Stereochemistry at carbon upon protonolysis of a late transition metal-alkyl bond: A reaction of relevance to catalytic enantioselective hydrogenation of olefins

Article abstract of DOI:10.1139/v01-051

Reaction of [Ru((R)-BINAP)(H)(MeCN)_n (acetone)_3-n](BF₄) (where n = 0-3) (2) with 1 equiv of the olefin substrate methyl α-acetamidoacrylate (MAA) in acetone at room temperature immediately generated a mixture (72:28) of two diastereomers of the complex [Ru((R)-BINAP)(MeCN)(MAA(H))](BF₄)(3). The olefin-hydride insertion reaction between 2 and MAA to generate 3 was regioselective, with transfer of the hydride to the β-olefinic carbon and transfer of ruthenium to the α-carbon in both diastereomers of 3. The two diastereomers of 3 differ by the absolute configuration at the α-carbon of MAA(H) ((S_cα)-3 and (R_cα)-3). The absolute configuration of the major ((S_cα)-3) diastereomer was determined by X-ray diffraction in conjunction with NMR spectroscopic data. Protonolysis of the ruthenium-carbon bond in 3 and in the methyl α-acetamidocinnamate (MAC) analog ([Ru((R)-BINAP)(MeCN)((S)-MAC(H))](BF₄)((S_cα)-4)) by addition of 2 equiv HBF₄·Et₂O in CH₂ Cl₂ at room temperature was not stereospecific and did not occur with β-hydride elimination from the methyl or benzyl groups.

Full text of DOI:10.1139/v01-051

1019
Stereochemistry at carbon upon protonolysis of a
late transition metal-alkyl bond: a reaction of
relevance to catalytic enantioselective
hydrogenation of olefins
Jason A. Wiles, Steven H. Bergens, and Victor G. Young, Jr.
Abstract: Reaction of [Ru((R)-BINAP)(H)(MeCN)n(acetone)3–n](BF4) (where n = 0–3) (2) with 1 equiv of the olefin
substrate methyl α-acetamidoacrylate (MAA) in acetone at room temperature immediately generated a mixture (72:28)
of two diastereomers of the complex [Ru((R)-BINAP)(MeCN)(MAA(H))](BF4) (3). The olefin–hydride insertion reac-
tion between 2 and MAA to generate 3 was regioselective, with transfer of the hydride to the β-olefinic carbon and
transfer of ruthenium to the α-carbon in both diastereomers of 3. The two diastereomers of 3 differ by the absolute
configuration at the α-carbon of MAA(H) ((SCα)-3 and (RCα)-3). The absolute configuration of the major ((SCα)-3)
diastereomer was determined by X-ray diffraction in conjunction with NMR spectroscopic data. Protonolysis of the ru-
thenium–carbon bond in 3 and in the methyl α-acetamidocinnamate (MAC) analog ([Ru((R)-BINAP)(MeCN)((S)-
MAC(H))](BF4) ((SCα)-4)) by addition of 2 equiv HBF4·Et2O in CH2Cl2 at room temperature was not stereospecific and
did not occur with β-hydride elimination from the methyl or benzyl groups.
Key words: ruthenium, BINAP, enantioselective, hydrogenation, catalysis.
Résumé : La réaction du [Ru((R)-BINAP(H)(MeCN)n(acétone)3–n](BF4) (dans lequel n = 0–3) (2) avec un équivalent
du substrat oléfinique α-acétamidoacétate de méthyle (“MAA”), dans l’acétone, à la température ambiante, conduit im-
médiatement à la formation d’un mélange (72:28) de deux diastéréomères du complexe [Ru((R)-
BINAP(MeCN)(“MAA”(H))](BF4) (3). La réaction d’insertion oléfine–hydrure entre 2 et “MAA” pour générer 3 est ré-
giosélective; dans les deux diastéréomères de 3, le transfert de l’hydrure se portant sur le carbone oléfinique β et le
transfert de ruthénium sur le carbone α. Les deux diastéréomères de 3 diffèrent par la configuration absolue au niveau
du carbone en α du “MAA”(H) ((SCα)-3) et ((RCα)-3). On a déterminé la configuration absolue du produit principal, le
diastéréomère ((SCα)-3), par diffraction des rayons X alliée aux données de spectroscopie RMN. La protonolyse de la
liaison ruthénium–carbone présente dans le composé 3 et dans son analogue α-acétamidocinnamate de méthyle
(“MAC”), le [Ru((R)-BINAP(MeCN)((S)-“MAC”(H))](BF4) ((SCα)-4), a été réalisée par addition de deux équivalents de
HBF4·Et2O, dans du CH2Cl2, à la température ambiante; cette réaction n’est pas stéréospécifique et elle ne se produit
pas par le biais d’une élimination β à partir des groupes méthyle ou benzyle.
Mots clés : ruthénium, BINAP, énantiosélective, hydrogénation, catalyseur.
[Traduit par la Rédaction] 1025
Introduction
Wiles et al.
