Conformational preferences driven by the C-methyl substituent in chelated o-diphenylphosphino-α-methyl-N,N-dimethylbenzylamine rhodium complexes

Article abstract of DOI:10.1021/ic034117a

The stereochemistry of the chelate rings of a number of rhodium aminophosphine complexes is studied by NMR spectroscopy. The similarity in the variable-temperature behavior for the different compounds is consistent with them having in common highly preferred chelate ring conformations. The six-membered metallacycle of coordinated (R)-P*N (P*N = o-diphenylphosphino-α-methyl-N,N-dimethylbenzylamine) adopts a δ conformation in the solid state. NMR experiments indicate that this conformation is strongly favored in solution as well. The preferred sense of helicity is imposed by the absolute configuration of the stereogenic carbon atom on the ligand, which exerts an important steric control. The complex [Rh(TFB){(C₆H₄CHMeNMe₂)₂ P(C₆H₄CHMeNHMe₂)}](BF₄) ₂·H₂O·Me₂CO crystallizes in the monoclinic space group P2(1) with a = 12.0548(11) A, b = 16.139(2) A, c = 12.1804(10) A, β = 100.742(9)°, Z = 4.

Full text of DOI:10.1021/ic034117a

Inorg. Chem. 2003, 42, 3856−3864
Conformational Preferences Driven by the C-Methyl Substituent in
Chelated o-Diphenylphosphino-r-methyl-N,N-dimethylbenzylamine
Rhodium Complexes
M. Ara´nzazu Alonso, Juan A. Casares, Pablo Espinet,* and Katerina Soulantica
Qu´ımica Inorga´nica, Facultad de Ciencias, UniVersidad de Valladolid, E-47005 Valladolid, Spain
A. Guy Orpen and Hirihattaya Phetmung
School of Chemistry, UniVersity of Bristol, Bristol BS8 1TS, U.K.
Received February 3, 2003
The stereochemistry of the chelate rings of a number of rhodium aminophosphine complexes is studied by NMR
spectroscopy. The similarity in the variable-temperature behavior for the different compounds is consistent with
them having in common highly preferred chelate ring conformations. The six-membered metallacycle of coordinated
(R)-P*N (P*N ) o-diphenylphosphino-R-methyl-N,N-dimethylbenzylamine) adopts a δ conformation in the solid
state. NMR experiments indicate that this conformation is strongly favored in solution as well. The preferred sense
of helicity is imposed by the absolute configuration of the stereogenic carbon atom on the ligand, which exerts an
important steric control. The complex [Rh(TFB){(C H CHMeNMe2)2P(C H CHMeNHMe2)}](BF ) ‚H O‚Me2CO
6
4
6
4
4 2
2
crystallizes in the monoclinic space group P2(1) with a ) 12.0548(11) Å, b ) 16.139(2) Å, c ) 12.1804(10) Å,
â ) 100.742(9)°, Z ) 4.
Introduction
uents in the ring modifies their energy and can eventually
lead to conformational locking by favoring one particular
conformer with respect to the others, or by slowing the
interchange between them.
NMR spectroscopy is the technique of choice for studying
conformation interconversions in solution. The methodology
for the analysis of asymmetric induction is well established
and has been applied to different P,N-donor ligands used in
catalysis.4
Chiral multidentate ligands combining phosphorus and
nitrogen donor atoms are of interest for enantioselective
homogeneous catalysis due to their efficiency in reactions
such as allylic alkylation, allylic amination, hydroboration,
hydrosilylation, or Grignard cross-coupling.1
The steric effect of the ligands is a crucial factor for effec-
tive chirality induction in stereoselective reactions at the
metal center. An essential component of asymmetric induc-
tion for many enantioselective catalytic systems is the confor-
mation of the chiral ligand framework. Conformational rig-
idity is a frequent feature of highly enantioselective catalysts.1b
The conformational behavior of chelates with more than
five atoms in the ring is open to the coexistence of several
conformers of similar energy.2,3 The introduction of substit-
We are interested in the structural properties of the P,N-
multidentate ligands and have reported on the coordination
(2) Harrowfield, J. M.; Wild, S. B. In ComprehensiVe Coordination
Chemistry; Wilkinson, S. G., Gillard, R. D., McCleverty, J. A., Eds.;
Pergamon Press: Oxford, 1987; Vol. 1, Chapter 5, p 179.
(3) (a) Clifford, J. H.; Palmer, J. A. Coord. Chem. ReV. 1982, 44, 1. (b)
Brubaker, G. R.; Johnson, D. W. Coord. Chem. ReV. 1984, 53, 1.
(4) (a) Berger, H.; Nesper, R.; Pregosin, P. S.; Ru¨egger, H.; Wo¨rle, M.
Inorg. Chim. Acta 1994, 76, 1520. (b) Pregosin, P. S.; Salzmann, R.;
Togni, A. Organometallics 1995, 14, 842. (c) Carmona, D.; Lahoz,
F. J.; Oro, L. A.; Lamata, M. P.; Viguri, F.; San Jose´, E. Organome-
tallics 1996, 15, 2961 (d). Albinati, A.; Eckert, J.; Pregosin, P. S.;
Ruegger, H.; Salzmann, R.; Stoessel, C. Organometallics 1997, 16,
579. (e). Feiken, N.; Pregosin, P.; Trabesinger, G. Organometallics
1998, 17, 4510. (f) Crociani, B.; Antonaroli, S.; Di Vona, M. L.;
Licoccia, S. J. Organomet. Chem. 2001, 631, 117. (g) Manzano, B.
R.; Jalo´n, F. A.; Go´mez-de la Torre, F.; Lo´pez-Agenjo, A. M.;
Rodr´ıguez, A. M.; Mereiter, K.; Weissensteiner, W.; Sturm, T.
Organometallics 2002, 21, 789-802.
* Author to whom correspondence should be addressed. E-mail:
espinet@qi.uva.es.
(1) (a) Sawamura, M.; Ito, Y. Chem. ReV. 1992, 92, 857. (b) Ojima, I.
Catalytic Asymmetric Synthesis; VCH: New York, 1993. (c) Salva-
kumer, K.; Valentini, M.; Pregosin, P. S. Organometallics 2000, 19,
1299. (d) Brunner, H.; Deml, I.; Dirnberger, W.; Ittner, k. P.; Reisser,
W.; Zimmernam, M. Eur. J. Inorg. Chem. 1999, 51. (e) Blo¨chl, P. E.;
Togni, A. Organometallics 1996, 15, 4125. (f) Abbenhuis, H. C. L.;
Burckhardt, U.; Gramlich, V.; Martelletti, A.; Spencer, J.; Steiner, I.;
Togni, A. Organometallics 1996, 15, 1614. (g) Togni, A. Angew.
Chem., Int. Ed. Engl. 1996, 35, 1475.
3856 Inorganic Chemistry, Vol. 42, No. 12, 2003
10.1021/ic034117a CCC: $25.00 © 2003 American Chemical Society
Published on Web 05/15/2003

Rhodium Aminophosphine Complexes
Scheme 1
Chart 1
Scheme 2
In all of the new complexes 1-7 the shift of the NMe2
signals and 31P resonances with respect to the free ligands
support a bidentate P,N-chelate coordination.7 The values
of 1J(Rh-P) are typical for square planar species of Rh(I).8
As already reported by Roundhill et al. and by van Koten et
al., the chelate ring puckering of the two N-methyl groups
in this type of complex makes the benzylic protons and the
PAr2 groups diastereotopic (Chart 1).6,9 In this low symmetry
and fluxional behavior of P(CH2CH2Py)nPh3-n (Py )
2-pyridyl) Pd and Rh complexes and complexes with
other pyridylphosphine ligands.5 In this paper, we explore
two families of other P,N-multidentate ligands, namely,
P(C6H4CH2NMe2)nPh3-n (PNn) and the enantiomerically pure
P(C6H4CHMeNMe2)nPh3-n (P*Nn). In principle, any non-
planar P,N-chelate ring can adopt a chiral conformation and
thereby endow chirality on the complex as a whole. Apart
from a chiral conformation, some of these ligands contain
stereogenic centers, either at phosphorus or at the R-carbon
atom of the ligand framework. This work is focused on the
study of analogies and differences between PNn and P*Nn
complexes. The relationship between substituents, confor-
mational preferences, and dynamic behavior is discussed, and
the activation barriers for the different dynamic processes
(exchange of amino groups, conformational inversion, olefin
rotation) are analyzed.
