In situ NMR detection of dihydrides in the systems [RhH(SnCl3)5]3- /tertiary phosphanes/parahydrogen

Article abstract of DOI:10.1002/(SICI)1099-0682(200005)2000:5<889::AID-EJIC889>3.0.CO;2-O

The oxidative addition of dihydrogen to the [RhH(SnCl₃)₅]³-/ PR₃ system (PR₃ = PPh₃, PEtPh₂, PEt₃) leads to the formation of previously unknown dihydride complexes, the ¹H-NMR spectra of which have been studied by means of the ParaHydrogen Induced Polarization (PHIP) method. The composition of the resulting complexes crucially depends on the type of the added phosphane. With PEt₃ as the phosphane and acetonitrile as the solvent, a complex with a SnCl₂L ligand (L = CD₃CN) can be detected. All systems examined catalyze the hydrogenation of phenylacetylene. During these reactions, both the ¹H-NMR resonances of the dihydride complexes and those of styrene, the hydrogenation product of phenylacetylene, can be detected simultaneously. In the case of SnBr₃ ligands, hydrogen addition in the presence of phosphanes leads to similar dihydride complexes, which were also identified via ¹H-NMR spectroscopy. Furthermore, a mixed complex of the structure [Rh(SnBr₃)(n)Br6-n)]^3- has been isolated.

Full text of DOI:10.1002/(SICI)1099-0682(200005)2000:5<889::AID-EJIC889>3.0.CO;2-O

FULL PAPER
In situ NMR Detection of Dihydrides in the Systems [RhH(SnCl3)5]3–/Tertiary
Phosphanes/Parahydrogen
Claudia Ulrich,[a] Alexei Permin,[b] Valery Petrosyan,[b] and Joachim Bargon*[a]
Keywords: Rhodium hydride complexes / Parahydrogen / Tin ligands / Hydrogenations
The oxidative addition of dihydrogen to the [RhH(SnCl3)5]3–
PR3 system (PR3 = PPh3, PEtPh2, PEt3) leads to the formation
of previously unknown dihydride complexes, the 1H-NMR
/
the hydrogenation of phenylacetylene. During these reac-
tions, both the 1H-NMR resonances of the dihydride com-
plexes and those of styrene, the hydrogenation product of
spectra of which have been studied by means of the ParaHy- phenylacetylene, can be detected simultaneously. In the case
drogen Induced Polarization (PHIP) method. The composi- of SnBr3 ligands, hydrogen addition in the presence of phos-
tion of the resulting complexes crucially depends on the type
of the added phosphane. With PEt3 as the phosphane and
acetonitrile as the solvent, a complex with a SnCl2L ligand mixed complex of the structure [Rh(SnBr3)nBr6–n
phanes leads to similar dihydride complexes, which were
also identified via 1H-NMR spectroscopy. Furthermore, a
3–
]
has been
(L = CD3CN) can be detected. All systems examined catalyze
isolated.
Introduction
The catalytic activity of rhodium complexes containing
tin trichloride ligands has been the subject of many studies
ever since 1970, when their activity in the dehydrogenation
of 2-propanol has first been noted.[1] This reaction and, in
particular, the structure of the responsible rhodium-tin
complexes have been examined before using 119Sn-NMR
spectroscopy.[2] Furthermore, the rhodium(III) monohyd-
ride complex 1 has previously been isolated from hydro-
chloric acid solutions of RhCl3 and SnCl2 and identified
with this technique.[3] Reactions of these complexes with
tertiary phosphanes have also been studied with 31P- and
1H-NMR spectroscopy, and upon addition of dihydrogen
to these systems the formation of two dihydrido complexes
2 and 3 was detected (Scheme 1).[4]
Scheme 1. Formation of dihydrides from [HRh(SnCl3)5]3– in pres-
ence of phosphanes and hydrogen, Sn ϭ SnCl3, P ϭ PR3.
