Boryl-dihydrideborate osmium complexes: Preparation, structure, and dynamic behavior in solution

Article abstract of DOI:10.1021/om501309g

The metal fragment Os(CO)(PⁱPr₃)₂ stabilizes boryl-dihydrideborate species, which can be viewed as snapshots of states of B-H oxidative addition of a R₂BH molecule and frustrated B-H bond activation of a second one. Complex OsH₂(η²-CH₂=CHEt)(CO)(PⁱPr₃)₂ (2) shows a tendency to dissociate the olefin. The resulting dihydride OsH₂(CO)(PⁱPr₃)₂ (3) rapidly coordinates catecholborane (HBcat) and pinacolborane (HBpin) to give the corresponding σ-borane derivatives OsH₂(η²-HBR₂)(CO)(PⁱPr₃)₂ (BR₂ = Bcat (4), Bpin (5)). Complex 4 reacts with a second molecule of HBcat to release H₂ and to afford the octahedral boryl dihydride borate derivative Os(Bcat)(κ²-H₂Bcat)(CO)(PⁱPr₃)₂ (6), which undergoes a thermally activated Bcat site exchange process in solution. Borane displaces catecholborane from the dihydride-borate of 6 to generate the boryl-tetrahydrideborate Os(Bcat)(κ²-H₂BH₂)(CO)(PⁱPr₃)₂ (7). This compound and the Bpin counterpart Os(Bpin)(κ²-H₂BH₂)(CO)(PⁱPr₃)₂ (8) have also been prepared by reaction of the corresponding Os(BR₂)Cl(CO)(PⁱPr₃)₂ with Na[BH₄].

Full text of DOI:10.1021/om501309g

Article
pubs.acs.org/Organometallics
Boryl-Dihydrideborate Osmium Complexes: Preparation, Structure,
and Dynamic Behavior in Solution
Miguel A. Esteruelas,* Ana M. Lopez, Malka Mora, and Enrique Onate
́
̃
́ ́ ́ ́
Departamento de Química Inorganica, Instituto de Síntesis Química y Catalisis Homogenea (ISQCH), Centro de Innovacion en
Química Avanzada (ORFEO-CINQA), Universidad de Zaragoza-CSIC, 50009 Zaragoza, Spain
S
* Supporting Information
ABSTRACT: The metal fragment Os(CO)(PiPr3)2 stabilizes
boryl-dihydrideborate species, which can be viewed as
snapshots of states of B−H oxidative addition of a R2BH
molecule and frustrated B−H bond activation of a second one.
Complex OsH2(η2-CH2CHEt)(CO)(PiPr3)2 (2) shows a
tendency to dissociate the olefin. The resulting dihydride
OsH2(CO)(PiPr3)2 (3) rapidly coordinates catecholborane (HBcat) and pinacolborane (HBpin) to give the corresponding σ-
borane derivatives OsH2(η2-HBR2)(CO)(PiPr3)2 (BR2 = Bcat (4), Bpin (5)). Complex 4 reacts with a second molecule of HBcat
to release H2 and to afford the octahedral boryl dihydride borate derivative Os(Bcat)(κ2-H2Bcat)(CO)(PiPr3)2 (6), which
undergoes a thermally activated Bcat site exchange process in solution. Borane displaces catecholborane from the dihydride-
borate of 6 to generate the boryl-tetrahydrideborate Os(Bcat)(κ2-H2BH2)(CO)(PiPr3)2 (7). This compound and the Bpin
counterpart Os(Bpin)(κ2-H2BH2)(CO)(PiPr3)2 (8) have also been prepared by reaction of the corresponding Os(BR2)Cl-
(CO)(PiPr3)2 with Na[BH4].
Scheme 1. Possible Compounds with Two R2BH Units in
the Metal Coordination Sphere
INTRODUCTION
■
The activation of B−H bonds is a reaction of great interest in
connection with relevant catalytic processes including the
hydroboration of unsaturated organic molecules,1 the dehydro-
genative borylation of hydrocarbons,2 and the dehydrocoupling
of Lewis adducts, mainly ammonia-borane.3 It is well
established that the first step for the cleavage of the B−H
bond is its coordination to an unsaturated transition metal to
form M(η2-H−BR2) σ-complexes, from which a limited
number have been isolated and characterized.4 These
intermediates can evolve by oxidative addition,5 heterolytic
cleavage,6 or σ-bond metathesis7 depending upon the nature of
the metal center and the coligands of the complex.
The simultaneous or sequential activation of the B−H bond
of two R2BH molecules shows high complexity. This is in part
due to the number and variety of possible reactions between
the B−H units and the ligands of the precusors.8 On the other
hand, it has been proposed9 that the release of labile and inert
groups from the metal coordination sphere allows the
formation of six different types of compounds (Scheme 1):
di(σ-borane) (I), dihydride-diboryl (II), boryl-dihydrideborate
(III), hydride-boryl-σ-borane (IV), diboryl-dihydrogen (V),
and dihydride-diborane (VI). However, only di(σ-borane)10
and dihydride-diboryl9,11 species have been previously isolated
and characterized. In this paper, we report the first compounds
of the boryl-dihydrideborate type. They are formed via a σ-
borane intermediate.
