Synthesis of new mixed phosphine～iminophosphorane bidentate ligands and their coordination to group 10 metal centers

Article abstract of DOI:10.1021/om0490684

The selective monobromation of a symmetrical bidentate diphosphine (dppm = bisdiphenylphosphinomethane) yielding a highly reactive intermediate, 2 (P～PBr⁺-Br^-), is reported. Two methods of trapping were devised to produce mixed phosphine-aminophosphonium salts 3 (P～PNHR⁺·Br^-). The first method relies on the reaction of 2 with 2 equiv of primary amine to give 3a-c (P～PNHR ⁺-Br^-, R = p-Me-Bn, p-MeO-Bn, Ph). The second method utilizes 1 equiv of primary amine and DABCO as trapping agent to give 3a-e (P～PNHR⁺-Br^-, R = p-Me-Bn, p-MeO-Bn, Ph, nBu, α(+)-Me-benzyl). These salts were then deprotonated quantitatively to yield the desired new phosphine-iminophosphorane ligands 4a-e (P～PNR). This simple strategy allows for a wide variation of the R substituent at the nitrogen donor group (R = alkyl, aryl, benzyl). In particular, the optically pure ligand 4e (R = α(+)-Me-benzyl) was obtained in one pot from commercially available α(+)-Me-benzylamine. Reaction of 4 with Pd(COD)Cl₂ affords the complexes 5 via coordination to Pd(II) centers and revealed the chelating behavior of these ligands. X-ray crystal structures of 5a (presented in ESI), 5c, and 5e are reported. Complexes of platinum(II), 6c and 6e, were also synthesized and characterized crystallographically. The complex of nickel(II), 7a, adopts a tetrahedral geometry as shown by X-ray analysis and consistent with a lack of NMR signal.

Full text of DOI:10.1021/om0490684

Organometallics 2005, 24, 1065-1074
1065
Articles
Synthesis of New Mixed Phosphine∼Iminophosphorane
Bidentate Ligands and Their Coordination to Group 10
Metal Centers
Le¨ıla Boubekeur, Louis Ricard, Nicolas Me´zailles,* and Pascal Le Floch*
Laboratoire “He´te´roe´le´ments et Coordination”, UMR CNRS 7653 (DCPH),
De´partement de Chimie, Ecole Polytechnique, 91128 Palaiseau Ce´dex, France
Received November 29, 2004
The selective monobromation of a symmetrical bidentate diphosphine (dppm ) bis-
diphenylphosphinomethane) yielding a highly reactive intermediate, 2 (P∼PBr+‚Br-), is
reported. Two methods of trapping were devised to produce mixed phosphine-aminophos-
phonium salts 3 (P∼PNHR+‚Br-). The first method relies on the reaction of 2 with 2 equiv
of primary amine to give 3a-c (P∼PNHR+‚Br-, R ) p-Me-Bn, p-MeO-Bn, Ph). The second
method utilizes 1 equiv of primary amine and DABCO as trapping agent to give 3a-e
(P∼PNHR+‚Br-, R ) p-Me-Bn, p-MeO-Bn, Ph, nBu, R(+)-Me-benzyl). These salts were then
deprotonated quantitatively to yield the desired new phosphine-iminophosphorane ligands
4a-e (P∼PNR). This simple strategy allows for a wide variation of the R substituent at the
nitrogen donor group (R ) alkyl, aryl, benzyl). In particular, the optically pure ligand 4e (R
) R(+)-Me-benzyl) was obtained in one pot from commercially available R(+)-Me-benzyl-
amine. Reaction of 4 with Pd(COD)Cl2 affords the complexes 5 via coordination to Pd(II)
centers and revealed the chelating behavior of these ligands. X-ray crystal structures of 5a
(presented in ESI), 5c, and 5e are reported. Complexes of platinum(II), 6c and 6e, were
also synthesized and characterized crystallographically. The complex of nickel(II), 7a, adopts
a tetrahedral geometry as shown by X-ray analysis and consistent with a lack of NMR signal.
Scheme 1
Introduction
Mixed P∼N bidentate ligands, such as phosphine-
imine1 or phosphine-oxazoline,2 have found numerous
applications in coordination chemistry and catalysis. In
particular, Pfaltz and co-workers have had excellent
results in the palladium-catalyzed enantioselective nu-
cleophilic substitution of allylic acetates using chiral
2,3
enantiopure phosphine-oxazolines.
In this system,
only one stereocenter is present on the bidentate ligand,
on the carbon R to the nitrogen atom, as shown in
Scheme 1. Following studies have rationalized the
results in terms of electronic differentiation of the two
allylic termini: trans to the phosphorus atom and trans
to the nitrogen atom. They have shown that nucleophilic
attack occurred preferentially trans to the phosphorus
atom, and thus cis to the sterically biased nitrogen
atom.4 Hence, only the chiral center R to the nitrogen
atom was necessary.
From another standpoint, iminophosphoranes (nitro-
gen analogues of phosphorus ylides) are seldom used
as ligands, probably because the PdN bond is usually
reactive toward many media. Indeed, it is well known
in organic chemistry that iminophosphoranes are readily
transformed into amines upon hydrolysis. However, few
examples of the utilization of chiral bidentate bis-
iminophosphorane complexes in catalysis have been
reported by the groups of Re´au and Reetz in the late
1990s.5,6 These groups have thus shown that the imi-
* To whom correspondence should be addressed. Tel: +33 1 69 33
45 70. Fax: +33 1 69 33 39 90. E-mail: lefloch@poly.polytechnique.fr;
mezaille@poly.polytechnique.fr.
(1) Reddy, K. R.; Surekha, K.; Lee, G. H.; Peng, S. M.; Liu, S. T.
Organometallics 2001, 20, 5557. Liu, X. M.; Mok, K. F.; Vittal, J. J.;
Leung, P. H. Organometallics 2000, 19, 3722. Crochet, P.; Gimeno, J.;
Borge, J.; Garcia-Granda, S. New J. Chem. 2003, 27, 414.
(2) Vonmatt, P.; Pfaltz, A. Angew. Chem., Int. Ed. Engl. 1993, 32,
566.
(4) Helmchen, G.; Pfaltz, A. Acc. Chem. Res. 2000, 33, 336. Pfaltz,
A. Acc. Chem. Res. 1993, 26, 339. Sprinz, J.; Kiefer, M.; Helmchen,
G.; Huttner, G.; Walter, O.; Zsolnai, L.; Reggelin, M. Tetrahedron Lett.
1994, 35, 1523.
(3) Trost, B. M.; Crawley, M. L. Chem. Rev. 2003, 103, 2921. Trost,
B. M.; VanVranken, D. L. Chem. Rev. 1996, 96, 395.
10.1021/om0490684 CCC: $30.25 © 2005 American Chemical Society
Publication on Web 02/11/2005

1066 Organometallics, Vol. 24, No. 6, 2005
Boubekeur et al.
Scheme 2
Scheme 3
nophosphorane moiety, once coordinated, could with-
stand conditions that decompose the free ligand. Be-
cause of the intrinsic electronic differences between
iminophosphorane, imine, and oxazoline, we felt that
it was worthwile developing the synthesis of new mixed
bidentate P∼N ligands incorporating an iminophospho-
rane moiety. Only a handful of examples have been
reported of such ligands,7-9 whose coordination chem-
istry has been investigated.10,11 These groups used some
of the complexes in catalysis.9,12
Another important goal of our study was to develop
an easy, straightforward synthesis using any available
starting diphosphine (commercially or not) that could
be amenable to larger scale if needed and allowing for
the preparation of optically pure derivatives. In this
article, we selected the diphosphine dppm (1,2-bis-
diphenylphosphinomethane) as starting material and
present our results on the synthesis of such P∼N
bidentate ligands and their coordinating behavior to-
ward group 10 metal centers (Ni(II), Pd(II), Pt(II)).
followed by trapping with activated RNH2, such as
amides, cyanides, or sulfonamides (eq 2).16
This second method suffers from the low yields
obtained for the mono-iminophosphorane derivatives
and is limited to very peculiar activated amine deriva-
tives.
Results and Discussion
The third method toward iminophosphoranes was
developed by Kirsanov et al. in 1950.14,17 It relies on the
bromination of a phosphine followed by trapping with
primary amines in the presence of an amine to trap
released HBr (Scheme 2). The intermediate salt can be
isolated and subsequently treated with a base to yield
the desired iminophosphorane. The enormous advan-
tage of this method is the potential use of any com-
mercially available amine and, in particular, optically
pure ones. Its major drawback is the use of toxic
bromine. This quite powerful method has been used
recently to synthesize bidentate N∼N chiral ligands,5
which were subsequently tested in asymmetric cataly-
sis.6 However, prior to our work, the Kirsanov approach
had not been used to obtain mixed P∼N ligands. The
overall strategy is presented in Scheme 3.
Three methods can be used, a priori, for the synthesis
of the iminophosphorane (which can also be called
phosphinimine) moiety of the mixed P∼N ligands we
set out to develop. The first one is the Staudinger
reaction,13,14 which relies on the addition of an azide to
a phosphine (eq 1). This method has been used with
great success by Cavell et al. (R ) SiMe3)7,11,15 and more
recently by Gimeno et al. (R ) P(X)(OR)2).9 Indeed, with
1 equiv of azide, the mixed ligands are obtained in high
yields. The significant drawback of this method is the
use of azides, which are usually difficult to prepare or
hazardous, and in fact the two above-mentioned groups
use commercially available azides.
