Rhenium nitrosyl complexes for hydrogenations and hydrosilylations

Article abstract of DOI:10.1021/om7011024

The tris(acetonitrile)dibromonitrosylrhenium(I) compound (1a) was obtained by reduction of the paramagnetic [NMe₄]₂[Re(NO)Br ₅] salt with Zn in MeCN. Subsequent reaction of la with THF produced the THF derivative [Re(NO)(THF)(MeCN)₂Br₂] (1b). Reaction of 1b with PiPr₃, Pcy₃, or P(p-tolyl)₃ yielded bis(acetonitrile)-cis-dibromo(nitrosyl)-trans-bis(phosphine)rhenium complexes (R = iPr 2a, cy 2b, p-tolyl 2c). Treatment of 2a,b with excess NaBH₄ produced the known borohydride complexes [Re(H)(η²-BH ₄)(NO)(PR₃)₂] (R = iPr 3a, cy 3b). Replacement of the BH₃ moiety of 3a,b in THF by ethylene (1 bar) produced the dihydride complexes [Re(H)₂(η²-C₂H ₄)(NO)(PR₃)₂] (4) (R = iPr a, cy b). Protonation of 4a,b with HBF₄ · OEt₂ afforded H₂ and the monohydrido tetrafluoroborato species [Re(H)(NO)(PR ₃)₂(η²-C₂H₄)(BF ₄)] (R = iPr 5a, cy 5b). X-ray diffraction studies were carried out on 1a, 2b,c, and 5b. Complexes 4a,b are catalytically active in olefin, imine, and ketone hydrogenations and in olefin and ketone hydrosilylations, as well as in the scrambling of H₂/D₂ to give HD under mild conditions.

Full text of DOI:10.1021/om7011024

3474
Organometallics 2008, 27, 3474–3481
Rhenium Nitrosyl Complexes for Hydrogenations and
Hydrosilylations
A. Choualeb, E. Maccaroni, O. Blacque, H. W. Schmalle, and H. Berke*
Anorganisch-Chemisches Institut UniVersita¨t Zu¨rich, Winterthurerstrasse 190, CH-8057, Switzerland
ReceiVed NoVember 1, 2007
The tris(acetonitrile)dibromonitrosylrhenium(I) compound (1a) was obtained by reduction of the
paramagnetic [NMe4]2[Re(NO)Br5] salt with Zn in MeCN. Subsequent reaction of 1a with THF produced
the THF derivative [Re(NO)(THF)(MeCN)2Br2] (1b). Reaction of 1b with PiPr3, Pcy3, or P(p-tolyl)3
yielded bis(acetonitrile)-cis-dibromo(nitrosyl)-trans-bis(phosphine)rhenium complexes (R ) iPr 2a, cy
2b, p-tolyl 2c). Treatment of 2a,b with excess NaBH4 produced the known borohydride complexes
[Re(H)(η2-BH4)(NO)(PR3)2] (R ) iPr 3a, cy 3b). Replacement of the BH3 moiety of 3a,b in THF by
ethylene (1 bar) produced the dihydride complexes [Re(H)2(η2-C2H4)(NO)(PR3)2] (4) (R ) iPr a, cy b).
Protonation of 4a,b with HBF4 · OEt2 afforded H2 and the monohydrido tetrafluoroborato species
[Re(H)(NO)(PR3)2(η2-C2H4)(BF4)] (R ) iPr 5a, cy 5b). X-ray diffraction studies were carried out on 1a,
2b,c, and 5b. Complexes 4a,b are catalytically active in olefin, imine, and ketone hydrogenations and in
olefin and ketone hydrosilylations, as well as in the scrambling of H2/D2 to give HD under mild conditions.
1a has decent solubility only in MeCN (≈17 g/L at 25 °C) and
I. Introduction
CH2Cl2, has low solubility in MeOH and acetone, and is only
As a ″noninnocent″ ligand nitrosyl may take over special roles
in transition metal chemistry. It supports different oxidation
states of metal centers often accompanied by different coordina-
tion modes, and furthermore it exerts a relatively strong trans-
influence or trans-effect, thus activating metal-ligand bonds.
Manifestations of the latter influences are nitrosyl-substituted
transition metal hydrides,1 in which the M-H bonds show
increased hydride transfer activity. In the attempt to exploit the
ability of NO to tune transition metal hydrides toward catalytic
activity, we were specifically interested in the development of
new rhenium hydride catalysts for hydrogenations and hydrosi-
lylations of unsaturated organic molecules. Our group recently
reported several examples of rhenium mono- and dinitrosyl
complexes that are active in these or related catalyzes.2,3 We
also studied the ethylene chemistry of Re(I) mononitrosyl
hydride complexes, which demonstrated the general disposition
to coordinate ethylene and to undergo organometallic reactions.
In extension of this work we wanted to further explore the
hydrogen/olefin chemistry and the catalytic potential of such
complexes.
sparingly soluble in Et2O, THF, ethanol, and dioxane. 1H NMR
samples of 1a in CH2Cl2 indeed showed two signals at 3.02
and 2.97 ppm (1:2 ratio), confirming the presence of the mer-
substitution pattern (Scheme 1), but revealed after approximately
15 min also a signal for free MeCN originating from decoor-
dination and gradual decomposition in this solvent.
In the 1H NMR and 13C NMR spectra of 1a distinct
resonances could be detected for the two trans and the unique
trans Br Me groups and CN groups of the MeCN ligands. ATR-
IR spectroscopy of 1a did not reveal bands for the mer-(MeCN)3
rhenium unit, which presumably is due to their too low
intensities. The expected ν(NO) band was found to appear at
1691 cm-1
.
1a was additionally characterized by an X-ray diffraction
study. Single crystals were grown in an NMR tube from a
MeCN solution saturated at 60 °C and slow cooling to room
temperature. Selected bond lengths and angles are reported in
Table 1. As shown in Figure 1, 1a possesses a pseudo-octahedral
structurewithmer-arrangedMeCNligands.TheO(1)-N(1)-Re(1)
angle of around 177° and the relatively short N(1)-O(1) bond
length of 1.1260(9) Å gave evidence for a linear nitrosyl ligand
(average bond length 1.18-1.22 Å).5 The three MeCN mol-
ecules are coordinated practically linear to rhenium with
N(3)-Re(1)-N(2) and N(4)-Re(1)-Br(2) angles of 173.3(3)°
and 174.8(2)°, respectively.
The air-stable mixed solvento complex [Re(NO)(THF)-
(MeCN)2Br2] (1b) (Scheme 1) was obtained dissolving 1a in
THF and was isolated in pure form after recrystallization from
THF/pentane. The facile MeCN exchange in 1a is thought to
originate mainly from the cis-labilization effect exerted by one
of the two bromide ligands. In the 1H NMR spectrum the
coordinated THF of 1b was indicated by multiplets at 1.81 and
3.64 ppm for the methylene groups and also in the 13C NMR
spectrum by singlets at 26.3 and 68.3 ppm for the corresponding
II. Results and Discussion
IIa. Preparation of Phosphine-Substituted Dibromo
Nitrosyl Rhenium(I) Complexes. The orange complex mer-
[Re(NO)(MeCN)3Br2] (1a) is obtained as a solvate complex
1a · MeCN by reduction of the paramagnetic salt [NMe4]2-
[Re(NO)Br5]4 with Zn in MeCN and direct crystallization from
this solvent. The solvate molecule can be removed in Vacuo.
* To whom correspondence should be addressed. E-mail: hberke@
aci.uzh.ch. Fax: int +41-1-6356802.
(1) Berke, H.; Burger, P. Comments Inorg. Chem. 1994, 16, 279–312.
(a) Jacobsen H., Berke H. In Recent AdVances in Hydride Chemistry; Poli,
R., Ed.; Elsevier: Amsterdam, Holland, 2001; pp 89-116.
