Stepwise functionalization of two alkyne moieties in a dialkynylphosphine complex leading to the formation of a bifunctionalized phosphine complex bearing a stereogenic center at phosphorus

Article abstract of DOI:10.1021/om900502a

Stepwise functionalization of the two alkyne moieties in a dialkynylphosphine complex has been studied. The two alkynyl groups underwent stepwise hydrophosphination and insertion to yield two different substituents on the stereogenic phosphorus. Coordinat

Full text of DOI:10.1021/om900502a

6266 Organometallics 2009, 28, 6266–6274
DOI: 10.1021/om900502a
Stepwise Functionalization of Two Alkyne Moieties in
a Dialkynylphosphine Complex Leading to the Formation
of a Bifunctionalized Phosphine Complex Bearing a Stereogenic
Center at Phosphorus
Ding Luo, Yongxin Li, Kien-Wee Tan, and Pak-Hing Leung*
Division of Chemistry and Biological Chemistry, School of Physical & Mathematical Sciences,
Nanyang Technological University, Singapore 637371, Singapore
Received June 12, 2009
Stepwise functionalization of the two alkyne moieties in a dialkynylphosphine complex has been studied.
The two alkynyl groups underwent stepwise hydrophosphination and insertion to yield two different
substituents on the stereogenic phosphorus. Coordination of the dialkynylphosphine ligand PPh-
(CtCCH3)2 to the ruthenium center generated the complex [Ru(η6-benzene){PPh(CtCCH3)2}Cl2].
Removal of one Cl atom by AgPF6 followed by coordination of HPPh2 to ruthenium promoted the
hydrophosphination reaction with high stereoselectivity. The hydrophosphination products then under-
went insertion into the Pd-C bond of a cyclopalladated complex to give a bimetallic complex bearing a
stereogenic phosphorus center with expected substituents. The product contains also a tridentate ligand
chelating to palladium, which is believed to have been generated through a proton exchange process aided
by palladium. Furthermore, this complex exists as two interconvertable conformations in a ratio of 3:1. The
structures of complexes were confirmed by X-ray crystallographic analyses and 2D ROESY NMR studies.
Introduction
hydrogenation1 and coupling reactions.2 There are also
reports of applications of phosphines in the biological field;
one example is gold complexes containing phosphines, which
have been reported to exhibit anticancer activities.3
Phosphines, especially chiral phosphines, and correspond-
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organic and organometallic synthesis because of their im-
portant roles in both biologically active compounds and
organic catalysis. For example, it is well known that rho-
dium, ruthenium, and palladium complexes, after coordina-
tion by phosphine ligands, have been widely used to catalyze
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*To whom correspondence should be addressed. E-mail: pakhing@
ntu.edu.sg. Fax: þ65 6791 1961. Tel: þ65 6316 8899.
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r
pubs.acs.org/Organometallics
Published on Web 10/14/2009
2009 American Chemical Society

Article
Many methods to synthesize phosphines have been deve-
Organometallics, Vol. 28, No. 21, 2009 6267
Scheme 1
loped. Hydrophosphination, as an efficient and atom-
economic method, has become a powerful tool to form the
P-C bond. The classic process proceeds by thermal,4 acidic,5
basic,6 or free radical7 pathways. However, the use of
transition metal complexes for such reactions often offers
vast improvement in rate, selectivity, and stereocontrol.8
Apart from catalytic processes, there are examples of hydro-
phosphination reactions that are promoted by stoichio-
metric quantities of transition metal complexes.9
the chiral auxiliary 1-(dimethylamino)ethylnaphthalene, a
variety of chiral phosphine and arsine ligands were obtained
in high stereoselectivities by the corresponding reactions
including [4þ2]11,13 and [2þ2]14 cycloaddition, hydro-
phosphination,9f-o hydroamination,15 and hydroarsina-
tion.16 Through functionalization of one CdC bond in
dialkenyl phosphine (or one CtC bond in dialkynyl phos-
phine), the P-chirality can be successfully induced.11,13a-13c,15 It
is noteworthy that the remaining free olefin or alkyne moiety
in these products may not be a functionally valuable sub-
stituent, although the P-chiral center is formed stereoselec-
tively. However, the alkenyl or alkynyl group is still reactive
toward further organic or organometallic reactions and is
available to be further functionalized. This present study
gives the first example involving such further functionaliza-
tion, i.e., stepwise functionalization of the two alkynyl
groups in a coordinated dialkynylphosphine metal complex
(Scheme 1). Although stereocontrol was not involved in the
formation of the stereogenic phosphorus center, the valuable
strategy presented can be widely used in the synthesis of
chiral phosphines. Furthermore, the latter functionalization
provides for the insertion of the alkyne moiety in the
coordinated alkynyldiphosphine complex into the metal-
carbon bond. Similar insertions involving alkynylphos-
phines in metal complexes are rarely reported.17
Among phosphine ligands, chiral diphosphines are espe-
cially important due to the enhanced steric and stereocontrol
they offer for organic reactions. Diphosphines can be synthe-
sized mainly through two pathways. The first is via the
hydrophosphination of the olefin or alkyne moiety in an
alkenyl- or alkynylphosphine;9d,10 the second is the reaction
of alkyne and 2 equiv of diphenylphosphine.9g To synthesize
chiral phosphines bearing C- or P-chirality, asymmetric
hydrophosphination involving chiral auxiliaries on the metal
have also been utilized. For example, using the chiral amine
as the auxiliary on palladium to synthesize C-chiral dimethyl-
1,2-bis-(diphenylphosphino)-1,2-ethanedicarboxylate, the (RC,
RC) and (SC,SC) products form with a ratio of 6:1.9g The iron
complexes bearing chiral bis(phosphine) ligands {C5H5(diphos)-
Fe[P(R)H2]}BF4 (diphos=DIOP, CHIRAPHOS) have also
been used to provide stereocontrol of the hydrophosphina-
tion process involving primary phosphine (PRH2) and ole-
fin, therefore yielding the P-chiral phosphine.9e Another
important strategy to generate a P-chiral center includes
stereoselective functionalization of a prochiral phosphine
bearing two similar functional groups such as dialkenyl or
dialkynyl groups. For example, the dialkenylphenylphos-
phine, after coordination to the chiral palladium template,
underwent the Diels-Alder reaction with DMPP (3,4-di-
methyl-1-phenylphosphole) to give one of the two possible
diastereoisomers. The newly generated bicyclo[2.2.1] group,
the phenyl group, and the remaining alkenyl group led to the
generation of a stereogenic center at phosphorus.11,12
Activated by the coordination of dialkynylphosphine to
ruthenium, one of the two alkyne moieties underwent hydro-
phosphination to give a diphosphine ruthenium complex.
