÀOsÀP-
(2) = 106.00(6).
1
shows a singlet at 33.9 ppm. In the H NMR spectrum, the
2. Reactions with Pyrrole. Five-membered heterorings con-
taining two CÀC double bonds can also have an aromatic sextet
if the heteroatom has an unshared pair of electrons. Such is the
case of pyrrole. Thus, since the unshared pair is needed for the
aromatic sextet, the basicity of the nitrogen atom is much weaker
than that of pyridine and the NH-hydrogen has some protic
character, although its pKa value is about five units higher than
that of phenol. In agreement with this weak Brønsted acidic
nature of the heterocycle and the significant Brønsted basicity of
1, the treatment of the toluene solutions of the hexahydride with
6.0 equiv of pyrrole for 7 h under reflux produces the release of
molecular hydrogen, as a consequence of the abstraction of the
NH-hydrogen with the hydride ligands. The resulting unsatu-
rated metal fragment is stabilized by coordination of the gener-
ated pyrrolide in a η5-fashion. The formed half-sandwich
derivative, OsH(η5-C4H4N)(PiPr3)2 (7), is isolated as a beige
solid in 55% yield, according to Scheme 2.
hydride resonance appears at À14.50 ppm as a triplet with a
HÀP coupling constant of 28.6 Hz, whereas the pyrrolide signals
are observed as singlets at 6.60 and 6.02 ppm. In the 13C{1H}
NMR spectrum, the aromatic carbon atoms display singlets at
104.7 and 90.4 ppm. It should be noted that the oxidation of the
1
metal center produces the displacement of the H and 13C
pyrrolide resonances toward lower field.
3. Reactions with Methylcyclopentadienes. Cyclopenta-
dienes have acidic properties, since on loss of a proton, the
resulting carbanion is stabilized by a resonance that is greater
than in pyrrole. Thus some cyclopentadienyl derivatives have
been prepared by displacement of Brønsted base ligands with
these dienes.23 In agreement with the Brønsted basicity of 1, the
hexahydride deprotonates methylcyclopentadienes to afford
osmium(II)- and osmium(IV)-methylcyclopentadiene half-
sandwich derivatives. The oxidation state of the metal center
and the experimental conditions of the synthesis depend upon
the number of the methyl substituents of the dienes.
Figure 4 shows a view of the structure of 7. The geometry
around the osmium center is close to octahedral, with the
aromatic ring occupying three sites of a face. The mutually cis
disposed phosphine groups experience a large steric hindrance,
as a consequence of their cone angle (160°).20 Thus, the
P(1)ÀOsÀP(2) angle of 106.00(6)° strongly deviates from the
ideal value of 90°. This angle is similar to other PÀMÀP angles
previously found in complexes with two triisopropylphosphine
ligands mutually cis disposed.4d,19,21 The pyrrolide ligand is
almost planar, with a maximum deviation of 0.0133(41) Å for
C(1), with statistically identical CÀC bond lengths of 1.396(11)
Å (C(1)ÀC(2)), 1.412(11) Å (C(2)ÀC(3)), and 1.404(11) Å
(C(3)ÀC(4)) and CÀN distances of 1.390(10) Å (NÀC(1))
and 1.384(10) Å (NÀC(4)).
Treatment of the toluene solutions of 1 with 6.0 equiv of
methylcyclopentadiene for 24 h under reflux leads to the
osmium(II) hydride OsH(η5-C5H4Me)(PiPr3)2 (9), which is
isolated as a pale yellow oil in 74% yield according to Scheme 3.
This compound is analogous with 7, containing a CMe moiety
instead of a nitrogen atom. In agreement with the latter, its
31P{1H} NMR spectrum in benzene-d6 at room temperature
shows a singlet at 28.9 ppm, whereas in the 1H NMR spectrum,
the hydride resonance appears at À15.66 ppm as a triplet with a
HÀP coupling constant of 30.2 Hz.
The metal center of 9 undergoes protonation, like that of 7.
The addition of 1.2 equiv of HBF4 to its diethyl ether solutions
produces the instantaneous precipitation of the dihydride deri-
vative [OsH2(η5-C5H4Me)(PiPr3)2]BF4 (10), counterpart of 8,
as a white solid in 75% yield. Characteristic data of 10 are a singlet
The 31P{1H}, 1H, and 13C{1H} NMR spectra of 7 in benzene-
d6 at room temperature are consistent with the structure shown
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Scheme 4
at 32.1 ppm in the 31P{1H} NMR spectrum in dichloromethane-
d2 and a triplet (JHÀP = 29.2 Hz) at À14.14 ppm in the 1H NMR
spectrum. The spectroscopic data of both 10 and 9 compare well
with those of related cyclopentadiene compounds.4a
OsH3(η5-C5H5)(PiPr3)25 and OsH3(η5-C5Me5)L (L = AsPh3,
PPh3, PCy3, PEt3).26 Between 223 and 183 K, the resonance at
higher field splits into two signals, suggesting that at tempera-
tures lower than 223 K the rotation of the cyclopentadienyl
group around a cyclopentadienylÀosmium axis is stopped. This
reduces the symmetry of the molecule, and as a consequence, the
transoid hydride ligands become inequivalent.