OsH2(η2-CH2CHEt)(CO)(PiPr3)2 (2), as a consequence
of the substitution of the chloride ligand by a butyl group and a
subsequent β-hydrogen elimination reaction at the alkyl unit.13
This compound shows a tendency to dissociate the olefin, at
room temperature, and the resulting unsaturated dihydride
OsH2(CO)(PiPr3)2 (3) has been shown to promote the release
of 1 equiv of molecular hydrogen from ammonia-borane and
RESULTS AND DISCUSSION
■
12
The five-coordinate complex OsHCl(CO)(PiPr3)2 (1) reacts
Received: December 19, 2014
with nBuLi to afford the dihydride-1-butene derivative
© XXXX American Chemical Society
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the formation of polyaminoborane via a Shimoi-type
intermediate.14 In accordance with this precedent, we have
now discovered that the addition of 1.0 equiv of catecholborane
(HBcat) and pinacolborane (HBpin) to pentane solutions of 2
gives rise to the coordination of the B−H bond of the boranes
to 3 to form the σ-borane derivatives OsH2(η2-HBR2)(CO)-
(PiPr3)2 (BR2 = Bcat (4), Bpin (5)), which are isolated as
yellow (4) and white (5) solids in high yield (70% (4), 75%
(5)), according to eq 1. These compounds are diagonal
observed. The presence of a coordinated HBcat group in 4 is
also supported by the 11B NMR spectrum, which shows a broad
signal at 38 ppm. The 31P{1H} NMR spectrum contains a
singlet at 39 ppm, in accordance with equivalent phosphines.
The exchange processes can be rationalized according to
Scheme 2. The hydride−hydride site exchange could take place
via dihydrogen species, whereas the hydride−BH site exchange
should proceed through trihydride-boryl intermediates related
to the trihydride-silyl counterparts, previously mentioned,
hydride-boryl-dihydrogen derivatives, and hydride-dihydride-
borate species.20
The M(η2-H−BR2) interaction involves σ-donation from the
σ-orbital of the coordinated B−H bond to empty orbitals of the
metal and back-bonding from the metal into the boron pz-
orbital, which competes with oxygen π-donation from the
boron substituents, for 4 and 5. The decrease of the oxygen π-
donation strengthens the metal back-bonding and therefore
increases the stability of the σ-complex. In contrast to
pinacolborane, the catecholate oxygens have the possibility of
delocalizing electron density into the aromatic system. As a
result the catecholborane complex 4 is more stable than the
pinacolborane derivative 5. Thus, at 243 K, the addition of 1.2
equiv of HBcat to pentane solutions of 5 leads after 7 days to
the equilibrium shown in eq 2 with an equilibrium constant K
of 16, determined by 31P{1H} NMR spectroscopy (Figure S1).
counterparts of the trihydride-silyl derivatives OsH3(SiR3)-
(CO)(PiPr3)2 (SiR3 = SiHPh2, SiPh3, Si(OMe)2Ph),15 which
were obtained from the hydride-tetrahydrideborate complex
16
OsH(κ2-H2BH2)(CO)(PiPr3)2 by replacement of the BH3
moiety by the corresponding HSiR3 silane and a subsequent
oxidative addition of the Si−H bond.
Complex 5 has been previously generated in situ from the
borylthiolate-dihydrogen complex OsH(SBpin)(η2-H2)(CO)-
(PiPr3)2 by means of a borylthiol−pinacolborane exchange and
characterized by NMR spectroscopy.17 The 1H, 11B, and
31P{1H} NMR spectra of 4, in toluene-d8, are consistent with
those of 5. The hydrogen atoms bonded to the metal center
undergo two thermally activated site exchange processes,
involving the hydride positions and those with the B−H site.
1
Figure 1 shows the H{11B} NMR spectrum, in the high-field
Complex 4, in contrast to 5, reacts with a second molecule of
HBcat, at room temperature. Treatment of pentane solutions of
4 with 1.2 equiv of the boron hydride for 3 h affords molecular
hydrogen and the novel boryl-dihydrideborate complex Os-
(Bcat)(κ2-H2Bcat)(CO)(PiPr3)2 (6), which was isolated as a
white solid in almost quantitative yield. The reaction is
reversible at room temperature, and under 1.2 atm of H2, the
benzene-d6 solutions of 6 regenerate 4 and HBcat (eq 3).
Figure 1. High-field region of the 1H{11B} NMR spectrum (300 MHz,
toluene-d8) of 4 as a function of temperature.
Complex 6 was characterized by X-ray diffraction analysis.