The remaining free alkynyl group subsequently inserted into
the Pd-C bond of an organopalladium complex to gene-
rate a unique heterobimetallic ruthenium(II)-palladium(II)
complex.
Our group has been interested in the asymmetric synthesis
of chiral phosphines by means of metal template-promoted
reactions.12 Aided by the Pd or Pt complexes containing
Results and Discussion
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Preparation of Intermediate Complex 2 with Labile Ligand.
[Ru(η6-benzene){PPh(CtCCH3)2}Cl2] (1) was synthesized
quantitatively using a modified literature method.18 The
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J. Organomet. Chem. 2009, 694, 1929.
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6268 Organometallics, Vol. 28, No. 21, 2009
Luo et al.
Scheme 2
intermolecular hydrophosphination of complex 1 and free
diphenylphosphine was found to be very slow when mon-
itored by 31P{1H} NMR spectroscopy. However, coordina-
tion of HPPh2 to the ruthenium center of 1 dramatically
accelerated the P-H addition process. This strategy has
been also widely used in syntheses of phosphine com-
plexes promoted by cyclopalladated or cycloplatinated com-
plexes.9f-j,12
Since the Ru-Cl bond is very stable, i.e., the anionic
chloride in ruthenium complex 1 is inert to ligand exchange
reaction with diphenylphosphine, one chloride of the two
was replaced with a labile ligand, acetonitrile, before the
coordination of HPPh2 to ruthenium. Complex 1 was quan-
titatively treated with AgPF6 in the mixed solvent
DCM-acetonitrile (1:2) for 1 day at room temperature to
give the intermediate [Ru(η6-benzene){PPh(CtCCH3)2}-
(NtCCH3)Cl] (2) as a brown solid in 98% yield (Scheme 2).
The coordinated phosphine in 2 showed a singlet at δ -19.8 in
the 31P{1H} NMR spectrum. Complex 2 is an air-stable solid
and thus can be stored for long time, which is different from
similar products resulting from replacement of chloride with
perchlorate. Such complexes containing perchlorate generally
need to be prepared in situ,12 which makes the synthetic
protocol less convenient.
Figure 1. Possible absolute configurations of complex 4.
Figure 1. However, only one of the two pairs of isomers,
viz., (RP,RRu) and (SP,SRu) (Figure 1a), was found to form
and was subsequently isolated. In both structures the alkyne
moiety is occupying a position distal to the Cl atom on
ruthenium.
The fact that the hydrophosphination reaction of complex
2 generated only (RP,RRu)-4 and (SP,SRu)-4 indicates the
stereoselectivity of this process. The reason for the stereo-
selectivity is proposed to be related to the steric bulk of the
1
HPPh2 in the intermediate 3. In the H NMR spectrum of
complex 1, the NMR signals of the two methyl groups
showed up as only one doublet peak at δ 2.12, which
indicates the two methyl groups are magnetically equivalent.
In contrast, these two methyl groups exhibit two doublet
peaks at δ 2.20 and 2.25 in the 1H NMR spectrum of complex
1
2. Moreover, the H NMR spectrum of the crude 3 also
showed two distinct doublet peaks at δ 2.07 and 2.13,
although the pure intermediate 3 could not be isolated. The
difference in these spectra indicates that the more bulky
acetonitrile and HPPh2 both can limit the free rotation of
the Ru-P bond at room temperature and fix the orientation
of PPh(CtCCH3)2 in these molecules. Therefore the reac-
tion takes place when the intermediate 3 adopts the sterically
favored confirmation, which leads to the addition of the
activated diphenylphosphine with good stereoselectivity.
Recrystallization of complexes (RP,RRu)-4 and (SP,SRu)-4
from DCM-hexane gave yellow prisms, which were suitable
for X-ray structural analysis. The X-ray crystallographic
analysis confirmed the structures of (RP,RRu)-4 and (SP,
SRu)-4 (Table 1 and Figure 2). A pair of enantiomers exists
with a ratio of 1:1 in each crystal unit cell. The cation (RP,
RRu)-4þ shown in Figure 2 exhibits the expected and usual
“three-legged piano-stool” disposition with the benzene
ligand occupying the “stool” position. The angles at the
ruthenium center are in the range 82.3(2)-88.5(2)°, which
are unexceptional for (η6-arene)rutheniumchlorophosphine
derivatives.18,20 The newly generated diphosphine coordi-
nates to ruthenium as a bidentate ligand via the two phos-
phorus atoms. The slightly shorter distance of Ru(1)-P(2)
Hydrophosphination Reaction of Complex 2. The ligand
exchange reaction between the coordinated acetonitrile and
HPPh2 was carried out in DCM at room temperature. This
process was found to be complete in 1 day when monitored
by 31P{1H} NMR spectroscopy. After the coordination, the
31P{1H} NMR spectrum of the reaction mixture showed a
2
pair of doublets at δ -16.7 (d, JPP = 63.5 Hz) and 36.1
(d, 2JPP = 63.5 Hz), which indicated the formation of inter-
mediate 3. Subsequent addition of a trace amount of Et3N to
the reaction solution promoted the hydrophosphination
reaction to give a pair of enantiomers (RP,RRu)-4 and
(SP,SRu)-4 as yellow solids (Scheme 2). The hydrophosphi-
nation process was completed in 3 h, and the overall yield
was 47%. The 31P{1H} NMR spectrum of the enantiomers
(RP,RRu)-4/(SP,SRu)-4 in CDCl3 showed a pair of doublets at
δ 79.8 (d, 3JPP = 35.0 Hz) and 28.8 (d, 3JPP = 35.0 Hz).