James’ further development of the first enantioselective cat-
alytic hydrogenation using a ruthenium catalyst containing a
chiral bis(phosphine) ligand (2). These papers helped found
and inspire the development of ruthenium – chiral bis(phos-
phine) catalysts, the most versatile and widely used catalyst
systems for the enantioselective hydrogenation of olefins
and ketones.
The first reported use of ruthenium complexes as homoge-
neous catalysts for hydrogenation of olefins was a landmark
paper published by James and co-workers (1) nearly 40
years ago. This paper, in part, laid the groundwork for
Received September 1, 2000. Published on the NRC Research
Press Web at http://canjchem.nrc.ca site on July 11, 2001.
The mechanisms for hydrogenations catalyzed by ruthenium–
bis(phosphine)-halide complexes, as well as the chemistry of
such compounds, have been extensively studied by James et
al. (3). Mechanistic studies by James, Noyori, and others
showed that hydrogenation of α,β-unsaturated acids (e.g.,
tiglic acid ((E)-CH3CH=C(CH3)CO2H)) using Ru((R)-
BINAP)(O2CCH3)2 (1) as catalyst in MeOH proceeds by
heterolytic cleavage of H2 and subsequent protonolysis of a
ruthenium(II)–alkyl bond (4). As the putative ruthenium(II)–
alkyl intermediate occurred after the turnover-limiting step
in the catalytic cycle, it was impossible to detect in solution,
and the stereochemistry of this key enantio-determining step
Dedicated to Professor Brian James on the occasion of his
65th birthday.
J.A. Wiles and S.H. Bergens.1 Department of Chemistry,
University of Alberta, Edmonton, AB T6G 2G2, Canada.
V.G. Young, Jr. X-ray Crystallographic Laboratory, 160
Kolthoff Hall, Chemistry Department, 207 Pleasant St. S.E.,
The University of Minnesota, Minneapolis, MN 55455,
U.S.A.
1Corresponding author (telephone: (780) 492-9703; fax: (780)
492-8231; e-mail: steve.bergens@ualberta.ca).
Can. J. Chem. 79: 1019–1025 (2001)
DOI: 10.1139/cjc-79-5/6-1019
© 2001 NRC Canada

1020
Can. J. Chem. Vol. 79, 2001
Fig. 1. Structure of (SCα)-3 as determined by X-ray diffraction.2,3
could not be directly observed. A comparison of NMR data
for the isotopomers of CH3CHDCD(CH3)CO2H obtained from
deuterations of tiglic acid in MeOD using 1 and using
RhCl(PPh3)3 as a catalyst lead to the conclusion that
protonolysis proceeded via retention of configuration at car-
bon (4b). Most catalytic hydrogenations of olefins that in-
volve protonolysis (solvolysis) of a metal–carbon bond are
believed to, or have been shown to, proceed via a net syn-
addition of H2 across the olefin; the presumed consequence
of retention at carbon during the protonolysis. There are re-
ported examples, however, for which direct protonolysis of
Pt–C σ bonds through back-side attack was postulated to ac-
count for catalytic net anti-addition of deuterium to certain
olefins using platinum–tin complexes as catalysts (5). We
now report the first direct observations of protonolysis of the
catalyst–alkyl bond in two putative diastereomeric interme-
diates for catalytic hydrogenation of olefins.
C1
C2
N1
C4
P2
C3
O1
Ru1
C5
P1
O2
O3
N2
C6
C7
Results and discussion
Reaction of [Ru((R)-BINAP)(H)(MeCN)n(acetone)3–n](BF4)
(where n = 0–3) (2) (6) with 1 equiv of methyl
α-acetamidoacrylate (MAA) in acetone at room temperature
generated upon mixing (>99% by NMR analysis) a mixture
of two species in a ratio of 72:28 (eq. [1]).
chemical shifts and coupling constants for both
diastereomers of 3 parallel those previously found for (SCα)-4.
For example, 13C{1H} NMR signals from the coordinated
amido and the ester carbonyls, as well as from the α-carbon
of 3 (that σ-bonded to ruthenium) are comparable to those of
(SCα)-4. From these similarities, we conclude that the two
diastereomers of 3 differ by the absolute configuration at the
α-carbon of MAA(H) ((SCα)-3 and (RCα)-3). The absolute
configuration of the major (72%) diastereomer was deter-
mined as follows.
NMR spectroscopy, electrospray-ionization mass spectrom-
etry (EI-MS), and microanalysis indicated that these species
were two diastereomeric forms of the complex [Ru((R)-
BINAP)(MeCN)(MAA(H))](BF4) (3). Complex 3 resulted
from olefin–hydride insertion between MAA and 2. We pre-
viously reported the preparation, solid-state structure, and re-
activity of a related complex formed by reaction between 2 and
methyl α-acetamidocinnamate (MAC) in >99% diastereomeric
excess (de), viz., [Ru((R)-BINAP)(MeCN)((S)-MAC(H))](BF4)
((SCα)-4) (6). In accord with (SCα)-4, the olefin–hydride in-
sertion reaction between 2 and MAA was regioselective,
with transfer of the hydride to the β-olefinic carbon in MAA
and transfer of ruthenium to the α-carbon in both
diastereomers of 3 (for similar regioselective insertion of
MAA into Ru–H bonds of chiral clusters, see ref. 7). NMR
Slow liquid–liquid diffusion of di-n-butyl ether into a 1,2-
dimethoxyethane solution of 3 (72:28) at room temperature
produced X-ray quality crystals.2 Diffraction data was col-
lected from two separate samples. In both cases, the molecu-
lar structure of the isolated species was of (SCα)-3, as shown
in Fig. 1. The molecular structures of (SCα)-3 and (SCα)-4 are
quite similar.
