Direct use of chiral or achiral organophosphorus boranes as pro-ligands for transition metal catalyzed reactions

Article abstract of DOI:10.1016/S0022-328X(01)00666-0

Chiral or achiral organophosphorus borane complexes were used without isolation of the free tricoordinate P(III) ligand; thus, the borane adducts could be used either directly with metal salts to perform the catalysis, or they could be decomplexed by DABCO, or cyclooctadiene, and used in situ to generate the catalytic species. Chiral copper, palladium and rhodium complexes prepared using this method, were tested in asymmetric organometallic catalyzed 1,4-addition to 2-cyclohexenone, allylation of Schiff base and hydrogenation of α-acetamidocinnamic acid derivatives, respectively.

Full text of DOI:10.1016/S0022-328X(01)00666-0

Journal of Organometallic Chemistry 624 (2001) 333–343
www.elsevier.nl/locate/jorganchem
Direct use of chiral or achiral organophosphorus boranes as
pro-ligands for transition metal catalyzed reactions
Christophe Darcel a, El Bachir Kaloun a, Rachid Merde`s b,1, Dominique Moulin a,
a,
Nade`ge Riegel a, Serge Thorimbert b,2, Jean Pierre Geneˆt b, Sylvain Juge´ *
a Unite´ Mixte Uni6ersite´ de Cergy-Pontoise/ESCOM, ‘Synthe`se Organique Se´lecti6e et Chimie Organome´tallique’, FRE CNRS 2126,
5 mail Gay Lussac, 95031 Cergy-Pontoise, Cedex, France
b Laboratoire de Synthe`se Organique Se´lecti6e et Produits Naturels, UMR 7573, ENSCP, 11 rue Pierre et Marie Curie, 75005 Paris, France
Received 16 November 2000; accepted 4 January 2001
Abstract
Chiral or achiral organophosphorus borane complexes were used without isolation of the free tricoordinate P(III) ligand; thus,
the borane adducts could be used either directly with metal salts to perform the catalysis, or they could be decomplexed by
DABCO, or cyclooctadiene, and used in situ to generate the catalytic species. Chiral copper, palladium and rhodium complexes
prepared using this method, were tested in asymmetric organometallic catalyzed 1,4-addition to 2-cyclohexenone, allylation of
Schiff base and hydrogenation of a-acetamidocinnamic acid derivatives, respectively. © 2001 Elsevier Science B.V. All rights
reserved.
Keywords: Phosphine boranes; Rhodium catalysts; Copper catalysts; Palladium catalysts; Asymmetric synthesis; Catalysis; Addition reaction;
Hydrogenation; Allylation
Although the chirality of the ligands was generally
borne on the carbon backbone, significant strides have
1. Introduction
been achieved in the asymmetric synthesis of P-chiro-
Since the first examples of asymmetric cyclopropana-
genic phosphine ligands, owing to the use of borane
tion [1] and hydrogenation [2], transition metal catalysis
protecting groups [8–12]. Recently, P-chirogenic triva-
has become an important methodology for the prepara-
lent phosphines have received a renewed interest [13],
tion of enantiomerically enriched products from prochi-
because the chirality is closer to the metal center. Thus,
ral substrates [3]. In this area, the usefulness of chiral
new kinds of bulky [14], hybrid or chelating monophos-
P(III)-organophosphorus derivatives (diphosphines [4],
phine ligands [15,16] were studied in order to perfect
diphosphinites [5], aminophosphine phosphinites [6],
highly stereoselective catalytic species. Moreover, the
chelating monophosphines or P(III) derivatives) [7], has
design of ligands with both chirogenic carbon and
been widely demonstrated.
phosphorus groups [9g,17], allowed to increase the
number of available catalysts.
In connection with our continued work on the asym-
metric synthesis of organophosphorus compounds, we
have investigated the direct use of borane complexes in
Scheme 1.
order to avoid the use of P(III) labile ligands. The
reductive properties of the borane protecting group are
of particular interest for the preparations of Pd(0) or
Rh(I) phosphine complexes, from Pd(II) or Rh(III)
salts; Taking into account that such preparations were
currently achieved with partial oxidation of the phos-
phine into the oxide derivative [18].
* Corresponding author. Tel.: +33-1-34257066; fax: +33-1-
34257067.
E-mail address: sylvain.juge@chim.u-cergy.fr (S. Juge´).
1 Present addresses: Medjez, SFA, W. Guelma, Algeria.
2 Present address: Laboratoire de Chimie Organique de Synthe`se,
Universite´ Pierre et Marie Curie, 4 place Jussieu, BP 229, 75231 Paris
Cedex 05, France.
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)00666-0

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C. Darcel et al. / Journal of Organometallic Chemistry 624 (2001) 333–343
Table 1
Conjugate addition to 2-cyclohexenone (9) catalyzed by chiral or achiral copper(I) complexes 5
ing ligands and halide salts in appropriate stoichiomet-
ric ratios. Nevertheless, it may be pointed out that pure
compounds were often difficult to obtain, because the
reaction leads to different stoichiometric mixtures,
whose attempted purification entailed disproportions.
Furthermore, complexes often retained the solvents of
crystallization, rather difficult to remove even at high
temperature and under vacuum [23].