The hydrophosphination reaction can theoretically pro-
duce two diastereomerically related pairs of enantiomers
(Figure 1). The absolute configuration at ruthenium is
assigned assuming the following priority number: 1 (η6-
benzene), 2 (Cl atom), 3 (Ph2P group), and 4 (MeCtCPPh
group).19 The four isomers are designated as shown in
(19) (a) Fernandez, S.; Pfeffer, M.; Ritleng, V.; Sirlin, C. Organome-
tallics 1999, 18, 2390. (b) Stanley, K.; Baird, M. C. J. Am. Chem. Soc. 1975,
97, 6598.
(20) Pinto, P.; Marconi, G.; Heinemann, F. W.; Zenneck, U. Orga-
nometallics 2004, 23, 374.

Article
Organometallics, Vol. 28, No. 21, 2009 6269
˚
Table 1. Selected Bond Lengths (A) and Angles (deg) of
(RP,RRu)-4/(SP,SRu)-4
Scheme 3
Ru(1)-P(1)
Ru(1)-Cl(1)
P(1)-C(13)
P(2)-C(21)
P(2)-C(25)
C(20)-C(21)
2.320(1)
2.400(1)
1.834(2)
1.806(2)
1.818(2)
1.336(3)
Ru(1)-P(2)
P(1)-C(7)
P(1)-C(20)
P(2)-C(22)
C(19)-C(20)
2.292(1)
1.825(2)
1.847(2)
1.757(2)
1.506(3)
P(1)-Ru(1)-P(2)
P(2)-Ru(1)-Cl(1)
C(13)-P(1)-Ru(1)
C(7)-P(1)-C(13)
C(13)-P(1)-C(20)
C(22)-P(2)-Ru(1)
C(21)-P(2)-C(25)
C(22)-P(2)-C(25)
C(21)-C(20)-P(1)
C(20)-C(21)-P(2)
82.3(2)
82.9(2)
P(1)-Ru(1)-Cl(1)
C(7)-P(1)-Ru(1)
C(20)-P(1)-Ru(1)
C(7)-P(1)-C(20)
C(21)-P(2)-Ru(1)
C(25)-P(2)-Ru(1)
C(21)-P(2)-C(22)
C(19)-C(20)-P(1)
C(19)-C(20)-C(21)
88.5(2)
117.7(1)
109.9(6)
107.9(1)
110.3(1)
118.3(1)
101.7(1)
122.0(1)
122.1(2)
In the presence of a 50% excess amount of the organo-
palladium complex 5, the insertion reaction was found to be
complete in 7 days in DCM at room temperature when
monitored using 31P{1H} NMR spectroscopy. The crude
reaction mixture was then purified through silica gel column
chromatography to give the bimetallic product 6 as a yellow
solid in 25% yield (Scheme 3). In this reaction, the excess
amount of complex 5 was used in order to convert complexes
(RP,RRu)-4/(SP,SRu)-4 completely. On the other hand, a
moderate yield was obtained for product 6 since it is not
stable under the reaction conditions, which is indicated by
the fact that the peaks of complex 6 in the 31P{1H} NMR
spectrum of the reaction mixture decreased slowly as the
reaction time progressed.
113.7(6)
104.9(1)
101.5(1)
114.4(1)
107.0(1)
103.6(1)
115.7(2)
119.7 (2)
Complex 6 exists as two stable conformations, and the two
corresponding compounds, 6a and 6b as shown in Scheme 4
-
(PF6 is omitted for clarity), can be separated by silica gel
column chromatography to give pure products as yellow
solids with isolated yield of 22% (the major product, 6a) and
3% (the minor product, 6b), respectively. The 31P{1H} NMR
spectrum of 6a in CDCl3 showed a pair of doublets at δ 76.5
(d, 3JPP=32.8 Hz) and 47.5 (d, 3JPP=32.8 Hz), while a pair
of doublets at δ 75.5 (d, 3JPP =27.7 Hz) and 64.3 (d, 3JPP
=
27.7 Hz) was observed in the 31P{1H} NMR spectrum of 6b
in CDCl3. Recrystallization of 6a from DCM-Et2O gave
yellow prisms. The structure of 6b was then confirmed by 2D
ROESY NMR studies. It is necessary to note that both
compounds include a pair of enantiomers.
Figure 2. Molecular structure of the cationic complex (RP,
Ru)-4. (SP,SRu)-4 coexists with a ratio of 1:1 in each crystal
unit cell.
R
˚
˚
[2.292(1) A] than Ru(1)-P(1) [2.320(1) A] indicates that the
Ru-P(2) bond was strengthened by the alkynyl group on
P(2).18,21 At the stereogenic phosphorus center, the alkynyl
fragment on P(2) is distal to the Cl atom on ruthenium, which
Both 6a and 6b are stable in the solid state. However, in
DCM or CHCl3 solution, slow interconversion takes place
(Scheme 4). Attaining the chemical equilibrium at room
temperature requires 2 days, as supported by the 31P{1H}
NMR analysis. On the basis of the integration in the 31P{1H}
NMR spectrum of the mixture, the ratio of 6a to 6b is 3:1 in
the equilibrium state, thus indicating that the conformation
in 6a is thermodynamically favored.
designates these two enantiomers as (RP,RRu) and (SP,SRu
˚
)
configurations. Moreover, the C(19)-C(20) [1.506(3) A] and
˚
C(20)-C(21) [1.336(3) A] distances are typical for C-C and
CdC bonds, respectively. Selected bond distances and angles
for complexes (RP,RRu)-4/(SP,SRu)-4 are given in Table 1.
