Structure and reactivity of rhodium(I) complexes based on electron-withdrawing pyrrolyl-pcp-pincer ligands

Article abstract of DOI:10.1021/om800792y

Rhodium complexes based on the electron-withdrawing PCP-type pincer ligand dipyrrolylphoshi-noxylene (DPyPX, ^PyrPCP) were synthesized and their reactivity was studied. Reaction of Rh^I(^pyrPCP)PR ₃ (2) (R = Et (a)

Full text of DOI:10.1021/om800792y

Organometallics 2009, 28, 523–533
523
Structure and Reactivity of Rhodium(I) Complexes Based on
Electron-Withdrawing Pyrrolyl-PCP-Pincer Ligands
Elizaveta Kossoy,† Boris Rybtchinski,† Yael Diskin-Posner,‡ Linda J. W. Shimon,‡
Gregory Leitus,‡ and David Milstein*,†
Department of Organic Chemistry and Chemical Research Support,
Weizmann Institute of Science RehoVot, 76100 Israel
ReceiVed August 17, 2008
Rhodium complexes based on the electron-withdrawing PCP-type pincer ligand dipyrrolylphoshi-
noxylene (DPyPX, PyrPCP) were synthesized and their reactivity was studied. Reaction of
RhI(PyrPCP)PR3 (2) (R ) Et (a); Ph (b); Pyr (pyrrolyl, NC4H4) (c); Pyd (pyrrolydinyl, NC4H8) (d))
with MeI was strongly dependent on the sterics and nucleophilicity of PR3. Complex 2a (PEt3 cone
angle, Θ°, 132°) reacted with MeI to give isomers of RhIII(PyrPCP)Me(I)PEt3, 3. Reaction of 2b
(Θ°PR3 ) 145°, R ) Pyd (2d), Ph (2b), Pyr (2c)) with MeI was accompanied by release of PPh3 and
is thought to proceed via the 14e intermediate RhI(PyrPCP). While the PPyd3 complex 2d reacted
with MeI to give [RhIII(PyrPCP)Me(I)2][MePPyd3], 4a, the PPyr3 complex 2c did not react, owing to
steric hindrance around RhI and the low nucleophilicity of PPyr3. The aptitude of complexes 2 toward
activation of H2 was also examined. Our results support the involvement of 14e intermediates in the
olefin hydrogenation process. The ancillary ligand substitution at the RhI center of 2 was found to
proceed by an associative mechanism. ML5 d8 intermediates were clearly detected by 31P{1H} NMR
at 213 K during equilibrium between 2a and 2c.
Scheme 1. PyrPCP-H and the Coordination Mode
Introduction
of PyrPCP-Based Rhodium(I) Complexes
Since the pioneering work of Moulton and Shaw1 pincer-
type ligands have attracted much scientific interest.2 Late
transition metal complexes based on pincer ligands of the PCP
type were found to be active in a variety of important catalytic
processes2a and in the activation of strong bonds.2b,c They were
also invaluable for mechanistic studies and for the stabilization
of unusual structures,2d and useful as functional materials.2e
Although PCP ligands with a variety of electron-donating
phosphine substituents have been widely explored, electron-
accepting substituents were introduced only recently.3-5
PyrPCP-H (Scheme 1) was the first reported highly electron
accepting PCP-type pincer ligand.3,4 Its synthesis was inspired
by the work of Molloy and Petersen,6 who demonstrated that
N-pyrrolyl phosphines possess exceptional electron-accepting
* Corresponding author. E-mail: david.milstein@weizmann.ac.il.
† Department of Organic Chemistry.
‡ Chemical Research Support.
(1) Moulton, C. J.; Shaw, B. L. J. Chem. Soc., Dalton Trans. 1976, 11,
1020–1024.
properties. The π-accepting ability of trispyrrolylphosphine,
PPyr3, was found to be similar to that of P(C6F5)3 and to exceed
those of phosphites such as P(OPh)3. Contrary to many
perfluoroalkyl moieties, pyrrole-like precursors are readily
available and easily amenable to structural variations.
(2) (a) van der Boom, M. E.; Milstein, D. Chem. ReV. 2003, 103, 1759–
1792. (b) Rybtchinski, B.; Milstein, D. Angew. Chem., Int. Ed. 1999, 28,
870–883. (c) Rybtchinski, B.; Milstein, D. ACS Symp. Ser. 2004, 885, 70–
85. (d) Vigalok, A.; Milstein, D. Acc. Chem. Res. 2001, 34, 798–807. (e)
Albrecht, M.; van Koten, G. Angew. Chem., Int. Ed. 2001, 40, 3750–3781.
(f) Singleton, J. T. Tetrahedron 2003, 59, 1837–1857. (g) Milstein, D. Pure
Appl. Chem. 2003, 75, 445–460. (h) Jensen, C. M. Chem. Commun. 1999,
24, 2443–2449. (i) Morales-Morales, D.; Jensen, C. M. The Chemistry of
Pincer Compounds; Elsevier: Amsterdam, 2007.
(3) Kossoy, E.; Iron, M. A.; Rybtchinski, B.; Ben-David, Y.; Shimon,
L. J. W.; Konstantinovski, L.; Martin, J.; Milstein, D. Chem.-Eur. J. 2005,
11, 2319–2326.
(4) Another electron-withdrawing pincer ligand of PCP type with
perfluorophenyl substituents was reported a short time after our report about
PyrPCP-H: Chase, P. A.; Gagliardo, M.; Lutz, M.; Spek, A. L.; van Klink,
G. P. M.; van Koten, G. Organometallics 2005, 24, 2016–2019.
(5) Adams, J. J.; Lau, A.; Arulsamy, N.; Roddick, D. M. Inorg. Chem.
2007, 46, 11328–11334.
The high electron-accepting ability of the pyrrolyl moieties
in PyrPCP and the rigidity and synergetic effects typical of pincer-
type ligands2 are combined in order to create electron-deficient
and structurally well-defined metal centers. We have reported
that PyrPCP-based rhodium(I) complexes possess significantly
different coordination chemistry from those of RhI complexes
based on electron-donating pincer-type ligands.3 Namely, the
π-accepting nature of the PyrPCP ligand disfavors formation of
(6) Moloy, K. G.; Petersen, J. L. J. Am. Chem. Soc. 1995, 117, 7696–
7710.
10.1021/om800792y CCC: $40.75
2009 American Chemical Society
Publication on Web 12/22/2008

524 Organometallics, Vol. 28, No. 2, 2009
Kossoy et al.
Scheme 2. Ancillary Ligand Exchange of Complexes
the coordinately unsaturated ML4 complexes, leading to forma-
tion of the first stable d8 ML5 PCP complexes (Scheme 1).
We present here a study of the reactivity of RhI(PyrPCP)PR3
(R ) Et, Ph, Pyr, Pyd) complexes. Understanding the effect of
the electron-accepting PyrPCP pincer ligand on the reactivity of
the rhodium(I) center is essential for the development of catalytic
applications of this type of complexes.
2b-d (room temperature, toluene)
Results and Discussion
Preparation of RhI(PyrPCP)PR3 (R ) Et, Ph, Pyr)
Complexes. PCP-based rhodium(III) compounds are easily
prepared by oxidative addition of the Ar-H bond of R,R′-
diphosphine-m-xylenes to rhodium(I) metal centers.1,7 Similarly,
the compounds RhIII(PyrPCP)H(PR3)Cl (1a, R ) Et; 1b, R )
Ph) were obtained by the reaction of equivalent amounts of
PyrPCP-H, [RhI(COE)2µCl]2, and PR3 (R ) Et, Ph) in THF at
65 °C.8 Subsequent reaction of 1a,b with KOtBu resulted in
deprotonation of the hydride ligand and formation of the
rhodium(I) complexes RhI(PyrPCP)PR3 (2a, R ) Et; 2b, R )
Ph), respectively, as previously described.3 However, RhIII-
in associative ancillary ligands exchange. In the current work
we studied exchange between monodentate phosphines coor-
dinated to the PyrPCP-based rhodium(I) center.
The phosphines PPyr3, PPh3, and PPyd3 (trispyrollidinylphos-
phine) were reported as isosteric, possessing the same cone angle
of 145°.6 Reaction of 1 equiv of PPyd3 with either RhI(PyrPCP)-
PPh3, 2b, or RhI(PyrPCP)PPyr3, 2c, at room temperature (r.t.)
(
PyrPCP)H(PPyr3)Cl, bearing the electron-accepting ancillary
resulted in phosphine exchange to form the complex RhI(Pyr
-
ligand PPyr3, could not be prepared either via oxidative addition
of the Ar-H bond of PyrPCP-H to rhodium(I) (cyclometalation)
or by direct reaction of RhI(PyrPCP)PPyr3,3 2c, with HCl. The
latter reaction resulted in decomposition of 2c. It appears that
in the PyrPCP/PPyr3/Rh system coordination of three highly
electron accepting pyrrolylic moieties to the rhodium center
retards oxidative addition of the Ar-H bond or protonation of
the rhodium(I) metal center. Complex 2c was prepared by
adding 1 equiv of PPyr3 to the PPh3 complex 2b followed by 1
equiv of MeOTf to precipitate the displaced PPh3 as its
phosphonium salt.3 Indeed, the metal center of 2c has a
significantly lower electron density than in the case of 2a,b, as
reflected by its low back-donation ability to carbon monoxide.
Thus, the CO stretch in the IR spectrum of RhI(PyrPCP)-
PPyr3(CO) appears at a significantly higher frequency (2007
cm-1) than in the case of RhI(PyrPCP)PPh3(CO) (1987 cm-1) or
RhI(PyrPCP)PEt3(CO) (1975 cm-1).3 The synthetic route toward
2c described above took advantage of its low oxidative addition
reactivity, enabling removal of the displaced PPh3 with MeOTf
without affecting the metal center.
PCP)PPyd3, 2d, accompanied by release of 1 equiv of either
PPh3 or PPyr3, respectively (Scheme 2). However, addition of
either 1 equiv of PPyr3 to 2b or 1 equiv of PPh3 to 2c resulted
in equilibrium between 2b and 2c, strongly shifted toward
formation of 2c at 295 K (Keq ) 20.2) (Scheme 2).
Orange crystals of 2c were obtained at room temperature by
slow diffusion of hexane into a concentrated THF solution.
Yellow crystals of 2d were obtained from a saturated pentane
solution. The single-crystal X-ray structures of 2b,3 2c, and 2d
reveal distorted square-planar geometries (Table 1; Figure 1).
Counterintuitively, despite the electron-withdrawing pincer
ligand, the Rh-Pancillary bond was found to be remarkably shorter
for the electron-withdrawing PPyr3, Rh-PPyr3 being 2.244 Å,
as compared with Rh-PPh3 (2.315 Å) and Rh-PPyd3 (2.320
Å) (Table 1). It should be mentioned that the single-crystal X-ray
structures of 2b3 and 2c (Figure 1, left) did not reveal any
pronounced π-π interactions between PyrPCP and either PPyr3
or PPh3, which might have affected their coordination. More-
over, the smallest sum of Cipso-Rh and Rh-Pancillary bond lengths
was found for 2c (4.351(4) Å), while the largest was for 2d
(4.433(4) Å). Therefore, it is likely that the ancillary ligand
coordination to the PyrPCP-based RhI is governed by the trans
influences between the PCParyl and the ancillary ligands, despite
the overall reduction in electron density caused by chelation of
PyrPCP.