Scheme 2.
Before the recent development of the asymmetric
conjugate additions catalyzed by chiral phosphine or
phosphinite copper complexes [24], we have investi-
gated their preparation from organophosphorus borane
derivatives. When phosphine boranes 1 were heated at
50°C in THF with Cu(I) salts, no reaction occurred, but
with CuX2 2, the corresponding organophosphorus
copper(I) complexes 5 were obtained (Scheme 2).
Thus, heating the methyldiphenylphosphine borane
1a with one equivalent of copper dichloride, in THF at
50°C for 48 h, led to the copper complex 5a, isolated by
Scheme 3.
To the best of our knowledge, few examples of direct
reaction of organophosphorus boranes with transition
metal complexes have been reported until now: We can
underline the preparation of tungsten pentacarbonyl
complexes [19], or palladium–rhodium catalysts grafted
on a polypyrrole matrix [20], and some examples in
asymmetric catalysis [21,22].
We report herein the preparation of new copper,
palladium and rhodium complexes 5–7, from chiral
and achiral organophosphorus boranes 1 and the corre-
sponding transition metal salts 2–4 (Scheme 1). Then,
the catalytic properties of the complexes 5–7 were
investigated in asymmetric 1,4-addition, allylation and
hydrogenation reactions.
1
chromatography in 78% yield. H-NMR and elemental
analysis indicated the presence of solvent and a phos-
phorus–copper ratio of 3 which were in good agree-
ment with the structure (MePh2P)3CuCl for 5a.
Comparatively, direct complexation of CuCl with the
free phosphine gave a similar complex with a copper–
ligand ratio of 3. When the reaction was carried out
with dppe(BH3)2 1b or various copper (II) salts 2
(nitrate, sulfate, acetate, halide), complexes 5 were ob-
tained in low to good yields. Nevertheless, the isolated
complexes were unstable and their NMR analyses re-
vealed very often different stoichiometries and the pres-
ence of solvent.
2. Results and discussion
2.1. Preparation of phosphine copper(I) complexes
The Cu(I) complexes were usually prepared by mix-

C. Darcel et al. / Journal of Organometallic Chemistry 624 (2001) 333–343
335
2.2. Copper-catalyzed conjugate addition of
organometallic reagents to 2-cyclohexenone
In the presence of the complex 5a (10% mol), previ-
ously prepared in situ on heating CuCl2 with
MePh2PBH3 1a, addition of n-butylmagnesium bro-
mide to 2-cyclohexenone (9) at −40°C for 1 h, gave
the 3-butylcyclohexanone 10a in 70% yield (Scheme 3;
Table 1, entry 1).
Following the same methodology, several chiral cop-
per complexes 5 prepared from P-chirogenic organo-
phosphorus boranes 1c–e, were used to promote the
conjugate addition. The results are summarized in
Table 1.
When oxazaphospholidine, aminophosphine or phos-
phinite boranes 1c–e were used to generate the copper
catalysts from CuCl2, the reaction of 9 with n-butyl-
magnesium bromide, provides the 1,4-addition products
10a in 61–99% yields (entries 2, 4, 5). Unfortunately,
Fig. 1.
the enantiomeric excesses of 10a determined from 13C-
NMR data of the aminal derivative [25], were very low
(e.e.B5%). Nevertheless, in the case of the addition of
phenylmagnesium bromide, the oxazaphospholidine bo-
rane 1c led to the 3-phenylcyclohexanone 10b with 18%
e.e. (entry 3).
2.3. Asymmetric allylation catalyzed by chiral
organophosphorus palladium(0) complexes
We have described previously the direct use of phos-
phine boranes grafted on polypyrrole, in order to gen-
erate supported palladium catalysts applied to allylic
alkylation and Heck coupling reactions [20]. Effectively,
a simple addition of Pd(OAc)2 to a solution of
triphenylphosphine borane in THF, led to the forma-
tion of Pd(0) catalyst. Although the mechanism of the
formation of the Pd(0) complex 6 was unknown, it
could be explained by the reduction of Pd(II) into Pd(0)
by the borane, and simultaneously deprotection of the
phosphine ligand (Scheme 4).
Scheme 4.
Scheme 5.
Table 2
Pd(0) catalyzed asymmetric allylation of the Schiff base 11

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C. Darcel et al. / Journal of Organometallic Chemistry 624 (2001) 333–343
The preparation of rhodium complexes 7 was also
investigated, by reacting directly the rhodium(III)
trichloride 4 with phosphine boranes 1 (Scheme 6b).
Thus, the heating RhCl3 in refluxing ethanol with 3
equiv. of methyldiphenylphosphine borane 1a, pro-
vided two complexes which were characterized by 31P-
NMR spectroscopy. The 31P{1H}-NMR spectrum of
the crude mixture after 10 min of reaction, displayed
two groups of signals (Fig. 2a). The signals at −1.86
Scheme 6.
1
2
ppm (td, JPRh=113, JPP=24.5 Hz) and −4.27 ppm
New P-chirogenic organophosphorus borane com-
pounds were investigated as proligands for the in situ
preparation of chiral Pd(0) catalysts, and used in the
asymmetric allylation of the prochiral Schiff base 11
(Scheme 5) [26]. The synthesis of allylglycine 13, was
achieved using the carbanion of 11 generated by the
action of LiHMDS, and a catalyst with a phospho-
rus–Pd(0) ratio of 4. The results are summarized in
Table 2.