(2) Huang, W. J.; Berke, H. Chimia 2005, 59, 113–115.
(3) Liu, X. Y.; Venkatesan, K.; Schmalle, H. W.; Berke, H. Organo-
metallics 2004, 23, 3153–3163.
(4) Gusev, D.; Llamazares, A.; Artus, G.; Jacobsen, H.; Berke, H.
Organometallics 1999, 18, 75–89.
(5) Machura, B. Coord. Chem. ReV. 2005, 249, 2277–2307, and
references cited.
10.1021/om7011024 CCC: $40.75
2008 American Chemical Society
Publication on Web 06/03/2008

Rhenium Nitrosyl Complexes for Hydrogenations
Organometallics, Vol. 27, No. 14, 2008 3475
Scheme 1
Table 1. Selected Bond Distances and Bond Angles in
Scheme 2
ReBr2(MeCN)3(NO) · C2H3N (1a)
bond distances (Å)
bond angles (deg)
Re(1)-N(2)
2.073(8)
N(3)-Re(1)-N(2)
173.3(3)
Re(1)-N(3)
Re(1)-N(4)
Re(1)-N(1)
Re(1)-Br(1)
Re(1)-Br(2)
N(1)-O(1)
2.050(8)
2.065(8)
1.797(7)
2.5672(11)
2.5531(11)
1.126(9)
N(4)-Re(1)-Br(2)
N(1)-Re(1)-Br(1)
O(1)-N(1)-Re(1)
N(4)-Re(1)-N(2)
N(3)-Re(1)-Br(2)
N(2)-Re(1)-Br(2)
174.8(2)
179.5(2)
176.7(7)
89.9(3)
90.1(2)
90.4(2)
carbon atoms. The IR spectrum of 1b reveals in the solid state
a strong band at 1685 cm-1, which confirms the presence of
the NO ligand, and furthermore a weak band at 2277 cm-1
which is assigned to the coordinated MeCN groups.
,
For various ligand substitution reactions 1b turned out to be
a superior starting material in comparison with 1a, mainly
because of its higher solubilities in most organic solvents.
Therefore 1b was used for the preparation of various phosphine-
disubstituted complexes according to Scheme 2. Applying excess
phosphine ligands at room temperature in THF allowed access
to disubstituted [Re(NO)(MeCN)(PR3)2Br2] compounds (2) (R
) iPr a, cy b, p-tolyl c) obtained in good yields. Complexes
2a-c are very air sensitive in solution, and 2b and 2c have
low solubilities in many organic solvents.
originate from aromatic shielding of the phosphine substituents.
The 31P{1H} NMR spectra of 2a-c each show one singlet for
the two equivalent trans-phosphorus nuclei, and in the IR spectra
strong bands in the range of 1679 - 1700 cm-1 were attributed
to ν(NO) vibrations.
The pseudo-octahedral structures of 2b and 2c were deter-
mined by X-ray diffraction studies (Figure 2). Selected bond
distances and angles of 2b and 2c are given in Table 2. 2b
crystallizes with 2 THF solvate molecules in the asymmetric
unit, and in both structures NO and Br(2) are positionally
disordered. The phosphine ligands are disposed approximately
trans, slightly bending toward the bromides (P(1)-Re(1)-P(2)
) 172.60(7)° (2b) and 173.51(3)° (2c); Re-P distances
2.4608(10)-2.5138(18) Å5–7), the bromides are located cis, and
the MeCN and the nitrosyl ligands take places trans to a
bromide. The MeCN moieties in 2b and 2c are practically linear
with a Re(1)-N(2)-C(1) angle of 177.7(6)° (2b) and 172.2(4)°
(2c),8–11 and the Re-NCMe distances are 2.065(7) and 2.079(4)
Å, close to the average value of 2.098 Å.6,11 In addition the
carbon-nitrogen(1.099(10)and1.113(6)Å)andthecarbon-carbon
(1.488(13) and 1.464(7) Å) distances of the coordinated MeCN
ligand are at the 3σ level within the average values of 1.136
and 1.470 Å.12
1
2a-c were characterized by IR and H NMR spectroscopy
and elemental analyses. The 1H NMR spectra in CD2Cl2
displayed besides the signals for the phosphine substituents
singlets of the Meacetonitrile groups at 3.06, 3.08, and 1.77 ppm.
The lower chemical shift of the Me signal of 2c is suggested to
IIb. Synthesis of Di- and Monohydrido Ethylene
Rhenium Complexes. Treatment of 2a and 2b with excess
NaBH4 leads to formation of the known hydride borohydride
(6) Jacobsen, H.; Schmalle, H. W.; Messmer, A.; Berke, H. Inorg. Chim.
Acta 2000, 306, 153–159.
(7) (a) Hund, H. U.; Ruppli, U.; Berke, H. HelV. Chim. Acta 1993, 76,
963–975. (b) Choualeb, A.; Blacque, O.; Schmalle, H. W.; Fox, T.;
Hiltebrand, T.; Berke, H. Eur. J. Inorg. Chem. 2007, 5246–5261.
(8) Ciani, G.; Giusto, D.; Manassero, M.; Sansoni, M. J. Chem. Soc.,
Dalton Trans. 1975, 2156–2161.
(9) Drew, M. G. B.; Tisley, D. G.; Walton, R. A. J. Chem. Soc., Chem.
Commun. 1970, 600–601.
(10) Veghini, D.; Berke, H. Inorg. Chem. 1996, 35, 4770–4778.
(11) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson,
D. G.; Taylor, R. J. Chem. Soc., Dalton Trans. 1989, S1.
(12) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen,
A. G.; Taylor, R. J. Chem. Soc., Perkin Trans. 2 1987, S1-S19.
Figure 1. X-ray structure of complex 1a (ORTEP representation
with selected atomic labels). All hydrogen atoms and the MeCN
solvate are omitted for clarity. The displacement ellipsoids are
drawn with 50% probability.

3476 Organometallics, Vol. 27, No. 14, 2008
Choualeb et al.
Figure 2. ORTEP drawing of the molecular structures of 2b (left) and 2c (right) (thermal ellipsoids are drawn at the 50% probability level).
For both structures the observed disorder between the trans NO and Br ligands and all hydrogen atoms have been omitted for clarity. For
2b the THF solvates are not shown, as well.
Table 2. Selected Bond Lengths (Å) and Bond Angles (deg) for 2b,c
(values of disordered atoms are not given)
The room-temperature NMR spectra of 4a,b were interpreted
in terms of hindered ethylene rotation and prefered alignment
of the CdC bond along the P-Re-P vector.14–17 This observa-
tion is consistent with those of the related Re(NO)L2Br2(η2-
C2H4) structures, where the same olefin orientation was
found.7b,18–21 Two 1H NMR resonances for two pairs of ethylene
Z-protons and additionally a single 13C NMR resonance
provided evidence for this. The two hydride ligands HA (trans
to NO) and HB (trans to ethylene) are observed as doublets of
triplets: -0.75 Re-HA, -5.92 Re-HB for 4a and -0.68
Re-HA, -5.51 Re-HB for 4b (compare ref 7a7a).
