Synthesis and evaluation of side-arm-alkylated phosphametallocene phosphines

Article abstract of DOI:10.1021/om100845p

Syntheses permitting the introduction of one or two methyl substituents at the sp³-hybridized carbon atom in the backbone of enantiopure 2-phospharuthenocenemethyl phosphines are presented. Preliminary Rh-catalyzed hydrogenations of enamides su

Full text of DOI:10.1021/om100845p

ARTICLE
pubs.acs.org/Organometallics
Synthesis and Evaluation of Side-Arm-Alkylated
Phosphametallocene Phosphines
,
†
†,§
†
‡
†
Duncan Carmichael,* J €u rgen Klankermayer, Eric Muller, K Michal Pietrusiewicz, Louis Ricard,
†
†,‡
†,‡
Nicolas Seeboth, Sylwia Sowa, and Marek Stankeviꢀc
†
Laboratoire “H ꢁe t ꢁe ro ꢁe l ꢁe ments et Coordination”, Ecole Polytechnique, CNRS, 91128 Palaiseau cedex, France
‡
Department of Organic Chemistry, Marie-Curie Sklodowska University, ul. Gliniana 33/120, 20-614 Lublin, Poland
S Supporting Information
b
ABSTRACT: Syntheses permitting the introduction of one or two
3
methyl substituents at the sp -hybridized carbon atom in the
backbone of enantiopure 2-phospharuthenocenemethyl phos-
phines are presented. Preliminary Rh-catalyzed hydrogenations
of enamides suggest that the interaction of the Cp* group with the
side-arm methyl group lying endo to the phosphametallocene
modifies enantioselectivity significantly with respect to the side-
arm- unsubstituted analogue.
The explosive growth in the design and use of enantiopure
1-6
ferrocenephosphines
last 10 years has been mainly driven by the excellent performance
(Figure 1) that has occurred over the
7,8
of ligands derived from the Ugi amine 1 and reflects the facile
changes in sterical and electronic properties that can be achieved
within a metallocene phosphine through modification of the two
phosphorus donors, intervening bridging atoms, the metal
center, and/or trans-cyclopentadienyl elements. Appropriate
matching of these components has brought exceptional perfor-
mance over a wide range of processes, as exemplified in scalemic9
industrial syntheses of compounds including metolachlor,
Figure 1. Ugi’s amine (1), ferrocene phosphines (2, 3), and a phos-
phametallocenephosphine (4).
bond, is more susceptible to electronic modulation by the metal
3
center than the sp donors of the metallocene-phosphine
1
0
11
12
27,28
biotin, dihydrojasmonate, napththylalanines, a peroxime
class.
In sterical terms, the situation is more nuanced. A
13
2
proliferator activated receptor agonist, the antihypertensive
priori, the position of the sp phosphorus, which is buried within
the metallocene skeleton and therefore likely to draw any
P-coordinated metal close to the phosphametallocene architec-
ture, might be expected to project the sterical influence of the
metallocene component more efficiently into the P-coordinated
metal coordination sphere than could a metallocenephosphine,
thus probably dominating the effects of the side arm. However,
recent crystallographic evidence has shown quite clearly that the
1
4
15
aliskiren, and ramelteon, a melatonin receptor agonist.
There has been a parallel interest in enantiopure planar-chiral
16
phosphametallocenes as ligands since their near-simultaneous
17
18
introduction by Ganter and (subsequently) Fu; this interest
reflects the modular structure that phosphametallocenes share
with ferrocenephosphines, but also the presence of the unusual
2
sp -hybridized donor atom. Phosphametallocenes such as 4
2
differ from metallocene phosphines significantly, in terms of
both electronic and steric effects, and phosphametallocene
derivatives have given benchmark performance in processes such
rather nondirectional nature of the sp donor allows the con-
formational needs of the side arm to be expressed quite strongly.
For example, the very different localization of the platinum atoms
1
9,20
29,30
as enantioselective allylic alcohol isomerizations,
Kinugasa
in complexes 5 and 6
(Figure 2) reflects leverage from the
2
1
22
reactions, dipolar cycloadditions, and enyne hydrosilyla-
tions. From an electronic standpoint, the low-lying and quite
naphthyl group and demonstrates the responsiveness of the
2
3
24
2
5,26
2
spherical
phosphametallocene sp lone pair is very different
Received: August 31, 2010
Published: March 10, 2011
from those in classical phosphines and, because of a direct M-P
r 2011 American Chemical Society
1804
dx.doi.org/10.1021/om100845p
|Organometallics 2011, 30, 1804–1811

Organometallics
ARTICLE
Scheme 1. Synthesis of Phospharuthenocene-1-
a
ethylphosphines
Figure 2. Side-arm influence upon coordination geometry. Displace-
ment of Pt from the best phospholyl plane: 5, 0.62 Å; 6, 1.06 Å.
phosphametallocene element to the sterical preferences of the
3
31,32
sp phosphorus atom.