1
all of the diolefin protons are nonequivalent, and the H
spectrum at low temperature displays 12 signals for the COD
protons and six signals for the TFB protons. In solution, the
cationic products are fluxional. Their behavior in solution
1
was studied by H NMR at different temperatures and also
1
by 2D phase sensitive H NMR NOESY experiments.
Characterization and Dynamic Behavior of the New
Derivatives (1-7). (a) Rhodium-PN1-Diolefin and Rho-
1
dium-P*N1-Diolefin Complexes. The signals in the H
NMR spectrum of the complexes with PNn ligand (1 and
2), including the olefinic hydrogens (trans to N or trans to
P), have been fully assigned. The olefinic protons that usually
are assigned by their chemical shifts10 have been unambigu-
ously assigned by the NOE effect observed between N-Me
signals and the olefinic signals at lowest field (4.5-6.5 ppm
depending on the complex, see Experimental Section).
The VT-1H NMR analysis of [Rh(TFB)(PN1)]BF4 (1) and
[Rh(COD)(PN1)]BF4 (2) shows the coalescence of the
nonequivalent methyl group signals. The ∆Gq value has been
calculated at the coalescence temperature (1, ∆Gq ) 41.52
( 0.2 kJ mol-1, Tc ) 210.6 K; and 2, ∆Gq, 51.64 ( 0.2 kJ
mol-1, Tc ) 253 K).11 The fluxional process producing this
coalescence is clearly based on the flexibility of the boat
conformation formed by the chelating aminophosphine. This
phenomenon is well-known and has been studied for [RhCl-
(CO)(PN1)], [Pd(Me)(OR)(PN1)], and more recently [Pt{(o-
Me2Si)2C6H4}(PN1)].6,9,12
Results
Synthesis of the Ligands. The new ligands P(C6H4CH2-
NMe2)2Ph (PN2) and P(C6H4CHMeNMe2)3 (P*N3) were
prepared according to Scheme 1, following the general
procedure developed by Roundhill et al.6
Solution Structures and NMR Spectroscopy for the
Diene Complexes. The Rh(diolefin) complexes were pre-
pared from the corresponding [(µ-Cl)2Rh2(L-L)2] species
(L-L ) TFB (tetrafluorobenzobicyclo[2.2.2.]octatriene, tet-
rafluorobenzobarralene) or COD (1,5-cyclooctadiene)) using
the aminophosphines P(C6H4CH2NMe2)nPh3-n (PNn) and
P(C6H4CHMeNMe2)nPh3-n (P*Nn), as shown in Scheme 2.
All of the compounds were characterized by elemental
For the (R)-P*N complex [Rh(TFB)(P*N)]BF4 (3), two
conformers are observed at low temperature. At 203 K the
31P{1H} NMR spectrum displays two signals in the propor-
1
analysis, IR, and NMR (1H, 31P). Standard COSY H-1H
and NOESY 1H-1H experiments were used to help with the
assignments.
(7) Garrou, P. E. Chem. ReV. 1981, 81, 229.
(8) Pregosin, P. S. Phosphorus-31 NMR Spectroscopy in Stereochemical
Analysis; Verkade, J.-G., Quin, L. D., Eds.; VCH: Deerfield Beach,
FL. 1987; Vol. 8, p 465 and references therein.
(9) Kapteijn, G. M.; Spee, M. P. R.; Grove, D. M.; Kooijman, H.; Spek,
A. L.; van Koten, G. Organometallics 1996, 15, 1405.
(10) (a) Yang, H.; Lugan, N.; Mathieu, R. Organometallics 1997, 16, 2089.
(b) Denise, B.; Pannetier, G. J. Organomet. Chem. 1978, 148, 155.
(11) Sandstro¨m J. Dynamic NMR Spectroscopy; Academic Press: London,
1982.
(5) (a) Casares, J. A.; Espinet, P.; Soulantica, K.; Pascual, I.; Orpen, A.
G. Inorg. Chem. 1997, 36, 5251. (b) Alonso, M. A.; Casares, J. A.;
Espinet, P.; Soulantica, K. Charmant, J. P. H.; Orpen, A. G. Inorg.
Chem. 2000, 39, 705. (c) Casares, J. A.; Espinet, P.; Mart´ın-AÄ lvarez,
J.; Espino, G.; Pe´rez-Manrique, M.; Vattier, F. Eur. J. Inorg. Chem.
2001, 289. (d) Espinet, P.; Soulantica, K. Coord. Chem. ReV. 1999,
499-556. (e) Zhang, Z. Z.; Cheng, H. Coord. Chem. ReV. 1996, 147,
1-39. (f) Newkome, G. R. Chem. ReV. 1993, 93, 2067-2089.
(6) Rauchfuss, T. B.; Patino, F. T.; Roundhill, D. M. Inorg. Chem. 1975,
14, 652.
(12) Pfeiffer, J.; Kickelbick, G.; Schubert, U. Organometallics 2000, 19,
62.
Inorganic Chemistry, Vol. 42, No. 12, 2003 3857

Alonso et al.
Scheme 3. Schematic Representation for the Major Isomer of the
Complexes [Rh(TFB)(P*Nn)]BF4 (3) and Newman Projection along the
C*-N Bonda
Scheme 4. NOE Contacts for Complex 4
coordinated benzylamino group, both in the N(CH3)2 signals
and in the benzylic groups. Exchange of the protons in the
diolefin can also be observed in the cross peaks correlating
endo-exo (relative to the boat) olefinic protons.
a The arrows indicate the most important NOE contacts between protons
that were used for determining the conformation of the major isomer.
For [Rh(TFB)(PN2)]BF4 (5) an equilibrium between the
Chart 2
two diastereomeric boat conformers exists in solution. At
1
213 K, 31P{1H}, H, and 19F spectra show two compounds
in proportion 33:1. The rate of conformational exchange was
calculated from the coalescence of these signals at 242 K,
using spectra simulation.13 The value obtained is kmajor-minor
) 300 s-1 and corresponds to ∆Gq242 ) 47.2 ( 0.2 kJ mol-1.
Furthermore, exchange of amino groups was observed in
solution, which renders equivalent the olefinic protons of
the TFB ligands. The rate of this process has been measured
at the coalescence temperature of olefinic signal cis to
nitrogen, giving a value of ∆Gq ) 41.7 ( 0.2 kJ mol-1.
211
Another interesting example of conformational analysis
concerns the homologous complex [Rh(TFB)(P*N2)]BF4 (6).
For a square planar geometry of Rh, coordination of the
ligand can create two different isomers (depending on which
amino group is coordinated), and each one can adopt two
different conformations (Chart 2). The 31P{1H} NMR shows
the existence of two compounds in approximately 10:1
proportion, at 26.1 ppm (1JRh-P ) 172 Hz) and 31.2 ppm
tion 10:1, at 24.4 and 25.5 ppm, respectively (1JRh-P ) 174
Hz for both). The signals for two conformers are also seen
in the 1H NMR spectrum recorded under the same conditions.
The major conformer shows six nonequivalent signals for
the TFB ligand as well as the nonequivalence of the N-methyl
groups. A NOESY experiment allows us to establish the
conformation of the metallacycle in the major isomer as δ
(NOE contacts are shown in Scheme 3). The19F NMR data
are in agreement with the31P{1H} and 1H results. The minor
isomer has the corresponding λ conformation, although not
(1JRh-P ) 170 Hz). In agreement with the 31P results, the 19
F
spectrum in CDCl3 at 263 K shows two compounds in the
same proportion (10:1), corresponding to a mixture of the
two isomers in equilibrium. According to the 1H NOE results,
the major complex can be assigned as δ (R) (again the most
important NOE interactions found are as indicated in Scheme
3). The 1H NMR spectrum of δ (R) at 253 K (300.16 MHz)
shows six nonequivalent protons for the TFB ligand, two
complex signals attributable to the benzylic protons of the
diamino arms (coordinated and noncoordinated), and two
doublets for the C*-methyl group (coordinated and nonco-
ordinated). Also, two signals for the NMe2 groups of the
amine coordinated and one for the noncoordinated are
observed. Assignment of the proton signals for the major
isomer of 6 was possible using COSY and NOESY experi-
ments. The correlation between the NMe2 groups of the
coordinated amino unit and the olefinic protons (at 5.8 and
5.4 ppm, which confirms their assignment to the protons trans
to P), as well as with the benzylic proton, proves that the
major isomer has a P,N-chelate ring in a twisted-boat
conformation, with an absolute configuration δ and an axial
C*-methyl group (Chart 2). Furthermore, strong NOEs also
occur between one of the methyl groups of the coordinated
1
all the signals can be observed distinctly in the H and
NOESY spectra.
