Controlled oxidative addition of amino acid esters to Rh(I)

Article abstract of DOI:10.1016/S0022-328X(99)00311-3

The new sterically demanding phosphine 2-(di-o-tolylphosphino)phenol was prepared and used to create a series of esters with N-acylated amino acids. The phosphine-containing esters react within 30-60 min at room temperature with [(μ-Cl)Rh(cyclooctene)₂]₂ to give products of oxidative addition of the ester carbonyl-oxygen bond to the Rh center. The N-acyl carbonyl oxygen is bound to the Rh in these initial adducts, but is displaced upon addition of PMe₃. Remarkably, both initial products and their PMe₃ adducts are formed as single five-coordinate diastereomers in essentially quantitative yields.

Full text of DOI:10.1016/S0022-328X(99)00311-3

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 589 (1999) 115–121
Communication
Controlled oxidative addition of amino acid esters to Rh(I)
Douglas B. Grotjahn a,*, Camil Joubran b,1, David Combs a
a Department of Chemistry, San Diego State Uni6ersity, 5500 Campanile Dri6e, San Diego, CA 92182-1030, USA
b Department of Chemistry and Biochemistry, Arizona State Uni6ersity, Box 871604, Tempe, AZ 85287-1604, USA
Received 9 April 1999
Abstract
The new sterically demanding phosphine 2-(di-o-tolylphosphino)phenol was prepared and used to create a series of esters with
N-acylated amino acids. The phosphine-containing esters react within 30–60 min at room temperature with [(m-
Cl)Rh(cyclooctene)2]2 to give products of oxidative addition of the ester carbonyl–oxygen bond to the Rh center. The N-acyl
carbonyl oxygen is bound to the Rh in these initial adducts, but is displaced upon addition of PMe3. Remarkably, both initial
products and their PMe3 adducts are formed as single five-coordinate diastereomers in essentially quantitative yields. © 1999
Elsevier Science S.A. All rights reserved.
Keywords: Amino acids; CꢀO bond activation; Oxidative addition; Peptides; Rhodium
1. Introduction
transformations has involved changes in the amino acid
or peptide framework.
Both coordination [1] and organometallic [2] com-
plexes of amino acids and peptides have been exten-
sively studied, but these studies have so far focused on
maintaining and using the robust amino acid frame-
work [2], for instance, in the creation of chiral com-
plexes or catalysts. For example, many organometallic
fragments have been attached directly to N, O or S
heteroatoms in amino acids and proteins from natural
sources [2,3], or to P atoms in helical polypeptides
containing unnatural amino acids [4]. Alternatively,
organometallic reagents with reactive organic moieties
at the periphery have been attached indirectly to het-
eroatoms using organic reactions such as amide bond
formation [5]. Our interest in amino acid complexes has
included direct p-complexation of amino acids and
proteins in water or organic solvents [6,7], and dias-
teroselective formation [3y] and reactions [3w,x,8] of
amino acid chelate complexes. However, none of these
Although transformations of amino acids have been
used to make chiral nitrogen-containing compounds
(including ligands for chiral organometallic complexes
[9]), with few exceptions, these reactions have not in-
volved transition-metal organometallics. Castan˜o and
Echavarren have reported the formation of nickelacy-
cles from cyclic anhydrides derived from glutamic acid,
reactions which involve oxidative addition of the anhy-
dride to the Ni(0) center and subsequent decarbonyla-
tion [10]. Hungate et al. used [CpFe(CO)2]− and mixed
anhydrides of amino acid derivatives to create chiral
acyl complexes for further asymmetric transformations
[11]. In this communication, we report preliminary
attempts to explore organometallic transformations of
amino acid esters, illustrated in Scheme 1. Esterification
of an N-acylated amino acid derivative 1 with a phos-
phine-containing alcohol such as 2 was anticipated to
give 3. Addition of a soft, low-valent metal complex to
3 would be expected to give 4, which could undergo
chelate-driven oxidative addition [12], providing 5, and
then chelate 6. Alkyl migration in 6 would lead to 7. In
this paper, we report the clean formation of oxidative
* Corresponding author. Fax: +1-619-5944634.
