Rhodium cyclopentyl phosphine complexes of wide-bite-angle ligands DPEphos and xantphos

Article abstract of DOI:10.1021/om201034m

Rh(I) and Rh(III) complexes of tricyclopentylphosphine (PCyp₃), or its dehydrogenated variant PCyp₂(η²-C ₅H₇), partnered with wide-bite-angle chelating diphosphine ligands DPEphos and Xantphos have been prepared and characterized in solution and the solid state with the aim of studying their potential for reversible dehydrogenation of the PCyp₃ ligand. The complexes fac-[Rh(κ³-P,O,P-L){PCyp₂(η²-C ₅H₇)}][BAr^F₄] (L = DPEphos, Xantphos) show pseudo-trigonal-bipyramidal structures in which the dehydrogenated phosphine alkene ligand acts in a chelating manner. Addition of H₂ to fac-[Rh(κ³-P,O,P-DPEphos){PCyp ₂(η²-C₅H₇)}][BAr ^F₄] resulted in an equilibrium mixture of hydride and hydride-dihydrogen complexes, fac-[Rh(κ³-P,O,P-DPEphos)(H) ₂(PCyp₃)][BAr^F₄] and [Rh(κ²-P,P-DPEphos)(η²-H₂)(H) ₂(PCyp₃)][BAr^F₄], in which the DPEphos acts as a hemilabile ligand. For the more rigid Xantphos ligand two dihydride isomers, fac-[Rh(κ³-P,O,P-Xantphos)(H) ₂(PCyp₃)][BAr^F₄] and mer-[Rh(κ³-P,O,P-Xantphos)(H)₂(PCyp ₃)][BAr^F₄], are formed, which are also in equilibrium with one another. A van′t Hoff analysis of this mixture shows that enthalpically there is very little difference between the two geometries for this system, with the driving force for the preferred fac-geometry being entropic. Addition of MeCN to these hydrido complexes results in the central oxygen atom being displaced to form [Rh(κ²-P,P-L)(PCyp ₃)(H)₂(MeCN)][BAr^F₄], while removal of H₂ from the hydrido complexes (under vacuum or on addition of a hydrogen acceptor) forms the Rh(I) complexes [Rh(κ³-P,O,P-L) (PCyp₃)][BAr^F₄], which are characterized as having square-planar geometries with meridonial coordination of the respective chelating phosphines. Dehydrogenation of the PCyp₃ ligand in these complexes to re-form the phosphine-alkene ligands does not occur, even under forcing conditions.

Full text of DOI:10.1021/om201034m

Article
pubs.acs.org/Organometallics
Rhodium Cyclopentyl Phosphine Complexes of Wide-Bite-Angle
Ligands DPEphos and Xantphos
Romaeo Dallanegra, Adrian B. Chaplin, and Andrew S. Weller*
Department of Chemistry, Inorganic Chemistry Laboratories, University of Oxford, Oxford, OX1 3QR, U.K.
S
* Supporting Information
ABSTRACT: Rh(I) and Rh(III) complexes of tricyclopentylphosphine (PCyp3), or its dehydrogenated variant PCyp2(η2-
C5H7), partnered with wide-bite-angle chelating diphosphine ligands DPEphos and Xantphos have been prepared and
characterized in solution and the solid state with the aim of studying their potential for reversible dehydrogenation of the PCyp3
ligand. The complexes fac-[Rh(κ3-P,O,P-L){PCyp2(η2-C5H7)}][BArF ] (L = DPEphos, Xantphos) show pseudo-trigonal-
4
bipyramidal structures in which the dehydrogenated phosphine alkene ligand acts in a chelating manner. Addition of H2 to fac-
[Rh(κ3-P,O,P-DPEphos){PCyp2(η2-C5H7)}][BArF ] resulted in an equilibrium mixture of hydride and hydride-dihydrogen
4
complexes, fac-[Rh(κ3-P,O,P-DPEphos)(H)2(PCyp3)][BArF ] and [Rh(κ2-P,P-DPEphos)(η2-H2)(H)2(PCyp3)][BArF ], in
4
4
which the DPEphos acts as a hemilabile ligand. For the more rigid Xantphos ligand two dihydride isomers, fac-[Rh(κ3-P,O,P-
Xantphos)(H)2(PCyp3)][BArF ] and mer-[Rh(κ3-P,O,P-Xantphos)(H)2(PCyp3)][BArF ], are formed, which are also in
4
4
equilibrium with one another. A van’t Hoff analysis of this mixture shows that enthalpically there is very little difference
between the two geometries for this system, with the driving force for the preferred fac-geometry being entropic. Addition of
MeCN to these hydrido complexes results in the central oxygen atom being displaced to form [Rh(κ2-P,P-L)(PCyp3)-
(H)2(MeCN)][BArF ], while removal of H2 from the hydrido complexes (under vacuum or on addition of a hydrogen acceptor)
4
forms the Rh(I) complexes [Rh(κ3-P,O,P-L)(PCyp3)][BArF ], which are characterized as having square-planar geometries with
4
meridonial coordination of the respective chelating phosphines. Dehydrogenation of the PCyp3 ligand in these complexes to re-
form the phosphine−alkene ligands does not occur, even under forcing conditions.
acceptorless dehydrogenation for acyclic phosphines, C,13 as
INTRODUCTION
■
have others.14,15 In some cases the dehydrogenation is fully
reversible, and addition of H2 re-hydrogenates the double bond
to re-form the phosphine with a saturated alkyl group.3,5,9,11,13
There is also interest in phosphine−alkene and related, hybrid
ligands due to roles that they can play in directing metal-
mediated catalytic transformations.2,16−20
We have recently reported on the rhodium-mediated
dehydrogenation1 of cyclopentylphosphine, or cyclopentyl
thioether, ligands to form hybrid chelating Lewis-base/alkene
ligands (Chart 1a). For example treatment of the complex
Rh{Ph2P(CH2)2PPh2}(PCyp3)Cl with Na[BArF ] results in the
4
rapid, acceptorless, dehydrogenation of one of the cyclopentyl
As previously we have used simple chelating phosphines,
such as Ph2P(CH2)nPPh2 (n = 2 or 3), as supporting ligands on
the metal center for these dehydrogenation reactions, we were
particularly interested in extending our studies to include
chelating phosphine ligands which have a wide bite angle, such
as DPEphos and Xantphos (DPEphos, bite angle = 101°;
Xantphos, 111°;21 Chart 2). These ligands have been shown to
promote catalysis through a combination of steric and
electronic factors.21−23 Moreover we,24 and others,25 have
demonstrated the hemilabile role26−28 that DPEphos can play
in catalytic processes, being able to interconvert between a
groups to form [Rh{Ph2P(CH2)2PPh2}{PCyp2(η2-C5H7)}]-
[BArF ] A [Cyp = cyclo-C5H9; ArF = C6H3-3,5-(CF3)2]
4
(Chart 1b).2,3 Analogously, addition of SCypPh to [Rh{Ph2P-
(CH2)3PPh2}(η6-C6H4F2)][BArF4] forms Rh{Ph2P-
(CH2)3PPh2}{SPh(η2-C5H7)}][BArF ], B.4 These processes
4
can also occur in the solid state,5 with different supporting
ligand sets other than chelating phosphines,3,6,7 or metals other
than Rh.3,8 Competition experiments indicate that the Cyp unit
is particularly well set up for dehydrogenation, compared with
cyclohexyl or isopropyl substitutents.3,7 Others (notably the
groups of Sabo-Etienne, e.g., D,9,10 Grutzmacher, e.g., E,11 and
̈
Bergman, e.g., F,12 Chart 1b) have also reported on related
dehydrogenations of cyclic alkyl phopshines, using either PCyp3
or closely related ligands, with or without the requirement for a
sacrificial hydrogen acceptor. We have also reported similar
Special Issue: F. Gordon A. Stone Commemorative Issue
Received: October 25, 2011
Published: January 6, 2012
© 2012 American Chemical Society
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a
complex, fac-[Rh(κ3-P,O,P-Xantphos){PCyp2(η2-C5H7)}]-
Chart 1
[BArF ] (2), was isolated in an analogous manner (Scheme 1).