The stereocenter found R to the ferrocene ring in ferrocene-
phosphines has a significant effect upon enantioselectivity, and
3
3
the Josiphos 2 class of ligands can show better ee’s than their
34
simple planar-chiral analogues 3. Thus it seemed likely that
elaborating the side arm of the phosphametallocen-2-ylmethyl-
phosphines should also set up conformational relays that might
modify ligand properties and performance quite profoundly.
Well-developed functionalization chemistry of this kind is avail-
able only for rac- phosphaferrocenes, a class that includes an
35
analogue of compound 2 described here; the generation of
1
7-19,23,36-55
enantiopure phosphametallocenes,
or those based
27-31,49,56-65
upon late transition metals other than iron,
is still in
its infancy. The study presented here shows that resolved ligands
having side-arm C-functionalization are quite easily accessed
from the readily available enantiopure phospharuthenocene
3
1,60
source 7
stability
through syntheses that exploit the extreme
of the previously unknown mono- and dimeth-
3
1,61,66,67
yl-substituted phospharuthenocenemethylium ions. A prelimin-
ary catalytic study indicates that the side-chain substitution
pattern has a significant effect upon the outcome of rhodium-
catalyzed hydrogenation of enamides.
a
Reagents and conditions: i: LiAlH , (2 equiv) THF, rt, 4 h, ii:
4
Monomethyl-Substituted Derivatives. Racemic phospha-
ferroceneethylium ions have been amply described by Roberts
HBF4 Et O (1.2 equiv), CH Cl , 0 °C to RT, 20 min. iii: PPh , THF
3
2
2
2
3
(1 equiv), -78 °C to RT, 15 min, 30 s, iv: n-BuLi (1.2 equiv), -78 °C
to RT, 45 min, then HCHO (3 equiv), -78 °C to RT, 30 min. v:
6
8
and Silver and later, in a thorough physicochemical study, by
3
5
HBF
4
Et
2
O (1.1 equiv), CH
2
Cl
2
2
, -78 °C, 15 min. vi: HPPh (1.1
Ganter. The methodology chosen here to prepare the phos-
pharuthenoceneethylium ion (Scheme 1) involves the homo-
logation of the enantiopure phospharuthenocenemethylium ion
3
equiv), 0 °C, 15 min, then NaOH (1 M aq, excess). vii: [Rh(acac)(1,5-
cod)] (1.0 equiv), HBF Et O (1.0 equiv), THF, 0 °C to RT, 5 min,
4
2
3
3
1
then 13 (1.0 equiv), 5 min.
9
,
through reaction with triphenylphosphine to give the
69
corresponding Wittig precursor 10, which then reacts with
butyllithium and paraformaldehyde to give the corresponding
phosphine at the cationic center on a trajectory exo to the
phospharuthenocene.
2
-vinylphospharuthenocene 11. Because of the high stability of
ruthenocenemethylium ions, this compound is easily and quan-
The configuration of the colorless air- and moisture-stable
solid product 13 was confirmed by an X-ray study (Figure 3).
Dimethyl-Substituted Derivatives. For dimethyl-substi-
tuted compounds, an enantiopure 2-phospharuthenocenoic acid
is required as the ligand precursor, and such species have not
67,70
titatively protonated
to a single isomer of the corresponding
cation 12 by fluoroboric acid etherate. Consideration of steric
factors, which are expected to favor placing the methyl group of
the ethylium fragment syn to the phosphorus on the less hindered
side of the phospharuthenocene, and analogy with Ganter and
colleagues’ observation of a preference for Z- over E-substituted
72
been available previously. Attempts to oxidize the phosphar-
uthenocenemethanol 8 classically (MnO , Dess Martin period-
2
35
inone, etc.) predictably provoked oxidation at phosphorus, and a
more direct pathway involving hydrolysis of 7 under forcing
conditions was preferred.
phosphaferrocenethylium ions imply that the single observable
phospharuthenocenethylium ion product should show the struc-
ture 12. The nonobservation of the E-product probably stems
6
The menthyl group could not be removed from 7 upon
from the pronounced η -fulvene character of ruthenocene-
73
74
methylium ions relative to their ferrocenemethylium ana-
treatment with either TMSI or TMSOTf over a month at
71
logues, which prevents E- to Z-equilibration of the sort observed
40 °C in dichloromethane, but essentially quantitative hydrolysis
35
75
in the phosphaferrocenylethylium series. Subsequent reaction
with diphenylphosphine and deprotonation of the resulting
phosphonium salt provided ligand 13, whose stereochemistry
could be achieved in pure trifluoroacetic acid at room tem-
perature over three days. However, a second, more evolved and
7
6
convenient approach based upon Vavra et al.’s method invol-
ving the adsorption of a sample of 7 and triflic acid onto a
35
is in accord with the anticipated attack of the incoming
1
805
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Organometallics
ARTICLE
Figure 3. Views of the two independent molecules in the crystal of phospharuthenocenephosphine 13 (30% thermal ellipsoids) showing the (S )(R )-
C
Rc
absolute structure. Selected bond lengths (Å) and angles (deg): P1-C1 1.793(2), P1-C4 1.789(2), C1-C2 1.425(3), C2-C3 1.428(3), C3-C4 1.427(3), C4-
C5 1.499(3), P2-C5 1.874(3), C5-C6 1.540(3), C4-P1-C1 89.3(1), C5-C4-P1 122.1(2), C4-C5-P2 107.8(2), P1-C4-C5-P2 -75.8, C3-C4-C5-
C6 -144.8, P1-C1-C7-C8 -128.1, P(3)-C(40)-C(41)-P(4) -72.5, C(39)-C(40)-C(41)-C(42) -145.0, P(3)-C(37)-C(45)-C(46) -134.2.