The clean formation of the monobromo adduct of
dppm is essential for the success of the overall synthesis
as a mixture of compounds would not be separable or
purified. The first experiments were indeed very en-
couraging, as the addition of 1 equiv of bromine to a
cooled solution (-78 °C) of dppm in methylene chloride
followed by warming to room temperature yielded a
yellow solution whose 31P NMR spectrum consisted of
two sets of doublets at -22.8 ppm (2JPP ) 84.0 Hz) and
+58.5 ppm. These signals are consistent with PPh2 and
“PPh2Br2” moieties, respectively. Then, following the
initial procedures, the solution was cooled to -78 °C,
and both p-methoxybenzylamine and triethylamine
were added in a first attempt. The bath was then re-
moved and the mixture warmed back to room temper-
ature. After 15 min a 31P NMR spectrum was recorded
that showed the clean dismutation of the intermediate
2 into starting dppm, 1 (singlet at -23 ppm), and the
bis-bromo adduct A (singlet at + 48 ppm) (eq 3).
The second method relies on the reactivity of phos-
phines with DEAD (DEAD ) diethylazodicarboxylate)
(5) Reetz, M. T.; Bohres, E.; Goddard, R. Chem. Commun. 1998, 935.
(6) Sauthier, M.; Fornies-Camer, J.; Toupet, L.; Reau, R. Organo-
metallics 2000, 19, 553.
(7) Katti, K. V.; Santarsiero, B. D.; Pinkerton, A. A.; Cavell, R. G.
Inorg. Chem. 1993, 32, 5919.
(8) Katti, K. V.; Cavell, R. G. Inorg. Chem. 1989, 28, 413.
(9) Cadierno, V.; Crochet, P.; Diez, J.; Garcia-Alvarez, J.; Garcia-
Garrido, S. E.; Garcia-Granda, S.; Gimeno, J.; Rodriguez, M. A. Dalton
Trans. 2003, 3240.
(10) Katti, K. V.; Cavell, R. G. Organometallics 1989, 8, 2147. Katti,
K. V.; Batchelor, R. J.; Einstein, F. W. B.; Cavell, R. G. Inorg. Chem.
1990, 29, 808. Li, J.; McDonald, R.; Cavell, R. G. Organometallics 1996,
15, 1033. Li, J.; Pinkerton, A. A.; Finnen, D. C.; Kummer, M.; Martin,
A.; Wiesemann, F.; Cavell, R. G. Inorg. Chem. 1996, 35, 5684.
Pandurangi, R. S.; Katti, K. V.; Stillwell, L.; Barnes, C. L. J. Am. Chem.
Soc. 1998, 120, 11364. Cadierno, V.; Diez, J.; Garcia-Alvarez, J.;
Gimeno, J. Organometallics 2004, 23, 3425.
(11) Katti, K. V.; Cavell, R. G., Inorg. Chem. 1989, 28, 3033.
(12) Law, D. J.; Cavell, R. G. J. Mol. Catal. 1994, 91, 175. Cadierno,
V.; Diez, J.; Garcia-Garrido, S. E.; Garcia-Granda, S.; Gimeno, J. J.
Chem. Soc., Dalton Trans. 2002, 1465. Cadierno, V.; Crochet, P.;
Garcia-Alvarez, J.; Garcia-Garrido, S. E.; Gimeno, J. J. Organomet.
Chem. 2002, 663, 32.
(13) Gololobov, Y. G.; Kasukhin, L. F. Tetrahedron 1992, 48, 1353.
(14) Johnson, A. W. In Ylides and Imines of Phosphorus; Wiley: New
York, 1999; p 403.
This very deceiving and puzzling result prompted us
to explore several other approaches. First, as P-Cl
derivatives are usually less reactive than their P-Br
(15) Cavell, R. G.; Reed, R. W.; Katti, K. V.; Balakrishna, M. S.;
Collins, P. W.; Mozol, V.; Bartz, I. Phosphorus Sulfur Silicon Relat.
Elem. 1993, 76, 269.

Phosphine∼Iminophosphorane Bidentate Ligands
Organometallics, Vol. 24, No. 6, 2005 1067
Scheme 4
Table 1. 31P NMR and H NMR Data for
1
analogues, the synthesis of the compound resulting from
the monoaddition of “Cl2” was attempted. However,
using the usual chlorinating agents such as PCl5, CCl4,
or C2Cl6 in CH2Cl2,18 several products resulting from
partial (or total) P-C bond cleavage in dppm were
observed (as evidenced by the formation of Ph2PCl at
82 ppm by 31P NMR). Being stuck working with the
monobromo adduct 2, variation of the tertiary amine
was attempted. In fact, a clue to the understanding of
the mechanism of the reaction was brought by the
reaction of the intermediate 2 with NEt3 alone. Again
the dismutation reaction was observed, which clearly
indicated that the amine can serve as bromine transfer
agent. Two reactions were therefore in competition:
dismutation and nucleophilic substitution. To favor the
nucleophilic substitution, conditions that limited to a
minimum the presence of “bromine transfer agent” in
solution were required, namely, precipitating the amine‚
HBr salt. Several amines whose ammonium salts could
be insoluble were then tested without success: pyridine,
(2,2′)-bipy, triphenylamine, (N,N)-dimethylbenzylamine,
etc. We then envisioned the use of 2 equiv of primary
amine: one as nucleophile and the second as proton
trap. This method proved very successful in several
cases (for which the ammonium salts fell rapidly from
the solution mixture) and led to the isolation of the
desired phosphino-phosphiniminium salt in good yields
(72-90%) (method A, Scheme 4). The same dismutation
reaction occurred when the ammonium salt did not
precipitate, in particular when using the chiral R-(+)-
methylbenzylamine. A convenient, reliable method was
eventually devised (method B, Scheme 4), using 0.5
equiv of DABCO (DABCO ) diazabicyclooctane), whose
bis-HBr salt does precipitate from CH2Cl2. This allowed
us to prepare the above mentioned derivatives 3a-c in
slightly lower yields than with method A, and the new
derivatives 3d-e.
Compounds 3 and 4
31P NMR
1H NMR (bridging CH2)
δP(III)
2JPP
δP(V)
δ
2JH-P(V)
in Hz
compound in ppm in Hz in ppm
in ppm
3a
3b
3c
3d
3e
4a
4b
4c
4d
4e
-30.7
-30.4
-30.8
-30.6
-30.1
-28.9
-29.1
-27.2
-28.4
-28.7
73
73
73
73
71
51
51
52
56
49
41.5
41.8
34.5
40.7
39.7
4.8
5.2
0.4
0.5
0.8
3.96
3.92
4.21
4.08
4.06
3.25
3.30
3.08
3.02
3.12
14.0
15.6
16.5
16.4
63.5a
12.4
12.0
12.2
broad
66.4a
a ∑JH-P(V)
.
are all air and water stable, crystalline salts that can
be stored indefinitely. They have been fully character-
ized by classical NMR techniques and elemental analy-
ses. In 31P NMR, they are characterized by two sets of
doublets at about -30 ppm (2JPP ≈ 70 Hz) for the PPh2
moiety and at about +40 ppm for the iminophospho-
1
nium moiety (Table 1). In the H NMR, the signal for
the bridging methylene is observed at about 4.0 ppm
as a surprising doublet only for 3b and 3c instead of
the expected doublet of doublets (coupling with two
1
different phosphorus atoms) (Table 1). HETCOR H-
31P experiments were carried out and revealed that in
these two cases the bridging methylene hydrogens do
not couple with the PPh2 moiety but with the PPh2d
NR moiety. In the case of 3e the signal of the diaste-
reotopic methylenic protons appears as expected as a
complex ABXY spin system. In the 13C NMR the signal
of the bridging carbon atom for all compounds 3 is
observed as a doublet of doublets with a large (1JCP
≈
66 Hz) and a smaller (1JCP ≈ 34 Hz) coupling constant,
This second method, B, seems therefore general and,
more importantly, allowed for the preparation of the
optically pure derivative 3e in one pot from com-
mercially available dppm. These five new derivatives
because of the coupling with two inequivalent P atoms.
These salts could then be deprotonated in quantita-
tive yield with 1 equiv of nBuLi in THF at low temper-
ature to give the expected phosphine-iminophospho-
rane ligands 4a-e (eq 4). The isolated yields of the
ligands, after extraction in toluene and filtration of the
LiBr salts, are very good (80 to 85%). As expected, and
consistent with the known chemical behavior of imino-
phosphoranes, the ligands 4 are very sensitive. In
particular, they react with ketones, aldehydes, protic
(16) Bittner, S.; Assaf, Y.; Krief, P.; Pomerantz, M.; Ziemnicka, B.
T.; Smith, C. G. J. Org. Chem. 1985, 50, 1712. Bittner, S.; Assaf, Y.;
Pomerantz, M. J. Org. Chem. 1982, 47, 99. Bittner, S.; Pomerantz,
M.; Assaf, Y.; Krief, P.; Xi, S. K.; Witczak, M. K. J. Org. Chem 1988,
53, 1.
(17) Kirsanov, A. V. Isv. Akad. Nauk. SSSR 1950, 426.
(18) Appel, R.; Kleinstu, R.; Ziehn, K. D.; Knoll, F. Chem. Ber.-Recl.
1970, 103, 3631.

1068 Organometallics, Vol. 24, No. 6, 2005
Boubekeur et al.
