π-accepting-pincer rhodium complexes: An unusual coordination mode of PCP-type systems

Article abstract of DOI:10.1002/chem.200401116

The novel π-accepting, pincer-type ligand, dipyrrolylphoshinoxylene (DPyPX), is introduced. This ligand has the strongest π-accepting phosphines used so far in the PCP family of ligands and this results in some unusual coordination chemistry. The rhodium(

Full text of DOI:10.1002/chem.200401116

FULL PAPER
p-Accepting-Pincer Rhodium Complexes: An Unusual Coordination Mode
of PCP-Type Systems
Elizaveta Kossoy,[a] Mark A. Iron,[a] Boris Rybtchinski,[a] Yehoshoa Ben-David,[a]
Linda J. W. Shimon,[b] Leonid Konstantinovski,[b] Jan M. L. Martin,*[a] and
David Milstein*[a]
Abstract: The novel p-accepting,
pincer-type ligand, dipyrrolylphoshi-
noxylene (DPyPX), is introduced. This
ligand has the strongest p-accepting
phosphines used so far in the PCP
family of ligands and this results in
some unusual coordination chemistry.
[(DPyPX)Rh(CO)(PR3)] (4, R=Ph,
Et, pyrrolyl) is prepared by treating
the relevant [(DPyPX)Rh(PR3)] (3)
complex with CO and is remarkably re-
sistant to loss of either ligand. X-ray
crystallographic analysis of complex 4b
(R=Et) reveals an unusual cisoid coor-
dination of the PCP phosphine ligands.
These observations are supported by
density functional theory (DFT) calcu-
lations.
Keywords: coordination modes · P
ligands · pincer ligands · rhodium ·
tridentate ligands
The
rhodium(i)
complex,
Introduction
rigid coordination, which can lead to new properties and ap-
plications.
The rigid chelation in pincer ECE ligands (ECE=tridentate
monoanionic species, E is a neutral donor moiety) gives rise
to exceptionally stable metal complexes. In addition, excel-
lent electronic and steric tuning of the metal center can be
achieved.[1,2] Pincer-type complexes are active in a variety of
important catalytic processes, invaluable for mechanistic
studies and for the stabilization of unusual structures, and
useful as functional materials, as described in recent re-
views.[1–7] A variety of donors (E=N, P, As, O, S) have been
used in ECE systems. Nonetheless, no moieties with strong
p-accepting abilities have been introduced. In such a system,
back donation from the metal to the ECE ligand will lower
the electron density on the metal center while retaining the
Here we report on the synthesis of the first p-accepting
PCP ligand bearing pyrrolyl substituents, dipyrrolylphosphi-
noxylene (1, DPyPX-H), and the synthesis of rhodium com-
plexes based on this ligand. The coordination chemistry of
Rh-DPyPX complexes differs from that of typical pincer
complexes. Thus, due to the strong p-accepting ability of
DPyPX, formation of the first stable d8 ML5 PCP-based
complexes was observed. Moreover, the PCP phosphorus
atoms in these complexes adopt a cisoid rather than trans
configuration, in contrast to the structures of all the PCP
type complexes reported so far.[2]
Results and Discussion
[a] E. Kossoy, M. A. Iron, Dr. B. Rybtchinski, Y. Ben-David,
Prof. J. M. L. Martin, Prof. D. Milstein
Department of Organic Chemistry
The Weizmann Institute of Science
Rehovot, 76100 (Israel)
Ligand 1 was prepared by the reaction of ClPPyr2 (Pyr=N-
pyrrolyl) with the Grignard reagent derived from a,a’-di-
chloro-m-xylene. To the best of our knowledge, this ligand
has the strongest p-accepting phosphine ligands in the PCP
ligand family. The p-accepting ability of tris(N-pyrrolyl)-
phosphine (PPyr3) was found to fit the following trend: fluo-
roalkyl phosphines > PPyr3 ꢀP(C6F5)3 > P(OPh)3.[8]
Fax : (+972)8-934-4142
E-mail: comartin@wicc.weizmann.ac.il
david.milstein@weizmann.ac.il
[b] Dr. L. J. W. Shimon, Dr. L. Konstantinovski
Chemical Research Support
The reaction of stoichiometric amounts of [{Rh(coe)2m-
Cl}2] (coe=cyclooctene) with L (a: L=PPh3; b: L=PEt3)
and the DPyPX ligand 1 at 658C in THF resulted in metala-
tion to yield the rhodium(iii) hydride complexes 2a,b
(Scheme 1). Both complexes were characterized by NMR
The Weizmann Institute of Science
Rehovot, 76100 (Israel)
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
Chem. Eur. J. 2005, 11, 2319 – 2326
DOI: 10.1002/chem.200401116
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2319

were characterized by NMR
and IR spectroscopy, and ele-
mental analysis. Remarkably,
none of these compounds loses
CO or PR3, either under
vacuum or by bubbling with
inert gas.
An X-ray diffraction study
reveals that complex 4b[11] has
a trigonal-bipyramidal (tbp) ge-
ometry.[12,13] The carbonyl group
is coordinated trans to the ipso-
carbon atom (Figure 2), while
all three phosphine groups
occupy equatorial positions. The
DPyPX phosphine ligands coor-
Scheme 1. Synthesis of complexes 3.
spectroscopy. Subsequent addition of KOtBu to solutions of
crude 2a and 2b resulted in deprotonation to form the rho-
dium(i) complexes 3a and 3b, respectively (Scheme 1). Both
complexes were characterized by NMR spectroscopy and el-
emental analysis. The 31P{1H} NMR spectrum of complex 3a
2
exhibits a dd[9] at d=124.6 ppm (1JRh,P =208.3 Hz, JP, P
=
38.2 Hz, 2P) and a dt at d=36.9 ppm (1JRh,P =119.0 Hz, 1P).
The methylene groups of the “arms” give rise to an unre-
1
solved virtual triplet (vt) in the H NMR spectrum at d=
3.8 ppm, indicating that the complex has two symmetry
planes passing through the PCP-metal chelate core (i.e., a
C2v symmetry on the NMR time scale). The signal of the
ipso carbon atom in the 13C{1H} NMR spectrum appears as
2
a ddt centered at 172.8 ppm with JP, C, t rans =69.9 Hz, confirm-
ing the trans Ar-Rh-L arrangement. Complex 3b has similar
NMR spectral features. An X-ray diffraction study on a
crystal of 3a[10] confirmed its square-planar geometry
(Figure 1).
Complex 3c was obtained by adding one equivalent of
PPyr3 to 3a followed by one equivalent of MeOTf to precip-
itate the displaced PPh3 as its phosphonium salt (Scheme 1).
Complex 3c was characterized by NMR spectroscopy and
elemental analysis, and was found to have similar NMR
spectral features as complexes 3a,b indicating a similar
structure. Complex 3c is an example of a complex in which
all neutral donor ligands are p-accepting pyrrolyl phos-
phines.
Figure 1. Molecular structure of 3a (ORTEP drawing; hydrogen atoms
omitted for clarity).
dinated to the rhodium center form an unprecedented
narrow angle for a PCP system of 128.318.
Interestingly, complexes 3a–c react with one equivalent of
CO to form pentacoordinate rhodium(i) PCP-based com-
plexes 4a–c (Scheme 2). These thermally stable complexes
The 31P{1H} NMR spectrum of 4b exhibits a dd at d=
2
124.06 ppm (1JRh,P =190.8 Hz, JP, P =164 Hz, 2P) and a td at
d=4.63 ppm (1JRh,P =132.4 Hz, 1P). The methylene groups
1
of DPyPX give rise to two signals in H NMR spectrum: a
2
dvt at d=3.92 ppm (2JH,H =15.9 Hz, JP, H =5.3 Hz) and a d at
d=3.71 ppm (2JH,H =15.9 Hz), indicating that the compound
has only one symmetry plane passing perpendicular to the
PCP–Rh plane. The 13C {1H} NMR signal of the ipso-carbon
atom appears as a ddt centered at 166.3 ppm (1JRh,C =22 Hz,
2JP,C,DPyPX =2JPC,PEt =11 Hz); and the 13C {1H} NMR signal of
3
the CO appears as a ddt centered at 204.2 ppm (1JRh,C
=
48 Hz, 2JP,C,DPyPX =2JPC,PEt =11 Hz). Similarity between
3
2
Scheme 2. Formation of pentacoordinate, cisoid complexes 4.
