[BArF4]: A latent low-coordinate rhodium(I) PNP pincer compound

Article abstract of DOI:10.1021/om2004964

An expedient new route to the cationic [(PNP^tBu)Rh(L)] ⁺ metal fragments (PNP^tBu = κ³-NC ₅H₃-2,6-(CH₂P ^tBu₂) ₂; L = CO, acetone, ethene, MeCN, N₂) by the synthesis of, then substitution of PCy₃ in, [(PNP^tBu)Rh(PCy ₃)][BAr^F₄] is reported. This synthetic route also allows for the synthesis of the new dihydrogen complex [(PNP ^tBu)Rh(H₂)][BAr^F₄]. [(PNP ^R)Rh(PCy₃)][BAr^F₄] (R= Ph, Cy, Mes) are also reported, in which the PCy₃ ligand is more tightly bound to the metal center.

Full text of DOI:10.1021/om2004964

NOTE
pubs.acs.org/Organometallics
[Rh{NC5H3-2,6-(CH2PtBu2)2}(PCy3)][BArF ]: A Latent Low-Coordinate
Rhodium(I) PNP Pincer Compound
4
Adrian B. Chaplin and Andrew S. Weller*
Department of Chemistry, Inorganic Chemistry Laboratory, University of Oxford, Oxford, OX1 3QR, U.K.
S Supporting Information
b
ABSTRACT: An expedient new route to the cationic
[(PNPtBu)Rh(L)]+ metal fragments (PNPtBu = k3-NC5H3-2,6-
t
(CH2P Bu2)2; L = CO, acetone, ethene, MeCN, N2) by the
synthesis of, then substitution of PCy3 in, [(PNPtBu)Rh-
(PCy3)][BArF ] is reported. This synthetic route also allows
4
for the synthesis of the new dihydrogen complex [(PNPtBu)-
Rh(H2)][BArF ]. [(PNPR)Rh(PCy3)][BArF ] (R= Ph, Cy, Mes) are also reported, in which the PCy3 ligand is more tightly bound
4
4
to the metal center.
ultidentate “pincer” typeÀligands exemplified by PNPR,
Scheme 1
M
PCPR, and PONOPR play an ever-increasing role in
organometallic and catalytic chemistry (PNPR = k3-NC5H3-
2,6-(CH2PR2)2; PCPR = k3-C6H3-1,3-(CH2PR2)2; PONOPR =
k3-NC5H3-2,6-(OPR2)2; R = alkyl, aryl).1À3 One of the attrac-
tive properties of these ligand sets is their apparent ability to
support the generation of low-coordinate reactive metal species
that are implicated in many catalytic cycles, as demonstrated by
their role in alkane dehydrogenation4,5 and the characterization
of a σ-methane complex.6 In some cases these ligands can also act
in a noninnocent manner, undergoing reversible dearomatization
and subsequent cooperative reactivity between the ligand and
the metal.7À10 With regard to group 9 complexes of PNPR lig-
ands, cationic complexes of the general formula [(PNPtBu)-
Rh(L)]+ (L = weakly bound ligand11À13) are potentially useful
precursors to such reactive 14-electron species. Here we report
a new route to [(PNPtBu)Rh(L)]+ cations by the expedient syn-
In a similar manner, we now report that addition of the pincer
ligands PNPR (R = Ph, Cy, Mes, tBu; Mes = 2,4,6-Me3C6H2) to
[Rh(Binor-S)(PCy3)][BArF ] (1) results in the formation of the
4
new Rh(I) complexes [(PNPR)Rh(PCy3)][BArF ] (2a, R = Ph;
4
2b, R = Cy; 2c, R = Mes; 2d, R = tBu), which are all isolated in
reasonable yield by recrystallization (Scheme 1). The NMR
spectroscopic data in CD2Cl2 for 2a,b are unremarkable and
are fully consistent with pseudo-square-planar structure with
time-averaged C2v symmetry. In particular, two mutually coupled
signals are observed in the 31P{1H} NMR spectrum in a 2:1 ratio,
and a single, integral 4H environment is observed for the PNPR
methylene protons in the 1H NMR spectrum. For 2c the bulky
Mes group has restricted rotation of the aryl groups, and C2
symmetry is observed: i.e., six equal-intensity (6H) methyl and
thesis and onward reactivity of [(PNPtBu)Rh(PCy3)][BArF ], in
4
which steric pressure between the tBu and Cy groups invokes a
reactive {(PNPtBu)Rh}+ fragment which combines readily with a
variety of ligands (CO,11 acetone,11 ethene,12 MeCN,12 N213) to
give [(PNPtBu)Rh(L)][BArF ]. We demonstrate that this syn-
4
thetic route to a latent 14-electron complex allows for the syn-
1
two CH2 environments in the H NMR spectrum (CD2Cl2).