2b
2c
Re(1)-P(1)
2.5138(18)
2.5085(18)
2.065(7)
2.5804(10)
172.60(7)
86.31(5)
92.74(16)
86.84(5)
93.89(16)
175.83(17)
2.4760(10)
2.4608(10)
2.079(4)
2.5608(6)
173.51(3)
89.89(3)
90.35(9)
87.29(3)
92.81(9)
176.60(10)
Re(1)-P(2)
Re(1)-N(2)
Re(1)-Br(1)
P(1)-Re(1)-P(2)
P(1)-Re(1)-Br(1)
P(1)-Re(1)-N(2)
P(2)-Re(1)-Br(1)
P(2)-Re(1)-N(2)
Br(1)-Re(1)-N(2)
Protonation of 4a,b with an equimolar amount of HBF4 · OEt2
produced the monohydrido tetrafluoroborato compounds [Re-
(H)(NO)(PR3)2(η2-C2H4)(BF4)] (R ) iPr 5a, cy 5b) (Scheme
2) presumably via initial generation of unstable cationic H2
complexes, in which the H2 ligands then get replaced with the
complexes [Re(H)(η2-BH4)(NO)(PR3)2] (3) (R ) iPr a, cy b)
(Scheme 2). 3a,b were obtained earlier by the reaction of the
dihydrogen complexes [Re(Br)2(η2-H2)(NO)(PR3)2] with
[NBu4]BH4.4 In contrast to this reaction mode, substitution with
sterically less hindered phosphines as in the [Re(NO)-
(MeCN)(PMe3)2Cl2] complex afforded in the reaction with
[BH4]- reduction of the CN triple bond6,13 or under different
reaction conditions formation of the dihydrido trisphosphine
species [Re(H)2(NO)(PMe3)3]. Removal of the BH3 moieties
of 3a,b was achieved in the presence of THF, forming
H3B · THF and ethylene (1 bar). The reactions to generate the
substitution compounds [Re(H)2(η2-C2H4)(NO)(PR3)2] (R ) iPr
4a, cy 4b) were instantaneous (Scheme 2).
-
BF4 anion. 5a,b were characterized by their analytical and
spectroscopic data, and their structures were confirmed by an
exemplary single-crystal X-ray diffraction study of 5b. The
molecular structure is shown in Figure 3, and selected bond
(14) Saillard, J. Y.; Hoffmann, R. J. Am. Chem. Soc. 1984, 106, 2006–
2026.
(15) Dedieu, A. Transition Metal Hydrides; VCH: New York, 1992.
(16) Jean, Y.; Eisenstein, O.; Volatron, F.; Maouche, B.; Sefta, F. J. Am.
Chem. Soc. 1986, 108, 6587–6592.
(17) Eckert, J.; Kubas, G. J.; Hall, J. H.; Hay, P. J.; Boyle, C. M. J. Am.
Chem. Soc. 1990, 112, 2324–2332.
(18) Kubas, G. J.; Ryan, R. R.; Swanson, B. I.; Vergamini, P. J.;
Wasserman, H. J. J. Am. Chem. Soc. 1984, 106, 451–452.
(19) Kubas, G. J.; Unkefer, C. J.; Swanson, B. I.; Fukushima, E. J. Am.
Chem. Soc. 1986, 108, 7000–7009.
(20) Kubas, G. J. Acc. Chem. Res. 1988, 21, 120–128.
(21) Casey, C. P. Science 1993, 261, 668–668, and references therein.
(22) Chen, J. Y.; Grundy, k. R.; Robertson, K. N. Can. J. Chem. 1989,
67, 1187.
(23) Albertin, G.; Antoniutti, S.; Bacchi, A.; Fregolent, B.; Pelizzi, G.
Eur. J. Inorg. Chem. 2004, 1922–1938.
(24) (a) Feracin, S.; Burgi, T.; Bakhmutov, V. I.; Eremenko, I.;
Vorontsov, E. V.; Vimenits, A. B.; Berke, H. Organometallics 1994, 13,
4194–4202. (b) Nietlispach, D.; Bakhmutov, V. I.; Berke, H. J. Am. Chem.
Soc. 1993, 115, 9191–9195.
4a,b were characterized by spectroscopic means (IR, 1H,
31P{1H}, and 13C{1H} NMR). A satisfactory elemental analysis
was obtained for 4a, but not for 4b presumably due to its liquid
nature. In both cases the ATR IR spectrum and the spectrum in
KBr indicated the presence of the coordinated ethylene (4a
ν(C-H) 2925, 2875, 2835 cm-1, 4b ν(C-H), 2929, 2848
cm-1). ν(CdC) bands were not detected. The coordinated NO
ligand gave rise to ν(NO) bands at 1619 (4a) and 1614 cm-1
(4b).
(13) Hillier, A. C.; Fox, T.; Schmalle, H. W.; Berke, H. J. Organomet.
Chem. 2003, 669, 14–24.

Rhenium Nitrosyl Complexes for Hydrogenations
Organometallics, Vol. 27, No. 14, 2008 3477
1
The H NMR spectra of compounds 5a,b showed unusual
low-field resonances for the hydride ligands at 6.38 and 6.58
ppm, which appeared as doublets of triplets due to coupling
with one fluorine atom and two magnetically equivalent
phosphine ligands. This together with doublets observed at 32.5
-
and 26.2 ppm in the 31P{1H} NMR spectra suggests that BF4
coordination is persistent in solution. Hindered rotation of the
Re-bound ethylene at room temperature as perhaps suggested
1
by the X-ray structure of 5b is not supported by the H NMR
spectra of 5a,b, since for 5a the corresponding resonances are
broad and have no specific structure, and in the case of 5b they
are buried under the signals of the cyclohexyl groups. In the
IR spectra of 5a,b the ν(NO) absorptions are shifted by 65 and
62 cm-1 to higher wavenumbers in comparison with 4a,b,
confirming the cationic nature of these species.
The protonation of 4a,b occurred regioselectively in accord
with the findings for the protonation of the structurally related
trisphosphine rhenium dihydride with HClO4, giving the
[Re(H)(NO)(CO)(PPh3)3(ClO4)] complex with the hydride
ligand assigned also cis to NO.22 The protonation of the
phosphonite dihydride complex [Re(H)2(NO)(PPh2OEt)3] ap-
plying again strong acids such as HBF4 · OEt2 and CF3SO3H
was found to produce the thermally unstable cis-
[Re(H)(NO)(PPh2OEt)3(Y)] species (Y ) BF4 or CF3SO3),
which were trapped in its stereochemistry by regiospecific
replacement of the Y group with hydrazines, forming cis-
[Re(H)(NO)(NH2NHR)(PPh2OEt)3] compounds.23 However, in
the case of the [Re(H)2(NO)(CO)(PR3)2] compounds (R ) Me,
iPr, OiPr) the protonation with the weaker acid CF3COOH was
stereochemically different, generating trans H/NO complexes
of the [Re(H)(NO)(CO)(PR3)2(OOCF3)]24a type. Summarizing
these observations it is anticipated that the regioselectivity of
the protonation of cis-ReH2(NO)(PR3)2L compounds follows
roughly the acid strength. Stronger acids protonate the H ligand
trans to NO, which appears to be the slightly more negatively
charged (“hydridic”) H positions, as established by measure-
ments of the deuterium quadrupole coupling constants of the
corresponding deuterides.24b Weaker acids protonate and sub-
stitute trans to L.
Figure 3. ORTEP drawing of the molecular structure of 5b (thermal
ellipsoids are drawn at the 30% probability level). The toluene
solvate and selected hydrogen atoms have been omitted for clarity.