When DIPAMP (R,R)-1f% was used as ligand, the
allylic alkylation afforded the expected product (R)-12
in 70% yield, after 1.5 h at −35°C (Table 2, entry 1).
A very low enantiomeric excess (10% e.e.) was ob-
tained in this case. When the DIPAMP diborane com-
plex (R,R)-1f was used to generate the palladium
catalyst, the compound 12 was obtained in similar
yield and enantioselectivity, 66% and 13% e.e. respec-
tively (entry 2). More interestingly, the modified (S,S)-
DIPAMP pro-ligand 1g, having a three atom bridge
between the two phosphorus, gave the allylated
product 12 with a (S)-configuration and 43% e.e. (en-
try 3). This result can be explained by the conforma-
tion of the six membered chelated palladium ring (I),
which must give a better spatial interaction at the
p-allyl end with the prochiral nucleophile, than the
corresponding DIPAMP 1f% adduct (Fig. 1). It may be
pointed out that this effect is in good agreement with
the ‘pocket model’ proposed by Trost [27].
1
2
(dd, JPRh=85, JPP=24.5 Hz), were assigned to the
phosphorus (ii) and (i) respectively in the Rh(III) hex-
acoordinated intermediate 14, while the tetracoordi-
nated Rh(I) complex 7b gave rise to the signals at
1
2
+33.15 ppm (td, JPRh=138, JPP=27 Hz), and +
1
2
20.45 ppm (dd, JPRh=98, JPP=27 Hz), correspond-
ing to phosphorus (ii) and (i), respectively. No signal
was observed in the 30 ppm region, indicating that
methyl diphenyl phosphine oxide was not produced
under these conditions. After longer heating, the sig-
nals at higher field decreased in favour of the 31P-
NMR pattern at +20 and +33 ppm. Indeed, this
spectrum was in very good agreement with the forma-
tion of the Rh(III) hexacoordinated intermediate 14,
which then led to the Rh(I) complex 7b (Fig. 2a).
On the other hand, reaction of RhCl3 with the dibo-
rane complex (S,S)-1i was carried out according to a
second method, using cyclooctadiene as borane trap-
ping reagent. It is noteworthy that 1i, prepared by
oxidative coupling of methylphosphinite borane (S)-1h
(Scheme 7) [9e], provided a rare example of a C2-sym-
metric P-chirogenic bidendate ligand, bearing phos-
phorus heteroatom bonds.
Heating the diphosphinite borane 1i with one equiv-
alent of RhCl3 and cyclooctadiene (4 equiv.), in reflux-
ing THF for 19 h, produced a yellow solid after
evaporation of the solvent. The 31P-NMR spectrum of
the solid obtained after cristallization in ethanol, dis-
Finally, the mono and diphosphinite boranes 1h and
1i also exhibited their efficiency in promoting the pal-
ladium catalysis, entailing allylic alkylation of the
Schiff base 11 in yields up to 80% (entry 4,5); But in
this case also, very low enantioselectivities were ob-
served.
1
played a signal at 153.6 ppm (d, JPRh=129 Hz) car-
acteristic of a rhodium(I) complex, having certainly
the dimeric structure 7c (Fig. 2b).
2.5. Asymmetric hydrogenation catalyzed by
organophosphorus rhodium(I) complexes
2.4. Preparation of rhodium(I) complexes
The asymmetric hydrogenation induced by the
rhodium(I) catalysts 7, prepared from various P-chiro-
genic organophosphorus boranes 1, was tested with
the a-acetamidocinnamic acid derivatives 15 (Scheme
8). After 24 h under 10 atm of H2, the N-acetylpheny-
lalanine derivatives 16a, b were obtained quantitatively
(Table 3).
The hydrogenation of 15a in MeOH under 10 atm
of H2, in presence of the catalyst prepared from
DIPAMP (S,S)-1f% and [Rh(COD)Cl]2, led to the
phenylalanine derivative (R)-16a after 18 h, with 87%
The Wilkinson catalyst Rh(PPh3)3Cl 7a, certainly
the most representative of the transition metal com-
plexes used for homogeneous catalysis, is usually pre-
pared with an excess of triphenylphosphine (4 equiv.
or more), in order to reduce the Rh(III) chloride into
Rh(I) species (Scheme 6a) [18a]. In fact, a part of the
phosphine was transformed into the oxide derivative,
involving the decomposition of a dichlorotriphenyl
phosphorane intermediate, in ethanol.

C. Darcel et al. / Journal of Organometallic Chemistry 624 (2001) 333–343
337
Fig. 2. 31P-NMR spectra of the RhCl3 mixture, heated after: (a) 10 min in EtOH at 78°C with MePh2PBH3 (1a). (b) 19 h in refluxing THF with
diborane 1i.
1f was used to form the catalyst by reaction with
RhCl3. Using the diphosphine borane (R,R)-1j, pre-
pared by grafting two (R)-methyl phenyl o-tolyl phos-
phine boranes 1n with dichloro diphenylsilane [9e], the
Scheme 7.
resulting catalyst with RhCl3, gave the phenyl alanine
derivative (S)-16a with 52% e.e.(entry 3).
