trans-[Os(η2-H2)(CH3CN)(dppe)2](BF4)2
Organometallics, Vol. 15, No. 9, 1996 2277
C54H52N192OsP4, 1030; obsd 1030 (weak, M+), 989 (M+ - CH3-
CN), 987 (M+ - CH3CN, 2H). E1/2{MH+/MH} vs Fc+/Fc [0.2
Con clu sion s
The very acidic but stable η2-H2 complex trans-[Os(η2-
H2)(CH3CN)(dppe)2](BF4)2 has been synthesized and
fully characterized. Its stability and acidity (estimated
pKa ) -2) were correctly predicted by the application
of a ligand additivity model. In a comparison of the
series of complexes [Os(η2-H2)(Lz)(dppe)2](z+2)+ (Lz ) H,
CH3CN, Cl, Br), several trends in the influence of the
trans ligand on the characteristic properties of the η2-
H2 ligand are observed. The H-H distances, as deter-
mined or estimated by neutron, X-ray, or NMR methods,
increase in the order H- < CH3CN < Cl- < Br-. In
the same order there is a decrease in the observed
J (H,D) coupling values and the calculated ∆HBDE, where
∆HBDE is the amount of energy required to remove a
hydrogen atom from the M(η2-H2) unit. The H-H
distances, J (H,D), and ∆HBDE can qualitatively be
correlated with an effective spectrochemical parameter
f*(Lz) of the trans ligand that accounts for the influence
of the charge of the ligand.
While the pKa values of the complexes do increase as
the E1/2 values of the corresponding monohydride com-
plexes decrease, the relationship is not linear. In order
to explain the observed trend, the influence of the trans
ligand on the amount of H-H bonding as reflected by
∆HBDE must be taken into account. A correlation
between ∆HBDE and the parameter f*(Lz) might be
useful in this regard.
M
nBu4NPF6 in CH2Cl2; scan rate 250 mV/s] ) 584 mV. 1H
NMR (CD2Cl2, 400 MHz): -16.63 (qnt, 1H, J (H,P) ) 16.2 Hz,
OsH), 1.81 (s, 3H, CH3CN), 2.06 (m, 4H, CH2), 2.54 (m, 4H,
CH2), 6.7 (br s), 7.1-7.4 (m), (40 H, Ph). 31P{1H} NMR (CH2-
Cl2): 33.3 (s), 33.3 (d, J (P,Os) ) 195.0 Hz). IR: ν(Os-H) 2066
cm-1, ν(CN) 2267 cm-1 (w, br, Nujol mull).
tr a n s-[Os(η2-H2)(CH3CN)(d p p e)2](BF 4)2 (3). [Os(H)(CH3-
CN)(dppe)2]BF4 (0.200 g, 0.179 mmol) was dissolved in 5 mL
of CH2Cl2 to give a clear colorless solution. HBF4‚Et2O (85%
in Et2O) (50 µL, 0.239 mmol) was added causing the transient
appearance of a red color. Addition of 15 mL of Et2O to the
clear, light pink to colorless solution resulted in the formation
of a white precipitate. Isolated yield: 0.175 g, 0.142 mmol,
80% (washing even with small amounts of dry Et2O leads to
partial deprotonation of the product). 1H NMR (CD2Cl2, 400
MHz): -9.85 (br, 2H, Os(η2-H2)), +1.7 (s, 3H, CH3CN), 2.4 (m,
4H, CH2), 3.0 (m, 4H, CH2), 6.5 (m, br), 7.1-7.8 (m) (40 H,
Ph). T1(min) (400 MHz, CD2Cl2): 28 ms at 253 K. 31P{1H}
NMR (CH2Cl2): 27.68 (s), 27.68 (d, J (P,Os) ) 161.6 Hz). The
IR spectrum of 3 could not be obtained due to its limited
solubility in suitable solvents and extreme sensitivity to
moisture.
Obser vation of tr a n s-[Os(η2-HD)(CH3CN)(dppe)2](BF4)2.
D2 gas was bubbled into a solution of trans-[Os(η2-H2)(CH3-
CN)(dppe)2](BF4)2 and excess HBF4‚Et2O in CD2Cl2. The
solution was transferred into an NMR tube fitted with a Teflon
screw top, and the tube was sealed under an atmosphere of
D2(g). After 72 h partial incorporation of deuterium into the
dihydrogen ligand had occurred. The η2-HD complex was
observed by nulling out the signal of the η2-H2 complex with
an inversion recovery pulse sequence using its known T1 value
at room temperature. J (H,D) ) 21.4 Hz, and J (H,P) ) 5 Hz.