(b) Rhodium-PN2-Diolefin and Rhodium-P*N2-
Diolefin Complexes. The coordination of the ligand PN2
through the phosphorus and only one nitrogen renders
nonequivalent the coordinated and the uncoordinated amino
groups and converts the phosphorus atom to a chiral center
(R or S). Therefore chelation by P*N2 can give rise to four
diastereoisomers δ(R), λ(S), δ(S), and λ(R) of different
energies (Chart 2).
The complex [Rh(COD)(PN2)]BF4 (4) exists as one
1
conformer according to their 31P{1H} and H spectra. The
NOE effect observed between the noncoordinated benzy-
lamino group and the diolefin allows us to conclude that the
P,N-ligand adopts a boat conformation with the free benzy-
lamino group occupying an axial site (Scheme 4). The
diagonal phase of the NOESY experiment (EXSY spectrum)
shows cross peaks due to the exchange between free and
(13) Line shape analysis was carried out using the standard DNMR 6
program: DNMR6. Quantum Chemical Program Exchange (QCPE
633); Indiana University: Bloomington, IN, 1995.
3858 Inorganic Chemistry, Vol. 42, No. 12, 2003

Rhodium Aminophosphine Complexes
Scheme 5
Chart 3. Representation of the Two Conformers Observed for the
Complex [Rh(TFB)(P*N3)]BF4 (7)
amino moiety and the C-H proton of the pendant phenyl-
ethylamine end. A correlation between the C-methyl group
of the noncoordinated amino group and olefinic protons cis
to N can also be observed. Altogether the evidence indicates
that the major isomer is the δ form with an R configuration
for the chiral phosphorus atom. In the complexes with PN2
(4 and 5) the configuration found at the phosphorus was the
opposite, with the noncoordinated benzylic amine in an axial
position. Thus the configuration found in 6 is controlled by
the C-methyl stereocenter in the chelate. Note that there is
another possible stereoisomer in which both the C-methyl
and the noncoordinated benzylamine group are in axial posi-
tion (stereoisomer δ(S) in Chart 2), but this geometry maxi-
mizes the steric hindrance on this face of the chelating ring.
The EXSY spectrum of 6 shows cross peaks correlating
the N-Me groups of the coordinated nitrogen of the major
isomer and the N(Me)2 of the free nitrogen in the minor one
(a similar exchange was observed between the signal
corresponding to the substituents of the R-carbon free and
coordinated). The process involved is a substitution reaction
with exchange of the uncoordinated and coordinated amines.
The reaction equilibrates isomers with opposite absolute
configuration at the phosphorus atom, R or S. On the other
hand, at 263 K interconversion of the olefinic protons was
observed. These data indicate the occurrence of a dynamic
process that selectively exchanges the two olefinic protons
trans to P with those trans to N (Scheme 5). This process is
often observed in Rh(I)-diolefin complexes. It has been
proposed to occur by a Berry mechanism in pentacoordinated
intermediates formed by coordination of coordinating sol-
compared to the exchange under discussion here.16 A disso-
ciative pathway should be favored for the complex with the
higher steric hindrance (PN3 > PN2 > PN1), again in contrast
with the observation. For this reason we favor an associative
pathway involving solvent or the anion as the entering ligand.
(c) Rhodium-PN3-Diolefin and Rhodium-P*N3-
Diolefin Complexes. We have reported previously the
dynamic behavior of diene complexes with the ligand PN3.16
The Rh complexes are square planar in solution and undergo
two intramolecular fluxional processes: conformational
inversion and exchange of coordinated for the pendant amino
groups. EXSY and magnetization transfer experiments
demonstrated that both processes are not simultaneous but,
on the contrary, the ligand exchange is ca. 100 times faster
than the conformational change.
The complex with P*N3 behaves similarly to the analogous
complex with P*N. The only difference between them is the
1
steric hindrance around phosphorus. 31P{1H} and H NMR
spectra at 263 K show two conformers in equilibrium in the
proportion 4:1 (Chart 3). The COSY and NOESY data
confirm that the chelate has δ conformation in the major
isomer. The assignments based on NOE contacts are as for
P*N1 (Scheme 3).
Several dynamic processes were observed in the EXSY
spectra of 7 at 263 K. For the major conformer we detected
the following: (i) All of the methyls of the amino groups,
whether coordinated or not, exchange with each other. The
same applies with the CHMe groups. (ii) The double bonds
exchange their coordination as a result of rotation of TFB
ligand (Scheme 5). Furthermore, at the same temperature
the experiment shows that conformer interconversion is
occurring. The spectrum shows cross peaks correlating
CHMe groups of the major isomer with others in the minor
isomer. Although not every exchange can be observed in
the complex spectrum, it can be seen clearly that the C*-
Me group of the coordinated amino arm of the major isomer
and the C*-Me signal of the pendant amine arm in the minor
isomer do exchange. Therefore, overall the difference
between rates of conformational inversion and rates of ligand
substitution is smaller here than in the homologous complex
with the nonchiral PN3 (9, see Experimental Section).
X-ray Structure of Complex (8). Compound 8, [Rh-
(TFB){(C6H4CHMeNMe2)2P(C6H4CHMeNHMe2)}](BF4)2‚
H2O‚Me2CO, was obtained as a decomposition product when
we tried to obtain single crystals of [Rh(TFB)(P*N3)]BF4
- 14
vents or anions such as BF4 . Other authors propose a
different mechanism involving intermediates with a mono-
dentate P,N-ligand.15 The first step would involve Rh-N
cleavage to form a three-coordinated species. Topomerization
of the T-shaped intermediate is followed by rotation around
the Rh-P bond and N recoordination. These mechanisms
are indistinguishable by NMR experiments. In our complexes
the exchange rate follows the order PN1 > PN2 > PN3, and
this excludes the intervention of the pendant amine groups
to give a pentacoordinated intermediate, since in such a case
the ligand with two pendant amino groups should be the
fastest. Moreover, we have previously measured this process
for diene complexes with the ligand PN3 and it is very slow
(14) (a) Haarman, H. F.; Ernsting, J. M.; Kranenburg, M.; Kooijman, H.;
Veldamn, N.; Spek, A. L.; van Leeuwen, P. W. N. M. Organometallics
1997, 16, 887. (b) Heitner, H. I.; Lippard, S. J. Inorg. Chem. 1972,
11, 1447. (c) Vrieze, K.; van Leeuwen, P. W. N. M. Prog. Inorg.
Chem. 1971, 14, 1. (d) Heitner, H. I.; Lippard, S. J. J. Am. Chem.
Soc. 1970, 92, 3486.
(15) (a) Berger, H.; Nesper, R.; Pregosin, P. S.; Ru¨egger, H.; Wo¨rle, M.
HelV. Chim. Acta 1993, 76, 1520. (b) Yang, H.; Lugan, N.; Mathieu,
R. Organometallics 1997, 16, 2089. (c) Selvakumar, K.; Valentini,
M.; Pregosin, P. S. Organometallics 2000, 19, 1299.
(16) Alonso, M. A.; Casares, J. A.; Espinet, P.; Soulantica, K. Angew.
Chem., Int. Ed. 1999, 38, 533.
Inorganic Chemistry, Vol. 42, No. 12, 2003 3859

Alonso et al.
The Rh-C bond lengths reflect the stronger trans influence
of the phosphine compared with the tertiary amine. The
structure features a six-membered metallacycle, Rh-P(1)-
C(21)-C(26)-C(27)-N(1) with a twisted-boat conformation
of absolute configuration δ and with the C(28) methyl group
in an axial site. The protonated amino group occupies a
pseudo-axial position and is hydrogen bonded to the water
molecule (see Figure 1).
Complex 8 could not be prepared by the reaction between
7 and aqueous HBF4 in which extensive decomposition
occurred. However, the protonation of 7 by H(OEt2)2BAF
(BAF: tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) in an
NMR tube allowed us to complete the spectroscopic char-
acterization of the dication of 8, [Rh(TFB){(C6H4CHMe-
NMe2)2P(C6H4CHMeNHMe2)}]2+.
Figure 1. Thermal ellipsoid plot of the dication of [Rh(TFB){(C6H4-
CHMeNMe2)2P(C6H4CHMeNHMe2)}](BF4)2‚H2O‚Me2CO and the water
molecule to which it is hydrogen bonded. Ellipsoids are shown at the 40%
probability level.