Both are best described as the enolates of MAA(H)– and
MAC(H)– bonded to ruthenium through Cα (C3) and through
CH3
C
+
H
H
O
N
CH3
CH3
P
H
O
O
O
Ru
+
(RCα)-3
2
+
*
[1]
CH3
N
O
P
N
28%
H
O
CH3
-
BF4
CH3
(SCα)-3
72%
2 Crystal data for (SCα)-3: C52H45BF4N2O3P2Ru, FW = 995.72, yellow plate, crystal size 0.40 × 0.25 × 0.13 mm, orthorhombic, C2221, a =
21.4849(2), b = 29.7175(2), c = 18.8513(2) Å, V = 12036.1(2) Å3, Z = 8, ρcalcd. = 1.099 g cm–3, µ (Mo Kα) = 0.361 mm–1, T = 173(2) K,
λ (Mo Kα) = 0.71073 Å. Data were collected using a Siemens SMART Platform CCD diffractometer (θ range for data collection of 1.17 to
25.04°); 10589 independent reflections (8758 with Fo2 > 2σ(Fo2 )) were measured. The structure was solved via direct methods (SHELXTL-
V5.0). Full-matrix least-squares refinement on F2 (SHELXTL-V5.0) yielded R1 = 0.0480 (Fo2 > 2σ(Fo2 )) and wR2 = 0.1261 (all data). GoF
on F2 = 1.041.
© 2001 NRC Canada

Wiles et al.
1021
the amido and ester carbonyl groups.3 To determine if (SCα)-3
was the major or minor diastereomer, the crystal used for
one of the two structure determinations was dissolved at –78°C
alkyl complexes (SCα)-3′ and (RCα)-3′ by protonation at the
ruthenium centre. These dicationic diastereomers could in
principle interconvert via β-H elimination from the methyl
group before elimination of MAA(H)2. To investigate this
possibility, we prepared 3-d1 (in which one β-H of Ru-Cα-CH3
was replaced by deuterium, prepared by reaction of 2-d1 with
MAA) and reacted it with 2 equiv HBF4·Et2O. After treat-
ment with MeCN and purification, the recovered MAA(H)2
consisted of MAA(H)2-β-d1 as the sole isotopomer. β-H
elimination at the methyl group of 3′, face flip of the coordi-
nated olefin, and olefin–hydride insertion is expected to
cause some scrambling of deuterium between the α- and β-
positions of MAA(H)2. The absence of any such scrambling
shows that if the dicationic diastereomers (SCα)-3′ and
(RCα)-3′ do form, they do not interconvert via β-H elimina-
tion from the methyl group.
1
in CD2Cl2. The H NMR spectrum revealed a 95:5 (ma-
jor:minor) mixture of the diastereomers of 3 within the crys-
tal.4 These X-ray and NMR data show that the major
diastereomer of 3 formed by reaction of MAA and 2 is
(SCα)-3. As stated above, use of MAC results in almost ex-
clusive formation of this diastereomer ((SCα)-4).5
Crystals of the minor diastereomer suitable for X-ray dif-
fraction could not be obtained. In an attempt to confirm that
it was (RCα)-3, we effected the protolytic cleavage of the
Ru–Cα bond with HBF4·Et2O in CH2Cl2 solution. Addition
of 2 equiv HBF4·Et2O to a solution of 3 (72:28) in CH2Cl2 at
room temperature followed by addition of excess MeCN (9.5
equiv) generates N-acetylalanine methyl ester (MAA(H)2)
Although these experiments indicated that protonolysis of
the ruthenium–carbon bonds in (SCα)-3 and (RCα)-3 proceeded
by inversion, protonation of a sample enriched in (SCα)-3
(95:5) using 2 equiv HBF4·Et2O yielded, after treatment with
MeCN and purification, MAA(H)2 in 44% ee (S). This is the
same ee as that obtained from the 72:28 mixture of (SCα)-3
and (RCα)-3, respectively, and it shows that the protonolysis
is not stereospecific. This result is confirmed by protonolysis
of (SCα)-4-d1, the MAC derivative of (SCα)-3-d1 (where one
β-H of Ru-Cα-CH2Ph was replaced by deuterium), prepared
by reaction of 2-d1 with MAC (6a). Reaction of (SCα)-4-d1
with 2 equiv HBF4·Et2O yielded, after treatment with MeCN
and purification, MAC(H)2-β-d1 as the sole isotopomer in
12% ee (R). Thus, protonolysis of the ruthenium–carbon
bond in (SCα)-4-d1 is also not stereospecific, and it too does
not involve β-H elimination from the benzyl group.
and
the
known
dicationic
compound
[Ru((R)-
BINAP)(MeCN)4](BF4)2 (8). Protonolysis with retention of
configuration at Cα of the mixture of (SCα)-3 and (RCα)-3
(72:28) will generate MAA(H)2 in 44% (R) enantiomeric ex-
cess (ee) (72% (R)-MAA(H)2 and 28% (S)-MAA(H)2). The
ee of the MAA(H)2 isolated from the protonolysis was
44% (S); the protonolysis of the Ru–C bond in 3 occurred
with apparent inversion of configuration at carbon.6 This ex-
periment was repeated twice.