Scheme 2. Synthesis of Side-Chain Dimethyl-Substituted
Phospharuthenocenemethylphosphines
extraction and chromatography under strictly oxygen-free conditions
give a near-quantitative yield of the requisite acid 15. Despite the
vigorous conditions, total retention of planar chirality was
demonstrated by conversion to the corresponding acid chloride
a
1
6 with PCl and subsequent re-esterification with (-)-menthol.
5
Transformation of the acid 15 into the desired cation pre-
cursor 17 was effected straightforwardly through functionaliza-
tion with phosphorus pentachloride and subsequent treatment
with excess methylmagnesium bromide. The anticipated phos-
pharuthenocenedimethylcarbinol 17 underwent partial dehydra-
tion during workup, but both 17 and 18 can be converted cleanly
upon reaction with fluoroboric acid etherate into the desired
carbocation, so that the crude mixture could be used directly as
7
7
the source of cation 19. This strongly ether-solvated com-
pound was precipitated, washed with ether, and dried prior to use
and can be stored without decomposition on the bench under
nitrogen over a period of several months. In this particularly
hindered case, phosphination occurred readily, but attempts to
deprotonate 20 with strong bases (nBuLi, aqueous KOH) failed.
The proligand was therefore stored as the phosphonium salt,
with the proton being lost during the synthesis of the rhodium
78,79
precatalyst.
31
As in our prior study of 22, precatalysts 14 and 21 were
prepared by addition of the ligand (or phosphonium salt) to a
þ
80
solution of [Rh(1,5-cod)THF2] and isolated prior to use.
Both complexes proved quite stable and could be stored without
special precautions under nitrogen in Schlenk tubes. Under an
3
1
identical set of conditions to those of our previous study of 22,
room-temperature ethanol solutions of p-F, p-MeO, and p-H
methyl-N-acetylcinnamates (MACs) could be hydrogenated
using 1 mol % loadings of precatalysts 14 and 21 (Scheme 3)
81
at rates that appear to be modest relative to many more classical
31
phosphine ligands. Comparison of data with 22 also shows that
the presence of either one or two methyl groups causes the ee to
diminish significantly, with double methylation provoking the
poorest excesses.
a
Reagents and conditions: i: MgSO , TfOH (excess) 110 °C, 10 min. ii:
4
PCl (1 equiv), CH Cl , 0 °C to RT, 30 min, iii: MeMgBr (5 equiv),
-
1
5
2
2
78 °C to RT, 30 min, iv: SiO
2
v: HBF
4
.Et
2
O (1.1 equiv), CH
2 2
Cl , 0 °C,
0 min, vi: HPPh (1.1 equiv), CH
2
2
Cl , 20 °C, 20 min. vii:
2
’
CONCLUSION
[
Rh(acac)(1,5-cod)] (1.0 equiv), HBF .Et O (1.0 equiv), THF, 0 °C
4
2
to RT, 5 min, then 20 (1.0 equiv), 5 min.
This article provides methodologies for the elaboration and
fine-tuning of the phospharuthenocene coordination sphere and
confirms that side-arm alkylation can exert a significant influence
upon ee. The relative configuration of the planar and central
magnesium sulfate surface and flash hydrolysis by immersion for
0 minutes in an oil bath at 110 °C is generally preferable. Simple
1
1
806
dx.doi.org/10.1021/om100845p |Organometallics 2011, 30, 1804–1811

Organometallics
ARTICLE
Scheme 3. Enantioselective Hydrogenation of p-Substituted N-Acetyl Cinnamate Esters Using Precatalysts 14, 21, and 22
a
Showing the Hand of the Product, the ee (%), and the Conversion (%)
a
All catalytic studies were performed at 25 °C under 1 bar of hydrogen and over a period of 16 h.
82
means to strongly influence ee in different processes. Given the
8
4
great complexity of the enamide hydrogenation manifold,
a
simple study such as the one given here will obviously not
identify the factors influencing the ee of the product with any
precision. However, in the absence of detailed studies, one simple
working hypothesis for the ee differences observed in the three
ligands might be that the interaction of the endo-methyl group at
the bridge carbon with the Cp* ligand has non-negligible
consequences for enantioselectivity, so that 22, having only
H-substituents at the side chain, performs differently from 14
and 21. These, both showing the endo-methyl configurational
lock, perform less well and broadly equivalently.