4
a
Scheme 1. Synthesis of 1 and 2
a
[BArF ] anions are not shown.
a
[BArF ] anions not shown.
4
4
Complexes 1 and 2 were characterized by NMR spectros-
copy, ESI-MS, microanalysis, and single-crystal X-ray diffraction
(Figure 1). These data show that the PCyp-derived ligand
remains coordinated to the metal, which adopts a pseudo-
trigonal-bipyramidal geometry with the phosphorus atoms of
the diphosphine located in equatorial positions cis to each other
and opposite the alkene, which itself lies in an equatorial
orientation, as expected for a formally d8 metal center (i.e.,
Rh(I)) interacting with a π-acceptor with this geometry.30,31
The DPEphos and Xantphos oxygen atoms are located in the
axial position trans to the phosphorus atom of the
tricyclopentylphosphine-derived ligand. The Rh−O bond
length for 2 is shorter than that of 1 [2.184(2) Å (2) vs
2.250(2) Å (1)], presumably a result of the more rigid
backbone of the Xantphos ligand, compared to DPEphos,
which enforces the oxygen atom in a position closer to the
metal. That the Rh−P1 distances are the same within error
between the two complexes [2.2256(7) Å (1) vs 2.2285(8) Å
(2)], and in solution the Rh−P1 coupling constants of 1 and 2
are similar [145 Hz (1); 152 Hz (2)], vide infra, suggests a
similar interaction of the cyclopentyl phosphine in both cases
and, thus, similar Rh−O bond strengths. The CC bond
lengths for the two complexes are also the same within error
[1.425(4) Å (1) and 1.416(4) Å (2)] and are also comparable
with complexes A and G [1.372(3), 1.401(4) Å respectively].3
The P2−Rh1−P3 angle is larger in 2 than in 1 [118.17(3)°
versus 110.83(2)°, respectively], reflecting the larger bite angle
of the Xantphos ligand. Five-coordinate Rh(I) species are
known as both cationic32,33 and neutral species.33−35
Chart 2
bidentate κ2-P,P-coordination mode and a tridentate κ3-P,O,P
pincer ligand-like coordination geometry (either fac or mer). In
a similar manner, Xantphos can also adopt a number of
different coordination modes.29 Such flexible behavior might
promote C−H activation and β-hydrogen transfer through the
generation of a suitable cis vacant site on the metal center, steps
both necessary for dehydrogenation of alkyl phosphines. We
were interested to see if all these above factors combined to
allow access to a catalytic regime for dehydrogenation of the
PCyp3 ligand. To this end, this paper reports on an
investigation of the coordination chemistry of PCyp3, and its
dehydrogenated variant PCyp2(η2-C5H7), on Rh(I) and Rh(III)
centers also bound with Xantphos and DPEphos.
RESULTS AND DISCUSSION
■
Synthesis of Complexes [Rh(L){PCyp2(η2-C5H7)}]-
[BArF ], L = DPEphos, Xantphos. The Rh(I) diphosphine
4
precursor complex Rh(DPEphos)(PCyp3)Cl was first targeted
as a suitable precursor to fac-[Rh(DPEphos){PCyp2(η2-
In both complexes the coordinated alkene is confirmed by
1
C5H7)}][BArF ] (1), by analogy with Rh{Ph2P(CH2)2PPh2}-
diagnostic signals in their respective H NMR spectra: δ 3.84
4
(PCyp3)Cl, which forms [Rh(Ph2P(CH2)2PPh2){PCyp2(η2-
(2H) (1); 3.58 (2H) (2) (cf. δ 3.89 A). Complex 2 also shows
two inequivalent methyl environments for the Xantphos ligand,
δ 1.86 (s, 3H), 1.37 (s, 3H). The 13C{1H} NMR spectra also
demonstrate the coordination of an alkene unit [δ 74.9 (br)
(1); δ 62.2 (dd, J = 22, 12 Hz) (2)]. These shifts are broadly
similar to previously reported phosphine−alkene complexes,
e.g., A and G, δ 96.2 and 65.0, respectively.3 The 31P{1H} NMR
spectra show an A2MX spin system for both 1 and 2, with two
mutually coupled phosphorus environments observed in a 1:2
C5H7)}][BArF ] (A) on halide abstraction and subsequent
4
rapid dehydrogenation.3 Unfortunately, despite repeated
attempts we were unable to make the required precursor
Rh(DPEphos)(PCyp3)Cl. Instead the direct synthesis of the
coordinated dehydrogenated ligand was achieved, by addition
of DPEphos to [Rh(η6-C6H5F){PCyp2(η2-C5H7)}][BArF ]
4
(G)3 to form fac-[Rh(κ3-P,O,P-DPEphos){PCyp2(η2-C5H7)}]-
[BArF ] (1) in quantitative yield. The equivalent Xantphos
4
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hydrogenation of the bound alkene, as characterized by the
1
disappearance of the alkene signal in the H NMR spectrum,
and the generation of fac-[Rh(κ3-P,O,P-DPEphos)-
1
(H)2(PCyp3)][BArF ] (3) (Scheme 2). The H spectrum of
4
complex 3 shows two broad, integral 1H, hydride environments
at 298 K, suggesting a slow exchange process at room
temperature. On cooling to 223 K, these resolve into complex
signals centered at δ −8.66 ppm [apparent doublet of quintets J
= 149 Hz, 13 Hz] and −22.95 [apparent triplet, J = 13 Hz],
which have not shifted appreciably from those at 298 K. The
large 31P−1H coupling constant [J = 149 Hz] for the resonance
at δ −8.66 ppm shows that this hydride is opposite a
phosphorus atom. The 31P{1H} spectrum at 233 K reveals three
environments in a 1:1:1 ratio. Each phosphorus couples to
103Rh as well as two inequivalent phosphorus nuclei, with a pair
of phosphorus atoms lying trans to each other [J(PP) = 319
Hz] and the remaining phosphorus atom in a mutually cis
orientation to the others. In addition to these signals, at 223 K
under a pressure of H2 (4 atm) three new broad resonances are
observed at δ −1.79 (2H), −10.94 (1H), and −13.18 (1H),
which are attributed to the dihydrogen dihydride complex
[Rh(κ2-P,P-DPEphos)(η2-H2)(H)2(PCyp3)][BArF ] (4). The
4
ratio of 3:4 is 17:1 at this temperature. Although we have no
direct evidence, we assume that, to retain an 18-electron
configuration in 4, the central ether linkage of the DPEphos is
not bound and the DPEphos ligand is acting as a hemilabile
ligand.28−30
Evidence for a dynamic equilibrium between 3 and 4 was
obtained by cooling further to 198 K (500 MHz), whereby the
ratio of complexes 3:4 changed to 5:1. T1 relaxation
measurements37,38 for 4 were also gathered at this temperature.