Scheme 5
Table 2. 31P NMR Data for Complexes 5 and 6
solvents, and even traces of acid in chlorinated solvents.
Thus, in practice they were manipulated in THF or
toluene.
compound
δP(III) in ppm
2JPP in Hz
δP(V) in ppm
5b
5c
5d
5e
6c
6e
21.3
20.1
23.0
17.2
10.7
-5.3
33
32
34
35
12
23
49.9
44.9
49.8
42.8
46.0
46.0
D, starting from the isolated ligands 4a-e freed from
LiBr, was tested. As expected, only two sets of doublets
were observed in the crude 31P NMR spectrum, corre-
sponding to the major species obtained by method C.
The complexes were then characterized by the usual
NMR techniques and elemental analyses. In the 31P
NMR, a significant downfield shift (∆δ ≈ 50 ppm) for
each phosphorus center was observed showing the
coordination of both PPh2 and N-R moieties to the
palladium center of 5a-e (Table 2). Typically, unbound
PPh2 resonates at about -30 ppm in 3 or 4 and at +23
ppm in 5, and unbound PPh2dNR resonates at around
0 ppm in 4 and +49 ppm in 5. For platinum complex
6e, coupling of the two phosphorus atoms with the 195Pt
nucleus was observed as expected. The magnitude of
1JPt-P of 3845 Hz corresponds to a rather high s
character for the P(III) phosphorus center and is also
consistent with a structure in which the two halogens
These compounds are characterized by two sets of
doublets at about -29 ppm (2JPP ≈ 50 Hz) and about 0
ppm in the 31P NMR. As observed in Table 1, there is
only a minor change in the chemical shift of the PPh2
moiety, whereas there is a significant upfield shift going
from the salt to the neutral iminophosphorane moiety
(∆δ ≈ - 40 ppm). A decrease in the magnitude of the
coupling constant is also observed (from about 73 Hz in
1
3 to about 51 Hz in 4). In the H NMR (see Table 1),
the most significant modification is found for the bridg-
ing methylene group, whose signal is upfield shifted
(from about 4.0 ppm in 3 to about 3.1 ppm in 4). This
seems natural, as the positive charge at phosphorus
decreases going from 3 to 4. As in the case of 3e, the
two protons in 4e are diastereotopic and thus give rise
to a complex signal that is consistent with a classical
phosphorus coupled AB spin system pattern.
2
are in “cis” position. The JPt-P of 275 Hz between the
Having in hands five salts each representing a class
of substituents at the nitrogensaromatic, alkyl, benzyl
(chiral or not)swe then studied their coordinating
behavior toward group 10 metal centers. Two ap-
proaches were utilized. The first one, method C, starts
from the salt that is deprotonated in situ, then reacted
with the appropriate precursor. This method presents
both advantages of using water- and air-stable salt 3
and minimizes the loss of product via extraction of the
ligand (4) as explained above. The palladium complexes
5 starting with ligand 3 were thus synthesized as well
as a representative platinum complex 6e starting from
3e (Scheme 5).
platinum and the P(V) center also clearly indicated the
coordination of the nitrogen atom to the platinum
center. Each complex 5 precipitated out from the crude
THF solution within 15 min stirring at room tempera-
ture and was thus obtained by simple filtration. The
platinum complex 6e was synthesized according to
method C, and it also precipitated out from solution
within 10 min as pale yellow microcrystals. In this last
case only one isomer was observed in the 31P NMR
spectrum of the crude mixture. These complexes have
been fully characterized by usual NMR techniques and
elemental analyses. As a test to their robustness, and
therefore potential use in catalysis, all the complexes
were dissolved in CH2Cl2, and large amounts (over 10
equiv) of alcohol, water, or acetone were added. Impor-
tantly, in each case no decomposition occurred, suggest-
ing that coordination efficiently stabilizes the phosphino-
iminophosphorane ligands. Crystals were obtained for
complexes synthesized by either method: 5c (method
D) and 5e (method D), and 6e (method C) by slow
diffusion of hexanes in a CH2Cl2 solution of the complex.
Views of molecular structures of complexes 5c, 5e, and
6e are presented in Figures 1, 2, and 3, respectively.
Pertinent bond distances and bond angles are presented
below the structures. We also obtained crystals of the
complex 5e synthesized according to method C: 5′e. In
this complex, a 16% exchange of the Cl trans to the N
Following the progress of the reaction by 31P NMR
spectroscopy revealed that several sets of doublets
corresponding to different complexes were formed.
However these products were very similar in terms of
chemical shifts and therefore electronic environments.
Clearly, this pointed toward statistical methatetical
reactions of LiBr salts with Pd-Cl or Pt-Cl bonds. In
some instances the four potential isomers were observed
1
in the 31P NMR spectrum. However, H NMR spectra
of the crude mixture revealed every time the formation
of a “single” product. In practice then, replacement of
Cl by Br on the metal center does not influence the
electronic environment of the various protons of the
bidentate ligand. To check on this hypothesis, method

Phosphine∼Iminophosphorane Bidentate Ligands
Organometallics, Vol. 24, No. 6, 2005 1069
Figure 3. Molecular structure of complex 6e. Thermal
ellipsoids are drawn to the 30% probability level. Hydrogen
atoms were omitted for clarity. Selected bond distances (Å)
and bond angles (deg): Pt(1)-N(1) ) 2.090(4); Pt(1)-P(2)
) 2.203(1); P(1)-N(1) ) 1.599(4); P(1)-C(1) ) 1.815(5);
P(2)-C(1) ) 1.842(5); Pt(1)-Cl(1) ) 2.364(1); Pt(1)-Br(1)
) 2.4400(6); N(1)-Pt(1)-P(2) ) 89.9(1); N(1)-Pt(1)-Cl-
(1) ) 89.8(1); Br(1)-Pt(1)-P(2) ) 91.29(4); Cl(1)-Pt(1)-
Br(1) ) 89.35(4); Pt(1)-N(1)-P(1) ) 110.6(2); C(1)-P(2)-
Pt(1) ) 107.1(2); P(1)-C(1)-P(2) ) 104.6(3); N(1)-P(1)-
C(1) ) 107.8(3).
Figure 1. Molecular structure of complex 5c. Thermal
ellipsoids are drawn to the 30% probability level. Hydrogen
atoms were omitted for clarity. Selected bond distances (Å)
and bond angles (deg). Pd(1)-N(1) ) 2.076(2); Pd(1)-P(1)
) 2.2135(6); P(2)-N(1) ) 1.619(2); P(1)-C(13) ) 1.842(2);
P(2)-C(13) ) 1.800(2); Pd(1)-Cl(1) ) 2.3035(6); Pd(1)-
Cl(2) ) 2.3668(5); N(1)-Pd(1)-P(1) ) 88.90(5); P(1)-Pd-
(1)-Cl(1) ) 87.25(2); N(1)-Pd(1)-Cl(2) ) 92.39(5); Cl(1)-
Pd(1)-Cl(2) ) 91.67(2); Pd(1)-P(1)-C(1) ) 117.25(7);
C(13)-P(1)-Pd(1) ) 106.03(7); P(1)-C(13)-P(2) ) 107.1-
(1); N(1)-P(2)-C(13) ) 104.2(1).
are very different: 1.842 Å (average) for P(III)-C
compared to 1.807 Å (average) for P(V)-C. The first one
is quite long for a single P-C bond, and usually this
bond length is found when very bulky groups (such as
tBu) are bound to the phosphorus atom.19 The Pd-P of
2.228 Å (average) and Pd-N of 2.085 Å (average) are
typical values for Pd(II). The same stands for the
platinum complexes: Pt-P(III) of 2.203 Å and Pt-N of
2.090 Å. In the case of 5e, we obtained crystals using
the two methods (the X-ray structure of complex 5′e in
which a 16% exchange of the Cl trans to the N atom by
Br is presented in the ESI), and no significant change
in the bond distance for either Pd-P(III) or Pd-N was
observed. In the structure of 6e, in accordance with the
31P NMR spectrum, a single isomer was observed, in
which the Cl atom trans to the nitrogen atom is replaced
by a Br atom. This fact is in full accord with the known
trans effect and shows that the imino-phosphorane is
both a better σ and π donor than the phosphine.
Quite surprisingly, in only one case was the outcome
of the reaction different. When the reaction between 3c/
BuLi (method C, Scheme 6) (or 4c, method D, Scheme
6) and [Pt(COD)Cl2] was carried out, the expected two
sets of doublets, corresponding to a 1:1 ratio of ligand
to metal, were quickly replaced by two sets of triplets
(with platinum satellites) in the 31P NMR spectrum at
+10 ppm (1JPt-P ) 3433 Hz) and +46 ppm (2JPt-P ) 198
Hz), respectively. This pointed toward the formation of
a complex with a ligand-to-metal ratio of 2:1. This
complex rapidly precipitated out from solution and was
thus isolated by simple filtration in 45% yield (method
D, X ) Cl). In a second attempt, the ligand-to-metal
ratio of 2:1 was used and conducted to the formation of
complex 6c in 91% yield.