Discussion
Conformational Preferences in the Solid State and in
Solution. The twisted-boat conformation of the metallacycles
formed by the chelating ligands in this work is chiral and
exists in δ and λ forms.20 Solid state structures of transition
metal complexes (e.g., Rh, Pd, Pt, Ni) with ligands closely
related to ours have been reported and confirm that the
preferred conformation is related to the configuration of the
R-carbon stereocenter. For example, this is observed in Rh
complexes with (R)-N,N-dimethyl-1-phenylethylamine, [(1R)-
N,N-dimethyl{o-[bis-tert-butylphosphino]phenyl}ethylamine-
N,P],21 or (R,S)-R-(2-diphenylphosphinoferrocenyl)ethyl-
dimethylamine,22 and in the Ni complex [Ni{(R)-o-(C6H11)2-
PC6H4CHCH3N(CH3)2}(NCS)2].23 On the contrary, when
the configuration of the carbon stereocenter is S, the P,N-
chelate ring presents a twisted-boat conformation with an
absolute configuration λ and an axial C-methyl group. This
is observed in the Rh complexes with (S,S)-bis[2-(1-N,N-
dimethylaminoethyl)phenyl]phenyl)phosphine or (S)-[2-(1-
N,N-dimethylaminoethyl)phenyl]diphenylarsine,21 and in the
structure of cis-dichloro[(1S)-N,N-dimethyl-1-{2-[(S)-tert-
butylphenylphosphino]phenyl}ethylamine-N,P]platinum-
(II).24 In conclusion, for R R-carbon stereocenters the six-
membered ring adopts the conformation δ, and for S
R-carbon stereocenters the conformation will be λ.
Table 1. Selected Bond Lengths (Å) and Angles (deg) for 8
Rh(1)-C(10)
Rh(1)-C(1)
Rh(1)-N(1)
Rh(1)-C(11)
2.133(3)
2.144(3)
2.176(2)
2.246(3)
Rh(1)-C(12)
Rh(1)-P(1)
P(1)-C(31)
2.250(3)
2.3035(8)
1.830(3)
C(10)-Rh(1)-C(1)
C(10)-Rh(1)-N(1)
C(1)-Rh(1)-N(1)
C(10)-Rh(1)-C(11)
C(1)-Rh(1)-C(11)
N(1)-Rh(1)-C(11)
C(10)-Rh(1)-C(12)
C(1)-Rh(1)-C(12)
38.03(11) N(1)-Rh(1)-C(12)
155.06(10) C(11)-Rh(1)-C(12)
161.08(10) C(10)-Rh(1)-P(1)
64.91(12) C(1)-Rh(1)-P(1)
76.90(13) N(1)-Rh(1)-P(1)
98.60(12) C(11)-Rh(1)-P(1)
76.68(12) C(12)-Rh(1)-P(1)
64.41(12)
101.14(11)
35.66(10)
97.67(8)
98.73(8)
92.23(7)
157.16(8)
159.25(9)
(7). The molecular structure of the dication and the associated
hydrogen-bonded water molecule is shown in Figure 1. Table
1 contains a selection of bond distances and angles of interest.
The structure belongs to the monoclinic system with
space group P21 and contains only the enantiomer shown
in Figure 1 of the [Rh(TFB){P(C6H4CHMeNMe2)2(C6H4CH-
MeNHMe2)}] dication together with BF4- anions and water
and acetone molecules.
The dication of 8 contains a pseudo-square-planar rho-
dium bonded to the phosphorus and a nitrogen atom of
the bidentate protonated P(C6H4CHMeNMe2)2(C6H4CH-
MeNHMe2) ligand (PN*3H+) and to the olefinic bonds of a
tetrafluorobenzobarrelene (TFB) ligand. The TFB ligand
shows no peculiar structural features and has Rh-C bond
distances similar to those in other such complexes.17,18
Coordination of the TFB leads to C-Rh-C angles well
below 90°, as expected for its small bite angle. The P-Rh-
N(1) angle, however, is close to 90°. The Rh-P and Rh-N
distances are within the normal ranges for Rh(I) complexes.19
Similarly for the P*Nn ligands the preferred conformation
of the metallacycle is that minimizing the steric interactions
between the methyl substituent and those on the N atom,25-27
and the δ configuration will be expected for the chelate ring
(19) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson, D.
G.; Taylor, R. J. Chem. Soc., Dalton Trans. 1989, S1-S83.
(20) Eliel, E. L.; Wilen, S. H. Stereochemistry of Organic Compounds;
John Wiley & Sons: New York, 1994.
(21) McKay, I. D.; Payne, N. Can. J. Chem. 1986, 64, 1930.
(22) Cullen, W. R.; Eisentein, F. W. B.; Huang, C.-H.; Willis, A. C.; San
Yeh, E. J. Am. Chem. Soc. 1980, 102, 988.
(23) McKay, I. D.; Payne, N. C. Acta Crystallogr., Sect. C: Cryst. Struct.
Commun. 1986, 42, 307.
(24) Payne, N. C.; Tobin, G. R. Acta Crystallogr. 1992, C48, 45.
(25) Yamada, I.; Ohkouchi, M.; Yamaguchi, M.; Yamagishi, T. J. Chem.
Soc., Perkin Trans. 1 1997, 1869.
(26) Payne, N.; Stephan, D. W. Inorg. Chem. 1982, 21, 182.
(27) Chooi, S. Y. M.; Leung, P. H.; Mok, K. F. Inorg. Chem. 1994, 33,
3096.
(17) (a) Lahoz, F. J.; Tiripicchio, A.; Camellini, T. M.; Oro, L. A.; Pinillos,
M. T. J. Chem. Soc., Dalton Trans. 1985, 1487. (b) Ciriano, M. A.;
Perez-Torrente, J. J.; Viguri, F.; Lahoz, F. J.; Oro, L. A.; Tiripicchio,
A.; Camellini, T. M. J. Chem. Soc., Dalton Trans. 1990, 1493. (c)
Esteruelas, M. A.; Lahoz, F. J.; Oliva´n, M.; On˜ate, E.; Oro, L. A.
Organometallics 1994, 13, 3315. (d) Atencio, R.; Casado, M. A.;
Ciriano, M. A.; Lahoz, F. J.; Perez-Torrente, J. J.; Tiripicchio, A.;
Oro, L. A. J. Organomet. Chem. 1996, 514, 103.
(18) Esteruelas, M. A.; Oro, L. A. Coord. Chem. ReV. 1999, 193-195,
557.
3860 Inorganic Chemistry, Vol. 42, No. 12, 2003

Rhodium Aminophosphine Complexes
Chart 4. Schematic Representations of δ and λ Twisted-Boat
Conformations (for (R)-C*-Me Stereocenter), Showing the Overlap of
the Me Groups in the λ Conformer
energies for the conformational isomers, making any com-
parison of boat-exchange energies difficult.
However, it is very interesting to note that, in the homo-
logous complexes with P*Nn (where the ligands have a Me
group as the R-carbon substituent), the conformational
inversion rates decrease considerably. For instance the
conformational inversion for the complex [Rh(TFB)(P*N1)]-
BF4 (3) is so slow that the coalescence in acetone-d6 of the
olefin signals of the major with those of the minor isomer is
above room temperature, whereas for [Rh(TFB)(PN1)]BF4
(1) the coalescence temperature is 213 K. Therefore an
important effect of the C-Me substituent in the P*Nn ligands
is to increase the activation energy for the exchange between
the two conformers. These results are in agreement with the
work of Crociani et al. on the influence of steric factors on
ring inversion observed for iminophosphine-rhodium
derivatives.4f
Exchange of Amino Groups. Exchange of pendant and
coordinated amino groups was observed for the PN2 com-
plexes 5 and 4 and is thought to occur by an associative
mechanism, which requires the formation of pentacoordinated
species. In fact the rate of substitution is moderately faster
for 5 than 4, as expected if we consider that the stabilization
of the transition state is bigger for the TFB complex (stronger
π-back-bonding due to the strained chelate formed) than for
the COD complex. The same fluxional behavior is observed
for the compounds with the PN3 ligands (9 and 10, see
Experimental Section). The exchange observed is slightly
slower than for the homologous complex with PN2, likely
due to the increase in the relative steric crowding around
phosphorus. As for the conformational inversion, the C-Me
substituent in complexes with P*Nn ligands increases the
activation energy associated with the exchange of amino
groups.