The relative 2 H integral assigned to 4 at δ −1.79 has a
measured T1 of 21 ms (at 500 MHz), consistent with a
dihydrogen ligand, while the low-frequency hydride resonances
relax at 400 ms, typical of a hydride ligand.37,38 These data can
be compared with those for the closely related complexes
Figure 1. Solid-state structure of the cationic portion of 1 and 2.
Hydrogen atoms are omitted for clarity. Thermal ellipsoids are
presented at the 50% probability level. Selected bond lengths [Å] and
angles [deg], 1: Rh1−P1 2.2256(7), Rh1−P2 2.3270(7), Rh1−P3
2.3969(7), Rh1−O1 2.250(2), Rh1−C3 2.128(3), Rh1−C4 2.175(3),
C3−C4 1.425(4); P1−Rh1−P2 101.00(2), P1−Rh1−P3 108.95(2),
P2−Rh1−P3 110.83(2); 2: Rh1−P1 2.2285(8), Rh1−P2 2.4007(7),
Rh1−P3 2.3529(7), Rh1−O1 2.184(2), Rh1−C3 2.151(3), Rh1−C4
2.165(3), C3−C4 1.416(4); P1−Rh1−P2 105.87(3), P1−Rh1−P3
103.63(3), P2−Rh1−P3 118.17(3).
[Rh{Ph2P(CH2)2PPh2}(η2-H2)(H)2(PCyp3)][BArF ], η2-H2 19
4
ms, (H)2 215 ms (500 MHz),3 and [Ru(κ3-P,O,P-DPEphos)-
(η2-H2)(H)(PPh3)][BArF ], η2-H2 9.6 ms (400 MHz), (H)2
4
324 ms (400 MHz).39
The solid-state structure of 3, using crystals obtained by
recrystallization under H2 (vide infra), is consistent with the
NMR spectroscopic data for this complex and shows a distorted
six-coordinate octahedral geometry. Both hydride ligands were
located in the final difference map (Figure 2). The
tricyclopentylphosphine ligand is located trans to one
phosphorus atom of the DPEphos ligand (which itself adopts
a fac geometry at the metal center), and one of the hydride
ligands lies trans to the other phosphorus atom of the
diphosphine. The Rh−O distance [2.308(2) Å] is longer than
in 1, consistent with the high trans influence of the hydride,
ratio. Relatively small 31P−31P coupling constants (42 Hz, 1; 22
Hz, 2) show that the phosphorus atoms are located cis to each
other, similar to other Rh(I)−trisphosphine−alkene com-
plexes.36 These solution data are fully consistent with a fac
geometry for the phosphine ligands, as observed in the solid
state, and that the dehydrogenated PCyp ligand is bound tightly
to the metal center.
Reactivity of 1 and 2 with H2. Addition of hydrogen (4
atm, 10 min) to 1 at 298 K in CD2Cl2 solution results in the
a
Scheme 2
a
[BArF ] anions not shown.
4
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At 298 K complex 2 undergoes hydrogenation considerably
slower than 1 (5 days compared with 10 min). Two dihydride
isomers, fac-[Rh(κ3-P,O,P-Xantphos)(H)2(PCyp3)][BArF ] (5)
4
and mer-[Rh(κ3-P,O,P-Xantphos)(H)2(PCyp3)][BArF ] (6),
4
are formed (Scheme 3), unlike DPEphos, which gives rise to
only the fac-isomer. As breaking the Rh−O bond and
coordination of H2 in 1 and 2 is presumably the first step in
these reactions, prior to oxidative cleavage of H2, this difference
in reaction time supports a stronger or, at the very least, less
flexible nature of the Rh−O bond in 2 compared to 1. No
dihydrogen complex was observed for Xantphos.
1
The H NMR spectra of 5 and 6 at room temperature are
characterized by pairs of complex multiplet hydride environ-
ments at room temperature in a 2.2:1 ratio of 5:6, reflecting the
formation of two isomers: δ −9.33, −22.19 (5) and δ −7.93,
−20.49 (6). The signals at δ−9.33 (5) and −7.93 (6) show
distinctive trans coupling to 31P, J(PH) = 143 and 135 Hz,
respectively, as confirmed by 1H{31P} experiments. The signals
due to 5 were broadened slightly, compared to 6, which are
sharp at 298 K. The wide difference in chemical shifts between
the two hydride environments of each complex reflects the
nature of the substituent located trans to the hydride:
phosphorus or less strongly bound oxygen.40 The room-
temperature 31P{1H} spectrum exhibits three broadened
phosphorus environments for 5 (1:1:1 ratio), two of which
display both cis and trans 31P−31P coupling, while only two
sharp signals (2:1 ratio) are observed for 6, which show only cis
coupling. Upon cooling a solution containing a mixture of 5
and 6 from 293 to 253 K, the relative integrals of the hydride
resonances changed slightly from 1:2.2 6:5 to 1:1.7 6:5. This
suggests the presence of an equilibrium between the two
species. Moreover at low temperature, NMR signals due to 5
sharpen considerably. There is no significant change in
chemical shifts on cooling. The hydride resonances were
successfully simulated using gNMR41 as an ABMXYZ system in
Figure 2. Solid-state structure of the cationic portion of 3. Hydrogen
atoms (except hydride ligands) are omitted for clarity. Thermal
ellipsoids are presented at the 50% probability level. Selected bond
lengths [Å] and angles [deg]: Rh1−P1 2.3135(10), Rh1−P2
2.3349(10), Rh1−P3 2.3514(10), Rh1−O1 2.308(2), Rh1−H0A
1.49(4), Rh1−H0B 1.54(3); P1−Rh1−P2 153.78(4), P1−Rh1−P3
106.99(4), P2−Rh1−P3 99.20(3), O1−Rh1−P1 104.07(7), O1−
Rh1−P2 78.42(7), O1−Rh1−P3 81.12(6).
especially given the move from Rh(I) to smaller Rh(III) in 3.