We had reported the high stereoselectivity of the
catalyzed hydrogenation of 15b with the aminophos-
phine-phosphinite (AMPP) 1k, as rhodium ligand (99%
e.e., entry 4) [9g]. Unfortunately, when the correspond-
Scheme 8.
ing AMPP diborane 1l was heated with RhCl3 in
refluxing ethanol, a degradation of the ligand occurred
as observed by 31P-NMR analysis, and the catalyzed
hydrogenation of 15a gave unreproducible results.
Likewise, when the decomplexation of AMPP diborane
e.e. (Table 3, entry 1; see Ref. [2d]: 94% e.e., with run
in MeOH). (R)-16a was obtained with a similar result
(90% e.e., entry 2), when the DIPAMP diborane (S,S)-

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C. Darcel et al. / Journal of Organometallic Chemistry 624 (2001) 333–343
Table 3
Rh(I) catalyzed asymmetric hydrogenation of substrate 15a,b
On the other hand, palladium complexes were simply
generated by mixing Pd(OAc)2 with organophosphorus
boranes; Their catalytic properties were studied in the
asymmetric allylation of the Schiff base 11. Although,
DIPAMP 1f% or its borane adduct 1f, entailed low e.e.,
however promising asymmetric induction has been ob-
tained with the modified DIPAMP diborane 1g, since
the allylated Schiff base 12 was obtained with 43% e.e.
Finally, rhodium(I) complexes were prepared either
on heating organophosphorus boranes with RhCl3 in
refluxing ethanol, or in the presence of cyclooctadiene;
Better results were obtained by carrying out the borane
decomplexation in situ. Several chiral rhodium cata-
lysts, prepared from P-chirogenic phosphorus borane
complexes, have been investigated for the asymmetric
hydrogenation of a-acetamido cinnamic acid deriva-
tives 15b, to yield the phenylalanine derivatives 16b
with 96% e.e.
1l was carried out in situ with DABCO, in the presence
of the precatalyst [Rh(COD)Cl]2 and AgBF4, the cata-
lyzed hydrogenation led to a poor result (8% e.e., entry
5). But, when the catalyst was prepared in a one pot
procedure, with three consecutive steps: decomplexa-
tion of 1l by DABCO, addition of [Rh(COD)Cl]2 and
AgBF4, and then addition of ether to precipitate the
rhodium complex, the hydrogenated product (S)-16b
was obtained with 96% e.e. (entry 6).
3. Conclusions
A new versatile method for generating transition
metal catalysts from organophosphorus borane adducts
has been investigated. The preparation of copper (I)
complexes was described for the first time, by direct
reaction of copper (II) salts with phosphine boranes.
Chiral copper complexes, prepared from P-chirogenic
phosphine boranes, have been tested in the asymmetric
conjugate addition of organomagnesium reagents to
2-cyclohexenone, entailing enantioselectivities lower
than 18%.
Consequently, this transition metal complex synthe-
sis, involving easily handled and stable organophospho-
rus boranes, as pro-ligands, provides
a suitable
methodology towards asymmetric catalysis. New P-chi-
rogenic phosphorus ligands, synthesized via their bo-
rane complexes, which are very difficult to isolate in

C. Darcel et al. / Journal of Organometallic Chemistry 624 (2001) 333–343
339
tricoordinate form, could now be tested in asymmetric
catalysis. Therefore, very promising developments of
such transition metal catalysts can be expected.
phosphine and borane dimethylsulfide in THF, then
recrystallized in cyclohexane or toluene respectively (1a:
m.p.=55°C; 1b: m.p.=166–168°C). The complexes
(2S,4R,5S)-(−)-3,4-dimethyl-2,5-diphenyl-1,3,2-oxaza
phospholidine borane 1c, (Sp)-(+)-N-methyl-N-
[(1S,2R)-(1-hydroxy-2-methyl-1-phenyl-2-propyl)]-
aminomethylphenyl phosphine borane 1d, (S)-(+)-[(O-
methyl)-o-anisylphenylphosphinite] borane (1e), (R,R)-
(+)-1,2-bis(o-anisylphenylphosphino borane) ethane 1f
and (R,R)-(−)-1,2-bis(o-anisylphenylphosphino)ethane
1f%, were prepared from the (+)-ephedrine according to
the published procedure [9b,9f]. Likewise, (S)-(−)-
[(O-methyl)-methylphenylphosphinite]borane 1h, (S,S)-
(−)-1,2-bis(o-anisyl phenylphosphinoborane)ethane 1f,
and (S,S)-(+)-1,2-bis(o-anisylphenylphosphino)ethane
1f%, were obtained starting from the (−)-ephedrine.
(Rp)-N-Methyl-N-{(1R,2S)-[2-(diphenylphosphinito)-
1 - methyl - 2 - phenyl]ethyl}amino - o - anisylphenylphos-
phine 1k and its diborane complex 1l, were prepared as
previously described [9g].