Table 2. Selected Values of Activation Energies for the
Conformational Inversion of the Ligand PN1
complexes
∆Gq (kJ mol-1
)
Tc (K)
ref
[RhCl(CO)(PN1)]
36.66
41.66
41.66
51.00
55.00
57.00
41.52
51.64
221
215a
215a
266
276
289
211
253
6
[Pd(Me)(OCH(CF3)2(PN1)]
[Pd(Me)(OC6H5)(PN1)]
[Pt(o-Me2Si(C6H4))(PN1)]
[Pt(Me)2(PN1)]
9
9
12
12
12
[PtI(Me)(PN1)]
[Rh(TFB)(PN1)]BF4
[Rh(COD)(PN1)]BF4
this work
this work
a The coalescence temperature for these complexes was not reported and
has been calculated from the reported ∆δ and ∆Gq values.
when the absolute configuration of the carbon stereocenter
is R. This is in fact the configuration observed in the structure
of 8.
In solution we can observe this conformational preference
for the complexes 3, 6, and 7. In fact the variable-temperature
1
31P{IH} and H NMR spectra show the two conformers in
equilibrium, but the preferred one is always very dominant
(3 100:3, 6 10:1, 7 4:1). This conformation is independent
of the steric hindrance around the phosphorus center. The
preference observed for coordinated P,N-ligands agrees with
that suggested even by simple ball-and-stick models, which
suggest severe steric repulsions between the methyl on the
R-carbon and the equatorial methyl of the syn-amine group
in the λ(R) conformation (Chart 4). This steric repulsion
disappears in the δ configuration. This probably dictates the
conformational preference observed.
Dynamic Behavior in Solution. The complexes reported
here show at least two dynamic processes in solution: (i)
inversion of the conformation of the nonplanar metallacycle
and (ii) exchange of amino groups, which depends on the
geometrical restrictions around phosphorus, the stereogenic
centers, and the corresponding diolefin ligands.
Conformational Exchange. The complexes with PN1,
[Rh(TFB)(PN1)]BF4 (1) and [Rh(COD)(PN)]BF4 (2), are
involved in a fast conformational inversion of the metalla-
cycle formed by the chelating ligand, which is plane-averaged
on the NMR time scale. Table 2 gathers the activation free
energy for 1 and for 2 along with other values reported in
the literature. The wide range of variation does not permit
one to establish meaningful comparisons.
Finally, it is remarkable that the relative difference in rates
of substitution is lower between complexes with P*N2 and
P*N3 than for the couple PN2 and PN3. This reflects that the
steric effect of C-Me substituents is more important than the
increase of the steric crowding.
Experimental Section
General Methods. All reactions were carried out under N2 using
standard Schlenk techniques. Solvents were distilled using standard
procedures and degassed under nitrogen before use. The precursors
[Rh2(µ-Cl)2(1,5-COD)2],28 [Rh2(µ-Cl)2(TFB)2],29 the ligands
PN3,30 P*N,31 and P*N2,32 and TlBF4 were prepared by published
methods.33 Combustion CHN analyses were made on a Perkin-
Elmer 2400 CHN microanalyzer. Optical rotations were measured
1
with a Perkin-Elmer 241 polarimeter using 10-cm cells. H NMR
(300.16 MHz), 19F NMR (282.4 MHz), 31P{1H} NMR (121.4 MHz),
and 13C{1H} (75.47 MHz) spectra were recorded on Bruker ARX
300 and AC 300 instruments equipped with a VT-100 variable-
If we compare the complexes with ligands PN1 (with two
Ph pendant groups) with those with PN3 (having two
benzylamino pendant groups), we observe that an increase
in the number of benzylamine groups leads to a slower
conformational inversion. For PN2 the pendant substituents
of phosphorus are different from each other (one Ph and one
benzylamino), and this is a factor that leads to very different
(28) Giordano, G.; Crabtree, R. H. Inorg. Synth. 1990, 28, 88.
(29) Roe, D. M.; Massey, A. G. J. Organomet. Chem. 1971, 28, 273.
(30) Chuit, C.; Corrin, J. P. R.; Monforte, P.; Reye´, C.; Declereq, J.-P.;
Duborg, A. Angew. Chem., Int. Ed. Engl. 1993, 32, 1430.
(31) Horner, L.; Simons, G. Phosphorus Sulfur Relat. Elem. 1983, 15, 171.
(32) Yamada, I.; Ohkouchi, M.; Yamaguchi, M.; Yamagishi, T. J. Chem.
Soc., Perkin Trans. 1 1997, 1869.
(33) Arna´iz, J. J. Chem. Educ. 1997, 74, 1332.
Inorganic Chemistry, Vol. 42, No. 12, 2003 3861

Alonso et al.
temperature probe. Chemical shifts are reported in parts per million
[Rh(TFB)(PN)]BF4 (1). To a stirred suspension of [Rh2(µ-Cl)2
1
from tetramethylsilane for H and 13C; CCl3F for 19F; and H3PO4
(TFB)
2] (248 mg, 0.34 mmol) in acetone (20 mL) were added solid
PN (217 mg, 0.68 mmol) and TlBF4 (198 mg, 0.68 mmol). After
1 h the TlCl was removed by filtration. The yellow solution was
concentrated to 10 mL, and after addition of ethanol (10 mL) it
was allowed to crystallize. The bright yellow crystals formed were
washed with ethanol and dried under vacuum. Yield: 342 mg
(68%). Anal. Calcd for C33H28BF8NPRh: C, 53.91; H, 3.84; N,
1.91. Found: C, 54.47; H, 1.93; N, 4.04. 31P{1H} NMR (CD2Cl2,
25 °C): δ 30.88 (d, JRh-P ) 174.4 Hz). 1H NMR (CD2Cl2, 25 °C):
δ 7.00-7.70 (m, 10H, Ar), δ 7.32 (m, 3H, Ar), δ 7.00 (m, 1H,
Ar), δ 5.80 (br, 2H, H-Cbridge(TFB)), δ 5.10 (br, 2H, Holef-
cisN(TFB)), δ 3.65 (m, 2H, Holef-transN(TFB)), δ 2.60 (s, 6H,
NcoordCH3 + NcoordCH3). 19F NMR (CD2Cl2, 25 °C): δ -159.04
(m, 2F), δ -146.33 (m, 2F), δ -152.19 (s, 10BF4), δ -152.25 (s,
11BF4).
(85%) for 31P; positive shifts downfield at ambient probe temper-
ature unless otherwise stated. NOESY experiments were recorded
in phase sensitive mode, using the average of the relaxation times
as mixing time.
[(2-N,N-Dimethylaminomethyl)phenyl]diphenylphosphine(PN1).
This ligand, first prepared by Roundhill et al., was synthesized
according to the published method6 with minor modifications. To
a solution of BuLi (26 mL, 42 mmol) in hexane (40 mL), prepared
by dilution of a commercial solution (1.6 M in hexane), were added
ether (30 mL) and N,N-dimethylbenzylamine (6 mL, 40 mmol) just
after, and the mixture was refluxed for 5 h. This orange solution
was cooled -78 °C and a solution of freshly distilled Ph2PCl (6.47
mL, 36 mmol), in ether (20 mL) was added slowly during 1 h.
This mixture was allowed to react at low temperature overnight,
and then the solvent was evaporated and the excess of lithium salts
hydrolyzed by adding ethanol (3 mL) and then water (30 mL). The
phosphine was extracted with dichloromethane (90 mL in three
portions), dried with magnesium sulfate, and concentrated to
dryness. The product was crystallized by adding ethanol (25 mL)
and cooling at -20 °C. Yield: 9.2 g (90%).
Bis[(2-N,N-Dimethylaminomethyl)phenyl]phenylphosphine
(PN2). The procedure was as described for PN, but PhPCl2 (2.2
mL, 17 mmol) was added instead of Ph2PCl. The crude product
was purified by column chromatography on silica gel using ethyl
acetate as eluent Yield: 4.09 g (64%). Anal. Calcd for C24H29N2P:
C, 76.75; H, 7.76; N, 7.44. Found: C, 76.73; H, 7.35; N, 7.71.