’
EXPERIMENTAL SECTION
All operations were performed either using cannula techniques on
Schlenk lines under an atmosphere of dry nitrogen or in a Braun
Labmaster 130 drybox under dry purified argon. Column chromatogra-
phy was performed under nitrogen on 63-200 μm silica or 50-160 μm
Figure 4. Hard-spheres model of the structure obtained upon the
addition of two methyl groups to the crystallographically determined
80
neutral alumina as appropriate. [Rh(acac)(cod)] and complexes 9 and
-
structure of 22 (1,5-cod and BF
4
counterion omitted for clarity) while
31,60
7
were obtained as described previously;
enamide substrates were
holding the structure rigid. Note the short distances between a Cp*
methyl carbon and the phosphametallocene endo-methyl carbon (ca.
85,86
prepared by standard protocols.
Solvents distilled under dry nitro-
gen included ethanol and methanol from the corresponding magnesium
or sodium alkoxide, THF from sodium-benzophenone ketyl, pentane
from sodium-benzophenone ketyl- tetraglyme, diethyl ether from
2.60 Å) as well as the side-chain exo-methyl carbon and the methyl
carbon at the C3 phospholyl position (ca. 3.14 Å).
4 10
sodium hydride or calcium hydride, and dichloromethane from P O .
8
2
chiralities in 13 is a rare “counter-Ugi” type, and it is interesting
to note that a simple “hard spheres” model predicts that introduc-
ing methyl groups into the structure of precatalyst 22 at idealized
distances from the bridging carbon (Figure 4) will generate
strong nonbonding interactions between the Cp* group and the
methyl endo to the metallocene (ca. 2.60 Å) and also a moder-
ately close contact between the exo-methyl group and the methyl
The last was stored for short periods over 4 Å molecular sieves.
Deuterobenzene, deuteroacetone, and deuterotetrahydrofuran were
used as received from Eurisotop (Saclay), and deuterochloroform was
deacidified through neutral alumina prior to use. NMR measurements
were made on a Bruker Avance 300 spectrometer and are referenced to
internal C D H or CHCl and external H PO as appropriate. Mass
6
5
3
3
4
spectra were obtained under 70 eV electron impact or chemical
ionization using ammonia on a Hewlett-Packard 5989B spectrometer;
HRMS was obtained under EI on a JEOL GCmate apparatus. Enantio-
meric excesses were determined on a Waters 510 HPLC apparatus fitted
82
group at the C3 position of the phospholyl ligand (ca. 3.14 Å).
The sensitivity of the P-aryl group orientation in space to the
precise angle imposed by these interactions should provide the
1
807
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Organometallics
ARTICLE
with a Daicel chiralcel OD-H column and a photodiode detector
operating at 254 nm. Optical rotations were obtained on a Perkin-Elmer
PE 241 polarimeter operating at 589 nm. Combustion analyses were
performed by the “Service de Microanalyse du CNRS”, at the ICSN, Gif
sur Yvette, France.
Catalytic Determinations. These were performed in duplicate.
The substrate (4-G-MAC, 5 mmol) and the catalyst precursor (50
μmol) were placed in freshly distilled ethanol (6 mL) in a Teflon-tapped
128.0, 127.9, 125.8, 105.3 (dd, JPC = 60.4 Hz, JPC = 20.7 Hz, PCCH),
100.4 (d, JPC = 57.5 Hz, PCPh), 93.5 (dd, JPC = 5.4 Hz, JPC = 2.2 Hz,
PCCMe), 91.5 (d, JPC = 4.0 Hz, PCCMe), 87.3 (Cp*), 32.5 (dd, JPC
=
17.4 Hz, JPC = 13.5 Hz, CH), 19.7 (t, JPC = 14.6 Hz, MeCH), 13.3 (Me),
2
5
12.28 (d, JPC = 4.3 Hz, Me), 10.8 (Me Cp*). [R]
= þ14.9 (c 1.0,
D
DCM). HRMS (EI 70 eV): calcd for C H P Ru 636.1649, found
36 40 2
636.1645.
15: Magnesium sulfate (4 g, excess) was dried in a Schlenk tube under
vacuum at 125 °C for 2 h, cooled to room temperature, and treated with
80 mL Carius tube that was fitted with a micro stirrer bar and attached to
-
3
an atmospheric pressure source of hydrogen. The mixture was degassed
by three freeze-pump-thaw cycles, refilled with hydrogen, and then
returned to room temperature. At this point the flask was sealed and the
mixture was stirred for 12 h. Conversion was determined by drying the
trifluororomethanesulfonic acid (270 μL, 3.05 ꢀ 10 M). A solution of
-3
the diastereopure phospharuthenocenyl ester 7 (1.0 g, 1.9 ꢀ 10 M) in
dichloromethane (5 mL) was added; the mixture was stirred for 5 min
and then evaporated to dryness under reduced pressure. The resulting
solid was placed in a bath at 125 °C and stirred gently for 10 min. The
dark product was tipped onto a silica column with careful exclusion of air
and purified by chromatography on alumina using degassed dichlor-
omethane-diethyl ether, 1:1, as eluent. Pale yellow air stable 15 was
1
crude sample under reduced pressure and analysis by H NMR;
enantiomeric excess was determined, after freeing the product from
organometallic impurities by filtration through a 2 ꢀ 1 ( ) cm silica
column in ether, by chiral HPLC on a chiraldex OD-H column using 9:1
hexane-2-propanol eluents with flow rates of 1 mL min- . For G = H:
elution time: R 9.7, S 12.4 min; for G = F: elution time: R 11.7 S 14.9
min; for G = MeO: elution time: R 15.0, S 19.0 min.