Figure 2. Molecular structure of complex 5e. Thermal
ellipsoids are drawn to the 30% probability level. Hydrogen
atoms were omitted for clarity. Selected bond distances (Å)
and bond angles (deg): Pd(1)-N(9) ) 2.094(2); Pd(1)-P(2)
) 2.2425(6); P(1)-N(9) ) 1.601(2); P(1)-C(1) ) 1.805(3);
P(2)-C(1) ) 1.834(2); N(9)-C(26) ) 1.499(3); Pd(1)-Cl(1)
) 2.3265(6); Pd(1)-Cl(2) ) 2.3687(7); N(9)-Pd(1)-P(2) )
89.35(6); N(9)-Pd(1)-Cl(2) ) 91.37(6); Cl(1)-Pd(1)-P(2)
) 89.04(2); Cl(1)-Pd(1)-Cl(2) ) 90.23(2); Pd(1)-N(9)-P(1)
) 106.4(1); C(1)-P(2)-Pd(1) ) 106.14(8); P(1)-C(1)-P(2)
) 104.1(1); N(9)-P(1)-C(1) ) 108.6(1).
atom by Br was found by X-ray analysis. This structure
is presented in the ESI.
These X-ray structures are in full accord with the
structures proposed based on NMR experiments. As
expected for a d8 metal center, the palladium and
platinum complexes are square planar. The PN bond
distance is normal at about 1.600 Å. Apparent from the
structures is the fact that the two PC bond distances
This complex was fully characterized by usual NMR
techniques (Table 2) and elemental analysis.
(19) Moores, A.; Ricard, L.; Le Floch, P.; Me´zailles, N. Organome-
tallics 2003, 22, 1960.

1070 Organometallics, Vol. 24, No. 6, 2005
Boubekeur et al.
Scheme 6
In 6c, the chemical shift of the PPh2 moiety was
observed at lower field compared to 6e, and the mag-
metal are not planar. The bridging carbon atom of the
ligand escapes from the plane, as evidenced by the di-
hedral angles N(2)-Pt(1)-P(3)-C(44) of +38.4° and
N(1)-Pt(1)-P(1)-C(1) of -35.0°. This leads to the po-
tential formation of diastereomers in which the two car-
bon atoms adopt either a cis or a trans position relative
to the plane of the molecule. In the crystal structure,
only the trans isomer is observed. DFT calculations are
being carried out in order to gain information on the
relative energies of the several possible isomers.
Finally, the synthesis of a representative nickel
complex was attempted according to a similar strategy
using the salt 3a and [Ni(dme)Br2] as precursor (method
C).
2
nitude of the coupling constant JP-P was divided by a
factor of 2. The different NMR spectra did not allow for
the discrimination between the two isomers (cis and
trans), but fortunately crystals were obtained by slow
diffusion of hexanes in a CH2Cl2 solution of the complex
(method C). X-ray crystal analysis definitely showed the
complex to have a cis arrangement between the two
ligands. The molecular structure is presented below.
Significant bond distances and angles are reported
below it.
After in situ formation of the iminophosphorane-
phosphine 4a by deprotonation of 3a, the metal salt was
added, which resulted in instantaneous color change
from colorless to blue. Disappearance of the 31P NMR
signals pointed toward a tetrahedral geometry at the
Figure 4. Molecular structure of complex 6c.Thermal
ellipsoids are drawn to the 30% probability level. Hydrogen
atoms were omitted for clarity. Selected bond distances (Å)
and bond angles (deg): Pt(1)-N(1) ) 2.135(2); Pt(1)-N(2)
) 2.118(2); Pt(1)-P(1) ) 2.2191(7); Pt(1)-P(3) ) 2.2251-
(8); P(2)-N(1) ) 1.614(2); P(4)-N(2) ) 1.616(3); P(1)-C(1)
) 1.834(3); P(2)-C(1) ) 1.808(3); P(3)-C(44) ) 1.837(3);
P(4)-C(44) ) 1.799(3); N(1)-Pt(1)-N(2) ) 92.9(1); N(1)-
Pt(1)-P(1) ) 84.55(7); N(1)-Pt(1)-P(1) ) 83.47(7); P(1)-
Pt(1)-P(3) ) 99.75(3); N(1)-P(2)-C(1) ) 103.2(1); N(2)-
P(4)-C(44) ) 103.1(1); Pt(1)-N(1)-P(2) ) 121.5(1); Pt(1)-
N(2)-P(4) ) 121.8(1); C(1)-P(1)-Pt(1) ) 101.8(1); C(44)-
P(3)-Pt(1) ) 100.9(1); P(1)-C(1)-P(2) ) 107.6(3); P(3)-
C(44)-P(4) ) 107.2(2).
First one can note a very minor inequivalency in the
two ligands in the structure that is obviously not
retained in solution. The Pt(1)-N(1) and Pt(1)-N(2)
bond distances (average ) 2.1265 Å) are slightly longer
than in complex 6e (2.090 Å). The same is observed in
the Pt(1)-P(2) and Pt(1)-P(3) bond distances (average
) 2.2221 Å) compared to 2.203 Å in 6e. The complex
deviates significantly from the expected square planar
geometry, as shown by the N(1)-Pt(1)-N(2) (92.9(1)°)
and P(1)-Pt(1)-P(3) (99.75(3)°) bond angles. Moreover,
the five-membered rings defined by the ligand and the
Figure 5. Molecular structure of complex 7a. Thermal
ellipsoids are drawn to the 30% probability level. Hydrogen
atoms were omitted for clarity. Selected bond distances (Å)
and bond angles (deg): Ni(1)-N(1) ) 1.987(2); Ni(1)-P(2)
) 2.3010(7); P(1)-N(1) ) 1.596(2); P(1)-C(1) ) 1.809(2);
P(2)-C(1) ) 1.838(3); Ni(1)-Br(1) ) 2.3743(5); Ni(1)-Br-
(2) ) 2.3545(4); N(1)-Ni(1)-P(2) ) 88.35(6); N(1)-Ni(1)-
Br(1) ) 106.44(7); N(1)-Ni(1)-Br(2) ) 108.68(6); Br(2)-
Ni(1)-P(2) ) 123.83(2); Br(1)-Ni(1)-P(2) ) 98.21(2);
Br(1)-Ni(1)-Br(2) ) 124.71(2); Ni(1)-N(1)-P(1) ) 121.1-
(1); C(1)-P(2)-Ni(1) ) 96.70(8); P(1)-C(1)-P(2) ) 109.2-
(1); N(1)-P(1)-C(1) ) 105.5(1).

Phosphine∼Iminophosphorane Bidentate Ligands
Organometallics, Vol. 24, No. 6, 2005 1071
[Pt(COD)Cl2],21 and [Ni(DME)Br2]22 were prepared according
to literature procedures. Nuclear magnetic resonance spectra
were recorded on a Bruker Avance 300 spectrometer operating
nickel center (paramagnetic d8 center). As for the Pd
and Pt analogues, the complex precipitated out from
solution. It was thus collected by simple filtration,
followed by washing first with THF then hexanes.
Elemental analysis confirmed the composition of the
complex. X-ray quality crystals were obtained by heat-
ing a THF suspension of the complex followed by slow
cooling. These were subjected to X-ray diffraction analy-
sis. A view of the molecular structure of 7a is presented
in Figure 5 together with significant bond distances and
angles.
As expected from the lack of NMR spectra for 7a the
geometry at the nickel center is tetrahedral (bond angles
N(1)-Ni(1)-Br of 106.44(7)° and 108.68(6)°). One can
note that the Ni(1)-N(1) (1.987 Å) is slightly shorter
than the other M-N bond distances (M ) Pd or Pt),
and the Ni(1)-P(2) is in turn slightly longer than the
other M-P. Otherwise, the metric parameters compare
with those of the Pd and Pt and do not deserve further
comment.
1
at 300 MHz for H, 75.5 MHz for 13C, and 121.5 MHz for 31P.
1H and 13C chemical shifts are reported in ppm relative to Me4-
Si as external standard. 31P are relative to a 85% H3PO4
external reference. Coupling constants are expressed in hertz.
The following abbreviations are used: b, broad; s, singlet; d,
doublet; dd, doublet of doublet; t, triplet; m, multiplet; v,
virtual.
Crystallography. Orange needles of complex 5c were
obtained by slow diffusion of THF into a solution of the
complex in dichloromethane at RT. Orange plates of complex
5e were obtained by slow diffusion of hexanes into a solution
of the complex in dichloromethane at RT. Colorless blocks of
complex 6c were obtained by slow diffusion of hexanes into a
solution of the complex in dichloromethane at RT. Yellow
plates of complex 6e were obtained by slow diffusion of THF
into a solution of the complex in dichloromethane at RT. Blue
plates of complex 7a were obtained by slow diffusion of THF
into a solution of the complex in dichloromethane at RT. Data
were collected on a Nonius Kappa CCD diffractometer using
a Mo KR (λ ) 0.71073 Å) X-ray source and a graphite
monochromator. Experimental details are described in Tables
1 and 3. The crystal structure was solved using SIR 97 and
SHELXL-97. Molecular drawings were made using ORTEP III
for Windows, then POV-Ray. CCDC-262280 to -262286 contain
the supplementary crystallographic data for this paper. These
data can be obtained free of charge at www.ccdc.cam.ac.uk/
conts/retrieving.html [or from the Cambridge Crystallographic
Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax:
+44-1223/336-033; E-mail: deposit@ccdc.cam.ac.uk].