Ancillary Ligand Exchange in Complexes 2a-d. Ligand
substitution reactions at rhodium(I) centers were reported to
follow both associative9 and dissociative10 mechanisms. In our
previous report3 we considered d8 ML5 rhodium RhI(PyrPCP)-
PR3(CO) compounds (Scheme 1) as “arrested intermediates”
However, our results indicate that coordination of PPyd3 is
thermodynamically more favorable than coordination of either
PPh3 or PPyr3, leading to complete substitution of PPh3/PPyr3
with 1 equiv of PPyd3. A possible reason for stabilization of
the PPyd3 adduct may be interaction of a C-H bond with the
rhodium center. We found that the distance between H39B and
rhodium in 2d (Figure 1, right; Table 1) is relatively short,
2.82(3) Å, compared to the hydrogen atoms closest to rhodium
in the compounds 2b (Rh-H42C, 2.94(3) Å) and 2c (Rh-H53A,
2.97(3) Å) (Table 1). Such M-H(C) bonds in square-planar d8
complexes11 are usually described as anagostic, largely elec-
(7) (a) Nemeh, S.; Jensen, C.; Binamira-Soriaga, E.; Kaska, W. C.
Organometallics 1983, 2, 1442–1447. (b) Weisman, A.; Gozin, M.; Kraatz,
H.-B.; Milstein, D. Inorg. Chem. 1996, 35, 1792. (c) Liou, S.-Y.; Gozin,
M.; Milstein, D. J. Chem. Soc., Chem. Commun. 1995, 1965. (d) van der
Boom, M. E.; Zubkov, T.; Shukla, A. D.; Rybtchinski, B.; Shimon, L. J. W.;
Rozenberg, H.; Ben-David, Y.; Milstein, D. Angew. Chem., Int. Ed. 2004,
43 (44), 5961–5963.
(8) Synthesis of 1a,b by cyclometalation required heating of the reaction
mixture to 65 °C. Therefore, preparation of RhIII Pyr
PCP)H(PPyd3)Cl was
(
not possible using this procedure because of the thermal instability of PPyd3.
Compound 2d was prepared by synthesis of RhI(PyrPCP)(norbornene) with
subsequent norbornene substitution with PPyd3.
(9) (a) Garrou, P. E.; Hartwell, G. E. Inorg. Chem. 1976, 15, 646–650.
(b) Leipoldt, J. G.; Lamprecht, G. J.; Steynberg, E. C. J. Organomet. Chem.
1990, 397, 239–244. (c) Leipoldt, J. G.; Lamprecht, G. J.; Steynberg, E. C.
J. Organomet. Chem. 1991, 402, 259–263. (d) Alonso, M. A.; Casares,
J. A.; Espinet, P.; Soulantica, K. Angew. Chem., Int. Ed. 1999, 38, 533–
535.
(11) In [RhCl(PPh3)3]: (a) Bennet, M. J.; Donaldson, P. B.; Hitchcock,
P. B.; Mason, R. Inorg. Chim. Acta 1975, 12, L9–L10. (b) Bennett, M. J.;
Donaldson, P. B. Inorg. Chem. 1977, 16, 655–660. In d8 Ni, Pd, and Pt
compounds: (c) Mukhopadhyay, A.; Pal, S. Eur. J. Inorg. Chem. 2006, 23,
4879–4887.
(10) (a) Crociani, B.; Antonaroli, S.; Di Vona, M. L.; Licoccia, S. J.
Organomet. Chem. 2001, 631, 117–124. (b) Bossio, R. E.; Hoffman, N. W.;
Cundari, T. R.; Marshall, A. G. Organometallics 2004, 23, 144–148.

Rh(I) Complexes with Pyrrolyl-PCP-Pincer Ligands
Organometallics, Vol. 28, No. 2, 2009 525
Figure 1. ORTEP diagrams of molecules of complexes 2c (left) and 2d (right) at the 50% probability level. Hydrogen atoms, except H39B,
were omitted for clarity.
Table 1. Selected Bond Lengths (Å) and Angles (deg) of 2b,3 2c, and 2d
Rh(PyrPCP)PPyd3, 2d
Rh(PyrPCP)PPh3, 2b
Rh(PyrPCP)PPyr3, 2c
Rh1-C2ipso
2.113(3)
2.212(1)
2.257(1)
2.320(1)
79.24(7)
77.05(7)
173.12(7)
155.14(3)
2.82(3)
Rh1-C1ipso
2.079(3)
2.228(1)
2.229(1)
2.315(1)
80.98(8)
77.88(7)
172.43(7)
154.12(3)
2.94(3)
Rh2-C65ipso
2.107(3)
2.266(1)
2.236(1)
2.244(1)
79.06(9)
78.16(9)
171.83(8)
157.10(3)
2.97(3)
Rh1-P4
Rh1-P2
Rh2-P4
Rh1-P5
Rh1-P3
Rh2-P5
Rh1-P3ancillary
C2-Rh1-P4
C2-Rh1-P5
C2-Rh1-P3
P4-Rh1-P5
Rh1-H39B
Rh1-P4ancillary
C1-Rh1-P2
C1-Rh1-P3
C1-Rh1-P4
P2-Rh1-P3
Rh1-H42C
Rh2-P6ancillary
C65-Rh2-P4
C65-Rh2-P5
C65-Rh2-P6
P4-Rh2-P5
Rh2-H53A
Scheme 3. Ancillary Ligand Exchange of Complexes
trostatic interactions.12 Structural characteristics of the Rh-H39B
bond in 2d meet those anagostic interactions observed for several
square-planar d8 complexes. Namely, the Rh-H distance of
2.82(3) Å and the Rh-H-C angle of 116° fall within the range
of ca. 2.3-2.9 Å and ca. 110-170°, respectively.12
2a-c (room temperature, toluene)
It is worthwhile to mention the stronger trans influence of
PPyd3 as compared to PPh3. While the Rh-PPh3 and Rh-PPyd3
bond lengths are similar, 2.315 and 2.320 Å, respectively, the
Cipso-Rh bond of 2d (2.113 Å) is longer than that of 2b (2.079
Å), as a result of coordination of the stronger electron donor,
PPyd3, trans to the ipso carbon.
Next we studied exchange with PEt3. Reaction of 1 equiv of
PEt3 (cone angle 132°13) with RhI(PyrPCP)PPh3, 2b, at room
temperature resulted in formation of RhI(PyrPCP)PEt3, 2a,
accompanied by release of 1 equiv of PPh3 (Scheme 3).
However, reaction of either 1 equiv of PEt3 with RhI(PyrPCP)-
PPyr3, 2c, or 1 equiv of PPyr3 with 2a resulted in equilibrium
between 2a and 2c, which was strongly shifted toward formation
of 2a at 295 K (Keq ) 12.2) (Scheme 3). At 295 K, the 31P{1H}
NMR spectrum showed broad signals at chemical shifts similar
to those of 2a and 2c. Upon cooling to 213 K, the 31P{1H} NMR
spectrum showed signals that could be attributed to pentaco-
ordinate compounds of the type d8 ML5, Rh(PyrPCP)(PEt3)PPyr3,
2a′,c′, with both monodentate phosphines coordinated to the
rhodium center (Scheme 3, Table 2). Relying on the 31P{1H}
NMR (213 K) spectrum of compounds 2a′ and 2c′ (Table 2)
we can conclude that 2a′ and 2c′ are two stereoisomers that
differ by the position of the monodentate phosphines: PEt3 is
bound in the apical position in 2a′ (double quartet at 8.1, 1JRhP
Table 2. Signals of 2a′ and 2c′ in 31P{1H} NMR (213 K, tol-d8)
Spectrum
P atom
chemical shift multiplicity
coupling constants
1
2a′-PyrPCP 120.3
ddd
2JPP ) 312 Hz, JRhP ) 192 Hz,
2JPP ) 44 Hz
2a′-PPyr3 98.9
m
dq
ddd
2
2a′-PEt3
8.1
1JRhP ) 93 Hz, JPP ) 42 Hz
1
2c′-PyrPCP 112.46
2JPP ) 201 Hz, JRhP ) 191 Hz,
2JPP ) 42 Hz
2c′-PPyr3 obscured by other
peaks
1
2c′-PEt3
1.4
tdd
2JPP ) 202 Hz, JRhP ) 142 Hz,
2JPP ) 44 Hz
2
) 93 Hz, JPP ) 42 Hz) and in an equatorial position in 2c′
2
1
(triple doublet of doublets at 1.4, JPP ) 202 Hz, JRhP ) 142
(12) (a) Zhang, Y.; Lewis, J. C.; Bergman, R. G.; Ellman, J. A.; Oldfield,
E. Organometallics 2006, 25, 3515–3519. (b) Brookhart, M.; Green,
M. L. H.; Parkin, G. Proc. Natl. Acad. Sci. 2007, 104, 6908–6914.
(13) Tolman, C. A. Chem. ReV. 1977, 77, 313.
2
Hz, JPP ) 44 Hz). X-ray diffraction study of the compound
RhI(PyrPCP)PEt3CO3 points out the possibility of cisoid coor-
dination of PyrPCP.

526 Organometallics, Vol. 28, No. 2, 2009
Kossoy et al.
Scheme 4. Reaction of 2a-d with MeI
Figure 2. ORTEP diagram of a molecule of complex 3a at the
50% probability level. Hydrogen atoms were omitted for clarity.
The equilibrium between 2a and 2c is a clear example of
associative ancillary ligand exchange of a square-planar d8 ML4
metal center. Associative ligand exchange is likely to be more
suitable for electron-deficient metal centers. This is due to two
facts: first, the dissociative pathway demands formation of highly
electron deficient 14e species; second, filled-filled orbital
8
2
repulsions between HOMO orbitals of a d ML4 compound (dz )
and an incoming ligand are less pronounced for electron-
deficient d8 ML4 complexes, because of overall reduction in
the energy of the metal d-orbitals.3
All three products are RhIII complexes based on 1JRhP coupling
constants. Namely, the 31P{1H} NMR spectrum of 3a revealed
1
a doublet of doublets at δ 113.8 ppm with JRhP ) 144.5 Hz
H2 Activation by 2a-d. Although no reaction was observed
when 1 equiv of hydrogen gas was added to 2a-d, activation
of H2 was evident from the ability of complexes 2a-d to
catalyze the hydrogenation of styrene to ethyl benzene. In a
typical experiment, a 1 mL toluene-d8 solution containing 0.029
mmol of the complex and 30 equiv of styrene was stirred at
room temperature under H2 (25 psi) and analyzed after 30 min,
for the purpose of comparison between complexes 2a-d. The
conversion to ethyl benzene after that period was 2b (22%), 2a
(9.4%), 2d (1.7%), and 2c (0.5%). However, some decomposi-
tion was observed in the cases of 2c,d, rendering comparison
impossible in these cases. No decomposition was observed with
2a,b under the same reaction conditions. The higher catalytic
activity of 2b for styrene hydrogenation as compared with 2a
might be due to PPh3 being more loosely bound than PEt3,
suggesting that 14e intermediates are the active species during
olefin hydrogenation14 with PyrPCP-rhodium(I).
Reaction of 2a-d with MeI. The nucleophilicity of 2 was
examined using MeI as an electrophile. Oxidative addition of
alkyl halides to transition metals is a process of much interest
since it is involved in important catalytic processes, such as
carbonylation of alkyl15 and aryl16 halides and the iodide-
promoted methanol carbonylation to acetic acid.17
Reaction of 2a with 1 equiv of MeI in THF was complete
after 3.5 h at room temperature (Scheme 4), leading to formation
of three new compounds, 3a-c. Multinuclear NMR analysis
revealed the geometries of the main products 3a (80% yield by
31P{1H} NMR) and 3b (15% NMR yield). However, we could
not establish the geometry of the very minor product (5%), 3c.