2JP,C,DPyPX and JPC,PEt coupling constants suggests that all
3
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Chem. Eur. J. 2005, 11, 2319 – 2326

Pincer Complexes
FULL PAPER
complex and the HOMO orbital of the incoming ligand.[28]
Such interactions are especially pronounced in rigid pincer
systems. Previous theoretical studies showed that the addi-
tion of a fifth ligand can proceed via a bent ML4 geome-
try.[29] The key consequence of bending
a
planar
[Ru(CO)2(PH3)2] complex is a dramatic stabilization of the
dz2 orbital and its replacement by dyz as the HOMO.[30] The
p-accepting pyrrolyl ligands will enhance this effect, further
facilitating the coordination of the fifth ligand.[31]
To evaluate the effect of the pyrrolyl substituents on the
coordination of the fifth ligand, calculations were carried
out at the COSMO(C6H6)-B97–1/SDB-cc-pVDZ//B97–1/
SDD level of theory[32] on two model compounds, 4d and
4d’ (as 4d, but with the PCP Pyr substituents replaced by H
atoms) (Scheme 3). In all cases, the computed geometries
Figure 2. Molecular structure of 4b (ORTEP drawing; hydrogen atoms
omitted for clarity).
Scheme 3. Model compounds for computations.
three phosphine ligands of 4b occupy similar positions rela-
tive to the carbonyl ligand and the ipso-carbon atoms.
Unlike the NMR spectrum of complex 4b, the signals in the
NMR spectra of 4a,c at 293 K are broad, as a result of an
equilibrium involving free PR3, indicated by the fact that
the coordinatively saturated complex 4c reacts with PPh3 to
form complex 4a, which in turn reacts with PEt3 to form 4b.
Low-temperature (243 K) NMR spectra of 4a–c are very
similar, suggesting that the ligands in 4a,c are arranged in a
similar fashion as in 4b. As expected, the p-backbonding to
CO increases with increasing electron donation ability of
the ancillary phosphine ligand (n: 2008 (4c), 1987 (4a), 1975
(4b) cmÀ1 (CꢁO)).
were very similar to the experimentally determined struc-
tures. The loss of either CO or PH3 from these complexes
was examined. In both cases, the loss of CO is unfavorable
(DG298 =11.1 (4d’) and 12.3 (4d) kcalmolÀ1). The loss of
PH3 from 4d’, as expected, occurs (DG298 =À5.1 kcalmolÀ1).
From 4d, however, the loss is only DG298 =À1.2 kcalmolÀ1, a
value that is isoergonic to within the expected error of the
computational method. Nonetheless, one can clearly see
that both ligands are more strongly bound in 4d.
À
The result that the Rh CO bond is stronger in 4d than in
4d’ seems counter-intuitive. Because of the electron with-
drawing PCP ligand in 4d, one would expect that coordina-
tion of strong p-accepting ligands, such as CO, would be un-
favorable. The rhodium(i) center in 4d, however, is now so
electron-poor that it would benefit from any s-donating
ligand, even if they are p-accepting. In fact, loss of an equa-
torial CO from [(PCP)Rh(CO)2] (4e, 4e’) (Scheme 3) was
calculated to be disfavored by 3.3 and 2.4 kcalmolÀ1, respec-
tively. The retention of the second CO can be explained by
p-backdonation from Rh being dominant in the electron-
rich 4e’, whereas the electron-poor Rh center in 4e makes
s-donation from CO the major factor.
Although pentacoordinate rhodium(i) complexes are
known,[14–16] to the best of our knowledge 4a–c are the first
stable PCP d8 ML5 complexes. CO usually replaces an ancil-
lary ligand when it reacts with PCP rhodium(i) com-
plexes.[17,18] For example, [(DiPPX)RhPEt3] (DiPPX=diiso-
propylphosphinoxylene) reacts with one equivalent of CO in
benzene to give [(DiPPX)RhCO] (see Experimental Section
for details). Reversible formation of NCN d8 ML5 (M=Pt,
Ni) was previously reported.[19,20] Interestingly, X-ray diffrac-
tion studies revealed square-pyramidal geometries with
trans-disposed amine donors, rather than trigonal-bipyrami-
dal geometries, for these complexes.[21]
Ligand substitutions at rhodium(i) centers have been ob-
served to follow both associative[22–25] and dissociative[26,27]
mechanisms. Complexes 4a–c can be viewed as arrested in-
termediates in an associative substitution process involving
PCP type complexes.
The stability of the pentacoordinate 4a–c may in part be
explained by the effects the electron-withdrawing pyrrolyl
groups have on the molecular orbitals of 3. Figure 3 depicts
the metal d orbital energy diagram of complexes 3d and 3d’
(as 3d, but with the PCP pyrrolyl substituents replaced by H
atoms) (Scheme 3) and compares them to those in which the
PCP phosphine arms have been bent into a “see-saw” con-
figuration to allow CO coordination. There are two most
dramatic observations. The first is that all of the orbitals are
lower in energy in complex 3d. The second is that the ef-
In general, the addition of a fifth ligand to square-planar
d8 ML4 is unfavorable due to occupied–occupied orbital re-
pulsive interactions between the dz2 (HOMO) orbital of the
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J. M. L. Martin, D. Milstein et al.
in a Vacuum Atmospheres glove box
equipped with a MO 40–2 inert gas
purifier or using standard Schlenk
techniques. All solvents were reagent
grade or better. All non-deuterated
solvents were refluxed over sodium/
benzophenone ketyl and distilled
under argon atmosphere. Deuterated
solvents were used as received. All the
solvents were degassed with argon and
kept in the glove box over 4 ꢁ molec-
ular sieves. Commercially available re-
agents were used as received.
[{Rh(coe)2m-Cl}2] was prepared accord-
ing to a literature procedure.[35]
1H, 13C, and 31P NMR spectra were re-
corded at 400 MHz, 100 MHz, and
162 MHz, respectively, using a Bruker
AMX-400 NMR spectrometer. All
spectra were recorded at 295 K, unless
otherwise noted. 1H NMR and 13C{1H}
NMR chemical shifts are reported in
ppm downfield from tetramethylsilane.
Figure 3. Partial molecular orbital diagram showing the metal d-orbitals of complexes 3d (right) and 3d’ (left),
and their bent configurations (see text).
31P NMR chemical shifts are reported
in ppm downfield from H3PO4 and ref-
erenced to an external 85% solution
of phosphoric acid in D2O. The
fects of bending the PCP arms are attenuated. While in both
cases bending causes a large rise in the energy of the dxz or-
bital, so much so that it rises above dz2 to become the
HOMO, in 3d this stabilizes the dz2 orbital. Furthermore, be-
cause the rise in energy of dxz is reduced, the energy of the
HOMO in complex 3d barely changes (DE=À0.07 eV) as a
result of the bending. Thus, the Pyr ligands clearly makes 3d
much more amenable to ligand coordination than its elec-
tron donating counterparts.
1H{103Rh} NMR spectrum (2a) was measured at 9.4T on a Bruker AMX-
400 spectrometer and standard four-pulse HMQC sequence with continu-
ous proton decoupling was applied. The 31P{103Rh} NMR spectra (3a–c)
were measured at 11.7 T on a Bruker “Avance”-500 spectrometer, equip-
ped with triple-resonance inverse probe with 1H, 31P and broadband
channels. Typical conditions for HMBC experiment: 31P and 103Rh pulse
lengths were 11.2 ms and 70 ms correspondingly, a spectral width in f2 (31P)
was 40–140 ppm, in f1 (103Rh) was 80–1000 ppm (resolution in f1 5 Hz per
point). 103Rh chemical shifts were referenced to 3.16 MHz at a tempera-
ture 295 K.
Overall, the geometries of the d8 ML5-type complexes are
determined by the preference of the s-donating aryl ligand
to occupy an axial, rather than equatorial, position[33,34] and
by the steric demand of the large phosphines which dictates
that they occupy the equatorial plane of the tbp complex.[33]
Elemental analyses were performed by H. Kolbe, Mikroanalytisches Lab-
oratorium, Muelheim, Germany.
Synthesis of DPyPX (1): Mg was activated with 1,2-dibromoethane
before use. To prepare the Grignard reagent, bis-a-chloro-m-xylene
(11.080 g) in dry THF (780 mL) was added dropwise to Mg (6.2 g) in dry
THF (90 mL). The resulting solution was stirred for 24 h at room temper-
ature and then cannulated under argon pressure into a 1 L dropping
funnel. ClP(pyrrolyl)2 (26.362 g, 133 mmol) in dry THF (350 mL) was
placed in a 1 L Schlenk flask equipped with a magnetic stirring bar and
the above dropping funnel, and then cooled to À308C. Then the
Grignard reagent was added dropwise over a few hours. The resulting so-
lution was allowed to warm up to room temperature and then stirred for
48 h at ambient temperature. Solvents were removed under high vacuum.
The residue was introduced into the glovebox, treated with toluene
(450 mL), filtered by using a sinter funnel, and dried under high vacuum,
resulting in white crystals. The compound was mixed with pentane
(300 mL) and filtered again, then dissolved in hot toluene, treated with
carbon black, filtered, and crystallized by the addition of pentane to give
white crystals (18.105 g; 80%).