By contrast Rh−P3 is not significantly longer than Rh−P2
[2.3514(10) versus 2.3349(10) Å] even though P3 is also trans
to a hydride. These similar bond lengths are reflected in similar
103Rh−31P coupling constants for the phosphines (104−114
Hz) in solution. This suggests that the bound oxygen ligand is
more susceptible to trans ligand influence than the phosphine,
which is consistent with the fact that it can be displaced by H2.
a
Scheme 3
a
[BArF ] anions not shown.
4
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5 and an ABMX2Y system in 6. Overall, these data support the
assigned κ3-fac and κ3-mer coordination geometries for 5 and 6,
respectively, with the κ3-mer isomer preferred marginally over
the κ3-fac. We suggest that the isomerization may occur via
decordination of the central oxygen atom to reveal a five-
coordinate intermediate.
before in DPEphos and Xantphos complexes on reaction with
MeCN.24,42
Complexes 3/4 and 5/6 lose H2 readily. When placed under
vacuum or upon addition of tbe (tbe = tertbutylethene), they
form the Rh(I) complexes [Rh(κ3-P,O,P-DPEphos)(PCyp3)]-
[BArF ] (9) and [Rh(κ3-P,O,P-Xantphos)(PCyp3)][BArF ]
4
4
A van’t Hoff plot (Scheme 3) for the equilibrium between 6
and 5 yields a straight line, from which the enthalpy of +4.4
0.2 kJ mol−1 and entropy, +21.3 0.6 J K−1 mol−1, associated
with this equilibrium were determined, giving an overall
(10), respectively, in quantitative yield by NMR spectroscopy
(Scheme 5). Complexes 5/6 lose H2 rapidly (one freeze−
thaw−degas cycle), while H2 loss is much slower for 3/4 (5
cycles). The rapid loss of H2 for 5/6 meant that the relative
rates of disappearance of the fac and mer isomers could not be
measured. It is interesting to note that the Xantphos ligand
promotes this reductive elimination faster than DPEphos,
although we cannot definitively say whether this is a steric or
electronic effect.21,23,49
ΔG(298 K) = −1.9
0.4 kJ mol−1 for 6 to 5. These data
show that enthalpically there is very little difference between
the κ3-fac and κ3-mer geometries in this system, and the driving
force for the preferred fac geometry in this particular case is
entropic. Although Xantphos can be considered to be a κ3-
meridonial-coordinating ligand,29,39,42−47 examples of κ3-fac
coordination are also known.29,42 Neither are that common,
however, compared to the κ2-P,P coordination mode.48 The
broadening of the NMR signals of 5 at room temperature might
suggest the ability to access greater conformational freedom
compared to 6, consistent with an increase in entropy. As the
relative order of these thermodynamic parameters for this fac
over mer preference are likely to be rather system-specific, we
are reluctant to generalize this result to other Xantphos
complexes.
The 31P{1H} NMR spectra for both 9 and 10 reveal two
mutally cis phosphorus environments in a 2:1 ratio, which show
1
coupling to a Rh(I) center. The H NMR spectra show no
evidence for hydrides, and for 10 a single, 6H, methyl
environment is observed for the Xantphos ligand. The solid-
state structures of 9 and 10 demonstrate square-planar
geometries (sum of the angles around the Rh center =
359.99° and 361.15°, respectively) (Figure 4). The chelating
phosphorus atoms approach a trans configuration [156.61(5)°
(9); 158.409(7)° (10)]. The Rh−O bond distance in 9 is
significantly shorter than in 1 [2.189(3) Å (9) vs 2.2503(17) Å
(1)] on moving to this Rh(I) square-planar geometry, while
that for 10 lengthens compared to 2 [2.222(5) Å (10) vs
2.1837(19) Å (2)]. The structural metrics of 9 and 10 compare
favorably with other Rh(I) complexes containing κ3-P,O,P-trans
spanning Xantphos-type ligands.44,47 Complexes 9 and 10 do
not react further with respect to the bound PCyp3 ligand, and
no dehydrogenation (via C−H activation/β-hydrogen transfer)
is observed even under forcing conditions in the presence of a
hydrogen acceptor (tbe, 313 K). By contrast complexes 9 and
10 react with H2 (4 atm) to re-form mixtures of 3/4 and 5/6,
respectively, as monitored by NMR spectroscopy.
The results so far reported suggest that 16-electron, low-
coordinate, intermediates are accessible, probably via O-
decoordination in the DPEphos and Xantphos compounds.
To explicitly probe this, an excess of MeCN (10 equivalents)
was added to CH2Cl2 solutions of mixtures of complexes 3/4
and 5/6 under an atmosphere of H2, to avoid loss of H2 from
the metal center (vide infra). This afforded mer-[Rh(κ2-P,P−
DPEphos)(PCyp3)(H)2(MeCN)][BArF ] (7) and mer-[Rh(κ2-
4
P,P-Xantphos)(PCyp3)(H)2(MeCN)][BArF ] (8), respectively,
4
in quantitative yield by NMR spectroscopy (Scheme 4). The
a
Scheme 4
CONCLUSIONS
■
We have studied a number of rhodium complexes of the
tricyclopentylphosphine ligand partnered with wide-bite-angle
chelating diphosphine ligands DPEphos and Xantphos. Our
initial hopes that these ligands would support dehydrogenation
of the PCyp3 ligand were not realized due to the relatively
strong κ3-P,O,P binding of the chelate diphosphine ligand, at
least compared to a weak C−H agostic bond that would
precede the desired C−H activation. Instead we have shown
that the Xantphos ligand is actually rather flexible, for example,
with fac-κ3-P,O,P and mer-κ3-P,O,P geometries closely matched
in terms of enthalpy, with entropy playing an unexpected role
in determining the overall position of equilibrium between the
two. As each conformation has a different ligand bite angle
associated with the metal center (i.e., fac-κ3-P,O,P 107° in 3,
mer-κ3-P,O,P 156° in 10), it is tempting to suggest that the
ability for the ligand to adopt both coordination geometries
(and be in equilibrium between them) might have a significant
bearing on other metal-centered processes that are intimately
linked to the relative demands of the phosphines, such as the
relative rates of hydride insertion into an alkene or reductive
elimination.23
a
[BArF ] anions not shown.
4
formation of 7 and 8 was demonstrated by the observation of
three separate environments in their respective 31P{1H} NMR
spectra, for which a pair of resonances in each show trans
31P−31P coupling. In the 1H NMR spectra of 7 and 8, two sharp
hydride multiplets were observed for each complex. Selective
1H{31P} NMR spectroscopy experiments removed several
orders of fine structure in these resonances to reveal the H−
H and Rh−H coupling constants for these signals. Large P−H
coupling constants, J(PHtrans) = 149 and 149 Hz respectively
for 7 and 8, locate one hydride trans to a phosphine.