thesis of the new dihydrogen complex [(PNPtBu)Rh(H2)][BArF ]
The 31P{1H} NMR spectrum shows two mutually coupled
signals in a 2:1 ratio that also couple to 103Rh. The structure of
2c was confirmed by single-crystal X-ray diffraction, and although
the final structural refinement was poor, the connectivity was
confirmed (Supporting Information). For PNPtBu steric influ-
ences now become more important and the 31P{1H} NMR
spectrum of the isolated material in 1,2-C6H4F2 solution shows
two species, one with bound PCy3 (δ 63.3, 2P, dd; δ 47.4, 1P, dt)
identified as 2d and one with a broad signal at δ 67.3 that is
accompanied by free PCy3 (δ 11.2). In the 1H NMR spectrum
and also report the synthesis of [(PNPR)Rh(PCy3)][BArF4]
4
(R = Ph, Cy, Mes), in which the PCy3 ligand is more tightly
bound.
’ RESULTS AND DISCUSSION
We have previously reported that addition of Lewis Bases to
the straightforwardly prepared CÀC σ complexes [Rh(Binor-S)-
(PR3)][BArF ] (Binor-S = 1,2,4,5,6,8-dimetheno-S-indacene,
4
R = iPr, Cy (1); ArF = C6H3(CF3)2) leads to reductive elimina-
tion of free Binor-S, the generation of {Rh(PR3)}+ fragments,
and the subsequent rapid coordination of the Lewis base.14À16
Received: June 8, 2011
Published: July 29, 2011
r
2011 American Chemical Society
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dx.doi.org/10.1021/om2004964 Organometallics 2011, 30, 4466–4469
|

Organometallics
NOTE
Scheme 2
Scheme 3
Scheme 4a
Figure 1. Solid-state structure of 2d. Thermal ellipsoids are depicted at
the 50% probability level. Hydrogen atoms and the anion are omitted for
clarity. Key bond lengths (Å) and angles (deg): Rh1ÀN1, 2.159(2);
Rh1ÀP1, 2.3470(9); Rh1ÀP2, 2.4240(9); Rh1ÀP3, 2.3293(8);
N1ÀRh1ÀP3, 174.51(7); P1ÀRh1ÀP2, 155.45(3); —{lsq plane
(Rh1, N1, P1, P2, P3); lsq plane (N1, C1, C2, C3, C4, C5, C6, C7)},
25.31(7); N1ÀC1ÀC6ÀP1, 36.2(4); N1ÀC5ÀC7ÀP2, 28.5(4).
a [BArF ]À anions not shown.