E-mail address: grotjahn@sundown.sdsu.edu (D.B. Grotjahn)
1 Present address: Astra Research Center Boston, 128 Sidney
Street, Cambridge, MA 02139, USA.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00311-3

116
D.B. Grotjahn et al. / Journal of Organometallic Chemistry 589 (1999) 115–121
Scheme 1.
addition products of type 6 using Rh complexes. That
these reactions proceed in essentially quantitative yields
is significant because we have previously noted [13] that
whereas addition of the alkyl CꢀO bond in allylic esters
(Scheme 2a) is well known and leads to useful organic
chemistry [14], the alternative addition of the carbonyl–
oxygen bond in esters (Scheme 2b) is a rare, and usually
messy reaction [15].
2. Results and discussion
Known 2-(diphenylphosphino)phenol 2a [16] was
used to esterify N-acetylglycine in the presence of dicy-
clohexylcarbodiimide (DCC) and 4-(N,N-dimethyl-
amino)pyridine (DMAP) to give 3 (R=Ph, R1=H,
R2=CH3) in 79% yield [17]. Preliminary experiments
[17] using this ester and the Ir(I) dimer [(m-
Cl)Ir(cyclooctene)2]2 quickly led to two tentative con-
clusions: despite maintaining a stoichiometry of one
phosphine per metal, there was a strong tendency to
form mixtures of bis(phosphine) complexes, which then
reacted rather slowly. Therefore, the subsequent experi-
ments described here were conducted using the
analogous Rh(I) dimer and bulkier phosphines. Because
the cone angles of tris–(o-tolyl)phosphine and
triphenylphosphine are 194 and 145°, respectively [18],
the synthesis of the phenol 2b, a new compound, was
undertaken.
Scheme 3.
tolyl)2 [19] gave crude 9, which was treated with
aqueous HCl and neutralized with bicarbonate to give
2b as a white solid in 81% overall yield. Interestingly,
Luo et al. found that treatment of other meth-
oxymethyl-protected phenols bearing phosphine groups
with HCl led to phosphonium salts because of the
basicity of the phosphine moiety [20]. As the authors
noted, in the previously reported preparation of 2a [16],
a base-neutralization step was omitted but the crude
product was sublimed, consistent with known loss of
HCl from phosphonium salts at elevated temperatures.
In fact, whereas 2b in our hands exhibited a single
31P{1H} resonance at l −43.57 ppm, omission of the
base neutralization step led to material (presumably the
hydrochloride salt of 2b, although this has not been
investigated further) with a P nucleus absorbing at
−15.38 ppm.
The requisite phosphine 2b was readily made by
adapting procedures used to make 2a [16]. Directed
deprotonation of methoxymethyl-protected phenol 8
with t-BuLi (Scheme 3) followed by addition of ClP(o-
In order to explore the scope of oxidative addition
chemistry, a variety of N-acylated amino acid deriva-
tives 3 (Scheme 4) were made, representing the achiral
acid glycine (3a), its N-alkylated derivative sarcosine
(3b, 3c), and the dipeptide glycylglycine (3d) protected
with a N-terminal carbobenzoxy (Cbz) group. Typical
DCC coupling of the N-acylated amino acids 1 and the
phenol 2b required about 20 h for completion, and
yields ranged from 32 to 57%. A catalytic amount of
DMAP [21,22] was added to inhibit N-acylurea forma-
Scheme 2.

D.B. Grotjahn et al. / Journal of Organometallic Chemistry 589 (1999) 115–121
117
topic (2JHH=11.0 Hz), indicating a stereogenic element
is present in 6a. Both the sarcosine esters 3b and 3c
reacted with [(m-Cl)Rh(cyclooctene)2]2 to give single
products 6b and 6c in quantitative yield. Very similar
NMR and IR spectral data were obtained (Table 1).
Unfortunately, the available data do not allow us to
determine the geometry of 6a–6c. The literature con-
tains many examples of stable five-coordinate rhodium
acyl complexes, whether square pyramidal or trigonal
bipyramidal [12b,27]; alternatively, cyclooctene could
occupy a sixth site, making 6a–6c octahedral. Some
evidence for alkene involvement when a smaller alkene
(and presumably better ligand) was involved came from
reactions of the ethylene analog [(m-Cl)Rh(ethylene)2]2
with 3a; the resulting spectrum contained sharp reso-
nances for 6a, but a somewhat broadened resonance for
Scheme 4.
tion from the activated O-acyl urea, because the attack
of rather hindered nucleophile 2b on the activated
intermediate was feared to be slow.