the enhanced resonances, reliable information about the
structure of species present in only minor quantities in
reaction mixture can thus be obtained. This approach
yields valuable insight into both the stereo- and regio-
chemistry of initial stages of the dihydrogen addition to the
substrate.[8]
The development of an in situ NMR technique based
on ParaHydrogen Induced Polarization (PHIP) allows an
extensive study of rhodium dihydride complexes, both
1
stable and transient, via their H-NMR spectra, which can
be observed during homogeneous catalyzed hydrogena-
tions.[5] Recently, the structure and reactivity of rhodium
dihydrides relevant to both Wilkinson- and Schrock-type
catalysts as well as their hydrogenation activity were exten-
sively examined by use of PHIP-NMR spectroscopy. This
method provides an extraordinary sensitivity for the detec-
tion of metal hydrides; therefore, it has been used to observe
these typically unstable catalytic intermediates.[5–7] Due to
Since reports on tin-containing rhodium dihydrides and
the knowledge of their role in homogeneous catalysis are
scarce, we have used the PHIP technique to study the reac-
tions of two characteristic prototypes with parahydrogen,
namely of the systems [RhH(SnCl3)5]3–/tertiary phosphane
and RhBr3/SnBr2/tertiary phosphane. Recently, plat-
inum(II)-tin hydride complexes were studied in this way,[9]
providing a pool of new information about the mechanism
of homogeneous, platinum-tin catalyzed hydrogenations of
alkynes and alkenes thanks to the identification of previ-
ously unknown intermediates. In this study here, we were
interested in identifying the consequences, in particular the
intermediate products, resulting from the addition of dihy-
drogen to a variety of tin-containing rhodium complexes.
By use of PHIP-NMR spectroscopy we wanted to detect
[a]
Institute of Physical and Theoretical Chemistry,
University of Bonn,
Wegelerstrasse 12, D-53115 Bonn, Germany
Fax (internat.) ϩ 49(0)228/739424
E-mail: bargon@uni-bonn.de
[b]
Department of Chemistry,
M. V. Lomonosov Moscow State University,
Vorobyevy Gory, 119899 Moscow, Russia,
Fax: (internat.) ϩ 7–095/9395546
E-mail: alp@org.chem.msu.su
Eur. J. Inorg. Chem. 2000, 889Ϫ894
WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
1434Ϫ1948/00/0505Ϫ0889 $ 17.50ϩ.50/0
889

C. Ulrich, A. Permin, V. Petrosyan, J. Bargon
FULL PAPER
previously elusive intermediates occurring during the step-
The subsequent fate of the RhI complex is either substitu-
wise tin-for-phosphane substitution as originally described tion of the tin ligands by phosphane or back-protonation
in 1985,[4] in order to obtain more detailed information to 1 as soon as a proton is liberated during the substitution.
about the hydrogenation activity of this rhodium-tin system Addition of parahydrogen at room temperature gives rise to
in particular.
three dihydrides, two of them occurring in polarization
(Figure 2).
Results and Discussion
Of the two rhodium-tin-systems investigated here, the
first complex, [HRh(SnCl3)5]3–, has been obtained and
characterized earlier as an isolated rhodium monohyd-
ride,[2,3] whereas the second system, RhBr3/SnBr2/HBr, has
not been investigated before.
Figure 1. 119Sn-NMR spectrum of the RhBr3/SnBr2/HBr system in
CD3CN at –40° C (chemical shifts referenced to external Me4Sn)
Action of NEt4ϩ onto the latter yields a solid, which was
studied by means of NMR spectroscopy. The 119Sn-NMR
spectrum (Figure 1) exhibits four main resonances A, B, C,
and D, which are due to rhodium-tin-complexes of the type
3–
[Rh(SnBr3)nBr6–n
]
with typical shifts and coupling values
for tin coordinated to rhodium[10] (see Experimental Sec-
tion). Upon addition of parahydrogen, the H-NMR spec-
Figure 2. 1H-NMR spectra of the system [RhH(SnCl3)5]3–/PPh3/H2
in CD3CN; a) PHIP spectrum on heating; b) PHIPϩϩ simulation
of 6a and 5a; c) PHIP-1H{31P}-NMR spectrum on heating; d)
product spectrum after decay of the polarization
1
trum in acetonitrile reveals no signals of any hydride, by
contrast to the chloride analogue. The lack of formation
of a monohydride upon addition of tetraethylammonium
cations to the RhBr3/SnBr2/HBr system seems to be due to
the lower reductive ability of tin dibromide in comparison
to tin dichloride, which would explain the lack of RhI
formation and, therefore, the lack of subsequent pro-
tonation.