Table 3. Selected Bond Lengths (Å) and Bond Angles (deg) for 5b
Re(1)-P(1)
2.4813(14) N(1)-Re(1)-P(1)
2.4817(13) N(1)-Re(1)-P(2)
93.94(15)
87.50(15)
81.17(17)
84.12(17)
90.85(9)
88.24(8)
Re(1)-P(2)
Re(1)-N(1)
Re(1)-C(37)
Re(1)-C(38)
Re(1)-F(1)
C(37)-C(38)
N(1)-O(1)
F(1)-B(1)
P(1)-Re(1)-P(2)
N(1)-Re(1)-F(1)
N(1)-Re(1)-C(37) 96.8(2)
N(1)-Re(1)-C(38) 96.8(2)
1.704(5)
2.215(5)
2.227(5)
2.177(3)
1.404(8)
1.219(6)
1.485(7)
146.83(4)
F(1)-Re(1)-C(37)
F(1)-Re(1)-C(38)
F(1)-Re(1)-P(1)
F(1)-Re(1)-P2
C(37)-Re(1)-C(38) 36.9(2)
C(37)-Re(1)-P(1)
C(37)-Re(1)-P(2)
C(38)-Re(1)-P(1)
120.66(15)
91.96(15)
83.98(16)
128.81(16)
175.6(4)
175.19(17) C(38)-Re(1)-P(2)
Re(1)-N(1)-O(1)
Re(1)-F(1)-B(1)
152.3(4)
III. Catalytic Explorations
distances and bond angles are given in Table 3. The coordination
sphere of 5b is pseudo-octahedral with the hydride cis to NO,
which became evident from the X-ray diffraction study showing
vacancy at this location. The phosphine ligands in 5b are
markedly bent toward the H ligand (P(1)-Re-P(2) ) 146.83(4)°)
favored by steric and electronic factors.25,26 The CdC distance
of 1.404(8) Å is close to that in the complex [Re(cy2PCH2SiMe2-
NSiMe2CH2Pcy2)(C-CH3)(C2H4)]27 (1.422(3) Å) and is sub-
stantially elongated compared to free ethylene (1.337(2) Å).28
The ethylene ligand is found in a conformation parallel to the
P-Re-P axis, maximizing π back-bonding in this orientation.
The nitrosyl ligand is approximately linear (Re-N-O angle
of 175.6(4)°) with a Re-N distance of 1.704(5) Å in accordance
with the values found in the literature.5 Related to this, the
N(1)-O(1) distance of 1.219(6) Å lies in the range 1.10-1.38
Å expected for linear NO+ type binding.5,29
IIIa. Reactions of 4a,b with Hydrogen and H2/D2 Scram-
bling. 4a,b were reacted at room temperature with H2 in benzene
or toluene with hydrogenation of the ethylene ligand to ethane
and formation of the classical tetrahydride species [Re(H)4-
(NO)(PR3)2] (R ) iPr 6a, cy 6b)4 (Scheme 3). 31P NMR
monitoring at room temperature revealed that the reaction time
is dependent on the H2 pressure: it took 30 min with a p(H2) of
1.4 bar, but approximately 90 min when p(H2) was 0.7 bar.
The formation of ethane was confirmed by a singlet at 0.76
1
ppm in the H NMR spectrum.
Scheme 3 sketches a possible mechanism for the hydrogenation
process of the ethylene ligand. The pathway is assumed to start
with C2H4 insertion into a Re-H bond of 4a,b and subsequent
oxidative addition of H2. The formed ethyl trihydrides undergo
reductive elimination of C2H6, leaving a vacant site, to which H2
can eventually be added, forming 6a,b. Previous studies on 6a,b
made it plausible that these compounds have approximate pentagonal-
bipyramidal geometries with a hydride and the NO group in apical
positions and three hydrides and the two phosphines in the
equatorial plane. The 1H NMR spectrum of 6a,b showed at room
(25) Van der Zeijden, A. A. H.; Sontag, C.; Bosch, H. W.; Shklover,
V.; Berke, H.; Nanz, D.; Von Philipsborn, W. HelV. Chim. Acta 1991, 74,
1194–1204.
(26) Peters, J. C.; Hillhouse, G. L. Polyhedron 1994, 13, 1741–1746.
(27) Ozerov, O. V.; Huffman, J. C.; Watson, L. A.; Caulton, K. G.
Organometallics 2003, 22, 2539–2541.
(28) Bartell, L. S.; Roth, E. A.; Hollowel, C.; Kuchitsu, K.; Young, J. E.
J. Chem. Phys. 1965, 42, 2683–2686.
(29) Richter-Addo, G. B.; Legzdins, P. Metal Nitrosyl; Oxford University
Press: Oxford, 1992.

3478 Organometallics, Vol. 27, No. 14, 2008
Choualeb et al.
Table 5. Results of Catalytic Hydrosilylation of Cyclohexene and
Ketones
Scheme 3
cat/sub
cat. (mol %)
temp time
TOF
conv
(%)
substrate
(°C)
(h)
(h-1
)
cyclohexene/Et3SiH
PhCOMe/Ph3SiH
PhCOMe/Ph3SiH
PhCOMe/Et3SiH
PhCOMe/Et3SiH
4a
4a
4b
4a
4b
0.5
0.1
0.5
0.5
0.5
80
70
70
70
70
3
2
2
0.25
0.25
54
500
100
800
800
81
100
100
100
100
4b good activity with 100% conversion. Monitoring the catalytic
hydrogenation reaction of phenyl acetylene with 1H NMR
spectroscopy revealed selective formation of styrene, and under
the given conditions styrene could not be hydrogenated further
to ethyl benzene. For the cyclic olefin cyclohexene the reaction
time was quite long without reaching completion of the
conversion. Hydrogenation of the imine PhCHdNPh was
sluggish, with both derivatives 4a,b generating the correspond-
ing amine at such a slow pace that the reaction could not easily
be distinguished from a stoichiometric process. The catalytic
performances of 4a,b were moderate, and as far as the small
number of selected substrates allows to conclude some chemose-
lectivity can be deduced in favor of olefinic species and ketones.
There was no great difference in the performance of 4a and
4b.
IIIc. Catalytic Activity of 4a,b in Homogeneous Hydrosi-
lylations. The catalytic activity of 4a,b in hydrogenations
prompted us to study also hydrosilylations, which are considered
to be related to hydrogenations.31 Traditional hydrosilylation
catalysts are Pt-32 or Rh-based,33 although several highly active
early transition metals34,35 and lanthanide-based catalysts36 have
also been reported. In contrast, efforts to develop homogeneous
rhenium-based catalysts for hydrosilylations with rhenium in
low oxidation states have been limited. For instance the rhenium
dinitrosyl complexes [Re(PiPr3)2(NO)2][B(C6F5)4], [Re(H)-
(PiPr3)2(NO)(NOB(C6F5)3], and [Re(H)(PiPr3)2(NO)(NOEt)]-
[(B(C6F5)4] were found to be effective in ketone hydrosilylation.2
The progress of each reaction according to Table 5 was
monitored by NMR spectroscopy, and the identity of each
hydrosilylation product was assured by 1H NMR spectroscopy
and GC-MS. As a general manifestation the rates of hydrosi-
lylations normally do not follow the same trends as for
hydrogenations. This is also seen in this work. For instance
hydrosilylation of the linear olefin 1-hexene and the imine of
Table 4 could not be achieved at all, while these substrates
showed at least some hydrogenation activities. On the other hand
the catalytic hydrosilylations of cyclohexene and benzophenone
with either Et3SiH or Ph3SiH and 4a,b showed much better
performances than in the hydrogenation cases. The hydrosily-
lations of acetophenone even rapidly and selectively produced
products over the course of 15 to 20 min in the case of Et3SiH
and 2 h in the case of Ph3SiH (Table 5).