2
and JPP ) 24.1 Hz and a doublet of triplets at δ -14.4 ppm
1
with JRhP ) 74.8 Hz (3b,c showed similar signals to those of
3a in the31P{1H} NMR). PEt3 is coordinated trans to the CH3
group in 3a, as deduced from the 13C{1H} NMR spectrum,
which revealed a doublet of doublets of triplets at δ –3.32 with
2JPC, trans ) 72.7 Hz, 1JRhC ) 15.5 Hz, and 2JPC, cis ) 6.6 Hz for
Rh-CH3. In complex 3b PEt3 is bound cis to CH3, which
appeared in the 13C{1H} NMR spectrum as a doublet of quartets
1
2
at δ -4.8 with JRhC ) 15.8 Hz and JPC,
) 5.3 Hz. The
cis
geometry of 3a was also revealed by a single-crystal X-ray study
(Figure 2, Table 3). Yellow prismatic crystals of 3a were
obtained at room temperature from a concentrated MeOH
solution of a mixture of complexes 3. Complex 3a exhibits a
distorted octahedral coordination geometry, with a ligand
arrangement consistent with the multinuclear NMR data.
Reaction of 2d with 2 equiv of MeI was complete after 3.5 h
at room temperature, resulting in quantitative formation of
[Rh(PyrPCP)Me(I)2][MePPyd3], 4a (Scheme 4). When 1 equiv
of MeI was used, only half the amount of 2d was consumed to
give 4a, the other half of 2d remaining unreacted. The 31P{1H}
NMR spectrum of 4a showed a doublet at δ 113.5 ppm with
2JRhP ) 151.3 Hz for PyrPCP and a singlet at δ 43.86 for
[MePPyd3]+. The aryl ipso carbon, Cipso-Rh, appeared as a
doublet of triplets at δ 169.1 with 1JRhC ) 34.0 Hz (unresolved
triplet) in the 13C{1H} NMR. The methyl group, Rh-CH3,
appeared in the 1H NMR spectrum as a triplet of doublets at δ
3
2
0.116 with JPH ) 6.3 Hz and JRhH ) 1.92 Hz, and in the
13C{1H} NMR spectrum it gave rise to a doublet of triplets at
δ -0.233 with 1JRhC ) 22.3 Hz and 2JPC ) 4.7 Hz. Reaction of
4a with 1 equiv of PEt3 resulted in formation of 3a and 3b
(90% and 10% yield by 31P{1H} NMR, respectively) ac-
companied by precipitation of [MePPyd3]I (Scheme 4). The
prevaling formation of 3a indicates a stronger trans influence
of the methyl ligand compared to the aryl ligand. The trans
influence is reflected by the weaker binding of the iodide trans
(14) Daniel, C.; Koga, N.; Han, J.; Fu, X. Y.; Morokuma, K. J. Am.
Chem. Soc. 1988, 110, 3773–87, and references therein.
(15) Ellis, P. R.; Pearson, J. M.; Haynes, A.; Adams, H.; Bailey, N. A.;
Maitlis, P. M. Organometallics 1994, 13, 3215–26.
(16) Mizuno, T.; Alper, H. J. Mol. Catal. A: Chem. 1997, 123, 21–24.
(17) Maitlis, P. M.; Haynes, A.; Sunley, G. J.; Howard, M. J. J. Chem.
Soc., Dalton Trans. 1996, 2187–2196.

Rh(I) Complexes with Pyrrolyl-PCP-Pincer Ligands
Organometallics, Vol. 28, No. 2, 2009 527
Rh(PyrPCP)CO, 2e
Table 3. Selected Bond Lengths (Å) and Angles (deg) of 3a, 4b, and 2e
Rh(PyrPCP)Me(I)PEt3, 3a
[Rh(PyrPCP)Me(I)2]NBu4, 4b
Rh1-C2ipso
2.068(5)
2.274(2)
2.280(2)
2.156(5)
2.791(1)
2.434(2)
86.4(2)
95.3(2)
169.7(2)
93.7(1)
Rh1-C2ipso
2.048(6)
2.268(2)
2.287(2)
2.115(5)
2.784(1)
2.815(1)
91.4(3)
Rh1-C1ipso
Rh1-P1
2.094(2)
2.249 (1)
2.270(1)
1.884(3)
1.147(3)
78.10(8)
78.70(7)
156.75(3)
174.3(1)
175.8(2)
Rh1-P3
Rh1-P3
Rh1-P4
Rh1-P4
Rh1-P2
Rh1-C33
Rh1-C34
Rh1-I32
Rh1-C25
C25-O1
C1-Rh1-P1
C1-Rh1-P2
P1-Rh1-P2
C1-Rh1-C25
Rh1-C25-O1
Rh1-I32
Rh1-P34ancil.
C2-Rh1-C33
C2-Rh1-P34
C2-Rh1-I32
P34-Rh1-I32
Rh1-I33
C2-Rh1-C34
C2-Rh1-I33
C2-Rh1-I32
88.7(2)
179.8(2)
Scheme 5. Effect of Iodide on the Reaction of 2b,c with MeI
to the methyl group in 4b (Figure 3 and Table 3 describe the
single-crystal X-ray study of 4b (Vide infra)). Addition of an
excess of PEt3 did not result in further reaction.
Addition of 1 equiv of MeI to RhI(PyrPCP)PPh3, 2b, resulted
in immediate formation of an inseparable complex product
mixture. However, based on the 31P{1H} NMR spectrum
1
(doublets at 114-116 ppm, JRhP ) 148-150 Hz) one can
conclude that oxidative addition of MeI to rhodium(I) took place,
accompanied by dissociation of PPh3.
accompanied by release of PPyr3 (Scheme 5).18 Colorless
prismatic crystals of 4b were obtained from a 1:1 THF/pentane
solution. The single-crystal X-ray structure of 4b revealed a
distorted octahedral geometry with cis arrangement of the iodide
ligands (Figure 3). As mentioned above, the stronger trans
influence of the methyl ligand as compared with the aryl ligand
results in weaker binding of the iodide trans to the methyl group,
than to the aryl, as reflected in the bond lengths: 2.815 and 2.784
Å, respectively.
Remarkably, no reaction was obserVed during more than 24 h
after addition of MeI to RhI(PyrPCP)PPyr3, 2c.
It seems that the reaction of 2 with MeI strongly depends on
the sterics and nucleophilicity of the ancillary ligand bound to
PyrPCP-RhI. The remarkable stability of 2c toward oxidative
addition of MeI can arise from low nucleophilicity of the metal
center as well as from the steric hindrance caused by the
relatively bulky PPyr3. Unlike PPyd3, dissociation of PPyr3 from
the rhodium center cannot be promoted by formation of its
phosphonium iodide salt, since PPyr3 is not nucleophilic enough
to react with MeI. This quaternization reaction drives the
dissociation equilibrium of PPyd3 to the right and also generates
the iodide anion, which might also affect the oxidative addition
reaction.
In order to examine the impact of steric hindrance on the
lack of reactivity of 2c with MeI, we explored the reaction of
RhI(PyrPCP)CO, 2e, with MeI. Unlike 2c, complex 2e has a
strongly π-accepting, but sterically undemanding ancillary ligand
(CO).
The synthesis of 2e is summarized in the Scheme 6. The
cationic rhodium(I) precursor [Rh(COE)2(THF)n](OTf)19 was
prepared in situ by adding 2 equiv of AgOTf to [RhI(COE)2µCl]2
in THF at room temperature. Then 2 equiv of PyrPCP-H and an
excess of norbornene were added, and the reaction mixture was
heated in THF at 70 °C for 40 min. Subsequent addition of
KOtBu resulted in formation of the rhodium(I) complex RhI-
In order to explore the iodide effect on the oxidative addition
of MeI, complex 2c was reacted with 1 equiv of MeI in the
presence of 1 equiv of the iodide salt [NBu4]I. Interestingly, as
opposed to the lack of reaction in the absence of iodide, the
reaction was complete after 2.5 h, leading to formation of 4b
(
PyrPCP)(nor) (nor ) norbornene), which was stable only in the
presence of excess norbornene, making impossible its purifica-
tion and full characterization. The 31P{1H} NMR spectrum of
RhI(PyrPCP)(nor) revealed a doublet at 132 ppm with JRhP
)
1
201 Hz, which is characteristic of PyrPCP-RhI complexes. The
methylene protons of the PyrPCP appeared in the H NMR
1
2
spectrum at 4.29 ppm as a virtual triplet with JPH ) 3.6 Hz,
indicating the C2V symmetry of the complex. Bubbling of CO
through the crude solution of RhI(PyrPCP)(nor) resulted in
formation of 2e. The 31P{1H} NMR spectrum of 2e exhibited a
doublet at 119.8 ppm (1JRhP ) 194.4 Hz). The methylene protons
of the PyrPCP gave rise to a virtual triplet at 4.49 ppm with 2JPH
) 4.7 Hz in 1H NMR, thus indicating the C2V symmetry of the
complex. The ipso carbon, Cipso-Rh, appeared as a doublet of
(18) 31P{1H} NMR (THF) showed a significant broadening of the
spectrum of 2c in the presence of [NBu4]I: full width at half-height (fwhh)
was equal to 25 Hz in the presence of 1 equiv of [NBu4]I and 7 Hz for
pure 2c. No compound, other than 2c, was observed at low temperature
(down to 213 K). The same shapes of signals were observed at a certain
temperature, whether reached by cooling or heating.
(19) (a) Osborn, J. A.; Schrock, R. R. J. Am. Chem. Soc. 1971, 93, 3089–
3091. (b) Gandelman, M.; Konstantinovski, L.; Rozenberg, H.; Milstein,
D. Chem.-Eur. J. 2003, 9, 2595–2602.
Figure 3. ORTEP diagram of a molecule of complex 4b at the
50% probability level. Hydrogen atoms and counteranion [NBu4]-
were omitted for clarity.

528 Organometallics, Vol. 28, No. 2, 2009
Kossoy et al.
Scheme 6. Synthesis of Complexes 2e,f
triplets at 172.16 ppm (1JRhC ) 28.2 Hz, 2JPC ) 9.25 Hz) in the
13C{1H} NMR spectrum. The carbonyl group gave rise to a
doublet of triplets at 196.62 ppm (1JRhC ) 55.3 Hz, 2JPC ) 14.2
Hz) in the 13C{1H} NMR spectrum and exhibited a strong IR
absorption band at 1969 cm-1. Yellow crystals of 2e were
obtained by slow diffusion of pentane into a concentrated THF
solution of 2e. The single-crystal X-ray structure of 2e exhibits
a distorted square-planar geometry (Figure 4, Table 3), in
agreement with the multinuclear NMR spectra.