4
single environments due to the tBu groups and PNP backbone
are observed for both species, indicating time-averaged C2v
symmetry for both. Variable-temperature studies were frustrated
by this mixture reacting with suitable low-temperature solvents,
e.g. CD2Cl2, to give unidentified products. We speculate this
occurs via the reaction of a putative {(PNPtBu)Rh}+ fragment. In
contrast, 2aÀc are stable in CD2Cl2. Addition of excess PCy3 (10
equiv) pushes the equilibrium between the two species in
complete favor of 2d and enables clean 31P{1H} NMR spectra
to be acquired for 2d. We have not been able to identify the other
species in equilibrium with 2d at low [PCy3] but suggest that it
might be a {(PNPtBu)Rh}+ fragment, [2dÀPCy3]+, stabilized by
solvent (difluorobenzene), agostic interactions, or rapid/rever-
salts and 1 equiv of PCy3 (L = CO,11 acetone,11 ethene,12 MeCN,12
N213) in quantitative yield by NMR spectroscopy (3aÀ3e;Scheme3).
The liberated PCy3 can be conveniently removed by washing with
pentane. A further demonstration that 2d acts as such a precursor
comes from addition of H2 (1 atm) to 2d, which immediately forms
the new complex [(PNPtBu)Rh(H2)][BArF ] (3f).
4
NMR data for 3f in 1,2-C6H4F2 solution show a C2v-symmetric
structure and a low-frequency relative 2H signal at δ À10.79 (T1
71 ( 2 ms, 500 MHz, 298 K) as a broad doublet of triplets
showing coupling to 31P and 103Rh (5 and 27 Hz, respectively),
confirmed by 1H{31P} NMR experiments. In contrast to the case
for 2d, 3f is sufficiently stable in CD2Cl2 to allow for the
t
sible CÀH activation from the Bu ligands.17,18 The solid-state
structure of 2d (Figure 1) shows the expected pseudo-square-
planar environment around Rh. The RhÀP distances are all
relatively long (2.3293(8) À 2.4240(9) Å), indicative of
the steric pressure (cf. [(PNPtBu)Rh(CO)][BF4] 2.301(3) Å11).
The PNPtBu ligand is twisted, with the pyridine group lying
25.31(7)ꢀ relative to the N1, P1, Rh1, P2, P3 plane. The related
complexes [(PNPtBu)Rh(PR3)][BF4] (R = Et, Ph) have been
previously synthesized from reduction of the Rh(II) complex
[(PNPtBu)Rh(acetone)][BF4]2 with PR3/H2O.11
1
collection of variable-temperature H NMR spectra and the
measurement of T1 relaxation time as a function of temperature.
At the lowest temperature accessed (200 K, 500 MHz) T1 =21.5ms,
clearly placing the ligand as dihydrogen.21 Further support
for this assignment comes from addition of HD(g) to a 1,2-
C6H4F2 solution of 2d, which resulted in the rapid formation of a
mixture of isotopomers, [(PNPtBu)Rh(H2)][BArF ] (3f-H2),
[(PNPtBu)Rh(HD)][BArF ] (3f-HD), and [(PNPtB4u)Rh(D2)]-
4
1
[BArF ] (3f-D2), for which the H NMR spectrum showed an
4
Increasing steric pressure between the pincer and PCy3
ligands by changing the appended groups on the PNPR ligand
is demonstrated by the relative rates of substitution of the PCy3
ligand in 2aÀd by excess MeCN to form [(PNPR)Rh(NCMe)]-
overlapping set of signals for bound HD and H2 in the high-field
region (Scheme 4; Supporting Information). For the complex 3f-
HD a signal is observed at δ À10.73 as an apparent quartet of
