Synthesis of stibine SbPhR1R2 and their use as ligand in the amidocarbonylation of alkenes with Co2(CO)8 as precursor

Article abstract of DOI:10.1016/j.molcata.2007.04.018

Treatment of bis(1-phenylethynyl)-phenylstibine with 2,4,6-trimethyl magnesium bromide promotes the nucleophilic displacement of one ethynyl group, as was previously reported by Kurita, affording the phenyl (1-phenylethynyl)mesitylstibine. This antimony compound was used as a ligand in order to modify the Co₂(CO)₈ catalytic system for the amidocarbonylation (Wakamatsu reaction) of cyclohexene, cyclopentene, 1-hexene, and 1-pentene. This new modified catalytic system is capable of affording moderate yields of N-acetyl-α-aminoacids.

Full text of DOI:10.1016/j.molcata.2007.04.018

Journal of Molecular Catalysis A: Chemical 274 (2007) 65–67
Synthesis of stibine SbPhR1R2 and their use as ligand in the
amidocarbonylation of alkenes with Co2(CO)8 as precursor
a,∗
b
a
´
´
´
Rosa Maria Gomez , Armando Cabrera , Claudia Garcıa Velazquez
a Universidad Auto´noma del Estado de Me´xico, Toluca, Paseo Colo´n esquina con Paseo Tollocan 50120, Me´xico
b Instituto de Qu´ımica, Universidad Nacional Auto´noma de Me´xico, Ciudad Universitaria Circuito Exterior, Coyoaca´n 04510, Me´xico
Received 26 November 2006; received in revised form 11 April 2007; accepted 16 April 2007
Available online 20 April 2007
Abstract
Treatmentofbis(1-phenylethynyl)-phenylstibinewith2,4,6-trimethylmagnesiumbromidepromotesthenucleophilicdisplacementofoneethynyl
group, as was previously reported by Kurita, affording the phenyl (1-phenylethynyl)mesitylstibine. This antimony compound was used as a ligand
in order to modify the Co2(CO)8 catalytic system for the amidocarbonylation (Wakamatsu reaction) of cyclohexene, cyclopentene, 1-hexene, and
1-pentene. This new modified catalytic system is capable of affording moderate yields of N-acetyl-␣-aminoacids.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Antimony; Stibine ligands; Amidocarbonylation; Wakamatsu reaction; Homogeneous catalysis
1. Introduction
ands, and the study showed that the latter have better yields and
are more selective to the linear amino acids than that presented
by the phosphine ligands.
The preparation of organometallic compounds of some ele-
ments of the group 15 involves the nucleophilic displacement
of the halogen group on appropriate metal halides (MR3, M = P,
As, Sb, Bi) [1]. However, this method has been proved to be
unsatisfactory for the preparation of unsymmetrical compounds,
all the halogen atoms are replaced simultaneously because the
halogen moieties are highly reactive as leaving groups and also
organomagnesium and organolithium reagents have high nucle-
ophilicity. Only a few limited examples have been reported
regarding success in the preparation of asymmetric stibines.
The alkene amidocarbonylation reaction (Wakamatsu’s reac-
tion) [2] constitutes an excellent method to introducing two
carbonyl groups in a one pot process, starting with olefins as
substrates. This reaction has been used in obtaining N-acyl
aminoacids, which have a wide range of applications.
Forbus and Brown [4] reported the effect of the steric
requirements, as well as the basicity of different phosphines
in octacarbonyldicobalt substitution reactions. These study
demonstrated that the rate-limiting step in the process is the
dissociation of carbon monoxide from the Co2(CO)8. Further-
more, Wendt and Elding [5] carried out a comparative study of
the trans influence and trans effect of triphenyl stibine and phos-
phines in transition metal complexes, and concluded that SbPh3
has a greater trans effect than PPh3. In that report, stibinic Pt (II)
complexes reacted ca. 16 times faster than their phosphorous
analogous.
This paper reports the use of a cobalt system modified with a
PhR1R2Sb ligand, as a catalytic precursor in the amidocarbony-
lation reaction of some alkenes under mild operating conditions.
To the best of our knowledge R1R2R3Sb compounds have not
been previously used in the named process (Scheme 1).
We have previously reported results obtained in the synthesis
ofN-acylaminoacids, usingtriarylstibinesandtriarylphosphines
as ligands in a homogenous-phase system with cobalt as a cat-
alytic precursor in the amidocarbonylation process [3]. The
effect of the phosphines was compared to that of the stibinic lig-
2. Experimental
2.1. Synthesis of phenyl (1-phenylethynyl)mesitylstibine
∗
2,4,6-Trimethylphenyl magnesiumbromide (5.5 mmol) at
0 ◦C was added (under nitrogen) to a stirred solution of 5 mmol
Corresponding author. Tel.: +52 722 173890; fax: +52 722 173890.
E-mail address: rmge@uaemex.mx (R.M. Go´mez).
1381-1169/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2007.04.018