The reaction of 2e with MeI, in contrast to the remarkable
stability of 2c toward MeI, highlights the impact of steric
hindrance on reactivity of the metal center. It is important to
mention that MeI attack is likely to proceed on the rhodium
center of 2e, rather than directly on the ipso carbon of the aryl
ring; otherwise 2c would be expected to react in a similar way
to 2e, since the ipso carbon is not strongly affected by sterics
of an ancillary ligand, as can be seen from the single-crystal
X-ray studies of the compounds 2b-e. Consequently, addition
of MeI to 2e probably proceeds by an SN2 mechanism.20 Thus,
nucleophilic attack of rhodium on the methyl group results in
formation of an electron-deficient cationic rhodium(III) species,
[RhIII(PyrPCP)CO(Me)]+, which undergoes C-C reductive elimi-
nation to give 5. Square-planar d8 rhodium complexes usually
react easily with methyl iodide to afford octahedral d6 com-
pounds.21 However, the electron density around the metal center
plays a key role in the addition of MeI. For example, as
published by our group, RhI(PiPr3)2-η2-OTf showed remarkable
stability toward MeI addition, unlike RhI(PEt3)3Cl.22 Although
coordination of the electron-accepting PyrPCP and PPyr3 to
rhodium(I) resulted in reduction of the electron density on the
metal center, it is more likely that the stability of 2c toward
oxidative addition of MeI in the absence of added iodide, I-, is
due to steric hindrance at the metal center and low nucleophi-
licity of PPyr3 (Vide infra).
Reaction of 2e with MeI resulted in C-C bond formation
with the ipso carbon to give η2-(PyrPCP-Me)RhICO(I), 5 (Scheme
7). The reaction was complete after 2 weeks at ambient
temperature (38% and 78% spectral conversions were observed
after 3 and 7 days, respectively). The 31P{1H} NMR spectrum
of 5 exhibited a doublet at 102.4 ppm (1JRhP ) 154.6 Hz). The
methylene groups of the PyrPCP ligand appeared at 4.84 ppm
1
as a broad singlet in the H NMR spectrum and as a virtual
triplet at 38.89 ppm (1JPC ) 16.7 Hz) in the 13C{1H} NMR
spectrum. The carbonyl group gave rise to a doublet of triplets
2
at 181.5 ppm (1JRhC ) 76 Hz, JPC ) 14 Hz) in the 13C{1H}
NMR spectrum, and in the IR spectrum it gave rise to a strong
absorption band at 2008 cm-1. The 31P{1H} NMR spectrum of
the phosphines and the 13C{1H} NMR spectrum of the meth-
ylene and the carbonyl groups revealed the trans coordination
of the phosphines. No signal was detected for the aryl carbon
bound to the rhodium center. The methyl group gave rise to a
Although reaction of 2e with MeI resulted in the demetalated
rhodium(I) product 5, and no RhIII(PyrPCP)Me(I)CO was de-
tected, this fact does not exclude the possibility of existence of
RhIII(PyrPCP)Me(I)CO. Indeed, reaction of 4 with CO in THF
resulted in formation of RhIII(PyrPCP)Me(I)CO, 6a and 6b (1:
1), accompanied by dissociation of the corresponding iodide
salt, as either [NBu4]I or [MePPyd3]I (Scheme 7). In the
presence of an equivalent amount of [NBu4]I or [MePPyd3]I,
CO binds reversibly to the rhodium center of 6a,b and can be
easily removed by bubbling N2 through the reaction mixture.
The 31P{1H} NMR spectrum of 6a,b showed doublets at δ 120.5
(1JRhP ) 133.6 Hz) and 111.8 (1JRhP ) 135.4 Hz). The methyl
groups, Rh-CH3, appeared in the 1H NMR spectrum as triplets
1
singlet at 1.42 ppm in the H NMR spectrum and a singlet at
14.61 ppm in the 13C{1H} NMR spectrum, as confirmed by
C-H correlation. The methylated PyrPCP pincer ligand (PyrPCP-
Me) was released from the metal center by its substitution with
PiPr3 and was purified and characterized separately (Scheme
7).
2
of doublets at δ 0.303 (3JPH ) 8.16 Hz, JRhH ) 1.81 Hz) and
2
0.014 (3JPH ) 6.04 Hz, JRhH ) 2.1 Hz) and in the 13C{1H}
NMR spectrum as doublets of triplets at δ -2.78 (1JRhC ) 15.5
2
Hz, JPC ) 5.9 Hz) and -6.9 (1JRhC ) 20.47 Hz, unresolved
(20) Chauby, V.; Daran, J.-C.; Serra-Le Berre, C.; Malbosc, F.; Kalck,
P.; Gonzales, O. D.; Haslam, C. E.; Haynes, A. Inorg. Chem. 2002, 41,
3280–3290.
(21) (a) Sharp, P. R. In ComprehensiVe Organometallic Chemistry II;
Abel, E. W., Stone, F. G. A., Wilkinson, G., Atwood, J. D., Eds.; Pergamon,
1995; Vol.8, pp 190-200. (b) Aullon, G.; Alvarez, S. Inorg. Chem. 1996,
35, 3137–44.
(22) Goikhman, R.; Milstein, D. Angew. Chem., Int. Ed. 2001, 40, 1119–
1122.
Figure 4. ORTEP diagram of a molecule of complex 2e at the
50% probability level. Hydrogen atoms were omitted for clarity.

Rh(I) Complexes with Pyrrolyl-PCP-Pincer Ligands
Organometallics, Vol. 28, No. 2, 2009 529
Scheme 7. Reaction of 2e with MeI
2b, with MeI is fast. Although we did not succeed in separating
the products, it is important to note that only 1 equiv of MeI
was required to complete the reaction, which was accompanied
by dissociation of PPh3. These observations suggest involvement
of 14e RhI(PyrPCP) species in the reaction of 2b with MeI. MeI
addition to the highly electron deficient 14e species may proceed
either by a three-centered mechanism24 or by addition of iodide
prior to methyl addition.25 Dissociation of PPh3 results in
liberation of RhI(PyrPCP) 14e species, which is likely to be more
reactive toward MeI than PPh3. Therefore, the amount of the
phosphonium salt [MePPh3]I, which can play the role of the
iodide donor, like [MePPyd3]I, is insufficient. Indeed, upon
addition of 1 equiv of [NBu4]I the reaction of 2b with 1 equiv
of MeI was complete after 15 min, leading to quantitative
formation of 4b (Figure 3, Table 3) accompanied by release of
PPh3 (Scheme 5).26 Addition of 1 equiv of TlPF6 to 4b in the
presence of 1 equiv of PPh3 resulted in formation of the same
complex mixture as during reaction of 2b with 1 equiv of MeI.
Acceleration of oxidative addition reactions by halide ions
has been reported.27 For example, the catalytic action of Pd0L2
complexes in cross-coupling of aryl halides with nucleophiles
and in the Heck reaction was found to depend on the concentra-
tion of an additive anion, e.g., Cl-, thus indicating involvement
of a trivalent anionic complex, [Pd0L2Cl]-, in the catalytic cycle,
which makes the latter more efficient.28 [NBu4]I can affect either
the transition or ground state of the reaction of 2b,c with MeI.
Concerning its effect on the ground state, the much faster
reaction of 2b, compared to 2c, points at [RhI(PyrPCP)I]NBu4
as a reactive specie, since the Rh-PPh3 bond is weaker than
Rh-PPyr3. Indeed, [RhI(PyrPCP)I]NBu4 immediately reacted
with MeI to give 4b.
triplet). The carbonyl groups appeared at δ 189.5 and 180.9
ppm, and the aryl ipso carbons, Cipso-Rh, appeared at 166.1 and
161.0 ppm in the 13C{1H} NMR spectrum.
Interestingly, formation of 6a,b was also observed during
reaction of 2e with MeI in the presence of 1 equiv of [NBu4]I.
It was complete after 9 h, leading to the formation of 4b, 6a,
and 6b (9:1:1, respectively). The reaction was also examined
at earlier stages, e.g., 4 h after adding MeI, and 31P{1H} NMR
showed that ca. 70% of 2e had reacted to give 4b:6a:6b ≈ 4:1:
1. Obviously, 4b was formed after CO dissociation from 6a,b
in the presence of [NBu4]I. No interaction was observed between
2e and [NBu4]I at room temperature by 31P{1H} NMR, and
[RhI(PyrPCP)I][NBu4], 2f, was not observed after 3 days of
stirring at room temperature. To confirm this, complex 2f was
prepared separately by reaction of RhI(PyrPCP)(nor) with [NBu4]I
(Scheme 6). 31P{1H} NMR of 2f exhibited a doublet at 108.2
ppm (1JRhP ) 221.27 Hz). The methylene protons of the PyrPCP
appeared at 3.96 ppm as a virtual triplet with 2JPH ) 4.2 Hz in
the1H NMR spectrum, thus indicating the C2V symmetry of the
complex. The ipso carbon, Cipso-Rh, appeared as a doublet of
Conclusions
The reactivity of rhodium(I) complexes based on the recently
reported strongly electron accepting PCP-pincer ligand dipyr-
rolylphoshinoxylene (PyrPCP) was investigated. Complexes of
the type RhI(PyrPCP)PR3 (R ) Et, Ph, Pyr, PPyd) (2) were
synthesized.
The ancillary ligand coordination is governed by trans effect,
rather than by the overall reduction in electron density at the
rhodium center caused by PyrPCP chelation.
2
triplets at 173.49 ppm (1JRhC ) 41.1 Hz, JPC ) 8.6 Hz) in the
13C{1H} NMR spectrum.
The ancillary ligand substitution process at the PyrPCP-based
rhodium(I) center proceeds via an associative mechanism. An
associative, contrary to dissociative, ligand exchange mechanism
is likely to be more suitable for electron-deficient metal centers
due to avoiding formation of electron-deficient 14e species and
due to overall stabilization of the metal d-orbitals,3 which leads
In the presence of [NBu4]I C-C reductive elimination is
prevented during the reaction of 2e with MeI. This indicates
that C-C reductive elimination probably proceeds by a dis-
sociative mechanism, involving prior iodide dissociation to form
the coordinatively unsaturated 16e cationic [RhIII(PyrPCP)Me-
(CO)]+ species. The requirement for ligand dissociation prior
to C-H and C-C reductive elimination of octahedral rhod-
ium(III) complexes was reported.23
(24) Venter, J. A.; Leipoldt, J. G.; van Eldik, R. Inorg. Chem. 1991,
30, 2207–2209.
(25) (a) Louw, W. J.; de Waal, D. J. A.; Chapman, J. E. Chem. Commun.
1977, 845–846. (b) Ashworth, T. V.; Singleton, J. E.; de Waal, D. J. A.;
Louw, W. J.; Singleton, E.; van der Stok, E. J. Chem. Soc., Dalton Trans.
1978, 340–347. (c) Crabtree, R. H.; Quirk, J. M.; Fillebeen-Khan, T.; Morris,
G. E. J. Organomet. Chem. 1979, 181, 203–212. (d) Crabtree, R. H.; Quirk,
J. M. J. Organomet. Chem. 1980, 199, 99–106.
Since PPyd3 and PPyr3 are isosteric, the rhodium center of
2d, similarly to that of 2c, seems to be too stericly hindered for
a direct attack on MeI. The reaction proceeds via formation of
[MePPyd3]I (Scheme 4). Once formed, [MePPyd3]I may be
involved in the addition of MeI to the rhodium center. Indeed,
in the presence of 1 equiv of [NBu4]I the reaction proceeded
faster and was completed after 2 h. Nevertheless, almost 2 equiv
of MeI were required to complete the reaction.
(26) 31P{1H} NMR (THF) showed a slight broadening of the spectrum
of 2b in the presence of [NBu4]I: fwhh was equal to 8 Hz in the presence
of 1 equiv of [NBu4]I and 4.3 Hz for a pure 2b. No compound, other than
2b, was observed at low temperature (down to 213 K). The same shapes of
signals were observed at a certain temperature, whether reached by cooling
or heating.
