Rhenium nitrosyl complexes bearing large-bite-angle diphosphines

Article abstract of DOI:10.1021/om200092y

A series of [ReBr₂(MeCN)(NO)(P∩P)] complexes (P∩P = 1,10-bis(diphenylphosphino)ferrocene (dppfc) (1a), 1,10- bis(diisopropylphosphino)ferrocene (diprpfc) (1b), 2,20-bis(diphenylphosphino) diphenyl ether (dpephos) (1c), 10,11-dihydro-4,5-bis(diphenylphosphino) dibenzo[b,f]oxepine (homoxantphos) (1d), 4,6-bis(diphenylphosphino)-10,10- dimethylphenoxasilin (Sixantphos) (1e)) were prepared with diphosphines varying in the P-Re-P bite angles. 1a,c-e were obtained from the reaction of [ReBr ₅(NO)][NEt₄]₂ with an excess of the respective diphosphine in MeCN or MeCN/THF mixtures at elevated temperatures. Compound 1b was obtained by an alternative route, cleaving the dinuclear [{ReBr(μ2- Br)(NO)(diprpfc)}₂] unit (2b) with MeCN. 2b was prepared from the reaction of [ReBr₅(NO)][NEt₄]₂ with diprpfc in EtOH. The reaction of 1a-d with HSiEt₂ gave the seven-coordinate [ReBr(H)₂(SiEt₃)(NO)(PnP)] compounds 4a-d, of which 4a,c,d are only stable in solution in the presence of HSiEt₃. The SiMe3 (4f) and SiCl₃ (4g) derivatives of 4b were also prepared by applying the reaction of 1b with HSiMe₃ and HSiCl₃. 1a,c,e, 2b, and 4f,g were structurally characterized. For 1c,e, 2b, and 4f,g NO/Br disorder was observed, which originates from the presence of two isomeric forms in the crystals of the respective compounds. For 1c,d fast interconversion of these isomers could be observed in their 31P{1H} NMR spectra at room temperature.

Full text of DOI:10.1021/om200092y

ARTICLE
pubs.acs.org/Organometallics
Rhenium Nitrosyl Complexes Bearing Large-Bite-Angle Diphosphines
Balz Dudle, Kunjanpillai Rajesh, Olivier Blacque, and Heinz Berke*
Institute of Inorganic Chemistry, University of Z€urich, Winterthurerstrasse 190, CH-8057 Z€urich, Switzerland
S Supporting Information
b
ABSTRACT: A series of [ReBr2(MeCN)(NO)(P∩P)] com-
plexes (P∩P = 1,10-bis(diphenylphosphino)ferrocene (dppfc)
(1a), 1,10-bis(diisopropylphosphino)ferrocene (diprpfc) (1b),
2,20-bis(diphenylphosphino)diphenyl ether (dpephos) (1c),
10,11-dihydro-4,5-bis(diphenylphosphino)dibenzo[b,f]oxepine
(homoxantphos) (1d), 4,6-bis(diphenylphosphino)-10,10-di-
methylphenoxasilin (Sixantphos) (1e)) were prepared with
diphosphines varying in the PꢀReꢀP bite angles. 1a,cꢀe were
obtained from the reaction of [ReBr5(NO)][NEt4]2 with an
excess of the respective diphosphine in MeCN or MeCN/THF
mixtures at elevated temperatures. Compound 1b was obtained by an alternative route, cleaving the dinuclear [{ReBr(μ2-
Br)(NO)(diprpfc)}2] unit (2b) with MeCN. 2b was prepared from the reaction of [ReBr5(NO)][NEt4]2 with diprpfc in
EtOH. The reaction of 1aꢀd with HSiEt3 gave the seven-coordinate [ReBr(H)2(SiEt3)(NO)(P∩P)] compounds 4aꢀd, of
which 4a,c,d are only stable in solution in the presence of HSiEt3. The SiMe3 (4f) and SiCl3 (4g) derivatives of 4b were also
prepared by applying the reaction of 1b with HSiMe3 and HSiCl3. 1a,c,e, 2b, and 4f,g were structurally characterized. For 1c,e,
2b, and 4f,g NO/Br disorder was observed, which originates from the presence of two isomeric forms in the crystals of the
respective compounds. For 1c,d fast interconversion of these isomers could be observed in their 31P{1H} NMR spectra at
room temperature.
’ INTRODUCTION
for binding and activation of substrates. Catalytic rhenium com-
plexes have therefore to be tuned for ligand lability, which was
thought to be accomplishable by ligand effects, such as cis
labilization via π donors and the trans influence and trans effect
of ligands, via ligands with variable electron counts and the use of
large-bite-angle diphosphines.
Rhenium indeed possesses substantial affinity for hydrogen so
that hydride and dihydrogen ligands are stabilized in compounds
with low and high coordination numbers (CN = 5,1 6,2 7,3 8,4 94).
Rhenium polyhydrides also exist and can be associated with
relatively high formal oxidation states of the rhenium centers.2,4
Often these polyhydrides were seen to be dynamic either by
polytopal rearrangements5 or by dihydride/dihydrogen ligand
transformations (Re(H2) / Re(H)2) via oxidative addition/
reductive elimination equilibria.6 These latter steps require the
ability of rhenium centers to undergo facile Re(n)/Re(nþII)
changes. Together with the high affinity of rhenium for olefins7
and acetylenes,8 this points to the general disposition of rhenium
compounds to enable hydrogenation catalysis.
Catalytic hydrogenation is an important toolkit facet of
modern organic synthesis. This area is, however, dominated by
homogeneous catalysts based on platinum-group metals.9 Al-
though these catalysts are as yet unmatched in activity and
selectivity, their use is to a certain extent problematic, since they
are expensive and too toxic10 for pharmaceutical applications.
Therefore, products have to be freed from these metals to the
ppm level11 and laborious catalyst recycling might be required.