Tetramethylcyclopentadiene, in contrast to methylcyclopen-
tadiene, generates osmium(IV) species, as expected for a stron-
ger electron donor character of the tetramethylcyclopentadienyl
group with regard to the methylcyclopentadienyl ligand. Treat-
ment of toluene solutions of 1 with the tetrasubstituted diene for
5 h under reflux leads to a mixture of osmium(IV) compounds,
including the trihydride OsH3(η5-C5HMe4)(PiPr3) (11; 56%)
and the dihydride-tolyl derivatives OsH2(m-tolyl)(η5-C5HMe4)-
(PiPr3) (12; 14%) and OsH2(p-tolyl)(η5-C5HMe4)(PiPr3)
(13; 30%). The tolyl compounds 12 and 13 are the result of
the respective meta- and para-CH bond activations of toluene
promoted by 1 before the deprotonation of the diene. In this
context, it should be noted that the hexahydride complex
catalyzes the H/D exchange between pyridines and benzene-
d6.10i The CÀH bond activation processes generate bispho-
sphine osmium hydride tolyl intermediates,24 which deprotonate
the diene. The subsequent coordination of the resulting cyclo-
pentadienyl group to the metal center stabilizes the osmium(IV)-
tolyl complexes. In agreement with this, we have also observed
that the treatment of n-octane solutions of 1 with 6.0 equiv of
tetramethylcyclopentadiene for 4 h under reflux gives 11, which
does not react with toluene under reflux to afford 12 and 13
(Scheme 4).
The osmium(IV)-dihydride-tolyl complexes 12 and 13 are
rare examples of products resulting from CÀH activation
reactions with the late transition metal in high oxidation
state27 (d4 ion). They have been fully characterized by 31P-
1
{1H}, H, and 13C{1H} NMR spectroscopy. The 31P{1H}
NMR spectrum of 12 in benzene-d6 at room temperature
contains a singlet at 42.4 ppm. In the 1H NMR spectrum, the
hydride ligands display at À12.69 ppm a doublet with a HÀP
coupling constant of 37 Hz, whereas the tolyl group gives rise
to four signals between 7.78 and 6.85 ppm corresponding to its
four inequivalent aromatic hydrogen atoms. In agreement with
the 1H NMR spectrum, six aromatic tolyl resonances are
observed between 164.1 and 119.9 ppm in the 13C{1H}
NMR spectrum. Characteristic spectroscopic data of 13 are a
singlet at 42.3 ppm in the 31P{1H} NMR spectrum, a doublet
(JHÀP = 37.0 Hz) at À12.65 ppm due to the hydride ligands,
and two doublets (JHÀH = 7.2 Hz) at 7.79 and 6.77 ppm
assigned to the aromatic tolyl hydrogen atoms in the 1H NMR
spectrum and four singlets between 157.8 and 119.6 ppm
corresponding to the aromatic tolyl carbon atoms in the 13C{1H}
NMR spectrum.
The pentamethylcyclopentadienyl group also shows a strong
tendency to stabilize osmium(IV) species. The additional methyl
group increases the electron richness of the five-membered ring
but, however, also augments its steric requirement, which
appears to prevent the formation of pentamethylcyclopentadie-
nyl counterparts of 12 and 13, most probably as a consequence of
the steric hindrance experienced between the methyl substitu-
ents and the tolyl groups. Thus, the treatment of toluene
solutions of 1 with 6.0 equiv of pentamethylcyclopentadiene
for 24 h under reflux leads to the selective formation of the
trihydride derivative OsH3(η5-C5Me5)(PiPr3) (14), which is
isolated as a yellow oil in 80% yield, according to eq 2. The
31P{1H} and 1H NMR spectra of 14 are consistent with those of
11. In toluene at room temperature, the 31P{1H} NMR spectrum
contains a singlet at 47.3 ppm, whereas the hydride resonances in
the 1H NMR spectrum appear as a singlet at À14.47 ppm and a
doublet (JHÀP = 33.3 Hz) at À14.82 ppm in a 1:2 intensity ratio.
At temperatures higher than 273 K, the hydride ligands are also
involved in a thermally activated site exchange process. In this
The trihydride complex 11 is isolated as a pale yellow oil, in
85% yield, from the reaction in n-octane. Its 31P{1H} NMR
spectrum in toluene-d8 at room temperature shows a singlet at
50.5 ppm, whereas in the 1H NMR spectrum, the hydride ligands
display a singlet at À14.06 ppm and a doublet (JHÀP = 32.6 Hz)
at À14.85 ppm in a 1:2 intensity ratio. These 1H resonances are
temperature dependent between 373 and 183 K. The spectrum at
373 K contains a broad signal centered at about À14.6 ppm,
which is consistent with the operation of a thermally activated
site exchange process between the unique hydride and the pair of
equivalent hydride ligands. The exchange process proceeds at a
sufficient rate to lead to a single hydride resonance. Between 353
and 343 K, decoalescence occurs, and between 343 and 233 K
the expected two resonances are observed. Line shape analysis
of these spectra yields rate constants at different temperatures.
The activation parameters obtained from the Eyring analysis are
ΔHq = 16.0 (0.9 kcal molÀ1 and ΔSq =À2.9 (1.6 cal molÀ1 KÀ1.
3
3
3
The value of the entropy of activation close to zero is in
agreement with an intramolecular process, while the value
of the enthalpy of activation lies in the range reported for
3848
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case, the activation parameters for the exchange are ΔHq =
C6H6O), 72.0 (s, CH C6H6O), 68.6 (s, CH C6H6O), 56.6 (s, CH
C6H6O), 34.7 (s, CH2 C6H6O), 29.4 (s, CH C6H6O), 29.4 (vt, N = 27,
PCH(CH3)2), 28.8 (s, CH, C6H6O), 20.7 and 20.4 (both s, PCH-
(CH3)2).
15.7 ( 1.2 kcal molÀ1 and ΔSq = À2.0 ( 2.4 cal molÀ1 KÀ1
.
