Studies relevant to palladium-catalyzed carbonylation processes. Mechanisms of formation of esters and amides from benzylpalladium and (phenylacetyl)palladium complexes on reactions with alcohols and amines

Article abstract of DOI:10.1021/om980234f

Benzylpalladium and (phenylacetyl)palladium complexes having two PMe₃ or PPh₃ ligands or a dppe ligand (P2-type complexes) have been prepared as models to study the mechanisms of carbonylation reactions to convert benzyl halides into single and double carbonylation products. Removal of one of the tertiary phosphine ligands in the P2-type monophosphine complexes, trans-PdCl(COCH₂Ph)(PR₃)₂ (R = Ph, Me), by treatment with PdCl₂(PhCN)₂ led to the P1-type chloride-bridged dimers [PdCl(COCH₂Ph)(PR₃)]₂, which were split on interaction with secondary amines to give amine-coordinated complexes, PdCl(COCH₂Ph)-(PR₃)(NHEt₂). Examination of the reactions of the (phenylacetyl)palladium complexes with secondary amines and alcohols provided evidence for operation of different types of mechanisms for yielding amides and esters. The amide formation proceeds faster when more basic secondary amine is used. The process is proposed to proceed through coordination of the amine to palladium followed by its nucleophilic attack on the acyl group aided by a base. On the other hand, the ester formation from the (phenylacetyl)palladium complex proceeds more readily when more acidic alcohols were used. The formation of the ester is compatible with the reaction mechanism proceeding through an intermediate acyl-alkoxide complex. For the amide formation from the benzylpalladium complexes on reactions with secondary amines under CO pressure, operation of two routes has been revealed; one involves the attack of an amine on the CO-coordinated benzylpalladium species to give a benzyl-(carbamoyl)palladium intermediate, and the other involves (phenylacetyl)(amine)palladium species, each giving the amide on reductive elimination or amine migration to the acyl ligand. Competition reactions using mixtures of secondary amines and alcohols toward the acylpalladium complexes furnished the supporting evidence for the reaction mechanisms to give esters involving the reductive elimination of phenylacetyl-alkoxide intermediates.

Full text of DOI:10.1021/om980234f

3466
Organometallics 1998, 17, 3466-3478
Stu d ies Releva n t to P a lla d iu m -Ca ta lyzed Ca r bon yla tion
P r ocesses. Mech a n ism s of F or m a tion of Ester s a n d
Am id es fr om Ben zylp a lla d iu m a n d
(P h en yla cetyl)p a lla d iu m Com p lexes on Rea ction s w ith
Alcoh ols a n d Am in es
Yong-Shou Lin and Akio Yamamoto*
Department of Applied Chemistry, Graduate School of Science and Engineering, Advanced
Research Center for Science and Engineering, Waseda University, 3-4-1,
Ohkubo, Shinjuku, Tokyo 169-8555, J apan
Received March 27, 1998
Benzylpalladium and (phenylacetyl)palladium complexes having two PMe3 or PPh3 ligands
or a dppe ligand (P2-type complexes) have been prepared as models to study the mechanisms
of carbonylation reactions to convert benzyl halides into single and double carbonylation
products. Removal of one of the tertiary phosphine ligands in the P2-type monophosphine
complexes, trans-PdCl(COCH2Ph)(PR3)2 (R ) Ph, Me), by treatment with PdCl2(PhCN)2 led
to the P1-type chloride-bridged dimers [PdCl(COCH2Ph)(PR3)]2, which were split on
interaction with secondary amines to give amine-coordinated complexes, PdCl(COCH2Ph)-
(PR3)(NHEt2). Examination of the reactions of the (phenylacetyl)palladium complexes with
secondary amines and alcohols provided evidence for operation of different types of
mechanisms for yielding amides and esters. The amide formation proceeds faster when
more basic secondary amine is used. The process is proposed to proceed through coordination
of the amine to palladium followed by its nucleophilic attack on the acyl group aided by a
base. On the other hand, the ester formation from the (phenylacetyl)palladium complex
proceeds more readily when more acidic alcohols were used. The formation of the ester is
compatible with the reaction mechanism proceeding through an intermediate acyl-alkoxide
complex. For the amide formation from the benzylpalladium complexes on reactions with
secondary amines under CO pressure, operation of two routes has been revealed; one involves
the attack of an amine on the CO-coordinated benzylpalladium species to give a benzyl-
(carbamoyl)palladium intermediate, and the other involves (phenylacetyl)(amine)palladium
species, each giving the amide on reductive elimination or amine migration to the acyl ligand.