New non platinum group element based hydrogenation catalyses
are thus sought to be developed. However, for the development
of alternative middle-transition-metal catalysts, such as rhenium
complexes, we face the difficulty that they possess a low tendency
to form 16e or even 14e complexes, an ability required in catalysis
In our group we systematically approached nitrosyl hydride
rhenium chemistry with the NO and H groups as trans effect and
trans influence ligands. The ReꢀNO fragment, in addition, was
thought to be especially suited for hydrogenations, since it also is
isoelectronic with RuꢀCO or RuꢀPR3 and RhꢀX fragments,
often encountered in hydrogenation12 and hydroformylation13
reactions. The idea to mimic ruthenium group chemistry with
isoelectronic rhenium fragments initiated developments in
[ReH(X)(L)(NO)(PR3)2] complexes (X = H, Br; L= labile
ligand, R = Cy, i-Pr) catalyzing hydrogenations,14 dehydrogena-
tive silylations,1 and dehydrogenative aminoborane coupling15
reactions. An in-depth DFT study of Liu et al. on the hydro-
genation with the trans-[Re(H)2(η2-C2H4)(NO)(PMe3)2]
model system16 revealed that this fragment would suffer from
unfavorable, but crucial stereochemical circumstances appearing
during catalysis. The trans-phosphine arrangement17 is expected
to support strong binding of olefin ligands14 and thus impedes
catalytic hydrogenations. We therefore tried to approach
Received: February 1, 2011
Published: May 16, 2011
r
2011 American Chemical Society
2986
dx.doi.org/10.1021/om200092y Organometallics 2011, 30, 2986–2992
|

Organometallics
ARTICLE
Scheme 1. Synthetic Access to [ReBr2(MeCN)(NO)(P∩P)]
Complexes
Figure 1. ORTEP diagram of 2b(down), with ellipsoids drawn at the
50% probability level. Solvent molecules, H atoms, and NO/Br disorder
are omitted for clarity. Selected bond lengths (Å): Br1ꢀRe = 2.6457(5),
Br2ꢀRe = 2.6493(5), Br3ꢀRe = 2.5694(6), NꢀRe = 1.776(5), NꢀO =
1.124(7), P1ꢀRe = 2.4150(13), P2ꢀRe = 2.4384(14). Selected bond
angles (deg): Br1ꢀReꢀBr2 = 80.205(19), Br1ꢀReꢀP1 = 170.95(3),
Br1ꢀReꢀP2 = 90.81(3), Br2ꢀReꢀP1 = 91.03(3), Br2ꢀReꢀP2 =
170.68(3), Br3ꢀReꢀN = 175.95(14), O1ꢀN1ꢀRe = 179.4(6),
P1ꢀReꢀP2 = 97.84(4).
being stable only with large-bite-angle diphosphines. Consequently
we employed dpephos, homoxantphos, and Sixantphos from van
Leeuwen’s large-bite-angle 2,20-bis(diphenylphosphino)phenyl
ether ligand series21 (Scheme 1). While the bite angle of the
bidentate phosphine in this series was varied, the donicity of the
ligand was kept approximately constant. In contrast to the known
substitution reactions with monodentate phosphine ligands,14
only moderate to low yields were obtained in the substitution
processes of [ReBr2(MeCN)3(NO)], with the ferrocenyl dipho-
sphines forming the complexes [ReBr2(MeCN)(NO)(dppfc)]
(1a, 63%) and [ReBr2(MeCN)(NO)(diprpfc)] (1b, 31%). Fol-
lowing the synthetic route to the [ReBr2(η2-H2)(NO)(PR3)2]
(R = i-Pr, Cy) species,3 we attempted also to employ [ReBr5-
(NO)][NEt4]2 as a starting material, reacting it with an excess of
dppfc or diprpfc in ethanol at 80ꢀ85 °C. According to Scheme 1
the combined ligand substitution and reduction of the rhenium
center to concomitantly form P(þV) compounds of the type
[PR3Br]Br or [PR3Br2]22 worked better only with the diprpfc
ligand, furnishing the dinuclear μ2-Br substitution product
[{ReBr(μ2-Br)(NO)(diprpfc)}2] (2b) in 78% yield. An X-ray
diffraction study revealed the dinuclear structure of 2b with trans
NO and Br ligands and cis Pdiphosphine atoms (Figure 1). No NMR
spectra of 2b could be recorded, due to the low solubility of 2b in
noncoordinating solvents.
Stirring 2b at room temperature in a DCM/MeCN mixture
resulted in the splitting of the μ2-Br bridges with quantitative
formation of the MeCN complex 1b. The reaction of
[ReBr5(NO)][NEt4]2 with an excess of dppfc in a 7:3 mixture
of MeCN and THF furnished the direct formation of 1a in 74%
yield based on the [ReIIBr5(NO)][NEt4]2 starting material
(Scheme 1). In this reaction again the diphosphine served as a
ligand, as well as a reducing agent of the Re(þII) center
producing P(þV) compounds, which was indicated by the
appearance of additional signals in the 31P{1H} NMR spectra
of the reaction solutions. This facile access to 1a,b prompted us
to try also the preparation of other structurally related complexes
bearing large-bite-angle diphosphines. Unlike the ferrocene-
based ligands, dpephos (c), homoxantphos (d) and Sixantphos
(e) were found to withstand temperatures of 180ꢀ200 °C. In
this range of temperatures the ligands, as well as the
[ReBr5(NO)][NEt4]2 salt, became soluble in MeCN and the
combined redox and substitution reactions according to
Scheme 1 went to completion within 3ꢀ5 h with moderate to
high yields producing the desired Re(þI) substitution products
improvement of the potential for catalysis of [ReH2(η2-C2H4)-
(NO)(PR3)2] systems by changing the coordination pattern from
a trans to a cis phosphine arrangement, which we thought to be
accomplishable best with chelating diphosphine ligands or even
more effectively with [ReBr2(MeCN)(NO)(P∩P)] complexes
bearing large-bite-angle diphosphines enhancing further the
stabilization of 16e species and thus providing promising hydro-
genation catalysts.
’ RESULTS AND DISCUSSION
Preparation of Rhenium Nitrosyl Complexes Bearing Bi-
dentate Large-Bite-Angle Diphosphines. Bidentate dipho-
sphine ligands are characterized in electronic terms by their
donicity,18 in size by their bulk19 (cone angle at each P center)
and by their bite angle.20 For many catalytic processes it is the state
of the art to use large-bite-angle diphosphines, since their catalytic
performance often turns out to be superior to that of large-cone-
angle monophosphines.21 The preparation of the large-bite-angle
[ReBr2(MeCN)(NO)(P∩P)] derivatives was achieved via ligand
substitution reactions starting from [ReIBr2(MeCN)3(NO)] and
[ReIIBr5(NO)][NEt4]2 compounds developed earlier in our
group.3 It should be noted that attempts to prepare small-bite-
angle analogues employing dmpe/dppe or dppm from [ReBr2-
(MeCN)3(NO)] or [ReBr5(NO)][NEt4]2 failed. This could be
interpreted in terms of [ReBr2(MeCN)(NO)(P∩P)] complexes
2987
dx.doi.org/10.1021/om200092y |Organometallics 2011, 30, 2986–2992

Organometallics
ARTICLE
Scheme 2. General Sketch of Isomerism in
[ReXYBr(NO)(P∩P)] Complexes
Figure 2. ORTEP diagram of 1e(down), with ellipsoids drawn at the
50% probability level. Solvent molecules, H atoms, and NO/Br disorder
are omitted for clarity. Selected bond lengths (Å): Br1ꢀRe = 2.5591(6),
Br2ꢀRe = 2.6090(5), N1ꢀRe = 1.716(5), N1ꢀO1 = 1.290(6), N2ꢀ
Re = 2.125(3), P1ꢀRe = 2.4434(10), P2ꢀRe = 2.4049(10). Selected
bond angles (deg): Br1ꢀReꢀN1 = 174.75(13), Br2ꢀReꢀP1 =
Scheme 3. Mono- and Dinuclear Racemization Pathways of
1aꢀe for the Br/MeCN Exchange and Virtual Exchange of the
Diphosphine Sides
167.78(3), Br2ꢀReꢀP2
=
89.40(3), N2ꢀReꢀP1
= 89.53(8),
N2ꢀReꢀP2 = 173.27(8), O1ꢀN1ꢀRe = 179(2), N2ꢀReꢀBr2 =
84.47(8), P1ꢀReꢀP2 = 97.00(3).
ligands could by no means be forced into the PꢀReꢀP plane.