triplets that collapses to an apparent quartet on decoupling 31P,
which shows the HÀD coupling to be 27 Hz, the same as
the 103Rh coupling, and J(PH) = 6 Hz. 3f-H2 is observed in a
relative molar ratio of 0.5 relative to 3f-HD, consistent with a
statistical distribution of H and D. The observation of HD
coupling in 3f-HD supports the assignment of a bound H2 ligand
and is very similar to that observed in the CoÀdihydrogen
complex (POCOP)Co(HD) (28 Hz, δ À11.2) as well as
(PCPtBu)Rh(HD) (33 Hz).22 Remarkably, these dihydrogen
isotopomers are stable under ESI-MS conditions, which shows
[BArF ] and free PCy3 (Scheme 2). 2a does not undergo
4
exchange at 333 K and 2b,c undergo substitution at 333 K that
follows a first-order rate law with the latter being considerably
faster, while for 2d exchange is effectively instant at room
temperature. The exchange of phosphine ligands in Rh(I) pincer
systems has been previously reported.19,20
We have extended this substitution chemistry with 2d, as it is a
useful precursor to the reactive {(PNPtBu)Rh}+ fragment through
ultimate dissociation of PCy3. Thus, addition of a variety of Lewis
bases to 2d gives the known cations [(PNPtBu)Rh(L)]+[BArF ]
4
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Organometallics
NOTE
all three in an approximate 1:2:1 ratio, respectively (Supporting
Information). The observation of all three possible H/D ex-
change products suggests that an accessible dihydrogen/dihydride
tautomerism operates for 3f that invokes a dihydrogen/dihydride
intermediate.23 Complex 3f adds to this small number of group 9
pincer complexes with dihydrogen ligands6,23À26 and is also
Complex 2c. 1H NMR (CD2Cl2, 500 MHz): δ 7.70À7.74 (m, 8H,
ArF), 7.56 (br, 4H, ArF), 7.14 (t, 3JHH = 7.7, 1H, C5H3N), 7.04 (s, 2H,
C6H2Me3), 6.81 (s, 2H, C6H2Me3), 6.66 (d, 3JHH = 7.7, 2H, C5H3N),
6.62 (s, 2H, C6H2Me3), 6.56 (s, 2H, C6H2Me3), 4.68 (d, 2JHH = 13.6,
2H, PCH2), 4.07 (dt, 2JHH = 13.6, JPH = 4.6, 2H, PCH2), 3.75 (s, 6H,
C6H2Me3), 2.92 (s, 6H, C6H2Me3), 2.28 (s, 6H, C6H2Me3), 2.05 (s, 6H,
C6H2Me3), 1.92À2.08 (m, 6H, Cy), 1.95 (s, 6H, C6H2Me3), 1.72 (s, 6H,
C6H2Me3), 1.42À1.68 (m, 18H, Cy), 1.03À1.15 (m, 3H, Cy),
0.75À0.87 (m, 3H, Cy), 0.49À0.61 (m, 3H, Cy). 31P{1H} NMR
related to the σ-methane complex [(PONOP)Rh(H4C)][BArF ]
4
that is observed at low temperature in solution.6
In conclusion, we report a new route to a series of cationic
[(PNPR)Rh(PCy3)]+ salts. For PNPtBu we also demonstrate
ready displacement of the phosphine by a range of ligands, one of
which is H2, which forms the new dihydrogen complex
1
2
(CD2Cl2, 202 MHz): δ 42.5 (dt, JRhP = 163, JPP = 32, 1P, PCy3),
25.3 (dd, 1JRhP = 150, 2JPP = 32, 2P, PMes2). 31P{1H} NMR (MeCN,
1
2
202 MHz): δ 43.2 (dt, JRhP = 162, JPP = 32, 1P, PCy3), 25.8 (dd,
1JRhP = 151, JPP = 32, 2P, PPh2). ESI-MS (CH2Cl2, 60 ꢀC, 4.5 kV,
2
[(PNPtBu)Rh(H2)][BArF ]. This expedient synthetic route to
positive ion): m/z 1026.482 [M]+ (calcd 1026.487). Anal. Calcd for
C93H96BF24NP3Rh (1890.391 g molÀ1): C, 59.09; H, 5.12; N, 0.74.
Found: C, 58.92; H, 5.04; N, 0.98.