Competition reactions using mixtures of secondary amines and alcohols toward the
acylpalladium complexes furnished the supporting evidence for the reaction mechanisms to
give esters involving the reductive elimination of phenylacetyl-alkoxide intermediates.
In tr od u ction
may vary depending on the nucleophiles and reaction
conditions employed.
Palladium-catalyzed carbonylation of organic halides
to give carboxylic acids, esters, and amides has been
extensively used for production of carbonyl-containing
compounds in laboratory synthesis as well as in indus-
trial processes.1 Aryl halides have been used most
extensively, whereas successful catalytic carbonylation
of aliphatic halides are limited to allylic halides2,3 and
fluorinated alkyl halides.4 To expand the scope of
application of the carbonylation process, it is necessary
to explore the possibility of utilizing aliphatic substrates
on the basis of information regarding the reactivities
of model organopalladium complexes that are considered
to be involved in the possible catalytic processes.
The most often assumed process involves migratory
insertion of a coordinated carbon monoxide ligand in C
to give an acylpalladium halide (D), which reacts further
with a nucleophile (NuH) and a base to liberate RCONu
(1) (a) Cornils, B.; Herrmann, W. A. Applied Homogeneous Catalysis
with Organometallic Compounds; VCH: Weinheim, 1996; Vol. 1. (b)
Tsuji, J . Palladium Reagents and Catalysts; Wiley: New York, 1995.
(c) Beller, M.; Cornils, B.; Frohning, C. D.; Kohlpaintner, C. W. J . Mol.
Catal. 1995, 104, 17. (d) Bates, R. W. In Comprehensive Organometallic
Chemistry. A Review of the Literature 1982-1994; Abel, E. W., Stone,
F. G. A., Wilkinson, G., Eds.; Pergamon Press: New York, 1995; Vol.
12, p 349. (e) Colquhoun, H. M.; Thompson, D. J .; Twigg, M. V.
Carbonylation. Direct Synthesis of Carbonyl Compounds; Plenum: New
York, 1991. (f) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R.
G. Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987. (g) Yamamoto, A.
Organotransition Metal Chemistry. Fundamental Concepts and Ap-
plications; Wiley-Interscience: New York, 1986. (h) Heck, R. F.
Palladium Reagents in Organic Syntheses; Academic Press: New York,
1985. (i) Tkatchenko, I. In Comprehensive Organometallic Chemistry;
Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon Press:
Oxford, U.K., 1982; Vol. 8.
From the mechanistic studies reported so far, it is
generally accepted that an organopalladium halide (B)
is produced by oxidative addition of an organic halide
to a Pd(0) species (A) formed in the catalytic system
(Scheme 1) but the later course of the catalytic reaction
S0276-7333(98)00234-9 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 07/09/1998

Pd-Catalyzed Carbonylation Processes
Organometallics, Vol. 17, No. 16, 1998 3467
Sch em e 1a
a
L ) tertiary phosphine, X ) halide, HNu ) HNR2, HOR, or H2O.
as carboxylic acid, ester, or amide, depending on the
nucleophile (path b, Scheme 1).1 The alternative route
to path b is displacement of the halide ligand in C by
CO to give a CO-coordinated cationic organopalladium
species (E)5 that undergoes the nucleophilic attack in
the presence of a base to give an organo(acyl)palladium
species (F ).6 Reductive elimination from F liberates
RCONu as the carboxylic acid or its derivatives (path
a , Scheme 1). A previous study using trimethylphos-
phine-coordinated phenylpalladium complexes, which
gave phenyl(carbamoyl)palladium complexes on treat-
ment with diethylamine under CO, provided the sup-
porting evidence for path a involving the reductive
elimination of the aryl and carbamoyl ligands.6a It was
further demonstrated that combination of the CO inser-
tion into the organopalladium bond to give the acylpal-
ladium complex D with attack of a nucleophile on the
coordinated CO in G to give a bis(acyl)-type palladium
complex (H) provides the route to R-keto amides and
esters, respectively, by reductive elimination of the acyl
and the carbamoyl or of the acyl and alkoxycarbonyl
ligands (Scheme 1).6a,7 However, very few reports have
been made to support the operation of path a , whereas
operation of path b involving the acyl intermediate has
been implicitly assumed in most of the catalytic
carbonylation processes without sound experimental
evidence supporting the mechanism.