Insertion Reactions of Complexes (RP,RRu)-4/(SP,SRu)-4.
Insertion of an alkyne into the Pd-C bond of a cyclopalla-
dated complex involving benzylamine and its analogues has
been rarely reported with coordinated alkynylphosphine
complexes17 and exhibits high reactivity.22 In the present
study, the remaining free alkynyl group in complexes (RP,
RRu)-4/(SP,SRu)-4 was also converted into the alkene moiety
through an insertion reaction.
The structure of 6a was determined by X-ray crystallo-
graphy (Table 2 and Figure 3). A pair of enantiomers exists
with a ratio of 1:1 in each crystal cell. The geometry at the
ruthenium center exhibits the “three-legged piano-stool”
disposition; the η6-coordinated arene is in a “stool” position,
while the “legs” comprise P and Cl atoms. The angles at the
ruthenium center are in the range 79.5(1)-87.4(1)°. The
diphosphine coordinates to ruthenium as a bidentate ligand
via the two phosphorus atoms. The bond lengths of Ru(1)-
˚
P(1) and Ru(1)-P(2) are 2.294(1) and 2.299(1) A, respec-
tively. The alkyne moiety in (RP,RRu)-4 or (SP,SRu)-4 has
been converted into a CdC bond, C(28)-C(29), forming a
new carbon-carbon bond, C(29)-C(31). The olefin, C(28)-
C(29), coordinates to palladium, which leads to the short
(21) For examples for carbon-carbon triple bond strengthening the
Ru-P bond, see: (a) Chaplin, A. B.; Scopelliti, R.; Dyson, P. J. Eur. J.
Inorg. Chem. 2005, 4762. (b) Elsegood, M. R. J.; Smith, M. B.; Sanchez-
Ballester, N. M. Acta Crystallogr. 2006, E62, m2838.
(22) (a) Arlen, C.; Pfeffer, M.; Bars, M.; Grandjean, D. J. Chem. Soc.,
Dalton Trans. 1983, 1535. (b) G€ul, N.; Nelson, J. H.; Willis, A. C.; Rae, A. D.
Organometallics 2002, 21, 2041. (c) Spencer, J.; Pfeffer, M. Tetrahedron:
Asymmetry 1995, 6, 419. (d) Spencer, J.; Pfeffer, M.; Kyritsakas, N.; Fischer,
J. Organometallics 1995, 14, 2214. (e) Bahsoun, A.; Dehand, J.; Pfeffer, M.;
Zinsius, M. J. Chem. Soc., Dalton Trans. 1979, 547. (f) Ryabov, A. D.;
van Eldik, R.; Le Borgne, G.; Pfeffer, M. Organometallics 1993, 12, 1386.
˚
distances of Pd(1)-C(28) [2.123(3) A] and Pd(1)-C(29)
[2.322(3) A]. Weakened by the coordination, the CdC bond
˚
˚
length of 1.398(4) A is slightly longer than the typical value.
Furthermore, the P(1)Ph group connects to palladium
through the ortho carbon-metal bond, C(27)-Pd(1), with

6270 Organometallics, Vol. 28, No. 21, 2009
Luo et al.
Scheme 4
˚
Table 2. Selected Bond Lengths (A) and Angles (deg) of 6a
Pd(1)-C(27)
Pd(1)-C(29)
Pd(1)-Cl(2)
Ru(1)-P(2)
P(1)-C(21)
P(1)-C(28)
C(29)-C(30)
2.011(3)
2.322(3)
2.321(1)
2.299(1)
1.811(3)
1.828(3)
1.520(4)
Pd(1)-C(28)
Pd(1)-N(1)
Ru(1)-P(1)
Ru(1)-Cl(1)
P(1)-C(22)
C(28)-C(29)
C(29)-C(31)
2.123(3)
2.211(3)
2.294(1)
2.402(1)
1.793(3)
1.398(4)
1.510(4)
C(27)-Pd(1)-C(28)
C(27)-Pd(1)-N(1)
C(28)-Pd(1)-C(29)
C(28)-Pd(1)-Cl(2)
C(29)-Pd(1)-Cl(2)
P(1)-Ru(1)-P(2)
P(2)-Ru(1)-Cl(1)
C(21)-P(1)-C(28)
C(22)-P(1)-C(28)
C(28)-P(1)-Ru(1)
P(1)-C(28)- C(29)
C(28)-C(29)-C(30)
C(28)-C(29)-Pd(1)
C(30)-C(29)-Pd(1)
86.6(1)
175.9(1)
36.3(1)
159.2(1)
163.6(1)
79.5(1)
C(27)-Pd(1)-C(29)
C(27)-Pd(1)-Cl(2)
C(28)-Pd(1)-N(1)
C(29)-Pd(1)- N(1)
N(1)-Pd(1)-Cl(2)
P(1)-Ru(1)-Cl(1)
C(21)-P(1)-C(22)
C(21)-P(1)-Ru(1)
C(22)-P(1)-Ru(1)
P(1)-C(28)-Pd(1)
C(29)-C(28)-Pd(1)
C(28)-C(29)-C(31)
C(30)-C(29)-C(31)
C(31)-C(29)-Pd(1)
90.9(1)
87.1(1)
95.1(1)
92.7(1)
90.0(1)
84.7(1)
108.6(2)
107.5(1)
119.7(1)
106.3(1)
79.6(2)
120.2(3)
114.7(3)
113.5(2)
87.4(1)
105.1(1)
101.1(2)
114.0(1)
127.3(2)
122.1(3)
64.1(2)
Figure 3. Molecular structure of the cationic complex 6a. A pair
of enantiomers exists with a ratio of 1:1 in each crystal unit cell.