4
these materials potentially allows for a wide range of Rh(I) pincer
complexes to be prepared from the same starting material (1) as
well as for the relatively robust, noncoordinating [BArF ]À anion
4
Complex 2d. This compound is best characterized in 1,2-C6H4F2
solution in the presence of excess PCy3 to suppress ligand dissociation
(0.008 g of 2d, 0.014 g of PCy3, 0.5 mL of 1,2-C6H4F2). In the absence of
excess PCy3 a poorly characterized species, {[2d-PCy3]}, is observed
with δ 67.3 (br d, 1JRhP ∼ 100) alongside 2d and uncoordinated PCy3 in
an approximate ratio of 1:0.85:0.5 in 1,2-C6H4F2 by 31P NMR
spectroscopy.
to be incorporated straightforwardly into these salts.
’ EXPERIMENTAL SECTION
General Experimental Methods. All manipulations were per-
formed under an atmosphere of argon, using Schlenk and glovebox
techniques. Glassware was oven-dried at 130 ꢀC overnight and flamed
under vacuum prior to use. CH2Cl2, MeCN, and pentane were dried
using a Grubbs type solvent purification system (MBraun SPS-800) and
degassed by successive freezeÀpumpÀthaw cycles. CD2Cl2 and 1,2-
C6H4F2 were dried over CaH2, vacuum-distilled, and stored over 3 Å
molecular sieves. Acetone (less than 0.0075% H2O) was purchased from
VWR and degassed by successive freezeÀpumpÀthaw cycles. 1,27
1H NMR (1,2-C6H4F2, 500 MHz, selected data, intramolecular
3
integrations): δ 7.82 (t, JHH = 7.9, 1H, C5H3N {[2d-PCy3]}), 7.63
(t, 3JHH = 7.7, 1H, C5H3N {2d}), 7.54 (d, 3JHH = 7.9, 2H, C5H3N {[2d-
PCy3]}), 3.84 (app t, JPH = 3, 4H, PCH2 {[2d-PCy3]}), 3.51 (app t,
JPH = 3, 4H, PCH2 {2d}), 1.36 (br app t, JPH = 6, 36H, tBu {2d}), 1.21
(app t, JPH = 7.2, 36H, tBu {[2d-PCy3]}). 1H NMR (1,2-C6H4F2 + 10
PCy3/Rh, 500 MHz): δ 8.30À8.35 (m, 8H, ArF), 7.68 (br, 4H, ArF),
7.63 (t, 3JHH = 7.7, 1H, C5H3N), 3.51 (app t, JPH = 3, 4H, PCH2), 1.36
t
PNPtBu,12PNPMes 28 PNPCy,29 and PNPPh 30 were prepared using litera-
,
(obscured, 36H, Bu). The 2H C5H3N resonance was not located,
presumably as it is obscured by solvent resonances. 31P{1H} NMR (1,2-
C6H4F2 + 10 PCy3/Rh, 202 MHz): δ 63.3 (br dd, 1JRhP = 140, 2JPP = 32,
ture methods. NMR spectra were recorded on a Bruker DRX 500 MHz
spectrometer at 298 K, unless otherwise stated. Chemical shirts are
quoted in ppm and coupling constants in Hz. Microanalyses were
performed at Elemental Microanalysis Ltd. ESI-MS were recorded on
a Bruker MicroOTOF instrument.31
1
2
2P, PtBu2), 47.4 (dt, JRhP = 159, JPP = 32, 1P, PCy3). ESI-MS (1,2-
C6H4F2, 60 ꢀC, 4.5 kV, positive ion): m/z, 778.423 [M]+ (calcd
778.425). Anal. Calcd for C73H88BF24NP3Rh (1642.108 g molÀ1): C,
53.40; H, 5.40; N, 0.85. Found: C, 53.57; H, 5.35; N, 0.92.
Synthesis of 2. In a Schlenk flask charged with 1 (0.050 g,
0.035 mmol) and PNPtBu (0.014 g, 0.035 mmol) was added 1,2-
C6H4F2 (1 mL), and resulting solution was stirred at room temperature
for 30 min. Recrystallization from 1,2-C6H4F2Àpentane gave the
product as orange-red crystals. Yield: 0.031 g (2d, 54%). 2aÀc were
prepared analogously in 46, 41, and 53% isolated yields, respectively. 2a,
b clathrate solvent, which could not be removed completely, even under
prolonged high vacuum.