1
3
1
1
obtained in 91% yield. P NMR (CDCl ): δ -24.0 ppm. H NMR
3
(
1
J
CDCl
.97 (s, 3H, Me), 1.72 (s, 15H, Cp*). C NMR (CDCl
P-C = 19.3 Hz, CdO), 138.2 (d, JP-C = 17.5 Hz), 129.9 (d, JP-C
3
): δ 7.29-7.14 (m, 5H), 6.2 (br, 1H, OH), 2.20 (s, 3H, Me),
13
3
): δ 177.0 (d,
-
5
1
1: Carbocation 9 (50.0 mg, 9.6 ꢀ 10
M) was added to
=
-
4
triphenylphosphine (26.2 mg, 1.0 ꢀ 10 M) in THF at -78 °C, and
the reaction mixture was warmed to room temperature, stirred for 15
min, and then returned to -78 °C. n-Butyllithium in hexane (73 μL of
6.8 Hz), 129.4, 126.2, 105.9 (d, JP-C = 56.5 Hz, PCCMe), 95.5 (d, JP-C
=
5.3 Hz, PCCMe), 95.2 (d, JP-C = 4.5 Hz, PCCMe), 88.9 (Cp*), 79.9
(
[
d, JP-C = 60.1 Hz, PCCMe), 13.0 (Me), 12.6 (Me), 10.1 (Cp*).
-
4
2
5
1
.6 M; 1.2 ꢀ 10 M) was added over 3 min, and after a further 10 min,
R] = þ168.4 (c 1.0, DCM). HRMS (EI 70 eV): calcd for C H O
D
23 27 2-
the solution was warmed to room temperature, stirred for 45 min, and
PRu 468.0793, found 468.0790. Anal. Calcd for C23
27 2
H O PRu: C,
-
4
recooled to -78 °C. Paraformaldehyde (8.6 mg, 2.9 ꢀ 10 M) was
added; the solution was stirred for a further 25 min and then warmed to
room temperature. After stirring for 2.5 h, the mixture was treated with a
drop of degassed water, filtered through a plug of alumina, and purified
by flash chromatography on silica in pentane. The solvents were
removed under reduced pressure to give 11 as a pale yellow solid
5
9,09; H, 5,82. Found: C; 59.30, H: 5.44.
-
3
1
7: Solid phosphorus pentachloride (320 mg, 1.5 ꢀ 10 M) was
added in one portion to an ice-bath-cooled dichloromethane (5 mL)
solution of the enantiopure phospharuthenocenoic acid 15 (700 mg,
-
3
1
.5 ꢀ 10 M). The mixture was stirred for 30 min, and the solution was
evaporated to dryness under reduced pressure on a Schlenk line. The
crude acid chloride product 16 was resuspended in THF (5 mL) at -
78 °C, and methylmagnesium bromide (6.4 mL of 1.2 M solution, 7.7 ꢀ
31
1
(
32.7 mg, 76%). P NMR (CD
2 2
Cl ): δ -44.6 ppm. H NMR
(
CD Cl ): δ 7.28-7.06 (m, 5H), 6.12 (dt, JPH = 10.3 Hz, JHH = 10.3
2
2
-
3
Hz, JHH = 17.1 Hz, 1H, PCCH), 5.24 (dt, JPH = 1.9 Hz, JHH = 17.1 Hz,
10 M) was added over 2 min from a syringe. The reaction mixture was
stirred for 30 min and then brought slowly to room temperature. After
recooling to 0 °C, the mixture was partitioned between 1 M sodium
carbonate solution (15 mL) and dichloromethane (15 mL); the organic
layer was separated, further washed sequentially with brine (10 mL) and
water (10 mL), and evaporated to dryness under reduced pressure. The
product was purified by flash chromatography though a 2 ꢀ 1 ( ) cm
silica column in acetone. Traces of the faster running elimination
J
HH = 1.9 Hz, 1H, CH2), 4.99 (dd, JHH = 10.6 Hz, JHH = 1.8 Hz, 1H,
1
3
2
CH ), 1.97 (s, 3H, Me), 1.94 (s, 3H, Me), 1.69 (s, 15H, Cp*). C NMR
(
CD Cl ): δ 139.9 (d, J = 17.4 Hz, ipso-Ph), 134.9 (d, JPC = 17.0 Hz,
2 2 PC
CH), 130.2 (d, JPC = 6.8 Hz, o-Ph), 128.1 (m-Ph), 126.0 (p-Ph), 112.3
(
d, JPC = 14.2 Hz, CH ), 101.3 (d, J = 56.6 Hz, PCPh), 94.8(d, JPC =
2 PC
57.0 Hz, PCCH), 93.8 (d, JPC = 4.5 Hz, PCCMe), 92.6 (d, JPC = 4.3 Hz,
PCCMe), 88.2 (Cp*), 13.4 (Me), 11.9 (Me), 10.7 (Me Cp*). HRMS:
calcd for C H PRu 450.1050, found 450.1059.
product 18 can be recovered by prior elution with dichloromethane-
24 29
-4
31
1
3: A solution of 11 (65.3 mg, 1.43 ꢀ 10 M) in dichloromethane
pentane (1:4) as a pale yellow air-stable solid (29 mg, 9%).