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R.M. Go´mez et al. / Journal of Molecular Catalysis A: Chemical 274 (2007) 65–67
Scheme 1. Synthesis of phenyl (1-phenylethynyl)mesitylstibine.
of phenyldiethynylstibine (1) (which was prepared according to
previous reports [6]) in dry ether (50 ml). The reaction mixture
was stirred for 6 h, and then diluted with hexane and degassed
water. The organic layer was washed with a solution of NaCl
(10%) and dried over Na2SO4. After removal of the solvent
in vacuo, the residue was eluted in a silica gel column chro-
matography (hexane 100%), affording a white solid (2) (73%),
m/z (EI) 418(82)M+, μmax/cm−1 , 2929 ( CH3), 2135 (C C),
RMN δ(500 MHz, CDCl3) 2.53 (3H, s, Mesityl-Me) 2.68 (6H, s
Mesityl-Me), 6.89 (1H, s, Mesityl-H, Ph, J = 1 Hz), 6.897 (1H,
s, Mesityl-H, Ph, J = 1Hz), 7.29–7.35 (6H, m, Ph-H, J = 3.5 Hz),
7.47 (2H, dd, Mesityl-Ph-H, J = 6.9 Hz), 7.6 (2H, dd, Ph-H,
J = 7.5 Hz).
2.2. General catalytic procedure
A solution of 3.46 mmol of the alkene, 5.20 mmol acetamide,
0.12 mmol of Co2(CO)8 and 0.12 mmol of PhR1R2Sb, in 10 ml
of dry THF (in a Schlenk tube), was transferred to a stainless
steel reactor (PARR) under nitrogen. Then, the reaction was
taken to the desired pressure (28 bar, CO/H2, 3/1), and warmed
in an oil bath, at 120 ◦C for 20 h. At the end of this period,
the reactor was cooled and the gases liberated. The solution
was worked up in order to obtain the reaction products [3]. The
named solution was also analyzed by GC and GC–MS in order
to quantify the remaining substrate and the by-products of the
reaction (aldehydes and alcohols).
Table 1
N-Acetylaminoacids via co-stibine catalysed amidocarbonylation
T = 120 ◦C, t = 20 h; Co2(CO)8/Sb(phenyl)(1−phenylethynyl)mesityl (1:1) 0.12 mmol:acetamide 5.20 mmol (1.5 equiv.), alkene 3.46 mmol (1 equiv.); syn−gas pres-
sure CO/H2 (3:1) (28 bar); THF 10 ml.

R.M. Go´mez et al. / Journal of Molecular Catalysis A: Chemical 274 (2007) 65–67
67
Scheme 2. Mechanism of amidocarbonylation reaction PhR1R2Sb/Co system.
3. Results and discussion
Acknowledgments
´
´
We thanks to Dr. P. Sharma, Dr. F. Cortes-Guzman, J. Perez-
Flores, and L. Velasco, for their valuables comments. They
would also like to thank PROMEP 103.5/04/1352 and SIyEA
UAEM 1933 for financial support provided.
Previous reports using R3Sb organoantimony compounds as
ligands in a modified cobalt system for the hydroformylation
and amidocarbonylation reactions of alkenes [3,7–9], confirmed
the importance of the stibines as ligands in the aforementioned
homogeneous catalytic process. We found that this modified
catalytic system not only increases the activity, but also improves
the selectivity of the reaction to the linear products in very good
proportion, compared to the behaviour of phosphines ligands
[7].
Based on the foregoing results, we carried out some
experiments using compound 2 as ligand in the afore-
mentioned modified cobalt precursor, with the aim of
proving its efficiency. The results are shown in Table 1.
As may be observed, this catalytic system promotes the
reaction.
References
[1] (a) S. Patai, The Chemistry of Organic Arsenic, Antimony and Bismuth
compounds, Wiley, 1944;
(b) N.C. Norman, Chemistry of Arsenic, Antimony and Bismuth, Blackie
Academic and Professional, London, 1998.
[2] H. Wakamatsu, J. Uda, N. Yamakami, Chem. Commun. (1971) 1540.
[3] R.M. Gomez, P. Sharma, J.L. Arias, J. Perez-Flores, L. Velasco, A. Cabrera,
J. Mol. Catal. A: Chem. 170 (2001) 271.
[4] N.P. Forbus, T.L. Brown, Inorg. Chem. (1981) 4343.
[5] O.F. Wendt, L.I. Elding, J. Chem. Soc., Dalton Trans. (1997) 4725.
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[7] R.F. Heck, D.S. Breslow, J. Am. Chem. Soc. 83 (1961) 4023.
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J.L. Arias, C.V. Ambrouse, Main Group Met. Chem. 21 (1998) 303.
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J. Mol. Catal. A: Chem. 212 (2004) 19.
In Scheme 2, a possible reaction pathway of amidocar-
bonylation is suggested as sequence of hydroformylation cycle,
imide formation and a carbonylation cycle. Studies regarding
the influence of R1R2R3Sb ligands on possible stereocontrol in
Wakamatsu’s reaction are in progress.