1
To a room-temperature solution of the glycine ester
3a and internal standard [(CH3)3Si]4C in C6D6 was
added one equivalent (0.5 mol) of the rhodium (I)
dimer [(m-Cl)Rh(cyclooctene)2]2 [23]. Remarkably,
within 30–60 min, one product formed in quantitative
yield as determined by NMR integrations. The struc-
ture shown for 6a (Scheme 5) is consistent with all
spectroscopic data (Table 1). The 31P{1H}-NMR spec-
trum of 6a contains a doublet that is coupled to
rhodium (1JRhP=174 Hz) and provides the evidence for
rhodium-bound phosphine [24]. The IR absorptions of
6a at 1726 and 1584 cm−1 were consistent with metal-
acyl [12b] and metal-coordinated amide [25], respec-
tively. For comparison, the amide stretching frequency
in starting material 3a is 1678 cm−1. In the 13C{1H}-
NMR spectrum of 6a, the most downfield resonance at
l 209.35 (dd, 1JRhC=34.0 Hz, 2JPC=4.4 Hz) also
confirms the existence of a metal-acyl, and hence oxida-
tive addition of the ester acyl–oxygen bond to Rh [13].
Although the precise stereochemistry of 6 cannot be
ethylene. Upon standing in C6D6 for 12–15 h, the H-
and 31P-NMR spectra of acyl complex 6a degrade, and
no identifiable features appear in replacement. Potential
decomposition pathways include alkyl migration fol-
lowed by b-hydride elimination involving the NꢀH
group. In support of this idea, rhodium acyl complexes
6b and 6c featuring N-methyl groups were more stable
in solution, persisting for 24–48 h. Nonetheless, com-
plexes 6 could not be obtained in analytically pure
form.
Therefore, trimethylphosphine was added to the
complex 6a to prevent decomposition by saturating the
coordination sites. Once the phosphine is added to a
solution of 6a in benzene, the color changes from
yellow to orange and spectral data (Table 1) implicate
formation of a single product 10a in greater than 95%
yield. Similar results were obtained for 6b–d, giving
10b–d. Significantly, the PMe3 adduct 10a remains
stable in solution for
a
week. The incoming
trimethylphosphine ligand seemed to take up the site of
the coordinated amide as revealed by the IR absorption
at 1686 cm−1 (cf. 1678 cm−1 for free ligand 3a). Also,
the 31P spectrum contained two separate resonances,
2
assigned, the small value of JPC shows unequivocally
that the acyl and phosphine ligands are mutually cis
[13,26]. The methylene protons (Ha, Hb) are diastereo-
1
both doublets of doublets (2JPP=389 Hz, JRhP=111
Hz). Large splittings of each resonance indicate that the
phosphines are mutually trans [23], with the acyl mutu-
ally cis to both phosphines: the 13C{1H}-NMR data for
the acyl carbon showed a larger splitting by Rh
(1JRhC=34.0 Hz) and two smaller and equal splittings
by the P nuclei (2JPC=2JP%C=6.3 Hz). The complexes
are five coordinate, although at this point we do not
know if they are square pyramidal or trigonal bipyra-
midal. Complex 10d gives correct elemental analysis
data, and its 31P{1H}-NMR and IR data (see Section 4)
are very similar to those for simpler analogues 10a–c,
1
but its H-NMR spectrum exhibited several broadened
resonances, perhaps because of hydrogen bonding of
the three carbonyl groups and two NH groups in either
an intramolecular or intermolecular sense.
Scheme 5.