Conclusion
We have developed a simple method for the mono-
bromation of a bisphosphine ligand. From this very
reactive intermediate, 2, two methods were devised to
obtain mixed P∼N salts. The first one, method A, gives
higher yields and relies on the reaction of the interme-
diate with 2 equiv of a primary amine. This method is
successful only if the ammonium salt precipitates from
the solution. If not, a second method, B, can be used
that depends on DABCO to trap released HBr. Either
one or the other method allowed us to prepare five
representative mixed P∼N salts, 3a-e. Starting from
these, the corresponding phosphine-iminophospho-
ranes 4a-e could be synthesized in good isolated yields
by simple deprotonation. The versatility of the method
allowed for the preparation of P∼NR ligands with R
varying from alkyl, aromatic, or benzyl. Moreover,
introduction of chirality at R was easily achieved using
commercially available R-Me-benzylamine. The coordi-
nation of these ligands with group 10 metal centers (M
) Ni, Pd, Pt) was then studied and revealed that the
complexes are quite robust (unlike the free ligands),
which is a prerequisite to their use in catalysis. Alter-
natively, a one-pot method starting from the water- and
air-stable salts, 3, to the complexes was devised. It was
higher yielding, but metathesis between halogen ligands
was observed. Altogether we have devised a straight-
forward, and amenable to large scale, new approach to
mixed P∼N bidentate ligands starting from commer-
cially available products. We are currently studying the
behavior of our Ni, Pd, and Pt (II) complexes in catalysis,
and results will be presented in due course.
General Procedure for the Preparation of Phos-
phine-Aminophosphonium Bromide 3a-e. Preparation
of DPPMBr2 2: Bromine (40 µL, 0.78 mmol) was added
dropwise to a solution of dppm (0.30 g, 0.78 mmol) in 20 mL
of dichloromethane cooled at -78 °C. The cold bath was
removed, and the solution was allowed to warm to room
temperature. 31P{1H} (CH2Cl2): δ -22.8 (d, 2JPP ) 84 Hz), 58.5
2
(d, JPP ) 84 Hz). This very sensitive derivative was used
without further purification.
Method A. The amine (1.48 mmol) was added dropwise to
a solution of dppmBr2 (0.78 mmol) in 20 mL of dichlo-
romethane cooled at -78 °C. The resulting mixture became
immediatly cloudy, and the cold bath was removed. After 2 h
of stirring at room temperature, the solution was washed twice
with water, the organic layer was dried over MgSO4, and
solvent was removed under vacuum. The residue was washed
with diethyl ether, and each derivative 3a-c was obtained as
a white solid.
2
3a: Yield 90% (421 mg). 31P{1H} (CDCl3): δ -30.7 (d, JPP
) 73 Hz, P(III)), 41.5 (d, 2JPP ) 73 Hz, P(V)). 1H (CDCl3): δ 3.72
1
1
(s, 3H, MeO), 3.89 (dd, 2H, JHP(V) ) 16.3 Hz, JHP(III) ) 0.7
3
3
Hz, PCH2P), 3.96 (dd, 2H, JHP ) 14.0 Hz, JHH ) 7.2 Hz,
3
CH2N), 6.68 (d, 2H, JHH ) 8.7 Hz, m-H (p-MeOPh)), 7.10 (d,
3
2H, JHH ) 8.7 Hz, o-H (p-MeOPh)), 7.15-7.31 (m, 10H,
Ph2P(V)), 7.43 (vtd, 4H, JHH ) 7.5 Hz, JHP ) 3.5 Hz, m-H
3
4
(Ph2P(III)), 7.61 (vdtt, 2H, JHH ) 7.5 Hz, JHP ) 1.8 Hz, p-H
3
5
(Ph2P(III)), 7.66-7.77 (m, 4H, o-H (Ph2P(III)), 8.10 (dt, 1H, 3JHH
1
)
2JHP ) 7.2 Hz, NH). 13C{1H} (CDCl3): δ 24.9 (dd, JCP
)
Experimental Section
65.3 Hz, 1JCP ) 33.6 Hz, PCH2P), 45.2 (d, 2JCP ) 2.4 Hz, CNH),
All experiments were performed under an atmosphere of
dry nitrogen or argon using standard Schlenk and glovebox
techniques. Solvents were freshly distilled under argon from
Na/benzophenone (THF, diethyl ether, hexanes), from Na
(toluene), or from P2O5 (dichloromethane, CDCl3, NEt3). Dppm,
R-(+)-methylbenzylamine, p-methoxybenzylamine, p-methyl-
benzylamine, n-butylamine, and aniline were obtained from
Aldrich and used without further purification. [Pd(COD)Cl2],20
1
55.2 (s, OMe), 113.8 (s, m-CH (p-MeOPh)), 120.2 (d, JCP
)
4
98.6 Hz, CIV-P(III)), 128.8 (d, JCP ) 7.9 Hz, p-CH (Ph2P(V))),
129.3 (d, JCP ) 12.5 Hz, m-CH (Ph2P(V))), 129.4 (s, m-CH
3
(Ph2P(III))), 129.5 (s, o-CH (p-MeOPh)), 129.7 (d, 1JCP ) 5.3 Hz,
CIV (p-MeOPh)), 132.7 (d, 2JCP ) 21.4 Hz, o-CH (Ph2P(V)), 133.3
(21) McDermott, J. X.; White, J. F.; Whitesides, J. F. J. Am. Chem.
Soc. 1976, 98, 6521.
(22) King, R. B. Organometallic Syntheses Academic 1965, Vol. 1,
(20) Drew, D.; Doyle, J. R. Inorg. Synth. 1990, 28, 348.
71.

1072 Organometallics, Vol. 24, No. 6, 2005
Table 3. Crystal Data and Structural Refinement Details for 5c and 5e
Boubekeur et al.
5c
5e
formula
Mr
C
31H27Cl2NP2Pd
C33H31Cl2NP2Pd
680.83
652.78
T [K]
150.0(1)
monoclinic
P21/c
150.0(1)
orthorhombic
P212121
cryst syst
space group
a [Å]
b [Å]
c [Å]
11.3600(10)
14.8220(10)
17.0950(10)
90.00
12.3350(10)
13.6480(10)
17.6430(10)
90.00
R [deg]
â [deg]
γ [deg]
V [Å3]
Z
105.1700(10)
90.00
90.00
90.00
2778.1(3)
4
2970.2(4)
4
F [g cm-3
]
1.561
0.998
1.523
0.937
µ [cm-1
]
cryst size [mm]
F(000)
0.22 × 0.16 × 0.14
0.20 × 0.16 × 0.05
1320
1384
index ranges
-15 15; -19 20; -24 24
phi and omega scans
29.99/I > 2σI
334; 18
-17 17; -19 19; -24 24
scan type
phi and omega scans
2θmax [deg]/criterion
no. of params refined; data/param
reflections collected
no. of indep reflns
no. of reflns used
wR2
30.02/I > 2σI
354; 20
14300
8575
8054
8575
6288
7398
0.0939
0.0819
R1
0.0341
0.0337
goodness of fit
1.019
1.008
largest diff peak/hole [e Å-3
]
1.096(0.092)/ -1.123(0.092)
0.857(0.087)/ -0.923(0.087)
Table 4. Crystal Data and Structural Refinement Details for 6c, 6e, and 7a
6c
6ea
7a
formula
C
62H54N2P4Pt,2.5
C
33H31BrClNP2Pt,C4H8O,
CH2Cl2
C
33H31Br2NNiOP2,
C4H8O
(CH2Cl2), (Br), (Cl)
Mr
T [K]
1473.72
971.01
810.16
150.0(1)
150.0(1)
150.0(1)
cryst syst
space group
a [Å]
triclinic
monoclinic
monoclinic
P21/c
P1h
P21
12.4100(10)
12.6440(10)
21.6810(10)
75.6000(10)
75.8500(10)
81.0400(10)
3178.8(4)
2
8.5010(10)
19.9970(10)
9.7900(10)
17.6700(10)
90.00
b [Å]
c [Å]
16.3370(10)
13.5450(10)
R [deg]
â [deg]
γ [deg]
V[Å3]
Z
90.00
94.0500(10)
95.4000(10)
90.00
90.00
1876.4(3)
3443.9(4)
4
2
F [g cm-3
]
1.540
3.229
1.719
1.563
3.011
µ [cm-1
]
5.134
cryst size [mm]
F(000)
0.20 × 0.20 × 0.20
0.20 × 0.18 × 0.05
0.22 × 0.18 × 0.03
1470
956
1648
index ranges
-17 12; -17 17; -30 29
phi and omega scans
30.03/I > 2σI
722; 21
-11 11; -22 20; -19 19
-25 25; -10 12; -22 22
phi and omega scans
27.47/I > 2σI
407; 14
scan type
phi and omega scans
2θmax [deg]/criterion
no. of params refined; data/param
no. of reflns collected
no. of indep reflns
no. of reflns used
wR2
30.02/I > 2σI
400; 22
25 128
10 110
14 102
18 447
10 110
7871
15 385
9116
5916
0.1012
0.1001
0.0903
R1
0.0379
0.0390
0.0350
goodness of fit
1.058
1.005
1.039
largest diff peak/hole [e Å-3
]
1.985(0.118)/ -1.871(0.118)
1.405(0.157)/ -2.506(0.157)
0.907(0.079)/ -0.669(0.079)
a Note for structure 6e, a highly disordered half CH2Cl2 molecule was accounted for using the Platon SQUEEZE function.