Therefore, the backbone of these ligands adopt either an “up”/
“down” or “twisted-a”/“twisted-b” conformation. This could
result theoretically in four enantiomeric pairs of diastereomers/
conformers as depicted in Scheme 2. Up, down, and twisted
denote therelative positionsof the ligandbackbonewith respect to
the NO/Br axis, while twisted-a/twisted-b would denote the
arrangement of the X/Y ligands. The question arises, which
isomers are formed, and whether there is a substantial barrier for
their interconversions. Such diastereomer interconversions and
racemizations between up/down, respectively, and twisted-a/
twisted-b diastereomers could principally occur via the inversion
of the ligand backbone and/or on/off reactions and shift of the
rhenium bound leg of the diphosphine to the other side
(Scheme 3). It is noteworthy that a mechanism which intercon-
verts up into down diastereomers would also racemize the twisted
isomers and vice versa. Inversions of the free ligand backbones
seemed more probable for the free diprpfc, dppfc, and dpephos
ligands but not necessarily for the bound form in the complexes.
The existence of bromide-bridged dimers of type 2 and the
observed dynamics in the NMR spectra (vide infra) indicated
that isomerization/racemization processes via MeCN dissociation
are ongoing reactions in solution at ambient temperatures.
The complexes 1a,c,e were characterized by X-ray diffraction
studies. The ORTEP drawing of 1e shows a representative
example of type 1 complexes (Figure 2). As expected, 1e
possesses a distorted-octahedral structure with a trans NO/Br
axis and a cis diphosphine arrangement with respect to this axis.
The bond lengths were found to be in the range of typical BrꢀRe,
MeCNꢀRe, PꢀRe, and ReꢀNO bonds. However, the large-
bite-angle diphosphine causes steric congestion in the PꢀReꢀP
plane, which is reflected in the compression of the N2ꢀReꢀBr2
angle down to 84.47(8)°. Except for 1a, the structures of all
complexes showed NO/Br disorder at varying ratios of the
diastereomers. 1c,e and 2b crystallize as mixtures of the up and
down diastereomers (up, 1c 10%, 1e 14%, 2b 8%; down, 1c 90%,
1e 86%, 2b 92%), while 1a and 4e,f (vide infra) crystallize in the
twisted form (twisted-a, 1a 0%, 4e 47%, 4f 38%; twisted-b, 1a
100%, 4e 53%, 4f 62%). The preference for up or down isomers
[ReBr2(MeCN)(NO)(dpephos)] (1c; 88%), [ReBr2(MeCN)-
(NO)(homoxantphos)] (1d; 72%), and [ReBr2(MeCN)(NO)-
(Sixantphos)] (1e; 56%). For octahedral complexes bearing a
rigid bidentate ligand various constitutional and conformational
isomers are expected to exist.23 However, since the trans
arrangement of the NO and one Br ligand is favored due to a
stabilizing strong “pushꢀpull” π-interaction, the cis position of
the diphosphines with respect to the NO/Br axis became
enforced by the given electronic conditions.24 Consequently
the other two ligands MeCN and Br had to arrange trans to
the Pdiphosphine atoms. Therefore, only one type of constitutional
isomer of 1cꢀe could be formed possessing a chiral rhenium
center. The backbone of such rigid large-bite-angle diphosphine
2988
dx.doi.org/10.1021/om200092y |Organometallics 2011, 30, 2986–2992

Organometallics
ARTICLE
seemed to be governed by steric factors. Generally the down
conformations are favored apparently avoiding van der Waals
contacts of the Br ligand with one of the diphosphine phenyl
groups with the closest Br HPh significantly below the typical
3 3 3
distance25 of 2.95 Å. This effect causes a slight tilting of the NO/
Br axis in the up isomers. However, the X-ray studies of 1a,c,e
and 2b revealed that the orientation of the NO/Br axis with
respect to the ligand backbone has otherwise only minor
influence on the overall structural features of these complexes.
The X-ray studies allowed also to determine the PꢀReꢀP angles,
which were found to be quite similar for all the structurally
investigated derivatives: 1a (98.90(3)°), 1c (100.79(4)°), and 1e
(97.00(3)°), despite the fact that dppfc (97°), dpephos and
homxantphos (102°), and Sixanphos (109°) possess substan-
tially different natural bite angles.20,21 To explain this discre-
pancy, one has to take into account that the quoted natural bite
angles20 are determined by molecular dynamic simulations with a
standard-type PꢀM distance of 2.3 Å. Since the actual ReꢀP
distances in 1aꢀe are about 2.45 Å, the natural bite angles are
systematically too low for rhenium complexes. The “corrected
natural bite angles” would thus be 89° (dppfc, diprpfc), 95°
(dpephos, homoxantphos), and 100° (Sixantphos). Even if one
took these corrected values as the reference values, we would still
be left with deviations, which presumably originate on the one
hand from a high degree of conformational flexibility of the
diphosphine backbones and on the other hand from thermo-
dynamically very strong ReꢀP bonds, for which an optimal
orbital overlap between the phosphorus atoms and the rhenium
center is crucial. Thus, the optimization of the ReꢀP orbital
overlaps outweighs the deformation energies of the ligand
backbones.
Figure 3. 31P{1H} NMR spectra of 1c at various temperatures (CDCl3,
162 MHz).
However, the acetonitrile dissociation pathway looks more
plausible to occur than the genuine P atom exchange of the
diphosphine, since only acetonitrile dissociation could lead to
strongly broadened NMR signals for MeCN (bound and free).