31P{1H} NMR (C6D6): d=68.75 (s); 1H NMR (C6D6): d=6.79 (m, 8H;
Pyr, HC-N), 6.48 (m, 3H; Ar), 6.3 (m, 1H; Ar), 6.25 (m, 8H; Pyr, HC-
CH-N), 3.08 ppm (d, 2JP, H =3.47 Hz, 4H; Ar-CH2-P); 13C{1H} NMR
(C6D6): d=133.93 (m, 2C; Ar, C1, C3), 130.27 (m, 1C; Ar, C2), 128.93 (m,
2C; Ar, C4, C6), 127.57 (br s, 1C; Ar, C5), 123.50 (d, 2JP,C =14.03 Hz, 8C;
Pyr, CH-N), 112.35 (d, 3JP, C =4.11 Hz, 8C; CH-CH-N), 38.2 ppm (d,
1JP, C =13.71 Hz, 2C; Ar-CH2-P).
Summary
A novel p-accepting PCP ligand and its rhodium complexes
were synthesized. The coordination chemistry of this system
differs significantly from that of other pincer-type ligands.
Thus, the first stable d8 ML5 PCP complexes were synthe-
sized. Moreover, the pincer framework of these complexes
bears the phosphine donor atoms in cisoid (rather than in
the normally observed trans) positions. Their unusual stabili-
ty is due to the p-accepting nature of the PCP ligand, which
disfavors formation of the coordinately unsaturated ML4
complexes. The implications of these features for catalysis
are currently under study.
[Rh(DPyPX)H(PPh3)Cl] (2a): A solution of PPh3 (219 mg, 0.835 mmol)
in THF (2 mL) was slowly added to a solution of [{Rh(coe)2m-Cl}2]
(300 mg, 0.418 mmol) in THF (3 mL). The resulting solution was stirred
for 5 min at room temperature during which time it became clear orange.
Then a solution of ligand 1 (359.9 mg, 0.836 mmol) in THF (2 mL) was
Experimental Section
General procedures: All experiments with metal complexes and phos-
phine ligands were carried out under an atmosphere of purified nitrogen
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Chem. Eur. J. 2005, 11, 2319 – 2326

Pincer Complexes
FULL PAPER
added dropwise while stirring. The resulting mixture was heated under
stirring at 658C for 1.5 h to give a deep red solution of 2a. The 31P {1H}
NMR showed that no starting material remained.
X-ray analysis of the structure of [Rh(DPyPX)PPh3] (3a): Orange mon-
oclinic crystals of 3a were obtained by slow diffusion of pentane into a
concentrated solution of 3a in toluene, in a 5 mm NMR tube, left at
room temperature for three days.
31P{1H} NMR (C6D6): d=121.5 (dd, 1JRh,P =138.52, 2JP, P =31.38 Hz, 2P),
19.3 ppm (dt, 1JRh,P =83.33, 2JP, P =31.38 Hz, 1P); 1H NMR (C6D6): d=7.6
(m, 6H; Ph, ortho to P), 7.25–6.7 (m, 20H; Ph meta and para to P; Ar,
meta and para to Rh; Pyr, HC-N), 6.3 (br s, 4H; Pyr, HC-CH-N), 6.0 (br
s, 4H; Pyr, HC-CH-N), 4.6 (dvt, ABX2 pattern, 2JH,H =16 Hz, unresolved
t, 2H; Ar-CH(H)-P), 3.6 (dvt, ABX2 pattern, 2JH,H =16, 2JP, H =4.8 Hz,
2H; Ar-CH(H)-P), À15.5 ppm (ddt, 1JRh,H =22.3, 2JP, H =13.3 Hz, 1H; H-
Crystal data: C42H38N4P3Rh, orange, plate, 0.2ꢂ0.2ꢂ0.2 mm3, monoclinic,
P2(1)/n (no.14), a=14.390(3), b=12.275(3), c=21.659(3) ꢁ, b=
108.75(3)8, from 15 degrees of data, T=120(2) K, V=3622.7(13) ꢁ3, Z=
4, Fw=794.58, 1calcd =1.457 MgmÀ3, m=0.641 mmÀ1
.
Data collection and processing: Nonius KappaCCD diffractometer, MoKa
(l=0.71073 ꢁ), graphite monochromator, 0ꢂhꢂ17, 0ꢂkꢂ14, À25ꢂlꢂ
24, frame scan width=1.58, scan speed 1.08 per 60 s, typical peak mosaici-
ty 0.428, 6944 independent reflections (Rint =0.040). The data were proc-
essed with Denzo-Scalepack.
2
1
Rh); 13C{1H} NMR (C6D6): d=162.10 (ddt, JP, C, trans =93.72 Hz, JRh,C
=
24.49 Hz, unresolved t, 1C; Cipso-Rh), 140.12 (vtd, 2JP,C =9.89, J=3.06 Hz,
2C; Ar, C-C-Rh), 135–126 (m, 19C; Ph Ar, CH-CH-C-C-Rh), 124.26 (t,
unresolved, 4C; Pyr, CH-N-P), 124.17 (vt, JP, C =3 Hz, 4C; Pyr, CH-N-P),
2
Solution and refinement: structure was solved by direct methods with
SHELXS-97. Full-matrix least-squares refinement based on F2 with
SHELXS-97. A total of 451 parameters with 0 restraints, final R1 =0.0359
(based on F2) for data with I>2s(I) and, R1 =0.0525 on 6609 reflections,
123.25 (vtd, 3JP, C =10.83, J=4.74 Hz, 2C; Ar, CH-C-C-Rh), 112.60 (vt,
3JP, C =2.83 Hz, 4C; Pyr, CH-CH-N-P), 112.46 (t, J=2.59 Hz, 4C; Pyr, CH-
CH-N-P), 51.97 ppm (vtdd, 1JP, C =19.78 Hz, unresolved dd, 2C; Ar-CH2-
P); 103Rh NMR ([D8]toluene): d=À89.5 ppm.
goodness-of-fit on F2 =1.036, largest electron density peak=
[Rh(DPyPX)H(PEt3)Cl] (2b): Neat PEt3 (7.6 mL, 5.6ꢂ10À5 mol) was
slowly added to [{Rh(coe)2m-Cl}2] (20 mg, 2.8ꢂ10À5 mol) in THF (1 mL).
The resulting solution was left to stir for 5 min at room temperature
during which time it became clear red. Then ligand 1 (24 mg, 5.6ꢂ
10À5 mol) in THF (1 mL) was added dropwise while stirring. The resulting
mixture was heated under stirring to 658C for 1.5 h to give a deep yellow
solution of 2b. The 31P{1H} NMR spectra showed that no starting materi-
al remained.
[10]
0.847 eꢁÀ3
.
[Rh(DPyPX)PEt3] (3b): A solution of KOtBu (6.2 mg, 5.6ꢂ10À5 mol) in
THF (0.5 mL) was added dropwise under stirring to a solution of 2b
(5.6ꢂ10À5 mol, see synthesis of 2b) in THF. The reaction mixture became
darker immediately and it was heated to 658C for 1 h 40 min while stir-
ring. Then the solvent was evaporated under vacuum and the resulting
solid was redissolved in toluene, filtered through a cotton pad, and the
solvent was removed under vacuum to yield 3b (32.6 mg; 89.9%). (Note:
in one preparation, trace impurities were present and these were re-
31P{1H} NMR ([D8]THF): d=123 (dd, 1JRh,P =138, 2JP, P =30.3 Hz, 2P),
8.8 ppm (dt, 1JRh,P =83.8, 2JP, P =30.3 Hz, 1P); 1H NMR ([D8]THF): d=
moved by extraction of 3b with MeOH.)