2
4
(dd, JCP ) 10.6 Hz, JCP ) 3.1 Hz, o-CH (Ph2P(III))), 134.4 (d,
4JCP ) 2.9 Hz, p-CH (Ph2P(III))), 135.1 (dd, 1JCP ) 12.1 Hz, 3JCP
) 8.7 Hz, CIV-P(V)), 158.9 (s, CIV-OMe). Anal. Calcd for C33H32-
BrNOP2: C, 66.01; H, 5.37. Found: C, 65.89; H, 5.62.
Hz, CH, Ph2P), 129.5 (s, CH, Ph2P), 130.9 (dd, JCP ) 9.6 Hz,
JCP ) 1.5 Hz, CH, Ph2P), 132.7 (d, JCP ) 21.4 Hz, CH, Ph2P),
133.3 (dd, JCP ) 10.6 Hz, JCP ) 1.0 Hz, CH, Ph2P), 134.4 (d,
3JCP ) 2.9 Hz, CIV (p-Me-Ph)), 135.1 (dd, 1JCP ) 11.4 Hz, 3JCP
) 8.9 Hz, CIV-P(V)), 137.2 (s, CIV-CH3). Anal. Calcd for C33H32-
BrNP2: C, 67.81; H, 5.52. Found: C, 67.49; H, 5.59.
3b: Yield 86% (390 mg). 31P{1H} (CDCl3): δ -30.4 (d, JPP
2
) 73 Hz, P(III)), 41.8 (d, 2JPP ) 73 Hz, P(V)). 1H (CDCl3): δ 2.24
(s, 3H, CH3), 3.92 (d, A2XY, 2H, 2JP(V)H ) 15.6 Hz, 3JP(III)H ) 0
Hz, PCH2P), 3.97 (dd, A2MX, 2H, 3JHH ) 7.1 Hz, 3JP(V)H ) 13.7
Hz, CH2NH), 6.96 (d, 2H, 3JHH ) 7.9 Hz, m-H (p-Me-Ph)), 7.07
(d, 2H, 3JHH ) 7.9 Hz, o-H (p-Me-Ph)), 7.15-7.81 (m, 20H, Ph2-
2
3c: Yield 92% (m). 31P{1H} (CD2Cl2): δ -30.8 (d, JPP ) 73
2
1
Hz, P(III)), 34.5 (d, JPP ) 73 Hz, P(V)). H (CD2Cl2): δ 4.21 (d,
2JHP ) 16.5 Hz, 2H, PCH2P), 6.87-7.46 (m, 19H, Ph), 7.48-
7.60 (m, 2H, Ph), 7.69-7.86 (m, 4H, Ph). 13C{1H} (CD2Cl2): δ
P), 8.08 (dd, 1H, JHH ) 7.1 Hz, JP(V)H ) 15.6 Hz, NH). 13C-
3
2
25.7 (dd, JCP ) 66 Hz, JCP ) 34 Hz, PCH2P), 119.4 (s, CIV-
P(III)), 120.1, 123.2, 128.7 (d, JCP ) 8 Hz), 128.9, 129.4, 129.5
(d, JCP ) 9 Hz), 132.7 (d, JCP ) 21 Hz), 133.1 (dd, JCP ) 4 Hz,
JCP ) 11 Hz), 134.6 (d, JCP ) 3 Hz), 134.9 (m, CIV-P(V)), 138.2
1
1
{1H} (CDCl3): δ 21.0 (s, CH3), 24.8 (dd, AXY, 1JCP ) 66.5 Hz,
1
1JCP ) 31.5 Hz, PCH2P), 45.4 (s, CNH), 120.3 (d, JCP ) 98.6
Hz, CIV-P(III)), 128.0 (s, o-CH (p-Me-Ph)), 128.8 (d, JCP ) 7.9
Hz, CH, Ph2P), 129.1 (s, m-CH (p-Me-Ph)), 129.3 (d, JCP ) 13

Phosphine∼Iminophosphorane Bidentate Ligands
Organometallics, Vol. 24, No. 6, 2005 1073
2
(d, JCP ) 3 Hz, Cipso of PhNH). Anal. Calcd for C31H28BrNP2:
o-CH (p-Me-Ph)), 128.8 (s, m-CH (p-Me-Ph)), 129.0, 131.5 (d,
JCP ) 3 Hz), 132.7 (dd, JCP ) 10 Hz, JCP ) 9 Hz), 133.5, 133.9
(d, JCP ) 20 Hz), 134.1 (d, JCP ) 21 Hz), 134.5 (s, CIV-P(V)),
C, 66.92; H, 5.07. Found: C, 66.52; H, 5.22.
Method B. A solution of DABCO (43 mg, 0.39 mmol) and
the amine (0.78 mmol) in 5 mL of dichloromethane was added
via a cannula to the solution of DPPMBr2 2 (0.78 mmol) cooled
at -78 °C. The resulting mixture became immediatly cloudy,
and the cold bath was removed. After 2 h of stirring at room
temperature, the solution was washed twice with water, the
organic layer was dried over MgSO4, and solvent was removed
under vacuum. The residue was washed with diethyl ether,
and each derivative 3d-e was obtained as a white solid.
3
1
134.6 (s, CIV-CH3), 140.6 (dd, JCP ) 7 Hz, JCP ) 16 Hz, CIV-
3
P(III)), 144.5 (d, JCP ) 23 Hz, CIV (p-MePh)). Anal. Calcd for
C33H31NP2: C, 78.71; H, 6.21. Found: C, 78.39; H, 5.98.
4c: Yield 97% (166 mg). 31P{1H} (C6D6): δ -27.2 (d, 2JPP
)
2
1
52 Hz, P(III)), 0.4 (d, JPP ) 52 Hz, P(V)). H (C6D6): δ 3.08 (d,
2
2H, JHP ) 12.2 Hz, PCH2P), 6.73-6.82 (m, 1H), 6.90-7.14
(m, 16H), 7.33-7.43 (m, 4H), 7.66-7.77 (m, 4H). 13C{1H}
1
1
(C6D6): δ 31.2 (dd, JCP ) 34 Hz, JCP ) 74 Hz), 117.9, 124.1
(d, JCP ) 19 Hz), 128.7, 128.9 (d, JCP ) 6 Hz), 129.0, 129.1,
3d: Yield 55% (256 mg). 31P{1H} (CDCl3): δ -30.6 (d, JPP
2
) 73 Hz, P(III)), 40.7 (d, 2JPP ) 73 Hz, P(V)). 1H (CDCl3): δ 0.73
(t, 3JHH ) 7.3 Hz, 3H, CH3 of nBu), 1.19 (vsext, ΣJ ) 36.8 Hz,
2H, CH2-CH3 of nBu), 1.54 (vq, ΣJ ) 29.8 Hz, 2H, CH2-CH2-
CH3 of nBu), 2.71 (vq, ΣJ ) 30.5 Hz, 2H, CH2-NH), 4.08 (d,
129.4 (d, JCP ) 2 Hz), 131.7 (d, JCP ) 3 Hz), 132.6 (dd, JCP
)
9 Hz, JCP ) 2 Hz, CIV-P(III)), 133.7 (d, JCP ) 20 Hz), 139.8 (dd,
JCP ) 16 Hz, JCP ) 7 Hz, CIV-P(V)), 152.5 (d, JCP ) 3 Hz, Cipso
of aniline). Anal. Calcd for C31H27NP2: C, 78.30; H, 5.72.
Found: C, 78.07; H, 5.71.
2JHP ) 16.4, 2H, PCH2P), 7.16-7.88 (m, 20H, Ph2P). 13C{1H}
4d: Yield 85% (144 mg). 31P{1H} (C6D6): δ -28.4 (d, 2JPP
)
1
(CDCl3): δ 13.5 (s, CH3), 19.8 (s, CH2-CH3), 24.1 (dd, JCP
)
56 Hz, P(III)), 0.5 (d, JPP ) 56 Hz, P(V)). H (C6D6): δ 0.79 (t,
3H, 3JHH ) 7.4 Hz, CH3 of nBu), 1.33 (m, 2H, CH2-CH3 of nBu),
1.77 (m, 2H, CH2-CH2-CH3 of nBu), 3.02 (b, 2H, CH2-N), 3.94
(b, 2H, PCH2P), 6.88-7.13 (m, 12H), 7.57-7.77 (m, 8H). 13C-
{1H} (C6D6): δ 14.2 (s, CH3 of nBu), 20.7 (s, CH2-CH3 of nBu),
27.1 (b, PCH2P), 36.1 (s, CH2-CH2-CH3 of nBu), 44.5 (s, CH2-
NH), 128.6, 128.7, 129.0, 132.2, 133.2 (d, JCP ) 9 Hz) 133.8
2
1
66 Hz, 1JCP ) 33 Hz, PCH2P), 32.8 (d, 4JCP ) 8 Hz, CH2-CH2-
3
1
CH3), 42.0 (d, JCP ) 3 Hz, CH2NH), 120.3 (d, JCP ) 98 Hz,
CIV-P(III)), 128.7 (d, JCP ) 8 Hz, p-CH (Ph2P(V)), 129.4 (d, JCP
) 13 Hz, m-CH (Ph2P(V)), 130.9 (dd, 3JCP ) 9 Hz, 5JCP ) 2 Hz,
m-CH (Ph2P(III)), 132.8 (d, 2JCP ) 21 Hz, o-CH (Ph2P(V)), 133.2
4
3
(dd, JCP ) 10 Hz, JCP ) 3 Hz, o-CH (Ph2P(III)), 134.4 (d, JCP
) 3 Hz, p-CH (Ph2P(III)), 135.1 (dd, 1JCP ) 12 Hz, 3JCP ) 9 Hz,
CIV-P(V)). Anal. Calcd for C29H32BrNP2: C, 64.93; H, 6.01.