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D.B. Grotjahn et al. / Journal of Organometallic Chemistry 589 (1999) 115–121
Table 1
NMR data for Rh acyl complexes 6 and 10 in C6D6 (shifts l in ppm, coupling constants J in Hz)
Complex
1H-NMR
31P{1H}
Methylenes
ArꢀCH3
ArꢀH
NꢀCH3, COCH3 or
P(CH3)3
6a
3.43 (d, J=11.0, 1 H)
4.04 (d, J=11.0, 1 H)
2.55 (s, 3 H)
2.86 (s, 3 H)
6.47 (t, J=7.5, 1 H)
6.63 (t, J=5.7, 1 H)
6.73 (t, J=7.5, 1 H)
6.82 (t, J=7.8, 2 H)
6.95–7.20 (m, 4 H)
7.38 (t, J=10.8, 2 H)
8.12 (dd, J=12.3, 7.5, 1
H)
1.92 (s, 3 H)
+52.48 (d, J=174)
6b
3.42 (d, J=12.0, 1 H)
3.89 (d, J=12.0, 1 H)
2.61 (s, 3 H)
2.93 (s, 3 H)
6.47 (t, J=6.6, 1 H)
6.63 (t, J=6.0, 1 H)
6.74 (t, J=7.2, 1 H)
6.82 (t, J=7.2, 1 H)
6.97–7.24 (m, 6 H)
7.42 (t, J=6.9, 1 H)
8.22 (dd, J=13.2, 7.5, 1
H)
1.71 (s, 3 H)
1.75 (s, 3 H)
+53.88 (d, J=176)
6c
3.18 (d, J=16.0, 1 H)
3.39 (d, J=16.0, 1 H)
3.49 (d, J=12.5, 1 H)
3.91 (d, J=12.5, 1 H)
2.60 (s, 3 H)
2.86 (s, 3 H)
6.48 (t, J=7.0, 1 H)
6.66 (t, J=6.5, 1 H)
6.75 (t, J=7.5, 1 H)
6.83 (t, J=7.5, 1 H)
6.85–7.21 (m, 10 H)
7.42 (t, J=8.0, 1 H)
8.23 (dd, J=13.5, 8.0, 1
H)
1.89 (s, 3 H)
+53.81 (d, J=177)
10a
3.83 (dd, J=18.1, 5.7, 1
H)
4.34 (dd, J=18.1, 7.2, 1
2.34 (s, 3 H)
2.69 (s, 3 H)
6.51 (t, J=6.6, 1 H)
1.28 (s, 3 H)
+32.46 (dd, J=389,
111)
+6.04 (dd, J=389,
6.78–6.87 (m, 3 H)
1.46 (dd, J=11.4, 2.7, 9
H)
H)
111)
6.94–7.24 (m, 5 H)
7.36 (t, J=8.1, 1 H)
7.61 (dd, J=11.1, 8.4, 1
H)
10b
10c
3.86 (d, J=17.7, 1 H)
4.45 (d, J=17.7, 1 H)
2.36 (s, 3 H)
2.71 (s, 3 H)
6.51 (t, J=6.6, 1 H)
1.54 (s, 3 H)
+32.10 (dd, J=388,
113)
+6.55 (dd, J=388,
113)
6.74–7.25 (m, 9 H)
1.58 (dd, J=11.4, 3.0, 9
H)
1.64 (s, 3 H)
7.34(t, J=6.9, 1 H)
7.60 (dd, J=10.8, 7.8, 1
H)
3.10 (s, 2 H)
2.33 (s, 3 H)
2.70 (s, 3 H)
6.50 (t, J=7.2, 1 H)
1.53 (dd, J=10.8, 2.7, 9
H)
1.67 (s, 3 H)
+32.19 (dd, J=386,
113)
+6.49 (dd, J=386,
113)
3.87 (d, J=17.0, 1 H)
4.48 (d, J=17.0, 1 H)
6.70–7.25 (m, 13 H)
7.31 (t, J=8.1, 1 H)
7.58 (dd, J=11.1, 7.8, 1
H)
3. Conclusions
trolled the stoichiometry of subsequent reactions with
Rh(I) dimer [(m-Cl)Rh(cyclooctene)2]2, so that within 1
h at room temperature, single products 6 were ob-
tained in essentially quantitative yields. It is clear that
in conversion of 3 to 6, the ester COꢀO bond has
A new phenolic phosphine, 2b, was prepared and its
esters with four N-acylated amino acids were obtained.
The steric hindrance about the phosphorus center con-

D.B. Grotjahn et al. / Journal of Organometallic Chemistry 589 (1999) 115–121
119
been added to the Rh center to form five-coordinate
(phenoxy)(acyl) complexes featuring a coordinated
amide group. Addition of PMe3 displaces the amide,
giving five-coordinate acyls 10 in which the new ligand
appears trans to the bulky phosphine. Future reports
will attempt to clarify the bonding in 6 and 10 and the
effects of an amino acid chiral center on the
diastereoselectivity of the type of transformations de-
scribed here.