As concluded from the results described in the previous
sections, the Rh-PPh3 bond is the weakest among the examined
Rh-PR3 (R ) Et, Pyd, Ph, Pyr). The reaction of RhI(PCP)PPh3,
(27) Fairlamb, I. J. S.; Taylor, R. J. K.; Serrano, J. L.; Sanchez, G. New
J. Chem. 2006, 30, 1695–1704.
(28) (a) Amatore, C.; Jutand, A. J. Organomet. Chem. 1999, 576, 254–
278. (b) Amatore, C.; Jutand, A. Acc. Chem. Res. 2000, 33, 314–321. (c)
Kozuch, S.; Amatore, C.; Jutand, A.; Shaik, S. Organometallics 2005, 24,
2319–2330.
(23) (a) Milstein, D. J. Am. Chem. Soc. 1982, 104, 5227–5228. (b)
Milstein, D. Acc. Chem. Res. 1984, 17, 221–226.

530 Organometallics, Vol. 28, No. 2, 2009
Kossoy et al.
mL) while stirring. The reaction mixture became dark brown
immediately. The yield of RhI(PyrPCP)norbornene was 60% by
31P{1H} NMR integration. The complex was not stable to vacuum
and was stabilized only in the presence of excess norbornene,
making impossible its purification and full characterization.
to reduced filled-filled orbital repulsions between HOMO
8
2
orbitals of a d ML4 compound (dz ) and an incoming ligand.
Complexes 2 catalyze styrene hydrogenation to ethyl benzene.
Comparison between the reactivities of 2a and 2b suggests,
although does not prove, that a 14e intermediate is the active
species in this process.
1
1
31P{1H} NMR (THF-H8): 132 (d, JRhP ) 201 Hz). H NMR
(THF-H8): 7.04 (br s, Py, 8 HC-N, 8H), 6.31 (br s, Py, 8 HC-HC-
The ability of 2 to oxidatively add MeI depends on the sterics,
nucleophilicity, and binding strength of the ancillary ligand to
the rhodium center. The complexes RhI(PyrPCP)L are thought
to follow a two-step SN2 mechanism when the metal center is
not sterically hindered, e.g., L ) PEt3 (2a), CO (2e). Coordina-
tion of relatively bulky PR3 (R ) Pyd, Ph, Pyr; cone angle 145°)
to the rhodium(I) sterically hinders nucleophilic attack by d8
RhL4 on MeI.
2
N, 8H), 4.29 (vt, JPH ) 3.6 Hz, 2 Ar-H2C-P, 4H).
Synthesis of 2d from RhI(PyrPCP)norbornene. To a crude
solution of RhI(PyrPCP)norbornene (made from 50 mg of
[RhI(COE)2µCl]2) was added PPyd3 (30.5 µL, 0.133 mmol),
resulting in formation of 2d. The product was dried by vacuum,
extracted with pentane, dried, washed with a small amount of
pentane (0.5 mL), and dried again to give 81.7 mg (76%) of 2d as
a yellow solid.
Reaction of RhI(PyrPCP)PPh3, 2b, with MeI is thought to
proceed via the RhI(PyrPCP) 14-electron species, owing to the
relatively weak Rh-PPh3 bond.
31P{1H} NMR (C6D6): 122.4 (dd, 1JRhP ) 214.4 Hz, 2JPP ) 44.1
1
1
Hz, 2P), 110.6 (dt, JRhP ) 147.4 Hz, 1P). H NMR (C6D6): 7.13
(m, Pyr, HC-N, 8H), 6.95 (m, Ar), 6.26 (m, Pyr, HC-HC-N, 8H),
3.82 (vt, 2JPH ) 3 Hz, Ar-CH2-P, 4H), 2.92 (m, Pyd, H2C-N, 12H),
1.37 (m, Pyd, H3C-H2C-P, 12H). 13C{1H} NMR (C6D6): 173.6 (ddt,
2JPC, trans ) 87.4 Hz, 1JRhC ) 27.9 Hz, 2JPC,cis ) 10.2 Hz, Cipso-Rh,
The inertness of RhI(PyrPCP)PPyr3, 2c, toward oxidative
addition of MeI is due to a number of factors: steric hindrance
at the metal center, Rh-PPyr3 bond strength, and the low
nucleophilicity of PPyr3. Steric hindrance disfavors an SN2
mechanism; strong binding of PPyr3 to the rhodium center
disfavors intermediacy of a 14-electron species; low nucleo-
philicity of PPyr3 disfavors a reaction involving formation of
[MePPyr3]I, unlike the case of RhI(PyrPCP)PPyd3, 2d.
2
1C), 144.05 (vt, JPC ) 12.3 Hz, Ar, C-C-Rh, 2C), 125.51 (s, Ar,
2
CH-CH-C-C-Rh, 1C), 124.42 (vt, JPC ) 3.4 Hz, Pyr, CH-N-P,
3
8C), 122.2 (vtd, JPC ) 10.5 Hz, J ) 3.8 Hz, Ar, CH-C-C-Rh,
1
2C), 111.73 (br s, Pyr, CH-CH-N-P, 8C), 53.61 (vtt, JPC ) 16.5
2
Hz, J ) 5.2 Hz, Ar-CH2-P, 2C), 47.85 (d, JPC ) 8.85 Hz, Pyd,
CH2-N-P, 6C), 25.95 (d, 3JPC ) 6.18 Hz, Pyd, CH2-CH2-N-P, 6C).
Anal. (%) Found (Calc): C 56.08 (55.89), H 6.07 (6.12).
Synthesis of RhI(PyrPCP)CO (2e). CO was bubbled for 30 min
through a brown crude solution of RhI(PyrPCP)norbornene (made
from 100 mg of [RhI(COE)2µCl]2; as described in the procedure
for the synthesis of 2d), resulting in formation of 2e. The solvent
was removed under vacuum, and the residue was washed with
toluene (3 × 3 mL), dried under vacuum, redissolved in CH2Cl2,
and filtered. The solvent was removed under vacuum to give 92
mg (59%) of 2e as a yellow solid.
Experimental Section
General Procedures. All experiments with metal complexes and
phosphine ligands were carried out under an atmosphere of purified
nitrogen in a Vacuum Atmospheres glovebox equipped with a MO
40-2 inert gas purifier or using standard Schlenk techniques. All
solvents were reagent grade or better. All nondeuterated 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 glovebox
over 4 Å molecular sieves. Commercially available reagents were
used as received. [RhI(COE)2µCl]2,29 1a,b, and 2a-c3 were
prepared according to a literature procedure.
31P{1H} NMR (THF-d8): 119.76 (d, 1JRhP ) 194.42 Hz). 1H NMR
3
(THF-d8): 7.26 (m, Pyr, HC-N, 8H), 7.1 (d, JHH ) 7.47 Hz, Ar,
meta to Rh, 2H), 6.97 (t,3JHH ) 7.47 Hz, Ar, para to Rh, 1H), 6.28
(m, Pyr, HC-HC-N, 8H), 4.49 (vt, 2JPH ) 4.7 Hz, Ar-CH2-P, 4H).
13C{1H} NMR (THF-d8): 196.62 (dt, 1JRhC ) 55.3 Hz, 2JPC ) 14.2
1H, 13C, 31P, and 19F NMR spectra were recorded at 400, 100,
162, and 376 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 and referenced to the residual
signals of an appropriate deuterated solvent. 31P NMR chemical
shifts are reported in ppm downfield from H3PO4 and referenced
to an external 85% solution of phosphoric acid in D2O. 19F NMR
chemical shifts are reported in ppm downfield from CFCl3 and
referenced to an external solution of C6F6 (δ ) -163 ppm) in
CDCl3.
Hz, CdO, 1C), 172.16 (dt, 1JRhC ) 28.2 Hz, 2JPC ) 9.25 Hz, Cipso
-
Rh, 1C), 147.61 (vtd, 2JPC ) 14.9 Hz, 2JRhC ) 2.1 Hz, Ar, C-C-Rh,
2
2C), 128.37 (s, Ar, CH-CH-C-C-Rh, 1C), 124.76 (vt, JPC ) 4.46
3
Hz, Pyr, CH-N-P, 8C), 123.13 (vt, JPC ) 12.7 Hz, Ar, CH-C-C-
Rh, 2C), 113.40 (vt, 3JPC ) 3.23 Pyr, CH-CH-N-P, 8C), 50.0 (vtd,
2
1JPC ) 19.1 Hz, JRhC ) 4.1 Hz, Ar-CH2-P, 2C). IR (film): νCO
)
1969 cm-. Anal. (%) Found (Calc): C 53.43 (53.59), H 4.11 (4.14).
Reaction of RhI(PyrPCP)PPh3 (2b) with PPyd3. PPyd3 (neat,
6.3 µL, 0.027 mmol) was added to a toluene (0.7 mL) solution of
2b (21.9 mg, 0.027 mmol), resulting in formation of 2d ac-
companied by release of 1 equiv of free PPh3, as detected by
31P{1H} NMR.
Elemental analyses were performed by H. Kolbe, Mikroana-
lytisches Laboratorium, Muelheim, Germany.
Reaction of RhI(PyrPCP)PPyr3 (2c) with PPyd3. To a toluene
(1 mL) solution of 2c (23.5 mg, 0.031 mmol) was added PPyd3
(neat, 7.1 µL, 0.031 mmol), resulting in formation of 2d ac-
companied by release of 1 equiv of free PPyr3, as detected by
31P{1H} NMR.
Synthesis of Rh(PyrPCP)PPyd3 (2d).
Synthesis of RhI(PyrPCP)norbornene. AgOTf (14.3 mg, 0.056
mmol) in THF (1 mL) was added dropwise to [RhI(COE)2µCl]2
(20 mg, 0.028 mmol) in THF (1.5 mL). A gray precipitate appeared
immediately. The resulting mixture was left at r.t. for 10 min while
stirring, and then it was filtered through a Celite column (2 cm
long, in a Pasteur pipette). To the resulting deep yellow solution
was added dropwise the ligand PyrPCP-H (24 mg, 0.056 mmol) in
THF (0.5 mL) and norbornene (80 mg, 0.85 mmol). The mixture
was heated at 70 °C for 40 min. To the resulting brown solution
was added dropwise KOtBu (6.2 mg, 0.056 mmol) in THF (0.5
Reaction of RhI(PyrPCP)PPh3 (2b) with PEt3. PEt3 (neat, 3.4
µL, 0.025 mmol) was added to a toluene (0.7 mL) solution of 2b
(19.7 mg, 0.025 mmol), resulting in formation of 2a accompanied
by release of 1 equiv of free PPh3, as detected by 31P{1H} NMR.
Equilibrium between RhI(PyrPCP)PEt3 (2a) and RhI-
(
PyrPCP)PPyr3 (2c). Addition of either 1 equiv of PPyr3 (8.8 mg,
0.038 mmol) to 2a (25.0 mg, 0.038 mmol) or 1 equiv of PEt3 (neat,
4.5 µL, 0.033 mmol) to 2c (25.5 mg, 0.033 mmol) in toluene (1
mL) resulted in equilibrium between 2a and 2c (2a:2c ) 3.5:1).
(29) Hofmann, P.; Meier, C.; Englert, U.; Schmidt, M. U. Chem. Ber.
1992, 125, 353–365.