3
3
3
Reaction of OsH3Cl(PiPr3)2 (5) with NaOPh: Preparation of
OsH3(OPh)(PiPr3)2 (2). A brown solution of 5 (100 mg, 0.18 mmol)
in 10 mL of THF was treated with 5 equiv of sodium phenoxide (106 mg,
1.09 mmol) and stirred at room temperature for 20 min. The solvent was
evaporated. The brown residue obtained was dissolved in toluene and
filtered through Celite. The solution was evaporated to dryness and
dissolved in pentane. The solvent was removed in vacuo, and a brown
solid was obtained. Yield: 105 mg (96%). IR (cmÀ1): ν(OsH) 2091 (w),
ν(CdC) 1583 (m). 1H NMR (300 MHz, C7D8, 298 K): δ 7.25 (m, 3H,
o- and p-OPh), 6.77 (t, JHÀH = 7.2, 2H, m-OPh), 1.83 (m, 6H,
PCH(CH3)2), 1.10 (dvt, JHÀH = 7.0, N = 13.1, 36H, PCH(CH3)2),
À18.60 (t, JPÀH = 11.4, 3H, OsH3). 31P{1H} NMR (121.48 MHz, C7D8,
298 K): δ 53.2 (s). 13C{1H} NMR (75.5 MHz, C6D6, 298 K): δ 175.6 (s,
Cipso Ph), 128.8, 116.9 (both s, CH Ph), 27.3 (vt, N = 23.4, PCH-
(CH3)2), 20.7 (s, PCH(CH3)2). T1(min) (ms, OsH3, 300 MHz, C7D8,
203 K): 133 ( 1.
Isomerization of 2 into 3. In a 5 mm NMR tube 2 (20 mg, 0.03
mmol) was dissolved in 0.4 mL of toluene, and the sample was
monitored by 31P{1H} NMR periodically. After 48 h at room tempera-
ture the 31P{1H} NMR spectrum showed a 93:7 mixture of 2 and 3.
Isomerization of 2 into 3 in the Presence of 3 equiv of
Phenol. In a 5 mm NMR tube 2 (20 mg, 0.03 mmol) and phenol
(9.3 mg, 0.098 mmol) were dissolved in 0.4 mL of toluene, and the
sample was monitored by 31P{1H} NMR periodically. After 48 h at room
temperature the 31P{1H} NMR spectrum showed a 33:67 mixture
of 2 and 3.
’ CONCLUDING REMARKS
This study shows that the hexahydride complex OsH6(PiPr3)2
deprotonates phenol, pyrrole, and methylcyclopentadienes to
afford half-sandwich osmium(II) hydride or osmium(IV) trihy-
dride derivatives, depending upon the electron richness and the
steric requeriment of the conjugated base. These observations
reveal a new general method to prepare half-sandwich osmium
complexes, including those with a heteroaromatic ligand. The
method is a consequence of the existence of transition-metal
polyhydride compounds that are Brønsted bases capable of
deprotonating weak acids. When the conjugated base of these
acids is aromatic, its coordination to the unsaturated metal center
resulting from the hydride abstraction generates a half-sandwich
complex.
’ EXPERIMENTAL SECTION
General Information. All reactions were carried out with rigorous
exclusion of air using Schlenk-tube techniques. Solvents (except n-octane,
which was dried over sodium and distilled under argon) were obtained
oxygen- and water-free from an MBraun solvent purification apparatus.
1H, 31P{1H}, and 13C{1H} NMR spectra were recorded on Bruker 300
ARX, Bruker Avance 300 MHz, Bruker Avance 400 MHz, and Bruker
Avance 500 MHz instruments. Chemical shifts (expressed in parts per
million) are referenced to residual solvent peaks (1H, 13C{1H}) or to
external 85% H3PO4 (31P{1H}). Coupling constants J and N are given in
hertz. Infrared spectra were recorded on a Perkin-Elmer Spectrum 100
spectrometer as neat solids or oils. C, H, and N analyses were carried out
in a Perkin-Elmer 2400 CHNS/O analyzer. High-resolution electro-
spray mass spectra were acquired using a MicroTOF-Q hybrid quadru-
pole time-of-flight spectrometer (Bruker Daltonics, Bremen, Germany).
OsH6(PiPr3)2,12c OsH3Cl(PiPr3)2,14b and NaOPh18c were prepared by
published methods.
Isomerization of 2 into 3 in the Presence of 6 equiv of
Phenol. In a 5 mm NMR tube 2 (20 mg, 0.03 mmol) and phenol
(18.8 mg, 0.19 mmol) were dissolved in 0.4 mL of toluene, and the
sample was monitored by 31P{1H} NMR periodically. After 48 h at room
temperature the 31P{1H} NMR spectrum showed a 10:90 mixture
of 2 and 3.