Table 3. Selected 31P and 1H NMR Spectra Chemical Shift
Values of 6a and 6b in CDCl3 (coupling constants in Hz are given
in parentheses)
109.2(2)
˚
a bond length of 2.011(3) A. C(27), the olefin, and N(1)
constitute a tridentate ligand that coordinates to the palla-
dium center. Additionally, the absolute configuration at P(1)
remained unchanged, which was deduced from the fact that
the olefin, C(28)-C(29), resulting from the conversion of the
original alkyne, kept the distal position relative to the Cl
atom on ruthenium. Selected bond distances and angles for
complex 6a are given in Table 2.
6a
6b
31P
47.5 d
(3JPP =32.8)
76.5 d
64.3 d
(3JPP =27.7)
75.5 d
(3JPP =32.8)
2.03 ddd
(3JPP =27.7)
2.22 ddd
Me2
(3JPH =9.1, 4JPH
=
(3JPH =9.0, 4JPH
=
1.6, 4JHH =1.6)
1.4, 4JHH =1.4)
Me12
2.12 s
2.26 s
2.19 s
2.29 s
2D ROESY Studies of Compounds 6a and 6b. Unfortu-
nately, crystals of 6b could not be obtained although various
crystallization methods were tried. However, the structure of
6b was studied through several experiments including the 2D
rotating frame nuclear Overhauser enhancement (ROESY)
1H NMR technique. Scheme 4 shows the numbering scheme
of compounds 6a and 6b used in the 2D ROESY NMR
NMe(ax)
NMe(eq)
H19(eq)
2.92 s
3.41 d
2.78 s
3.15 d
(2JHH =15.0)
3.99 d
(2JHH =14.0)
4.02 d
H19(ax)
H11
(2JHH =15.0)
5.17 d
(2JHH =14.0)
5.40 d
(2JPH =20.9)
6.17 s
(2JPH =13.5)
5.90 s
analysis. Selected 31P and H NMR data of 6a and 6b are
1
C6H6

Article
Organometallics, Vol. 28, No. 21, 2009 6271
1
Figure 4. Two-dimensional H ROESY NMR spectrum of complex 6a in CDCl3. All off-diagonal peaks are of negative intensity
except signal A. Selected NOE contracts: B, H19(eq)-Me20(ax); C, H19(eq)-Me20(eq); D, H19(ax)-Me20(eq); E, H19(ax)-H19-
(eq); F, H11-H19(ax); G, C6H6-Me20(ax); H, C6H6-Me20(eq); I, C6H6-H19(ax); J, C6H6-H11; K, H17-H19(eq); L, H17-
Me20(ax); M, H3, Ph1-Me2; N, Ph1-Me12; O, Ph1-H11; PQ, Ph1-C6H6; R, Ph1-Me2; S, Me12-H14; T-W, signals of 6b.
given in Table 3. These NMR assignments are based on a
series of 1H, 31P, 1H{31P}, and 2D ROESY NMR studies of
these two compounds. Figures 4 and 5 show the 2D 1H-1H
ROESY NMR spectrum of 6a and 6b, respectively.
Several similar interactions in 6a and 6b are found. The
expected interactions within the benzylamine moiety are
clearly shown in both spectra. The signals of interactions
between H19 and the NMe groups [B, H19(eq)-Me20(ax); C,
H19(eq)-Me20(eq); D, H19(ax)-Me20(eq); no signal result-
ing from the interaction H19(ax)-Me20(ax)] are typical15 and
obvious in both spectra. Additionally, other interactions have
also been observed in both spectra. H19(eq) and Me20(ax)
interact with the proton on the neighboring phenyl group
(H17) [K, H17-H19(eq); L, H17-Me20(ax) in the case of 6a;
and H, H17-H19(eq); I, H17-Me20(ax) in the case of 6b].
The interaction between Me12 and the nearby proton H14 on
the neighboring phenyl group also takes place in each com-
pound, which has been recorded as signal S in the case of 6a
and R in the case of 6b. Moreover, H19(ax) interacts with H11
to give the strong signal F due to their extreme proximity.
The differences between the spectra of 6a and 6b, which are
more important, are also obvious. The 2D ROESY NMR
spectrum of 6a shows the interactions between the two
NMe groups and the coordinated benzene ligand (G, H).
The signal H is stronger than G because Me20(eq) is closer
The 1H NMR spectra of 6a and 6b are quite similar. Their
elemental analysis data are also in accordance with the
calculated value. Furthermore, the LCMS (ESI) spectra of
both compounds show an obvious peak of 863, which is
consistent with the cation peak M(6þ). Therefore it is
deduced that 6a and 6b have very similar structures with
the same molecular formulas. Through a Dreiding model
study, the structure of 6b is suggested as shown in Scheme 4.
It is believed that several differences in the structures of 6a
and 6b will be reflected in their 2D ROESY NMR spectra. In
6a, two NMe groups and H19(ax) are close to the coordi-
nated benzene ligand on the Ru metal, while Me12 is far
away. Contrastingly, in 6b, those two corresponding NMe
groups and H19(ax) are far away from the coordinated
benzene ligand, while Me12 is close to it. Moreover, the
distance between the coordinated benzene ligand and H11 in
6a is longer than that in 6b.

6272 Organometallics, Vol. 28, No. 21, 2009
Luo et al.