The structure (Figure 2) proves the boryl-dihydrideborate
nature of the compound. The coordination geometry around
the osmium atom can be described as a distorted octahedron,
with trans phosphines (P1−Os−P2 = 173.239(19)°). The
perpendicular plane is formed by the chelate dihydrideborate
ligand, which acts with a H01−Os−H02 bite angle of
68.4(11)°, and the boryl and carbonyl groups. The separation
between the metal center and the borate boron atom of
2.244(3) Å is in keeping with other crystallographically
characterized osmium-hydrideborate complexes.21 According
to an sp3-hybridization at the borate boron atom, the angles
around B1 are between 104.5(16)° and 113.4(10)°. The
osmium-boryl bond length of 2.076(3) Å (Os−B2) compares
well with those reported for other osmium-boryl derivatives.22
region, as a function of the temperature. In agreement with 5
and the dihydride-iridium complex IrH2(tBuPOCOP)(η2-H−
Bpin) (tBuPOCOP = κ3-C6H3-1,3-[OP(tBu)2]2),18 the hy-
dride−hydride site exchange needs an activation energy
significantly lower than the hydride−BH site exchange. Thus,
1
the H{11B} NMR spectrum, at 183 K, shows two high-field
resonances at −8.5 and −10.1 ppm, in a 1:2 intensity ratio,
corresponding to the BH-hydrogen atom and the hydride
ligands, respectively. As expected for the classical nature of the
hydride ligands, a 300 MHz T1(min) value of 167 ms was found
at 213 K for the highest field signal, in spite of the presence of
the boron atom.19 At about 253 K, the coalescence between the
hydride and BH resonances occurs, and at temperatures higher
than 253 K, only one resonance centered at −9.7 ppm is
B
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Scheme 2. Exchange Processes in 4
Scheme 3. Bcat Position Exchange in 6
Figure 2. Molecular diagram of 6 with 50% probability ellipsoids. The
labels of the carbon atoms of the phosphine and Bcat groups are
omitted for clarity. Selected bond lengths (Å) and angles (deg): Os−
B2 2.076(3), Os−H01 1.84(2), Os−H02 1.72(3), B1−H01 1.26(2),
B1−H02 1.27(2); P1−Os−P2 173.239(19), H01−Os−H02 68.4(11),
H01−B1−H02 104.5(16), H01−B1−O1 113.1(10), H01−B1−O2
112.1(9), H02−B1−O1 106.8(10), H02−B1−O2 113.4(10), O4−
B2−Os 129.07(19), O5−B2−Os 123.43(18).
quantitative generation of the boryl-tetrahydrideborate deriva-
tive Os(Bcat)(κ2-H2BH2)(CO)(PiPr3)2 (7), which was isolated
as a white solid in 99% yield (eq 3). This compound can be also
prepared in an isolated yield of 63%, by means of the
replacement of the chloride ligand of the five-coordinate boryl
8c
complex Os(Bcat)Cl(CO)(PiPr3)2 with a tetrahydride-borate
anion (eq 4). Similarly, treatment of tetrahydrofuran solutions
The O4−B2−Os and O5−B2−Os angles of 129.07(19)° and
123.43(18)°, respectively, support the sp2-hybridization at B2.
The Bcat groups of 6 exchange their position, in solution, at
room temperature. Thus, the 11B NMR spectrum in toluene-d8
shows only a broad resonance centered at 38 ppm, whereas, in
the 1H NMR spectrum, the inequivalent OsHB-hydrogen
atoms display only one resonance, at −6.9 ppm. At 183 K, both
resonances split into two signals, which appear at 47 (OsBcat)
and 29 (Os(κ2-H2Bcat)) and −6.2 and −7.5 ppm, respectively.
The fluxional process could take place via hydride-boryl-σ-
borane intermediates in equilibrium with di(σ-borane) and
dihydride-diboryl species, according to Scheme 3. In agreement
with equivalent phosphines, the 31P{1H} NMR spectrum
contains a singlet at 23.7 ppm.
22j
of Os(Bpin)Cl(CO)(PiPr3)2 with 2.0 equiv of Na[BH4], for
50 min, at room temperature affords the pinacolboryl
counterpart Os(Bpin)(κ2-H2BH2)(CO)(PiPr3)2 (8) along
with about 23% of the hydride OsH(κ2-H2BH2)(CO)-
(PiPr3)2.16 After recrystallization in pentane at 243 K, complex
8 was obtained as pure yellow crystals in 18% yield.
Borane displaces catecholborane from the dihydrideborate of
6, in agreement with the niobium complex Nb(η5-C5Me5)(κ2-
H2Bcat′) (cat′ = O2C6H3-4-tBu)23 and as expected for the
transitory formation of a more stable M(η2-H−BH2)
intermediate. Thus, the addition of 1.0 equiv of BH3·THF to
pentane solutions of 6 gives rise to the instantaneous and
Complex 7 was also characterized by X-ray diffraction
analysis. The structure has two molecules that are chemically
equivalent but crystallographically independent in the asym-
metric unit. Figure 3 shows a view of one of them. The
coordination polyhedron around the osmium atom is like that
of 6 with the tetrahydrideborate ligand occupying the position
C
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dried by the usual procedures and distilled under argon prior to use or
obtained oxygen- and water-free from an MBraun solvent purification
apparatus. Pentane was stored over P2O5 in the drybox. Pinacolborane
(HBpin = 4,4,5,5-tetramethyl-1,3,2-dioxaborolane) was purchased
from commercial sources and used without further purification.
Catecholborane (HBcat = 1,3,2-benzodioxaborolane) was purchased
from commercial sources and distilled in a Kugelrohr distillation oven.
The starting materials OsH2(η2-CH2CHEt)(CO)(PiPr3)2 (1),13
Os(Bcat)Cl(CO)(PiPr3)2,8c and Os(Bpin)Cl(CO)(PiPr3)2,22j were
prepared according to published methods. NMR spectra were
recorded on a Varian Gemini 2000, a Bruker ARX 300, a Bruker
Avance 300 MHz, or a Bruker Avance 400 MHz instrument. Chemical
shifts (expressed in parts per million) are referenced to residual solvent
peaks (1H, 13C{1H}), external H3PO4 (31P{1H}), or BF3·OEt2 (11B).
́
Coupling constants, J and N (N = JH−P + JH−P or JC−P + JC−P′), are
given in hertz. Infrared spectra were recorded on a PerkinElmer
Spectrum One spectrometer (ATR). C and H analyses were carried
out in a PerkinElmer 2400 CHNS/O analyzer.