Found: C, 64.41; H, 6.06.
2
4
4
1
3
(d, JCP ) 21 Hz), 137.6 (dd, JCP ) 12 Hz, JCP ) 7 Hz, CIV-
P(V)). Anal. Calcd for C29H31NP2: C, 76.47; H, 6.86. Found: C,
77.15; H, 6.94.
3e: Yield 65% (296 mg). 31P{1H} (CD2Cl2): δ -30.1 (d, 2JPP
4e: Yield 78% (134 mg). 31P{1H} (THF-d8): δ -28.7 (d, 2JPP
) 50 Hz, P(III)), 0.8 (d, 2JPP ) 50 Hz, P(V)). 1H (THF-d8): δ 1.24
(d, 3H, 3JHH ) 6.5 Hz, CH3), 3.12 (ABXY, 2H, 2JHH ) 14.5 Hz,
2
1
3
) 71 Hz), 39.7 (d, JPP ) 71 Hz). H (CD2Cl2): δ 1.55 (d, JHH
) 6.8 Hz, 3H, CH3), 4.06 (ABXY, 2H, ΣJ ) 63.5 Hz, PCH2P),
4.05 (vt, 1H, CHN), 7.09-7.56 (m, 23H), 7.75-7.88 (m, 2H),
3
3
8.21 (vt, 1H, JHH ) JHP ) 9.1 Hz, NH). 13C{1H} (CD2Cl2): δ
3
3
ΣJ ) 66.4 Hz, PCH2P), 4.33 (dq, 1H, JHH ) 6.5 Hz, JHP(V)
)
24.5 (dd, 1JCP ) 66 Hz, 1JCP ) 34 Hz, PCH2P), 25.7 (d, 3JCP
)
20.1 Hz, CHN), 6.97-7.55 (m, 21H, Ph), 7.57-7.2 (m, 4H, Ph).
13C{1H} (THF-d8): δ 30.8 (s, CH3), 31.1 (dd, 1JCP ) 32 Hz, 1JCP
8 Hz, CH3), 54.7 (s, CNH), 120.5 (dd, JCP ) 55 Hz, 1JCP ) 97
Hz, CIV-P(III)), 126.7 (s, o-CH (PhCHN)), 127.5 and 128.7 (s,
m-CH, p-CH (PhCHN)), 128.9 and 129.0 (d, JCP ) 8 Hz), 129.3
(d, JCP )13 Hz), 129.7, 132.0 (d, JCP ) 21 Hz), 133.5 and 133.6
(d, JCP ) 3 Hz), 134.5 and 134.8 (d, JCP ) 3 Hz), 135.8 (dd,
3
2
) 69 Hz, PCH2P), 55.6 (d, JCP ) 3 Hz, CHN), 125.8, 127.2,
128.1, 128.7, 128.9, 129.6, 131.3, 132.7 (d, JCP ) 9 Hz), 133.7
1
(d, JCP ) 21 Hz), 133.9 (d, JCP ) 21 Hz), 135.2 (d, JCP ) 90
Hz, CIV-P(V)), 135.3 (d, 1JCP ) 90 Hz, C′ IV-P(V)), 140.8 (vdd, ΣJCP
) 25 Hz, CIV-P(III)), 152.8 (d, JCP ) 12 Hz, CIV (Ph)). Anal.
3
1JCP ) 9 Hz, JCP ) 6 Hz, CIV-P(V)), 144.0 (d, JCP ) 3 Hz, Ci
(PhCHN)). Anal. Calcd for C33H32BrNP2: C, 67.81; H, 5.52.
Found: C, 67.63; H, 5.66.
3
3
Calcd for C33H31NP2: C, 78.71; H, 6.21. Found: C, 79.09; H,
6.28.
General Procedure for the Preparation of Palladium
and Platinum Complexes 5a-e. Method C. To a solution
of 3a-e (100 mg, 1 equiv) in 5 mL of THF cooled at -78 °C
was added dropwise n-butyllithium (1 equiv). The cold bath
was removed, and the solution allowed to warm back to room
temperature. [Pd(COD)Cl2] (1 equiv) was added, and the
solution turned immediately from colorless to orange. After
10 min of stirring, the product precipitated as an orange solid.
The latter was isolated by filtration, washed with THF then
hexanes, and dried under vacuum.
Method D. To a solution of freshly prepared 4a-e (0.171
mmol) in 5 mL of THF was added [Pd(COD)Cl2] (49 mg, 0.171
mmol). The solution turned immediately from colorless to
orange, and after 10 min of stirring, the product precipitated
as an orange solid. The latter was isolated by filtration, washed
with hexanes, and dried under vacuum.
General Procedure for the Preparation of Iminophos-
phoranes 4a-e. n-Butyllithium (1 equiv) was added dropwise
to a solution of aminophosphonium bromide 3a-e (100 mg, 1
equiv) in 5 mL of THF cooled at -78 °C. After 5 min, the cold
bath was removed and the solution was allowed to warm to
RT. The solvent was removed under vacuum and the residue
dissolved in toluene. The resulting cloudy solution was filtered
and the solvent removed under vacuum.
4a: Yield 96% (166 mg). 31P{1H} (THF-d8): δ -28.9 (d, 2JPP
2
1
) 51 Hz, P(III)), 4.8 Hz (d, JPP ) 51 Hz, P(V)). H (THF-d8): δ
2
3.25 (d, 2H, JHP ) 12.4 Hz, PCH2P), 3.71 (s, 3H, MeO), 4.13
3
3
(d, 2H, JHP ) 16.6 Hz, CH2Ph), 6.73 (d, 2H, JHH ) 8.7 Hz,
m-H (p-MeOPh)), 7.04-7.51 (m, 16H, PPh2), 7.26 (d, 2H, 3JHH
) 8.7 Hz, o-H (p-MeOPh)), 7.69-7.80 (m, 4H). 13C{1H} (THF-
1
1
d8): δ 30.8 (dd, JCP ) 66 Hz, JCP ) 32 Hz, PCH2P), 48.8 (s,
CNH), 55.4 (s, OMe), 113.6 (s, m-CH (p-MeOPh)), 126.0 (s, CIV-
P(III)), 128.9 (d, JCP ) 5 Hz, p-CH (Ph2P(V))), 129.0 (s, m-CH
5a: Yield 95% (113 mg). The complex obtained was too
poorly soluble to obtain NMR spectra. Crystals suitable for
X-ray diffraction were obtained by heating the powder 5a with
THF at 90 °C in a sealed tube over 2 days. Elemental analysis
was carried out on the complex synthesized via method D.
Anal. Calcd for C33H31Cl2NOP2Pd: C, 56.88; H, 4.48. Found:
4
(Ph2P(V))), 129.7 (s, m-CH (Ph2P(III))), 131.5 (d, JCP ) 3 Hz,
4
o-CH (p-MeOPh)), 132.7 (dd, 2JCP ) 11 Hz, 4JCP ) 3 Hz, o-CH
(Ph2P(III))), 133.9 (d, JCP ) 21 Hz, o-CH (Ph2P(V))), 139.5 (d,
2
JCP ) 22 Hz, CIV), 140.7 (dd, JCP ) 16 Hz, JCP ) 7 Hz, CIV-
P(V)), 158.7 (s, CIV-OMe). Anal. Calcd for C33H31NOP2: C, 76.29;
H, 6.01. Found: C, 75.87; H, 6.24.
1
3
C, 57.13; H, 4.66.
2
4b: Yield 92% (159 mg). 31P{1H} (THF-d8): δ -29.1 (d, 2JPP
5b: Yield 72% (84 mg). 31P{1H} (CD2Cl2): δ 49.9 (d, JPP
)
) 51 Hz, P(III)), 5.2 (d, 2JPP ) 51 Hz, P(V)). 1H (THF-d8): δ 2.27
33 Hz), 21.3 (d, 2JPP ) 33 Hz). 1H (CD2Cl2): δ 2.31 (s, 3H, CH3),
2
(s, 3H, Me), 3.30 (d, 2H, JHP ) 12 Hz, PCH2P), 4.11 (d, 2H,
3.29 (dd, 2H, 2JHP ) 20.0 Hz, 2JHP ) 10.7 Hz, PCH2P), 4.29 (d,
3
3
3JHP ) 16 Hz, CH2N), 6.97 (d, 2H, 3JHH ) 7.9 Hz, m-H (p-Me-
2H, JHP ) 9.3 Hz, CH2N), 7.00 (d, 2H, JHH ) 8.3 Hz), 7.15
3
3
Ph)), 7.26 (d, 2H, JHH ) 7.9 Hz, o-H (p-Me-Ph)), 7.15-7.52
(d, 2H, JHH ) 8.3 Hz), 7.29-7.39 (m, 4H, Ph2P), 7.45-7.72
(m, 20H, Ph2P). 13C{1H} (THF-d8): δ 21.3 (s, Me), 30.6 (dd,
1JCP ) 65 Hz, 1JCP ) 33 Hz, PCH2P), 49.0 (s, CH2N), 127.7 (s,
(m, 16H, Ph2P). 13C{1H} (CD2Cl2): δ 21.4 (s, CH3), 34.5 (broad,
PCH2P), 51.0 (d, JCP ) 23 Hz, CH2N), 125.9 (CIV-P(V)), 128.2,

1074 Organometallics, Vol. 24, No. 6, 2005
Boubekeur et al.