1
Figure 5. Two-dimensional H ROESY NMR spectrum of complex 6b in CDCl3. All off-diagonal peaks are of negative intensity
except signal A. Selected NOE contracts: B, H19(eq)-Me20(ax); C, H19(eq)-Me20(eq); D, H19(ax)-Me20(eq); E, H19(ax)-H19-
(eq); F, H11-H19(ax); G, C6H6-Me12; H, H17-H19(eq); I, H17-Me20(ax); JPQ, (H3, Ph1)-Me2; K, Ph1-H19(ax); L, Ph1-H11;
M-N, Ph1-C6H6; O, Ph4-C6H6; R, Me12-H14.
to the benzene group than Me20(ax). However, the cor-
responding signals have not been observed in the 2D
ROESY spectrum of 6b. Furthermore, in the case of 6a,
the coordinated benzene ligand also interacts with
H19(ax) and H11 to give signals I and J, respectively,
while the corresponding interactions are not found in the
case of 6b. In contrast, the 2D ROESY spectrum of 6a does
not show any signal due to the interaction between the
coordinated benzene ligand and Me12, while the corre-
sponding interaction has been recorded as an obvious
signal (G) in the 2D ROESY spectrum of 6b. These
differences between spectra of 6a and 6b indicate the
different orientation of the coordinated benzene ligand
in these two complexes. In the case of 6a, the coordinated
benzene ligand is close to the NMe groups and far away
from Me12. However, in the case of 6b, the opposite
scenario is evident.
ROESY experiment, which gave a few signals in the 2D
ROESY NMR spectrum of 6a (T-W).
Proposed Mechanism for the Insertion Reaction. Complex
6 is suggested to form through insertion of the alkyne
moiety into the Pd-C bond and the subsequent pro-
ton exchange process aided by palladium, as shown in
Scheme 5 (the square indicates the vacant coordination
site). The alkynyl group of 4 initially inserts into the Pd-C
bond of 5 to form the intermediate 7. A very important
feature of the structure of 7 is the vacant site on the Pd
atom; moreover, no free lone pair of electrons or ligands
are available that can occupy this site. The palladium
species with the vacant site then promotes the proton
exchange process between the phenyl and the alkenyl
group, which leads to the formation of complex 8. After
exchange, the agostic H (ortho to phosphorus) on the
phenyl group is transferred to the alkenyl group, forming
a connection between the phenyl group and palladium,
which generates a C-olefin-N tridentate ligand. The
subsequent coordination of the CdC unit makes the
tridentate ligand chelate to palladium, thus yielding
the product 6.
In conclusion, these two spectra are in agreement with the
interactions expected from the structures of the two com-
pounds in Scheme 4; therefore the structure of 6b is reason-
able. It is necessary to mention that because the equilibrium
exists, a small amount of 6b was generated during the 2D

Article
Organometallics, Vol. 28, No. 21, 2009 6273
Scheme 5
Diprop-1-ynylphenylphosphine (PPh(CtCCH3)224) and complex
118 were prepared using modified literature methods.
Synthesis of PPh(CtCCH3)2. A solution of BrMg-CtCCH3
(0.10 mmol) in 300 mL of THF was maintained at -78 °C, and
Cl2PPh (8.95 g, 0.05 mmol) was added dropwise slowly. The
mixture was then allowed to recover to room temperature and
stirred for 1.5 h, then refluxed for 2.5 h. The resulting solution
was cooled to room temperature and protected under argon
overnight. The solvent was removed through distillation, and
the residue was neutralized with saturated NH4Cl solution (ca.
200 mL) and extracted with Et2O (ca. 100 mL ꢀ 3). The organic
layer was separated, dried with MgSO4, and then distilled to
remove the solvent to give the crude product. Subsequent
purification through microdistillation (102-104 °C/0.65 mbar)
gave pure phosphine as a colorless liquid. Yield: 5.87 g (63%).
31P{1H} NMR (CDCl3, δ): -59.7 (s). 1H NMR (CDCl3, δ): 2.02
4
(d, JPH = 1.7 Hz, 6H, PCC-Me); 7.38-7.44 (3H), 7.71-7.77
(2H) (m, P-Ph).
Synthesis of Ru(η6-benzene){PPh(CtCCH3)2}Cl2, 1. Solid
[(η6-benzene)RuCl2]2 (0.70 g, 1.39 mmol) was added into the
solution of PPh(CtCCH3)2 (0.52 g, 2.79 mmol) in acetone
(30 mL), and this reddish-brown suspension was stirred for
1 day. The resulting reddish-orange suspension was then eva-
porated to dryness. The orange solid was washed with hexane
(ca. 30 mL) and dried in vacuo to give 1. Yield: 1.18 g (97%). This
solid was suitable for NMR analysis and used for next reactions
without further purification. MS ES (þ): m/z 895 [2M þ Na]þ
100%; 459 [M þ Na]þ 50%. Mp: 220-222 °C dec. 31P{1H}
Conclusions
In conclusion, the present study gives an example of stepwise
functionalization of two alkyne moieties of a dialkynylpho-
sphine through different reactions. The hydrophosphination
reaction followed by the insertion reaction yielded a hetero-
bimetallic ruthenium(II)-palladium(II) complex that con-
tained a stereogenic phosphine. This study gives the first
example including not only the generation of a chiral phos-
phorus center through conversion of one of the two functional
groups on a prochiral phosphorus but also the further functio-
nalization of the remaining free functional group. Although
racemic products were isolated due to lack of stereocontrol
during the formation of the stereogenic phosphorus, the strat-
egy presented is valuable for synthesis of chiral phosphines and
thus is worth being further investigated. Furthermore, as an
example involving a kind of rarely reported alkyne substrate,
the insertion of an alkyne moiety in the coordinated alkynyl
diphosphine complex into the Pd-C bond in the latter is also
significant. Further investigation into this reaction protocol
with a view of catalytic applications for the complexes involved
is currently underway.