31P{1H} NMR (CDCl3, 25 °C): δ -24.70 s. 1H NMR (CDCl3, 25
°C): δ 7.48 (ddd, J56 ) 4.2 Hz, J53 ) 1.25 Hz, J54 ) 7.6 Hz, 2H5),
δ 7.32 (m, 5H, Ph), δ 7.20 (m, 2H3), δ 7.12 (td, J43 ) 7.45 Hz, J45
[Rh(COD)(PN)](BF4) (2). To a stirred solution of [Rh2(µ-Cl)2-
(COD)2] (247 mg, 0.5 mmol) in acetone (30 mL) was added AgBF4
(196 mg, 1 mmol). After half an hour, the AgCl was removed by
filtration and solid PN (319 mg, 1 mmol) was added. The yellow
solution was concentrated and cooled for crystallization to -20
°C for 1 day. The bright yellow crystalline solid was filtered, washed
with acetone-ethanol (1:1), and dried in a vacuum. By concentra-
tion of the remaining solution a second crop of crystals was
obtained. Yield: 525 mg (85%). Anal. Calcd for C29H34BF4NPRh:
C, 56.43; H, 5.55; N, 2.27. Found: C, 56.33; H, 5.64; N, 2.22.
31P{1H} NMR (CDCl3, 213K): δ 25.05 (d, JRh-P ) 156.9 Hz). 1H
NMR (CDCl3, 213K): δ 8.08 (m, 1H, Ar), δ 7.8-7.0 (m, 13H,
Ar), δ 5.75 (m, 1H, CH(COD)), δ 5.15 (m, 1H, CH(COD)), δ 3.78
(m, 1H, CH2), δ 3.35 (m, 1H, CH2), δ 3.20 (m, 2H, CH(COD)), δ
2.85 (m, 2H, CH2(COD)), δ 2.68 (s, 3H, NcoordCH3), δ 2.51 (s,
3H, NcoordCH3), δ 2.39 (m, 3H, CH2 (COD)), 1.97 (m, 2H, CH2-
(COD)), 1.65 (m, 1H, CH2(COD)).
) 7.6 Hz, J46 ) 1.22 Hz, 2H4), δ 6.82 (dd, JH-P ) 6.8 Hz, J65
)
4.2 Hz, 2H6), δ 3.60 (system ABX, 4H, CH2), δ 2.18 (s, 12H,
N(CH ) ). 13C{1H} NMR (CDCl3, 25 °C): δ 144.13 (d, JC-P
)
2
3
[Rh(TFB)(P*N)]BF4 (3). This compound was prepared as
described for 1, but using (R)-P*N (225 mg, 0.68 mmol) instead
of PN. Yield: 326 mg (64%). Anal. Calcd for C34H30BF8NPRh:
C, 54.50; H, 4.04; N, 1.87. Found: C, 54.22; H, 4.04; N, 1.80.
22.6 Hz, CH), δ 138.51 (d, JC-P ) 10.5 Hz, CH), δ 137.51 (d,
JC-P ) 13.5 Hz, CH), δ 134.69 (s, CH), δ 134.50 (s, CH), δ 134.42
(s, CH), δ 129.49 (d, JC-P ) 9.8 Hz, CH), δ 128.94 (s, CH), δ
128.87 (s, CH), δ 128.74 (d, JC-P ) 5.3 Hz, CH), δ 127.45 (s,
CH), δ 62.61 (d, JC-P ) 19.6 Hz, CH2), δ 45.65 (s, CH3).
20
Optical rotation: [R]D ) -64.8 (c ) 0.95, in CDCl3). 31P{1H}
NMR (CDCl3, 25 °C): δ 23.6 (d, JRh-P ) 174 Hz). 31P{1H} NMR
(CD2Cl2, -70 °C): δ 24.6 (d, major conformer JRh-P ) 174 Hz);
δ 25.4 (d, minor conformer JRh-P ) 169 Hz). 1H NMR (CDCl3, 25
°C): δ 7.66 (m, 2H, Ar), 7.6-7.3 (m, 12H, Ar), δ 5.82 (m, 2H,
H-Cbridge), δ 5.67 (m, 1H, Holef-cisN (TFB)), δ 5.53 (m, 1H,
Holef-cisN (TFB)), δ 3.62 (m, 1H, CHMe), δ 3.22 (m, 1H, Holef-
transN (TFB)), δ 3.10 (m, 1H, Holef-transN (TFB)), δ 2.72 (s,
6H, NcoordCH3 + NcoordCH3), δ 1.79 (d, J ) 6.7 Hz, 3H, CHMe).
19F NMR (CDCl3, 25 °C): δ -145.76 (m, 1F), -146.28 (m, 1F),
-152.43 (s, 10BF4), -152.49 (s, 11BF4), -158.95 (m, 2F).
(R,R,R)-Tris-[2-(1-N,N-dimethylaminoethyl)phenyl]phos-
phine (P*N3). To a solution of BuLi (9 mL, 14 mmol) in hexane
(15 mL), prepared by dilution of a commercial solution (1.6 M in
hexane), were added tetraethylenediamine (2.1 mL, 14 mmol) and
(R)-(+)-R-N,N-dimethyl-1-phenylethylamine (2 g, 13 mmol) just
after, and the mixture was refluxed for 5 h. This orange solution
was added slowly during 1 h to a solution of freshly distilled PCl3
(0.3 mL, 3 mmol), in ether (10 mL). This mixture was allowed to
react at low temperature overnight, and then the excess of lithium
salts was hydrolyzed by adding a solution of saturated sodium
carbonate (25 mL). The phosphine was extracted with ether (30
mL in three portions), dried with magnesium sulfate, and concen-
trated to dryness. The phosphine was crystallized by adding
acetonitrile. Yield: 340 mg (47%). Anal. Calcd for C30H42N3P: C,
75.75; H, 8.90; N, 8.83. Found: C, 75.15; H, 8.49; N, 8.20. Optical
[Rh(COD)(PN2)](BF4) (4). This compound was prepared as
described for 2, but using PN2 (377 mg, 1 mmol) instead of PN.
Yield: 587 mg (87%). Anal. Calcd for C32H41BF4N2PRh: C, 56.99;
H, 6.13; N, 4.15. Found: C, 56.62; H, 6.16; N, 3.90. 31P{1H} NMR
(CDCl3, 233 K): δ 16.84 (d, JRh-P ) 159.5 Hz). 1H NMR (CDCl3,
233 K): δ 9.20 (dd, J ) 7.5 Hz, J ) 13.5 Hz, 1H, Ar), δ 7.85 (m,
2H, Ar), δ 7.60 (m, 2H, Ar), δ 7.34, (m, 5H, Ar), δ 7.12 (m, 3H,
Ar), δ 5.70 (m, 1H, CH(COD)), δ 5.31 (m, 1H, CH(COD)), δ 4.03
(d, J ) 13.2 Hz, 1H, CH2), δ 3.90 (d, J ) 16.3 Hz, 1H, CH2), δ
3.40 (m, 2H, CH2 + CH(COD)), δ 3.20 (d, J ) 15.6 Hz, 1H, CH2),
δ 2.98 (m, 1H, CH2(COD)), δ 2.80 (s, 3H, NcoordCH3), δ 2.75
(masked, 1H, CH2(COD)), δ 2.55 (s, 3H, NcoordCH3), δ 2.53 (m,
1H, CH2(COD)), δ 2.40 (s, 3H, CH2 (COD) + CH(COD)), δ 2.28
20
rotation: [R]D ) +122.6 (c ) 1, in CDCl3). 31P{1H} NMR
1
(CDCl3, 25 °C): δ -42.97 s. H NMR (CDCl3, 25 °C): δ 7.58
(dd, J ) 6.7 Hz, J ) 4.4 Hz, 3H, H6), δ 7.35 (t, J ) 7.2 Hz, 3H,
H5), δ 7.11 (t, J ) 7.3 Hz, 3H, H4), δ 6.75 (br, 3H, H3), δ 4.07 (br,
3H, CHMe), δ 2.28 (br, 18H, N(CH3)2), δ 0.95 (a, 9H, CHMe).
13C{1H} NMR (CDCl3, 25 °C): δ 149.80 (d, JC-P ) 21.3 Hz, CH),
δ 134.48 (d, JC-P ) 11 Hz, CH), δ 129.31 (s, CH), δ 126.71 (s,
CH), 115.16 (d, JC-P ) 5 Hz, CH), 61.83 (s, CH), 43.99 (s, CH3),
21.11 (s, CH3).
(s, 6H, N(CH3) ), δ 2.04-1.5 (m, 3H, CH2(COD)).