NMR Experiments. Reactions of 2aÀc with MeCN. Solutions of
2aÀc (0.005 mmol) in MeCN (ca. 0.5 mL) were prepared in J. Young
NMR tubes and monitored at 333 K in situ using 31P{1H} NMR
spectroscopy. 2a: no reaction observed after 70 h. 2b: first-order sub-
stitution (R2fit = 0.993) of PCy3 with a rate constant of (3.1 ( 0.2) Â
10À5 sÀ1. 2c: first-order substitution (R2fit = 0.998) of PCy3 with a rate
constant of (1.99 ( 0.08) Â 10À4 sÀ1
.
[Rh(PNPCy)(NCMe)]+: 31P{1H} NMR (CD2Cl2, 202 MHz) δ 46.9
Complex 2a. 1H NMR (CD2Cl2, 500 MHz): δ 7.82À7.89 (m, 8H,
1
o-C6H5), 7.70À7.74 (m, 8H, ArF), 7.56 (br, 4H, ArF), 7.42À7.53
(d, JRhP = 135); ESI-MS (CH2Cl2, 60 ꢀC, 4.5 kV, positive ion) m/z
643.282 [M]+ (calcd 643.282). [Rh(PNPMes)(NCMe)]+: 31P{1H}
NMR (CD2Cl2, 202 MHz) δ 16.7 (d, 1JRhP = 135); ESI-MS (CH2Cl2,
60 ꢀC, 4.5 kV, positive ion) m/z 787.280 [M]+ (calcd 787.282).
Reaction of 2d with Lewis Bases: General Procedure. Solutions of 2d
(8 mg, 0.005 mmol) in 1,2-C6H4F2 (ca. 0.5 mL) were prepared in J.
Young NMR tubes. Liquid reagents (0.01 mmol) were added under an
atmosphere of argon. Gaseous reagents were added by placing the
headspace of the J. Young NMR tube under the appropriate gas (1 atm).
Reactions were monitored at 298 K immediately using 31P{1H} NMR
spectroscopy and indicated rapid (<5 min) and quantitative formation of
3 and free PCy3.
3
(m, 13H, C5H3N {1H} + C6H5 {12H}), 7.05 (d, JHH = 7.7, 2H,
C5H3N), 4.06 (app t, JPH = 3.4, 4H, PCH2), 1.36À1.72 (m, 24H, Cy),
0.98À1.09 (m, 3H, Cy), 0.58À0.70 (m, 6H, Cy). 1H{31P} NMR
3
(CD2Cl2, 500 MHz, selected data): δ 7.86 (br d, JHH = 7.3, 8H,
o-C6H5). 31P{1H} NMR (CD2Cl2, 202 MHz): δ 51.4 (dt, 1JRhP = 154,
2JPP = 35, 1P, PCy3), 49.6 (dd, 1JRhP = 152, 2JPP = 35, 2P, PPh2). 31P{1H}
1
2
NMR (MeCN-d3, 202 MHz) δ 52.8 (dt, JRhP = 154, JPP = 34, 1P,
PCy3), 47.4 (dd, 1JRhP = 151, 2JPP = 34, 2P, PPh2). ESI-MS (CH2Cl2,
60 ꢀC, 4.5 kV, positive ion): m/z 858.296 [M]+ (calcd 858.299).
Complex 2b. 1H NMR (CD2Cl2, 500 MHz): δ 7.70À7.75 (m, 9H,
C5H3N {1H} + ArF {8H}), 7.56 (br, 4H, ArF), 7.33 (d, 3JHH = 7.7, 2H,
C5H3N), 3.42 (app t, JPH = 3.4, 4H, PCH2), 0.87À2.28 (m, 77H, Cy).