To gain further insight into the dynamics, we recorded the
31P{1H} spectra of 1a and 1cꢀe at low temperature, thus slowing
down the exchange processes. In the case of the dppfc complex 1a
the broad signals observed at room temperature sharpened indeed
into a pair of doublets at 6.83 and 0.37 (2JPP = 13 Hz) ppm -
(CDCl3, 240 K, 162 MHz). In contrast to the spectrum of 1a, the
two broad signals observed in the room-temperature spectrum of
the dpephos derivative 1c turned out to be coalescing signals
of two species, each giving rise to a set of two doublets at 0.54
and ꢀ1.84 (2JPP = 12 Hz) and at 4.61 and ꢀ7.66 (2JPP = 11 Hz)
ppm (CDCl3, 220 K, 162 MHz, Figure 3). At 220 K the 31P{1H}
NMR signals of 1d remained broad, providing no further informa-
tion on the involved dynamic processes. The room-temperature
spectrum of a solution of 1e in CDCl3 consisted of two broad
signals at 1.0 and ꢀ4.0 ppm assigned to 1e and a sharp signal at
26.1 ppm assigned to 2e. Warming the sample to 320 K leads to a
significant broadening of the signal of 2e at 26.1 ppm. At the
same time the two signals of 1e collapsed into a coalescing signal
at ꢀ5.2 ppm. Cooling a sample of 1e to 240 K led to a sharp signal
for 2e at26.0ppm (0.08P) andto foursets of doublets for1eat 4.7
and 0.1 ppm (0.10 P), at 0.3 and ꢀ3.4 ppm (2JPP = 10 Hz, 0.66 P),
at ꢀ3.7 and ꢀ11.4 ppm (0.04 P), and at ꢀ7.2 and ꢀ14.1
ppm (0.12 P). From these results we can conclude that at least
in the case of 1c,e different conformers are present in solution
(Figure 3). In the case of 1c the 31P{1H} NMR signals are
attributed to the 1c(up) and 1c(down) conformers and in the
case of the spectrum of 1e fourconformers are distinguishablewith
prevailing amounts of 1e(down), which would be in accord with
the results of the crystallographic analysis of 1e (vide supra).
Minor signals were assigned to 1e(up), 1e(twisted-a), and 1e-
(twisted-b) (Scheme 2). At room temperature these conformers
are in fast exchange on the NMR time scale. An additional
exchange is observed between 1e and 2e at elevated temperatures,
indicating that the isomerization pathway via the μ2-Br dimers is
operative at least in this case (Scheme 3). In the cases of 1a,d, for
which only one set of doublets or very broad signals could be
detected, we can neither confirm nor exclude the presence of more
than one conformer in solution, since the NMR spectra of these
diastereomers could be similar and practically indistinguishable.
Preparation of the Hydride Complexes 3aꢀf. On the basis
of the well-established hydride chemistry of [ReH(η2-BH4)-
(NO)(PR3)2] complexes (R = Cy, i-Pr, p-tolyl)3,14 with trans
monodentate phosphines, we attempted the transformation of
1aꢀe into the related rhenium hydride complexes applying
The IR spectra of 1aꢀe each displayed a single characteristic
1
ν(NO) band in the range of 1680ꢀ1700 cmꢀ1. The H NMR
spectra of 1aꢀe consisted of broadened signals for the dipho-
sphine and the MeCN ligands in a 1:1 ratio. For 1d,e broad and
overlapping signals for bound and free MeCN were observed,
which points to the presence of dissociation equilibria at room
temperature, while for 1aꢀc one signal for a rhenium-bound
MeCN was visible. The 31P{1H} NMR spectra of compounds
1aꢀe consisted of two broad resonances (1:1 integration ratio),
for which no coupling patterns were resolved. However, in the
case of 1c,e an additional 31P{1H} NMR signal became obser-
vable, which disappeared upon addition of MeCN. We inter-
preted this in terms of a dissociation equilibrium of the MeCN
complexes 1d and 1e forming the μ2-Br dimers 2d,e (Scheme 3).
Presumably the MeCN dissociation is promoted by “steric
pressure” imposed on this ligand by the large-bite-angle dipho-
sphines. The broadness of the 1H and the 31P{1H} NMR spectra
and the absence of the expected coupling pattern of the 31P{1H}
NMR signals can be explained by assuming dynamics with
exchange of the inequivalent 31P nuclei at a rate in the range of
the NMR time scale. This exchange might proceed via either
formation of μ2-Br intermediates (2aꢀe), which are assumed to
be cleaved randomly, or via the formation of a transient
unsaturated trigonal-bipyramidal intermediate, which can rebind
the freed MeCN at both sides of the Br ligand with equal
probability (Scheme 3).
Both types of rearrangements of the upper part of Scheme 3
lead to racemization of 1aꢀe. An alternative genuine P atom
exchange mechanism would involve dissociation of one “leg” of
the diphosphine followed by a combined shift and rotation of the
remaining ReꢀP bond, as depicted at the bottom of Scheme 3.
2989
dx.doi.org/10.1021/om200092y |Organometallics 2011, 30, 2986–2992

Organometallics
ARTICLE
Scheme 4. Reaction of 1aꢀd with HSiEt3
Figure 4. ORTEP diagram of 4f(twisted) with the ellipsoids drawn at
50% probability. NO/Br disorder and H atoms are omitted for clarity.
Selected bond lengths (Å): Br1ꢀRe = 2.5413(12), H1ꢀRe = 1.66,
H1ꢀRe = 1.59, NꢀO = 1.309(10), NꢀRe = 1.744(8), P1ꢀRe =
2.5271(7), P2ꢀRe = 2.5051(7), ReꢀSi = 2.5202(8). Selected bond
SiꢀRe bonds are 2.50ꢀ2.55 Å, somewhat longer than the ReꢀP
bonds (about 2.45 Å) in the type 1 complexes, but still in the
range of typical ReꢀP single bonds. The NOꢀReꢀBr axis
remains largely unaffected by the change from type 2b to type
4b complexes, showing only minor differences in the ReꢀNO
(4b, 1.744(8) Å; 2b, 1.776(5) Å) and the NO bond (4b,
1.309(10) Å; 2b, 1.124(7) Å), which may originate from some-
what stronger back-bonding in 4a. This is also reflected in the IR
spectra of 4b (ν(NO) 1693 cmꢀ1) and 2b (ν(NO) 1681 cmꢀ1).
Furthermore, a NO/Br disorder clearly demonstrates the pre-
sence of twisted-a and twisted-b diastereomers formed in a 47:53
ratio (Scheme 2). Since the discrimination between these
twisted-a and twisted-b species arises from the asymmetry
introduced by the SiR3 moiety, the interconversion of these
species is expected to be very fast, on the basis of reversible
HSiMe3 loss and readdition or/and rotation of the SiMe3 moiety.
angles (deg): Br1ꢀReꢀN
=
176.67(17), H1ꢀReꢀP2
= 73,
H1ꢀReꢀP1 = 69, NꢀOꢀRe = 178.6(9), P1ꢀReꢀP2 = 102.36(2),
P1ꢀReꢀSi = 131.70(3), P2ꢀReꢀSi = 125.63(3).