In our attempts to achieve catalytic double carbony-
lation of aliphatic substrates, we have found that allylic
chlorides can be successfully double-carbonylated to give
R-keto amides3 whereas attempts of palladium-cata-
lyzed carbonylation of alkyl halides have, so far, been
unsuccessful because of the direct conversion of alkyl
halides with secondary amines to tertiary amines.
Benzyl halides are considered as the next candidates
after allylic halides to examine their reactivities for
achieving the carbonylation of aryl-substituted aliphatic
compounds, since benzylic compounds have an allylic
nature and are situated between the purely aromatic
and aliphatic compounds. Since Heck,8 Stille,9 and
Hidai10 first reported that benzyl chloride and bromide
were converted into phenylacetates under CO pressure
in the presence of palladium catalysts in alcohols, many
studies have been made on the single carbonylation of
benzyl halides catalyzed by palladium complexes.1a,c
Milstein presented the evidence to support operation of
the mechanism proceeding through CO insertion into
the benzyl-palladium bond followed by alcoholysis.11
However, no detailed analysis of the alcoholysis process
has been provided.
(2) (a) Gabriele, B.; Salerno, G.; Costa, M.; Chiusoli, G. P. J . Mol.
Catal. 1996, 111, 43. (b) Naigre, R.; Alper, H. J . Mol. Catal. 1996, 111,
11. (c) Murahashi, S.-I.; Imada, Y.; Taniguchi, Y.; Higashiura, S. J .
Org. Chem. 1993, 58, 1538. (d) Itoh, K.; Hamaguchi, N.; Miura, M.;
Nomura, M. J . Mol. Catal. 1992, 75, 117. (e) Neibecker, D.; Poirier,
J .; Tkatchenko, I. J . Org. Chem. 1989, 54, 2459. (f) Kiji, J .; Okano, T.;
Nishiumi, W.; Konishi, H. Chem Lett. 1988, 957. (g) Tsuji, J . Tetra-
hedron 1986, 42, 4361 and references therein.
Concerning the formation of methyl benzoate from
bromobenzene and CO in the presence of methanol and
bases, Moser proposed a mechanism involving formation
of a methoxide anion that attacks the benzoylpalladium
complex.12 On the other hand, Alper has reported a
dimeric acylpalladium complex as an intermediate for
(3) Yamamoto, A. Bull. Chem. Soc. J pn. 1995, 68, 433.
(4) (a) Urata, H.; Kosukegawa, O.; Ishii, Y.; Yugari, H.; Fuchikami,
T. Tetrahedron Lett. 1989, 30, 4403. (b) Urata, H.; Ishii, Y.; Fuchikami,
T. Tetrahedron Lett. 1989, 30, 4407. For the carbonylation of other
alkyl derivatives, see examples: (c) Urata, H.; Goto, D.; Fuchikami,
T. Tetrahedron Lett. 1991, 32, 3091. (d) Zhou, H.; Lu, S.; Li, H.; Chen,
J .; Fu, H.; Wang, H. J . Mol. Catal. 1997, 116, 329.
(5) (a) Kayaki, Y.; Yamamoto, A. J . Synth. Org. Chem. (J apanese)
1998, 56, 96. (b) Kayaki, Y.; Shimizu, I.; Yamamoto, A. Bull. Chem.
Soc. J pn. 1997, 70, 1135. (c) Kayaki, Y.; Shimizu, I.; Yamamoto, A.