31P{1H} NMR (CD2Cl2, 202 MHz): δ 54.4 (dt, 1JRhP = 161, 2JPP = 35,
1P, PCy3), 49.6 (dd, 1JRhP = 139, 2JPP = 35, 2P, PMes2). 31P{1H} NMR
(MeCN-d3, 202 MHz): δ 55.6 (dt, 1JRhP = 162, 2JPP = 35, 1P, PCy3),
50.3 (dd, 1JRhP = 140, 2JPP = 35, 2P, PCy2). ESI-MS (CH2Cl2, 60 ꢀC, 4.5
kV, positive ion): m/z 882.482 [M]+ (calcd 882.487).
Reaction of 2d with Hydrogen. Synthesis followed the general
procedure. Removing the solvent in vacuo and redissolving in CD2Cl2
allowed characterization at low temperature. 3f has limited stability in
this solvent (t1/2 ≈ 16 h).
Complex 3f: 1H NMR (1,2-C6H4F2, 500 MHz, 298 K) δ 8.31À8.36
(m, 8H, ArF), 7.72 (t, 3JHH = 7.7, 1H, C5H3N), 7.69 (br, 4H, ArF), 7.43
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Organometallics
NOTE
(d, 3JHH = 7.7, 2H, C5H3N), 3.61 (app t, JPH = 3.4, 4H, PCH2), 1.31 (app
t, JPH = 3.4, 36H, tBu), À10.79 (br dt, 1JRhH = 26.8, 2JPH = 5, 2H, 71 (
2 ms, RhH); 31P{1H} NMR (1,2-C6H4F2, 202 MHz, 298 K) δ 83.0 (d,
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1
1JRhP = 120); H NMR (CD2Cl2, 500 MHz, 298 K, selected data)
δ À11.0 (br d, 1JRhH = 25.9, 2H, RhH); 31P{1H} NMR (CD2Cl2, 202
1
1
MHz, 298 K) δ 83.2 (d, JRhP = 120); H NMR (CD2Cl2, 500 MHz,
273 K, selected data) δ À10.9 (br d, 1JRhH ≈ 20, 2H, RhH); 31P{1H}
1
1
NMR (CD2Cl2, 202 MHz, 273 K) δ 83.0 (d, JRhP = 120); H NMR
(CD2Cl2, 500 MHz, 250 K, selected data) δ À10.9 (br d, 1JRhH ≈ 20,
2H, RhH); 31P{1H} NMR (CD2Cl2, 202 MHz, 250 K) δ 82.7 (d, 1JRhP
=
120); 1H NMR (CD2Cl2, 500 MHz, 225 K, selected data) δ À10.8 (br d,
1JRhH ≈ 20, 2H, RhH); 31P{1H} NMR (CD2Cl2, 202 MHz, 225 K)
δ 82.5 (d, 1JRhP = 120); 1H NMR (CD2Cl2, 500 MHz, 200 K, selected
1
data) δ À10.8 (br d, JRhH ≈ 20, 2H, RhH); 31P{1H} NMR (CD2Cl2,
202 MHz, 200 K) δ 82.3 (d, 1JRhP = 120); T1 measurements (CD2Cl2, 500
MHz) 88 ( 2 ms (298 K), 63 ( 2 ms (273 K), 43.0 ( 0.7 ms (250 K),
28.1 ( 0.4 ms (225 K), 21.5 ( 0.6 ms (200 K), T1(min, calc) = 20.3 ms
(180 K) from a second order polynomial fit (R2fit = 0.999); ESI-MS (1,2-
C6H4F2, 60 ꢀC, 4.5 kV, positive ion) m/z 500.206 [M]+ (calcd 500.208).