Rh(I) Complexes with Pyrrolyl-PCP-Pincer Ligands
Organometallics, Vol. 28, No. 2, 2009 531
31P{1H} NMR (tol-d8, 295 K): 126.9 (br s, PCP-2a, 2P), 121.4
(br dd, 1JRhP ) 197.5 Hz, 2JPP ) 45 Hz, PCP-2c, 2P), 111.3 (br d,
1JRhP ) 165.6 Hz, PPyr3-2c, 1P), 83.4 (br s, free PPyr3), 18.7 (br s,
PEt3-2a, 1P), -7.8 (s, free PEt3). 1H NMR (tol-d8, 295 K): 7.2-5.9
(Ar and Pyr of 2a, 2c and free PPyr3), 3.75 (br s, 2c, Ar-H2C-P,
4H), 3.70 (br s, 2a, Ar-H2C-P, 4H), 1.47(m, free PEt3, H2C-P, 6H),
1.08 (m, PEt3-2a, H2C-P, 6H), 0.97 (m, free PEt3, H3C-H2C-P, 9H),
0.83 (m, PEt3-2a, H3C-H2C-P, 9H). 31P{1H} NMR (tol-d8, 213 K):
of 4a occurred under reduced pressure, the product was precipitated
at -25 °C with pentane, the upper solution was decanted, and the
pale solid was dried to give 26 mg (58%) of the product.
31P{1H} NMR (THF-d8, 273 K): 113.5 (d, JRhP ) 151.3 Hz,
1
PPyr2, 2P), 43.86 (s, [MePPyd3]+, 1P). 1H NMR (THF-d8, 273 K):
7.58 (br s, Pyr, HC-N, 4H), 7.27 (br s, Pyr, HC-N, 4H), 7.10 (d,
3
3JHH ) 7.4 Hz, Ar, meta to Rh, 2H), 6.83 (t, JHH ) 7.4 Hz, Ar,
2
para to Rh, 1H), 6.08 (m, Pyr, HC-HC-N, 8H), 4.59 (dvt, JHH
)
2
1
2
16.9 Hz, 2JPH ) 5.4 Hz, Ar-CH(H)-P, 2H), 4.40 (dvt, 2JHH ) 16.9
Hz, 2JPH ) 5.3 Hz, Ar-CH(H)-P, 2H), 3.22 (m, [MePPyd3]+, P-N-
CH2, 12H), 2.02 (d, 2JPH ) 14.6 Hz, [MePPyd3]+, P-CH3, 3H), 1.87
120.3 (ddd, JPP ) 312 Hz, JRhP ) 192 Hz, JPP ) 44 Hz, PCP-
2
1
2
2a′, 2P), 112.46 (ddd, JPP ) 201 Hz, JRhP ) 191 Hz, JPP ) 42
1
Hz, PCP-2c′, 2P), 98.9 (m, PPyr3-2a′, 1P), 8.1 (dquartet, JRhP
)
93 Hz, 2JPP ) 42 Hz, PEt3-2a′, 1P), 1.4 (tdd, 2JPP ) 202 Hz, 1JRhP
(m, [MePPyd3]+, P-N-CH2-CH2, 12H), 0.116 (td, JPH ) 6.3 Hz,
3
2
2JRhH ) 1.92 Hz, Rh-CH3, 3H). 13C{1H} NMR (THF-d8, 273 K):
169.1 (dt, 1JRhC ) 34.0 Hz, unresolved t, Cipso-Rh, 1C), 142.66 (vt,
2JPC ) 11.9 Hz, Ar, C-C-Rh, 2C), 126.33 (s, Pyr, CH-N-P, 4C),
124.79 (s, Pyr, CH-N-P, 4C), 123.94 (s, Ar, CH-CH-C-C-Rh, 1C),
) 142 Hz, JPP ) 44 Hz, PEt3-2c′, 1P), the signal of the ancillary
PPyr3 of 2c′ is obscured by other peaks. 1H NMR (tol-d8, 213 K):
2
7.2-5.9 (Ar and Pyr of 2a′ and 2c′), 4.05 (br d, AB pattern, JHH
) 15 Hz, 2c′, Ar-H(H)C-P, 2H), 3.82 (br d, AB pattern, 2JHH ) 15
2
3
Hz, 2c′, Ar-H(H)C-P, 2H), 3.44 (br d, AB pattern, JHH ) 15.4
122.85 (vt, JPC ) 11.7 Hz, Ar, CH-C-C-Rh, 2C), 111.24 (s, CH-
CH-N-P, 4C), 110.76 (s, Pyr, CH-CH-N-P, 4C), 48.58 (vtd, JPC
2
1
Hz, 2a′, Ar-H(H)C-P, 2H), 3.34 (br d, AB pattern, JHH ) 15.4
2
3
Hz, 2c′, Ar-H(H)C-P, 2H), 1.43 (m, Et-2c′, H2C-P, 6H), 1.36 (br
s, Et-2a′, H2C-P, 6H), 0.92 (m, Et-2c′, H3C-H2C-P, 9H), 0.61 (m,
Et-2a′, H3C-H2C-P, 9H).
) 17.9 Hz, JRhC ) 3.1 Hz, Ar-CH2-P, 2C), 47.9 (d, JPC ) 4.41
Hz, [MePPyd3]+, P-N-CH2-CH2, 6C), 27.19 (d, JPC ) 7.88 Hz,
2
1
2
[MePPyd3]+, P-N-CH2, 6C), -0.233 (dt, JRhC ) 22.3 Hz, JPC
)
Equilibrium between RhI(PyrPCP)PPh3 (2b) and RhI(PyrPCP)-
PPyr3 (2c). Addition of either 1 equiv of PPyr3 (6.6 mg, 0.029
mmol) to 2b (22.8 mg, 0.029 mmol) or 1 equiv of PPh3 (7.7 mg,
0.029 mmol) to 2c (22.5 mg, 0.029 mmol) in toluene (1 mL)
resulted in equilibrium between 2b and 2c (2b:2c ) 1:4.5).
4.7 Hz, Rh-CH3, 1C). Confirmed by DEPT. Anal. (%) Found (Calc):
C 43.04 (43.16); H 4.96 (5.05).
Reaction of 4a with PEt3. PEt3 (neat, 4.6 µL, 0.034 mmol) was
added to 4a (35.5 mg, 0.034 mmol) in THF (1 mL), resulting in
formation of 3a:3b ) 10:1. The solvent was removed under vacuum
to give a brown, viscous solid. The products were recrystallized
from MeOH (0.7 mL) during overnight at room temperature. The
brown MeOH solution was decanted, and the resulting yellow
crystals were rinsed with a small amount of MeOH (0.2 mL) and
dried under vacuum, yielding the isomers (17.2 mg, 65%) as a
yellow solid.
Reaction of RhI(PyrPCP)PR3 (R ) Et (a); Ph (b); Pyr (c);
Pyd (d)) with H2. In a typical experiment a toluene-d8 solution (1
mL, final volume) of catalyst (0.029 mmol) was incubated with
styrene (0.87 mmol) under H2 (25 psi) in an 80 mL glass pressure
tube during 30 min at room temperature. No significant decrease
in H2 pressure was detected for 2a,c,d, while the pressure decreased
1
The cis to aryl coordination of the methyl group was confirmed
by NOE. Anal. (%) Found (Calc): C 47.20 (46.99); H 5.18 (5.22).
Reaction of 2e with MeI. To a solution of 2e (30 mg, 0.054
mmol) in THF (3 mL) was added MeI (neat, 3.5 µL, 0.056 mmol)
while stirring. The resulting reaction mixture was left stirring at
ambient temperature. The reaction was complete after 14 days,
resulting in formation of 5 (38% and 78% conversions were
observed by NMR after 3 and 7 days, respectively) together with
some minor products, which gave 31P{1H} NMR spectra similar to
5. No formation of 6a,b was observed at any stage of the reaction.
We were unable to isolate 5, which was characterized in solution.
to 22.5 psi for 2b. Percents of conversion were estimated by H
NMR spectroscopy, revealing reduction of styrene to ethyl benzene:
2a 9.4%, 2b 22%, 2c 0.5%, 2d 1.7%. Slight decay of 2c (5-10%)
and 2d (up to 10%) was observed by 31P{1H} NMR.
Reaction of 2a with MeI. To a solution of 2a (30.4 mg, 0.047
mmol) in toluene (1 mL) was added MeI (3 µL, 0.048 mmol),
resulting in a deep red solution. 31P{1H} NMR showed no starting
material left after incubation at RT for 1.5 h and formation of three
products (3) in the ratio (estimated by 31P{1H} NMR) 3a:3b:3c )
10:2:2.
31P{1H} NMR (toluene-d8) 3a: 113.8 (dd, 1JRhP ) 144.5 Hz, 2JPP
Upon addition of 2 equiv of PiPr3 to the reaction mixture, trans-
Rh(PiPr3)2CO(I)30 was formed accompanied by release of PyrPCP-
Me. The solvent was evaporated, and the yellow residue was washed
with a small amount of pentane to remove trans-Rh(PiPr3)2CO(I)
(yellow solution). The remaining pale residue was treated with a
small amount of Et2O and recrystallized at -25 °C to give pure
PyrPCP-Me as a pale solid, 16 mg (67%).
1
) 24.1 Hz, 2P), -14.4 (dt, JRhP ) 74.8 Hz, 1P); 3c: 116.0 (dd,
1JRhP ) 144.4 Hz, 2JPP ) 25.9 Hz, 2P), -8.0 (dt, 1JRhP ) 74.2 Hz,
1
2
1P); 3b: 121.1 (dd, JRhP ) 141.0 Hz, JPP ) 31.3 Hz, 2P), -9.6
1
1
(dt, JRhP ) 80.3 Hz, 1P). H NMR (toluene-d8) 3a: 7.3-6.8 (Ar,
meta and para to Rh, 3H; Pyr, HC-N, 8H), 6.15 (m, Pyr, HC-HC-
N, 4H), 6.13 (m, Pyr, HC-HC-N, 4H), 3.90 (dvt, ABX2, JHH
2
)
2
2
16.7 Hz, JPH ) 5.3 Hz, Ar-CH(H)-P, 2H), 3.69 (dvt, ABX2, JHH
) 16.7 Hz, 2JPH ) 3.8 Hz, Ar-CH(H)-P, 2H), 1.12 (m, H2C-P, 6H),
Spectral Data for 5. 31P{1H} NMR (THF-d8): 102.4 (d, 1JRhP
)
154.6 Hz). 1H NMR (THF-d8): 8.46 (d, 3JHH ) 7.6 Hz, Ar, meta to
0.57 (m, H3C-H2C-P, 9H), 0.07 (br q, 3JPH ) 6.4 Hz, H3C-Rh, 3H).