C20H19OP (306.36): C; 78.40, H; 6.26. Found: C;
78.00, H; 6.33.
4.2. 2-(Di-o-tolylphosphino)phenol ester of
N-acetylglycine (3a)
Phosphine 2b (0.574 g, 1.88 mmol) was placed in a
flask with deoxygenated dichloromethane and DMF
(20 ml each). DMAP (0.023 g, 0.19 mmol) and N-
acetylglycine (0.271 g, 2.31 mmol) were added to the
flask and the solution was stirred at 0°C. A solution
of DCC (0.427 g, 2.07 mmol) in dichloromethane (10
ml) was added via addition funnel over 30 min. The
reaction was stirred and allowed to warm to r.t.
overnight. The solution was filtered to remove DCU,
dried over magnesium sulfate, filtered, and the solvents
were removed on the high-vacuum line. The resulting
white solid was purified by chromatography (20:1
dichloromethane–ethyl acetate) yielding a white solid
4. Experimental
In addition to the general considerations reported in
Ref. [13], some NMR spectra reported here were ob-
tained using Varian Gemini 2000 200 MHz or Inova
500 MHz spectrometers.
4.1. 2-(Di-o-tolylphosphino)phenol (2b)
1
(0.246 g, 32%). H-NMR (C6D6, 300 MHz) l 1.37 (s,
A 100 ml Schlenk flask was charged with 8 (0.500 g,
3.62 mmol) and dry diethyl ether (15 ml) under N2
and the flask was immersed in a −40°C bath (CO2–
ethylene glycol). t-BuLi (2.13 ml of 1.70 M in hexane,
3.62 mmol) was added to the flask in one portion via
syringe. An immediate white precipitate formed and
the solution was stirred at −40°C for 1.5 h. A solu-
tion of ClP(o-tol)2 (0.900 g, 3.62 mmol) in diethyl
ether (20 ml) was transferred to the Schlenk flask via
cannula in one portion. After 1 h, the cooling bath
was removed and the reaction was stirred at room
temperature (r.t.) for 15 h. The reaction mixture was
diluted with deoxygenated diethyl ether (20 ml) and
washed with three portions of deoxygenated saturated
sodium chloride (20 ml). The organic layers were dried
over MgSO4, filtered, and solvents were removed in
vacuo. The resulting white solid was taken up in HCl-
saturated methanol (100 ml) and the resulting solution
stirred under N2 for 24 h. The methanol was removed
in vacuo, ethyl acetate (40 ml) was used to dissolve
the solid, and the resulting solution was washed with
saturated aqueous sodium bicarbonate (3×20 ml).
The organic layer was dried over MgSO4, filtered, and
solvent removed from the filtrate in vacuo. The re-
maining white solid was purified by chromatography
(5:1 dichloromethane–ethyl acetate) yielding a white
3 H), 2.41 (s, 6 H), 3.85 (d, J=5.4 Hz, 2 H), 4.65 (m,
1 H), 6.76 (dt, J=7.8, 1.8 Hz, 1 H), 6.86–7.10 (m, 11
H) ppm. 13C-NMR (C6D6, 126 MHz) l 21.18 (d, J=
21.7 Hz), 22.89, 41.40 (d, J=1.6 Hz), 122.55, 126.35,
126.85, 129.25, 130.28, 130.32, 133.26, 134.26 (d, J=
3.3 Hz), 142.75 (d, J=27.3 Hz), 152.79 (d, J=17.3
Hz), 168.05, 169.99 ppm. 31P-NMR (C6D6, 202.3
MHz) l −31.82 ppm. IR (C6D6, cm−1) 3437 (NꢀH),
1764 (CꢁO, ester), 1678 (CꢁO, amide). Anal. Calc. for
C24H24NO3P (395.46): C; 70.55, H; 6.17, N; 3.64.
Found: C; 71.08, H; 5.98, N; 3.46.