Reaction of OsH6(PiPr3)2 with 6 equiv of PhOH: Prepara-
tion of OsH(η5-PhO)(PiPr3)2 5(PhOH) (4). A colorless solution of
3
1 (100 mg, 0.19 mmol) in 15 mL of toluene was treated with 6 equiv of
phenol (108 mg, 1.14 mmol) and heated under reflux for 5 h. After this
time, the resulting brown solution was filtered through Celite and the
solvent was removed in vacuo to obtain a brown oil. Yield: 171 mg
(93%). HRMS (electrospray, m/z): calcd for C24H49OOsP2 [M + H]+
607.2869; found 607.2900. IR (cmÀ1): ν(OÀH) 3319 (br), ν(OsÀH)
2087 (w), ν(CdO) 1593 (s), ν(CÀO) 1227 (s). 1H NMR (300 MHz,
C6D6, 298 K): δ 8.68 (br, 5H, PhOH), 7.14À7.05 (m, 20H, o- and m-
PhOH), 6.78 (m, 5H, p-PhOH), 5.19 (d, JHÀH = 5.5, 2H, o-PhO), 5.00
(t, JHÀH = 5.5, 2H, m-PhO), 4.24 (t, JHÀH = 5.5, 1H, p-PhO), 1.80
(m, 6H, PCH(CH3)2), 0.96 (dvt, JHÀH = 7.0, N = 12.3, 18H, PCH-
(CH3)2), 0.92 (dvt, JHÀH = 7.0, N = 12.3, 18H, PCH(CH3)2), À14.20
(t, JPÀH = 33.5, 1H, OsH). 31P{1H} NMR (121.48 MHz, C6D6, 298 K):
δ 15.4 (s). 13C{1H} NMR plus HSQC (75.5 MHz, C6D6, 298 K):
δ 161.4 (s, CdO), 157.5 (s, Cipso PhOH), 129.8, 119.9, 116.1 (all s, CH
PhOH), 85.7 (s, m-C6H5O), 68.7 (s, o-C6H5O), 68.2 (s, p-C6H5O),
29.5 (vt, N = 20.2, PCH(CH3)2), 29.2 (vt, N = 19.4, PCH(CH3)2), 20.7
and 20.4 (both s, PCH(CH3)2).
Reaction of OsH6(PiPr3)2 (1) with 3 equiv of PhOH. A
colorless solution of 1 (100 mg, 0.19 mmol) in 15 mL of toluene was
treated with 3.0 equiv of phenol (54 mg, 0.57 mmol) and heated under
reflux for 5 h. The resulting brown solution was filtered through Celite,
and the solvent was removed in vacuo. 1H and 31P{1H} NMR spectra
show the presence of OsH3(OPh)(PiPr3)2 (2), OsH2(η4-2,4-cyclohex-
adien-1-one)(PiPr3)2 (3), and OsH(η5-PhO)(PiPr3)2 2(C6H5OH)
3
(4) in a ratio of 1.3:1:4.3.
Spectroscopic data for OsH2(η4-2,4-cyclohexadien-1-one)(PiPr3)2
(3): 1H NMR (300 MHz, C6D6, 298 K): δ 5.13 (dd, JHÀH = 3.8, JHÀH
=
5.1, 1H, C6H6O), 4.30 (dt, JHÀP = 4.8, JHÀH = 17.4, 1H, CH2 C6H6O),
4.14 (dd, JHÀH = 3.8, JHÀH = 4.2, 1H, C6H6O), 3.77 (d, JHÀH = 5.1, 1H,
CHCO C6H6O), 3.09 (dd, JHÀH = 3.2, JHÀH = 17.4, 1H, CH2 C6H6O),
2.76 (dd, JHÀH = 3.2, JHÀH = 4.2, 1H, dCHCH2 C6H6O), 1.77 (m, 6H,
PCH(CH3)2), 1.11 (dvt, JHÀH = 6.9, N = 13.8, PCH(CH3)2), 0.93 (dvt,
JHÀH = 6.9, N = 12.6, PCH(CH3)2), À13.40 (t, JHÀP = 30.8, 2H, OsH).
1H NMR (400 MHz, C7D8, 193 K, hydride region): δ À12.8 (br, 1H,
OsÀH), À15.7 (br, 1H, OsÀH). 31P{1H} NMR (121.4 MHz, C6D6,
298 K): δ 31.5 (s). 31P{1H} NMR (161.97 MHz, C7D8, 193 K): δ 33.6
(AB spin system, Δν = 930 Hz, JA-B = 661.0). 13C{1H} NMR plus
HSQC and HMBC (75.5 MHz, C6D6, 298 K): δ 201.2 (s, CdO
Reaction of OsH(η5-PhO)(PiPr3)2 5(PhOH) with HBF4: For-
3
mation of [OsH(η6-PhOH)(PiPr3)2]BF4 (6). A dark yellow solution
of 4 (100 mg, 0.09 mmol) in diethyl ether (10 mL) was treated with
1 equiv of HBF4 OEt2 (13 μL, 0.09 mmol) and stirred for 30 min at
3
room temperature. During the course of the reaction a white solid
appeared. The solvent was removed, and the solid was washed with
diethyl ether (3 Â 5 mL) and dried in vacuo. Yield: 95 mg (71%). Anal.
Calcd for C24H49BF4OOsP2: C, 41.62; H, 7.13. Found: C, 41.47; H,
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7.24. IR (cmÀ1): ν(OÀH) 3290 (br), ν(OsÀH) 2109 (w), ν(BF4) 1054
(vs). 1H NMR (400 MHz, CD2Cl2, 298 K): δ 8.21 (br, 1H, ÀOH), 5.59
(t, JHÀH = 5.5, 2H, m-PhOH), 5.56 (d, JHÀH = 5.5, 2H, o-PhOH), 5.49
(t, JHÀH = 5.5, 1H, p-PhOH), 2.16 (m, 6H, PCH(CH3)2), 1.28 (dvt,
JHÀH = 8.1, N = 13.1, 18H, PCH(CH3)2), 1.23 (dvt, JHÀH = 8.2, N =
13.3, 18H, PCH(CH3)2), À12.95 (t, JPÀH = 36.6, 1H, OsH). 31P{1H}
NMR (161.9 MHz, CD2Cl2, 298 K): δ 13.7 (s). 13C{1H} NMR (100.62
MHz, CD2Cl2, 298 K): δ 137.1 (s, COH), 83.4 (s, CH m-PhOH), 75.5
(s, CH p-PhOH), 67.4 (t, JCÀP = 2.2, CH o-PhOH), 29.9 (vt, N = 24.2,
PCH(CH3)2), 29.6 (vt, N = 22.9, PCH(CH3)2), 20.6 and 20.4 (both s,
PCH(CH3)2).