Bull. Chem. Soc. J pn. 1997, 70, 917. (d) Kayaki, Y.; Shimizu, I.;
Yamamoto, A. Chem Lett. 1995, 1089. (e) To´th, I.; Elsevier: C. J . J .
Am. Chem. Soc. 1993, 115, 10388.
(6) (a) Ozawa, F.; Soyama, H.; Yanagihara, H.; Aoyama, I.; Takino,
H.; Izawa, K.; Yamamoto, T.; Yamamoto, A. J . Am. Chem. Soc. 1985,
107, 3235. (b) Huang, L.; Ozawa, F.; Yamamoto, A. Organometallics
1990, 9, 2603. (c) Yamamoto, A.; Ozawa, F.; Osakada, K.; Huang, L.;
Son, T.; Kawasaki, N.; Doh, M.-K. Pure Appl. Chem. 1991, 63, 687.
(7) (a) Ozawa, F.; Kawasaki, N.; Okamoto, H.; Yamamoto, T.;
Yamamoto, A. Organometallics 1987, 6, 1640. (b) Chen, J .-T.; Sen, A.
J . Am. Chem. Soc. 1984, 106, 1506. (c) Tanaka, M.; Kobayashi, T.;
Sakakura, T. J . Chem. Soc., Chem. Commun. 1985, 837. (d) Sakakura,
T.; Yamashita, H.; Kobayashi, T.; Hayashi, T.; Tanaka, M. J . Org.
Chem. 1987, 52, 5733.
(8) Schoenberg, A.; Bartoletti, I.; Heck, R. F. J . Org. Chem. 1974,
39, 3318.
(9) Stille, J . K.; Wong, P. K. J . Org. Chem. 1975, 40, 532.
(10) Hidai, M.; Hikita, T.; Wada, Y.; Fujikura, Y.; Uchida, Y. Bull.
Chem. Soc. J pn. 1975, 48, 2075.
(11) (a) Milstein, D. J . Chem. Soc., Chem. Commun. 1986, 817. (b)
Milstein, D. Acc. Chem. Res. 1988, 21, 428.
(12) Moser, W. R.; Wang, A. W.; Kjeldahl, N. K. J . Am. Chem. Soc.
1988, 110, 2816.

3468 Organometallics, Vol. 17, No. 16, 1998
Lin and Yamamoto
Sch em e 2a
a
L ) tertiary phosphine; X ) halide; HNu ) HOR′, HNR2′′, and HOH.
the formation of carboxylic acid anion in the presence
of an alkali.13
from an acyl(alkoxy)palladium complex. An acyl(aryl-
oxy)palladium(II) complex has been prepared, and its
reductive elimination to give an ester has been stud-
ied.16 The mechanism for the formation of ester from a
three-coordinate benzoylpalladium alkoxide has been
proposed based on the kinetic studies.7a In this paper,
we report the results of detailed studies of the courses
of the reactions of nucleophiles with benzyl and (phen-
ylacetyl)palladium complexes that are regarded as
catalyst models of palladium-catalyzed carbonylation
reactions of benzylic compounds.
Our preliminary examination of the catalytic carbon-
ylation of benzyl halides with methanol and a base
showed that methyl phenylacetate was obtained as a
single carbonylation product, but no double carbonyla-
tion product was formed.14 On the other hand, our
recent study showed that benzyl alcohol and its ana-
logues can be catalytically converted into phenylacetic
acid and its analogues by a palladium-catalyzed carbon-
ylation in the presence of hydrogen iodide.15 Detailed
studies on the reaction mechanism revealed that benzyl
iodide, produced in situ from benzyl alcohol and HI,
forms a benzylpalladium iodide and that the subsequent
CO insertion affords (phenylacetyl)palladium iodide.
Phenylacetyl halides were found to be liberated from
the (phenylacetyl)palladium halides by reductive elimi-
nation, and its subsequent hydrolysis under acidic
conditions gave phenylacetic acid and hydrogen
halides.15b
Resu lts
P r ep a r a tion of Ben zyl- a n d (P h en yla cetyl)p a l-
la d iu m Com p lexes Ha vin g Mon o- a n d Bis-P h os-
p h in e Liga n d s. Chart 1 summarizes the benzyl- and
(phenylacetyl)palladium complexes prepared in the
present study for examining their properties relevant
to carbonylation processes. The complexes include those
prepared specifically for the present study as well as
some of the reported complexes and their analogues
having different tertiary phosphine ligands. To under-
stand the effect of the tertiary phosphine ligands, we
have prepared the benzyl- and (phenylacetyl)palladium
complexes having two (P2-type) and one (P1-type)
tertiary phosphine ligand(s), respectively.