4.3. 2-(Di-o-tolylphosphino)phenol ester of
N-acetyl-N-methylglyine (3b)
Using a procedure similar to that for 3a, phosphine
2b (0.417 g, 1.37 mmol) in dichloromethane (20 ml)
and DMF (20 ml) was treated with DMAP (0.017 g,
0.14 mmol) and N-acetyl-N-methylglycine (0.180 g,
1.37 mmol) at 0°C, followed by a solution of DCC
(0.311 g, 1.51 mmol) in dichloromethane (10 ml)
added over 30 min. The reaction was stirred and al-
lowed to warm to r.t. overnight. As in the preparation
of 3a, work-up followed by chromatography
(dichloromethane) gave a white solid (0.327 g, 57%).
NMR spectroscopy revealed the presence of major and
minor rotamers in a ratio of approximately 2 to 1.
1H-NMR (C6D6, 300 MHz) l 2.03 (s, 1.0 H, minor),
2.05 (s, 2.0 H, major), 2.35 (s, 2.0 H, minor), 2.38 (s,
4.0 H, major), 2.79 (s, 1.0 H, minor), 2.81 (s, 2.0 H,
major), 4.02 (s, 0.6 H, minor), 4.10 (s, 1.4 H, major),
6.70–6.80 (m, 1 H), 7.04–7.50 (m, 11 H) ppm. 31P-
NMR (C6D6, 202.3 MHz) l −30.30 (major), −31.60
(minor) ppm. Anal. Calc. for C25H26NO3P (419.52): C,
70.95; H, 6.51; N, 3.74. Found: C, 71.37; H, 6.46; N,
3.64.
1
solid (0.900 g, 81%). H-NMR (CDCl3, 400 MHz) l
2.38 (s, 6 H), 6.25 (bs, 1 H), 6.85–6.90 (m, 4 H), 6.97
(dd, J=8.0, 6.0 Hz, 1 H), 7.12 (t, J=7.2 Hz, 2 H),
7.20–7.30 (m, 5 H) ppm. 13C-NMR (CDCl3, 101
MHz) l 21.15 (d, J=20.4 Hz), 115.52, 121.13 (d,
J=2.5 Hz), 126.28 (d, J=1.3 Hz), 129.19, 130.37 (d,
J=5.1 Hz), 131.67, 132.59, 135.21 (d, J=4.4 Hz),
142.33 (d, J=24.9 Hz), 159.61 (d, J=17.8 Hz) ppm.
31P-NMR (CDCl3, 162 MHz) l −43.57 ppm. IR
(KBr, cm−1) 3385 (OꢀH), 1184 (CꢀO). Anal. Calc. for

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D.B. Grotjahn et al. / Journal of Organometallic Chemistry 589 (1999) 115–121
4.4. 2-(Di-o-tolylphosphino)phenol ester of
N-(4-chlorophenyl)acetyl-N-methylglyine (3c)
reaction was stirred for 30 min until a yellow color had
developed. The yellow reaction mixture was stirred an
additional 30 min to ensure complete reaction before
PMe3 (0.0094 g, 0.12 mmol) was added in one portion
and the solution immediately turned orange. The sol-
vent volume was reduced to 5 ml and hexane was added
to induce precipitation. The precipitate was filtered and
washed with hexane (3×5 ml) yielding a bright yellow
solid (0.072 g, 94%). NMR data: see Table 1 and text.
IR (C6D6, cm−1) 3432 (NꢀH), 1709 (CꢁO, acyl), 1686
(CꢁO, amide). Anal. Calc. For C26H33ClNO3P2Rh
(618.81): C, 52.31, H, 5.38, N, 2.26. Found: C, 52.54;
H, 5.45; N, 2.28.
Using a procedure similar to that for 3a, phosphine
2b (0.423 g, 1.39 mmol) in dichloromethane (10 ml) was
treated with DMAP (0.0206 g, 0.169 mmol) and N-(4-
chlorophenyl)acetyl-N-methylglycine (0.315 g, 1.30
mmol) at 0°C, followed by solid DCC (0.332 g, 1.61
mmol), using dichloromethane (ca. 1 ml) to rinse the
weighing container. The reaction was stirred and al-
lowed to warm to r.t. overnight. As in the preparation
of 3a, work-up followed by chromatography (ethyl
acetate/dichloromethane) gave a white solid (0.3521 g,
51%). NMR spectroscopy revealed the presence of ma-
jor and minor rotamers in a ratio of approximately 3.5
to 1. 1H-NMR (C6D6, 500 MHz) l 2.29 (s, 3 H, NꢀCH3
of major), 2.31 (s, 6 H, ArꢀCH3 of minor), 2.37 (s, 6 H,
ArꢀCH3 of major), 2.72 (s, 3 H, NꢀCH3 of minor), 3.16
(s, 2 H, ArCH2CO of major), 3.29 (s, 2 H, ArCH2CO
of minor), 3.55 (s, 2 H, NCH2CO of minor), 3.94 (s, 2
H, NCH2CO of major), 6.70–7.10 (m, 16 H for both
major and minor) ppm. 31P-NMR (C6D6, 80.95 MHz) l
−31.78 ppm (only one peak seen).