31P{1H} NMR ([D8]toluene): d=128.0 (dd, 1JRh,P =207.3 Hz, JP, P
3
2
7.38 (m, 4H; Pyr, HC-N-P), 6.99 (m, 4H; Pyr, HC-N-P), 6.83 (t, JH,H
=
=
39.5 Hz, 2P), 20.8 ppm (td, 1JRh,P =114.7, 2JP,P =39.5 Hz, 1P); 1H NMR
([D8]toluene): d=6.92 (m, 8H; Pyr, HC-N-P), 6.88 (br s, 3H; Ar, meta
and para to Rh), 6.24 (t, J=2.0 Hz, 8H; Pyr, HC-HC-N-P), 3.77 (vt,
2JP, H =3 Hz, 4H; Ar-H2C-P), 0.96 (m, 6H; Et, H2C-P), 0.83 ppm (m, 9H;
7.4 Hz, 1H; Ar, para to Rh), 6.27 (t, J=2.0 Hz, 4H; Pyr, HC-HC-N-P),
2
6.25 (t, J=2.0 Hz, 4H; Pyr, HC-HC-N-P), 4.9 (dvt, ABX2 pattern, JH,H
=
2
15.9, 2JP, H =4.8 Hz, 2H; Ar-H(H)C-P), 4.2 (dvt, ABX2 pattern, JH,H
=
15.9, 2JP, H =3.8 Hz, 2H; Ar-H(H)C-P), 1.16 (m, 6H; Et, H2C-P), 0.87 (m,
9H; Et, H3C), À16.1 ppm (ddt, 1JRh,H =23.8, 2JP, H =13.4 Hz, 1H; H-Rh);
2
Et, H3C); 13C{1H} NMR ([D8]toluene): d=174.43 (ddt, JP, C, trans =69.8,
2
13C{1H} NMR ([D8]THF): d=164.5 (ddt, JP, C, trans =92.4, 1JRh,C =23.2,
1JRh,C =29.4, 2JP, C,cis =9.6 Hz, 1C; Cipso-Rh), 143.63 (vtdd, unresolved dd,
2JP, C =12.5 Hz, 2C; Ar, C-C-Rh), 125.53 (s, 1C; Ar, CH-CH-C-C-Rh),
124.04 (vt, 2JP,C =4.0 Hz, 8C; Pyr, CH-N-P), 122.08 (vtd, 3JP, C =10.9 Hz,
J=3.3 Hz, 2C; Ar, CH-C-C-Rh), 112.23 (vt, 3JP, C =2.5 Hz, 8C; Pyr, CH-
CH-N-P), 52.73 (vtdd, 1JP,C =15.6, 2JRh,C =3JP, C =5.3 Hz, 2C; Ar-CH2-P),
18.79 (dt, 1JP, C =20.8, 3JP, C =3 Hz, 3C; Et, CH2-P), 9.24 ppm (s, 3C; Et,
CH3); 103Rh NMR (C6D6): d=À781 ppm; elemental analysis (%): calcd:
C 55.39, H 5.89; found: C 55.46, H 5.79.
2JP, C =5.5 Hz, 1C; Cipso-Rh), 141.5 (vtd 2JP,C =9.8, J=3.07 Hz, 2C; Ar, C-
C-Rh), 130.75 (s, 1C; Ar, CH-CH-C-C-Rh), 125.86 (t, J=2.46 Hz, 4C;
Pyr, CH-N-P), 124.91 (vt, 2JP, C =3.3 Hz, 4C; Pyr, CH-N-P), 123.2 (vtd,
3JP, C =11, J=4.8 Hz, 2C; Ar, CH-C-C-Rh), 113.06 (vt, 3JP, C =2.7 Hz, 4C;
Pyr, CH-CH-N-P), 112.67 (t, J=2.65 Hz, 4C; Pyr, CH-CH-N-P), 52.2
1
(vtdd, 1JP, C =20.5, 2JRh,C =3JP, C =4.3 Hz, 2C; Ar-CH2-P), 17.5 (d, JP, C
=
21.7 Hz, 3C; Et, CH2-P), 8.4 ppm (d, 2JP, C =3.13 Hz, 3C; CH3); elemental
[Rh(DPyPX)PPyr3] (3c): A solution of PPyr3 (30.5 mg, 1.3ꢂ10À4 mol) in
toluene (0.5 mL) was added to a solution of 3a (105.6 mg, 1.3ꢂ10À4 mol)
in toluene (0.5 mL). Neat MeOTf (14.95 mL, 1.3ꢂ10À4 mol) was added
and the suspension formed was left for 2 h at room temperature until a
clear solution was obtained. A white precipitate (MePPh3OTf) appeared.
The solution was left at À378C overnight, the precipitate was filtered off
using a cotton pad, and the solvent was removed from the resulting so-
lution by evaporation under vacuum to yield 3c as a yellow solid
(97.8 mg; 96.6%). (Note: in one case the product contained trace impuri-
ties and was recrystallized from pentane.)
analysis (%): calcd: C 52.45, H 5.72; found: C 52.54, H 5.81.
[Rh(DPyPX)PPh3] (3a): A solution of KOtBu (94 mg, 0.836 mmol) in
THF (1 mL) was added dropwise to a solution of crude 2a (0.835 mmol,
see synthesis of 2a) in THF, and the reaction mixture was stirred for
0.5 h inside the glove box. The solution became much darker immediate-
ly after the addition of KOtBu. The solvent was evaporated under
vacuum and the resulting solid was extracted with MeOH. Evaporation
of MeOH under vacuum resulted in a yellow solid that was redissolved
in benzene and filtered through a cotton pad. The solvent was evaporat-
ed under vacuum to yield compound 3a as a deep yellow solid (320 mg;
48%).
31P{1H} NMR (C6D6): d=123 (dd, 1JRh,P =198.5, 2JP,P =45.18 Hz, 2P),
108.8 ppm (dt, 1JRh,P =177.8, 2JP, P =45.38 Hz, 1P); 1H NMR (C6D6): d=
6.97 (t, 3JH,H =7.3 Hz, 1H; Ar, para to Rh), 6.88 (d, 3JH,H =7.3 Hz, 2H;
meta to Rh), 6.69 (m, 14H; Pyr, HC-N-P) 6.09 (m, 8H; Pyr, HC-HC-N-
31P{1H} NMR (C6D6): d=124.6 (dd, 1JRh,P =208.3, 2JP, P =38.2 Hz, 2P),
36.9 ppm (dt, 1JRh,P =119.0, 2JP,P =38.2 Hz, 1P); 1H NMR (C6D6): d=7.5
(m, 6H; Ph, ortho to P), 7.0–6.8 (m, 12H; Ph, meta and para to P, Ar,
meta and para to Rh), 6.72 (m, 8H; Pyr, HC-N), 6.01 (t, J=2.0 Hz, 8H;
Pyr, HC-HC-N), 3.8 ppm (vt, unresolved t, 4H; Ar-CH2-P); 13C{1H}
NMR (C6D6): d= 172.8 (ddt, 2JP, C,trans =69.9, 1JRh,C =30.4, 2JP, C, cis =9.6 Hz,
1C; Cipso-Rh), 143.8 (vt, 2JP,C =12.5 Hz, 2C; Ar, C-C-Rh), 137.6 (dvt,
2
P), 6.05 (m, 6H; Pyr, HC-HC-N-Pancillary), 3.72 ppm (vt, JP,H =3.4 Hz, 4H;
2
Ar-H2C-P); 13C{1H} NMR ([D8]toluene): d=171.5 (ddt, JP, C, trans =104.6,
2
1JRh,C =29.4, JP, C, cis =9.4 Hz, 1C; Cipso-Rh), 144.2 (vt, 2JP, C =12.8 Hz, 2C;
Ar, C-C-Rh), 123.7 (m, 14C; Pyr, CH-N-P), 122.7 (vtd, 3JP, C =11.4, J=
4.9 Hz, 2C; Ar, CH-C-C-Rh), 112.8 (m, 14C; Pyr, CH-CH-N-P), 51.9
(vtdd, 1JP, C =16.7, 2JRhC =3JP, C =5.7 Hz, 2C; Ar-CH2-P); 103Rh NMR
([D8]toluene): d=À853.7 ppm; elemental analysis (%): calcd: C 56.78, H
4.63; found: C 56.67, H 4.70.
3
1JP, C =34.6, JP, C =2 Hz, 3C; Ph, C-P), 134.3 (d, J=13.5 Hz, 6C; Ph), 129.5
(d, 4JP, C =1.6 Hz, 3C; Ph, CH-CH-CH-C-P), 125.9 (s, 1C; Ar, CH-CH-C-
C-Rh), 123.9 (vt, 2JP, C =3.7 Hz, 8C; Pyr, CH-N), 122.4 (vtd, 3JP,C =10.9,
J=3.1 Hz, 2C; Ar, CH-C-C-Rh), 111.8 (vt, 3JP, C =2.4 Hz, 8C; Pyr, CH-
CH-N), 52.7 ppm (vtdd, 1JP, C =16.1, 2JRh,C =3JP, C =5.2 Hz, 2C; Ar-CH2-P);
103Rh NMR ([D8]THF): d= À734 ppm; elemental analysis (%): calcd: C
63.48, H 4.82; found: C 63.70, H 4.76.