Table 4. Results of Catalytic Hydrogenation of Alkenes, Alkynes,
Ketones, And Imines with H2 under Pressure
cat./sub p(H2)
cat. (mol %) (bar) (°C)
T
time TOF
(h)
conv
(%)
substrate
1-hexene
(h-1
)
4a
4b
4a
4b
1.7
1.2
1
1.2
1.8
1.2
1.2
1.2
0.6
0.6
68
75
70
75
65
65
65
68
65
65
75
70
80 14
70
80 17.5
80 22.0
80
80
80
80
3
1.5
17
47
0.8
24
1
0.6
85
92.5a
24
29
33
16
46
100
92
4
cyclohexene
1
Ph-CHdN-Me 4a
4b
Ph-CO-Me
4a
4b
4a
4b
2.33 16
5
5
2
17
31
3.3
Ph-Ct CH
a Mixture with trans-2-hexene (7.5%).
temperature in toluene-d8 two broad high-field signals at -1.45
and -7.2 ppm, indicating at least two types of hydride ligands,
and the broadness of the signals points to dynamic behavior. Indeed
at -50 °C and below, the spectra split further into three resonances
(multiplets) in a 2:1:1 ratio at -1.55, -1.80, and -7.09 ppm. Under
C2H4 6a,b were converted back to 4a,b, promoting again hydro-
genation of C2H4 to C2H6 with the characteristics of a catalytic
reaction (Vide infra). This chemistry contrasts somewhat the H2/
C2H4 reaction found for the [(cy2PCH2SiMe2NSiMe2CH2Pcy2)-
ReH4] complex, leading eventually to a [(cy2PCH2SiMe2NSiMe2-
CH2Pcy2)ReH(C-CH3)] ethylidyne species involving C-H activa-
tion steps.27,30
In addition to hydrogenation observed for 4a,b, instantaneous
H2/D2 scrambling was observed to give HD at room temperature
when solutions of 4a,b were placed under 1.2 bar of an
equimolar mixture of H2 and D2. The 1H NMR spectra proved
equilibration to form HD, which can be explained assuming an
equilibrium between the coordinatively unsaturated [ReH2-
(NO)(PR3)2] derivatives (R ) iPr, cy) and the dihydrides 6a,b.4
Toggling back and forth between these species is accompanied
by addition and elimination of the various isotopomers of H2
(Scheme 3).
IIIb. Catalytic Activity of 4a,b in Homogeneous Hydro-
genations. Using 4a,b catalytic hydrogenations of several
olefins, alkynes, ketones, and imines were explored in benzene
in a steel autoclave at 70 or 80 °C and under pressures of around
70 bar of H2 (Table 4). For volatile, liquid substrates and
products the catalysts were separated by vacuum transfer or by
exposing the reaction mixture to air and filtration through silica.
For linear olefins, ketones, and alkynes the hydrogenations
furnished moderate turnover frequencies with however satisfying
conversions. The hydrogenation of acetophenone revealed with
IIId. Mechanism of the Hydrogenations and Hydrosily-
lations with 4a,b. A generalized catalytic cycle for the
hydrogenation and hydrosilylation with 4a,b is suggested in
Scheme 4. Starting from 4a,b the catalytic hydrogenations and
(31) Hiyama, T.; Kusumoto, T. In ComprehensiVe Organic Synthesis;
Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991.
(32) Speier, J. L. AdV. Organomet. Chem. 1977, 17, 407.
(33) Chalk, A. J. J. Organomet. Chem. 1970, 21, 207–213.
(34) Molander, G. A.; Dowdy, E. D.; Noll, B. C. Organometallics 1998,
17, 54–3758, 37.
(35) Molander, G. A.; Knight, E. E. J. Org. Chem. 1998, 63, 7009–
7012.
(30) Ozerov, O. V.; Watson, L. A.; Pink, M.; Caulton, K. G. J. Am.
Chem. Soc. 2004, 126, 6363–6378.
(36) Fu, P. F.; Brard, L.; Li, Y. W.; Marks, T. J. J. Am. Chem. Soc.
1995, 117, 7157–7168.

Rhenium Nitrosyl Complexes for Hydrogenations
Organometallics, Vol. 27, No. 14, 2008 3479
Scheme 4
none (C6D6, toluene-d8, THF-d8) or P2O5 (CD2Cl2, CD3CN) and
vacuum transferred for storage in Schlenk flasks fitted with Teflon
valves. NMR experiments were carried out on a Varian Gemini
300, Varian Mercury 200, or Bruker DRX 500 spectrometer using
5 mm diameter NMR tubes equipped with Teflon valves, which
allow degassing and further introduction of gases into the probe.
1
Chemical shifts are given in ppm. H and 13C{1H} NMR spectra
were referenced to the residual proton or 13C NMR resonances of
the deuterated solvent. 31P chemical shifts are relative to 85%
H3PO4. Microanalyses were carried out at the Anorganisch-
chemisches Institut of the University of Zu¨rich. IR spectra were
recorded on a Bio-Rad FTS-45 spectrometer. [NMe4]2[ReBr5(NO)]
was prepared analogous to ref 4.
Preparation of mer-[Re(NO)(MeCN)3Br2] (1a). A mixture of
[NMe4]2[ReBr5(NO)] (3.0 g, 3.9 mmol) and an excess of Zn powder
(2.56 g, 39 mmol) in 50 mL of MeCN was stirred for 3 days at
room temperature. After filtration the residue was washed with
MeCN (4 × 5 mL) and the solvent was removed in Vacuo to leave
behind an orange solid, which was washed with water (3 × 10
mL) and dried in Vacuo, which removes the MeCN solvate. Yield
of 1a: 1.45 g (73.8%). IR (ATR, cm-1): 1691 (vs, ν(NO)). 1H NMR
(300.1 MHz, CD3CN, ppm): δ 2.96 (s, 6H), 2.94 (s, 3H). 13C{1H}
NMR (125.8 MHz, CD3CN, ppm): δ 4.23 (s, CH3), 133.7 (s, 2
CN), 134.3 (s, CN). Anal. Calcd for C6H9N4OBr2Re: C, 14.44; H,
1.82; N, 11.22. Found: C, 14.60; H, 1.77; N, 11.14.
Preparation of [Re(NO)(THF)(MeCN)2Br2] (1b) from
[NMe4]2[ReBr5(NO)] via 1a. An excess of Zn (0.80 g, 12.3 mmol)
was added to a solution of [NMe4]2[ReBr5(NO)] (1.3 g, 1.7 mmol)
in 100 mL of MeCN. The mixture was stirred at room temperature
for 3 days, the orange solution of 1a was filtered, the residue was
washed with MeCN (4 × 5 mL), and the solvent was evaporated
in Vacuo. The solid was extracted with THF and recrystallized at
room temperature from THF/pentane to afford red crystals of 1b
(0.63 g, 1.26 mmol, 73%) after 2 days. IR (ATR, cm-1): 2277 (w,
hydrosylilations proceed first with insertion of the ethylene
ligand into the Re-H bond, and subsequently loss of ethane
occurs to give the 16e- species [ReH2(NO)(PR3)2]. On a side-
track the [ReH2(NO)(PR3)2] derivatives and 6a,b are in equi-
librium with each other following the H2/D2 scrambling pathway
of Scheme 3. The substrates Y ) CR1R2 (Y ) CH2, NH2, O)
are then added to the unsaturated species [ReH2(NO)(PR3)2],
which then undergoes insertion into the Re-Hcis bond, leaving
again a vacant site, to which H2 is supposed to be added.
Reductive elimination leads to liberation of the hydrogenated/
hydrosilated alkane/amine/alcohol products.
1
ν(MeCt N)), 1685 (vs, ν(NO)). H NMR (500.25 MHz, CD3CN,
ppm): 3.64 (m, 4H, (CH2CH2O)-Re), 2.98 (s, 6H, MeCN-Re), 1.81
(m, 4H, (CH2CH2O)-Re). 13C NMR (125.8 MHz, CD3CN, ppm):
133.9 (s, MeCN), 68.3 (s, (CH2CH2O)-Re), 26.3 (s, (CH2CH2O)-
Re) 4.3 (s, MeCN-Re). Anal. Calcd for C8H14Br2N3O2Re (530.23):
C, 18.12; H, 2.66; N, 7.92. Found: C, 18.4; H, 2.60; N, 8.03.