Two control experiments showed that (SCα)-3 and (RCα)-3
do not interconvert in the absence of acid under these condi-
tions. First, the compositions of 72:28 and 95:5 mixtures of
these diastereomers did not change over several days in CH2Cl2
at room temperature. Second, exposure of 3 to D2 (1 atm,
1 atm = 101.325 kPa) at room temperature does not result in
H–D exchange at Cβ (Ru-Cα-CH3). We previously showed
that formation of the MAC analogue ((SCα)-4) is reversible
under these conditions using a similar experiment (6b). Spe-
cifically, exposure of (SCα)-4 to D2 (1 atm) resulted in H–D
exchange at Cβ of MAC(H) (Ru-Cα-CH2Ph) via β-hydride
elimination and subsequent H–D exchange at the ruthenium-
hydride. Thus, conversion between (SCα)-3 and (RCα)-3 did
not occur to an appreciable extent prior to reaction with
acid.
Conclusions
Our previous report of the MAC compound (SCα)-4 was
the first solid-state structure of a diastereomeric catalyst–
substrate complex of the same absolute configuration as the
major product enantiomer of an olefin hydrogenation. This
report of the MAA compound (SCα)-3 is the second; as such,
it adds to the sparse knowledge base of the structures of
these diastereomeric putative catalytic intermediates. Reac-
tion of MAC with 2 favours almost exclusive formation of
There is the possibility that reaction of 3 with HBF4·Et2O
generated dicationic diastereomeric ruthenium(IV)–hydrido-
3 Selected bond lengths (Å) and angles (°) with estimated standard deviations for (SCα)-3 are as follows: Ru(1)—N(2) 1.995(4), Ru(1)—P(1)
2.3525(13), Ru(1)—P(2) 2.2640(11), Ru(1)—O(1) 2.072(3), Ru(1)—O(2) 2.278(3), Ru(1)—C(3) 2.230(5), Ru(1)—C(5) 2.345(5), C(3)—C(4)
1.515(7) Å; C(5)-C(3)-C(4) 119.1(4), N(1)-C(3)-C(5) 112.1(4), N(1)-C(3)-C(4) 111.4(4), Ru(1)-C(3)-N(1) 101.4(4), Ru(1)-C(3)-C(4)
132.0(3), Ru(1)-C(3)-C(5) 76.1(3)°.
4 We both dissolved the crystal and analyzed the resulting solution at low temperature to prevent any diastereomeric interconversion that may
occur. This precaution was not necessary as 31P NMR spectroscopic analysis of 3 (72:28 and 95:5 (major:minor) diastereomeric ratios) in
acetone-d6 over a range of temperatures from –80 to +25°C showed the ratios of diastereomers did not vary under these conditions. The
95:5 ratio observed in the crystal analyzed by X-ray diffraction was the same ratio found for the entire crop of crystals (bulk sample).
5 As we reported previously, only (SCα)-4 is observed in NMR spectra recorded at room temperature. Subsequent spectra recorded at low tem-
perature show the presence (8%) of the other fluctional diastereomer, (RCα)-4. Selected NMR data (CD2Cl2, –40°C) for (SCα)-4 and (RCα)-4
(the asterisks denote resonances attributed to the minor diastereomer ((RCα)-4): 13C{H} NMR (100.6 MHz) δ: 36.1 (s, PhCH2CRu*), 37.8 (s,
2
2
2
2
PhCH2CRu), 66.9 (dd, JP(B),C = 42.0 Hz, JP(A),C = 3.5 Hz, RuC), 70.0 (dd, JP(B′),C = 42.0 Hz, JP(A′),C = 3.5 Hz, RuC*), 157.9 (br s,
CO2CH3*), 159.7 (d, JP(B),C = 3.0 Hz, CO2CH3), 179.6 (d, JP(B),C = 7.0 Hz, NHCOCH3), 179.9 (d, JP(B′),C = 7.0 Hz, NHCOCH3*). 15N{H}
NMR INEPT (40.5 MHz) δ: 184.4 (dd, JP(A),N = 4.5 Hz, JP(B),N = 3.0 Hz, CH3CN-Ru). The corresponding 15N resonance for (RCα)-4 was
2
2
not observed; however, the 31P{1H} NMR spectrum of (RCα)-4 prepared using CH3C15N displayed JP(A′),N = 4.5 Hz and JP(B′),N = 3.0 Hz.