2
3862 Inorganic Chemistry, Vol. 42, No. 12, 2003

Rhodium Aminophosphine Complexes
Table 3. Crystallographic Data for 8
[Rh(TFB)(PN2)]BF4 (5). This compound was prepared as
described for 1, but using PN2 (256 mg, 0.68 mmol) instead of
PN. Yield: 431 mg (80%). Anal. Calcd for C36H35BF8N2PRh: C,
54.57; H, 4.45; N, 3.54. Found: C, 54.38; H, 4.52; N, 3.41. 31P-
{1H} NMR (CD2Cl2, 25 °C): δ 26.19 (d, JRh-P ) 172.7 Hz). 31P-
{1H} NMR (CD2Cl2, -90 °C): δ 24.2 (d, major conformer JRh-P
empirical formula
fw
temp
wavelength
cryst syst, space group
unit cell dimens
C45H57B2F12N3O2PRh
1055.44
173(2) K
0.71073 Å
monoclinic, P21
a ) 12.548(11) Å
b ) 16.139(2) Å
c ) 12.1804(10) Å
â ) 100.742(9)°
2328.2(4) Å3
1
) 172 Hz); 35.8 (d, minor conformer JRh-P ) 173 Hz). H NMR
(CD2Cl2, 25 °C): δ 7.96 (br, 2H, Ar), δ 7.55-7.40 (m, 7H, Ar), δ
7.25 (m, 2H, Ar), δ 7.12 (m, 2H, Ar), δ 5.68 (br, 2H, H-Cbridge-
(TFB)), δ 5.41 (br, 2H, Holef-cisN(TFB)), δ 3.45 (m, 4H, CH2), δ
2.88 (br, 2H, Holef-transN(TFB)), δ 2.32 (br, 12H, N(CH3)2 +
NcoordCH3 + NcoordCH3). 19F NMR (CD2Cl2, 25 °C): δ -158.80
(m, 2F), δ -146.11 (m, 2F), δ -151.94 (s, 10BF4), δ -152.00 (s,
vol
Z
4
density (calcd)
abs coeff
cryst size
θ range for data collection
reflns collected
indep reflns
abs correction
refinement meth
data/restraints/params
GOF on F2
1.506 Mg/m3
0.490 mm-1
0.42 × 0.40 × 0.30 mm
1
1.72-27.49
11BF4). H (CD2Cl2, 183 K): δ 9.15 (m, 1H, Ph), δ 7.71 (m, 2H,
14885
Ph), δ 7.5-6.9 (m, 9H, Ph), δ 6.62 (m, 1H, Ph), δ 5.90 (br, 1H,
Holef-cisN(TFB)), δ 5.60 (br, 1H, H-Cbridge(TFB)), δ 5.35 (br,
1H, Holef-cisN(TFB)), δ 5.17 (br, 1H, H-Cbridge(TFB)), δ 3.74
(m, 2H, CH2), δ 3.28 (br, 2H, Holef-transN(TFB) + CH2), δ 3.01
(br, 1H, CH2), δ 2.54 (br, 3H, NcoordCH3), δ 2.35 (br, 4H,
NcoordCH3 + Holef-transN(TFB)), δ 2.22 (br, 6H, N(CH3)2).
[Rh(TFB)(P*N2)]BF4 (6). This compound was prepared as
described for 1, but using (R, R)-P*N2 (275 mg, 0.68 mmol) instead
of PN. Yield: 502 mg (90%). Anal. Calcd for C38H39BF8N2PRh:
C, 55.63; H, 4.79; N, 3.41. Found: C, 54.50; H, 5.11; N, 2.92.
10196 [R(int) ) 0.0202]
SADABS
full-matrix least-squares on F2
10196/1/619
1.001
final R indices [I > 2σ(I)]
R indices (all data)
absolute structure param
R1 ) 0.031, wR2 ) 0.0668
R1 ) 0.0373, wR2 ) 0.0688
0.00(2)
A red oil precipitated immediately from the solution. The solvent
was decanted, and the oil was washed with n-hexane, vacuum-
dried, and dissolved in CD2Cl2 to obtain its spectroscopic data. 31P-
20
Optical rotation: [R]D ) -24.56 (c ) 1.25, in CDCl3). 31P{1H}
1
{1H} NMR: δ 31.2 (d, JRh-P ) 180 Hz). H NMR: δ 14.3 (br,
NMR (CDCl3, 25 °C): (a) major conformer, δ 26.13 (d, 1JRh-P
)
1H, N-H), 9.70, (m, 1H), 8.2-6.6 (m, 11H), 5.87 (br, 1H, TFB),
5.55 (br, 1H, TFB), 5.48 (br, 1H, TFB), 5.06 (br, 1H, TFB), 4.30
(m, 1H, CHMe), 3.98 (m, 1H, CHMe), 3.52 (m, 1H, CHMe), 3.34
(br, 1H, TFB), 2.50 (br, 1H, TFB), 2.60 (s, 3H, N-Me), 2.45 (s,
6H, N-Me), 2.14 (s, 3H, N-Me), 1.88 (s, 3H, N-Me), 1.41 (s,
3H, N-Me), 1.16 (d, J ) 6.7 Hz, 6H, two CHMe), 0.47 (d, J )
6.8 Hz, 3H, CHMe). 19F NMR: δ -62.6 (s, BAF), -145.7 (m,
2F, TFB), -149.9 (br, 4F, BF4), -157.4 (m, 2F, TFB).
[Rh(TFB){P(C6H4CHMeNMe2)2(C6H4CHMeNHMe2)}](BF4)2‚
H2O‚Me2CO (8): X-ray Structure. Crystal data and other details
of the structure analysis are presented in Table 3. Orange crystals
of 8 were obtained through recrystallization by slow diffusion in
acetone/hexane.
A crystal of 8 of dimension of 0.42 × 0.40 × 0.30 mm was
mounted on a glass fiber with grease. All diffraction measurements
were made at low temperature with a Siemens three-circle SMART
area detector diffractometer using graphite-monochromated Mo KR
radiation.34 All subsequent frames were referenced to a dark frame
reading taken at 10 s exposures without X-rays. Unit cell dimensions
were determined from reflections taken from 3 sets of 15 frames
(at 0.3° steps in ω) each at 10 s exposure. A full hemisphere of
reciprocal space was scanned by 0.3° ω steps at φ 0°, 90°, and
180° with the area detector center held at 2θ ) -29°. The
reflections were integrated using the SAINT program.35 A total of
14885 diffracted intensities were measured in a unique hemisphere
of reciprocal space for 2θ < 55°. The data were processed and
absorption correction was applied with SADABS.36 Effective
transmission coefficients were in the range 1.000 and 0.913,
respectively. A total of 10910 unique observations remained after
averaging of duplicate and equivalent measurements (Rint 0.044)
and deletion of the systematic absences. Of these, 9090 had I >
2σ(I). Lorentz and polarization corrections were applied.
1
172.6 Hz); (b) minor conformer, δ 31.20 (d, JRh-P ) 169.9 Hz).
1H NMR (CDCl3, 25 °C): major conformer, δ 9.17 (br, 1H), 7.98-
6.90 (mixture of conformers), δ 6.13 (br, 1H), δ 5.86 (br, 1 H), δ
5.45 (m, 2H), δ 3.52 (br, 2H), δ 3.25 (m, 1H), δ 2.77 (m, 6H), δ
2.13 (br, 1H), δ 2.03 (br, 6H), δ 1.96 (m, 3H), δ 1.40 (d, J ) 6.7
Hz, 3H). 19F NMR (CDCl3, 25 °C): δ -145.76 (m, 1F), -146.28
(m, 1F), -152.19 (s, 10BF4), -152.49 (s, 11BF4), -158.95 (m, 2F).
1H NMR (CDCl3, 253K): major conformer: δ 9.15 (m, 1H, Ar),
7.9-6.9 (mixture of conformers), δ 6.13 (m, 1H, H-Cbridge(TFB)),
δ 5.86 (m, 1H, Holef-cisN (TFB)), δ 5.42 (m, 1H, Holef-cisN
(TFB)), δ 5.33 (m, 1H, H-Cbridge(TFB)), δ 3.52 (m, 2H, Holef-
transN (TFB) + CHMecoord), δ 3.11 (m, 1H, CHMe), δ 2.77 (s,
6H, NcoordCH3), δ 2.68 (s, 3H, NcoordCH3), δ 2.01 (m, 10H,
N(CH3)2 + Holef-transN (TFB)+CHMe), δ 1.38 (d, J ) 6.2 Hz,
3H, CHMecoord).