3
13C{1H} NMR (C6D6) 3a: 164.9 (ddt, JRhC
) 32 Hz,
1
Rh, 2H), 7.60 (t, JHH ) 7.6 Hz, Ar, para to Rh, 1H), 6.87 (br s,
2JC-PEt3 ) 5 Hz, 2JC-PPyr2 ) 4 Hz, Cipso-Rh, 1C), 141.95 (vtd, 2JPC
)
Pyr, HC-N, 8H), 6.22 (s, Pyr, HC-HC-N, 8H), 4.84 (br s, Ar-CH2-
P, 4H), 1.42 (s, Ar-CH3, 3H), 13C{1H} NMR (THF-d8): 181.5 (dt,
1JRhC ) 76 Hz, 2JPC ) 14 Hz, CO, 1C), 141.15 (s, Ar, C-CH3, 1C),
132.18 (s, Ar, C-C-CH3, 2C), 131.0 (s, Ar, CH-C-C-CH3, 2C),
125.76 (s, Ar, CH-CH-C-C-CH3, 1C), 125.08 (br s, Pyr, CH-N-P,
11.2 Hz, J ) 1.5 Hz, Ar, C-C-Rh, 2C), 124.45 (s, Pyr, CH-N-P,
3
8C), 123.7 (s, Ar, CH-CH-C-C-Rh, 1C), 123.32 (vt, JPC ) 11.0
3
Hz, Ar, CH-C-C-Rh, 2C), 112.74 (vt, JPC ) 2.46 Hz, Pyr, CH-
3
CH-N-P, 4C), 112.37 (vt, JPC ) 3.1 Hz, Pyr, CH-CH-N-P, 4C),
1
49.43 (vtd, 1JPC ) 18.8 Hz, 2JRhC ) 3.55 Hz, Ar-CH2-P, 2C), 18.24
8C), 113.27 (s, Pyr, CH-CH-N-P, 8C), 38.89 (vt, JPC ) 16.7 Hz,
1
2
Ar-CH2-P, 2C), 14.61 (s, Ar-CH3, 1C). Confirmed by DEPT and
(d, JPC ) 18.0 Hz, Et, P-CH2, 3C), 9.65 (d, JPC ) 5.6 Hz, Et,
HMQC. IR (film): νCO ) 2008 cm-.
2
1
P-CH2-CH3, 3C), -3.32 (ddt, JPC,
Hz, JPC, cis ) 6.6 Hz, Rh-CH3, 1C).
) 72.7 Hz, JRhC ) 15.5
trans
Spectral Data for PyrPCP-Me. 31P{1H} NMR (CDCl3): 66.74
2
1
3
(s). H NMR (CDCl3): 6.97 (m, Pyr, HC-N, 8H), 6.73 (t, JHH
)
Reaction of 2d with MeI. A solution of 2d (33 mg, 0.043 mmol)
in THF (1 mL) was precooled to -25 °C. Then a MeI solution
precooled to -25 °C (neat, 5.3 µL, 0.085 mmol) was added. The
reaction mixture was left stirring at ambient temperature for 3.5 h,
resulting in quantitative formation of 4a. Since slight decomposition
7.7 Hz, Ar, para to Rh, 1H), 6.523 (d, 3JHH ) 7.7 Hz, Ar, meta to
(30) Moigno, D.; Kiefer, W.; Callejas-Gaspar, B.; Gil-Rubio, J.; Werner,
H. New J. Chem. 2001, 25, 1389–1397.

532 Organometallics, Vol. 28, No. 2, 2009
Kossoy et al.
2
Rh, 2H), 6.28 (m, Pyr, HC-HC-N, 8H), 3.72 (d, JPH ) 2.47 Hz,
Ar-CH2-P, 4H), 2.25 (s, Ar-CH3, 3H). 13C{1H} NMR (CDCl3):
N-CH2-CH2, 4C),. 19.95 (s, NBu4, N-(CH2)2-CH2, 4C), 14.06 (s,
NBu4, N-(CH2)3-CH3, 4C), -0.07 (dt, 1JRhC ) 22.1 Hz, 2JPC ) 4.9
Hz, Rh-CH3, 1C). Confirmed by DEPT and HSQC. Anal. (%)
Found (Calc): C 47.29 (47.19); H 6.01 (5.99).
Reaction of 2c with MeI in the Presence of [NBu4]I. A THF
(2 mL) solution of 2c (15.6 mg, 0.021 mmol) was added to a THF
(2 mL) suspension, of [NBu4]I (7.6 mg, 0.021 mmol), resulting in
a yellow suspension. MeI (neat, 1.3 µL, 0.021 mmol) was added.
The solution became clear yellow after 2.5 h stirring at r.t. 31P{1H}
NMR showed quantitative formation of 4b accompanied by PPyr3.
The product was precipitated with pentane (6 volumes) at –25 °C
overnight. The soluble fraction was decanted, and the light brown
solid was dried to give 19 mg (89%) of 4b.
Reaction of 2e with MeI in the Presence of [NBu4]I. To a
suspension of [NBu4]I (6.6 mg, 0.018 mmol) and 2e (10 mg, 0.018
mmol) in THF (2 mL) was added MeI (neat, 1.1 µL, 0.018 mmol).
The reaction was complete during 9 h stirring at ambient temper-
ature. 31P{1H} NMR showed formation of 4b:6a:6b ) 9:1:1. The
solution was left stirring at room temperature for 2 days, resulting
in formation of 4b.
2
135.14 (t, unresolved, Ar, C-CH3, 1C), 132.2 (dd, JPC ) 10.44
4
3
Hz, JPC ) 2.36 Hz, Ar, C-C-CH3, 2C), 129.0 (dd, Ar, JPC ) 6.4
5
4
Hz, JPC ) 3.5 Hz, CH-C-C-CH3, 2C), 126.23 (t, JPC ) 2.7 Hz,
Ar, CH-CH-C-C-CH3, 1C), 123.5 (d, 2JPC ) 13.9 Hz, Pyr, CH-N-
3
P, 8C), 112.14 (d, JPC ) 4.1 Hz, Pyr, CH-CH-N-P, 8C), 37.2 (d,
1JPC ) 14.5 Hz, Ar-CH2-P, 2C), 15.99 (t, JPC ) 5.4 Hz, Ar-CH3,
4
1C). Confirmed by DEPT.
Synthesis of 6a,b. CO was bubbled through a THF-d8 (1 mL)
solution of 4a (20 mg, 0.019 mmol) for a few minutes, resulting in
formation of 6a:6b ) 1:1, accompanied by precipitation of
[MePPyd3]I. The complexes 6a,b were not isolated because of slow
decomposition to form 5.
31P{1H} NMR (THF-d8): 120.5 (d, 1JRhP ) 133.6 Hz), 111.8 (d,
1JRhP ) 135.4 Hz), 45.1 (s, I[MePPyd3]). 1H NMR (THF-d8): 7.44
(m, Pyr, HC-N, 4H), 7.40 (m, Pyr, HC-N, 4H), 7.38-7.06(Ar, meta
and para to Rh), 7.02 (m, Pyr, HC-N, 4H), 6.85 (m, Pyr, HC-N,
4H), 6.32 (br s, Pyr, HC-HC-N, 4H), 6.28 (br s, Pyr, HC-HC-N,
8H), 6.25 (br s, Pyr, HC-HC-N, 4H), 4.86 (dvt, ABX2, 2JHH ) 16.7
Synthesis of [RhI(PyrPCP)I]NBu4 (2f). To a brown crude
solution of RhI(PyrPCP)norbornene (made from 50 mg of
[RhI(COE)2µCl]2 as described in the procedure for the synthesis of
2d) was added [NBu4]I (51.5 mg, 0.139 mmol). The resulting
reaction mixture was stirred for 24 h at rt, resulting in formation
of [RhI(PyrPCP)I]NBu4. We were not able to purify the product either
on a Florisil column or by extractions. The yield was estimated as
at least 60% by 31P{1H} NMR spectrum integration.
2
2
Hz, JPH ) 5.8 Hz, Ar-CH(H)-P, 2H), 4.71 (dvt, ABX2, JHH
)
2
2
18.2 Hz, JPH ) 5.8 Hz, Ar-CH(H)-P, 2H), 4.65 (dvt, ABX2, JHH
2
) 16.8 Hz, JPH ) 5.7 Hz, Ar-CH(H)-P, 2H), 4.57 (dvt, ABX2,
2JHH ) 18.1 Hz, JPH ) 5.3 Hz, Ar-CH(H)-P, 2H), 3.36 (m, P-N-
2
CH2, PPyd3), 2.32 (d, 2JRhH ) 14.9 Hz, P-CH3, I[MePPyd3]), 1.92
(m, P-N-CH2-CH2, I[MePPyd3]), 1.59 (m, P-N-CH2-CH2, I[MeP-
Pyd3]), 0.303 (td, 3JPH ) 8.16 Hz, 2JRhH ) 1.81 Hz, H3C-Rh, 3H),
0.014 (td, 3JPH ) 6.04 Hz, 2JRhH ) 2.1 Hz, H3C-Rh, 3H). 13C{1H}
NMR (THF-d8): 189.5 (m, unresolved, Rh-CO, 1C), 180.9 (m,
31P{1H} NMR (THF-d8): 108.2 (d, 1JRhP ) 221.27 Hz). 1H NMR
1
unresolved, Rh-CO, 1C), 166.1 (dt, JRhC ) 25.0 Hz, unresolved
3
(THF-d8): 7.64 (m, Pyr, HC-N, 8H), 6.79 (d, JHH ) 7.31 Hz, Ar,
1
triplet, Cipso-Rh, 1C), 161.0 (d, JRhC ) 31.33 Hz, Cipso-Rh, 1C),
meta to Rh, 2H), 6.65 (t, 3JHH ) 7.31 Hz, Ar, para to Rh 1H), 6.05
2
2
142.78 (vt, JPC ) 11.8 Hz, Ar, C-C-Rh, 2C), 142.28 (vt, JPC
)
2
(m, Pyr, HC-HC-N 8H), 3.96 (vt, JHP ) 4.2 Hz, Ar-H2C-P, 4H),
11.0 Hz, Ar, C-C-Rh, 2C), 125.15 (m, Pyr, CH-N-P, 4C), 125.06
(m, Pyr, CH-N-P, 4C), 124.80 (m, Pyr, CH-N-P, 4C), 124.20 (m,
Pyr, CH-N-P, 4C), 114.06 (m, Pyr, CH-CH-N-P, 4C), 113.80 (m,
Pyr, CH-CH-N-P, 4C), 113.40 (m, Pyr, CH-CH-N-P, 8C), 50.1 (vtd,
3.24 (m, NBu4, H2C-N, 8H), 1.64 (m, NBu4, H2C-CH2-N, 8H), 1.37
3
(m, NBu4, CH2-CH2-CH2-N, 8H), 0.96 (t, JHH ) 7.4 Hz, NBu4,
CH3-CH2-CH2-CH2-N, 12H). 13C NMR (THF-d8): 173.49 (dt, 1JRhC
) 41.1 Hz, 2JPC ) 8.6 Hz, Cipso-Rh, 1C), 146.11 (vtd, 2JPC ) 15.2
1JPC ) 20.3 Hz, 2JRhC ) 2.8 Hz, Ar-CH2-P, 2C), 48.3 (vtd, 1JPC
)
2
2
Hz, JRhC ) 2.2 Hz, Ar, C-C-Rh, 2C), 125.68 (vt, JPC ) 3.8 Hz,
2
3
19.3 Hz, JRhC ) 3.2 Hz, Ar-CH2-P, 2C), 48.1 (d, JPC ) 4.4 Hz,
P-N-CH2-CH2, I[MePPyd3], 6C), 27.2 (d, 2JPC ) 7.8 Hz, P-N-CH2,
3
Pyr, CH-N-P, 8C), 121.83 (vt, JPC ) 12.3 Hz, Ar, CH-C-C-Rh,
2C), 121.42 (s, Ar, CH-CH-C-C-Rh, 1C), 110.53 (unresolved vt,
Pyr, CH-CH-N-P, 8C), 59.19 (s, NBu4, CH2-N, 4C), 50.79 (vtd,
I[MePPyd3], 6C), -2.78 (dt, 1JRhC ) 15.5 Hz, JPC ) 5.9 Hz, Rh-
2
CH3, 1C), -6.9 (dt, 1JRhC ) 20.47 Hz, unresolved triplet, Rh-CH3,
1C). Confirmed by DEPT.