P
1
(
(
4 mL) was cooled to -78 °C, and tetrafluoroboric acid etherate
(CH
2 2 3
Cl ): δ -34.3 ppm H NMR (CDCl ): δ 7.25-7.21 (m, 4H),
-
4
21.0 μL of 55% solution in ether; 1.55 ꢀ 10 M) was added as
7.17-7.09 (m, 1H), 4.94 (d, JHH = 23.9, 2H, CH ), 2.02 (s, 3H, Me),
2
13
rapidly as possible. The solution was stirred for 15 min, allowed to warm
2.01 (s, 3H, Me), 1.93 (s, 3H, C(CH
3
)(CH
2
)), 1.72 (s, 15H, Cp*).
C
to ice-bath temperature, and treated with diphenylphosphine (27 μL,
NMR (CDCl ): δ 142.4 (d, JPC = 17.2 Hz, PCC(CH
3
2
)(CH )), 139.4
3
-4
29 mg, 1.56 ꢀ 10 M). After stirring for 15 min, the solution was
(d, JPC = 17.2 Hz, ipso-Ph), 129.7 (d, JPC = 7.0 Hz, o-Ph), 127.7 (m-Ph),
125.5 (p-Ph), 111.9 (d, JPC = 6.1 Hz, CH ), 102.6 (d, J = 57.7 Hz, PC),
diluted to 15 mL with dichloromethane and washed with degassed 1 M
sodium hydroxide solution (10 mL), brine (10 mL), and water (10 mL).
2
PC
100.4 (d, JPC = 56.5 Hz, PCPh), 92.1 (d, JPC = 3.9 Hz, PCC), 91.2 (d, JPC
The organic layer was separated, dried over MgSO
4
, and reduced to a
= 4.2 Hz, PCC), 87.7 (Cp*), 25.8 (d, JPC = 11.0 Hz, CH
3
CCH
2
), 14.1
þ
volume of 1 mL under reduced pressure. Degassed methanol (10 mL)
was added dropwise over 5 min, and the solution was stirred vigorously
before again being reduced in volume to 1 mL. Cooling to -78 °C
(Me), 13.5 (Me), 10.6 (Cp*). CI-MS (NH ) (m/z, %): 465 ([M þ H] ,
3
100%), 450 (M - Me, 26%). The product 17 was obtained as a pale
3
1
1
yellow solid (254 mg, 77%). P NMR (CDCl
NMR (CDCl ): δ 7.25-7.20 (m, 4H), 7.17-7.08 (m, 1H), 2.17 (s, 3H,
Me), 1.98 (s, 3H, Me), 1.75 (s, 15H, Cp*), 1.50 (s, 3H, C(CH )(CH )),
3
): δ -32.8 ppm. H
-
4
overnight gave 13 (81.9 mg, 1.3 ꢀ 10 M, 91%). An analytical sample
3
3
1
was recrystallized from methanol. P NMR (C D ): δ 9.4 (d, J = 19.9
6
6
PH
3
3
1
13
Hz), -40.0 (d, JPH = 19.9 Hz). H NMR (C
6
D
6
): δ 7.69-7.61 (m, 2H),
3 3 6
1.44 (d, JPH = 4.0 Hz, C(CH )(CH )). C NMR (d -acetone): δ 140.9
7
1
1
.47-7.35 (m, 4H), 7.22-7.0 (m, 9H), 3.11 (qdd, JHH = 6.9 Hz, JPH
=
(d, JPC = 17.5 Hz, ipso-Ph), 131.1 (d, JPC = 7.3 Hz, o-Ph), 129.5 (m-Ph),
127.1 (p-Ph), 113.9 (JPC = 62.7 Hz, PCCOH), 100.2 (d, JPC = 54.5 Hz,
PCPh), 94.3 (d, JPC = 5.2 Hz, PCCMe), 93.7 (d, JPC = 3.7 Hz, PCCMe),
89.4 (Cp*), 72.3 (d, JPC = 17.8 Hz, COH), 34.3 (d, JPC = 19.6 Hz, Me),
0.1 Hz, JPH = 2.8 Hz, 1H, CH), 1.87 (s, 3H, Me), 1.60 (s, 15H, Cp*),
.48 (dd, JPH = 12.2 Hz, JHH = 6.9 Hz, 3H, Me-CH), 1.43 (s, 3H, Me).
1
3
C NMR (C
6 6
D ): δ 140.4 (d, JPC = 17.7 Hz), 138.9 (d, JPC = 20.9 Hz),
1
36.3 (d, JPC = 20.5 Hz), 135.1 (d, JPC = 19.8 Hz), 133.64 (d, JPC = 16.5
31.9 (Me), 14.7 (Me), 14.2 (Me), 12.1 (Me Cp*). EI-MS (m/z, %): 482
þ
Hz), 130.0 (d, JPC = 7.45 Hz), 129.3, 128.6 (d, JPC = 6.9 Hz), 128.1,
([M] , 100%), 465 ([M - OH], 61%), 424 ([M - CMe OH], 82%).