Calcd for C22H48BF4NOsP2: C, 39.69; H, 7.27; N, 2.10. Found: C,
39.42; H, 7.33; N, 1.72. IR (cmÀ1): ν(OsH) 2152 (w); ν(BF4)
1052À1030 (vs). 1H NMR (300 MHz, CD2Cl2, 298 K): δ 6.60
(s, 2H, C4H4N), 6.02 (s, 2H, C4H4N), 2.12 (m, 6H, PCH(CH3)2),
1.27 (dvt, JHÀH = 7.2, N = 14, 36 H, PCH(CH3)2), À14.50 (t, JPÀH
=
28.6, 2H, OsH2). 31P{1H} NMR (121.5 MHz, CD2Cl2, 298 K): δ 33.9
(s). 13C{1H} NMR (75.47 MHz, CD2Cl2, 298 K): δ 104.7 (s, C4H4N),
90.4 (s, C4H4N), 30.3 (vt, N = 30.3, PCH(CH3)2), 19.6 (s, PCH-
(CH3)2). T1(min) (ms, OsH2, 400 MHz, CD2Cl2, 223 K): 325 ( 1.
Reaction of OsH6(PiPr3)2 with Methylcyclopentadiene:
Formation of OsH(η5-C5H4Me)(PiPr3)2 (9). A solution of 1 (100
mg, 0.19 mmol) in toluene (10 mL) was treated with 6 equiv of freshly
distilled methylcyclopentadiene (198 μL, 1.14 mmol) and heated under
reflux for 2 h. During this time the solution changed from colorless to
pale yellow. The resulting solution was filtered through Celite, and the
solvent was removed in vacuo, obtaining a pale yellow oil. Yield: 83 mg
(74%). HRMS (electrospray, m/z): calcd for C24H51OsP2 [M + H]+
593.3076; found 593.3047. IR (cmÀ1): ν(OsÀH) 2069 (m). 1H NMR
(300 MHz, C6D6, 298 K): δ 4.76 (s, 2H, C5H4Me), 4.08 (s, 2H,
C5H4Me), 2.35 (s, 3H, CH3), 1.98 (m, 6H, PCH(CH3)2), 1.18 (dvt,
JHÀH = 7, N = 15, 18H, PCH(CH3)2), 1.15 (dvt, JHÀH = 7, N = 15, 18H,
PCH(CH3)2), À15.66 (t, JPÀH = 30.2, 1H, OsÀH). 31P{1H} NMR
(121.48 MHz, C6D6, 298 K): δ 28.9 (s). 13C{1H} (75.4 MHz, C6D6,
298 K): δ 90.7 (s, CMe C5H4Me), 72.4 (s, CH C5H4Me), 70.1 (m, CH
C5H4Me), 31.3 (d, JCÀP = 24.5, PCH), 20.9 and 20.8 (both s, PCH-
(CH3)2), 16.1 (s, CH3).
Reaction of [OsH(η6-C6H5OH)(PiPr3)2]BF4 with KtBuO: For-
mation of [OsH(η5-PhO)(PiPr3)2]. A solution of [OsH(η6-C6H5OH)-
(PiPr3)2]BF4 (6) (100 mg, 0.14 mmol) in THF (5 mL) was treated with
1.2 equiv of KtBuO (19.6 mg, 0.17 mmol). After stirring for 20 min at room
temperature, the resulting suspension was filtered through Celite, and the
solution was taken to dryness, affording a brown oil. Yield: 64 mg (73%). 1H
NMR (300 MHz, C6D6, 298 K): δ 5.12 (t, JHÀH = 5.9, 2H, m-PhO), 4.93
(d, JHÀH = 5.9, 2H, o-PhO), 4.09 (t, JHÀH = 5.9, 1H, p-PhO), 2.03 (m, 6H,
PCH(CH3)2), 1.04 (dvt, JHÀH = 7.0, N = 12.5, 18H, PCH(CH3)2), 0.98
(dvt, JHÀH = 7.1, N = 12.5, 18H, PCH(CH3)2), À15.13 (t, JPÀH = 33.1, 1H,
OsH). 31P{1H} NMR (121.48 MHz, C6D6, 298 K): δ 17.2 (s).
Reaction of [OsH(η6-C6H5OH)(PiPr3)2]BF4 with NaOPh:
Formation of [OsH(η5-PhO)(PiPr3)2] HOPh. A solution of [OsH-
3
(η6-C6H5OH)(PiPr3)2]BF4 (6) (100 mg, 0.14 mmol) in THF (5 mL)
was treated with 1.1 equiv of PhONa (17.8 mg, 0.15 mmol). After
stirring for 20 min at room temperature, the resulting suspension was
filtered through Celite and the solution was taken to dryness, affording a
brown oil. Yield: 73.4 mg (75%). 1H NMR (500 MHz, C6D6, 298 K): δ
7.31 (d, JHÀH = 7.5, 2H, o-PhOH), 7.19 (t, JHÀH = 7.5, 2H, m-PhOH),
6.79 (t, JHÀH = 7.5, 1H, p-PhOH), 5.11 (t, JHÀH = 5.7, 2H, m-PhO), 5.03
(d, JHÀH = 5.7, 2H, o-PhO), 4.14 (t, JHÀH = 5.7, 1H, p-PhO), 1.98 (m,
6H, PCH(CH3)2), 1.04 (dvt, JHÀH = 7.1, N = 12.5, 18H, PCH(CH3)2),
Reaction of OsH(η5-C5H4Me)(PiPr3)2 with HBF4: Formation
of [OsH2(η5-C5H4Me)(PiPr3)2]BF4 (10). A solution of 9 (112 mg,
0.19 mmol) in diethyl ether (10 mL) was treated with 1.2 equiv of
HBF4 OEt2 (32 μL, 0.23 mmol). Immediately a white solid appeared.