Figure 3. Molecular diagram of 7 with 50% probability ellipsoids. The
labels of the carbon atoms of the phosphine and Bcat ligands are
omitted for clarity. Selected bond lengths (Å) and angles (deg): Os−
B1 2.067(6), 2.045(6); Os−H2a 1.75(6), 1.86(8); Os−H2b 1.83(6),
1.59(8); B2−H2a 1.20(4), 1.301(10); B2−H2b 1.27(4), 1.296(10);
B2−H2c 1.10(5), 1.05(6); B2−H 2d 1.12(5), 1.04(6); P1−Os−P2
176.45(5), 171.57(5); H2a−Os−H2b 64(2), 67.1(10).
Preparation of OsH2(η2-H−Bcat)(CO)(PiPr3)2 (4). Catecholbor-
ane (18.5 μL, 0.174 mmol) was added to a colorless solution of 1 (100
mg, 0.174 mmol) in 3 mL of pentane. The suspension was stirred at
room temperature for 5 min. After that, the suspension was filtered
through Celite. The filtrate was concentrated to dryness to give a
yellow solid. Yield: 80 mg (70%). Anal. Calcd for C25H49BO3OsP2: C,
45.45; H, 7.48. Found: C, 45.48; H, 7.69. IR (ATR, cm−1): ν(CO)
of the dihydridecatecholborate group and P1−Os−P2 and
H2a−Os−H2b angles of 176.45(5)° and 171.57(5)° and
64(2)° and 67.1(10)°, respectively. The osmium-boryl bond
lengths, Os−B1, of 2.067(6) and 2.045(6) Å are almost
statistically identical to that 6, whereas the separations between
the metal center and the tetrahydrideborate boron atom B2 of
2.313(7) and 2.304(9) Å are between 0.04 and 0.02 Å longer
than the separation between the metal center and the
dihydridecatecholborate boron atom of 6. The angles around
B1 and B2 support the respective sp2- and sp3-hybridizations at
these atoms (see Supporting Information) and therefore the
boryl and borate nature of the corresponding ligands.
1
1938 (s). H{11B} NMR (300 MHz, C7D8, 298 K): δ 6.88 (m, 2H,
Bcat), 6.72 (m, 2H, Bcat), 2.26 (m, 6H, PCHCH3), 1.21 (dvt, N =
14.0, JH−H = 7.0, 18H, PCHCH3), 1.16 (dvt, N = 13.8, JH−H = 7.0,
1
18H, PCHCH3), −9.7 (br, 3H, BH and OsH). H{11B} NMR (300
MHz, C7D8, 193 K): δ −8.5 (br, 1H, BH), −10.1 (br, 2H, OsH).
31P{1H} NMR (121.49 MHz, C7D8, 298 K): δ 38.7 (s). 11B NMR
(96.29 MHz, C7D8, 298 K): δ 38 (br).
Preparation of OsH2(η2-H−Bpin)(CO)(PiPr3)2 (5). Pinacolborane
(25.3 μL, 0.174 mmol) was added to a solution of 1 (100 mg, 0.174
mmol) in 3 mL of pentane. The suspension was stirred at room
temperature for 5 min. After that, the suspension was filtered through
Celite. The filtrate was concentrated to dryness to give a white solid.
Yield: 87 mg (75%). Anal. Calcd for C25H57BO3OsP2: C, 44.90; H,
8.59. Found: C, 44.84; H, 8.55. IR (ATR, cm−1): ν(CO) 1943 (s).
1H{11B} NMR (400 MHz, C7D8, 298 K): δ 2.30 (m, 6H, PCHCH3),
1.23 (dvt, N = 14, JH−H = 7.2, 18H, PCHCH3), 1.21 (dvt, N = 14.2,
JH−H = 7.0, 18H, PCHCH3), 1.1 (s, 12H, Bpin), −9.8 (br, 1H, BH),
1
The 11B, H, and 31P{1H} NMR spectra of 7 and 8, in
toluene-d8, at room temperature are consistent with the
structure shown in Figure 3. In agreement with the presence
of boryl and borate ligands, the 11B spectra contain two broad
resonances at 43 (Bcat) and 8 (BH4) ppm for 7 and at 37
1
−10.5 (br, 2H, OsH). H{11B} NMR (400 MHz, C7D8, 283 K): δ
1
(Bpin) and 7 (BH4) ppm for 8. In the H NMR spectra, the
−9.5 (br, 1H, BH), −9.8 (br, 1H, OsH), −11.2 (dt, 1H, JH−P = 20.1,
JH−H = 5.2, OsH). 31P{1H} NMR (162 MHz, C7D8, 298 K): δ 38.0 (s).
11B NMR (128 MHz, C7D8, 298 K): δ 34 (br). NMR spectroscopic
data are identical to those previously reported by us.17
inequivalent OsHB-hydrogen atoms display resonances, in the
high-field region, at −4.6 and −6.6 ppm for 7 and at −4.7 and
−6.7 ppm for 8, whereas the equivalent terminal BH2-hydrogen
atoms give rise in the low-field region to a broad signal centered
at about 6.4 ppm for 7 and at about 6.1 ppm for 8. The 31P{1H}
NMR spectra show singlets at 27.9 (7) and 26.6 (8) ppm, as
expected for equivalent phosphines.
Reaction of 5 with 1.2 equiv of Catecholborane. Catecholbor-
ane (18.5 μL, 0.174 mmol) was added to a colorless solution of 5 (100
mg, 0.150 mmol) in 2 mL of pentane. After 7 days at 243 K, the
31P{1H} and 11B NMR spectra of this solution showed the presence of
4 and 5 in a molar ratio of 1:0.17 (Figures S1 and S2).