2
1
808
dx.doi.org/10.1021/om100845p |Organometallics 2011, 30, 1804–1811

Organometallics
ARTICLE
2
5
[
4
6
R]
D
= þ270.7 (c 1.0, DCM). HRMS: calcd for C25
H
33OPRu
δ 7.92-7.14 (m, 15 H), 5.76 (b, 1H, CH), 5.03 (b, 1H, CH), 4.78
82.1313, found 482.1290. Anal. Calcd for C H OPRu: C, 62,35; H,
(b, 1H, CH), 4.48 (b, 1H, CH), 2.73-1.54 (m, 8H, CH , COD), 2.93
25
33
2
,91. Found: C, 62.41; H, 6.75.
9: Tetrafluoroboric acid etherate (200 μL of 55% solution in ether,
(s, 3H), 1.83 (s, 3H), 1.77 (s, 15H, Cp*), 1.50 (d, JPH = 12.9, 3H), 0.98
(d, JPH = 16.2, 3H).
1
-
3
1
.47 ꢀ 10 M) was added as rapidly as possible to an ice-bath-cooled
Crystal Data. 13: 2(C36
clinic, space group P2 , a = 8.369(1) Å, b = 30.250(1) Å, c = 12.931(1) Å,
β = 90.700(1)°, V = 3273.4(5) Å , Z = 4, D
1404; graphite-monochromated Mo KR radiation, λ = 0.71069 Å, μ =
H P Ru), CH Cl , M = 678.15, mono-
40 2 2 2
dichloromethane (12 mL) solution of the phospharuthenocene alco-
1
-
3
3
-3
hol 17 (560 mg, 1.2 ꢀ 10 M), and the mixture was stirred for 10 min.
After warming to room temperature, the mixture was evaporated to
dryness, washed with diethyl ether (3 ꢀ 10 mL), and filtered. The
= 1.376 g cm , F(000) =
c
-
1
0.68 cm , T = 150(1) K. Of 15 264 independent reflections collected
on a Kappa CCD diffractometer from a colorless block of dimensions
0.20 ꢀ 0.20 ꢀ 0.18 mm over h = -11 to 11, k = -38 to 42, l = -18 to 18,
3
1
product was obtained as an air-stable orange solid (368 mg, 56%).
P
1
NMR (CD
H), 7.37-7.30 (m, 4H), 4.78 (q, JHH = 6.8 Hz, 4H, O(CH
s, 6H, PCCCH ), 2.00 (s, 6H, (CH ) C), 1.95 (s, 6H, PCCCH ),
2
Cl
2
): δ 21.4 ppm. H NMR (CD
2
Cl
2
): δ 7.47-7.39 (m,
2
6
(
2
)
2
), 2.21
14 074 having I > 2σ(I) were refined on F using direct methods in
3
3 2
3
Shelxl. wR = 0.0626, R = 0.0295, GoF = 1.024. Flack’s parameter =
2
1
1
CH
.93 (s, 6H, (CH
3
)
2
C)), 1.64 (s, 30H, Cp*), 1.61 (t, JHH = 6.8 Hz, 6H,
-0.024(12).
1
3
3
CH
2
O). C NMR (CD Cl ): δ 135.8 (d, JPC = 19.7 Hz,
2
2
PCCMe )), 132.2 (d, J = 17.4 Hz, ipso-Ph), 129.6 (Ph), 129.3 (d,
2
PC
’
ASSOCIATED CONTENT
J
PC = 10 Hz, Ph), 129.3 (Ph), 123.7 (d, JPC = 59.4 Hz, PC), 113.5 (d,
JPC = 6.9 Hz, PCC), 109.9 (d, JPC = 64.32 Hz, PC), 101.4 (d, JPC = 4.0
Hz, PC), 98.9 (Cp*), 84.9 (CH O), 29.4 (d, JPC = 26.2 Hz, C(CH ),
6.4 (C(CH ), 14.6 (PCCCH ), 14.0 (PCCCH ), 12.9
CH CH O), 9.3 (Cp*) ppm.
S
Supporting Information. Full crystallographic data for
b
2
3 2
)
1
3. This material is available free of charge via the Internet at
2
3
)
2
3
3
http://pubs.acs.org.
(
3
2
-
4
2
0: Diphenylphosphine (31 μL, 33 mg, 1.78 ꢀ 10 M) was added
-4
’ AUTHOR INFORMATION
to a room-temperature solution of 19 (99.0 mg, 1.80 ꢀ 10 M) in
dichloromethane (5 mL). The mixture was stirred for 20 min, and the
solvent was then removed under reduced pressure. The solid cationic
product was crystallized by stirring under degassed methanol (1 mL)
at -78 °C and found to be sufficiently pure for further use (97 mg,
Corresponding Author
*
E-mail: Duncan.Carmichael@polytechnique.edu.