2
1JPC ) 16.5 Hz, JRhC ) 5.4 Hz, Ar-CH2-P, 2C), 24.74 (s, NBu4,
CH2-CH2-N, 4C), 20.54 (s, NBu4, CH2-CH2-CH2-N, 4C), 14.05 (s,
NBu4, CH3-CH2-CH2-CH2-N, 4C).
Reaction of 2b with MeI at the Presence of [NBu4]I. A THF
(1 mL) solution of 2b (20 mg, 0.025 mmol) was added to a THF
(0.5 mL) suspension of [NBu4]I (9.3 mg, 0.025 mmol), resulting
in a yellow suspension. MeI (neat, 1.6 µL, 0.026 mmol) was added.
The solution became clear yellow after 15 min stirring at r.t. 31P{1H}
NMR showed quantitative formation of 4b accompanied by PPh3.
The product was precipitated with pentane (6 volumes) at –25 °C.
The soluble fraction was decanted, giving 19 mg (72%) of 4b as
pale brown crystals.
Reaction of [RhI(PyrPCP)I]NBu4 with MeI. To a crude solution
of [RhI(PyrPCP)I]NBu4 (prepared form 50 mg of [RhI(COE)2µCl]2)
was added MeI (neat, 8.7 µL, 0.139 mmol). 31P{1H} NMR (THF-
H8) showed formation of 4b after 5 min at rt (about 70% spectral
yield). The product was dried, extracted with toluene, dried, and
quickly washed with Et2O (2 × 5 mL). The remaining brown solid
was dried, giving 101 mg (69%) of 4b.
General Information for X-ray Analysis of the Structures
2c-e, 3a, and 4b. Data were collected with a Nonius KappaCCD
diffractometer at 120(2) K, Mo KR (λ ) 0.71073 Å), graphite
monochromator. The data were processed with Denzo-Scalepack.
Structures were solved by direct methods with SHELXS-97 and
refined with full matrix least-squares refinement based on F2 by
SHELXL-97.
X-ray Analysis of the Structure of RhI(PyrPCP)PPyr3 (2c).
Orange needles of 2c were obtained by slow diffusion of hexane
into a concentrated solution of 2c in THF, in a 5 mm NMR tube,
at room temperature.
1
1
31P{1H} NMR (C6D6): 115.6 (d, JPRhP ) 151.1 Hz). H NMR
(C6D6): 7.90 (br s, Pyr, HC-N, 4H), 7.51 (br s, Pyr, HC-N, 4H),
7.3 (br s, Ar, para to Rh, 1H), 7.1 (m, Ar, meta to Rh, 2H), 6.46
(m, Pyr, HC-HC-N, 4H), 6.35 (m, Pyr, HC-HC-N, 4H), 4.65 (dvt,
2JHH ) 16.8 Hz, 2JPH ) 5.4 Hz, Ar-CH(H)-P, 2H), 4.24 (dvt, 2JHH
2
) 16.8 Hz, JPH ) 5.2 Hz, Ar-CH(H)-P, 2H), 2.99 (m, NBu4,
N-CH2, 8H), 1.37 (m, NBu4, N-CH2-(CH2)2, 16H), 1.03 (t, 3JHH
)
6.9 Hz, NBu4, N-(CH2)3-CH3, 12H), 0.795 (td, 3JPH ) 6.3 Hz, 2JRhH
) 1.8 Hz, Rh-CH3, 3H). 13C{1H} NMR (C6D6): 167.9 (dt, 1JRhC
)
2
34.1 Hz, unresolved t, Cipso-Rh, 1C), 142.06 (vt, JPC ) 11.8 Hz,
2
Ar, C-C-Rh, 2C), 126.21 (vt, JPC ) 2.34 Hz, Pyr, CH-N-P, 4C),
Crystal data: 2C36H35N7P3Rh+1/2(C6H14), 0.40 × 0.05 × 0.05
124.56 (s, Pyr, CH-N-P, 4C), 124.01 (s, Ar, CH-CH-C-C-Rh, 1C),
3
3
j
mm , triclinic, P1, a ) 9.180(0) Å, b ) 17.938(4) Å, c ) 22.503(5)
122.73 (vt, JPC ) 11.6 Hz, Ar, CH-C-C-Rh, 2C), 111.44 (vt,
3
Å, R ) 79.923(3)° ꢀ ) 78.612(1)° γ ) 82.986(1)°, T ) 120(2) K,
unresolved t, Pyr, CH-CH-N-P, 4C), 110.83 (vt, JPC ) 2.69 Hz,
Pyr, CH-CH-N-P, 4C), 58.68 (s, NBu4, N-CH2, 4C), 49.11 (vtd,
V ) 3562.4(12) Å3, Z ) 2, fw ) 1566.15, Dc ) 1.460 Mg m-3, µ
1JPC ) 17.5 Hz, JRhC ) 3.5 Hz, Ar-CH2-P, 2C), 24.31 (s, NBu4,
) 0.653 mm-1
.
2

Rh(I) Complexes with Pyrrolyl-PCP-Pincer Ligands
Organometallics, Vol. 28, No. 2, 2009 533
Data collection and processing: 0 e h e 11, -22 e k e 23,
-28 e l e 29, frame scan width ) 1.0°, scan speed 1.0° per 320 s,
typical peak mosaicity 0.47°, 59 988 reflections collected, 16 144
independent reflections (Rint ) 0.049).
X-ray Analysis of the Structure of RhI(PyrPCP)Me(I)PEt3
(3a). Yellow prism crystals were obtained at room temperature from
a concentrated MeOH solution of the mixture of 3.
Crystal data: C31H41IN4P3Rh, 0.25 × 0.07 × 0.07 mm3,
orthorhombic, Pca21, a ) 16.2351(2) Å, b ) 10.6516(4) Å, c )
19.0486(2) Å, T ) 120(2)K, V ) 3294.2(1) Å3, Z ) 4, fw ) 792.4
Solution and refinement: 863 parameters with 0 restraints, final
R1 ) 0.0427 (based on F2) for data with I > 2σ(I) and, R1 ) 0.0630
on 16 137 reflections, goodness-of-fit on F2 ) 1.016, largest electron
g/mol, Dc ) 1.598 Mg m-3, µ ) 1.628 mm-1
.
density peak ) 2.488 e Å-3
.
Data collection and processing: 0 e h e 21, 0 e k e 13, 0 e
l e 24, frame scan width ) 1.0°, scan speed 1.0° per 60 s, typical
peak mosaicity 0.551°, 31 184 reflections collected, 4251 indepen-
dent reflections (Rint ) 0.093).
X-ray Analysis of the Structure of RhI(PyrPCP)PPyd3 (2d).
A saturated pentane solution of 2d was put in a 20 mL vial, twice
concentrated by evaporation under reduced pressure, and left
overnight at room temperature in a closed evaporator without
normalizing the pressure. Yellow chunks of 2d were obtained.
Crystal data: C36H47N7P3Rh, 0.18 × 0.1 × 0.09 mm3, mono-
clinic, P21/n, a ) 16.7698(2) Å, b ) 12.2296(3) Å, c ) 18.4779(3)
Å, ꢀ ) 112.219(1)°, T ) 120(2)K, V ) 3508.1(1) Å3, Z ) 4, fw
Solution and refinement: 366 parameters with one restraint,
final R1 ) 0.0322 (based on F2) for data with I > 2σ(I) and, R1 )
0.0460 on 3899 reflections, goodness-of-fit on F2 ) 1.078, largest
electron density peak ) 0.855 e Å-3
.
X-ray Analysis of the Structure of [RhI(PyrPCP)Me(I)2]-
[NBu4] (4b). Colorless prism crystals of 4b were obtained from a
THF/pentane (1:1) solution of 4b in a 5 mm NMR tube. The crystals
appeared after 3 days at room temperature.
) 773.63, Dc ) 1.465 Mg m-3, µ ) 0.661 mm-1
.
Data collection and processing: -22 e h e 20, 0 e k e 16,
0 e l e 24, frame scan width ) 1.0°, scan speed 1.0° per 70 s,
typical peak mosaicity 0.411°, 45 263 reflections collected, 8732
independent reflections (Rint ) 0.104).
Crystal data: C25H26I2N4P2Rh+C16H36N+C4H8O, 0.25 × 0.25
× 0.15 mm3, monoclinic, P21, a ) 13.2256(2) Å, b ) 15.7831(3)
Å, c ) 13.3389(2) Å, ꢀ ) 119.5274(7)°, T ) 120(2) K, V )
2422.8(1) Å3, Z ) 2, fw ) 1115.71 g/mol, Dc ) 1.529 Mg m-3, µ
Solution and refinement: 430 parameters with no restraints, final
R1 ) 0.0416 (based on F2) for data with I > 2σ(I) and, R1 ) 0.0742
on 8331 reflections, goodness-of-fit on F2 ) 0.980, largest electron
) 1.730 mm-1
.
Data collection and processing: -16 e h e 14, 0 e k e 20,
0 e l e 17, frame scan width ) 1.0°, scan speed 1.0° per 30 s,
typical peak mosaicity 0.411°, 30 712 reflections collected, 6177
independent reflections (Rint ) 0.059).
density peak ) 0.932 e Å-3
.
X-ray Analysis of the Structure of RhI(PyrPCP)CO (2e).
Yellow prism crystals of 2e were obtained by slow diffusion of
pentane into a concentrated solution of 2e in THF, in a 5 mm NMR
tube, at room temperature.
Solution and refinement: 511 parameters with one restraint,
final R1 ) 0.0317 (based on F2) for data with I > 2σ(I) and R1 )
0.0424 on 5522 reflections, goodness-of-fit on F2 ) 1.142, largest
Crystal data: C25H23N4OP2Rh, 0.5 × 0.3 × 0.2 mm3, triclinic,
electron density peak ) 2.943 e Å-3
.
j
P1, a ) 9.385(2) Å, b ) 10.736(2) Å, c ) 12.812(3) Å, R )
107.29(3)° ꢀ ) 106.06(3)° γ ) 99.08(3)°, T ) 120(2)K, V )
Acknowledgment. This work was supported by the Israel
Science Foundation, by the DIP program for German-Israeli
cooperation, and by the Helen and Martin Kimmel Center
for Molecular Design. D.M. is the Israel Matz Professor of
Organic Chemistry.
1143.2(4) Å3, Z ) 2, fw ) 560.32 g/mol, Dc ) 1.628 Mg m-3, µ
) 0.914 mm-1
.
Data collection and processing: 25 507 reflections collected, 0
e h e 12, -13 e k e 13, -16 e l e 15, frame scan width )
1.0°, scan speed 1.0° per 20 s, typical peak mosaicity 0.381°, 5602
independent reflections (Rint ) 0.061).
Supporting Information Available: CIF files containing X-ray
crystallographic data for compounds 2c, 2d, 2e, 3a, and 4b. This
materialisavailablefreeofchargeviatheInternetathttp://pubs.acs.org.
Solution and refinement: 298 parameters with 0 restraints, final
R1 ) 0.0325 (based on F2) for data with I > 2σ(I) and R1 ) 0.0396
on 5194 reflections, goodness-of-fit on F2 ) 1.095, largest electron
density peak ) 1.926 e Å-3
.
OM800792Y