Preparation of Os(Bcat)(κ2-H2Bcat)(CO)(PiPr3)2 (6). Catechol-
borane (18.5 μL, 0.174 mmol) was added to a solution of 4 (100 mg,
0.151 mmol) in 1 mL of pentane. Immediately, the solution changed
from yellow to colorless. The solution was stirred at room temperature
for 3 h. During this time a white solid was formed. This solid was
separated by decantation and dried in vacuo. Yield: 114 mg (97%).
Anal. Calcd for C31H52B2O5OsP2: C, 47.82; H, 6.73. Found: C, 47.70;
H, 6.95. IR (ATR, cm−1): ν(CO) 1960 (s). 1H{11B} NMR (300 MHz,
C7D8, 298 K): δ 6.98 (m, 4H, Bcat), 6.78 (m, 4H, Bcat), 2.67 (m, 6H,
PCHCH3), 1.11 (dvt, N = 13.4, JH−H = 6.8, 36H, PCHCH3), −7.0 (br,
CONCLUDING REMARKS
■
14,24
In conclusion, the metal fragment Os(CO)(PiPr3)2
stabilizes boryl-dihydrideborate species, in contrast to Ti(η5-
C5H5)2 and M(η5-C5Me5) (M = Rh, Ir). Because boryl-
dihydrideborate complexes in reality are snapshots of states of
B−H oxidative addition of a R2BH molecule and frustrated B−
H bond activation of a second one, the compounds here
reported suggest that the nucleophilicity of the osmium unit
Os(CO)(PiPr3)2 is intermediate between those of the Ti(η5-
C5H5)2 and Rh(η5-C5Me5) metal fragments.
1
2H, BH). H{11B} NMR (300 MHz, C7D8, 183 K): δ −6.2 (br, 1H,
BH), −7.5 (br, 1H, BH). 31P{1H} NMR (121.49 MHz, C7D8, 298 K):
δ 23.7 (br). 11B NMR (96.29 MHz, C7D8, 298 K): δ 38 (br). 11B NMR
(96.29 MHz, C7D8, 183 K): δ 47 (br, OsBcat), 29 (br, Os(κ2-
H2Bcat)).
Reaction of 6 with H2. A Young NMR tube containing a solution
of 6 (15 mg, 0.019 mmol) in 0.5 mL of C6D6 was placed under a
EXPERIMENTAL SECTION
General Information. All manipulations were performed with
rigorous exclusion of air at an argon/vacuum manifold using standard
Schlenk-tube techniques or in a drybox (MB-UNILAB). Solvents were
■
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hydrogen atmosphere (1.2 atm). Immediately, the solution changed
from light yellow to colorless. The NMR spectra showed the complete
conversion of 6 to 4 along with the formation of HBcat.
101.268(2)°, V = 3460.7(7) Å3, Z = 4, Z′ = 1, Dcalc = 1.494 g cm−3,
F(000) = 1576, T = 100(2) K, μ = 3.812 mm−1; 26 959 measured
reflections (2θ: 3−58°, ω scans 0.3°), 8956 unique (Rint = 0.0279);
min/max transmn factors = 0.619/0.862. Final agreement factors were
R1 = 0.0216 (7865 observed reflections, I > 2σ(I)) and wR2 = 0.0552;
data/restraints/parameters = 8956/0/388; GoF = 1.003. Largest peak
and hole = 1.724 and −0.971 e/Å3.
Crystal data for 7: C25H50B2O3OsP2, Mw = 672.41, irregular block,
colorless (0.15 × 0.12 × 0.09), monoclinic, space group P21/c, a =
26.620(4) Å, b = 9.7721(14) Å, c = 24.328(3) Å, β = 108.669(2)°, V =
5995.6(15) Å3, Z = 8, Z′ = 2, Dcalc = 1.490 g cm−3, F(000) = 2720, T =
100(2) K, μ = 4.383 mm−1; 62 803 measured reflections (2θ: 3−51°,
ω scans 0.3°), 15 525 unique (Rint = 0.0415); min/max transmn
factors = 0.692/0.862. Final agreement factors were R1 = 0.0399
(12 285 observed reflections, I > 2σ(I)) and wR2 = 0.0890; data/
restraints/parameters = 15 525/28/616; GoF = 1.106. Largest peak
and hole = 2.482 and −2.123 e/Å3.
Preparation of Os(Bcat)(κ2-H2BH2)(CO)(PiPr3)2 (7). Method A.
BH3·THF (15.3 μL, 1.0 M, 0.015 mmol) was added to an NMR tube
containing a solution of 6 (12 mg, 0.015 mmol) in 0.5 mL of C7D8.
Immediately, the solution changed from light yellow to colorless. The
NMR spectra showed the complete conversion of 6 to 7 along with
the formation of HBcat.
Method B. NaBH4 (62 mg, 1.639 mmol) was added to a solution of
Os(Bcat)Cl(CO)(PiPr3)2 (200 mg, 0.289 mmol) in 5 mL of THF.
The suspension was stirred at room temperature for 20 min. During
this time the suspension changed from light yellow to colorless. The
solvent was removed under vacuum. Pentane (5 mL) was added, and
the resulting suspension was filtered through Celite. The filtrate was
concentrated to dryness to give a white solid. Yield: 122 mg (63%).