hydride reagents, such as [NBu4][BH4], LiAlH4, KH, and KH/
18-crown-6 in THF. Despite extensive variations of the reaction
temperatures and of the stoichiometries of the reactants, we
found the course of any of these reactions ending up in insepar-
able mixtures of compounds. However, when HSiEt3 was used as
a hydride source to react with 1aꢀd, the dihydride silyl com-
plexes [ReBr(H)2(SiEt3)(NO)(P∩P)] (4aꢀd) were formed
smoothly, for which we propose a pentagonal-bipyramidal
structure with the hydrides, the silyl moiety, and the diphosphine
in the pentagonal plane, in close analogy to the structurally fully
characterized 4f (Figure 4, vide infra). The analogous reaction
with 4e still furnished a mixture of products, which could not be
separated. We suppose that at least one of the products has a silyl
dihydride structure related to 4f. 4a,c,d were found to be stable in
solution, but only in the presence of the silane. These species
were therefore characterized via their NMR and IR spectra in
solution, which were in the hydride part similar to that of the
stable 4f complex. Attempts to isolate 4a,c,d led to the formation
of brick red precipitates, from which we concluded that 4a,c,d are
in equilibrium with the 16e complex [ReBrH(NO)(P∩P)]
(5aꢀd) and HSiEt3 according to Scheme 4, which subsequently
may oligomerize to μ2-H dimers, trimers, or even higher oligo-
mers composed of 5aꢀd units occurring already at low concen-
trations of the free intermediates 5aꢀd. Similar oligomerizations
of isoelectronic intermediates were reported to be formed with
Crabtree’s [Ir(diene)(PCy3)(pyridine)][PF6] catalysts in the
1
Therefore, it is not surprising that neither the H and 31P{1H}
NMR nor the IR spectra of 4aꢀd point to the presence of more
than one conformer. To probe the influence of the silicon
substituents, the SiCl3 derivative 4g was prepared via the reaction
of 1b with HSiCl3. The formation of 4g was accompanied by a
partial bromide/chloride exchange, yielding a mixture of pro-
ducts. Since this mixture could not be separated, [NEt4]Cl was
added to the reaction solution to achieve a quantitative Cl/Br
exchange. Chromatographic workup yielded pure 4g (66%). In
order to compare the structures of 4g,f, an X-ray diffraction study
on single crystals of 4g was carried out. On the basis of the
π-acceptor property of the SiCl3 moiety, the SiꢀRe distance in 4g
(2.3948(6) Å) was found to be significantly shorter than that of 4f
(2.5202(8) Å). This is reflected in the ν(NO) bands of 4f
(1678 cmꢀ1) and 4g (1718 cmꢀ1). From these observations
we concluded that electronic substituent effects of silyl ligands are
similar to those of respective phosphorus ligand series.18 More-
over, the significantly shorter ReꢀSi bond in 4g indicates a
drastically increased bond strength.
26
presence of H2 or the [Re(H)7(PPh3)2] complex at elevated
temperatures.4 In contrast to this observation for 1a,c,d, complex
1b bearing the more electron donating diprpfc ligand reacted with
HSiEt3, forming a stable seven-coordinate [ReBr(H)2(SiEt3)-
(NO)(diprpfc)] (4b) complex. Because of the liquid nature of 4b,
which therefore could not be characterized by a X-ray diffraction
study, the SiMe3 derivative 4f was also prepared and obtained in
92% yield by applying HSiMe3 and was studied by X-ray diffrac-
tion (Figure 4). As expected, the NO and Br ligands are trans and
the P atoms cis. The SiMe3 moiety lies in the PꢀReꢀP plane,
forming a triangle with the diprpfc P atoms (selected angles
(deg): P1ꢀReꢀP2 = 102.36(2), P1ꢀReꢀSi = 131.70(3),
P2ꢀReꢀSi = 125.63(3)). The two hydrides were located and
refined in this plane between the P and Si atoms. The PꢀRe and
’ CONCLUSION
This work established an efficient and versatile synthetic
approach to [ReBr2(MeCN)(NO)(P∩P)] complexes bearing
the large-bite-angle diphosphines dppfc, diprpfc, dpephos, homo-
xantphos, and Sixantphos. X-ray diffraction studies revealed that
these compounds can form backbone isomers of the type up,
down, and twisted, as confirmed by exemplary X-ray structures.
However, in the NMR and IR spectra of these compounds, the
interconversion of such isomers could not be pursued quantita-
tively, preventing the assessment of relative stabilities of these
isomers in solution. The large-bite-angle diphosphine rhenium
nitrosyl chemistry seemed to be dominated by the relative stability
2990
dx.doi.org/10.1021/om200092y |Organometallics 2011, 30, 2986–2992

Organometallics
ARTICLE
of the 16e intermediates of types 3and 5triggered supposedly mainly
by the large-bite-angle effect of the diphosphines, in addition
to the π-pushꢀpull effect of the NO/Br axis as a stabilizing factor. If
they are indeed long-lived enough, type 3 and 5 intermediates
could take over roles in important catalytic reactions, other-
wise accomplishable only with platinum-group-metal centers.
[ReBr2(MeCN)(NO)(dpephos)] (1c). A suspension of [ReBr5-
(NO)][NEt4]2 (1.000 g, 1.14 mmol) and dpephos (1.000 g, 1.85 mmol)
in MeCN (10 mL) was stirred for 3 h at 180 °C in a B€uchi pressure tube
(caution! pressure rises to 4ꢀ5 bar). The reaction mixture was allowed to
stand for 16 h at room temperature before the product was filtered off,
washed with EtOH (3 ꢁ 3 mL), and dried in vacuo to yield orange
crystalline 1c (0.960 g, 0.90 mmol, 88%).
IR (KBr pellet, cmꢀ1): 1693 (s, ν(NO)). 1H NMR (500 MHz,
CDCl3, 28 °C): δ 8.1ꢀ7.1 (overlapping multiplets, 1 H, dpephos H),
6.84 (s, 1 H, dpephos H), 6.72 (s, 1 H, dpephos H), 6.63 (s, 1 H,
dpephos H), 6.02 (s, 1 H, dpephos, H), 2.07 (s, 3 H, MeCN) ppm.
31P{1H} NMR (125 MHz, THF-d8, 28 °C): δ ꢀ2.8 (s broad, 1 P), ꢀ5.0
(s broad, 1 P) ppm. Anal. Calcd for C38H31Br4N2O2P2Re (955.63): C,
47.63; H, 3.27; N, 2.93. Found: C, 47.63; H, 3.22; N, 2.97.
[ReBr2(MeCN)(NO)(homoxantphos)] (1d). A mixture of [ReBr5-
(NO)][NEt4]2 (1.000 g, 1.14 mmol) and homoxantphos (1.000 g,
1.77 mmol) in MeCN (10 mL) was stirred for 5 h at 180 °C in a B€uchi
pressure tube (caution! pressure rises to 4ꢀ5 bar). The mixture was
allowed to stand for 16 h at room temperature before the product was
filtered off, washed with EtOH (3 ꢁ 3 mL), and dried in vacuo to yield 1d
as an orange microcrystalline solid (0.810 g, 0.83 mmol, 72%).