Replacement of the ether-oxygen (e.g., 3/4) with a more
strongly bound NCMe ligand (e.g., 7) results in a downfield
shift of 3−5 ppm for the trans hydride, as expected.40 These
signals were successfully modeled using gNMR (Figure 3).
Related κ3-P,O,P to κ2-P,P geometry changes have been noted
2724
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Organometallics
Article
1
1
Figure 3. Experimental and simulated H and H{31P} NMR spectra for 7 and 8.
a
Scheme 5
a
[BArF ] anions not shown.
4
EXPERIMENTAL SECTION
■
All manipulations, unless otherwise stated, were performed under an
atmosphere of argon, using standard Schlenk and glovebox techniques.
Glassware was oven-dried at 130 °C overnight and flamed under
vacuum prior to use. CH2Cl2, MeCN, hexane, and pentane were dried
using a Grubbs-type solvent purification system (MBraun SPS-800)
and degassed by successive freeze−pump−thaw cycles.50 CD2Cl2,
C6H5CF3, and C6H5F were distilled under vacuum from CaH2 and
stored over 3 Å molecular sieves. tert-Butylethylene was dried over
sodium, vacuum distilled, and stored over 3 Å molecular sieves.
Microanalyses were performed by Elemental Microanalysis Ltd. NMR
spectra were recorded on Varian Unity+ 500 MHz or Bruker AVII 500
MHz spectrometers at room temperature unless otherwise stated.
Residual protio solvent was used as reference for H and 13C NMR
1
spectra in deuterated solvent samples. 31P NMR spectra were
referenced against 85% H3PO4 (external). Chemical shirts are quoted
in ppm and coupling constants in Hz. Electrospray Ionization mass
spectrometry (ESI-MS) was recorded using a Bruker MicrOTOF
Figure 4. Solid-state structure of the cationic portion of 9 and 10.
Hydrogen atoms are omitted for clarity. Thermal ellipsoids are
presented at the 50% probability level. Selected bond lengths [Å] and
angles [deg], 9: Rh1−P1 2.2375(13), Rh1−P2 2.3247(12), Rh1−P3
2.2678(12), Rh1−O1 2.189(3); P1−Rh1−P2 102.71(5), P1−Rh1−P3
100.67(4), P2−Rh1−P3 156.61(5), O1−Rh1−P1 178.89(10), O1−
Rh1−P2 77.27(9), O1−Rh1−P3 79.34(9); 10: Rh1−P1 2.2458(19),
Rh1−P2 2.2985(19), Rh1−P3 2.2659(19), Rh1−O1 2.222(5); P1−
Rh1−P2 101.07(7), P1−Rh1−P3 97.83(7), P2−Rh1−P3 158.40(7),
O1−Rh1−P1 174.08(15), O1−Rh1−P2 80.80(14), O1−Rh1−P3
81.45(14).
instrument directly connected to a modified Innovative Technology
glovebox.51 Typical acquisition parameters were as follows: sample
flow rate (4 μL/min), nebulizer gas pressure (0.4 bar), drying gas
(argon at 60 °C, flowing at 4 L/min), capillary voltage (4.5 kV), funnel
voltage (200 V). MS samples were diluted to a concentration of 1 ×
10−6 M before running. [Rh(η6-C6H5F){PCyp2(η2-C5H7)}][BArF ], G,
4
was prepared by the literature procedure.3 All other chemicals were
used as received from Sigma-Aldrich, Acros, Fisher, Fluka,
Fluorochem, and Strem Chemicals.
Crystallography. Data were collected on an Enraf Nonius Kappa
CCD diffractometer using graphite-monochromated Mo Kα radiation
(λ = 0.71073 Å) and a low-temperature device [150(2) K];52 data
were collected using COLLECT, reduction and cell refinement were
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Table 1. Crystallographic Data for 1, 2, 3, 9, and 10
1
2
3
9
10
CCDC
849263
849264
849265
849266
849267
formula
C83H65BF24OP3Rh
1740.98
C86H69BF24OP3Rh
1781.04
C83H69BF24OP3Rh.C6H5F
1841.11
C83H67BF24OP3Rh
1743.00
C86H71BF24OP3Rh
1783.06
M
cryst syst
triclinic
triclinic
triclinic
monoclinic
P21/c
triclinic
space group
a [Å]
P1
P1
̅
P1
̅
P1
̅
̅
13.4238(1)
14.2954(1)
20.7081(2)
73.4829(4)
84.0057(4)
83.9868(4)
3777.28(5)
2
12.8119(1)
16.2707(2)
20.9044(2)
84.2396(4)
72.9026(4)
85.5884(4)
4138.93(7)
2
13.3042(3)
17.7665(3)
20.6626(5)
111.7567(9)
97.3499(8)
94.865(1)
4452.2(2)
2
13.9956(1)
33.5274(3)
17.8616(2)
90
12.8590(1)
17.1395(1)
21.8146(2)
99.1448(4)
106.8047(4)
100.7042(4)
4405.40(6)
2
b [Å]
c [Å]
α [deg]
β [deg]
108.1544(4)
90
γ [deg]
V [Å3]
7964.1(1)
4
Z
density [g cm−3]
μ [mm−1]
1.531
1.429
1.373
1.454
1.344
0.397
0.364
0.342
0.376
0.342
θ range [deg]
reflns collected
Rint
5.09 < θ < 25.03
24 027
5.09 < θ < 25.03
25 833
3.35 < θ < 25.03
23 438
5.10 < θ < 25.03
25 718
5.12 < θ < 25.03
27 541
0.0219
0.0243
0.0337
0.0419
0.0217
completeness
no. of data/restr/params
R1 [I > 2σ(I)]
wR2 [all data]
GoF
99.0%
98.9%
94.9%
98.8%
98.9%
13 197/507/1136
0.0329
14 469/382/1089
0.0420
14 947/764/1161
0.0510
13 918/1081/1129
0.0572
15 395/3812/1365
0.0991
0.0794
0.1190
0.1435
0.1396
0.2549
1.030
1.073
1.055
1.042
1.115
largest diff pk and hole [e Å−3]
0.611, −0.473
0.706, −0.399
0.685, −0.646
0.730, −0.688
1.466, −1.161
performed using DENZO/SCALEPACK.53 The structures were
solved by direct methods using SIR200454 and refined with full-matrix
least-squares on F2 using SHELXL-97.55 All non-hydrogen atoms were
refined anisotropically. Hydride and alkene hydrogen atoms were
located on the Fourier difference map; restraints were applied to their
1,2 and 1,3 bond distances, and their isotropic displacement
parameters were fixed to ride on the parent atoms. Other hydrogen
atoms were placed in calculated positions using the riding model.
Problematic solvent disorder in 2, 3, and 10 was treated using the
SQUEEZE algorithm.56 Details of other disorder modeling are
documented in the crystallographic information files under the
heading _refine_special_details. Minor disorder components are
omitted from the figures for clarity. Restraints to thermal parameters
were applied and were necessary in order to maintain sensible values.