4.6. Complex 10b
In the glove-box, following the procedure used to
make 10a, 3b (0.0622 g, 0.149 mmol) in benzene (10 ml)
was reacted with [(m-Cl)Rh(cyclooctene)2]2, (0.0533 g,
0.0743 mmol) for a total of 60 min before PMe3 (0.0113
g, 0.149 mmol) was added. After work-up, bright yel-
low solid (0.091 g, 97%) was obtained. NMR data: see
Table 1 and text. IR (C6D6, cm−1) 1711 (CꢁO,
Rhꢀacyl), 1657 (CꢁO, amide). Anal. Calc. for
C28H35ClNO3P2Rh (632.84): C, 53.14, H, 5.59, N, 2.21.
Found: C, 52.91; H; 5.45; N, 2.28.
4.4.1. 2-(Di-o-tolylphosphino)phenol ester of
CbzGlyGly (3d)
At 0°C, to a solution of phosphine 4 (0.518 g, 1.70
mmol) in dichloromethane (30 ml) and DMF (10 ml)
was added DMAP (0.021 g, 0.17 mmol) and CbzGly-
GlyOH (0.480 g, 1.71 mmol), followed by a solution of
DCC (0.386 g, 1.87 mmol) in dichloromethane (20 ml)
according to the procedure used for 7a. The crude solid
product was purified by chromatography (20:1
dichloromethane–ethyl acetate) yielding a white solid
4.7. Complex 10d
In the glove-box, following the procedure used to
make 10a, 3d (0.0680 g, 0.119 mmol) in benzene (10 ml)
was reacted with [(m-Cl)Rh(cyclooctene)2]2, (0.0430 g,
0.0596 mmol) for a total of 60 min before PMe3 (0.0091
g, 0.12 mmol) was added. After work-up, the yield of
bright yellow solid was 0.090 g (97%). Partial data:
31P{1H}-NMR (MHz) l 5.69 (dd, J=387, 114 Hz),
1
(0.416 g, 43%). H-NMR (C6D6, 300 MHz) l 2.40 (s, 6
H), 3.35 (d, J=4.8 Hz, 2 H), 3.75 (d, J=5.7 Hz, 2 H),
4.81 (bs, 1 H), 5.02 (s, 2 H), 5.42 (t, J=5.7 Hz, 1 H),
6.76 (dt, J=6.6, 1.5 Hz, 1 H), 6.70–7.25 (m, 16 H)
ppm. 13C-NMR (CDCl3, 101 MHz) l 21.11 (d, J=22.2
Hz), 41.03, 44.25, 67.25, 122.43, 122.46, 126.27, 126.84,
128.19 (d, J=13.1 Hz), 128.54, 128.61, 129.10, 130.20,
130.24, 133.15, 133.23, 134.24 (d, J=2.7 Hz), 136.03,
142.67 (d, J=27.1 Hz), 152.67 (d, J=17.3 Hz), 156.44,
167.63, 168.89 ppm. 31P-NMR (CDCl3, 161.9 MHz) l
−31.01 ppm. IR (C6D6, cm−1) 3416 (NꢀH), 1774
(CꢁO, ester), 1734 (CꢁO, carbamate), 1697 (CꢁO,
amide). Anal. Calc. for C32H31N2O5P (554.62): C,
69.29, H, 5.65, N, 5.05. Found: C, 69.05; H, 5.78; N,
5.20.
32.59 (dd, J=387, 110 Hz) ppm. IR (C6D6, cm−1
1734 (acyl), 1690 and 1709 (amide and carbamate).
Anal. Calc. For C35H40ClN2O5P2Rh (783.97): C, 53.62,
H, 5.15, N, 3.57. Found: C, 53.40; H, 5.32; N, 3.47.
)
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