’ EXPERIMENTAL SECTION
General Considerations. All manipulations were carried out
under an atmosphere of dry nitrogen using either standard Schlenk
techniques or an M. Braun glovebox. All solvents were dried, distilled,
and degassed according to standard laboratory procedures. The dipho-
sphine ligands [ReBr5(NO)][NEt4]2 and [ReBr2(MeCN)3(NO)] were
prepared according to published methods.3,14,21,27 NMR spectra were
recorded on a Bruker AV-2 500 spectrometer. Chemical shifts are
expressed in parts per million (ppm) and referenced to the solvent’s
residual signals28 or in the case of 31P{1H} NMR spectra to the external
standard 85% H3PO4 at δ 0.0 ppm. IR spectra were recorded on a
BioRad Excalibur spectrometer. Microanalyses were carried out at the
Anorganisch-Chemisches Institut of the University of Z€urich.
IR (cmꢀ1, KBr pellet): 1680 (s, ν(NO)). 1H NMR (500 MHz, CDCl3,
28 °C): δ 8.0ꢀ6.8 (overlapping multiplets, 28 H, arom H), 3.2ꢀ2.9
(broad multiplets, 4 H, ethylene bridge), 2.2ꢀ1.9 ppm (broad, 3 H,
MeCN). 31P{1H} NMR (125 MHz, THF-d8, 28 °C): δ 25.3 (s, broad),
1.2 (s broad), ꢀ0.3 (s broad) ppm. Anal. Calcd for C40H33B2N2O2P2Re
(981.66): C, 48.94; H, 3.39; N, 2.85. Found: C, 48.69; H, 3.58; N, 2.97.
[ReBr2(MeCN)(NO)(Sixantphos)] (1e). A suspension of [ReBr5-
(NO)][NEt4]2 (1.00 g, 1.14 mmol) and Sixantphos (0.82 g, 1.38 mmol)
in MeCN (12 mL) was stirred for 4 h at 200 °C in a B€uchi pressure tube
(caution! pressure rises to 4ꢀ5 bar). After it was cooled to room
temperature, the yellow solid was filtered off, washed with MeCN
(2 ꢁ 4 mL), and dried in vacuo to yield 1e as a yellow solid (0.65 g,
0.64 mmol, 56%).
Crystal Structure Determination. Relevant details about the
structure refinements are given in the Supporting Information. Crystal-
lographic data have been deposited with the Cambridge Crystallo-
graphic Data Center as CCDC 787668ꢀ78772 and 805674. These
data can be obtained free of charge from The Cambridge Crystal-
lographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif and
are also available as Supporting Information.
[ReBr2(MeCN)(NO)(dppfc)] (1a). Method 1. A suspension of
[ReBr2(MeCN)2(NO)(THF)] 2THF (0.240 g, 0.356 mmol) and dppfc
3
(0.224 g, 0.404 mmol) in THF (10 mL) was stirred for 5 h at 60 °C. The
resulting precipitate was filtered off, washed with a minimum of THF, and
dried in vacuo, yielding 1a THF (0.250 g, 0.239 mmol, 63%).
3
Method 2. A mixture of [ReBr5(NO)][NEt4]2 (1.003 g, 1.1 mmol)
and dppfc (1.000 g, 2.3 mmol) in THF (3 mL) and MeCN (7 mL) was
stirred for 12 h at 80 °C. The solution was filtered hot, and the product
was allowed to crystallize overnight before it was filtered off and washed
with EtOH (3 ꢁ 3 mL). After drying in vacuo bright yellow crystals of
IR (KBr pellet, cmꢀ1): 1680 (s, ν(NO)). 1H NMR (500 MHz,
CDCl3 þ 3 μL of CH3CN, 28 °C), 6.65ꢀ7.85 (m, 26 H, arom H), 2.19
(s, 3 H, MeCN), 0.62 (s, 3 H, SiMe3), 0.52 ppm (s, 3 H, SiMe3). 31
P
NMR (CDCl3, 121 MHz): δ ꢀ5.4 (s broad, 1 P), ꢀ2.5 (s broad, 1P);
Anal. Calcd for C40H35Br2N2O2P2ReSi (1011.77): C, 47.48; H, 3.49; N,
2.77. Found: C, 47.21; H, 3.37; N, 2.94.
1a THF were obtained (0.910 g, 0.8 mmol, 74%).
3
IR (cmꢀ1, KBr pellet): 1685 (s, ν(NO)). 1H NMR (500 MHz,
CDCl3, 27 °C): δ 8.09 (m, 2 H, phenyl), 7.00 (m, 2 H, phenyl), 7.53 (m,
4 H, phenyl), 7.43 (s, 4 H, phenyl), 7.32 (m, 8 H, phenyl), 5.82 (s, 1 H,
cp), 4.50 (s, 1 H, cp), 4.44 (s, 1 H, cp), 4.38 (s, 1 H, cp), 4.24 (s, 1 H, cp),
4.22 (s, 2 H, cp), 3.91 (s, 1 H, cp), 2.24 ppm (s, 3 H, MeCN). 31P{1H}
NMR (202 MHz, CDCl3, 27 °C): δ 4.95 (s broad, 1 P), ꢀ0.71 ppm (s
broad, 1P). Anal. Calcd for C40H39Br2FeN2O2P2Re (1043.56 g molꢀ1):
C, 46.04; H, 3.77; N, 2.68. Found: C, 46.00; H, 3.75; N, 2.59.
[(ReBr2(diprpfc)(NO))2] (2b). Asuspensionof[ReBr5(NO)][NEt4]2
(1.000 g, 1.14 mmol) and diprpfc (1.00 g, 2.39 mmol) in absolute EtOH
(10 mL) was stirred for 16 h at 80 °C. The orange precipitate was filtered off
and washed with EtOH (3 ꢁ 5 mL). After it was dried in vacuo, 2b (0.720 g,
0.45 mmol, 78%) was obtained as a yellow powder.
IR(cmꢀ1, KBrpellet):1693(s,ν(NO)). Anal. CalcdforC44H72Br4Fe2-
N2O2P4Re2 (1585.90): C, 33.26; H, 4.57; N, 1.76. Found: C, 33.20; H,
4.64; N, 1.82.
[ReBr2(MeCN)(NO)(diprpfc)] (1b). Method 1. A suspension of
[ReBr2(MeCN)2(NO)(THF)] 2THF (0.100 g, 0.148 mmol) and diprpfc
[ReBrH2(SiEt3)(NO)(P∩P)] Complexes (4aꢀd): Representa-
tive Procedure for 4c. An NMR tube was charged with a suspension
of 1c (10 mg, 0.01 mMol) in HSiEt3 (50 μL, 0.28 mMol) and THF-d8
(500 μL). The NMR tube was sonicated for 1 h at 50 °C before
3
(0.068 g, 0.162 mmol) in THF (5 mL) was stirred for 5 h at 60 °C. The
precipitate was filtered off, washed with a minimum of THF, and dried in
vacuo, yielding 1b as a yellow powder (0.044 g, 0.053 mmol, 32%).