Present Address
Institut f €u r Technische and Makromolekulare Chemie (ITMC),
3
1
§
7
7
4%). P NMR(CH Cl ): δ 22.6 (d, J = 7.2 Hz), -32.2 (d, JPP
.2 Hz) ppm. H NMR (CDCl ): δ 7.72-7.62 (m, 2H), 7.53-7.44
=
2
2
PP
1
RWTH Aachen, Worringerweg 1, 52074 Aachen, Germany.
3
(m, 2H), 7.39-7.31 (m, 3H), 7.25-7.06 (m, 8H), 1.99 (s, 3H, Me),
1
1
.97 (s, 3H, Me), 1.69 (s, 15H, Cp*), 1.42 (d, JPH = 13.4 Hz, CMeMe),
1
3
.38 (dd, JPH = 7.7, JPH = 2.4 Hz, CMeMe) ppm. C NMR (CD
2
Cl
2
):
’ ACKNOWLEDGMENT
δ 138.0 (d, JPC = 18.0 Hz, ipso-Ph Rc), 135.9-135.6 (m, 2C, p-Ph
phosphine), 135.2-134.8 (m, 4C, m-Ph phosphine), 130.6 (d, JPC
.6 Hz, 2C, o-Ph phosphine), 130.5 (d, JPC = 7.7 Hz, 2C, o-Ph
phosphine), 129.9 (d, JPC = 7.7 Hz, 2C, o-Ph Rc), 128.4 (m-Ph Rc),
26.6 (p-Ph Rc), 116.6 (d, JPC = 2.2 Hz, ipso-Ph phosphine), 115.6 (d,
We thank CNRS, Ecole Polytechnique (AMX grant to EM),
the ‘Fonds de l'Ecole Polytechnique’ (Gaspard Monge grant to
NS) the European Commission through FP5 contract HPRN-
CT-2001-172 (postdoctoral stipends for JK and MS), the French
Embassy in Warsaw (to SS) and the Egide “Polonium” program
=
7
1
JPC = 3.3 Hz, ipso-Ph phosphine), 100.9 (dd, JPC = 65.5 Hz, JPC
=
=
1
7788RL (to D.C. and M.S.) for funding. The Polytechnique
5
4
.0 Hz, PCCMe ), 100.7 (d, J = 53.9 Hz, PCPh), 94.7 (d, JPC
.3 Hz, PCCMe), 93.1 (dd, JPC = 4.8 Hz, JPC = 1.8 Hz, PCCMe), 89.5
2 PC
laboratory is part of the EC COST funded network “PhoSciNet”
CM0802.
(
Cp*), 41.9 (dd, JPC = 35.6 Hz, JPC = 14.9 Hz, CMe ), 28.6 (d, J
=
2
PC
2
4.5 Hz, Me bridge), 25.4 (d, JPC = 5.1 Hz, Me bridge), 14.0 (Me), 13.9
2
5
(Me), 11.3 (Me Cp*). [R]
D
= þ270.7 (c 1.0, DCM). HRMS: calcd
’ REFERENCES
for C37
H
42
P
2
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4
2
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(
4
2
solution was stirred for 2 min and then treated dropwise at -78 °C with
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(
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=
41 Hz), 38.5 (dd, JP-Rh = 170 Hz, JP-P = 41 Hz). H NMR (CDCl ):
P
3
1
809
dx.doi.org/10.1021/om100845p |Organometallics 2011, 30, 1804–1811

Organometallics
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810
dx.doi.org/10.1021/om100845p |Organometallics 2011, 30, 1804–1811

Organometallics
ARTICLE
(
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(
80) The combination of [Rh(cod)(acac)] and a strong electrophile
þ
provides a clean low- temperature access to [Rh(cod)(solv) ] species.
2
Upon reaction with phosphines, these often provide cleaner samples of
þ
[
Rh(cod)(PR
3
)
2
]
complexes than those which are obtained directly
þ
from the phosphine and the more conventional precursor [Rh(cod) ]
See: Brown, J. M.; Evans, P. L.; James, A. P. Organic Syntheses 1990,
2
.
68, 64–76. Chatt, J.; Venanzi, L. M. J. Chem. Soc. 1957, 4735–4741.
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þ
sphine/Rh catalysis of enamide hydrogenation constitutes a very
significant part of the entire reaction time if cod containing precursors
are used, so a full kinetic analysis will be required to interpret rates
adequately. However, the long periods (>12 h) required to ensure
completion suggest that activity is probably modest.
(
82) Grach, G.; Reboul, V.; Metzner, P. Tet. Asym. 2008,
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1
(
83) These interactions distinguish the new ligands described here
35
from the side chain- functionalised ligands described by Ganter in ref;
the latter, being Cp rather than Cp* derivatives, may be more flexible in
their sidearm conformations.
(
84) Brown, J. M. In Comprehensive Asymmetric Catalysis, Vol. 1;
Jacobsen, E. N.; Pfaltz, A.; Yamamoto, H., Eds.; Springer Verlag,
Heidelberg, 1999, 121; Brown, J. M. ’Mechanism of Enantioselective
Hydrogenation’ in Handbook of Homogeneous Hydrogenation Vol. 3
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therein.
(
(
85) Roper, J. M.; Bauer, D. P. Synthesis-Stuttgart 1983, 1041–1043.
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1
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