2
2
31P{H} NMR (161.9 MHz) δ: 32.9 (d, 2JP,P = 23.5 Hz, 1P, P(B)), 40.1 (d, 2JP,P = 24.0 Hz, 1P, P(B′)*), 55.2 (d, 2JP,P = 24.0 Hz, 1P, P(A′)*),
2
59.4 (d, JP,P = 23.5 Hz, 1P, P(A)).
6 The ee of MAA(H)2 was spectroscopically (1H NMR) determined using a chiral shift reagent ((+)-Eu(tfc)3) after separation from [Ru((R)-
BINAP)(MeCN)4](BF4)2 by colum chromatography (Florisil–EtOAc). The absolute configuration of the major enantiomer was determined
by comparison to authentic (S)-MAA(H)2.
© 2001 NRC Canada

1022
Can. J. Chem. Vol. 79, 2001
Scheme 1.
CH3
C
CH3
C
H+
[Ru]+
[Ru]+
H+
C
N C
N
(SCα)-3
H3C
[Ru]2+
C
H
+
O
C
NHCOCH3
H3C
O
CH3
C
CH3
+
2+
(S)-MAA(H)2
C
N
N
CH3
CH3
O
H+
P
P
P
O
Ru
Ru
O
*
*
CH3
CH3
O
H
O
P
N
N
H
O
H
CH3
CH3
(SCα)-3
(SCα)-4 as major diastereomer (6). The methyl analogue gen-
erated using MAA favours the same absolute configuration
as major diastereomer ((SCα)-3), but with a weaker bias
(72:28). The protonolysis of these compounds under the de-
scribed conditions is not stereospecific, and it does not pro-
ceed via β-H elimination from the benzyl or methyl groups.
Although the lack of observable β-H elimination from the
benzyl or methyl groups implies that equilibration of the
diastereomers does not occur during the protonolysis, such
equilibration may still occur via protonation at the amido ni-
trogen followed by β-H elimination to form an iminium.
These experiments and labeling studies are moot on this
point because of rapid proton exchange between the amido
group and HBF4AEt2O.
in the reversal of stereochemistry has appeared in the litera-
ture, see ref. 12).
Further experimentation (such as low-temperature NMR
studies) is required to investigate the stereochemical course
of these protonation reactions and their relevance to catalytic
hydrogenation of olefins. These results do show, however,
that protonolysis of a catalyst–carbon bond is a complicated
process, one that should not be assumed a priori to proceed
with strict retention.
Experimental
Another explanation for this lack of stereospecificity is
that two pathways operate in parallel for the protonolysis.
One pathway, resulting in retention at carbon, is protonation
at ruthenium followed by elimination of alkane. We note that
although there are few examples, all reported electrophilic
abstractions of alkyl or vinyl ligands from early or late tran-
sition-metal centres by protonolysis occur with retention of
configuration at carbon (9). The other pathway, resulting in
inversion at carbon, is electrophilic attack at the back side of
the Ru–C σ-bond (Scheme 1). Such a possibility has been
suggested to account for inversion of configuration at carbon
for alkyl abstraction from zirconium complexes by boranes
(10), and as discussed in the introduction, for the observed
net anti-addition of H2 in certain hydrogenations of olefins
(5).
Another explanation for this lack of stereospecificity is
prior protonation of a substrate lone pair followed by intra-
molecular proton transfer. Similar processes have been re-
ported in the literature (cleavage of a Fe–C σ-bond via
protonation at nitrogen has been observed, see ref. 11).
Scheme 1 shows such a pathway involving protonation of
the amido group of MAA(H), followed by a suprafacial
intramolecular proton delivery to C(3) with inversion of
stereochemistry (intramolecular proton delivery and its role
General considerations
All reactions were conducted under an atmosphere of dry
Ar (Praxair, 99.998%) using standard Schlenk and glovebox
techniques. NMR spectra were recorded using a Bruker AM-
2
400 (1H at 400.1 MHz, H at 61.4 MHz, 13C at 100.6 MHz,
15N at 40.5 MHz, and 31P at 161.9 MHz) spectrometer. The
1
2
chemical shifts for H, H, and 13C are reported in parts per
million (δ) relative to external TMS and were referenced to
residual solvent signals. The chemical shifts for 15N and 31P
are reported in parts per million (δ) relative to external liquid
NH3 and external 85% H3PO4, respectively. NMR abbrevia-
tions used: broad (br), singlet (s), doublet (d), doublet of
doublets (dd), doublet of doublet of doublets (ddd), triplet
(t), quartet (q), doublet of quartets (dq), doublet of triplets
(dt), and multiplet (m). Electron-impact high-resolution
mass spectrometry (EI-HRMS) of N-acetylalanine methyl
ester (MAA(H)2) was performed on a Kratos MS50 spec-
trometer. Mass spectrometric analysis of 3 (MeCN solution)
was performed on a Micromass ZabSpec Hybrid Sector-TOF
spectrometer using positive-mode electrospray ionization
(ESI-MS (pos)). Calculated m/z values refer to the isotopes
1
12C, H, 14N, 16O, 31P, and 102Ru. Microanalyses were per-
formed at the University of Alberta Microanalysis Labora-
tory.