Method 2. A mixture of 2b (0.300 g, 0.38 mmol), CH2Cl2 (10 mL) and
MeCN (1 mL) was stirred for 4 h. During this time the solid 2b dissolved
completely. The solvents were removed in vacuo, and 1b was obtained
quantitatively.
1
measuring the H and 31P{1H} spectra of the solution. The volatiles
were quickly removed in vacuo before the remaining solid was used for
IR spectroscopy.
Spectroscopic data of 4a are as follows. IR (KBr pellet, cmꢀ1): 1968
IR (cmꢀ1, KBr pellet): 1683 (s, ν(NO)). 1H NMR (500 MHz, CDCl3,
27 °C): δ 4.886 (s, 1 H, cp), 4.588 (s, 1 H, cp), 4.392 (s, 1 H, cp), 4.371 (s,
4 H, cp), 4.274 (s, 1 H, cp), 3.719 (s, 1 H, i-Pr CH(CH3)2), 3.199 (s, 1 H,
i-Pr CH(CH3)2), 3.007 (s, 1 H, i-Pr CH(CH3)2), 2.769 (m, 4 H, i-Pr
CH(CH3)2 and MeCN), 1.633ꢀ1.102 ppm (m, 24 H, i-Pr CH(CH3)2).
31P{1H} NMR(202 MHz, CDCl3, 28 °C): δ 2.27 (s, broad), 0.86 ppm (s,
broad). Anal. Calcd for C24H39Br2FeN2OP2Re (835.39 g molꢀ1): C,
34.51; H, 4.71; N, 3.35. Found: C, 34.33; H, 4.63; N, 3.19.
(m, broad, ν(ReH)), 1684 (s, ν(NO)). H NMR (500 MHz, THF,
1
28 °C): δ 8.45ꢀ7.00 (m, 20 H, phenyl), 5.152 (s, 1 H, cp), 4.656 (s, 1 H,
cp), 4.525 (s, 1 H, cp), 4.43ꢀ4.30 (m, 5 H, cp), 1.154 (m, 2 H, ReH),
1.18ꢀ0.54 ppm (overlapping signals of HSiEt3 and ReSiEt3). 31P{1H}
NMR (125 MHz, THF-d8, 28 °C): δ 3.9 ppm.
Spectroscopic data of 4b are as follows. IR (KBr pellet, cmꢀ1): 1981
1
(m, broad, ν(ReH)), 1671 (s, ν(NO)). H NMR (500 MHz, THF,
28 °C): δ 4.766 (s, 2 H, cp), 4.434 (s, 2 H, cp), 4.354 (s, 4 H, cp), 2.752
2991
dx.doi.org/10.1021/om200092y |Organometallics 2011, 30, 2986–2992

Organometallics
ARTICLE
(m, 2 H, i-Pr), 2.610 (m, 2 H, i-Pr), 1,6ꢀ0.5 (overlapping multiplets,
i-Pr, ReH, ReSiEt3, HSiEt3) ppm. 31P{1H} NMR (125 MHz, THF-d8,
28 °C): δ 12.0 ppm.
’ REFERENCES
(1) Jiang, Y.; Blacque, O.; Fox, T.; Frech, C., M.; Berke, H. Chem.
Eur. J. 2009, 15, 2121–2128.
(2) Green, M.; L., H.; Pratt, L.; Wilkinson, G. J. Chem. Soc. 1958,
3916–3922.
Spectroscopic data of 4c are as follows. IR (KBr pellet, cmꢀ1): 2004
1
(m, broad, ν(ReH)), 1678 (s, ν(NO)). H NMR (500 MHz, THF,
28 °C): δ 6.670 (m, 3 H, phenyl), 7.50ꢀ7.25 (m, 14 H, phenyl), 7.196
(m, 3 H, phenyl), 7.075 (m, 4 H, phenyl), 6.70 (m, 3 H, phenyl),
1.17ꢀ0.51 (overlapping signals HSiEt3 and ReSiEt3), 0.688 ppm (m, 2 H,
ReH). 31P{1H} NMR (125 MHz, THF-d8, 28 °C): δ ꢀ5.0 ppm.
Spectroscopic data of 4d are as follows. IR (KBr pellet, cmꢀ1): 2008
(3) Gusev, D.; Llamazares, A.; Artus, G.; Jacobsen, H.; Berke, H.
Organometallics 1999, 18, 75–89.
(4) Chatt, J.; Coffey, S. J. Chem. Soc. A 1969, 1963–1969.
(5) Luo, X. L.; Crabtree, R., H. J. Am. Chem. Soc. 1990, 112,
4813–4821.
(6) Gusev, D., G.; Nietlispack, D.; Eremenko, I., L.; Berke, H. Inorg.
Chem. 1993, 32, 3628–3636.
(7) Baudry, D.; Ephritikhine, M.; Felkin, H. J. Organomet. Chem.
1982, 224, 363–376. Herrmann, W. A.; Okuda, J. Angew. Chem. 1986,
98, 1109–1111. Jones, W. D.; Maguire, J., A. Organometallics 1987,
6, 1301–1311.
1
(m, broad, ν(ReH)), 1683 (s, ν(NO)). H NMR (500 MHz, THF,
28 °C): δ 6.648 (t, J = 9.0 Hz, 4 H, phenyl), 7.35ꢀ7.05 (m, 18 H,
phenyl), 6.901 (t, J = 7.5 Hz, 2H), 6.513 (t, J = 8.0 Hz, 2 H, phenyl),
3.25ꢀ3.05 (m, 4 H, homoxantphos-CH2CH2), 1.17ꢀ0.51 (overlapping
signals HSiEt3 and ReSiEt3), 0.755 ppm (m, 2 H, ReH). 31P{1H} NMR
(125 MHz, THF-d8, 28 °C): δ ꢀ0.2 ppm.
(8) Mayer, J., M.; Thorn, D., L.; Tulip, T., H. J. Am. Chem. Soc. 1985,
107, 7454–7462.
[ReBrH2(diprpfc)(NO)(SiMe3)] (4f). A suspension of 2b (0.105 g,
0.07 mmol) and 15% HSiMe3 in THF (0.4 mL, 0.57 mmol) in THF
(10 mL) was stirred for 6 h at room temperature. The resulting orange
solution was filtered through a short plug of Celite and dried in vacuo to
yield 4f (0.095 g, 0.12 mmol, 92%) as a yellow powder.
(9) Blaser, H. U.; Malan, C.; Pugin, B.; Spindler, F.; Steiner, H.;
Studer, M. Adv. Synth. Catal. 2003, 345, 103–151. Chen, B.; Dingerdissen,
U.; Krauter, J. G.; Rotgerink, H.; Mobus, K.; Ostgard, D. J.; Panster, P.;
Riermeier, T. H.; Seebald, S.; Tacke, T.; Trauthwein, H. Appl. Catal., A
2005, 280 (1), 17–46.