X-r a y Cr ysta l Str u ctu r e Deter m in a tion s of tr a n s-[Os-
(H )(CH 3CN)(d p p e)2]BF 4 (2), tr a n s-[Os(η2-H 2)(CH 3CN)-
(d p p e)2](BF 4)2‚CH2Cl2 (3a ), a n d tr a n s-[Os(η2-H2)(CH3CN)-
(d p p e)2](BF 4)2‚H BF 4‚CH 2Cl2 (3b ). Crystals of 2 were
prepared by slow diffusion of Et2O into a saturated solution
of the complex in CH2Cl2. Crystals of 3 were obtained by slow
diffusion of pentane into a saturated solution of 3 in CH2Cl2
(3a ) or by slow diffusion of Et2O into a solution of 2 (0.160 g,
0.143 mmol) in 3 mL of CH2Cl2 and 200 µL of HBF4‚Et2O (1.15
mmol, 10-fold excess) (3b). The complex crystallizes as 3b
with an additional 1 equiv of HBF4 in the asymmetric unit.
In all three cases NMR spectra of the crystals redissolved in
CD2Cl2 confirmed the identity of the compounds and the
presence of the hydride or dihydrogen ligand, respectively.
Intensity data were collected on a Siemens P4 diffractometer
using graphite monochromated Mo KR radiation (λ ) 0.710 73
Å). The ω scan technique was applied with variable scan
speeds. General data collection parameters are listed in Table
5. In each case the intensities of 3 standard reflections
measured every 97 reflections showed no decay. Data for the
compounds were corrected for Lorentz and polarization effects
and for absorption.55 For all structures the Os atom position
was solved by the Patterson method and other non-hydrogen
atoms were located by successive difference Fourier syntheses.
The structures were refined by full-matrix least squares on
F2. The weighting scheme was w ) 1/[σ2(Fo2) + (aP)2 + bP],
Exp er im en ta l Section
Oxygen and water were excluded at all times by the use of
a glovebox supplied with purified nitrogen or vacuum lines
supplied with purified N2 or Ar; N2 was used unless otherwise
stated. Et2O and pentane were dried over and distilled from
sodium-benzophenone ketyl. For the acidity studies this was
done immediately before use. CH2Cl2 and CH3CN were
distilled from calcium hydride. Deuterated solvents were dried
over Linde type 4 Å molecular sieves and degassed prior to
use. The phosphine ligands were used as purchased from
Aldrich, Strem Chemicals, or Digital Speciality Chemicals Ltd.
The complex trans-[Os(η2-H2)(H)(dppe)2]BF4 was prepared as
reported previously.21
NMR spectra were recorded on a Varian Unity 400 (400
MHz for 1H, 162 MHz for 31P), Varian Gemini 200 (200 MHz
for 1H), and Varian Gemini 300 (300 MHz for 1H, 120.5 MHz
for 31P) spectrometers. All 31P NMR were proton decoupled,
unless stated otherwise. 31P NMR chemical shifts were
measured relative to ∼1% P(OMe)3 in C6D6 sealed in coaxial
capillaries and are reported relative to H3PO4 by use of
δ(P(OMe)3) ) 140.4 ppm. 1H chemical shifts were measured
relative to partially deuterated solvent peaks but are reported
relative to tetramethylsilane. In all cases, high-frequency
shifts are reported as positive. Variable-temperature T1
measurements were made at 400 MHz, using the inversion
recovery method with calibration of the 90°/180° pulse at each
temperature. The temperature of the probes were calibrated
with the temperature dependence of the chemical shifts of
MeOH.
2
where P ) (Fo + 2Fc2)/3. Hydrogen atoms except for those
on the CH3 group on the CH3CN ligand and the hydride/
dihydrogen ligands were positioned on geometric grounds
(C-H 0.96 Å, Uiso ) 0.031(3) Å2 for 2; C-H 0.96 Å, Uiso ) 0.042-
(4) Å2 for 3a ; C-H 0.96 Å, Uiso ) 0.039(3) Å2 for 3b). In 3a
tr a n s-[Os(H )(CH 3CN)(d p p e)2]BF 4 (2). [Os(η2-H2)(H)-
(dppe)2]BF4 (0.250 g, 0.232 mmol) was dissolved in 10 mL of
CH3CN and stirred for 12 h, after which time quantitative
conversion to the product as monitored by 31P NMR of the
reaction mixture had occurred. The volume of the CH3CN
solution was reduced in vacuo to begin precipitation. Addition
of 20 mL of Et2O caused complete precipitation of a white
powder. Isolated yield: 0.240 g (0.215 mmol), >90%. Anal.
the hydrogen atoms bonded to Os were located from
a
difference Fourier and refined with isotropic thermal param-
eters (H(1Os), Uiso ) 0.062(33) Å2; H(2Os), Uiso ) 0.017(19)
Å)2). The hydrogen atoms bonded to Os in 2 and 3b were not
located. In structure 3a the phenyl ring defined by P(4)-C(71)
shows conformational disorder. For 3b the disorder extends
Calcd for
C54H52BF4NOsP4: C, 58.12; H, 4.70; N, 1.26.
Found: C, 57.77; H, 4.69; N, 1.56. FAB MS (m/z): calcd for
(55) Sheldrick, G. M. University of Go¨ttingen, Germany.
Schlaf, Marcel