The unpolarized hydride resonances at δ ϭ –17.19 are
assigned to the chemically equivalent protons of the sym-
metric complex 4a. This complex has already been de-
scribed before.[11] These hydride resonances occur with a
multiplicity consisting of doublet of triplets with
2
1J(HRh) ϭ –17.5 Hz and J(HP) ϭ 13 Hz (Table 1). The
System [RhH(SnCl3)5]3–/PPh3
polarized resonances, however, show coupling patterns typ-
The action of parahydrogen on the [RhH(SnCl3)5]3– an- ical for a bis-phosphane and a tris-phosphane complex, re-
ion in acetonitrile does not give rise to any detectable dihy- spectively. The bis-phosphane complex 5a shows one hy-
drides either. The addition of four equivalents of PPh3 to dride resonance H2, with a chemical shift value of δ ϭ –
the solution causes partial deprotonation of the hydride, 11.42, which is typical for a proton in trans position to a
1
since the hydride signal disappears in the H-NMR spec- trichlorostannato ligand. This resonance occurs as a doub-
trum. Furthermore, the 31P-NMR spectrum reveals the let of triplets which are further split into doublets with
presence of HPPh3ϩ at δ ϭ –3 (broad), which undergoes ‘‘antiphase’’ multiplicity. (In the following the designation
rapid chemical exchange with PPh3 on the NMR time scale. "antiphase multiplicity" will be used as an abbreviation uni-
This behaviour is similar to that of the already described versally when referring to multiplets in polarization and a
2
reaction with PBu3.[4]
splitting due to J(HHЈ) coupling between the former two
parahydrogen protons). The 31P-decoupled spectrum re-
(1) veals the rhodium coupling as 1J(H2Rh) ϭ 25 Hz. The
[HRh(SnCl3)5]3– ϩ PBu3 Ǟ [Rh(SnCl3)5]4– ϩ HPBuϩ3
890
Eur. J. Inorg. Chem. 2000, 889Ϫ894

NMR Detection of Dihydrides
FULL PAPER
1
Table 1. H-NMR data of the dihydride complexes
Formula
1Η δ [ppm], J [Hz]
6a
5a
H2Rh(PPh3)3L[a]
–16.64 (JHH ϭ –9.5, JHRh ϭ 10, JHP ϭ 13)
–10.08 (JHRh ϭ 9.5, JHPcis ϭ 14, JHPtrans ϭ 147)
–17.05 (JHH ϭ –4.5, JHRh ϭ 13, JHP ϭ 13)
–11.42 (JHRh ϭ 25, JHP ϭ 9)
H2Rh(PPh3)2(SnCl3)L[a]
[a]
4a
3b
H2Rh(PPh3)2L2
–17.19 (JHRh ϭ 17.5, JHP ϭ 13)
H2Rh(PEtPh2)3(SnCl3)
–12.07 (JHH ϭ –6, JHRh ϭ 20, JHP ϭ 10)
–10.67 (JHRh ϭ 10, JHPcis ϭ 13, JHPtrans ϭ 130.5, JHSn ϭ 1440)
–17.46 (JHH ϭ –8, JHRh ϭ 13, JHP ϭ 13)
6b
H2Rh(PEtPh2)3L[a]
–9.82 (JHRh ϭ 13.5, JHPcis ϭ 13.5, JHPtrans ϭ 148)
–12.52 (JHRh ϭ 25, JHP ϭ 11.5)
2c
3c
H2Rh(PEt3)2(SnCl3)2
H2Rh(PEt3)3(SnCl3)
–12.84 (JHH ϭ –5.5, JHRh ϭ 25, JHP ϭ 12, JH119Sn ϭ 1510, JH117Sn ϭ 1443)
–11.48 (JHRh ϭ 11.5, JHPcis ϭ 16, JHPtrans ϭ 131)