© 2001 NRC Canada

Wiles et al.
1023
NHCOCH3*), 3.77 (s, 3H, CO2CH3*), 3.85 (s, 3H,
CO2CH3), 6.4–8.1 (aromatic), 8.38 (br s, 1H, NHCOCH3),
9.02 (br s, 1H, NHCOCH3*). 1H NMR (400.1 MHz,
Materials
Argon gas (Praxair, 99.998%) was dried by passage
through a column containing 3 Å molecular sieves and phos-
phorus pentoxide before use. Dihydrogen gas (Praxair,
99.99%) was passed through an Alltech Oxy-Trap to remove
trace amounts of oxygen before use. Dideuterium gas
(Aldrich, 99.8%; Praxair, 99.7%) was used as received. All
protiated solvents (Anachemia, Caledon, and Fisher Scien-
tific) and deuterated solvents (99.5–99.9% D, Cambridge
Isotope Laboratories) were distilled from appropriate drying
agents (13) under an atmosphere of argon gas before use ex-
cept absolute ethanol (200 proof), which was used as re-
ceived. Unless stated otherwise, all reagents were used as
received from Aldrich. [Ru((R)-BINAP)(H)(MeCN)n(ace-
4
(CD3)2CO, –40°C) δ: 0.99 (d, JP,H = 5.0 Hz, 3H, RuC-
4
CH3*), 1.55 (d, JP,H = 5.0 Hz, 3H, RuC-CH3), 1.84 (s, 3H,
CH3CN), 1.89 (s, 3H, CH3CN*), 2.03 (s, 3H, NHCOCH3),
2.17 (s, 3H, NHCOCH3*), 3.74 (s, 3H, CO2CH3*), 3.82 (s,
3H, CO2CH3), 6.4–8.1 (aromatic), 8.69 (br s, 1H,
NHCOCH3), 9.28 (br s, 1H, NHCOCH3*). 13C{1H} NMR
(100.6 MHz, CD2Cl2, 25°C) δ: 4.2 (s, CH3CN-Ru*), 4.5 (s,
CH3CN-Ru), 17.4 (br s, RuC-CH3*), 18.8 (s, RuC-CH3),
19.7 (s, NHCOCH3*), 20.4 (s, NHCOCH3), 52.6 (s,
CO2CH3*), 52.9 (s, CO2CH3), 63.3 (dd, 2JP,C(trans) = 44.0 Hz,
2
2JP,C(cis) = 4.0 Hz, RuC), 66.4 (br d, JP,C(trans) = 43.0 Hz,
RuC*), 126–142 (overlapping aromatic and CH3CN), 161.5
(d, JP,C = 3.0 Hz, overlapping (SCα)-3 and (RCα)-3, CO2CH3),
179.3 (d, JP,C = 7.0 Hz, NHCOCH3), 179.9 (d, JP,C = 7.0 Hz,
NHCOCH3*). 13C{1H} NMR (100.6 MHz, CD2Cl2, –40°C)
δ: 4.1 (s, CH3CN-Ru*), 4.3 (s, CH3CN-Ru), 16.9 (s, RuC-
CH3*), 18.2 (s, RuC-CH3), 19.5 (s, NHCOCH3*), 20.1 (s,
NHCOCH3), 52.4 (s, CO2CH3*), 52.6 (s, CO2CH3), 63.0
tone)3–n](BF4) (where
n
=
0–3) (2), 2-d1, methyl
α-acetamidoacrylate (MAC), [Ru((R)-BINAP)(MeCN)((S)-
MAC(H))](BF4) ((SCα)-4 and (SCα)-4-d1) were prepared as
described previously (6). The ee and absolute configuration
of the MAC(H)2-β-d1 generated from protonolysis of (SCα)-4-d1
was determined as described previously (6). Methyl α-
acetamidoacrylate (MAA) was purified by column chroma-
tography on neutral alumina (acetone) before use. (rac)-
MAA(H)2 and (S)-MAA(H)2 were prepared by the esterification
of (rac)-N-acetylalanine and (S)-N-acetylalanine, respectively,
using diazomethane (14).
2
2
(dd, JP,C(trans) = 43.5 Hz, JP,C(cis) = 4.0 Hz, RuC), 66.8 (dd,
2
2JP,C(trans) = 44.5 Hz, JP,C(cis) = 3.0 Hz RuC*), 124–141
(overlapping aromatic and CH3CN), 159.1 (s, CO2CH3*),
160.1 (s, CO2CH3), 178.6 (d, JP,C = 7.0 Hz, NHCOCH3),
179.1 (d, JP,C = 6.5 Hz, NHCOCH3*). 15N NMR INEPT
(40.5 MHz, (CD3)2CO, 25°C) δ: 183.1 (dd, 2JP(A),N = 4.5 Hz,
Syntheses
2
2JP(B),N = 3.0 Hz, CH3CN-Ru), 184.8 (dd, JP(A),N = 4.0 Hz,
All glassware and syringes were successively treated with
ethanolic ammonium hydroxide solution, acetone, and oven-
dried before use. Organometallic products were isolated in a
glovebox filled with dinitrogen gas and were stored at –30°C
for prolonged periods.