Method C. BH3·THF (151 μL, 1.0 M, 0.151 mmol) was added to a
yellow solution of 4 (100 mg, 0.151 mmol) in 2 mL of pentane. The
resulting colorless solution was stirred at room temperature for 5 min.
After that, the solvent was removed under vacuum to give a white
solid. Yield: 101 mg (99%). Anal. Calcd for C25H50B2O3OsP2: C,
44.65; H, 7.49. Found: C, 44.75; H, 7.55. IR (ATR, cm−1): ν(BH)
ASSOCIATED CONTENT
* Supporting Information
■
S
31P{1H} and 11B NMR spectra of the reaction of 5 with 1.2
equiv of HBcat and CIF files giving positional and displacement
parameters, crystallographic data, and bond lengths and angles
of compounds 6 and 7. This material is available free of charge
via the Internet at http://pubs.acs.org.
1
2480, 2443 (w), ν(CO) 1924 (s). H{11B} NMR (300 MHz, C7D8,
298 K): δ 7.21 (m, 2H, Bcat), 6.84 (m, 2H, Bcat), 6.44 (br, 2H, BH),
2.56 (m, 6H, PCHCH3), 1.20 (dvt, N = 14.0, JH−H = 7.1, 18H,
PCHCH3), 1.00 (dvt, N = 13.0, JH−H = 6.8, 18H, PCHCH3), −4.6 (br,
1H, BH), −6.6 (br, 1H, BH). 31P{1H} NMR (121.49 MHz, C6D6, 298
K): δ 27.9 (s). 11B NMR (96.29 MHz, C6D6, 298 K): δ 43 (br, Bcat), 8
(br, BH4).
AUTHOR INFORMATION
Corresponding Author
*E-mail: maester@unizar.es.
■
Preparation of Os(Bpin)(κ2-H2BH2)(CO)(PiPr3)2 (8). NaBH4 (97
mg, 2.564 mmol) was added to a solution of Os(Bpin)Cl(CO)(PiPr3)2
(200 mg, 0.285 mmol) in 5 mL of THF. The suspension was stirred at
room temperature for 50 min. During this time the suspension
changed from yellow to light yellow. The solvent was removed in
vacuo. Pentane (5 mL) was added, and the resulting suspension was
filtered through Celite. The filtrate was concentrated to dryness to give
a 1:0.3 mixture of complexes 8 and OsH(κ2-H2BH2)(CO)(PiPr3)216 as
a light yellow solid (123 mg). This mixture was recrystallized in 3 mL
of pentane at −30 °C to give 8 as yellow crystals. Yield: 35 mg (18%).
Anal. Calcd for C25H58B2O3OsP2: C, 44.12; H, 8.59. Found: C, 44.10;
H, 8.63. IR (ATR, cm−1): ν(BH) 2474, 2455 (w), ν(CO) 1909 (s).
1H{11B} NMR (300 MHz, C7D8, 298 K): δ 6.13 (br, 2H, BH), 2.70
(m, 6H, PCHCH3), 1.37 (dvt, N = 13.9, JH−H = 7.0, 18H, PCHCH3),
1.20 (dvt, N = 13.4, JH−H = 6.1, 18H, PCHCH3), 1.22 (s, 12H, Bpin),
−4.7 (br, 1H, BH), −6.7 (br, 1H, BH). 31P{1H} NMR (121.49 MHz,
C6D6, 298 K): δ 26.6 (s). 11B NMR (96.29 MHz, C6D6, 298 K): δ 37
(br, Bpin), 7 (br, BH4).
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Financial support from the Spanish MINECO (Projects
CTQ2011-23459 and CTQ2014-51912-REDC), the DGA
(E35), and the European Social Fund (FSE) is acknowledged.
M.M. thanks the Spanish MEC for her FPU grant.
REFERENCES
■
(1) (a) Miyaura, N. Bull. Chem. Soc. Jpn. 2008, 81, 1535−1553.
(b) Crudden, C. M.; Glasspoole, B. W.; Lata, C. J. Chem. Commun.
2009, 6704−6716. (c) Dang, L.; Lin, Z.; Marder, T. B. Chem.
Commun. 2009, 3987−3995.
(2) (a) Mkhalid, I. A. I.; Barnard, J. H.; Marder, T. B.; Murphy, J. M.;
Structural Analysis of 6 and 7. X-ray data were collected on a
Bruker Smart APEX DUO diffractometer equipped with a normal
focus, 2.4 kW sealed tube source (Mo radiation, λ = 0.710 73 Å)
operating at 50 kV and 30 (6) or 40 (7) mA. Data were collected over
the complete sphere. Each frame exposure time was 10 s (6) or 30 s
(7) covering 0.3° in ω. Data were corrected for absorption by using a
multiscan method applied with the SADABS program.25 The
structures were solved by the direct methods. Refinement of both
complexes was performed by full-matrix least-squares on F2 with
SHELXL97,26 including isotropic and subsequently anisotropic
displacement parameters (for non-hydrogen nondisordered atoms).
The hydrogen atoms attached to boron and osmium atoms were found
in the last cycles of difference Fourier and refined freely in 6. However,
they did not refine properly in 7, so a restricted model was used to
force the same geometry around the boron atom in the two
independent molecules. The other hydrogen atoms were calculated
and refined riding on bonded atoms. In addition two triisopropyl-
phosphines were observed disordered and were refined with two
moieties and complementary occupancy factors and isotropic
displacement parameters.
Hartwig, J. F. Chem. Rev. 2010, 110, 890−931. (b) Ros, A.; Fernan
́
dez,
R.; Lassaletta, J. M. Chem. Soc. Rev. 2014, 43, 3229−3243.