[Rh(DPyPX)PPh3CO] (4a): CO (0.55 mL, 2.4ꢂ10À5 mol) was injected
with a syringe into a solution of 3a (19.3 mg, 2.4ꢂ10À5 mol) in toluene
(0.7 mL) in a reaction tube fitted with a septum. The reaction tube was
Chem. Eur. J. 2005, 11, 2319 – 2326
www.chemeurj.org
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2323

J. M. L. Martin, D. Milstein et al.
vigorously shaken until the solution became light yellow. The solvent was
removed under vacuum and the product was recrystallized from a satu-
CH-C-C-Rh), 124.01 (br s, 4C; Pyr, CH-N-P), 122.95 (vt, 3JP, C =10 Hz,
2C; Ar, CH-C-C-Rh), 122.73 (br s, 4C; Pyr, CH-N-P), 112.68 (s, 4C; Pyr,
CH-CH-N-P), 112.24 (s, 4C; Pyr, CH-CH-N-P), 52.78 (vt, 1JP,C =17 Hz,
2C; Ar-CH2-P), the signal of CH2-PEt overlaps with [D8]toluene signal,
6.92 ppm (s, 3C; Et, CH3); IR (film): n˜ =1975 cmÀ1 (CꢁO); elemental
analysis (%): calcd: C 54.88, H 5.65; found: C 55.04, H 5.58.
rated MeOH solution, to yield 4a as a yellow solid (12 mg; 61%).
31P{1H} NMR ([D8]toluene, 295 K): d=125.0 (br dd, 1JRh,P =195.5, JP, P
2
=
143), 21.2 ppm (br dt, 1JRh,P =130, 2JP,P =145 Hz); 1H NMR ([D8]toluene,
295 K): d=6.98 (s, 4H; Pyr, HC-N-P), 6.96 (m, 3H; Ph, para to P), 6.86
(br s, 12H; meta and ortho to P), 6.79 (t, 3JH,H =7.4 Hz, 1H; Ar, para to
Rh), 6.67 (d, 3JH,H =7.4 Hz, 2H; Ar, meta to Rh; 2H), 6.55 (br s, 4H;
Pyr, HC-N-P), 6.32 (br s, 4H; Pyr, HC-HC-N-P), 6.08 (br s, 4H; Pyr,
HC-HC-N-P), 3.52 (br s, 2H; Ar-H(H)C-P), 3.08 ppm (br s, 2H; Ar-
X-ray analysis of the structure of [Rh(DPyPX)PEt3CO] (4b): Colorless
orthorhombic crystals of 4b were obtained by recrystallization of 4b
from a pentane solution. For this purpose, a toluene solution of 4b
(20 mg) was dried under vacuum to obtain a solid film of 4b at the
bottom of a 20 mL Wheaton vial. Then the obtained layer was covered
by pentane (2 mL) and left at 15–208C for three days. Crystals appeared
on the bottom of the vial.
1
H(H)C-P); 13C{1H} NMR ([D8]toluene, 295 K): d=202.5 (dt, JRh,C =48.8,
2
2JP, P =14.5 Hz, 1C; CO), 166.14 (m, 1C; Cipso-Rh), 143.09 (vt, JP,C
=
16.3 Hz, 2C; Ar, C-C-Rh), 136.6 (d, 1JP,C =25.6 Hz, 3C; Ph, C-P), 133.1
(d, 2JP, C =13.8 Hz, 6C; Ph, CH-C-P), 130–127 (overlapped with [D8]tolu-
ene, 9C; Ph), 124.5 (s, 1C; Ar, CH-CH-C-C-Rh), 123.6, (br s, 4C; Pyr,
Crystal data: C31H38N4O1P3Rh, colorless, prism, 0.1ꢂ0.1ꢂ0.1 mm3, orthor-
rhombic, Pbca, a=15.2900(3), b=19.2050(2), c=21.4960(2) ꢁ, from 15
degrees of data, T=120(2 K, V=6312.18(15) ꢁ3, Z=8, Fw=678.47,
3
CH-N-P), 123.3 (vt, JP, C =11.3 Hz, 2C; Ar, CH-C-C-Rh), 123.0 (br s, 4C;
Pyr, CH-N-P), 112.5 (br s, 8C; Pyr, CH-CH-N-P), 50.75 ppm (vtd, unre-
solved d, 1JP, C =16.0 Hz, 2C; Ar-CH2-P); 31P{1H} NMR ([D8]toluene,
243 K); d=125.9 (dd, 1JRh,P =197.7 Hz, 2JP, P =154.8 Hz, 2P), 21.5 ppm (td,
1JRh,P =126.1, 2JP, P =154.8 Hz, 1P); 1H NMR ([D8]toluene, 243 K): d=
6.96 (s, 4H; Pyr, HC-N-P), 6.92 (m, 3H; Ph, para to P), 6.82 (m, 13H;
1calcd =1.428 MgmÀ3, m=0.724 mmÀ1
.
Data collection and processing: Nonius KappaCCD diffractometer, MoKa
(l=0.71073 ꢁ), graphite monochromator, À19ꢂhꢂ19, À24ꢂkꢂ24,
À27ꢂlꢂ27, frame scan width=1.08, scan speed 1.08 per 30 s, typical
peak mosaicity 0.648, 71911 reflections collected, 14813 independent re-
flections (Rint =0.094). The data were processed with Denzo-Scalepack.
3
Ph, meta and ortho to P, and Ar, para to Rh), 6.65 (d, JH,H =7.5 Hz, 2H;
Ar, meta to Rh), 6.59 (br s, 4H; Pyr, HC-N-P), 6.36 (t, J=2 Hz, 4H; Pyr,
HC-HC-N-P), 6.11 (t, J=2 Hz, 4H; Pyr, HC-HC-N-P), 3.42 (dvt, ABX2
pattern, 2JH,H =15.6, 2JP, H =5.6 Hz, 2H; Ar-H(H)C-P), 2.95 ppm (d, AB
Solution and refinement: structure was solved by direct methods with
SHELXS-97. Full-matrix least-squares refinement based on F2 with
SHELXS-97. 428 parameters with 0 restraints, final R1 =0.0404 (based on
F2) for data with I>2s(I) and, R1 =0.0688 on 7205 reflections, goodness-
of-fit on F2 =1.039, largest electron density peak=1.214.
[Rh(DPyPX)PPyr3CO] (4c): CO (0.4 mL, 2.0ꢂ10À5 mol) was added to a
solution of 3c (15 mg, 2.0ꢂ10À5 mol) in toluene (0.7 mL), resulting in the
quantitative formation of [Rh(PCP)PPyr3CO] (4c).
pattern, 2JH,H =15.6 Hz, 2H; Ar-H(H)C-P); 13C{1H} NMR ([D8]toluene,
2
243 K): d= 202.6 (dtd, 1JRhC =49, 2JPC,DPyPX =15, JPC,PPh =9.6 Hz, 1 C;
3
CO), 166.1 (ddt, 1JRh,C =22 Hz, 2JPC,DPyPX =2JPC,PPh =11 Hz, 1C; Cipso-Rh),
3
1
142.9 (vtd, 2JP, C =16.2 Hz, J=3.2 Hz, 2C; Ar, C-C-Rh), 136.2 (d, JP, C
=
2
26.6 Hz, 3C; Ph, C-P), 133.0 (d, JP, C =13.7 Hz, 6C; Ph, CH-C-P), 130–127
(overlapped with [D8]toluene, 9C; Ph), 124.4 (s, 1C, Ar, CH-CH-C-C-
3
Rh), 123.7 (s, 4C; Pyr, CH-N-P), 123.4 (vt, JP, C =10.2 Hz, 2C; Ar, CH-C-
31P{1H} NMR (C6D6, 295 K): d=119.6 (br d, 1JRh,P =184.9 Hz, 2P),
93.1 ppm (br s, 1P); 1H NMR (C6D6, 295 K): d=6.83 (t, 3JH,H =7.45 Hz,
1H; Ar, para to Rh), 6.70 (d, 2H; 3JH,H =7.45 Hz, meta to Rh), 7.0–6.55
(br s, 8H; Pyr, HC-N-P), 6.20 (br s, 8H; Pyr, HC-HC-N-P), 6.15 (br s,
6H; Pyr, HC-N-Pancillary), 6.06 (t, J=2.1 Hz, 6H; Pyr, HC-CH-N-Pancillary),
C-Rh), 123.0 (s, 4C; Pyr, CH-N-P), 112.8 (s, 4C; Pyr, CH-CH-N-P), 112.4
(s, 4C; Pyr, CH-CH-N-P), 50.4 ppm (vt, 1JP, C =16 Hz, 2C; Ar-CH2-P); IR
(film): n˜ =1987 cmÀ1 (CꢁO); elemental analysis (%): calcd: C 62.78, H
4.66; found: C 62.63, H 4.71.