3
The mixture was stirred at room temperature for 15 min; the solid was
separated by decantation, washed with diethyl ether, and dried in vacuo.
Yield: 97 mg (75%). Anal. Calcd for C24H51BF4OsP2: C, 42.48; H, 7.57.
Found: C, 42.62; H, 7.79. HRMS (electrospray, m/z): calcd for
C24H51OsP2 [M]+ 593.3076, found 593.3109. IR (cmÀ1): ν(OsÀH)
2150, 2105 (m); ν(BF4) 1059À1029 (vs). 1H NMR (300 MHz,
CD2Cl2, 298 K): δ 5.35 (s, 2H, C5H4Me), 5.19 (s, 2H, C5H4Me),
0.98 (dvt, JHÀH = 7.1, N = 12.4, 18H, PCH(CH3)2), À14.82 (t, JPÀH
=
33.4, 1H, OsH). 31P{1H} NMR (121.48 MHz, C6D6, 298 K): δ 15.4 (s).
Addition of Phenol to [OsH(η5-PhO)(PiPr3)2] HOPh. In a
3
5 mm NMR tube [OsH(η5-PhO)(PiPr3)2] HOPh (20 mg, 0.03 mmol)
3
was dissolved in 0.4 mL of benzene-d6. To this solution were added
sequentially up to 10 equiv of PhOH (8.78 M in benzene-d6), and the 1H
NMR spectrum was recorded after the addition of each equivalent.
Reaction of OsH6(PiPr3)2 with Pyrrole: Formation of OsH-
(η5-C4H4N)(PiPr3)2 (7). A colorless solution of 1 (100 mg, 0.193
mmol) in toluene (10 mL) was treated with 6 equiv of pyrrole (80 μL,
1.14 mmol) and heated under reflux for 7 h. The resulting yellow
solution was taken to dryness, and the yellow residue was dissolved in
pentane (20 mL) and filtered through Celite. Slow evaporation of
pentane caused the precipitation of a beige solid, which was washed with
pentane (2 Â 2 mL) and dried in vacuo. Yield: 61.0 mg (55%). Anal.
Calcd for C22H47NOsP2: C, 45.73; H, 8.20; N, 2.42. Found: C, 45.94; H,
2.37 (s, 3H, C5H4Me), 2.10 (m, 6H, PCH(CH3)2), 1.28 (dvt, JHÀH
=
7.1, N = 13.9, PCH(CH3)2), À14.14 (t, JPÀH = 29.2, 2H, OsÀH).
31P{1H} NMR (121.48 MHz, C6D6, 298 K): δ 32.1 (s). 13C{1H} NMR
(75.4 MHz, CD2Cl2, 298 K): δ 108.2 (s, CMe C5H4Me), 85.5 (t, JPÀC
=
1.8, CH C5H4Me), 77.0 (s, CH C5H4Me), 30.7 (vt, N = 31.7, PCH-
(CH3)2), 30.33 (vt, N = 30.9, PCH(CH3)2), 19.7 (s, PCH(CH3)2), 14.3
(s, C5H4Me). T1 (ms, 300 MHz, CD2Cl2, OsH2): 662 ( 1 (253 K),
609 ( 1 (243 K), 526 ( 1 (233 K), 440 ( 1 (223 K), 370 ( 1 (213 K),
297 ( 1 (203 K), 246 ( 1 (193 K), 221 ( 1 (183 K).
Reaction of OsH6(PiPr3)2 with Tetramethylcyclopenta-
diene in Toluene: Formation of OsH3(η5-C5HMe4)(PiPr3)
(11), OsH2(m-tolyl)(η5-C5HMe4)(PiPr3) (12), and OsH2-
(p-tolyl)(η5-C5HMe4)(PiPr3) (13). A solution of 1 (100 mg, 0.19
mmol) in 10 mL of toluene was treated with 6 equiv of tetramethyl-
cyclopentadiene (206 μL, 1.14 mmol) and heated under reflux for 5 h.
During this time the solution changed from colorless to pale yellow.
The resulting solution was filtered through Celite, and the solvent
1
7.52; N, 2.22. IR (cmÀ1): ν(OsH) 2077 (m). H NMR (300 MHz,
C6D6, 298 K): δ 5.88 (s, 2H, C4H4N), 4.85 (s, 2H, C4H4N), 1.93 (m,
6H, PCH(CH3)2), 1.16 (dd, JHÀH = 7.2, JPÀH = 15.8, 18H, PCH-
(CH3)2), 1.12 (dd, JHÀH = 7.2, JPÀH = 15.8, 18H, PCH(CH3)2), À18.88
(t, JPÀH = 29.8, 1H, OsH). 31P{1H} NMR (121.5 MHz, C6D6, 298 K): δ
1
was removed in vacuo, obtaining a pale yellow oil. H and 31P{1H}
27.7 (s). 13C{1H} NMR (75.47 MHz, C6D6, 298 K): δ 98.7 (t, JPÀC
=
1.5, C4H4N), 72.5 (t, JPÀC = 2.6, C4H4N), 30.6 (d, JPÀC = 25.3,
PCH(CH3)2), 20.8, 20.5 (both s, PCH(CH3)2).