This finding prompted us to examine the behavior of
the benzylpalladium halide and (phenylacetyl)palladium
halide complexes toward CO and various nucleophiles
for gaining further information to achieve catalytic
carbonylation and, if possible, double carbonylation of
benzylic substrates.
There are three possible paths that should be consid-
ered for formation of the carbonylation products from
an acylpalladium complex, as shown in Scheme 2. The
first is the direct attack of a nucleophile NuH on the
acyl group in the acylpalladium intermediate D (route
a ). This is the process intuitively assumed in analogy
with the behavior of simple carbonyl-containing organic
compounds. The second possible route involves coordi-
nation of a nucleophile to the palladium center followed
by deprotonation of the precoordinated nucleophile HNu
by a base. The process is followed by reductive elimina-
tion of the acyl and Nu ligands to give acid derivatives,
RCONu (route b). The third possibility is direct reduc-
tive elimination of an acyl halide, which is subsequently
attacked by the nucleophile to give amide, ester, or
carboxylic acid (route c).
The P2-type trans-(η1-benzyl)bis(triphenylphosphine)-
palladium(II) halides (1) were prepared by oxidative
addition of benzyl halides to Pd(PPh3)4.17 Their analo-
gous complex (2) having two PMe3 ligands was synthe-
sized by the reaction of Pd(PMe3)2(styrene) with benzyl
chloride.15b
Since the η1-benzylpalladium halide complexes can be
isomerized into η3-type isomers with dissociation of the
halide ligands, it is necessary to understand the behav-
ior of the η3-benzylpalladium complexes. Thus, cationic
η3-type complexes 3 and 4 were prepared by treating
1a and 2 with AgPF6.15b
Whereas the insertion of CO into the benzyl-pal-
ladium bond gives the (phenylacetyl)palladium com-
plexes, pure (phenylacetyl)palladium chloride complex
8 was prepared by an independent route involving
oxidative addition of PhCH2COCl with Pd(PPh3)4.18
There are limited reports of organometallic studies
on the formation of ester via a reductive elimination
(13) Grushin, V. V.; Alper, H. Organometallics 1993, 12, 1890.
(14) For example, carbonylation of benzyl bromide catalyzed by
PdCl2(PPh3)2 (2 mol %) in the presence of proton sponge in methanol
under high CO pressure (100 atm) at 60 °C gave methyl phenylacetate
in 70% yield together with methyl benzyl ether (28%): Lin, Y.-S.;
Yamamoto, A. Unpublished results.
(16) (a) Komiya, S.; Akai, Y.; Tanaka, K.; Yamamoto, T.; Yamamoto,
A. Organometallics 1985, 4, 1130. (b) Kohara, T.; Komiya, S.; Yama-
moto, T.; Yamamoto, A. Chem. Lett. 1979, 1513.
(17) Fitton, P.; McKeon, J . E.; Ream, B. C. J . Chem. Soc., Chem.
Commun. 1969, 370.
(18) (a) Kubota, M.; Boegeman, S. C.; Keil, R. N.; Webb, C. G.
Organometallics 1989, 8, 1616. (b) Fitton, P.; J ohnson, M. P.; Mckeon,
J . E. Chem Commun. 1968, 6.
(15) (a) Lin, Y.-S.; Yamamoto, A. Tetrahedron Lett. 1997, 38, 3747.
(b) Lin, Y.-S.; Yamamoto, A. Bull. Chem. Soc. J pn. 1998, 71, 723.