(3) (a) Hamilton, C. W.; Baker, R. T.; Staubitz, A.; Manners, I. Chem.
Soc. Rev. 2009, 38, 279−293. (b) Staubitz, A.; Robertson, A. P. M.;
Sloan, M. E.; Manners, I. Chem. Rev. 2010, 110, 4023−4078.
(c) Waterman, R. Chem. Soc. Rev. 2013, 42, 5629−5641. (d) John,
A. S.; Goldberg, K. I.; Heinekey, D. M. Top. Organomet. Chem. 2013,
40, 271−288.
(4) See for example: (a) Muhoro, C. N.; Hartwig, J. F. Angew. Chem.,
Int. Ed. 1997, 36, 1510−1512. (b) Schlecht, S.; Hartwig, J. F. J. Am.
Chem. Soc. 2000, 122, 9435−9443. (c) Crestani, M. G.; Munoz-
̃
́ ́
Hernandez, M.; Arevalo, A.; Acosta-Ramírez, A.; García, J. J. J. Am.
Chem. Soc. 2005, 127, 18066−18073. (d) Lin, Z. In Contemporary
Metal Boron Chemistry I Vol. 130; Marder, T. B.; Lin, Z., Eds: Springer:
́
Berlin, 2008; pp 123−148. (e) Gloaguen, Y.; Alcaraz, G.; Pecharman,
A.-F.; Clot, E.; Vendier, L.; Sabo-Etienne, S. Angew. Chem., Int. Ed.
2009, 48, 2964−2968.
(5) See for example: (a) Cook, K. S.; Incarvito, C. D.; Webster, C. E.;
Fan, Y.; Hall, M. B.; Hartwig, J. F. Angew. Chem., Int. Ed. 2004, 43,
Crystal data for 6: C31H52B2O5OsP2, Mw = 778.49, irregular block,
colorless (0.40 × 0.15 × 0.12), monoclinic, space group P21/c, a =
12.8512(15) Å, b = 16.8240(19) Å, c = 16.3209(18) Å, β =
̂
5474−5477. (b) Campian, M. V.; Harris, J. L.; Jasim, N.; Perutz, R. N.;
Marder, T. B.; Whitwood, A. C. Organometallics 2006, 25, 5093−5104.
(c) Cam
̂
pian, M. V.; Perutz, R. N.; Procacci, B.; Thatcher, R. J.;
E
DOI: 10.1021/om501309g
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Torres, O.; Whitwood, A. C. J. Am. Chem. Soc. 2012, 134, 3480−3497.
W. R.; Williamson, A.; Wright, L. J. J. Organomet. Chem. 2004, 689,
(d) Braunschweig, H.; Brenner, P.; Dewhurst, R. D.; Guethlein, F.;
1609−1616. (i) Buil, M. L.; Esteruelas, M. A.; Garces
Am. Chem. Soc. 2011, 133, 2250−2263. (j) Esteruelas, M. A.; Lop
M.; Mora, M.; Onate, E. Organometallics 2012, 31, 2965−2970.
́
, K.; Onate, E. J.
̃
́
ez, A.
Jimenez-Halla, J. O. C.; Radacki, K.; Wolf, J.; Zollner, L. Chem.Eur.
̈
J. 2012, 18, 8605−8609.
̃
(k) Buil, M. L.; Esteruelas, M. A.; Fernan
́
dez, I.; Izquierdo, S.; Onate,
̃
(6) See for example: (a) Salomon, M. A.; Braun, T.; Penner, A.
Angew. Chem., Int. Ed. 2008, 47, 8867−8871. (b) Fernandes, A. C.;
Fernandes, J. A.; Paz, F. A. A.; Romao, C. C. Dalton Trans. 2008,
E. Organometallics 2013, 32, 2744−2752.
(23) Lantero, D. R.; Ward, D. L.; Smith, M. R., III. J. Am. Chem. Soc.
1997, 119, 9699−9708.
̃
6686−6688. (c) Zhu, Y.; Chen, C.-H.; Fafard, C. M.; Foxman, B. M.;
(24) This metal fragment is the basis of relevant catalytic systems.
See: (a) Esteruelas, M. A.; Oro, L. A. Chem. Rev. 1998, 98, 577−588.
Ozerov, O. V. Inorg. Chem. 2011, 50, 7980−7987.
(7) Perutz, R. N.; Sabo-Etienne, S. Angew. Chem., Int. Ed. 2007, 46,
2578−2592.
́ ́
(b) Esteruelas, M. A.; Herrero, J.; Lopez, A. M.; Olivan, M.
Organometallics 2001, 20, 3202−3205. (c) Cobo, N.; Esteruelas, M.
A.; Gonzalez, F.; Herrero, J.; Lopez, A. M.; Lucio, P.; Olivan, M. J.
Catal. 2004, 223, 319−327. (d) Esteruelas, M. A.; García-Obregon, T.;
Herrero, J.; Olivan, M. Organometallics 2011, 30, 6402−6407.
(8) (a) Montiel-Palma, V.; Lumbierres, M.; Donnadieu, B.; Sabo-
Etienne, S.; Chaudret, B. J. Am. Chem. Soc. 2002, 124, 5624−5625.