2JP(B),N
=
3.0 Hz, CH3CN-Ru*). 15N NMR INEPT
(40.5 MHz, (CD3)2CO, –40°C) δ: 181.9 (br apparent t,
2
2JP(A),N = JP(B),N = 3.5 Hz, CH3CN-Ru), 183.5 (br, CH3CN-
Ru*). 31P{1H} NMR (161.9 MHz, (CD3)2CO, 25°C) δ: 33.8
2
2
(d, JP,P = 22.0 Hz, 1P, P(B)), 38.8 (br d, JP,P = 21.0 Hz,
2
1P, P(B′)*), 58.5 (br d, JP,P = 21.0 Hz, 1P, P(A′)*), 59.7 (d,
3 and 3-d1
2JP,P = 22.0 Hz, 1P, P(A)). 31P{1H} NMR (161.9 MHz,
[Ru((R)-BINAP)(1–3;5,6-η-C8H11)(MeCN)](BF4)
(6)
2
(CD3)2CO, –40°C) δ: 33.4 (d, JP,P = 23.0 Hz, 1P, P(B)),
(323.9 mg, 0.338 mmol) was partially dissolved in acetone
(15.0 mL) under an atmosphere of Ar and subjected to 3
freeze-pump-thaw cycles. The reactor was backfilled with
H2 (20 psig, 1 psig = 6.894 kPa) at room temperature and
vigorously shaken for 10 min. The resulting orange solution
was subjected to 3 freeze-pump-thaw cycles and backfilled
with Ar. To this solution at room temperature was added an
acetone solution (5.0 mL) of MAA (48.3 mg, 0.338 mmol).
The resulting amber solution was shaken for 1 min and the
solvent was removed under reduced pressure to give a yel-
low solid. Dropwise addition of Et2O (80 mL) to a CH2Cl2
(2.0 mL) solution of the product afforded a yellow powder.
The product was collected by filtration and washed with
Et2O (3 × 10 mL) to yield 310.7 mg (92%) of 3. NMR spec-
troscopic analysis showed that the product contained a
diastereomeric mixture of (SCα)-3 and (RCα)-3 (72:28). An in
situ reaction monitored by NMR spectroscopy displayed the
same ratio of diastereomers. The method used for the prepa-
ration of 3-d1 was the same as that for 3 with substitution of
D2 for H2. ESI-MS (pos) m/z: 909.2 ([M – BF4]+) (exact
mass calcd. for C52H45N2O3P2Ru, 909.2). NMR spectro-
scopic data for 3 (the asterisks denote resonances attributed to
the minor diastereomer ((RCα)-3): 1H NMR (400.1 MHz,
(CD3)2CO, 25°C) δ: 1.17 (d, 4JP,H = 5.0 Hz, 3H, RuC-CH3*),
1.61 (d, 4JP,H = 5.0 Hz, 3H, RuC-CH3), 1.83 (s, 3H, CH3CN),
1.92 (s, 3H, CH3CN*), 2.04 (s, 3H, NHCOCH3), 2.17 (s, 3H,
38.7 (d, 2JP,P = 22.0 Hz, 1P, P(B′)*), 57.1 (d, 2JP,P = 22.0 Hz,
2
1P, P(A′)*), 59.4 (d, JP,P = 23.0 Hz, 1P, P(A)). Anal. calcd.
for C52H45BF4N2O3P2Ru: C 62.72, H 4.56, N 2.81; found:
C 62.35, H 4.88, N 2.64.