[Rh(DPyPX)PEt3CO] (4b): CO (0.6 mL, 2.6ꢂ10À5 mol) was added to 3b
(17.4 mg, 2.6ꢂ10À5 mol) in benzene (0.7 mL). The solution was vigorously
shaken to dissolve CO, resulting in a lighter yellow color. The solvent
was removed by evaporation and the product was recrystallized from a
saturated pentane solution, to yielding 4b as a yellow solid (10 mg;
3.54 ppm (br s, 4H; Ar-CH2-P); 13C{1H} NMR (C6D6, 295 K): d=199.8
2
(br d, 1JRh,C =44.2 Hz, 1C; CO), 160 (br s, 1C; Cipso-Rh), 143.6 (vt, JP,C
=
15.4 Hz, 2C; Ar, C-C-Rh), 125.79 (s, 1C; Ar, CH-CH-C-C-Rh), 123.81
(vt, 3JP, C =10.9 Hz, 2C; Ar, CH-C-C-Rh), 123.41 (s, 8C; Pyr, CH-N-P),
123.36 (d, partially overlapped with the s at 123.41, 6C; Pyr, CH-N-Pancil-
55%).
3
lary), 113.37 (br s, 8C; Pyr, CH-CH-N-P), 112.86 (d, JP, C =4.7 Hz, 6C; Pyr,
2
31P{1H} NMR (C6D6, 295 K): d=124.06 (dd, 1JRh,P =190.8 Hz, JP, P
=
CH-CH-N-Pancillary), 51.10 ppm (vt, 1JP, C =16.3 Hz, 2C; Ar-CH2-P); 31P{1H}
164 Hz, 2P), 4.63 ppm (td, 1JRh,P =132.4 Hz, 2JP, P =164 Hz, 1P); 1H NMR
2
NMR ([D8]toluene, 243 K): d=126.27 (br dd, 1JRh,P =188 Hz, JP, P
=
3
([D8]toluene, 295 K): d=7.11 (m, 4H; Pyr, HC-N-P), 6.89 (d, JH,H
=
229 Hz, 2P), 99.5 ppm (ddd, 1JRh,P =194, 2JP, P =223.5, 2JP, P =234.5 Hz, 1P);
1H NMR ([D8]toluene, 243 K): d=6.86 (br s, 4H; Pyr, HC-N-P), 6.78 (m,
1H; Ar, para to Rh), 6.64 (d, 3JH,H =7.46 Hz, 2H; Ar, meta to Rh), 6.40
(br s, 4H; Pyr, HC-N-P), 6.29 (m, 6H; Pyr, HC-N-Pancillary), 6.03 (m, 14H;
Pyr, HC-HC-N-P), 3.43 (dvt, ABX2 pattern, 2JH,H =15.8, 2JP, H =5.45 Hz,
2H; Ar-H(H)C-P), 3.34 ppm (d, AB pattern, 2JH,H =15.9 Hz, 2H; Ar-
7 Hz, 2H; Ar, meta to Rh), 6.84 (t, 3JH,H =7 Hz, 1H; Ar, para-to-Rh),
6.52 (br s, 4H; Pyr, HC-N-P), 6.33 (br s, 4H; Pyr, HC-CH-N-P), 6.08 (br
2
s, 4H; Pyr, HC-CH-N-P), 3.92 (dvt, ABX2 pattern, 2JH,H =15.9, JP,H
=
5.3 Hz, 2H; Ar-CH(H)-P), 3.71 (d, AB pattern, 2JH,H =15.9 Hz, 2H; Ar-
CH(H)-P), 1.03 (m, 6H; Et, H2C-P), 0.46 ppm (m, 9H; Et, H3C-H2C-P);
2
13C{1H} NMR ([D8]toluene, 295 K): d=204.2 (ddt, 1JRh,C =48, JPC,DPyPX
=
1
H(H)C-P); 13C{1H} NMR ([D8]toluene, 243 K): d=199.76 (ddt, JRhC =49,
2JPC,PEt =11 Hz, 1C; CO), 166.3 (ddt, 1JRh,C =22, 2JPC,DPyPX =2JPC,PEt
=
2
2JPC,DPyPX =2J
=14 Hz, 1C; CO), 159.79 (ddt, 1JRh,C =19, JPC,DPyPX
=
3
3
PC,PPyr3
11 Hz, 1C; Cipso-Rh), 143.0 (vt, 2JP,C =16 Hz, 2C; Ar, C-C-Rh), 124.4 (s,
2JPC,PPyr =10 Hz, 1C; Cipso-Rh), 143.44 (vtd, 2JP, C =15.6 Hz, unresolved d,
2C; Ar, C-C-Rh), 125.62 (s, 1C; Ar, CH-CH-C-C-Rh), 123.74 (vt, JP, C
3
3
1C; Ar, CH-CH-C-C-Rh), 124.0 (br s, 4C; Pyr, CH-N-P), 122.9 (vt, JP, C
=
3
=
10 Hz, 2C; Ar, CH-C-C-Rh), 122.7 (br s, 4C; Pyr, CH-N-P), 112.6 (s, 4C;
9 Hz, 2C; Ar, CH-C-C-Rh), 123.5 (s, 4C; Pyr, CH-N-P), 123.23 (s, 4C;
Pyr, CH-N-P), 123.10 (d, 2JP, C =19.20 Hz, 6C; Pyr, CH-N-Pancillary), 113.68
(s, 4C; Pyr, CH-CH-N-P), 112.90 (s, 4C; Pyr, CH-CH-N-P), 112.73 (d,
partially overlapped with the s at 112.90, 6C; Pyr, CH-CH-N-Pancillary),
50.71 ppm (vt, 1JP, C =16.84 Hz, 2C; Ar-CH2-P); IR (film): n=2008 cmÀ1
(CꢁO); elemental analysis (%): calcd: C 56.28, H 4.47; found: C 56.41, H
4.51.
1
Pyr, CH-CH-N-P), 112.2 (s, 4C; Pyr, CH-CH-N-P), 53.0 (vt, JP,C
=
16.4 Hz, 2C; Ar-CH2-P), the signal of CH2-PEt overlaps with [D8]toluene
signal, 7.0 ppm (s, 3C; Et, CH3); 31P{1H} NMR ([D8]toluene, 243 K): d=
1
124.1 (dd, 1JRh,P =190.5 Hz, 2JP, P =165 Hz, 2P), 4.9 ppm (td, JRh,P
=
133.4 Hz, 2JP, P =165 Hz, 1P); 1H NMR ([D8]toluene, 243 K): d=7.11 (m,
4H; Pyr, HC-N-P), 6.92 (m, 3H; Ar, meta and para to Rh), 6.53 (m, 4H;
Pyr, HC-N-P), 6.37 (m, 4H; Pyr, HC-CH-N-P), 6.13 (m, 4H; Pyr, HC-
CH-N-P), 3.83 (dvt, ABX2 pattern, 2JH,H =15.8, 2JPH =5 Hz, 2H; Ar-
CH(H)-P), 3.60 (d, AB pattern, 2JH,H =15.9 Hz, 2H; Ar-CH(H)-P), 0.96
(m, 6H; Et, H2C-P), 0.39 ppm (m, 9H; Et, H3C); 13C{1H} NMR ([D8]tolu-
Reaction of [Rh(DPyPX)(PPy3)CO] (4c) with PPh3: PPh3 (6.5 mg, 2.5ꢂ
10À5 mol) in toluene (0.3 mL) was added to a solution of 4c (19.7 mg,
2.5ꢂ10À5 mol) in toluene (0.7 mL). The reaction became slightly darker
yellow. 31P{1H} and 1H NMR ([D8]toluene, 243 K) spectra indicated for-
mation of 4a, when 4a:4c=4:1. The 4a:4c ratio did not change after
heating the solution at 708C for 40 min.
ene, 243 K): d=204.4 (ddt, 1JRh,C =48, 2JPC,DPyPX =2JPC,PEt =13 Hz, 1C;
3
CO), 166.4 (ddt, 1JRhC =22, 2JP,C,DPyPX =2JPC,PEt =11 Hz, 1C; Cipso-Rh),
3
142.9 (vtd, 2JP, C =17, J=3.4 Hz, 2C; Ar, C-C-Rh), 124.4 (s, 1C; Ar, CH-
2324
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2005, 11, 2319 – 2326

Pincer Complexes
FULL PAPER
Reaction of [Rh(DPyPX)(PPh3)CO] (4a) with PEt3: Neat PEt3 (3.2 mL,
2.4ꢂ10À5 mol) was added to a solution of 4a (19.5 mg, 2.4ꢂ10À5 mol) in
et al.ꢃs reparameterization[4] of Beckeꢃs B97 functional.[39] Two basis set-
RECP (relativistic effective core potential) combinations were used. The
first, denoted SDD, is the combination of the Huzinaga-Dunning double-
z basis set on lighter elements with the Stuttgart–Dresden basis set-
RECP combination[40] on transition metals. The second, denoted SDB-cc-
pVDZ, combines the Dunning cc-pVDZ basis set[41] on the main group
elements and the Stuttgart-Dresden basis set-RECP on the transition
metals with an added f-type polarization exponent taken as the geometric
average of the two f-exponents given in the Appendix to reference [42].