NMR (CDCl3, δ): -20.2 (s). 1H NMR (CDCl3, δ): 2.12 (d, 4JPH
=
3
3.8 Hz, 6H, PCC-Me); 5.54 (d, JPH = 1.0 Hz, 6H, C6H6);
7.43-7.46 (3H), 8.02-8.10 (2H) (m, P-Ph).
Intermolecular Hydrophosphination Reaction. Solid 1 (0.101 g,
0.23 mmol) was added into the solution of HPPh2 (0.043 g,
0.23 mmol) in DCM (10 mL). Upon addition of a trace amount
of Et3N (ca. 0.005 g, 0.049 mmol), the mixture was then stirred at
room temperature for 4 days. The 31P{1H} NMR spectrum of
the resulting solution showed two very small doublets at δ 27.3
(d, 2JPP=34.3 Hz) and 78.1 (d, 2JPP=34.3 Hz), which indicated
only a small amount of the hydrophosphination product formed
(the yield was less than 10%, estimated value).
Synthesis of Ru(η6-benzene){PPh(CtCCH3)2}(NtCCH3)Cl,
2. The solution of 1 (0.54 g, 1.24 mmol) in DCM (120 mL) was
mixed with the solution of AgPF6 (0.31 g, 1.24 mmol) in
acetonitrile (240 mL) and stirred in the absence of light for
1 day. Then the yellow suspension was filtered through Celite to
remove AgCl. The yellow filtrate was evaporated and dried in
vacuo to give 2 as a brown solid. Yield: 0.71 g (98%). This solid
was suitable for NMR analysis and used for the next reactions
without further purification. MS ES (þ): m/z 442 [M - PF6]þ
100%; 401 [M - PF6 - NCMe]þ 40%. Mp: 116-119 °C.
31P{1H} NMR (CDCl3, δ): -143.7 (sept, PF6-); -19.8 (s). 1H
NMR (CDCl3, δ): 2.19 (s, 3H, NCMe); 2.20 (3H), 2.25 (3H) (d,
Experimental Section
3
4JPH = 4.1 Hz, PCC-Me); 5.91 (d, JPH = 1.1 Hz, 6H, C6H6);
Reactions involving air-sensitive compounds were performed
under an inert atmosphere of argon using standard Schlenk
techniques. NMR spectra were recorded at 25 °C on Bruker
Avance 300, 400, and 500 spectrometers. Melting points were
determined on a SRS Optimelt automated melting point system,
SRS MPA 100. Elemental analysis was performed by the
Elemental Analysis Laboratory of the Division of Chemistry
and Biological Chemistry at Nanyang Technological Univer-
sity. Mass spectra were recorded on an Finnigan LCQ Deca XP
MAX mass spectrometer using ES(þ) or ES(-) techniques.
Benzeneruthenium(II) chloride dimer (Aldrich), 1-propynyl-
magnesium bromide solution (0.5 M in THF, Aldrich), and
dichlorophenylphosphine (Alfa Aesar) were used as received from
commercial sources. The dimeric benzylamine palladium(II) com-
plex 5 was prepared according to the standard literature method.23
7.46-7.51 (3H), 7.84-7.92 (2H) (m, P-Ph).
Hydrophosphination Reaction, Synthesis of (RP,RRu)-4/(SP,
S
Ru)-4. A solution of HPPh2 (0.041 g, 0.22 mmol) in DCM
(20 mL) was stirred with 2 (0.13 g, 0.22 mmol) for 1 day to
generate the intermediate 3 in situ. Then a trace amount of Et3N
(ca. 0.005 g, 0.049 mmol) was added and stirred for a further 3 h
until the 31P{1H} NMR spectrum of the reaction mixture
indicated the conversion was complete. Removal of the solvent
gave the crude hydrophosphination product as a dark residue.
Subsequent purification of the crude product by silica gel
column chromatography (acetone-DCM, 1:25) gave pure
(24) (a) King, R. B.; Efraty, A. Inorg. Chem. 1969, 8, 2374.
(b) Louattani, E.; Lledos, A.; Suades, J.; Alvarez-Larena, A.; Piniella, J. F.
Organometallics 1995, 14, 1053. (c) Carty, A. J.; Hota, N. K.; Ng, T. W.;
Patel, H. A.; O'Connor, T. J. Can. J. Chem. 1971, 49, 2706. (d) Charrier, C.;
Chodkiewicz, W.; Cadiot, P. Bull. Soc. Chim. Fr. 1966, 1002.
(23) Roberts, N. K.; Wild, S. B. J. Chem. Soc., Dalton Trans. 1979,
2015.

6274 Organometallics, Vol. 28, No. 21, 2009
Luo et al.