4. Experimental
4.1. General
All reactions were carried out under argon or nitro-
gen atmosphere in dried glassware. Solvents were dried
and freshly distilled under nitrogen atmosphere over
sodium–benzophenone for THF, toluene and benzene,
P2O5 for CH2Cl2 and sodium ethylate for EtOH. Hex-
ane, ethanol and isopropanol for HPLC were of chro-
matographic grade and used without further
purification. Methyllithium, s-butyllithium, CuCl2,
CuBr2, Pd(OAc)2, RhCl3, BH3.S(CH3)2 in toluene,
diphenylmethylphosphine and 1,2-bis(diphenylphos-
phino)ethane (dppe), DABCO, a-acetamidocinnamic
acid 15a, were purchased from Aldrich, Acros and
Avocado. The [Rh(COD)Cl]2 complex was prepared
according to the previously described procedure [28],
and used without further purification. Methyl a-acet-
amido cinnamate 15b was obtained by reaction of 15a
with methyl iodide, in the presence of K2CO3 [29].
Commercially available bromobutane, and bromoben-
zene, were distilled before use. Flash chromatography
was performed on silica gel (60ACC, 35–70 mm; SDS)
or neutral aluminium oxide (Carlo Erba; ref. 417241).
HPLC analyses were performed on a Gilson 305/306
chromatograph equipped with an UV 116 detector. All
NMR spectra data were recorded on Bruker DPX 250
4.2.1. (S,S)-(−)-Bis[(o-anisylphenylphosphinoborane)
methylene]dimethylsilane 1g
In a 50 ml two-necked flask equipped with a mag-
netic stirrer and an argon inlet, 1 mmol of (S)-(+)-o-
anisylmethylphenylphosphine borane 1m [9b] was
dissolved in 1 ml of dry THF at −78°C. Then, 1 mmol
of s-butyllithium was slowly added under stirring. The
temperature of the mixture was kept at −78°C for 15
min, then allowed to warm at −30°C. After 1 h in
these conditions, the dimethyldichlorosilane (0.5 mmol)
was added and the mixture was hydrolyzed at 0°C.
After removal of the THF, the aqueous layer was
extracted with CH2Cl2. The solvent was removed and
the residue was purified by chromatography on silica
gel with a mixture toluene–hexane (3:1) as eluent (85%
yield).
1
spectrometer using TMS as internal reference for H
(250 MHz) and 13C-NMR (62.9 MHz) and 85% phos-
phoric acid as external reference for 31P-NMR (101.3
MHz). The l 31P-NMR chemical shifts are countered
negatively at higher field than phosphoric acid. IR
spectra were recorded on a Perkin–Elmer 1600 FT and
a Bruker Equinox 55. Melting points were determined
on a Bu¨chi melting point apparatus and are uncor-
rected. Optical rotations were measured at 20°C with a
Perkin–Elmer 241 polarimeter. Mass spectra analyses
and exact mass were performed on a JEOL MS 700 at
the Mass Spectroscopy Laboratories of ENS, Paris.
The major peak m/z is mentioned with the intensity as
a percentage of the base peak in brackets. Elemental
analyses were determined with a precision superior to
0.4% at the Microanalysis Laboratories of Pierre and
Marie Curie University, Paris.
White solid: m.p. 139–140°C (hexane); [h] 2D0 = −
69.1 (c=0.7, CHCl3); IR (KBr, w cm−1): 3052, 2972,
2403 (s, B–H), 2365 (s, B–H), 1589, 1478, 1431, 1276,
1
1249; H-NMR (CDCl3): l 8.13 (2H, ddd, J=1, J=7,
J=14 Hz, H arom), 7.80–7.72 (4H, m, H arom), 7.64
(2H, t, J=8 Hz, H arom), 7.54 (6H, sl, H arom), 7.22
(2H, t, J=7.5 Hz, H arom), 6.99 (2H, dd, J=8, J=3
2
Hz, H arom), 3.79 (6H, s, CH3O), 2.38 (2H, dd, JPH
=
=
2
18, 1JHH=14 Hz, PCHHSi), 1.80 (2H, t, JPH
1JHH=13.5 Hz PCHHSi), 1.9–0.4 (6H, ql, JHH=49
Hz, BH3), 0.0 (6H, s, (CH3)2Si); 13C-NMR (CDCl3): l
161.33 (C arom), 135.89 (d, JPC=15 Hz, C arom),
133.61 (C arom), 132.7 (C arom), 130.88–127.96 (C
arom), 120.93 (d, JPC=12 Hz, C arom), 118.13 (d,
1
J
PC=53 Hz), 110.99 (C arom), 55.20 (CH3O), 11.13 (d,
1JPC=23 Hz, PCH2Si), 0.13 (CH3Si); 31P-NMR
4.2. Preparation of the organophosphorus boranes 1
1
(CDCl3): l +12.9 (d, JPB=58 Hz); HRMS Calc. for
C30H40B2O2P2Si [M+]: 544.2459; Found: 544.2435;
Anal. Calc. for C30H40B2O2P2Si: C, 66.20; H, 7.41;
Found: C, 66.06; H, 7.42%.