́
́
́
́
́ ́
(b) Esteruelas, M. A.; Fernandez-Alvarez, F. J.; Lopez, A. M.; Mora,
́
M.; Onate, E. J. Am. Chem. Soc. 2010, 132, 5600−5601. (c) Esteruelas,
̃
(25) Blessing, R. H. Acta Crystallogr. 1995, A51, 33−38. SADABS:
Area-detector absorption correction; Bruker-AXS: Madison, WI, 1996.
(26) SHELXTL Package v. 6.10; Bruker-AXS: Madison, WI, 2000.
Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112−122.
́ ́
M. A.; Fernandez, I.; Lopez, A. M.; Mora, M.; Onate, E.
̃
Organometallics 2012, 31, 4646−4649.
(9) Hartwig, F. J.; Cook, K. S.; Hapke, M.; Incarvito, C. D.; Fan, Y.;
Webster, C. E.; Hall, M. B. J. Am. Chem. Soc. 2005, 127, 2538−2552.
(10) (a) Hartwig, J. F.; Muhoro, C. N.; He, X. J. Am. Chem. Soc.
1996, 118, 10936−10937. (b) Muhoro, C. N.; He, X.; Hartwig, J. F. J.
Am. Chem. Soc. 1999, 121, 5033−5046.
(11) Kawamura, K.; Hartwig, J. F. J. Am. Chem. Soc. 2001, 123,
8422−8423.
(12) (a) Esteruelas, M. A.; Werner, H. J. Organomet. Chem. 1986,
303, 221−231. (b) Esteruelas, M. A.; Oro, L. A. Adv. Organomet. Chem.
2001, 47, 1−59.
(13) Alben
L. A.; Zeier, B. Organometallics 1994, 13, 3746−3748.
(14) Esteruelas, M. A.; Lopez, A. M.; Mora, M.; Onate, E. ACS Catal.
2015, 5, 187−191.
(15) Buil, M. L.; Espinet, P.; Esteruelas, M. A.; Lahoz, F. J.; Lledos
́ ́
iz, M. J.; Buil, M. L.; Esteruelas, M. A.; Lopez, A. M.; Oro,
́
̃
́
,
A.; Martínez-Ilarduya, J. M.; Maseras, F.; Modrego, J.; Onate, E.; Oro,
̃
L. A.; Sola, E.; Valero, C. Inorg. Chem. 1996, 35, 1250−1256.
(16) Werner, H.; Esteruelas, M. A.; Meyer, U.; Wrackmeyer, B.
Chem. Ber. 1987, 120, 11−15.
́
(17) Esteruelas, M. A.; Lopez, A. M.; Mora, M.; Onate, E. Chem.
̃
Commun. 2013, 49, 7543−7545.
(18) Hebden, T. J.; Denney, M. C.; Pons, V.; Piccoli, P. M. B.;
Koetzle, T. F.; Schultz, A. J.; Kaminsky, W.; Goldberg, K. I.; Heinekey,
D. M. J. Am. Chem. Soc. 2008, 130, 10812−10820.
(19) The boron atoms have a marked influence on the relaxation of
the hydrides, decreasing the T1 values. See: Esteruelas, M. A.; Jean, Y.;
Lledos, A.; Oro, L. A.; Ruiz, N.; Volatron, F. Inorg. Chem. 1994, 33,
3609−3611.
(20) The formation of species of this type by reaction of transition-
metal hydride complexes and boranes is well known. See for example:
(a) Antinolo, A.; Carrillo-Hermosilla, F.; Fernan
́
dez-Baeza, J.; García-
̃
Yuste, S.; Otero, A.; Rodríguez, A. M.; San
E.; Gelabert, R.; Moreno, M.; Lluch, J. M.; Lledos
́
chez-Prada, J.; Villasenor,
̃
́
, A. Organometallics
2000, 19, 3654−3663. (b) Lachaize, S.; Essalah, K.; Montiel-Palma, V.;
Vendier, L.; Chaudret, B.; Barthelat, J.-C.; Sabo-Etienne, S. Organo-
metallics 2005, 24, 2935−2943. (c) Ohki, Y.; Hatanaka, T.; Tatsumi, K.
J. Am. Chem. Soc. 2008, 130, 17174−17186. (d) Hesp, K. D.; Rankin,
M. A.; McDonald, R.; Stradiotto, M. Inorg. Chem. 2008, 47, 7471−
7473.
(21) Frost, P. W.; Howard, J. A. K.; Spencer, J. L. J. Chem. Soc., Chem.
Commun. 1984, 1362−1363.
(22) See for example: (a) Irvine, G. J.; Roper, W. R.; Wright, L. J.
Organometallics 1997, 16, 2291−2296. (b) Rickard, C. E. F.; Roper, W.
R.; Williamson, A.; Wright, L. J. Organometallics 1998, 17, 4869−4874.
(c) Irvine, G. J.; Rickard, C. E. F.; Roper, W. R.; Williamson, A.;
Wright, L. J. Angew. Chem., Int. Ed. 2000, 39, 948−950. (d) Rickard, C.
E. F.; Roper, W. R.; Williamson, A.; Wright, L. J. Organometallics 2000,
19, 4344−4355. (e) Rickard, C. E. F.; Roper, W. R.; Williamson, A.;
Wright, L. J. Organometallics 2002, 21, 1714−1718. (f) Rickard, C. E.
F.; Roper, W. R.; Williamson, A.; Wright, L. J. Organometallics 2002,
21, 4862−4872. (g) Clark, G. R.; Irvine, G. J.; Roper, W. R.; Wright, L.
J. J. Organomet. Chem. 2003, 680, 81−88. (h) Rickard, C. E. F.; Roper,
F
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