Geometry optimizations were carried out using the former basis set,
while the energetics of the reaction were calculated at these reference ge-
ometries with the latter basis set; this level of theory is conventionally
denoted as B97–1/SDB-cc-pVDZ//B97–1/SDD. Bulk solvation effects[43]
were approximated using a conductor-like screening solvation model
(COSMO)[44, 45] with benzene as the solvent, just as with the experimental
system. The molecular orbitals (MOs) were visualized by using Gauss-
View[46] and the MO energies were taken as the Kohn–Sham (KS) orbital
energies, both from the B97–1/SDB-cc-pVDZ energy calculation. The ap-
plicability of the KS orbital energies as ionization energies, for valence
orbitals in closed shell systems, has been clearly demonstrated.[47–49]
1
toluene (0.7 mL). 31P{1H} and H NMR ([D8]toluene, 243 K) spectra indi-
cated immediate quantitative formation of 4b.
[Rh(DiPPX)H(PEt3)Cl]: PEt3 (7.6 mL, 5.6ꢂ10À5 mol) was added to a so-
lution of [{Rh(coe)2m-Cl2}] (20 mg, 2.8ꢂ10À5 mol) in THF (1.5 mL). To
the resulting mixture, a solution of DiPPX-H (1,3-bis[(diisopropylphos-
phino)methyl]benzene)[36] (21.5 mL, 5.6ꢂ10À5 mol) in THF (1 mL) was
added. The solution was heated under stirring at 658C for 2.5 h, to give
an orange solution of [Rh(DiPPX)H(PEt3)Cl]. The 31P{1H} NMR spec-
trum did not show any remaining starting material.
31P{1H} NMR (C6D6): d=64.15 (dd, 1JRh,P =106, 2JP, P =24.5 Hz, 2P),
2.37 ppm (dt, 1JRh,P =82.5, 2JP, P =24.5 Hz, 1P); 1H NMR (C6D6): d=7.2–
2
7.1 (Ar, 3H; meta and para to Rh), 3.79 (dvt, ABX2 pattern, JH,H =14.7,
2JP, H =3.4 Hz, 2H; Ar-CH(H)-P), 2.98 (dvt, ABX2 pattern, 2JH,H =14.7,
2JP, H =3.9 Hz, 2H; Ar-CH(H)-P), 2.3–0.7 (m, 43H; iPr, Et), À18.41 ppm
(ddt, 1JRh,H =23.64, 2JP, H =12.83 Hz, 1H; H-Rh); 13C{1H} NMR (C6D6):
d=168.6 (ddt, 2JP, C, trans =103.7 Hz , 1JRh,C =25.4 2JP, C, cis =4.2 Hz, 1C; Cipso
-
Rh), 145.8 (vtd, 2JP, C =7.64 Hz, unresolved d, 2C; Ar, C-C-Rh), 124.08 (s,
1C; Ar, CH-CH-C-C-Rh), 121.3 (vtd, 3JP, C =8.15, J=4.7 Hz, 2C; Ar, CH-
C-C-Rh), 36.84 (vtdd, 1JP, C =14.04, J=8.29 Hz, J=2.07 Hz, 2C; Ar-CH2-
P), 26.97 (vt, 1JP, C =10.01 Hz, 2C; iPr, CH-P), 25.36 (vt, 1JP, C =11.26 Hz,
2C; iPr, CH-P), 20.35 (dvt, 1JP, C =16.77 Hz, unresolved t, 3C; Et, CH2-P),
19.8 (s, 4C; iPr, CH3), 18.8 (s, 4C; iPr, CH3), 8.84 (d, 2JP, C =3.04 Hz, 3C;
Et, CH3).
Acknowledgements
[Rh(DiPPX)PEt3]: A solution of KOtBu (6.3 mg, 5.6ꢂ10À5 mol) in THF
This work was supported by the Israel Science Foundation (Jerusalem,
Israel), the Helen and Martin Kimmel Center for Molecular Design and
the Minerva Foundation (Munich, Germany). J.M.L.M. is the incumbent
of the Baroness Thatcher Professorial Chair in Chemistry and a member
of the Lise Meitner-Minerva Center for Computational Quantum
Chemistry. D.M. is the The Israel Matz Professorial Chair of Organic
Chemistry. E.K., M.A.I., and B.R. acknowledge the Feinberg Graduate
School of the Weizmann Institute of Science for Ph.D. fellowships.
(1 mL) was added dropwise to
a solution of crude [Rh(DiPPX)H-
(PEt3)Cl] (2.8ꢂ10À5 mol, see synthesis of [Rh(DiPPX)H(PEt3)Cl]) in
THF. The resulting solution was heated to 608C for 1 h to give almost
quantitative formation of dark brown [Rh(DiPPX)PEt3]. The product
was dried under vacuum and fully extracted with pentane, leaving KCl as
white solid. The pentane solvent was removed under vacuum, to yield
[Rh(DiPPX)PEt3] as a brown solid (30 mg; 96%).
31P{1H} NMR (C6D6): d=62.6 (dd, 1JRh,P =154.3, 2JP, P =30.8 Hz, 2P),
14.9 ppm (dt, 1JRh,P =113.7, 2JP, P =30.8 Hz, 1P); 1H NMR (C6D6): d=7.30
(d, 3JH,H =7.2 Hz, 2H; Ar, meta to Rh), 7.21 (t, 3JH,H =7.2 Hz, 1H; para
to Rh), 3.16 (vt, 2JP, H =3.5 Hz, 4H; Ar-CH2-P), 1.88 (m, 4H; iPr, CH-P),
1.59 (m, 6H; Et, CH2-P) 1.16 (m, 12H; iPr, CH3-CH-P), 1.08 (m, 9H; Et,
CH3-CH2-P), 0.95 ppm (m, 12H; iPr, CH3-CH-P); 13C{1H} NMR (C6D6):
[1] M. Albrecht, G. van Koten, Angew. Chem. 2001, 113, 3866–3898;
Angew. Chem. Int. Ed. 2001, 40, 3750–3781.
[2] M. E. van der Boom, D. Milstein, Chem. Rev. 2003, 103, 1759–1792.
[3] B. Rybtchinski, D. Milstein, Angew. Chem. 1999, 111, 918–932;
Angew. Chem. Int. Ed. 1999, 38, 870–883.
[4] J. T. Singleton, Tetrahedron 2003, 59, 1837–1857.
[5] A. Vigalok, D. Milstein, Acc. Chem. Res. 2001, 34, 798–807.
[6] D. Milstein, Pure Appl. Chem. 2003, 75, 445–460.
[7] C. M. Jensen, Chem. Commun. 1999, 24, 2443–2449.
[8] K. G. Moloy, J. L. Petersen, J. Am. Chem. Soc. 1995, 117, 7696–
7710.
[9] d=doublet, t=triplet, vt=virtual triplet, q=quartet, dd=doublet
of doublets, and so forth.
[10] CCDC-248612 contains the supplementary crystallographic data for
complex 3a. These data can be obtained free of charge from the
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
[11] CCDC-248613 contains the supplementary crystallographic data for
complex 4b. These data can be obtained free of charge from the
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
2
1
2
d=180.1 (ddt, JP, C, trans =85.0, JRh,C =32.2, JP, C, cis =7.62 Hz, 1C; Cipso-Rh),
2
149.79 (vt, JP, C =11.3 Hz, 2C; Ar, C-C-Rh), 123.19 (s, 1C; Ar, CH-CH-C-
C-Rh), 120.13 (vtd, 3JP, C =8.90, J=2.9 Hz, 2C; Ar, CH-C-C-Rh), 39.74
1
(vtdd, 1JP, C =12.05, J=9.3, J=2.85 Hz, 2C; Ar-CH2-P), 27.30 (vtd, JP,C
=
8.98, J=1.72 Hz, 4C; iPr, CH-P), 21.40 (dt, 1JP, C =16.0 Hz, unresolved t,
3C; Et, CH2-P), 20.16 (vt, 2JP, C =3.35 Hz, 4C; iPr, CH3), 19.34 (s, 4C; iPr,
CH3), 9.39 (s, 3C; Et, CH3); elemental analysis (%): calcd: C 55.91, H
9.02; found: C 55.73, H 8.85.
[Rh(DiPPX)CO]: CO (1.2 mL, 5.4ꢂ10À5 mol) was added to
[Rh(DiPPX)PEt3] (30 mg, 5.4ꢂ10À5 mol) in benzene (0.7 mL). The so-
lution was vigorously shaken to dissolve CO, resulting in the quantitative
formation of [Rh(DiPPX)CO], which is lighter brown in color than the
starting material. Volatile compounds were removed by evaporation.