Pd-Catalyzed Carbonylation Processes
Organometallics, Vol. 17, No. 16, 1998 3469
Ch a r t 1. Ben zyl- a n d (P h en yla cetyl)p a lla d iu m Com p lexes
Analogues of 8 having PMe3 and dppe (dppe ) 1,2-bis-
(diphenylphosphino)ethane) ligands, 9 and 10, were
prepared by replacement of the PPh3 ligands in 8 with
PMe3 and dppe ligands, respectively (see Experimental
Section).
be converted into the η3-benzylpalladium complex. Ad-
dition of an equilmolar amount of AgPF6 to a CD2Cl2
solution of 8 at room temperature immediately gave the
1
decarbonylation product 3, as observed by H and 31P
NMR and IR (eq 1). The result suggests that creation
The CO-coordinated η1-benzylpalladium complex 5
can be prepared by treatment of the η3-benzylpalladium
complex 4 with CO (10 atm) at -80 °C.15b The subse-
quent increase in the temperature above -40 °C leads
to CO insertion into the benzyl-palladium bond to give
the CO-coordinated (phenylacetyl)palladium complex 7.
The corresponding PPh3-coordinated cationic η3-ben-
zylpalladium complex 3 undergoes the CO insertion
more readily than the PMe3-coordinated analogue 4 to
give the CO-coordinated cationic (phenylacetyl)palla-
dium complex 6 without showing the sign of formation
of a CO-coodinated η1-benzylpalladium intermediate
corresponding to 5.19 Release of CO gas from solutions
containing 6 and 7 yields the starting cationic η3-
benzylpalladium complexes 3 and 4 with a faster
decarbonylation rate for the PPh3-coordinated complex
6.19 The neutral trans-(phenylacetyl)palladium chloride
complex 8 also shows a trend to decarbonylate and to
of a vacant site on the palladium center accelerates the
decarbonylation. Acceleration of the decarbonylation of
the 3-butenoylpalladium bromide complex by removal
of the halide with AgBF4 was previously reported.20
For evaluation of the effect of tertiary phosphine
ligands, it was necessary to prepare the (phenylacetyl)-
palladium complexes having one phosphine ligand per
palladium. The chloride-bridged P1-type complexes 11
and 12 were prepared as dimers by treatment of the
P2-type (phenylacetyl)palladium complexes 8 and 9 with
PdCl2(PhCN)2 in a way similar to the preparation of the
corresponding [PdCl(CH2Ph)(PPh3)]2,21 as shown in eq
2.22
(19) The reactions of complexes 3 and 4 with 13CO (10 atm) were
performed as described in ref 15b. At -80 °C, the reaction of the
trimethylphosphine-coordinated complex 4 with 13CO (10 atm) to give
-80°C
CO-coordinated complex 5 was first order in 4 (kobs
) (3.2 ( 0.1)
× 10-5 s-1). The first-order rate law was also obeyed in the conversion
of complex 5 to 7 at -40 °C (kobs
) (3.3 ( 0.2) × 10-4 s-1). On the
-40°C
Amine-coordinated complexes of the P1 type, 13 and
14, can be obtained by addition of 2 mol of Et2NH per 1
mol of the corresponding dimeric complexes 11 and 12
(eq 3).
other hand, conversion of complex 4 to 7 was also found to be a first-
order process at -40 °C (kobs-40°C ) (7.7 ( 0.1) × 10-5 s-1). The reaction
of 3 with 13CO to give 6 at -40 °C was first order (kobs
) (1.9 (
-40°C
0.1) × 10-4 s-1) and faster than that of 4 with 13CO. NMR data assigned
for 6: 1H NMR (270 MHz, δ, CD2Cl2, 233 K) 7.6-7.2 (m, 30H, PPh3),
6.73 (t, J ) 8 Hz, 3H, Ph), 5.77 (s br, 2H, Ph), 3.34 (s, 2H, PhCH2-).
13C NMR (67.9 MHz, δ, CD2Cl2, 233 K): 227.5 (s br, 13COCH2Ph), 179.6
(s br, 13CO). 31P NMR (109.4 MHz, δ, CD2Cl2, 233 K): 17.3 (s), -144.3
(sept, J ) 710 Hz).
(20) Ozawa, F.; Son, T.; Osakada, K.; Yamamoto, A. J . Chem. Soc.,
Chem. Commun. 1989, 1067.