Graphical representations of the structures were made using
ORTEP3.57 Crystallographic data are detailed in Table 1.
J(PC) 9.5, CH2]. ESI-MS (C6H5F, 373 K, 4.5 kV): positive ion m/z
877.2298 [M]+ (100% calc 877.2359). Anal. Calcd for
C83H65B1F24O1P3Rh1 (1741.003 g mol−1): C, 57.26; H, 3.74. Found:
C, 57.56; H, 3.16.
f ac-[Rh(κ3-P,O,P-Xantphos){P(Cyp)2(η2-C5H7)}][BArF ] (2).
4
Xantphos (22 mg, 0.038 mmol) was added to a solution of [Rh(η6-
C6H5F){PCyp2(η2-C5H7}][BArF ] (G) (49.5 mg, 0.038 mmol) in
4
CH2Cl2 (5 mL) and stirred for 2 h. The solvent was removed in vacuo,
and the residue was washed with pentane (2 × 3 mL) and dried under
reduced pressure. Diffusion of pentane into a solution of the residue in
CH2Cl2 gave 2 as orange crystals (50 mg, 74%).
1H NMR (500 MHz, CD2Cl2): δ 7.75 (m, 8H, BArF ), 7.57 (br, 4H
4
BArF ), 7.67−7.52 (m, 6H, ArH), 7.51−7.41 (m, 6H, ArH), 7.36−7.19
4
(m, 8H, ArH), 7.18−7.03 (m, 6H, ArH), 3.58 (s, 2H, HCCH), 1.86
(s, 3H, CH3), 1.85−1.17 (m, 21H, PCyp), 1.37 (s, 3H, CH3), 1.11 −
0.89 (m, 4H, PCyp). 31P{1H} NMR (202 MHz, CD2Cl2): δ 90.66 [dt,
J(RhP) 152, J(PPcis) 22], 26.56 [dd, J(RhP) 131, J(PPcis) 22].13C{1H}
f ac-[Rh(κ3-P,O,P-DPEphos){P(Cyp)2(η2-C5H7)}][BArF ] (1).
4
NMR (126 MHz, CD2Cl2): δ 162.10 [q, J(BC) 50, BArF ], 156.65 (t, J
DPEphos (16.5 mg, 0.031 mmol) was added to a solution of
4
[Rh(η6-C6H5F){PCyp2(η2-C5H7)}][BArF ] (G) (40 mg, 0.031 mmol)
= 8.8, C6H3OP), 136.36 (t, J = 18, C6H5), 135.30 (t, J = 2.3, C6H3OP),
4
135.14 (s, BArF ), 133.89 (s, C6H3OP), 133.67 (t, J = 11, C6H5),
in CH2Cl2 (5 mL) and stirred for 2 h. The solvent was removed in
vacuo, and the residue was washed with pentane (2 × 3 mL) and dried
under reduced pressure. Diffusion of pentane into a solution of the
residue in C6H5F gave 1 as red crystals. (43 mg, 80%).
4
133.03 (t, J = 7.3, C6H5), 132.45 (t, J = 6.1, C6H5), 130.48 (s, C6H5),
130.38 (s, C6H5), 129.31 (t, J = 4.6, C6H5), 129.21 [qq, J(FC) 31,
J(BC) 3.1, BArF ], 129.10 (t, J = 4.2, C6H5), 127.88 (s, C6H3OP),
4
1H NMR (500 MHz, CD2Cl2): δ 7.73 (m, 8H, BArF ), 7.56 (br, 4H,
127.27 (s, C6H3OP), 126.09 (dd, J = 17, J = 14, C6H3OP), 124.93 [q,
4
BArF ) 7.50−7.25 (m, 22H, ArH), 7.18 [dd, J(PH) 8.5, J(HH) 4.4,
J(FC) 272, BArF ], 117.81 [sept, J(FC) 3.8, BArF ], 62.22 (dd, J = 22, J
4
4
4
2H, POP bridging ArH], 7.06 (m, 4H, POP bridging ArH), 3.84 (s,
2H, HCCH), 2.04 (br s, 1H, PC5H7), 1.84 [apparent t, J(PH) 13,
2H, PCyp CH], 1.65−1.30 (m, 16H, PCyp), 1.25−1.00 (m, 4H,
PCyp). 31P{1H} NMR (202 MHz, CD2Cl2): δ 84.14 [dt, J(RhP) 145,
J(PPcis) 42], 18.99 [dd, J(RhP) 134, J(PPcis) 42].13C{1H} NMR (126
= 12, CC), 36.79 (s), 36.51 [br dt, J(PC) 25, J(PC) 4.6, CH], 35.24
[d, J(PC) 31, CH], 35.18 (s, CH2), 33.03 (s, CH3), 30.63 [d, J(PC)
5.3], 28.55 (s, CH2), 25.61 [d, J(PC) 9.9, CH2], 25.10 [d, J(PC) 11,
CH2], 22.85 (s, CH3). ESI-MS (C6H5F, 373 K, 4.5 kV): positive ion
m/z 917.2665 [M]+ (100% calcd 917.2672). Anal. Calcd for
C86H69B1O1F24P3Rh1 (1781.067 g mol−1): C, 57.99; H, 3.90. Found:
C, 58.16; H, 3.72.
MHz, CD2Cl2): δ 162.17 [q, J(BC) 51, BArF ], 160.05 (d, J = 12,
4
C6H4OP), 135.35 (s, C6H4OP), 135.20 (s, BArF ), 133.59 (d, J = 12,
4
fac-[Rh(κ3-P,O,P-DPEphos)(H)2(PCyp3)][BArF ] (3) and [Rh(κ2-
C6H5), 133.19 (d, J = 34, C6H5), 132.11 (s, C6H4OP), 130.79 (s,
4
C6H5), 129.07 [qq, J(FC) 32, J(BC) 2.9, BArF ], 129.00 (d, J = 9.5,
P,P-DPEphos)(H)2(η2-H2)(PCyp3)][BArF ] (4). (3) A solution of 1
4
4
C6H5), 126.74 (d, J = 32, C6H4OP), 126.36 (d, J = 4.8, C6H4OP),
(25 mg, 0.0144 mmol) in C6H5F (2 mL) was frozen in liquid nitrogen,
placed under vacuum and backfilled with H2, and shaken for 10 min. 4
was observed upon cooling this solution to 198 K at a ratio of 1:5
(3:4) and was characterized by H NMR spectroscopy. Diffusion of
hydrogen-saturated pentane into the resulting solution and shaking,
125.00 [q, J(FC) 273, BArF ], 120.03 (d, J = 4.8, C6H4OP), 117.87
4
[sept, J(FC) 3.8, BArF ], 74.90 (br s, CC), 36.95 [dt, J (PC) 23,
4
1
J(PC) 2.9, CH], 36.40 [d, J (PC) 2.9, CH2], 32.31 [d, J (PC) 28, CH],
31.56 (s, CH2), 29.15 (s, CH2), 25.92 [d, J(PC) 8.6, CH2], 25.49 [d,
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after cooling to 253 K, gave 3 as colorless crystals. Complex 3 loses H2
when removed from a H2 atmosphere, and thus microanalytical data
were not obtained.