The diphenylmethylphosphine borane 1a and 1,2-
bis(diphenylphosphino)ethane diborane 1b were pre-
pared as described [20b], from the corresponding

340
C. Darcel et al. / Journal of Organometallic Chemistry 624 (2001) 333–343
4.2.2. (S,S)-(−)-1,2-Bis(methoxyphenylphosphinoborane)
ethane 1i
IR (KBr, w cm−1): 3058, 2367 (B–H), 2339 (B–H),
1592, 1454, 1437; H-NMR (CDCl3): l 7.95–7.67 (2H,
1
The diphosphinite diborane 1i was prepared by cou-
pling the anion derived from the (S)-(−)-[(O-methyl)
methylphenylphosphinite) borane 1h, according to the
procedure described for the DIPAMP diborane 1f [9b].
In a 50 ml two-necked flask equipped with a mag-
netic stirrer and an argon inlet, 1 mmol of 1h was
dissolved in 2 ml of dry THF at −78°C. Then, 1 mmol
of s-butyl lithium was slowly added under stirring. The
temperature of the mixture was kept at −78°C for 15
min, then allowed to warm at −30°C. After 1 hour in
these conditions, dry CuCl2 (1.1 mmol) was added and
the temperature was brought to 0°C and allowed under
air. After 12 hours, the mixture was hydrolyzed by HCl
10%, and extracted with CH2Cl2. The solvent was re-
moved and the residue purified by chromatography on
silica gel with a mixture of hexane–CH2Cl2 (6:4) as
eluent (88% yield).
m, H arom), 7.63–7.43 (6H, m, H arom), 7.41–7.24
(1H, m, H arom), 2.23 (3H, s, CH3Ph), 1.87 (3H, d,
2JPH=10 Hz, CH3P), 1.4–0.3 (3H, m, BH3); 13C-NMR
(CDCl3): l 132.39–125.84 (C arom), 12.48 (d, 1JPC=42
1
Hz, PCH3); 31P-NMR (CDCl3): l +10.5 (d, JPB=71
Hz); MS (DCI, CH4) m/z (relative intensity): 214 (100),
199 (90), 165 (90), 121 (100), 103 (80), 91 (100), 77 (80);
Anal. Calc. for C14H18BP 228.08: C, 73.73; H, 7.95;
Found: C, 73.89; H, 7.94%.
4.2.5. Diphosphine diborane 1j
White solid: m.p. 197°C (toluene–hexane 7:3); Rf=
0.14 (toluene–hexane 3:1); [h] 2D0 = −3.9 (c=0.8,
CHCl3); IR (KBr, w cm−1): 3053, 2368 (B–H), 2343 (s,
1
B–H), 1428, 1108, 1062, 697; H-NMR (CDCl3): l 7.63
(2H, dd, J=3, J=2 Hz, H arom), 7.44–7.18 (20H, m,
H arom), 7.04–6.98 (6H, m, H arom), 2.77–2.45 (4H,
m, PCH2Si), 1.99 (6H, s, CH3Ph), 1.8–0.4 (6H, m,
BH3); 13C-NMR (CDCl3): l 141.6 (C arom), 135.3–
125.6 (C arom), 21.7 (CH3Ph), 9.12 (PCH2Si); 31P-
White solid: m.p. 114–115°C (hexane); Rf=0.48
(hexane–CH2Cl2 55:45); [h] 2D0 = −115.1 (c=1.3,
CHCl3); IR (KBr, w cm−1): 3058, 2941, 2844, 2370
1
1
(B–H), 1438, 1114, 1069, 1034; H-NMR (CDCl3): l
NMR (CDCl3): l +15.5 (d, JPB=36 Hz); MS (EI)
7.73–7.59 (4H, m, H arom), 7.59–7.45 (6H, m, H
arom), 3.52 (6H, distorted d, JPH=12 Hz, POCH3),
2.17–2.01 (2H, m, PCHH), 1.98–1.85 (2H, m, PCHH),
1.4–0.0 (6H, q, 1JBH=94 Hz, BH3); 13C-NMR
(CDCl3): l 132.82 (d, JPC=2 Hz, C arom), 132.44 (C
arom), 132.12 (d, JPC=2 Hz, C arom), 131.34 (d,
m/z (relative intensity): 622 (5), 609 (35), 531 (37), 517
(100), 409 (15), 304 (18), 259 (30), 197 (15), 91 (60);
HRMS (DCI, CH4) Calc. for C40H41BP2Si [M+−BH3]:
622.2546; Found: 622.2537; Anal. Calc. for
C40H44B2P2Si (636.4): C, 75.49; H, 6.97; Found: C,
75.10; H, 6.97%.
3
J
PC=11 Hz, C arom), 130.93 (distorted d, JPC=11 Hz,
C arom), 130.62 (d, JPC=11 Hz, C arom), 129.72 (d,
PC=55 Hz, C arom), 128.95–128.63 (C arom), 54.06
4.3. Preparation and applications of organophosphorus
copper(I) complexes 5
J
(s, OCH3), 23.14 (d, JPC=44 Hz); 31P-NMR (CDCl3):
l +118.4 (d, 1JPB=58 Hz); MS (DCI, CH4) m/z
(relative intensity): 302 (1), 270 (10), 229 (4), 192 (100),
180 (100), 148 (20), 123 (100), 77 (45), 58 (100); Anal.