Reaction of 2d with Deuterium Hydride. Synthesis followed the
general procedure. It resulted in quantitative formation of a 1:2:1
1
mixture of 3f-H2, 3f-HD, and 3f-D2 and free PCy3. H NMR (1,2-
C6H4F2, 500 MHz, selected data): δ 8.31À8.36 (m, 8H, ArF), À10.73
2
(app qt, J = 27, JPH = 6, 0.5H, Rh(HD)), À10.79 (obscured, 0.5H,
Rh(H2)); ESI-MS (1,2-C6H4F2, 60 ꢀC, 4.5 kV, positive ion) m/z
500.209 [Rh](H2)+ (calcd 500.208), 501.215 [Rh](HD)+ (calcd
501.214), 502.221 [Rh](D2)+ (calcd 502.220), peak intensities
approximately 1:2:1.
(16) Chaplin, A. B.; Weller, A. S. Angew. Chem., Int. Ed. 2010, 49,
581.
(17) Verat, A. Y.; Pink, M.; Fan, H.; Tomaszewski, J.; Caulton, K. G.
Organometallics 2007, 27, 166.
Crystallography. Details about the data collection and refinement
for the X-ray structure of 2d are documented in the Supporting
Information (CIF).
Crystallographic Data for 2d: C73H88BF24NP3Rh, M = 1642.07;
monoclinic, P21/n (Z = 4), a = 13.447 80(10) Å, b = 15.010 10(10) Å,
c = 37.0273(4) Å, β = 94.5047(4)ꢀ, V = 7450.98(11) Å3; T = 150(2) K,
5.10 e θ e 26.37ꢀ collected, 14 971 unique reflections (Rint = 0.0403),
completeness to 26.37ꢀ 98.2%; final R1 = 0.0469 (I > 2σ(I)), GoF = 1.035,
(18) Sewell, L. J.; Chaplin, A. B.; Abdalla, J. A. B.; Weller, A. S. Dalton
Trans. 2010, 39, 7437.
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L. J. W.; Konstantinovski, L.; Martin, J. M. L.; Milstein, D. Chem. Eur. J.
2005, 11, 2319.
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Leitus, G.; Milstein, D. Organometallics 2009, 28, 523.
(21) Kubas, G. J. Metal Dihydrogen and o-Bond Complexes; Kluwer
Academic/Plenum Publishers: New York, 2001.
(22) Xu, W.-w.; Rosini, G. P.; Krogh-Jespersen, K.; Goldman, A. S.;
Gupta, M.; Jensen, C. M.; Kaska, W. C. Chem. Commun. 1997, 2273.
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Goldberg, K. I.; Heinekey, D. M. Angew. Chem., Int. Ed. 2011, 50, 1873.
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Chem. Soc. 2006, 128, 7128.
(25) Vigalok, A.; Ben-David, Y.; Milstein, D. Organometallics 1996,
15, 1839.
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(28) Muller, G.; Klinga, M.; Leskela, M.; Rieger, B. Z. Anorg. Allg.
maximum/minimum residual electron density 0.897/À0.514 e ÅÀ3
.
’ ASSOCIATED CONTENT
S
Supporting Information. Figures giving a ball and stick
b
X-ray structure of 2c and NMR and ESI-MS spectra of the
reaction between 2d and hydrogen and deuterium hydride and a
CIF file giving crystallographic data for 2d. This material is
available free of charge via the Internet at http://pubs.acs.org.
Crystallographic data have also been deposited with the Cambridge
Crystallographic Data Centre under CCDC 827146. These data
can be obtained free of charge from The Cambridge Crystal-
lographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
’ AUTHOR INFORMATION
Chem. 2002, 628, 2839.
(29) Katayama, H.; Wada, C.; Taniguchi, K.; Ozawa, F. Organome-
tallics 2002, 21, 3285.
Corresponding Author
*E-mail: andrew.weller@chem.ox.ac.uk.
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(31) Lubben, A. T.; McIndoe, J. S.; Weller, A. S. Organometallics
2008, 27, 3303.
’ ACKNOWLEDGMENT
We thank the EPSRC for funding.
’ REFERENCES
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dx.doi.org/10.1021/om2004964 |Organometallics 2011, 30, 4466–4469