Preparation of [Re(NO)(PiPr3)2(MeCN)Br2] (2a). A solution
of [Re(NO)(THF)(MeCN)2Br2] (0.22 g, 0.42 mmol) and excess
PiPr3 (0.42 mL, 2.2 mmol) was heated in 40 mL of THF for 12 h.
The solution was filtered through Celite, and the solvent and the
excess phosphine were removed in Vacuo. Recrystallization of the
residue from THF/pentane afforded light orange crystals after 1
week at -30 °C. Yield of 2a: 0.25 g, 0.33 mmol, 80%. IR (ATR,
IV. Conclusion
In this paper the syntheses of the new rhenium precursors
[Re(NO)(MeCN)3Br2],[Re(NO)(THF)(MeCN)2Br2],and[Re(NO)-
(MeCN)(PR3)2Br2] were developed to establish a reactive
hydride chemistry with nitrosyl phosphine rhenium derivatives.
Key compounds were the dihydride-ethylene complexes [Re-
(H)2(η2-C2H4)(NO)(PR3)2]. Exploratory studies revealed a quite
unexpected olefin and hydrogen chemistry, which could be
turned into catalytic hydrogenations and hydrosilylations based
on the [Re(H)(NO)(PR3)2]+ fragments as the persistent and
invariant units in these catalyses. Although the performance of
these reactions was not yet optimum and comparable to the level
of full competitiveness with existing such processes, these
findings further promote rhenium as a metal with potential in
homogeneous catalysis.
1
cm-1): 2266(w, ν(MeCt N)), 1684 (vs, ν(NO)). H NMR (300.1
MHz, CD2Cl2, ppm): 3.07 (s, 3H, MeCN-Re), 3.03-2.86 (m, 6H,
(CH3)2CHP), 1.47-1.34 (m, 36H, (CH3)2CHP). 31P{1H} NMR
(80.9 MHz, C6D6, ppm): -7.2 (s). 13C{1H} NMR (75.5 MHz, C6D6,
ppm): 24.4 (t, J(PC) ) 10.7 Hz, (CH3)2CHP), 20.1 and 19.5
(2s,(CH3)2CHP). Anal. Calcd for C20H45Br2N2OP2Re (737.546) · 1/
4pentane: C, 33.78; H, 6.40; N, 3.71. Found: C, 33.92; H, 6.30; N,
3.80.
Preparation of [Re(NO)(Pcy3)2(MeCN)Br2] (2b). A solution
of [Re(NO)(THF)(MeCN)2Br2] (0.11 g, 0.21 mmol) and excess Pcy3
(0.30 g, 1.0 mmol) was heated in 35 mL of THF overnight. The
solution was filtered through Celite, and about 70 mL of hexane
was layered over this solution. After 1 week at room temperature,
light orange crystals were collected, washed with MeCN, cold
toluene (2 × 5 mL), cold THF (2 × 5 mL), and pentane, and dried
in Vacuo to give 2b (0.14 g, 0.15 mmol, 71%). IR (KBr, cm-1):
V. Experimental Section
All operations were carried out under a nitrogen atmosphere using
a M. Braun 150 G-B glovebox. The solvents were dried over
sodium/benzophenone (THF, Et2O, hydrocarbons) or P2O5 (CH2Cl2,
MeCN) and distilled under N2 prior to use. The deuterated solvents
used in the NMR experiments were dried over sodium/benzophe-
1
2259(w, ν(MeCt N)), 1679 (vs, ν(NO)). H NMR (300.1 MHz,
CD2Cl2, ppm): 3.08 (s, 3H, MeCN-Re), 2.78-1.27 (m, 66H,
P(C6H11)3). 31P{1H} NMR (121.5 MHz, CD2Cl2, ppm): -19.1 (s).
13C{1H} NMR (75.5 MHz, CD2Cl2, ppm): 35.5 (t, J(PC) ) 10.1

3480 Organometallics, Vol. 27, No. 14, 2008
Choualeb et al.
Hz, P(C6H11)3), 29.5, 28.4 and 27.1 (3s, P(C6H11)3). Anal. Calcd
for C38H69Br2 N2OP2Re (977.93): C, 46.67; H, 7.11; N, 2.86. Found:
C, 46.93; H, 7.00; N, 2.95.
(0.031 g, 0.054 mmol) in 8 mL of ether at -30 °C. The mixture
was allowed to stir at room temperature for 15 h, then filtered over
Celite. The solvent was removed in Vacuo, and the residue was
washed with pentane, extracted with toluene, and recrystallized from
toluene/pentane at -30 °C to afford the oily yellow complex 5a
(0.023 g, 0.04 mmol, 65%). IR (ATR, cm-1): 2969, 2936, 2878
(s, ν(C-Η)), 2025 (w, ν(Re-H)), 1684 (vs, ν(NO)). 1H NMR
(200.0 MHz, toluene-d8, ppm): 6.38 (dt, 1H, 2J(HF) ) 5.8 Hz,
2J(PH) ) 34.8 Hz), 2.85 (br, 4H, H2CdCH2), 2.58-2.37 (m, 6H,
(CH3)2CHP), 1.24-1.12 (m, 18H, (CH3)2CHP). 31P{1H} NMR
(80.9 MHz, toluene-d8, ppm): 32.5 (d, 2J(PF) ) 16.5 Hz). 13C{1H}
NMR (75.5 MHz, toluene-d8, ppm): 35.7 (br, H2Cd), 26.6 (t, J(PC)
) 12.3 Hz, (CH3)2CHP), 19.6 and 19.5 (2s,(CH3)2CHP). Anal.
Calcd for C20H47BF4NOP2Re (652.55): C, 36.81; H, 7.26; N, 2.14.
Found: C, 36.93; H, 7.45; N, 2.29.
Preparation of [Re(NO){P(p-tol)3}2(MeCN)Br2] (2c). A solu-
tion of [Re(NO)(THF)(MeCN)2Br2] (0.078 g, 0.147 mmol) and
excess of P(p-tol)3 (0.234 g, 0.772 mmol) was heated in 40 mL of
THF for 15 h. The solution was then concenterd, filtered over Celite,
and recrystallized at room temperature from THF/pentane to afford
after 5 days light orange crystals of 2c, which were dried in Vacuo
(0.117 g, 0.114 mmol, 77%). IR (KBr, cm-1): 2279(w, ν(MeCt N)),
1700 (vs, ν(NO)). 1H NMR (300.1 MHz, CD2Cl2, ppm): 7.75-7.19
(m, 24H, P(p-(C7H7)3), 2.37 (s, 18H, P(p-(C7H7)3), 1.77 (s, 3H,
MeCN-Re). 31P{1H} NMR (121.5 MHz, CD2Cl2, ppm): -6.3 (s).
13C{1H} NMR (75.5 MHz, CD2Cl2, ppm): 140.6 (s), 135.17 (m),
129.6 (t, J(PC) ) 24.1 Hz, 129.01 (m), 21.6 (s, P(p-(C7H7)3), 14.4
(s, MeCN-Re), 3.7 (s, MeCN-Re). Anal. Calcd for
C44H45Br2N2OP2Re (1025.8): C, 51.51; H, 4.42; N, 2.73. Found:
C, 51.41; H, 4.48; N, 3.15.