–12.40 (JHH ϭ –5, JHRh ϭ 26, JHP ϭ 13, JH119Sn ϭ 1510, JH117Sn ϭ 1443)
–10.88 (JHRh ϭ 11, JHPcis ϭ 16, JHPtrans ϭ 158)
–18.77 (JHH ϭ –4, JHRh ϭ 16.5, JHP ϭ 15)
8c
7c
9c
H2Rh(PEt3)3(SnCl2L)[a]
H2Rh(PEt3)2(SnCl3)2X[b]
H2Rh(PEt3)3(SnBr3)
–12.56 (JHRh ϭ 30, JHP ϭ 11)
–13.85 (JHH ϭ –5.5, JHRh ϭ –25, JHP ϭ 12.5)
–11.16 (JHRh ϭ 10.5, JHPcis ϭ 15, JHPtrans ϭ 130)
–13.26 (JHRh ϭ –25, JHPcis ϭ 11.5)
10c
11c
H2Rh(PEt3)2(SnBr3)2
H2Rh(PEt3)2(SnBr3)2X[b]
–18.77 (JHH ϭ –6, JHRh ϭ –15, JHPcis ϭ 15)
–12.56 (JHRh ϭ 31, JHPcis ϭ 12)
[a]
[b]
L ϭ CD3CN. – X ϭ Cl, Br, CD3CN.
other hydride proton, namely H1 trans to acetonitrile, oc- In addition, several signals in the range of δ ϭ 15 to 45
1
curs as a high-field pseudo-quadruplet at δ ϭ –17.05 with with typical J(PRh) coupling constants of 90 to 135 Hz
a rhodium coupling of J(H1Rh) ϭ 13 Hz. The presence of
acetonitrile in this complex is confirmed by the fact that the
1
Table 2. 31P-NMR data of the dihydride complexes
same signals are not detected in the system RhCl(PPh3)3/
SnCl2 (1:5) in [D6]acetone as the solvent until the addition
of minor quantities of acetonitrile.
Dihydride
Formula
Chemical shifts, δ [ppm],
coupling constants J [Hz]
6a
6b
3c
H2Rh(PPh3)3L[a]
42.8 (JPP ϭ 19, JPRh ϭ 111)
28.7 (JPRh ϭ 93)
In the tris-phosphane complex 6a the large value of
2J(H2P) ϭ 147 Hz is typical for a trans-alignment of the
ligands. The 31P-decoupled 1H-NMR spectrum approves
this assignment. The high-field shift of H1 is also due to a
H2Rh(PEtPh2)3L[a]
H2Rh(PEt3)3(SnCl3)
38.8 (JPP ϭ 20, JPRh ϭ 109)
24.3 (JPRh ϭ 96)
28.7 (JPP ϭ 22, JPRh ϭ 96)
15.6 (JPRh ϭ 88)
[a]
trans acetonitrile ligand, which is concluded from the obser-
L ϭ CD3CN
3–
vation that the [Rh(SnBr3)nBr6–n
]
system gives rise to the
are observed (Table 2). However, the deprotonation of the
monohydride does not occur completely, since it can still be
detected in the H-NMR spectrum.
same signals upon addition of parahydrogen. Furthermore,
these signals can also be detected in the system
RhCl(PPh3)3/SnCl2/PPh3 (1:5:7) in CD3CN.
1
The admission of parahydrogen gives rise to polarized
signals of two dihydrides, 3b and 6b, with coupling patterns
similar to those of the PPh3 analogues (Figure 3). The pres-
ence of an acetonitrile ligand in 6b is extrapolated from the
observation of the corresponding signals in the PHIP spec-
tra of the bromide system. The signals of 6b are also detect-
The complexes 4a and 6a are stable and can, therefore,
be characterized from their resonances observed in the ther-
mal, i.e., in the regular, ‘‘unpolarized’’ H-NMR spectra.