Calc. for C16H26B2O2P2 (333.95): C, 57.55; H, 7.85;
Found: C, 57.23; H, 7.78%.
1
4.3.1. Preparation of copper(I) complexes 5 from
phosphine boranes 1
4.3.1.1. Typical procedure. In a 50 ml two-necked flask
equipped with a magnetic stirrer and an argon inlet, 1
mmol of phosphine borane 1 was dissolved in 3 ml of
dry THF. Then, 1 mmol of CuX2 (2 mmol for the dppe
diborane 1b) was added under stirring, and the mixture
was heated at 50°C for 48 h. After cooling and filtra-
tion, the organic solvent was removed and the residue
was purified by chromatography on silica gel using a
mixture of toluene–EtOH as eluent.
4.2.3. (R,R)-(−)-Bis[(o-tolylphenylphosphino
borane)methylene] diphenylsilane 1j
The diphosphine diborane 1j was prepared by cou-
pling the anion derived from the (R)-(−)-
methylphenyl-o-tolyl phosphine borane 1n, with
dichlorodiphenylsilane (0.5 equiv.), according to the
same procedure described above for 1g (yield 80%).
4.3.1.2. (CH3PPh2)3CuCl complex 5a. Colorless solid
1
4.2.4. Synthesis of (R)-(−)-methylphenyl-o-tolyl
phosphine borane (1n)
(78% yield); Rf=0.5 (toluene–iPrOH 96:4); H-NMR
(CDCl3): l 7.4 (30H, m, H arom), 3.6 (8H, m, solvent),
2
The (R)-(−)-methylphenyl-o-tolylphosphine borane
1n was prepared from the starting complex 1c [9b], by
opening the oxazaphospholidine ring with o-tolyl
lithium reagent, then acid methanolysis of the
aminophosphine intermediate, and finally substitution
by methyllithium (overall yield \70%). Oil; Rf=0.60
(toluene –hexane 8:2); [h] 2D0 = −31.1 (c=0.8, CHCl3);
1.9 (9H, d, JPH=16 Hz, PCH3), 1.8 (12H, m, solvent);
Anal. Calc. for (CH3PPh2)3CuCl, 4 EtOH (881): C,
64.0; H, 6.8; O, 7.2; Cl, 4.0; P, 10.5; Found: C, 63.6; H,
6.3; O, 8.6; Cl, 4.7; P, 11.4%.
When methyl diphenylphosphine 1a (4 equiv.) was
complexed in EtOH by CuCl, colorless crystals was
obtained after cooling (yield 79%); Anal. Calc. for

C. Darcel et al. / Journal of Organometallic Chemistry 624 (2001) 333–343
341
(CH3PPh2)3CuCl (699.7) [23a]: C, 66.95; H, 5.62; Cl,
5.07; P, 13.28; Found: C, 67.17; H, 5.65; Cl, 5.38; P,
13.12%.
to the catalyst solution, cooled at the same tempera-
ture. The new mixture was stirred at −40°C and the
reaction was monitored by TLC. After 3 h, the reaction
was hydrolyzed by 2 ml of saturated NH4Cl solution
and allowed to warm at r.t.. The mixture was extracted
with 2×10 ml of ether. The combined organic extracts
were dried with MgSO4, and after filtration, the organic
solvent was removed under vacuum. The residue was
purified by chromatography on silica gel using a mix-
ture of hexane–AcOEt 4:1 as eluent, to yield the ally-
lated Schiff base 12 as a colorless oil.
4.3.2. Catalyzed conjugate addition of organomagnesium
reagent with 2-cyclohexenone 9, by copper(I) complexes
5 prepared from phosphine boranes 1
In a 10 ml flask equipped with a magnetic stirrer and
an argon inlet, 0.4 mmol of monophosphine borane
1a,c–e was dissolved in 1 ml of dry THF. Then, 0.2
mmol of CuCl2 was added under stirring, and the
mixture was heated at 50°C for 12 h. After cooling, the
copper complex was poured in a 100 ml two-necked
flask with 40 ml of toluene.The solution was cooled at
−40°C and the 2-cyclohexenone (2 mmol) was added.
Then, two equivalents of n-butyl (or phenyl) magne-
sium reagent was slowly added under stirring. After 1 h
in these conditions, the reaction was allowed to warm
at room temperature (r.t.) and hydrolyzed with 20 ml of
HCl 5 M. The mixture was extracted with 2×50 ml of
ether, and the combined organic extracts were washed
with H2O and dried with MgSO4. After filtration, the
organic solvent was removed and the residue was
purified by chromatography on silica gel using a mix-
ture of pentane–ether 8:2 as eluent, to give the 3-butyl
(or 3-phenyl) cyclohexanone 10a (or 10b) in 61–84%
yields. The enantiomeric excesses were determinated by
13C-NMR of the aminal derived with (R,R)-1,2-
diphenylethylene diamine [25].
1H-NMR (CDCl3): l 7.8–7.2 (10H, m, H arom),
6.0–5.5 (1H, m, CH2ꢀCH), 5.3–4.9 (2H, m, CH2ꢀCH),
4.2 (1H, t, CHCO2CH3), 3.75 (3H, s, CO2CH3), 2.65
(2H, m, CH2ꢀCHCH2).