NMR spectra recorded in C6D6 show a mixture of OsH3(η5-C5HMe4)-
(PiPr3) (11), OsH2(m-tolyl)(η5-C5HMe4)(PiPr3) (12), and OsH2-
(p-tolyl)(η5-C5HMe4)(PiPr3) (13) in a ratio of 56:14:30.
Reaction of OsH(η5-C4H4N)(PiPr3)2 with HBF4: Formation
of [OsH2(η5-C4H4N)(PiPr3)2]BF4 (8). A colorless solution of 7
(100 mg, 0.173 mmol) in diethyl ether (10 mL) was treated with 1
Spectroscopic data for OsH2(m-tolyl)(η5-C5HMe4)(PiPr3) (12): 1H
NMR (300 MHz, C6D6, 298 K): δ 7.78 (s, 1H, m-tolyl), 7.71 (d, JHÀH
=
equiv of HBF4 OEt2 (23.5 μL, 0.173 mmol) and stirred for 30 min at
7.5, 1H, m-tolyl), 6.93 (t, JHÀH = 7.5, 1H, m-tolyl), 6.85 (d, JHÀH = 7.5,
1H, m-tolyl), 4.49 (s, 1H, C5HMe4), 2.34 (s, 3H, CH3 m-tolyl), 1.88 (s,
6H, C5HMe4), 1.72 (s, 6H, C5HMe4), 1.81 (m, 3H, PCH(CH3)2), 1.06
(dd, JHÀP = 13.8, JHÀH = 7.3, 18H, PCH(CH3)2), À12.69 (d, JHÀP = 37,
3
room temperature. During the course of the reaction a white solid
formed. The solvent was removed, and the solid was washed with further
portions of diethyl ether and dried in vacuo. Yield: 95.6 mg (83%). Anal.
3850
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Organometallics
ARTICLE
2H, OsÀH). 31P{1H} NMR (121.48 MHz, C6D6, 298 K): δ 42.4 (s).
13C{1H} NMR (75.4 MHz, C6D6, 298 K): δ 164.1 (s, Cipso m-tolyl),
151.1 (s, Cortho m-tolyl), 147.5 (s, Cortho m-tolyl), 128.3 (s, Cpara m-
were solved by the Patterson (Os atom of 2 and 7) method and
conventional Fourier techniques and refined by full-matrix least-squares
on F2 with SHELXL97.29 Anisotropic parameters were used in the last
cycles of refinement for all non-hydrogen atoms. The hydrogen atoms
were observed or calculated and refined freely or using a restricted riding
model. Hydride ligands were observed in the difference Fourier maps
but refined with a restrained OsÀH bond length (1.59(1) Å, CSD). For
all structures the highest electronic residuals were observed in close
proximity of the Os centers and make no chemical sense.
Crystal data for 2: C24H50OOsP2, MW 606.78, brown, prism (0.10 Â
0.04 Â 0.02), monoclinic, space group P2(1)/c, a: 8.965(3) Å, b:
40.469(11) Å, c: 8.409(2) Å, R: 90.00°, β: 115.301(4)°, γ: 90.00o,
V = 2758.2(13) Å3, Z = 4, Dcalc: 1.461 g cmÀ3, F(000): 1232, T = 120(2)
K, μ 4.751 mmÀ1; 33 823 measured reflections (2θ: 2À58°, ω scans
0.3°), 6738 unique (Rint = 0.0894); minimum/maximum transmission
factors 0.631/0.829. Final agreement factors were R1 = 0.0356 (3968
observed reflections, I > 2σ(I)) and wR2 = 0.0482; data/restraints/
parameters 6738/4/275; GoF = 0.675. Largest peak and hole 0.880
and À1.445 e/Å3.
tolyl), 127.2 (s, Cmeta m-tolyl), 119.9 (s, Cmeta m-tolyl), 94.8 (d, JPÀC
=
4.4, CMe C5HMe4), 91.1 (d, JPÀC = 0.7, CMe C5HMe4), 77.4 (s, CH
C5HMe4), 29.1 (d, JCÀP = 30.6, PCH(CH3)2), 23.4 (s, CH3, m-tolyl),
19.6 (s, PCH(CH3)2), 13.0 and 10.2 (both s, C5HMe4).