1
Complex 5a, however, is a transient species which can only
be observed in situ, i.e., enhanced by PHIP. The extensive
incorporation of acetonitrile into the coordination sphere
of the dihydrides can be rationalized by the relatively high
π-acceptor properties of triphenylphosphane, which causes
its competition with the tin ligands for the filled d-orbitals
of rhodium. The tin trihalide ligands have been shown earl-
ier to be relatively strong π-acceptors as well.[12] The instab-
ility of complex 5a could be caused by the high trans effect
of H2; therefore, the lability of the tin ligand is enhanced,
which causes its dissociation with the formation of 4a.
1
able in the thermal H-NMR spectrum, whereas 3b is only
visible when enhanced by PHIP. The higher stability of 3b
as compared to that of the PPh3 system, can be explained
by the decrease of the π-acceptor properties of PEtPh2 relat-
ive to PPh3; therefore, its competition with the tin ligand is
less favourable. It should be mentioned that in this system
only tris-phosphane dihydrides are observed.
System [RhH(SnCl3)5]3–/PEt3
System [RhH(SnCl3)5]3–/PEtPh2
Upon addition of PEt3 to an acetonitrile solution of 1,
Upon addition of PEtPh2 to an acetonitrile solution of deprotonation of the monohydride becomes evident by the
1, deprotonation becomes evident by the appearance of appearance of HPEt3ϩ in the 31P-NMR spectrum at δ ϭ
HPEtPh2ϩ in the 31P-NMR spectrum at δ ϭ – 8.5 (broad). –13.7 (broad). Furthermore, four main signals with 1J(PRh)
Eur. J. Inorg. Chem. 2000, 889Ϫ894
891

C. Ulrich, A. Permin, V. Petrosyan, J. Bargon
FULL PAPER
and second PEt3: If three ligands are swiftly replaced by
PEt3, only the tris-phosphane is available for the oxidative
addition of parahydrogen.
Likewise, at lower PEt3 concentrations (Rh/P ϭ 1:4) the
first PHIP spectrum reveals the formation of 3c only (Fig-
ure 4, a). However, upon standing at room temperature, the
addition of parahydrogen leads to the emergence of a com-
plicated mixture of PHIP-active dihydrides, as can be con-
cluded from the spectra shown in Figure 4, f.
1
Figure 3. H-NMR spectra of the system [RhH(SnCl3)5]3–/PEtPh2/
H2 in CD3CN; a) PHIP spectrum on heating; b) PHIPϩϩ simula-
tion of 6b and 3b; c) PHIP-1H{31P}-NMR spectrum on heating
couplings of 90, 90, 116, and 137 Hz occur at δ ϭ 7.5, 20.6,
26.4, and 42.2, respectively.
The appearance of polarized dihydrides upon parahy-
drogen addition depends on the initial P/Rh ratio. When an
excess of phosphane (Rh/P ϭ 1:6) is used, the resonances
observed correspond to the tris-phosphane mer-
H2Rh(PEt3)3(SnCl3), 3c. This complex is also visible in the
thermal spectra together with the symmetric complex 2c,
which is formed after prolonged reaction time and upon
heating.
Figure 4. 1H-NMR spectra of the system [RhH(SnCl3)5]3–/
PEt3(1:4)/H2 in CD3CN; a) PHIP spectrum immediately after mix-
ing of the reagents; b) PHIPϩϩ simulation of 3c; c) PHIP spec-
trum in presence of AgBF4; d) PHIP spectrum on heating; e)
PHIPϩϩ simulation of 2c and 7c; f) PHIP spectrum after pro-
longed reaction time; g) PHIPϩϩ simulation of 1, 2c, 3c, 7c, and 8c
Heating of the solution changes the patterns (Figure 4,
d), apparently because of scrambling of the phosphane
throughout the whole system (Scheme 3). Consequently,
upon admission of parahydrogen two bis-phosphane dihy-
Scheme 2. Formation of a tris-phosphane rhodium dihydride at the
first stage of the reaction
The dihydride 3c is apparently the result of an oxidative drides, 2c and 7c, are obtained. The spectral patterns ob-
addition of parahydrogen to Rh(PEt3)3(SnCl3) formed at served correspond to overlapping signals of 2c (in which the
the very beginning of the reaction (Scheme 2). The lack of two former parahydrogen protons fail to appear in polariza-
evidence for the formation of any bis-phosphane dihydrides tion, possibly due to their maintained symmetry) and the
during the first stage of the reaction can be rationalized to polarized multiplet of 7c. This assignment has been con-
be the consequence of the activating trans effect of the first firmed by PHIPϩϩ simulation.