[Rh(TFB)(P*N3)]BF4‚2H2O (7). This compound was prepared
as described for 1, but using (R,R,R)-P*N3 (322 mg, 0.68 mmol)
instead of PN. Yield: 502 mg (81%). Anal. Calcd for C42H52-
BF8N3O2PRh: C, 54.38; H, 5.65; N, 4.53. Found: C, 54.21; H,
5.28; N, 4.26. Optical rotation: [R]D20 ) -48.20 (c ) 1, in CDCl3).
31P{1H}NMR (CDCl3, 25 °C): (a) major conformer, δ 36.8 (d,
JRh-P ) 171 Hz); (b) minor conformer, δ 34.3 (d, JRh-P ) 182
1
Hz). H NMR (CDCl3, 25 °C): major conformer only, δ 10.29
(m, 1H, Ar), 8.00 (m, 2H, Ar), 7.90 (m, 1H, Ar), 7.7-7.5 (m, 2H,
Ar), 7.5-7.4 (m, 3H, Ar), 7.47 (m, 1H, Ar), 7.08 (m, 1H, Ar),
6.65 (m, 1H, Ar), 6.02 (m, 1H, H-Cbridge(TFB)), 5.78 (m, 1H,
Holef-cisN (TFB)), 5.37 (m, 1H, H-Cbridge(TFB)), 5.22 (m, 1H,
Holef-cisN (TFB)), 3.81 (m, 1H, CHMe), 3.62 (m, 1H, CHMe),
3.50 (m, 1H, CHMecoord), 3.11 (m, 1H, Holef-transN (TFB)), 2.61
(s, 3H, NcoordCH3), 2.50 (s, 3H, NcoordCH3), 2.12 (s, 6H,
N(CH3)2), 1.83 (m, 1H, Holef-transN (TFB)), 1.71 (d, J ) 6.5 Hz,
3H, CHMe), 1.43 (s, 6H, N(CH3)2), 1.22 (d, J ) 6.4 Hz, 3H,
CHMe), 1.15 (d, J ) 6.9 Hz, 3H, CHMecoord). 19F NMR (CDCl3,
25 °C): δ -146.58 (m, 2F), -149.55 (s, 10BF4), -149.60 (s, 11BF4),
-160.06 (m, 2F).
(34) SMART Siemens Molecular Analysis Research Tool, V4.014; Siemens
Analytical X-ray Instruments, Madison, WI.
(35) SAINT (Siemens Area detector INTegration) program, Siemens
Analytical X-ray, Madison, WI.
(36) SADABS (Siemens Area Detector Absorption), G. Sheldrick. Uni-
versity of Go¨ttingen, Germany.
Protonation of 7. To a solution of 25 mg of 7 (0.028 mmol) in
CHCl3 (0.5 mL) was added 28 mg of H(OEt2)2BAF (0.028 mmol).
Inorganic Chemistry, Vol. 42, No. 12, 2003 3863

Alonso et al.
The structure was solved by direct methods and refined using
full-matrix least-squares refinement on F2 with the SHELXTL
program37 on a Silicon Graphics IRIS computer. All non-hydrogen
atoms were assigned anisotropic displacement parameters and
refined without positional constraints.
All hydrogen atoms were constrained to idealized geometries
and assigned isotropic displacement 1.2 times the Uiso for methylene
and aromatic carbons. Refinement of the 619 least-squares variables
converged to residual indices: R1 ) 0.0310, wR2 ) 0.0668, S )
CH2), δ 3.82 (d, J ) 16.5 Hz, 1H, CH2), δ 3.38 (d, J ) 16.3 Hz,
2H, CH2), δ 3.21 (m, 1H, Holef-transN (TFB)), δ 3.16 (d, J )
15.6 Hz, 1H, CH2), δ 2.89 (d, J ) 14.8 Hz, 1H, CH2), δ 2.79 (s,
3H, NcoordCH3), δ 2.43 (s, 6H, N(CH3)2), δ 2.39 (s, 3H,
NcoordCH3), δ 2.15 (m, 1H, Holef-transN(TFB)), δ 1.84 (s, 6H,
N(CH3)2). 19F NMR (CDCl3, 213K): δ -145.60 (m, 1F), -146.71
(m, 1F), -152.02 (s, 10BF4), -152.07 (s, 11BF4), -158.70 (m, 2F).
[Rh(COD)(PN3)](BF4) (10). This compound was prepared as
described for 4, but using PN3 (435 mg, 1 mmol) instead of PN.
Yield: 576 mg (78%). Anal. Calcd C35H48BF4N3PRh: C, 57.47;
H, 6.61; N, 5.75. Found: C, 57.19; H, 6.31; N, 5.88. 31P{1H} NMR
(CDCl3, 25 °C): δ 21.41 (d, JRh-P ) 153.3 Hz). 1H NMR (CDCl3,
25 °C): δ 10.08 (dd, J ) 16.9 Hz, J ) 7.4 Hz, 1H, Ar), δ 8.06 (m,
1H, Ar), δ 7.93 (m, 1H, Ar), δ 7.85 (m, 3H, Ar), δ 7.63 (m, 2H,
Ar), δ 7.50 (m, 1H, Ar), δ 7.4-7.2 (m, 3H, Ar), δ 5.60 (m, 1H,
CH(COD)), δ 5.25 (m, 1H, CH(COD)), δ 4.08 (d, J ) 12.8 Hz,
1H, CH2), δ 3.81 (d, J ) 15.5 Hz, 1H, CH2), δ 3.45 (m, 1H, CH2),
δ 3.39 (a, 2H, CH2 + CH(COD)), δ 3.12 (d, J ) 15.4 Hz, 1H,
CH2), δ 2.88 (m, 1H, CH(COD)), δ 2.80 (s, 3H, NcoordCH3), δ
2.72 (m, 2H, CH2 + CH2(COD)), δ 2.50 (m, 2H, CH2(COD)), 2.43
(s, 3H, NcoordCH3), 2.31 (s, 8H, N(CH3)2 + CH2(COD)), 1.82 (s,
6H, N(CH3)2), 1.78 (m, 2H, CH2(COD)), 1.57 (m, 1H, CH2(COD)).
2
-1
1.001. Weights, w, were set equal to 1/[σc2(Fo ) + (aP)2 + b]
where P ) [Max(Fo ,0) + 2Fc2]/3, σc2(Fo ) is the variance in Fo
due to counting statistics, and a ) 0.0302, b ) 0.000 were varied
to minimize the variation in S as a function of |Fo|. Final difference
electron density maps showed no features outside the range +0.976
to -0.550 Å-3, the largest being within 1.08 Å of F(5A). Tables
reporting the atomic positional parameters for the freely refined
atoms, the derived bond lengths and interbond angles, and the
atomic displacement parameters, hydrogen atom parameters, and
observed and calculated structure amplitudes are given in Supporting
Information.
2
2
2
[Rh(TFB)(PN3)]BF4 (9). This compound was prepared as
described for 1, but using PN3 (296 mg, 0.68 mmol) instead of
PN. Yield: 412 mg (71%). Anal. Calcd for C39H42BF8N3PRh: C,
55.14; H, 4.98; N, 4.95. Found: C, 54.94; H, 5.10; N, 4.53. 31P-
{1H} NMR (CDCl3, 213 K): δ 26.3 (d, JRh-P ) 172 Hz). 1H NMR
(CDCl3, 213K): δ 10.25 (dd, 1H, J ) 17.6 Hz, J ) 7.3 Hz, Ar),
δ 7.93 (m, 2H, Ar), δ 7.79 (m, 1H, Ar), δ 7.70 (m, 1H, Ar), δ 7.55
(m, 2H, Ar), δ 7.45 (m, 1H, Ar), δ 7.35 (m, 2H, Ar), δ 7.17 (m,
1H, Ar), δ 6.97 (m, 1H, Ar), δ 6.03 (m, 1H, H-Cbridge(TFB)), δ
5.88 (m, 1H, Holef-cisN(TFB)), δ 5.45 (m, 1H, H-Cbridge(TFB)),
δ 5.33 (m, 1H, Holef-cisN (TFB)), δ 4.01 (d, J ) 12.8 Hz, 1H,
Acknowledgment. The Junta de Castilla y Leo´n (Project
VA120-01) and the Ministerio de Ciencia y Tecnolog´ıa
(Project BQU2001-2015) are very gratefully acknowledged
for financial support.
Supporting Information Available: Tables of crystallographic
data for the structure 8, as well as data in CIF format. This material
is available free of charge via the Internet at http://pubs.acs.org.
(37) SHELXTL Rev. 5.03, Siemens Analytical X-ray, 1995.
IC034117A
3864 Inorganic Chemistry, Vol. 42, No. 12, 2003