Preparation of [Re(H)(η2-C2H4)(NO)(Pcy3)2][BF4] (5b). 5b
was prepared by the reaction of HBF4 · ether (54% in ether, 0.022
g, 0.07 mmol) diluted with 1 mL of ether with 4b (0.060 g, 0.07
mmol) in a mixture of 10 mL ether/toluene (4:1) at -30 °C. The
mixture was allowed to stir at room temperature for 17 h and then
filtered over Celite. The solvents were removed in Vacuo, and the
residue was washed with pentane and dried in Vacuo to afford 5b
as a yellow powder. Yield: 0.047 g, 0.05 mmol, 71%. Crystals
suitable for X-ray diffraction were obtained from a concentrated
solution of 5b in toluene by slow evaporation and were dried in
Vacuo. IR (ATR, cm-1): 2925, 2851 (s, ν(C-Η)), 1963 (w,
Preparation of [Re(H)(η2-BH4)(NO)(PiPr3)2] (3a). A solution
of 2a (0.157 g, 0.21 mmol) and excess of NaBH4 (0.036 g, 0.95
mmol) in 20 mL of THF was stirred at room temperature for 12 h.
The orange solution was filtered over Celite, and the solvent was
evaporated under vacuum. Extraction with pentane affords pure
[Re(H)(η2-BH4)(NO)(PiPr3)2] (3a) (0.095 g, 0.17 mmol, 81%). All
the spectroscopic data are in agreement with those previously
reported in the literature.4
Preparation of [Re(H)(η2-BH4)(NO)(Pcy3)2] (3b). A solution
of 2b (0.082 g, 0.08 mmol) and excess NaBH4 (0.015 g, 0.40 mmol)
in 20 mL of THF was stirred at room temperature for 24 h. The
orange solution was filtered over Celite, and the solvent was
evaporated under vacuum. Extraction with a mixture of pentane/
1
ν(Re-H)), 1687 (vs, ν(NO)). H NMR (200.0 MHz, toluene-d8,
ppm): 6.58 (dt, 1H, 2J(HF) ) 4.4 Hz, 2J(PH) ) 34.3 Hz), 2.82-0.89
(m, 70H, H2CdCH2 and P(C6H11)3). 31P{1H} NMR (80.9 MHz,
toluene-d8, ppm): 26.2 (d, 2J(PF) ) 17.5 Hz). 13C{1H} NMR (75.5
MHz, toluene-d8, ppm): 37.3 (t, J(PC) ) 11.4 Hz, P(C6H11)3), 36.2
(br, H2Cd), 31.58 and 31.20, 29.85 and 29.57, 28.28 and 28.21,
26.85 and 26.54 (4 × 2 s, P(C6H11)3). Anal. Calcd for
C38H71BF4NOP2Re (893.94). C, 51.11; H, 8.01; N, 1.57. Found:
C, 51.40; H, 8.21; N, 1.53.
toluene
(9:1)
affords
pure
[Re(H)(η2-BH4)(NO)-
(Pcy3)2] (3b) (0.06 g, 0.08 mmol, 92%). All the spectroscopic data
are in agreement with those previously reported in the literature.4
Preparation of [Re(H)2(η2-C2H4)(NO)(PiPr3)2] (4a). The com-
plex 3a (0.08 g, 0.15 mmol) was dissolved in 15 mL of THF in a
60 mL Young tap Schlenk vessel and sealed under 1 bar of C2H4.
The solution was stirred for 1 h, and then the solvent and the gas
were removed under reduced pressure. The residue was extracted
with pentane to give pure pale yellow, viscous 4a (0.068 g, 0.12
mmol, 83%). IR (ATR, cm-1): 2925, 2875, 2835 (s, ν(C-Η)), 1843
(w, ν(Re-H)), 1619 (vs, ν(NO)). 1H NMR (500.2 MHz, C6D6,
ppm): 2.24, (br, 2H, H2CdCH2), 2.12 (br, 2H, H2CdCH2),
3.07-2.97 (m, 6H, (CH3)2CHP), 1.57-1.41 (m, 18H, (CH3)2CHP),
Catalytic Hydrogenation Using Complexes 4a,b under
68-75 bar of H2. The reactions were carried out in a steel
autoclave. An appropriate amount of the catalyst (see ratios in Table
4) was dissolved in toluene-d8, and 1 mmol of 1-hexene, cyclo-
hexene, acetophenone, N-benzylidenemethylamine, or phenyl acety-
lene was added by a microsyringe. The autoclave was pressurized
with different H2 pressures (Table 4), and the reaction mixture was
stirred and heated to around 70-80 °C for several hours. The
reaction mixture was analyzed by NMR spectroscopy at given
reaction times. 1H NMR spectroscopy of the products: Hexane
(199.97 MHz, C6D6, 25 °C, ppm): 0.82 (m, J(H,H) ) 6.9 Hz, Me),
1.17 (br, CH2). Cyclohexane (199.97 MHz, C6D6, 25 °C, ppm):
1.40 (s). N-Methylbenzylamine (199.97 MHz, C6D6, 25 °C, ppm):
7.06 (m, br, CH Ph), 3.43 (br, CH2), 2.15 (br, Me), 2.04 (m, br,
NH). R-Methylbenzyl alcohol (199.97 MHz, C6D6, 25 °C, ppm):
1.30 (d, J(H,H) ) 6.5 Hz, CH3), 2.98 (br, OH), 4.62 (q, J(H,H) )
6.5 Hz, CH), 7.22 (m, CH Ph). Styrene (199.97 MHz, C6D6, 25
°C, ppm): 5.26 (d, J(H,H) ) 10.8 Hz, 1H CH2), 5.78 (d, J(H,H) )
17.4 Hz, 1H CH2), 6.75 (dd, J(H,H) ) 10.9 Hz, CH), 7.18-7.60
(m, CH Ph).
Catalytic Hydrosilylation with 4a,b. Complexes 4a,b were
mixed with the substances in a 1:1 ratio in C6D6 or toluene-d8.
The solution was transferred to a Young NMR tube and was frozen.
The N2 atmosphere was substituted by H2. The mixture was warmed
to the required temperature, and the NMR spectrum was recorded.
The conversions were determined by the integration of the olefin
and the alkane 1H NMR signals. Characteristic 1H NMR resonances
of the products: C6H11SiMe3 (199.97 MHz, toluene-d8, 80 °C, ppm):
1.39 (s, 16 H, Me, cy). PhCH(OSiEt3)Me (199.97 MHz, toluene-
d8, 80 °C, ppm): 1.38 (d, 3H, J(H,H) ) 6.3 Hz, Me), 4.75 (q, 1H,
J(H,H) ) 6.3 Hz, CH). PhCH(OSiPh3)Me (199.97 MHz, toluene-
1
2
1.39-1.31 (m, 18H, (CH3)2CHP), -0.75 (dt, H, J(HH) ) 6.9
Hz, 2J(PH) ) 35.9 Hz), Re-HA, -5.92 (dt, 1H, 2J(HH) ) 8.1 Hz,
2J(PH) ) 28.0 Hz, Re-HB). 31P{1H} NMR (121.5 MHz, C6D6,
ppm): 36.8 (s). 13C{1H} NMR (125.8 MHz, C6D6, ppm): 29.2 (t,
J(PC) ) 13.1 Hz, (CH3)2CHP), 23.1 (br, H2Cd), 21.0 and 19.3
(2s,(CH3)2CHP). The complex was a viscous liquid, and due to
this, a satisfactory elemental analysis could not be obtained.