27H, PCyp3), 1.38 (s, 3H, CH3), −11.92 [apparent multiplet,*
J(PtransH) 149, J(PcisH) 17.3, J(PcisH) 14.3, J(RhH) 10.8, J(HH) 9.2,
1H, RhH], −17.92 [apparent septet,* J(PcisH) 21.1, J(PcisH) 12.5,
J(RhH) 10.6, J(PcisH), J(RhH) 9.2, J(HH) 7.3, 1H, RhH]. *These
complex signals were simulated using gNMR to extract the
corresponding spectral parameters.
1
3. H NMR (500 MHz, CD2Cl2, 223 K): δ 7.80−7.16 (m, 21H,
ArH), 7.75 (m, 8H, BArF ), 7.56 (br, 4H, BArF ), 7.10 (apparent
4
4
triplet, J = 7.7, 1H, ArH), 7.00−6.84 (m, 3H ArH), 6.44 (apparent td, J
= 8.2, 1.6, 2H, ArH) 5.97 (m, 2H, ArH), 1.80−1.20 (m, 27H, PCyp3),
−8.66 [apparent doublet of quintets J(PHtrans) 149, J = 13, 1H, T1 =
0.52 s, RhH], −22.95 (apparent broad triplet, J = 13, 1H, T1 = 0.54 s,
RhH). 31P{1H} NMR (202 MHz, CD2Cl2, 223 K) δ 62.31 [ddd,
J(PPtrans) 319, J(RhP) 114, J(PPcis) 18], 34.00 [ddd, J(PP) 319, J(RhP)
106, J(PPcis) 22], 27.71 [apparent dt, J(RhP) 104, J(PPcis) 20]. ESI-MS
(C6H5F, 373 K, 4.5 kV): positive ion m/z, 879.2352 [M − H2]+
(100%, calcd 879.2515), 881.2477 [M]+ (65%, calcd 881.2672).
4. 1H NMR (500 MHz, CD2Cl2, 198 K): δ −1.79 (br s, 2H, T1 = 21
ms), −11.06 [br d, J(PHtrans) 149, 1H], −13.33 (br, 1H). T1 values for
the two hydride resonances are approximately 400 ms at this
temperature. Although we did not determine T1 min. values, their
relative magnitudes allow for a clear discrimination between hydride
and dihydrogen ligands.
31P{1H} NMR (202 MHz, CD2Cl2): δ 56.59 [ddd, J(PPtrans) 365,
J(RhP) 115, J(PPcis) 15], 20.03 [ddd, J(PPtrans) 365, J(RhP) 110,
J(PPcis) 20], 15.27 [ddd, J(RhP) 92, J(PPcis) 20, J(PPcis) 15]. ESI-MS
(1,2-C6H4F2, 333 K, 4.5 kV): positive ion m/z, 919.2881 [M − MeCN
− H2]+ (100% calcd 919.2828).
[Rh(κ3-P,O,P-DPEphos)(PCyp3)][BArF ] (9). A solution of 1 (25
4
mg, 0.0144 mmol) in C6H5F (2 mL) was frozen in liquid nitrogen,
placed under vacuum and backfilled with H2, and shaken for 10 min to
give 3. The H2 atmosphere was removed under vacuum by freeze/
pump/thaw of the solution three times followed by addition of 5 μL of
3,3-dimethylbut-1-ene. The solvent was then removed under reduced
pressure, and the resulting residue was washed with pentane (2 × 3
mL) and dried in vacuo. An orange crystal suitable for X-ray diffraction
was obtained by diffusion of pentane into a solution of 9 in C6H5CF3.
Despite repeated attempts, isolation of significant solid material
proved unsuccessful as the complex (although pure by NMR
spectroscopy) remained an oil.
[Rh(κ3-P,O,P-Xantphos)(H)2(PCyp3)][BArF ] isomers (fac-5/
mer-6). A solution of 2 (8 mg, 0.0045 mmol)4in CD2Cl2 (500 μL)
was frozen in liquid nitrogen, placed under vacuum and backfilled with
H2, shaken, and left to stand for 5 days. 5/6 were then characterized by
1H and 31P{1H} NMR spectroscopy.
1H NMR (500 MHz, CD2Cl2): δ 8.28 (br, 2H, ArH), 7.96−7.43 (m,
20H, ArH), 7.75 (m, 8H, BArF ), 7.58 (br, 4H BArF ), 7.29 (apparent
4
4
5. Selected 1H NMR (500 MHz, CD2Cl2): δ −9.33 [br d, J(PHtrans
)
td, J = 7.3, 1.6 2H, ArH, 7.16 (t, J = 7.6, 2H, ArH), 6.91 (br dt, J = 8.4,
2.0, 2H, ArH) 1.90−0.88 (m, 27H, PCyp3). 31P{1H} NMR (202 MHz,
CD2Cl2): δ 48.84 [dt, J(RhP) 190, J(PPcis) 35], 33.42 [dd, J(RhP) 156,
J(PPcis) 35]. 13C{1H} NMR (126 MHz, CD2Cl2): δ 162.31 [q, J(BC)
50, BArF ], 158.38 (t, J = 6.9, C6H4OP), 135.93 (br m, C6H5), 135.35
143, 1H, T1 = 0.25 s, RhH], −22.19 (br, 1H, T1 = 0.22 s, RhH).
31P{1H} NMR (202 MHz, CD2Cl2): δ 50.85 [br dd, J(PPtrans) 319,
J(RhP) 117], 35.36 [br d, J(RhP) 91], 27.34 [br d, J(RhP) 95]. ESI-
MS (C6H5F, 373 K, 4.5 kV): positive ion m/z, 919.2696 [M − H2]+
(100%, calcd 919.2828).
(s, BArF4), 133.64 (br m, C6H5), 133.39 (s, C6H4OP), 132.43 (s,
4
6. Selected 1H NMR (500 MHz, CD2Cl2): δ −7.93 [apparent dqd,*
J(PHtrans) 135, J(PcisH) 13, J(RhH) 13, J(HH) 5.8, 1H, T1 = 0.55 s,
RhH], δ −20.49 [apparent multiplet,* J(PcisH) 28.4, J(PcisH) 12.3,
J(RhH) 19.2, J(HH) 5.8, 1H, T1 = 0.43 s, RhH]. *These complex
signals were simulated using gNMR to extract the corresponding
spectral parameters. 31P{1H} NMR (202 MHz, CD2Cl2): δ 36.89 [dd,
J(RhP) 114, J(PPcis) 20], 20.71 [dt, J(RhP) 97, J(PPcis) 20].