Protonations of 3 and 3-d1
To a stirred solution of (SCα)-3 and (RCα)-3 (72:28)
(101.0 mg, 0.101 mmol) in CD2Cl2 (0.50 mL) at room tem-
perature was added a solution of HBF4·Et2O (54% w/w in
Et2O, 28.0 µL, 0.203 mmol). The originally orange colored
solution immediately turned red in color upon addition of
HBF4·Et2O. After stirring for 15 min, CD3CN (50.0 µL,
0.957 mmol) was added to the reaction mixture to generate a
yellow colored solution. Analysis of the reaction mixture by
1H and 31P NMR spectroscopy indicated that exclusive for-
mation of MAA(H)2 and [Ru((R)-BINAP)(CD3CN)4](BF4)2
occurred. The solution was evaporated to dryness and the
residue was thoroughly washed with EtOAc (3 × 5 mL) and
the wash was passed through a column of Florisil™ (0.5 cm ×
7.0 cm). The clear, colorless eluent was evaporated to dry-
ness to give pure MAA(H)2. Protonation of 3-d11 exclu-
sively liberated MAA(H)2-β-d1, as determined by H and
2H NMR spectroscopy (1H NMR (400.1 MHz, CDCl3,
3
3
25°C) δ: 1.39 (dt, JH,H = 7.0 Hz, JH,D = 2.0 Hz, 2H,
CHCH2D (Hβ)), 2.02 (s, 3H, NHCOCH3), 3.76 (s, 3H,
© 2001 NRC Canada

1024
Can. J. Chem. Vol. 79, 2001
3
CO2CH3), 4.60 (apparent q, JH,H = 7.0 Hz, 1H, CHCH2D
(Hα)), 6.05 (br s, 1H, NHCOCH3). 2H{1H} NMR
(61.4 MHz, CHCl3, 25°C) δ: 1.39 (s, CHCH2D)). The
enantiomeric excess (ee) and absolute configuration (44% (S))
of purified MAA(H)2 and MAA(H)2-β-d1 were determined
as follows. The ee was spectroscopically determined (1H
NMR) using a chiral lanthanide shift reagent (europium
tris[3-(trifluoromethylhydroxymethylene)-(+)-camphorate]
((+)-Eu(tfc)3)) in CDCl3. Sufficient shift reagent was added
(0.2–0.4 equiv) to separate the methoxy signals (ca. 4 ppm)
of the two enantiomers of MAA(H)2 (low-field enantiomer
(R), high-field enantiomer (S)). That these were signals of
the enantiomers of MAA(H)2 was confirmed by repeating
the experiment using (rac)-MAA(H)2. The ratio of these
methoxy signals was used to quantify the ee. The absolute
configuration of the major enantiomer of the product was
determined by addition of authentic (S)-MAA(H)2 to the
samples and subsequently determining the ee via NMR spec-
troscopy as described above. Addition of (S)-MAA(H)2
caused the intensity of the high-field ((S)-enantiomer)
methoxy signal to increase.
C(3)—C(4) 1.515(7) Å; C(5)-C(3)-C(4) 119.1(4),
N(1)-C(3)-C(5)
112.1(4),
Ru(1)-C(3)-N(1)101.4(3),
Ru(1)-C(3)-C(5)76.1(3)°.
N(1)-C(3)-C(4)
Ru(1)-C(3)-C(4)
111.4(4),
132.0(3),
Acknowledgments
We sincerely appreciate the technical support and helpful
discussions provided by Mr. G. Bigam, Mrs. G. Aarts, and
Dr. T. Nakashima of the University of Alberta High Field
NMR Laboratory. We also thank the Natural Sciences and
Engineering Research Council of Canada (NSERC) and the
University of Alberta for financial support.
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In a 5-mm NMR tube, (SCα)-3 and (RCα)-3 (72:28)
(10.3 mg, 0.0103 mmol) were dissolved in CD2Cl2
(0.50 mL) at room temperature under Ar. The headspace of
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1
30-min period by H NMR spectroscopy showed the genera-
tion of MAA(H)2-α-d1 (10%) and no detectable incorpora-
tion of deuterium in the two diastereomers of 3 ((SCα)-3 and
(RCα)-3).
Crystal structure determination of (SCα)-3
Slow liquid-liquid diffusion of di-n-butyl ether into a 1,2-
dimethoxyethane solution of 3 (72:28) at room temperature
produced X-ray quality crystals. The structure was deter-
mined as described in the supplementary material.7 Crystal
data for (SCα)-3: C52H45BF4N2O3P2Ru, FW = 995.72, yel-
low plate, crystal size 0.40 × 0.25 × 0.13 mm, orthorhombic,
C2221, a = 21.4849(2), b = 29.7175(2), and c =
18.8513(2) Å, V = 12036.1(2) Å3, Z = 8, ρcalcd.
=
1.099 g cm–3, µ (Mo Kα) = 0.361 mm–1, T = 173(2) K,
λ (Mo Kα) = 0.71073 Å. Data were collected using a
Siemens SMART Platform CCD diffractometer (θ range for
data collection of 1.17–25.04°); 10589 independent reflec-
tions (8758 with F2 > 2σ(F2)) were measured. The structure
was solved via direct moethods (SHELXTL-V5.0). Full-
o
matrix least-squares refinement on F2 (SHELXTL-V5.0)
yielded R1 = 0.0480 (F2 > 2σ(F2)) and wR2 = 0.1261 (all
data). GoF on F2 = 1.041. Selecoted bond lengths (Å) and
angles (°) with estimated standard deviations for (SCα)-3 are
as follows: Ru(1)—N(2) 1.995(4), Ru(1)—P(1) 2.3525(13),
Ru(1)—P(2) 2.2640(11), Ru(1)—O(1) 2.072(3), Ru(1)—O(2)
2.278(3), Ru(1)—C(3) 2.230(5), Ru(1)—C(5) 2.345(5),
o
7 Supplementary material may be purchased from the Depository of Unpublished Data, Document Delivery, CISTI, National Research Council
Canada, Ottawa, ON K1A 0S2, Canada. For information on obtaining material electronically go to http://www.nrc.ca/cisti/irm/unpub_e.shtml.
Crystallographic information has also been deposited with the Cambridge Crystallographic Data Centre. Copies of the data can be obtained,
free of charge, on application to the Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K. (fax: 44-1223-336033 or e-mail:
deposit@ccdc.cam.ac.uk).
© 2001 NRC Canada

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© 2001 NRC Canada