Preparation of [Re(H)2(η2-C2H4)(NO)(Pcy3)2] (4b). Similar to
the synthesis of 4a, compound 4b (0.051 g, 0.06 mmol, 84%) was
obtained by the reaction of 3b (0.06 g, 0.08 mmol) and C2H4. IR
(KBr, cm-1): 2929, 2848 (s, ν(C-Η)), 1858 (w, ν(Re-H)),1614
1
(vs, ν(NO)). H NMR (300.1 MHz, toluene-d8, ppm): 2.28-0.88
2
(m, 70H, H2CdCH2 and P(C6H11)3), -0.68(dt, 1H, J(HH) ) 7.9
Hz, 2J(PH) ) 36.3 Hz, Re-HA), -5.51 (dt, 1H, 2J(HH) ) 7.7
Hz), 2J(PH) ) 25.7 Hz, Re-HB). 31P{1H} NMR (121.5 MHz,
toluene-d8, ppm): 27.5 (s). 13C{1H} NMR (75.5 MHz, CD2Cl2,
ppm): 39.7 (t, J(PC) ) 12.8 Hz, P(C6H11)3), 31.6 and 31.2 (2s,
H2CdCH2), 30.5, 29.5, 28.3, and 27.3 (4s, P(C6H11)3). Anal. Calcd
for C38H72NOP2Re (807.138) · 1/3pentane: C, 57.32; H, 9.22; N,
1.68. Found: C, 57.70; H, 9.34; N, 1.79.
Preparation of [Re(H)(η2-C2H4)(NO)(PiPr3)2][BF4] (5a). A
cooled, dilute solution of HBF4 · ether (54% in ether, 0.016 g, 0.054
mmol) in 1 mL of ether was added dropwise to a solution of 4a

Rhenium Nitrosyl Complexes for Hydrogenations
Organometallics, Vol. 27, No. 14, 2008 3481
Table 6. Summary of Crystallographic Data for Complexes 1a, 2b, 2c, and 5b
1a
2b
2c
5b
empirical formula
molecular weight
color
cryst syst
space group
a (Å)
C6H9Br2N4ORe, C2H3N
540.25
orange
triclinic
P1
8.1046(13)
9.4847(15)
10.0314(17)
86.04(2)
82.60(2)
85.370(19)
761.6(2)
2(C38H69Br2N2OP2Re), 3(C4H8O) C44H45Br2N2OP2Re
2(C38H71BF4NOP2Re), C7H8
2172.12
orange
1025.78
1877.95
pale yellow
monoclinic
C 2/c
35.9176(15)
12.8715(6)
18.6666(7)
90
99.542(5)
90
8510.4(6)
4
light orange
triclinic
j
P1
triclinic
j
P1
9.9073(12)
14.117(2)
17.523(2)
106.501(16)
93.603(15)
96.888(16)
2320.8(5)
1
10.8340(13)
12.4513(15)
15.6724(18)
79.551(14)
86.688(14)
76.017(14)
2031.9(4)
2
b (Å)
c (Å)
R (deg)
ꢀ (deg)
γ (deg)
V (Å3)
Z
2
calcd density (g cm-3
)
2.356
13.126
0.778-0.925
1.554
1.677
1.466
2.981
0.714-0.805
0.07 × 0.08 × 0.12
µ (mm-1
)
4.447
5.072
transmn range
cryst size (mm)
hkl limiting indices
F(000)
0.752-0.909
0.320-0.813
0.31 × 0.17 × 0.14
0.02 × 0.05 × 0.21
0.04 × 0.14 × 0.18
-11/11, -13/13, -14/14 -11/12, -18/17, -23/23
-15/15, -17/17, -22/22 -44/43, -15/15, -22/22
1012
496
1108
3880
θ limits (deg)
2.89-30.52
2.71-28.04
2.77-30.43
1.96-25.93
no. of measd reflns
no. of unique reflns
no. of params
12 842
25 597
32 318
32 427
4210
159
10 310
462
11 163
476
8207
450
R1[I > 2 (I)], R1 all data
0.0449, 0.0600
0.0409, 0.0932
0.0771, 0.0850
0.688
0.0314, 0.0577
0.0618, 0.0663
0.817
0.0299, 0.0489
0.0697, 0.0709
0.729
wR2[I > 2 (I)], wR2 all data 0.1200, 0.1350
GOF (for F2)
1.086
max./min.
-4.19, 3.06
-1.55, 1.13
-1.93, 1.11
-0.58, 1.64
d8, 80 °C, ppm): 1.44 (d, 3H, J(H,H) ) 6.2 Hz, Me), 5.17 (q, 1H,
J(H,H) ) 6.2 Hz, CH).
97 program.39 Interpretation of the difference electron density maps,
preliminary plot generation, and checking for higher symmetry were
done with PLATON40 and with the LEPAGE program.41 All heavy
atoms were refined with the program SHELXL-9742 using aniso-
tropic displacement parameters; more crystallographic details are
given in Table 6 and in the exptl_special_details of the CIF files
(see CCDC deposition numbers). Positions of H atoms were
calculated after each refinement cycle (riding model). Structural
plots were generated using ORTEP.43
Catalytic H2/D2 Scrambling. Complexes 4a,b were dissolved
in C6D6 and transferred to a Young tap NMR tube, and the solution
was frozen. The N2 atmosphere was removed and substituted by
1200 mbar of a 1:1 mixture of H2 and D2. The 1H NMR spectrum
showed that the equilibration was instantaneous at room temper-
1
1
ature. H NMR (300.0 MHz, toluene-d8, ppm): 4.41 (t, J(HD) )
43 Hz).
X-ray Structure Analyses of Compounds 1a, 2b, 2c, and
5b. All four crystals were protected in hydrocarbon oil and prepared
for the X-ray experiment by using a polarizing microscope. Selected
crystals of 1a · MeCN, 2 2b · 3 THF, 2c, and 5b · C6H5Me were
crystallized from MeCN saturated at 60 °C, THF/pentane, THF/
pentane, and toluene, respectively. They were mounted on the tip
of a glass fiber and immediately transferred to the goniometer of
an imaging plate detector system (Stoe IPDS diffractometer). The
crystals were cooled to 183(2) K in an Oxford Cryogenic System.
The crystal-to-image distances were set to 50, 60, 50, and 70 mm,
resulting in θmax values given in Table 4. For compounds 2b and
5b oscillation and for 1a and 2c rotation scan modes were applied.
A total of 8000 reflections with I > 6σ(I) were selected for the
cell parameter refinements of all four structures. A total of 12 842
(1a), 25 597 (2b), 32 318 (2c), and 32 427 (5b) diffraction intensities
were collected, of which 4210, 10 310, 11 163, and 8207 were
unique (Rint ) 8.70, 9.08, 5.98, and 5.35%) after data reduction.
Numerical absorption corrections37 based on 11, 6, 9, and 6 crystal
faces were applied with FACEitVIDEO and XRED.38 The four
structures were solved by the Patterson methods using the SHELXS-
Acknowledgment. This work was supported by the Swiss
National Science Foundation and the University of Zu¨rich.
We would like to thank Dr. Thomas Fox for his help in
recording some of the NMR spectra.
Supporting Information Available: Tables of atomic coordi-
nates, thermal parameters, bond distances, and angles for 1a, 2b,
2c, and 5b, respectively. This material is available free of charge
via the Internet at http://pubs.acs.org. This material has also been
deposited in.cif format with the Cambridge Crystallographic Data
Centre as supplementary publications CCDC 664340 (1a), CCDC
664341 (2b), CCDC 664342 (2c), and CCDC 664343 (5b). Copies
of the data can be obtained free of charge on application to CCDC,
12 Union Road, Cambridge CB2 1EZ, UK (fax: (+44)1223-336-
033; e-mail: deposit@ccdc.cam.ac.uk).
OM7011024
(39) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467.
(40) Spek, A. L. PLUTON, A computer program for the graphical
representation of crystallographic models; University of Utrecht: The
Netherlands, 1991-1997.
(37) Coppens, P.; Leiserowitz, L.; Rabinovich, D. Acta Crystallogr.
1965, 18, 1035.
(38) STOE-IPDS Software package, Version 2.92/1999; STOE & Cie:
Darmstadt, Germany, 1999.
(41) Lepage, Y. J. Appl. Crystallogr. 1987, 20, 264.
(42) Sheldrick, G. M. SHELXL 97: A program for crystal sructure
refinement; University of Go¨ttingen: Germany, 1997; Release 97-2.
(43) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.