C6H4OP), 132.01 (br m, C6H5), 129.62 (t, J = 5.0, C6H5), 129.41 [qq,
J(FC) 31, J(BC) 3, BArF ], 126.62 (t, J = 3.1, C6H4OP), 125.14 [q,
4
J(FC) 272, BArF ], 118.02 [sept, J(FC) 3.8, BArF ], 115.57 (t, J = 2.3,
4
4
C6H4OP), 40.97 [d, J (PC) 29, CH], 30.39 (br m, CH2), 24.84 (br m,
CH2). ESI-MS (C6H5F, 373 K, 4.5 kV): positive ion m/z, 879.2429
[M]+ (100%, calcd 879.2515).
[Rh(κ3-P,O,P-Xantphos)(PCyp3)][BArF ] (10). A solution of 2 (25
4
[Rh(κ2-P,P−DPEphos)(PCyp3)(H)2(MeCN)][BArF ] (7). A solu-
4
mg, 0.0144 mmol) in C6H5F (2 mL) was placed under 4 atm of H2,
shaken, and left for 5 days to yield 5/6. The H2 was removed under
vacuum by freeze/pump/thaw of the solution. The solvent was then
removed under reduced pressure, and the resulting residue was washed
with pentane (2 × 3 mL) and dried in vacuo. A crystal of 10 suitable
for X-ray diffraction was obtained by diffusion of pentane into a
solution of the residue in C6H5F. Despite repeated attempts, isolation
of significant solid material proved unsuccessful, as the complex
(although pure by NMR spectroscopy) remained an oil.
tion of 1 (8 mg, 0.0046 mmol) in C6H5F (500 μL) was frozen in liquid
nitrogen, placed under vacuum and backfilled with H2, and shaken for
10 min to give 3. MeCN (2 μL) was added, and the product was
immediately characterized in situ by 1H and 31P{1H} NMR
spectroscopy at 298 K.
1H NMR (500 MHz, CD2Cl2): δ 7.74 (m, 8H, BArF ), 7.57 (br, 4H
4
BArF ), 7.56−7.37 (m, 12H, ArH), 7.34 (br t, 3H, ArH), 7.28−6.96
4
(m, 9H, ArH), 6.91 (br t, J = 7.3, 1H, ArH), 6.63 (br t, J = 7.1 1H,
ArH) 6.45−6.27 (m, 2H, ArH), 1.75−1.16 (m, 30H, PCyp3 and
coordinated MeCN), −11.34 [apparent doublet of quintets,*
J(PHtrans) 149, J(PcisH) 16.7, J(PcisH) 11.7, J(RhH) 14.4, J(HH) 8.5,
1H, RhH], −17.76 [apparent multiplet,* J(PcisH) 17.2, J(PcisH) 14.6,
J(PcisH) 12.0, J(RhH) 10.4, J(HH) 8.5, 1H, RhH]. *These complex
signals were simulated using gNMR to extract the corresponding
spectral parameters. 31P{1H} NMR (202 MHz, CD2Cl2): δ 50.85 [dd,
J(PPtrans) 357, J(RhP) 110], 32.08 [dd, J(PPtrans) 358, J(RhP) 112],
22.88 [d, J(RhP) 99]. ESI-MS (C6H5F, 373 K, 4.5 kV): positive ion m/
z, 879.2380 [M − MeCN − H2]+ (100% calcd 879.2515), 922.2783
[M]+ (10% calcd 922.2937). ESI-MSMS of peak 922.2783 m/z
(C6H5F): 881.2528 [M − MeCN]+ (calcd 881.2672), 879.2338 [M −
MeCN − H2]+ (calcd 879.2515).
1H NMR (500 MHz, CD2Cl2): δ 7.98 (m, 8H, ArH), 7.74 (br, 8H,
BArF ), 7.58 (m, 10H, BArF and ArH), 7.51 (m, 8H, ArH), 7.29 (m,
4
4
2H, C6H3OP), 7.21(t, 2H, J = 7.7 C6H3OP), 1.63 (s, 6H, CH3), 1.61
(br m, 3H, PCyp3), 1.48 (br m, 6H, PCyp3), 1.31 (br m, 12H, PCyp3),
0.99 (br m, 6H, PCyp3). 31P{1H} NMR (202 MHz, CD2Cl2): δ 44.33
[dt, J(RhP) 193, J(PPcis) 35], 33.08 [dd, J(RhP) 156, J(PPcis) 35].
13C{1H} NMR (126 MHz, CD2Cl2): δ 162.10 [q, J(BC) 50, BArF ],
4
153.05 (t, J = 8.1, C6H3OP), 135.13 (s, BArF ), 134.13 (t, J = 6.9,
4
C6H5), 133.44 (s, C6H3OP), 132.44 (t, J = 22, C6H5), 131.56 (s,
C6H5), 131.40 (t, J = 3.1, C6H3OP), 130.96 (s, C6H3OP), 129.32 (t, J
= 5.0, C6H5), 129.20 [qq, J(FC) 31, J(BC) 2.7, BArF ], 126.79 (t, J =
4
2.7, C6H3OP), 126.46 (t, J = 16, C6H3OP), 124.93 [q, J(FC) 272,
BArF ], 117.80 [sept, J(FC) 3.8, BArF ], 42.22 [br d, J(PC) 29, CH],
4
4
[Rh(κ2-P,P-Xantphos)(PCyp3)(H2)(MeCN)][BArF ] (8). A solu-
4
34.26 (s, qC), 33.55 (s, CH3), 30.60 (s, CH2), 25.00 [d, J(PC) 11,
CH2]. ESI-MS (C6H5F, 373 K, 4.5 kV): positive ion m/z, 919.2708
[M]+ (100% calcd 919.2828).
tion of 2 (8 mg, 0.0045 mmol) in CD2Cl2 (500 μL) was frozen in
liquid nitrogen, placed under vacuum and backfilled with H2, shaken,
and left for 5 days to yield 5/6. MeCN (2 μL) was added, and the
product was immediately characterized in situ by 1H and 31P{1H}
NMR spectroscopy at 298 K.
ASSOCIATED CONTENT
■
1H NMR (500 MHz, CD2Cl2): δ 7.72 (m, 8H, BArF ), 7.63 (ddd, J =
4
S
* Supporting Information
10.7, 7.7, 1.2, 2H, ArH), 7.56 (m, 4H, BArF ), 7.47−7.36 (m, 6H,
4
This material is available free of charge via the Internet at
http://pubs.acs.org.
ArH), 7.33 (m, 2H, ArH), 7.28−6.99 (m, 14H, ArH), 6.74 (m, 1H,
C6H3OP), 6.30 (m, 1H, C6H3OP), 1.92 (s, 3H, CH3), 1.85−1.19 (m,
2727
dx.doi.org/10.1021/om201034m | Organometallics 2012, 31, 2720−2728

Organometallics
Article
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AUTHOR INFORMATION
■
Corresponding Author
*E-mail: andrew.weller@chem.ox.ac.uk.
ACKNOWLEDGMENTS
We thank the EPSRC and the University of Oxford for support
■
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