892
Eur. J. Inorg. Chem. 2000, 889Ϫ894

NMR Detection of Dihydrides
FULL PAPER
the polarization pattern of the resulting styrene. The hydro-
genation activities are rather similar for all these systems.
Characteristically, in all cases investigated, the resonances
of the dihydrides are present during the hydrogenation of
phenylacetylene to styrene. The apparent lack of formation
of any substrate-hydride complexes – similar to those de-
tected in the previously investigated platinum-tin sys-
tems[9] – leads us to the conclusion that the observed dihy-
drides may not be directly included in the catalytic cycle of
the hydrogenation, but might just be the precursors for re-
lated, catalytically active species. Alternatively, the rates of
the individual steps for this catalytic cycle might well be
rather different from those of the previously studied plat-
inum-tin system, with the consequence that the rate-deter-
mining steps shift with the result that such intermediates, –
if they are formed at all -, occur in such minute concentra-
tions that they cannot be detected in spite of the signal en-
hancement associated with PHIP.
Scheme 3. Formation of bis-phosphane rhodium dihydrides after
prolonged reaction time
The complicated mixture of resonances observed in the
PHIP spectra at room temperature after prolonged reaction
times (Figure 4, f) could be analyzed to consist of the over-
lapping thermal and PHIP signals of 3c, 2c, 7c, and of the
starting complex 1, respectively. This analysis was con-
firmed via PHIPϩϩ simulation of the expected resonances
for the components of this system and a subsequent
weighted summation thereof (Figure 4, g).
Conclusions
However, in order to achieve a complete fitting of the
observed patterns in the case above, the presence of another
tris-phosphane dihydride has to be postulated, namely of
8c. Its coupling patterns clearly display the cis-position
alignment of three phosphorus ligands. The chemical shift
of the H1 proton in cis-position to phosphorus is character-
istic for a trans-alignment of the tin-ligand. The difference
between the two rather similar dihydrides 3c and 8c can
only be due to variations in the structure of the tin ligand.
As has already been shown before,[13,14] tin(II)chloride pos-
sesses additional coordination abilities; therefore, it can co-
ordinate Lewis bases, leading to the formation of SnCl2D
ligands (D ϭ donor). Since this process could be strongly
promoted by the abstraction of chloride, we have also re-
corded the spectra of this system in the presence of added
AgBF4 to check out the relevance of this hypothesis. The
result shows a strong enhancement of the signals of 8c, add-
ing support to this suggestion. In addition, tin satellites are
clearly visible for the resonance of H1, exhibiting a value
for 2J(HSn), which is close to that of the related complex 3c.
By contrast to the PPh3 and PEtPh2 chloride systems the
addition of parahydrogen to the corresponding bromide
systems gives rise to relatively stable, tin-containing dihy-
drides which appear in polarization in the PHIP-NMR
spectra. Upon heating, the signals of 9c, which is the brom-
ide analogue of 3c, are clearly visible. The complexes 10c
and 11c can also be detected, which appear to be the tin-
tribromide analogues of 2c and 7c, respectively. The high-
field shift of the hydrogen in trans-position to the tin ligand
indicates a lower trans-effect of SnBr3– as compared to that
of SnCl3–. Furthermore, the intensity of the PHIP signals
observed in the bromide systems is generally lower than in
the corresponding chloride system, apparently because of
the lower concentration of RhI.