Spectroscopic data for OsH2(p-tolyl)(η5-C5HMe4)(PiPr3) (13): 1H
NMR (300 MHz, C6D6, 298 K): δ 7.79 (d, JHÀH = 7.2, 2H, p-tolyl), 6.77
(d, JHÀH = 7.2, 2H, p-tolyl), 4.51 (s, 1H, C5HMe4), 2.35 (s, 3H, CH3
p-tolyl), 1.88 (s, 6H, C5HMe4), 1.72 (s, 6H, C5HMe4), 1.81 (m, 3H,
PCH(CH3)2), 1.11 (dd, JHÀP = 13.2, JHÀH = 7.1, 18H, PCH(CH3)2),
À12.65 (d, JHÀP = 37, 2H, OsÀH). 31P{1H} NMR (121.48 MHz, C6D6,
298 K): δ 42.3 (s). 13C{1H} NMR (75.4 MHz, C6D6, 298 K): δ 157.8
(s, Cipso p-tolyl), 150.0 (s, Corto p-tolyl), 121.4 (s, Cmeta p-tolyl), 119.6 (s,
Cpara p-tolyl), 94.9 (d, JPÀC = 4.5, CMe C5HMe4), 91.1 (d, JPÀC = 0.7,
CMe C5HMe4), 77.4 (s, CH C5HMe4), 29.1 (d, JCÀP = 30.6, PCH-
(CH3)2), 23.1 (s, CH3, m-tolyl), 19.6 (s, PCH(CH3)2), 13.0 and 10.2
(both s, C5HMe4)
Reaction of OsH6(PiPr3)2 with Tetramethylcyclopenta-
diene in n-Octane: Formation of OsH3(η5-C5HMe4)(PiPr3)
(11). A solution of 1 (100 mg, 0.19 mmol) in 10 mL of n-octane was
treated with 6 equiv of tetramethylcyclopentadiene (206 μL, 1.14
mmol) and heated under reflux for 4 h. During this time the solution
changed from colorless to pale yellow. The resulting solution was filtered
through Celite, and the solvent was removed in vacuo, resulting in a pale
yellow oil. Yield: 78 mg (85%). HRMS (electrospray, m/z): calcd for
C18H34OsP [M À 3H]+ 473.2008; found 473.2070. IR (cmÀ1):
Crystal data for 7: C22H47NOsP2, MW 577.75, colorless, prism
(0.08 Â 0.08 Â 0.06), monoclinic, space group P2(1)/c, a: 12.589(4) Å,
b: 11.559(4) Å, c: 16.492(6) Å, R: 90.00°, β: 96.380(6)°, γ: 90.00o,
V = 2385.1(14) Å3, Z = 4, Dcalc: 1.609 g cmÀ3, F(000): 1168, T = 120(2) K,
μ 5.488 mmÀ1; 28 346 measured reflections (2θ: 3À58°, ω scans
0.3°), 5974 unique (Rint = 0.0628); minimum/maximum transmission
factors 0.565/0.688. Final agreement factors were R1 = 0.0500 (5094
observed reflections, I > 2σ(I)) and wR2 = 0.1067; data/restraints/
parameters 5974/1/266; GoF = 1.133. Largest peak and hole 7.519
and À2.453 e/Å3
1
ν(OsÀH) 2075 (m). H NMR (300 MHz, C6D6, 298 K): δ 4.80 (s,
1H, C5HMe4), 2.14 (s, 6H, C5HMe4), 2.10 (s, 6H, C5HMe4), 1.71 (m,
3H, PCH(CH3)2), 1.01 (dd, JHÀH = 6.9, JHÀP = 13.1, 18H, PCH-
(CH3)2), À14.06 (br, 1H, OsÀHtrans to P), À14.85 (d, JHÀP = 32.6, 2H,
OsÀHcis to P). 1H{31P} NMR (300 MHz, C7D8, 183 K, hydride region):
δ À14.01 (br, 1H, OsH), À14.85 (br, 1H, OsH), À14.87 (br, 1H, OsH).
31P{1H} NMR (121.48 MHz, C6D6, 298 K): δ 50.5 (s). 13C{1H} NMR
(75.4 MHz, C6D6, 298 K): δ 92.4 (d, JPÀC = 4, CMe C5HMe4), 90.7 (d,
JPÀC = 1, CMe C5HMe4), 77.8 (s, CH C5HMe4), 29.3 (d, JCÀP = 29.4,
PCH(CH3)2), 20.4 (s, PCH(CH3)2), 14.2 and 12.7 (both s, C5HMe4).
T1(min) (ms, 300 MHz, tol-d8): 203 ( 1 (193 K).
’ ASSOCIATED CONTENT
S
Supporting Information. CIF files giving positional and
b
displacement parameters, crystallographic data, and bond
lengths and angles of compounds 2 and 7. This material is
available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Reaction of OsH6(PiPr3)2 with Pentamethylcyclopenta-
diene: Formation of OsH3(η5-C5Me5)(PiPr3) (14). A colorless
solution of 1 (100 mg, 0.19 mmol) in toluene (10 mL) was treated with
6 equiv of pentamethylcyclopentadiene (181 μL, 1.16 mmol) and heated
under reflux during 24 h. The resulting dark yellow solution was filtered
through Celite, and the solvent was removed in vacuo, producing a pale
yellow oil. Yield: 75 mg (80%). HRMS (electrospray, m/z): calcd for
C19H36OsP [M À 3H] 487.2164; found 487.2225. IR (cmÀ1): ν(OH)
2085 (m). 1H NMR (300 MHz, C6D6, 298 K): δ 2.11 (s, 15H, C5Me5),
1.70 (m, 3H, PCH(CH3)2), 1.01 (dd, JHÀH = 7.0, JPÀH = 13, 18H,
PCH(CH3)2), À14.47 (br, 1H, OsÀHtrans to P), À14.82 (d, JHÀP = 33.3,
2H, OsÀHcis to P). 31P{1H} NMR (121.48 MHz, C6D6, 298 K): δ 47.3
Corresponding Author
*E-mail: maester@unizar.es.
’ ACKNOWLEDGMENT
Financial support from the MICINN of Spain (Projects
CTQ2008-00810 and Consolider Ingenio 2010 CSD2007-
00006), the Departamento de Ciencia, Tecnología y Universidad
del Gobierno de Aragꢀon (E35), and the European Social Fund is
acknowledged.
(s). 13C{1H} NMR (75 MHz, C6D6, 298 K): δ 90.6 (d, JCÀP
=
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dx.doi.org/10.1021/om200371r |Organometallics 2011, 30, 3844–3852