(RP,RRu)-4 and (SP,SRu)-4 as yellow solids. Yield: 0.076 g
(47%). The product was recrystallized from DCM-hexane as
yellow prisms that were suitable for X-ray analysis. For 3 (crude
product): 31P{1H} NMR (CDCl3, δ): -143.6 (sept, PF6-);
-16.7 (d, 2JPP = 63.5 Hz, 1P); 36.1 (d, 2JPP = 63.5 Hz, 1P). 1H
NMR (CDCl3, δ): 2.07 (3H), 2.13 (3H) (d, 4JPH=4.1 Hz, PCC-
Me); 5.81 (s, 6H, C6H6); 6.29 (dd, 1JPH=418.1 Hz, 3JPH=2.9 Hz,
1H, HPPh2); 7.40-7.83 (m, 15H, P-Ph). For (RP,RRu)-4/(SP,SRu)-
4: MS ES (þ): m/z 587 [M - PF6]þ. Mp: 260-262 °C dec. 31P{1H}
NMR (CDCl3, δ): -143.6 (sept, PF6-); 28.8 (d, 3JPP = 35.0 Hz,
1P); 79.8 (d, 3JPP =35.0 Hz, 1P). 1H NMR (CDCl3, δ): 2.18 (ddd,
3JPH=8.4 Hz, 4JPH =1.6 Hz, 4JHH=1.6 Hz, 3H, CdC-Me); 2.25
(d, 4JPH = 3.8 Hz, 3H, PCC-Me); 5.79 (s, 6H, C6H6); 6.88 (ddq,
Table 4. Crystallographic Data for Complexes (RP,RRu)-4/(SP,
S
Ru)-4 and 6a
(RP,RRu)-4/(SP,SRu)-4
6a
formula
fw
C
731.95
30H28ClF6P3Ru
C40H42Cl4F6NP3PdRu
1092.93
P2(1)/c
monoclinic
12.5082(4)
16.1261(5)
21.6743(7)
90
space group
cryst syst
P2(1)/c
monoclinic
11.5490(6)
18.2762(10)
14.6245(8)
90
˚
a/A
˚
b/A
˚
c/A
R/deg
β/deg
γ/deg
102.269(2)
90
99.573(2)
90
3
4
2JPH = 52.9 Hz, JPH = 12.7 Hz, JHH = 1.4 Hz, 1H, CdC-H);
7.39-7.92 (m, 15H, aromatics). Anal. Calcd for C30H28ClF6P3Ru:
C, 49.2; H, 3.9. Found: C, 49.4; H, 3.9.
3
˚
V/A
3016.3(3)
4
173(2)
4311.0(2)
4
173(2)
Z
T/K
Insertion Reaction, Syntheses of 6a and 6b. To a solution of
(RP,RRu)-4 and (SP,SRu)-4 (0.13 g, 0.18 mmol) in DCM (15 mL)
was added solid 5 (0.075 g, 0.14 mmol) in portions during 4 days.
Then the mixture was stirred for a further 3 days. The resulting
dark yellow solution was concentrated and purified by silica
gel column chromatography (acetone-DCM, 1:25) to give pure
6a and 6b both as yellow solids. Yield: 6a, 0.040 g (22%); 6b,
0.0060 g (3%). The complex 6a was recrystallized from
DCM-Et2O as brown prisms that were suitable for X-ray
analysis. For 6a: MS ES (þ): m/z 863 [M - PF6]þ. Mp: 210-
212 °C dec. 31P{1H} NMR (CDCl3, δ): -143.8 (sept, PF6-); 47.5
(d, 3JPP =32.8 Hz, 1P); 76.5 (d, 3JPP = 32.8 Hz, 1P). 1H NMR
Dcalcd/g cm-3
1.612
1.684
˚
λ/A
0.71073
0.825
1472
0.71073
1.184
2184
μ/mm-1
F(000)
R1 (obsd data)a
wR2 (obsd data)b
P
0.0318
0.0736
P
0.0429
0.1076
P
P
a R1 =
Fo| - |Fc
/
|Fo|. b wR2 = { [w(Fo - Fc2)2]/ [w-
2
(Fo2)2]}1/2, w-1 = σ2(Fo)2 þ (aP)2 þ bP.
Anal. Calcd for C39H40Cl2F6NP3PdRu CH2Cl2: C, 44.0; H,
3
3.9; N, 1.3. Found: C, 44.4; H, 4.3; N, 1.5.
Crystal Structure Determination of (RP,RRu)-4/(SP,SRu)-4 and
6a. X-ray crystallographic data for the two complexes are given
in Table 4. Diffraction data were collected on a Bruker X8Apex
diffractometer with Mo KR radiation (graphite monochro-
mator). All non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were introduced at fixed distance from carbon
atoms and were assigned fixed thermal parameters.
3
4
4
(CDCl3, δ): 2.03 (ddd, JPH = 9.1 Hz, JPH =1.6 Hz, JHH =
1.6 Hz, 3H, Me2); 2.12 (s, 3H, Me12); 2.26 (s, 3H, NMeax); 2.92
2
(s, 3H, NMeeq); 3.41 (d, JHH = 15.0 Hz, 1H, H19,eq); 3.99 (d,
2JHH =15.0 Hz, 1H, H19,ax); 5.17 (d, 2JPH =20.9 Hz, 1H, H11);
6.17 (s, 6H, C6H6); 6.90-7.97 (m, 19H, H3 and aromatics). Anal.
Calcd for C39H40Cl2F6NP3PdRu CH2Cl2: C, 44.0; H, 3.9; N,
3
1.3. Found: C, 44.2; H, 4.0; N, 1.7. For 6b: MS ES (þ): m/z 863
[M - PF6]þ 30%; 828 [M - PF6 - Cl]þ 100%. Mp: 225-227 °C
dec. 31P{1H} NMR (CDCl3, δ): -143.9 (sept, PF6-); 64.3 (d,
Acknowledgment. We are grateful to Nanyang Tech-
nological University for supporting this research and for
the research scholarship to D.L.
3JPP = 27.7 Hz, 1P); 75.5 (d, JPP = 27.7 Hz, 1P). H NMR
3
1
3
(CDCl3, δ): 2.19 (s, 3H, Me12); 2.22 (ddd, JPH = 9.0 Hz,
4JPH =1.4 Hz, 4JHH = 1.4 Hz, 3H, Me2); 2.29 (s, 3H, NMeax);
2.78 (s, 3H, NMeeq); 3.15 (d, 2JHH = 14.0 Hz, 1H, H19,eq); 4.02
Supporting Information Available: Crystallographic data in
CIF format for complexes (RP,RRu)-4/(SP,SRu)-4 and 6a. This
material is available free of charge via the Internet at http://
pubs.acs.org.
2
2
(d, JHH = 14.0 Hz, 1H, H19,ax); 5.40 (d, JPH = 13.5 Hz, 1H,
H11); 5.90 (s, 6H, C6H6); 7.16-8.12 (m, 19H, H3 and aromatics).