31P{1H} NMR (C6D6): d=74.5 ppm (d, 1JRh,P =144.0 Hz, 2P); 1H NMR
(C6D6): d=7.19 (d, 3JH,H =7.4 Hz, 2H; Ar, meta to Rh), 7.13 (partially
2
overlapped with the solvent signal, 1H; Ar, para to Rh), 3.16 (vt, JP, H
=
4.1 Hz, 4H; Ar-CH2-P), 1.89 (m, 4H; iPr, HC-P), 1.17 (m, 12H; iPr,
H3C), 0.93 ppm (m, 12H; iPr, H3C); 13C {1H} NMR (C6D6): d=200.04
(dt, 1JRh,C =54.95, 2JP,C =12.05 Hz, 1C; CO), 178.83 (dt, 1JRh,C =29.8 Hz,
[12] P. Meakin, J. P. Jesson, J. Am. Chem. Soc. 1973, 95, 7272–7281.
[13] J. P. Jesson, P. Meakin, J. Am. Chem. Soc. 1973, 95, 1344–1346.
[14] J. P. Collman, F. D. Vastine, W. R. Roper, J. Am. Chem. Soc. 1968,
90, 2282–2287.
[15] H.-S. Lee, J.-Y. Bae, J. Ko, Y. S. Kang, H. S. Kim, S.-J. Kim, J.-H.
Chung, S. O. Kang, J. Organomet. Chem. 2000, 614–615, 83–91.
[16] M. C. Nicasio, M. Paneque, P. J. Pꢄrez, A. Pizzano, M. L. Poveda, L.
Rey, S. Sirol, S. Taboada, M. Trujillo, A. Monge, C. Ruiz, E. Carmo-
na, Inorg. Chem. 2000, 39, 180–188.
[17] A. Weisman, M. Gozin, H.-B. Kraatz, D. Milstein, Inorg. Chem.
1996, 35, 1792–1797.
[18] M. Gozin, Ph. D. Thesis, Weizmann Institute of Science, Rehovot,
Israel, January 1995.
2
2
2JP, C =6.96 Hz, Cipso-Rh, 1C), 152.88 (vtd, JP, C =12.35, JRh,C =3.12 Hz, 2C;
3
Ar, C-C-Rh), 125.55 (s, 1C; Ar, CH-CH-C-C-Rh), 120.99 (vt, JP, C
=
9.77 Hz, 2C; CH-C-C-Rh), 38.16 (vtd, 1JP,C =11.97, 2JRh,C =3.03 Hz, 2C;
2
Ar-CH2-P), 26.18 (vt, 1JP, C =11.26 Hz, 4C; iPr, CH-P), 19.79 (vt, JP,C
=
3.0 Hz, 4C; iPr, CH3), 18.85 ppm (s, 4C; iPr, CH3); IR (film): n˜ =
1943 cmÀ1 (CꢁO); elemental analysis (%): calcd: C 53.85, H 7.53; found:
C 53.72, H 7.52.
Computational details: All calculations were carried out using Gaussian
03 Rev B.02.[37] The density functional theory (DFT) B97–1 hybrid ex-
change-correlation functional[38] was used throughout. This is Handy
Chem. Eur. J. 2005, 11, 2319 – 2326
www.chemeurj.org
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2325

J. M. L. Martin, D. Milstein et al.
[19] J. Terheijden, G. van Koten, W. P. Mul, D. J. Stufkens, F. Muller,
C. H. Stam, Organometallics 1986, 5, 519–525.
[37] Gaussian 03, Revision B.02, M. J. Frisch, G. W. Trucks, H. B. Schle-
gel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgomer-
y, Jr., T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyen-
gar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N.
Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian,
J. B. Cross, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann,
O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, P. Y.
Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J. Dannenberg,
V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C. Strain, O.
Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B. Fores-
man, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cioslowski,
B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L.
Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Na-
nayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen,
M. W. Wong, C. Gonzalez, and J. A. Pople, Gaussian, Inc., Pitts-
burgh PA, 2003.
[38] F. A. Hamprecht, A. J. Cohen, D. J. Tozer, N. C. Handy, J. Chem.
Phys. 1998, 109, 6264–6271.
[39] A. D. Becke, J. Chem. Phys. 1997, 107, 8554–8560.
[40] M. Dolg in Modern Methods and Algorithms of Quantum Chemistry,
Vol. 1 (Ed.: J. Grotendorst), John von Neumann Institute for Com-
puting, Jꢅlich, 2000, pp. 479–508.
[41] T. H. Dunning Jr., J. Chem. Phys. 1989, 90, 1007–1023.
[42] J. M. L. Martin, A. Sundermann, J. Chem. Phys. 2001, 114, 3408–
3420.
[43] C. J. Cramer in Essentials of Computational Chemistry: Theories and
Models, Wiley, Chichester, UK, 2002, pp. 347–383.
[20] M. Albrecht, M. Lutz, A. M. M. Schreurs, E. T. H. Lutz, A. L. Spek,
G. van Koten, J. Chem. Soc. Dalton Trans. 2000, 3797–3804.
[21] Facial h3 coordination of an NCN-type ligand of a tantalum alkyli-
dene complex was reported: H. C. L. Abbenhuis, N. Feiken, D. M.
Grove, J. T. B. H. Jastrzebski, H. Kooijman, P. van der Sluis, W. J. J.
Smeets, A. L. Spek, G. van Koten, J. Am. Chem. Soc. 1992, 114,
9773–9781.
[22] P. E. Garrou, G. E. Hartwell, Inorg. Chem. 1976, 15, 646–650.
[23] J. G. Leipoldt, G. J. Lamprecht, E. C. Steynberg, J. Organomet.
Chem. 1990, 397, 239–244.
[24] J. G. Leipoldt, G. J. Lamprecht, E. C. Steynberg, J. Organomet.
Chem. 1991, 402, 259–263.
[25] M. A. Alonso, J. A. Casares, P. Espinet, K. Soulantica, Angew.
Chem. 1999, 111, 554–557; Angew. Chem. Int. Ed. 1999, 38, 533–
535.
[26] B. Crociani, S. Antonaroli, M. L. Di Vona, S. Licoccia, J. Organomet.
Chem. 2001, 631, 117–124.
[27] R. E. Bossio, N. W. Hoffman, T. R. Cundari, A. G. Marshall, Orga-
nometallics 2004, 23, 144–148.
[28] K. Krogh-Jespersen, M. Czerw, K. Zhu, B. Singh, M. Kanzelberger,
N. Darji, P. D. Achord, K. B. Renkema, A. S. Goldman, J. Am.
Chem. Soc. 2002, 124, 10797–10809.
[29] J.-Y. Saillard, R. Hoffmann, J. Am. Chem. Soc. 1984, 106, 2006–
2026.
[30] M. Ogasawara, S. A. Macgregor, W. E. Streib, K. Folting, O. Eisen-
stein, K. G. Caulton, J. Am. Chem. Soc. 1996, 118, 10189–10199.
[31] M. J. Burk, M. P. McGrath, R. Wheeler, R. H. Crabtree, J. Am.
Chem. Soc. 1988, 110, 5034–5039.
[32] M. J. Frisch, et al. Gaussian 03 rev. B.02, Gaussian Inc., Pittsburgh,
PA, 2003.
[33] M. Ogasawara, F. Maseras, N. Gallego-Planas, K. Kawamura, K. Ito,
K. Toyota, W. E. Streib, S. Komiya, O. Eisenstein, K. G. Caulton,
Organometallics 1997, 16, 1979–1993.
[34] A. R. Rossi, R. Hoffmann, Inorg. Chem. 1975, 14, 365–374.
[35] P. Hofmann, C. Meier, U. Englert, M. U. Schmidt, Chem. Ber. 1992,
125, 353–365.
[44] V. Barone, M. Cossi, J. Phys. Chem. A 1998, 102, 1995–2001.
[45] M. Cossi, N. Rega, G. Scalmani, V. Barone, J. Comput. Chem. 2003,
24, 669–681.
[46] GaussView 3.0, Gaussian Inc., Pittsburgh, PA, 2003.
[47] D. P. Chong, O. V. Gritsenko, E.-J. Baerends, J. Chem. Phys. 2002,
116, 1760–1772.
[48] O. V. Gritsenko, B. Braïda, E. J. Baerends, J. Chem. Phys. 2003, 119,
1937–1950.
[49] C.-G. Zhan, J. A. Nichols, D. A. Dixon, J. Phys. Chem. A 2003, 107,
4184–4195.
[36] B. Rybtchinski, Y. Ben-David, D. Milstein, Organometallics 1997,
16, 3786–3793.
Received: November 5, 2004
Published online: January 10, 2005
2326
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www.chemeurj.org
Chem. Eur. J. 2005, 11, 2319 – 2326