In comparison to PPh3, the PEt3 ligand has profound
electron donor properties, which causes an extensive incor-
poration of tin ligands into the resulting dihydrides. Accord-
ingly, when using PPh3 as the tertiary phosphane, the
formation of only one tin-containing dihydride is observed,
which is thermally unstable. By contrast, in the system
[RhH(SnCl3)5]3–/PEt3/CD3CN/parahydrogen four dihy-
drides are detectable, which all contain tin ligands. Two of
them, namely 3c and 2c, are rather stable species. The low
stability of the tin-containing complexes with PPh3 as the
ligand is apparently due to the competition of the tin and
phosphane ligands. Furthermore, this process is accompa-
nied by more extensive incorporation of acetonitrile into
the dihydrides.
In particular, the system [RhH(SnCl3)5]3–/PEtPh2/
CD3CN/parahydrogen is remarkable in the sense that it
gives rise to tris-phosphane complexes only. This fact can
be explained when assuming that there exists a fine balance
of σ-donating and π-accepting properties of the phosphane
which is apparently optimal for rhodium-phosphorus-bind-
ing here.
Experimental Section
1
1
General Remarks: All H, H PHIP-, 31P and 119Sn NMR spectra
1
were recorded using a Bruker AC 200 spectrometer; the H{31P}-
PHIP NMR spectra were obtained with a Bruker DRX 200 spec-
trometer. Chemical shifts are referenced to either external TMS
(1H), 85% H3PO4 (31P), or Sn(CH3)4 (119Sn), respectively. For re-
cording the 119Sn spectrum a repetition time of 0.5 s was used, and
the accumulation of 28000 scans was necessary to obtain a spec-
trum with a satisfactory signal-to-noise ratio. In order to obtain
the PHIP spectra, excitation pulses corresponding to a flip angle
of 45° were used. To record the conventional or "thermal" 1H
NMR spectra, however, the pulse width was set such that it corre-
Hydrogenation Experiments
Upon heating, all systems studied hydrogenate added
phenylacetylene in a cis-manner, as can be concluded from sponded to the conventional flip angle of 90°. The solvent CD3CN
Eur. J. Inorg. Chem. 2000, 889Ϫ894 893

C. Ulrich, A. Permin, V. Petrosyan, J. Bargon
FULL PAPER
was purchased from Aldrich, dried and degassed prior to use, and
stored under vacuum. – The simulations of the PHIP-1H NMR
spectra were performed using the OS/2-based PHIPϩϩ program,
developed by Greve.[15] – The complex [RhH(SnCl3)5][NEt4]3 was
prepared as reported in the literature.[3] All starting materials were
commercial products (Aldrich) which were used without addi-
tional purification.
Acknowledgments
We thank the Russian Foundation for Basic Research (RFBR), the
Deutsche Forschungsgemeinschaft (DFG), and the Fonds der
Chemischen Industrie, Frankfurt (Main), Germany, for financial
support.
[1]
H. B. Charman, J. Chem. Soc. (B) 1970, 584–587.
[2]
T. Yamakawa, S. Shinoda, Y. Saito, H. Moriyama, P. S. Prego-
sin, Magn. Reson.Chem. 1985, 23, 202–206.
[3]
Typical Preparation of Solutions for Hydrogenation Studies: The
RhIII complex, as well as PPh3, were placed into a screw-capped
NMR tube attached to a vacuum line. Then 0.7 mL of dry degassed
CD3CN was condensed into the tube. The weighted amounts of
PEt3 were vacuum-transferred to the sample. After thawing and
filling with dry argon, the sample tube was disconnected from the
vacuum line and fitted with a septum stopper. The necessary vol-
umes of PEtPh2 were added to the solution of the starting
RhIII complex using an Eppendorf micropipette. Parahy-
drogen was subsequently introduced into the NMR tube through a
stainless steel needle through the septum at a pressure of 3 bar.
After shaking of the solution in the parahydrogen atmosphere, the
D. P. KrutЈko, A. B. Permin, V. S. Petrosyan, O. A. Reutov, Izv.
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