The enantiomeric excess of 12 was determined by
HPLC on a Pirkle I column, with hexane–THF 95:5 as
eluent (flow rate 1 ml min−1; UV detection: u=254
nm; (R) enantiomer tR=9.3 min, (S) enantiomer tR=
9.7 min).
4.5. Preparation and applications of organophosphorus
rhodium (I) complexes from phosphine boranes 1
4.5.1. Typical procedure
In a 10 ml flask equipped with a stirrer, a condenser
and an argon inlet, 0.03 mmol (6 mg) of RhCl3 and
0.045 mmol (1.5 equiv., 22 mg) of DIPAMP(BH3)2 1f
were dissolved in 1 ml of dry ethanol. The mixture was
then heated at reflux for 1 h. After cooling, the solvent
was removed under vacuum. The precatalyst was used
without further purification.
4.3.2.1. 3-n-butylcyclohexan-1-one 10a. 1H-NMR
(CDCl3): l 2.45–0.72 (m); 13C-NMR (CDCl3): l 212.22
(CO), 48.27, 41.56, 39.09, 36.32, 31.35, 28.87, 25.34,
22.74, 14.04.
4.5.2. Alternati6e procedure using COD as borane trap-
ping reagent
4.3.2.2. 3-phenylcyclohexan-1-one 10b. 1H-NMR
(CDCl3): l 7.20–6.80 (5H, m, H arom), 2.35–0.90 (9H,
m, CH, CH2); 13C-NMR (CDCl3): l 211 (CO), 144 (C
arom), 128.7 (C arom), 126.7 (C arom), 126.6 (C arom),
48.9 (COCH2CHPh), 44.7 (CHPh), 41.2 (CH2CH2CO),
32.7 (CH2CH2CHPh), 25.5 (CH2CH2CHPh).
In a 10 ml flask equipped with a stirrer, a condenser
and an argon inlet, 10 mg (0.04 mol) of RhCl3·nH2O,
12.7 mg (1 equiv., 0.04 mmol) of the ligand 1i and 20 ml
(4 equiv., 0.16 mmol) of COD were dissolved in 1.5 ml
of dry and degassed THF. The mixture was then heated
at reflux for 15 h. After cooling, the solvent was
removed under vacuum and the residue was then pre-
cipitated in dry ethanol (1 ml). The yellow solid was
used without further purification (yield\80%).
31P-NMR (CDCl3): l 120 (d, JPRh=172 Hz), 92 (dl).
4.4. Allylation of Shiff base 11 catalyzed by a palla-
dium(0) complex generated from Pd(OAc)2 and phos-
phine boranes 1
4.4.1. Typical procedure
4.5.3. Alternati6e procedure: three steps in a one pot
procedure
A suspension of phosphine borane 1 (6 mol%) and
Pd(OAc)2 (3 mol%) in anhydrous THF (1 ml), was
stirred at r.t. for 30 min. Then, allylacetate (108 ml, 1.0
mmol) was added, and the mixture was stirred at r.t.
for 30 min. In another flask under argon atmosphere,
1.1 mmol of LiHMDS was added to a solution of Schiff
base 11 ([26], 1.0 mmol) in anhydrous THF (2 ml), and
the mixture was stirred at 0°C for 30 min. The resulting
anion was cooled at −50°C and slowly added dropwise
In a 10 ml flask equipped with a magnetic stirrer, a
condenser and an argon inlet, 0.020 mmol of diphos-
phorus borane ligand 1, 0.120 mmol of DABCO (6
equiv., 13.2 mg) were dissolved in 2 ml of dry and
degassed toluene. The mixture was then warmed at
50°C for 12 h. After cooling, the solution was added to
a mixture of 0.012 mmol of [Rh(COD)Cl]2, 0.048 mmol
(4 equiv.) of AgBF4 and 0.015 ml of COD. The mixture

342
C. Darcel et al. / Journal of Organometallic Chemistry 624 (2001) 333–343
was stirred at r.t. in the absence of light for 5 h. The
black suspension was then filtered through celite, which
was washed with 2×3 ml of dry CH2Cl2. The solvent
was removed under vacuum, and the yellow oil was
then precipated in ether. The yellow precipitate was
used without further purification.
also thank the students S. Lamy, S. Farau¨s for their
technical help during their undergraduate studies.
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4.5.4.1. Typical procedure. Into a 100 ml autoclave,
under argon atmosphere, were introduced 0.6 mmol of
Z-a-acetamidocinnamic acid derivative 15, 3% mol
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removed under reduced pressure. The residue was
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4.5.4.2. N-Acetyl phenylalanine 16a. The optical purity
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1H-NMR (DMSO-d6): l 7.30 (5H, s, H arom), 4.45
2
3
(1H, m, CH), 3.08 (1H, dd, JHH=14, JHH=4 Hz,
PhCH(H)), 2.86 (1H, dd, 2JHH=14, 3JHH=12 Hz),
2.50 (1H, sl, NH), 1.78 (3H, s, CH3CO).
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column (Daicel), with a hexane–iPrOH 95:5 mixture as
eluent, flow rate 1 ml min−1 and UV detection u=254
nm: (S)-enantiomer; tR=21.9 min, (R)-enantiomer;
tR=26.3 min.
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