1
IR (KBr pellet, cmꢀ1): 1974 (m, ν(ReH)), 1678 (s, ν(NO)). H
NMR (500 MHz, C6D6, 28 °C): δ 4.660 (s, 2 H, Cp), 4.190 (s, 2 H, Cp),
3.975 (s, 4 H, Cp), 2.652 (d heptet, 3JHH = 7 Hz, JPH = 9.5, 2 H, i-Pr CH),
2.350 (d heptet, 3JHH = 7 Hz, JPH = 8.5, 2 H, i-Pr CH), 1.839 (m, 2 H,
ReH), 1.644 (dt, 3JHH = 7 Hz, 3JPH = 15 Hz, 6 H, i-Pr CH), 1.484 (dt,
3JHH = 7 Hz, 3JPH = 14.5 Hz, 6 H, i-Pr CH), 1.220 (s, 9 H, Si(CH3)3),
1.091 ppm (m, 6 H, i-Pr CH). 31P{1H} NMR (125 MHz, THF-d8,
28 °C): δ 16.30 ppm. Anal. Calcd for C25H47BrFeNOP2ReSi (733.79).
C, 38.03; H, 6.00; N, 1.77. Found: C, 37.88; H, 5.90; N, 1.71.
(10) Zimmermann, S.; Sures, B. Environ. Sci. Pollut. Res. 2004, 11 (3),
194–199. Schmid, M.; Zimmermann, S.; Krug, H. F.; Sures, B. Environ.
Int. 2007, 33, 385–390.
(11) Garrett, C., E.; Prasad, K. Adv. Synth. Catal. 2004, 346,
889–900.
(12) Noyori, R.; Hashiguchi, S. Acc. Chem. Res. 1997, 30, 97–102.
(13) Kalck, P.; Peres, Y.; Jenck, J. Adv. Organomet. Chem. 1991, 32,
121–146.
(14) Choualeb, A.; Maccaroni, E.; Blacque, O.; Schmalle, H. W.;
Berke, H. Organometallics 2008, 27, 3474–3481. Maccaroni, E.; Dong,
H.; Blacque, O.; Schmalle, H., W.; Frech, C., M.; Berke, H. J. Organomet.
Chem. 2010, 695 (4), 487–494.
[ReBrH2(diprpfc)(NO)(SiCl3)] (4g). A suspension of 1b (0.100 g,
0.06 mmol) and [NEt4]Cl (0.250 g, 1.5 mmol) in CH2Cl2 (10 mL) was
stirred for 2 h at 39 °C. Then HSiCl3 (5 mL, 39.4 mmol) was added and
stirring was continued for 2 h at 39 °C. The volatiles were removed in
vacuo and the residue extracted with THF. The extract was dried in vacuo
and chromatographed on a silica gel column with CH2Cl2 as eluent. A
bright yellow fraction was collected and the solvent was removed in vacuo,
yielding 4g as bright yellow powder (0.065 g, 0.08 mmol, 66%).
(15) Jiang, Y.; Blacque, O.; Fox, T.; Frech, C., M.; Berke, H.
Organometallics 2009, 28, 5493–5504.
(16) Liu, L.; Bi, S.; Sun, M.; Yuan, X.; Zheng, N.; Li, P. J. Organomet.
Chem. 2009, 694, 3343–3348.
(17) Choualeb, A.; Blacque, O.; Schmalle, H. W.; Fox, T.; Hiltebrand,
T.; Berke, H. Eur. J. Inorg. Chem. 2007, 5246–5261.
(18) Tolman, C. A. J. Am. Chem. Soc. 1970, 92 (10), 2953–2956.
(19) Tolman, C. A. Chem. Rev. 1977, 77 (3), 313–348.
(20) Casey, C. P.; Whiteker, G. T. Isr. J. Chem. 1990, 30 (4),
299–304.
(21) Kranenburg, M.; van der Burgt, Y. E. M.; Kamer, P. C. J.;
van Leeuwen, P. W. N. M.; Goubitz, K.; Fraanje, J. Organometallics 1995,
14 (6), 3081–3089. van der Veen, L. A.; Keeven, P. H.; Schoemaker,
G. C.; Reek, J. N. H.; Kamer, P. C. J.; van Leeuwen, P. W. N. M.; Lutz,
M.; Spek, A. L. Organometallics 2000, 19, 872–883.
(22) Godfrey, S. M.; McAuliffe, C. A.; Mushtaq, I.; Pritchard, R. G.;
Sheffield, J. M. J. Chem. Soc., Dalton Trans. 1998, 3815–3818.
(23) von Zelewsky, A. Stereochemistry of coordination compounds.
In Inorganic Chemistry; Wiley: Chichester, U.K., 1995.
(24) Chatt, J.; Duncanson, L. A. J. Chem. Soc. 1953, 2939–2947.
(25) Rowland, S., R.; Taylor, R. J. Phys. Chem. 1996, 100, 7384–7391.
Bondi, A. J. Phys. Chem. 1964, 68, 441–451.
IR (cmꢀ1, KBr pellet): 2001, 1938 (m, ν(ReH)), 1718 (s, ν(NO)). 1H
NMR (500 MHz, THF-d8, 28 °C): δ 4.789 (s, 2 H, Cp), 4.560 (s, 2 H,
Cp), 4.539 (s, 2 H, Cp), 4.514 (s, 2 H, Cp), 3.005 (m, 2 H, ReH), 2.759
(m, 2 H, i-Pr CH), 2.712 (m, 2 H, i-Pr CH), 1.636 (dd, 3JHH = 7.0Hz, 3JHP
= 8.5 Hz, i-Pr CH3), 1.611 (dd, 3JHH = 7.0 Hz, 3JHP = 8.5 Hz, i-Pr CH3),
1.310 (dd, 3JHH = 7.0 Hz, 3JHP = 7.5 Hz, i-Pr CH3), 1.305 ppm (dd, 3JHH
=
3
7.0 Hz, JHP = 7.5 Hz, i-Pr CH3). 31P{1H} NMR (125 MHz, THF-d8,
28 °C): δ 24.01 ppm. Anal. Calcd for C22H38Cl4FeNOP2ReSi (806.44).
C, 32.77; H, 4.75; N, 1.74. Found: C, 32.69; H, 4.81; N, 1.76.
’ ASSOCIATED CONTENT
S
Supporting Information. CIF files, text, figures, and tables
b
giving details of the crystallographic structure determinations.
This material is available free of charge via the Internet at
http://pubs.acs.org.
(26) Crabtree, R. Acc. Chem. Res. 1979, 12, 331–337.
(27) Butler, I., R.; Cullen, W., R. Organometallics 1986, 5, 2537–2542.
(28) Gottlieb, H. E; Kotlyar, V.; Nudelman, A. J. Org. Chem. 1997,
62, 7512–7515.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: hberke@aci.uzh.ch.
’ ACKNOWLEDGMENT
We thank the Swiss National Science Foundation and the
University of Z€urich for financial support.
2992
dx.doi.org/10.1021/om200092y |Organometallics 2011, 30, 2986–2992