129.2 (d, JCP ) 9 Hz), 130.0 (d, JCP ) 12 Hz), 132.3, 133.4 (d,
JCP ) 10 Hz), 134.1 (d, JCP ) 12 Hz), 134.3 (d, JCP ) 12 Hz),
134.5, 136.5 (CIV-P(III)), 140.3 (CIV (p-MePh)). Anal. Calcd for
δ 10.7 (tt, 2JPP ) 12 Hz, 1JP-Pt ) 3433 Hz), 46.0 (tt, 2JPP ) 12
2
1
Hz, JP-Pt ) 198 Hz). H (CD2Cl2): δ 4.87 (b, 4H), 6.48-8.12
(m, 50H). 13C{1H} (CD2Cl2): δ 34.2 (m, PCH2P), 123.3, 123.8,
126.3, 127.3, 128.9, 129.4, 129.7, 132.9, 133.6, 134.8, 135.4,
146.3 (C of phenyl). Anal. Calcd (method D) for C62H54Cl2N2P4-
Pt: C, 61.19; H, 4.47. Found: C, 61.18; H, 4.56.
Platinum Complex of r-methylbenzylamine 6e. To a
solution of 3e (100 mg, 0.171 mmol) in 5 mL of THF cooled at
-78 °C was added dropwise nBuLi (107 µL). The cold bath
was removed, and the solution allowed to warm back to room
temperature. [Pt(COD)Cl2]was added in one portion, and after
10 min, a yellow crystalline solid precipitated. The solid was
isolated by filtration and washed with THF then hexanes.
Yield: 80% (110 mg). 31P{1H} (CD2Cl2): δ -5.3 (td, 2JPP ) 24
C33H31Cl2NP2Pd: C, 58.21; H, 4.59. Found: C, 58.59; H, 4.75.
2
5c: Yield 87% (97 mg). 31P{1H} (CD2Cl2): δ 20.1 (d, JPP
)
2
1
32 Hz), 44.9 (d, JPP ) 32 Hz). H (CD2Cl2): δ 3.35 (dd, 2H,
2JHP ) 11.1 Hz, JHP ) 8.7 Hz, PCH2P), 7.34-7.80 (m, 20H,
2
Ph2P), 6.80-6.87 (m, 1H, aniline), 6.91-6.97 (m, 4H). 13C{1H}
1
1
(CD2Cl2): δ 35.3 (dd, JCP ) 79 Hz, JCP ) 20 Hz, PCH2P),
123.7, 124.7 (dd, JCP ) 93 Hz, JCP ) 6 Hz, CIV-P(III)), 128.2,
128.7 (s, CIV-P(V)), 129.1 (d, JCP ) 9 Hz), 129.5 (d, JCP ) 12
Hz), 130.0 (d, JCP ) 12 Hz), 132.5 (d, JCP ) 3 Hz), 133.7 (d,
JCP ) 10 Hz), 134.1 (d, JCP ) 12 Hz), 134.6 (d, JCP ) 3 Hz),
147.5 (s, CIV-aniline). Anal. Calcd for C31H27Cl2NP2Pd: C,
1
3
1
2
2
57.03; H, 4.17. Found: C, 56.76; H, 4.16.
Hz, JP-Pt ) 3845 Hz), 46.0 (td, JPP ) 24 Hz, JP-Pt ) 275
2
5d: Yield 89% (96 mg). 31P{1H} (CD2Cl2): δ 49.8 (d, JPP
)
Hz). 1H (CD2Cl2): δ 1.60 (d, 3H, 3JHH ) 7.1 Hz, CH3), 3.19 (dd,
34 Hz), 23.0 (d, 2JPP ) 34 Hz). 1H (CD2Cl2): δ 0.64 (t, 3H, 3JHH
) 7.2 Hz, CH3 of nBu), 1.01 (vs, 2H, ΣJ ) 37.5 Hz, CH2-CH3
of nBu), 1.58 (vq, 2H, ΣJ ) 29.6 Hz, CH2-CH2-CH3 of nBu),
2H, JHP ) 9.3 Hz, JHP ) 10.6 Hz, PCH2P), 5.50 (q, 1H, JHH
) 7.1 Hz, CHN), 6.88-6.98 (m, 2H, m-H (Ph)), 7.00-7.09 (m,
1H, p-H (Ph)), 7.15-7.26 (m, 2H, o-H (Ph)), 7.30-7.79 (m, 20H,
2
2
3
2
1
3.02 (vq, 2H, ΣJ ) 22.9 Hz, CH2-N), 3.26 (d, 2H, JHP ) 9.3
Ph2P). 13C{1H} (CD2Cl2): δ 23.0 (s, CH3), 32.9 (dd, JCP ) 30
Hz, 2JHP′ ) 0 Hz, PCH2P), 7.10-7.79 (m, 20H, Ph2P). 13C{1H}
(CD2Cl2): δ 13.9 (s, CH3 of nBu), 19.7 (s, CH2-CH3 of nBu),
33.3 (b, PCH2P) 37.2 (s, CH2-CH2-CH3 of nBu), 47.9 (s, CH2-
N), 125.3, 128.7 (dd, JCP ) 8 Hz, JCP ) 20 Hz), 129.0, 129.4 (d,
JCP ) 12), 131.7, 132.7 (dd, JCP ) 3 Hz, JCP ) 13 Hz), 133.5,
133.8, CIV of Ph2P not observed. Anal. Calcd for C29H31Cl2NP2-
Pd: C, 55.04; H, 4.94. Found: C, 55.32; H, 5.11.
Hz, JCP ) 71, PCH2P), 58.2 (s, CHN), 126.5 (s, p-CH (Ph)),
1
127.6 (s, o-CH (Ph)), 128.1 (s, m-CH (Ph)), 128.8 and 128.9 (d,
JCP ) 12 Hz), 129.3 and 129.6 (d, JCP ) 13 Hz), 131.8 (b), 133.3
(d, JCP )11 Hz), 133.5 (dd, JCP ) 11 Hz, JCP ) 21 Hz), 133.9
(d, JCP ) 12 Hz), 145.8 (s, Cipso-Ph), CIV (Ph2P) not observed.
Anal. Calcd for C33H31BrClNP2Pt: C, 48.69; H, 3.84. Found:
C, 49.02; H, 3.97.
5e: Yield 93% (108 mg). Crystals suitable for X-ray diffrac-
tion were obtained by slow diffusion of THF into a solution of
5e in dichloromethane at RT. 31P{1H} (CD2Cl2): δ 42.8 (d, 2JPP
Synthesis of Nickel Complex 7a. To a solution of 3a (100
mg, 0.167 mmol) in 5 mL of THF cooled at -78 °C was added
dropwise nBuLi (104 µL, 0.167 mmol). The cold bath was
removed, and the solution allowed to warm to room temper-
ature. [Ni(dme)Br2] (51 mg, 0.167 mmol) was added, the
solution turned from colorless to blue immediately, and after
15 min, a blue solid precipitated. Filtration of the solution,
followed by solvent removal under vacuum, gave 7a. Yield:
96% (118 mg). Anal. Calcd for C33H31Br2NNiOP2: C, 53.70;
H, 4.23. Found: C, 54.00; H, 4.39.
2
1
) 35 Hz), 17.2 (d, JPP ) 35 Hz). H (CD2Cl2): δ 1.59 (d, 3H,
3JHH ) 6.9 Hz, CH3), 3.21-3.38 (m, 2H, PCH2P), 5.56 (b, 1H,
CHN), 7.00-7.96 (m, 25H, Ph2P and Ph). 13C{1H} (CD2Cl2): δ
3
23.8 (d, JCP ) 5 Hz, CH3), 34.7 (b, PCH2P), 58.9 (s, CHN),
115.1 (CIV-P(III)), 126.7, 127.7, 129.2, 129.3, 129.5 (d, JCP ) 12
Hz), 129.8 (d, JCP ) 12 Hz), 131.3, 132.1, 133.4 (d, JCP ) 11
Hz), 133.6 (d, JCP ) 11 Hz), 133.7, 133.8, 133.9, 134.0, 134.1,
134.2, 146.4 (d, 3JCP ) 3 Hz, Cipso of Ph). Anal. Calcd for C33H31-
Cl2NP2Pd: C, 58.21; H, 4.59. Found: C, 58.35; H, 4.75.
Synthesis of Platinum Complexes 6c and 6e. Method
C. Platinum complex of aniline 6c: To a solution of 3c (100
mg, 0.210 mmol) in 5 mL of THF was added dropwise nBuLi
(0.210 mmol). The cold bath was removed and the solution
allowed to warm to room temperature. [Pt(COD)Cl2] (40 mg,
0.105 mmol) was added in one portion, and after 10 min the
solution turned from yellow to colorless and became cloudy.
The solid was filtered and washed with THF then hexanes and
dried under vacuum. Yield: 91% (116 mg). 31P{1H} (CD2Cl2):
Acknowledgment. This work was supported by the
CNRS and the Ecole Polytechnique.
Supporting Information Available: CIF files and tables
giving crystallographic data for 5a, 5c, 5e, 5′e, 6c, 6e, and
7e, including atomic coordinates, bond lengths and angles, and
anisotropic displacement parameters. This material is avail-
able free of charge via the Internet at http://pubs.acs.org.
OM0490684