(21) Gretz, E.; Sen, A. J . Am. Chem. Soc. 1986, 108, 6038.

3470 Organometallics, Vol. 17, No. 16, 1998
Lin and Yamamoto
Ta ble 1. Rea ction of (P h en yla cetyl)p a lla d iu m (II)
Com p lexes w ith Secon d a r y Am in esa
entry
complex
amine
PhCH2CONR2 (mol %/Pd)b
1
2
3
4
5
6
7
8
9
11
12
10
8
Et2NH
Et2NH
Et2NH
Et2NH
Et2NH
piperidine
morpholine
88c
0d
76c
4d
82c
84
8
68e
a
Reaction conditions: palladium complex (0.04 mmol in Pd) in
CD2Cl2 (0.6 mL) was treated with amine (0.4 mmol) at room
b
temperature. Determined by 1H NMR after 1 day (PhSiMe3 as
an internal reference). c A trace of PhCH2COO- was detected.
d
(PhCH2)2 was detected in 3 days in entries 2 (10 mol %) and 4 (6
mol %). e 22% of 8 unreacted.
When the P1-type, diethylamine-coordinated complex
13 was treated with an equilmolar amount of PPh3 in
CD2Cl2, instant formation of trans-PdCl(COCH2Ph)-
(PPh3)2 (8) and release of a quantitative amount of Et2-
1
NH occurred, as confirmed by the analysis of H and
31P NMR spectra.
Both complexes can be isolated almost quantitatively
at low temperature. However, they are slowly decom-
posed at room temperature. In the solid state, both 13
and 14 are gradually decomposed at room temperature
in air in several days, releasing HNEt2 and generating
an unidentified black solid and the amine-free dimer
12. The decomposition of 13 is faster than that of 14.
In solution, PhCH2CONEt2 (15) was formed on decom-
position of 13 and 14 (see below). Coordination of amine
to the palladium atom in complexes 13 and 14 was
confirmed by 1H NMR. Proton signals of the ethyl
groups in Et2NH were observed at lower field than that
in free Et2NH, and the protons in the methylene moiety
in Et2NH exhibited two different resonances at lower
temperatures, at δ 2.63 and 2.52 as broad singlets at
-50 °C for 13 and at δ 2.65 and 2.47 as broad singlets
at -80 °C for 14, respectively. The cis arrangement of
the phenylacetyl group and the phosphine ligand in
complex 13 was concluded by observation of the coupling
of the methylene carbon in the benzylic group with
phosphorus with a coupling constant of 21 Hz in the13C-
{H} NMR spectrum of 13. The coupling constant is
reasonable for the cis configuration by comparison with
3J C-P values in the dppe-coordinated complex 10, 3J C-P(cis)
Rea ction s of th e (P h en yla cetyl)p a lla d iu m Com -
p lexes w ith Nu cleop h iles in th e Absen ce of CO. (1)
Rea ction s w ith Secon d a r y Am in es. To examine the
reaction courses of (phenylacetyl)palladium complexes
toward various nucleophiles, the neutral, mono-phos-
phine-coordinated (phenylacetyl)palladium complexes,
8, 9, 11, and 12, and the dppe-coordinated complex, 10,
were subjected to reactions with Et2NH, piperidine, and
morpholine (eq 4 and Table 1). The results show a
3
) 19 Hz and J C-P(trans) ) 37 Hz. With reference to the
marked influence of the tertiary phosphine ligands
employed. The PPh3-coordinated complexes 8 (entry 1)
and 11 (entry 3) produced amide 15 in high yields,
whereas the less electrophilic PMe3-coordinated com-
plexes 9 and 12 were found to be much less reactive
(entries 2 and 4).
On the other hand, the dppe-coordinated complex 10
exhibited a reactivity similar to complexes 8 and 11
having the PPh3 ligand(s). The results suggest that the
basicity of the tertiary phosphine ligands has a decisive
influence on the reactivity of the (phenylacetyl)palla-
dium complexes toward HNEt2. A decrease in the
reactivity of benzoylpalladium complexes, trans-PdX-
(COPh)(PR3)2 (X ) Cl and Br), on replacement of the
PPh3 with PMePh2 was previously noted.6b
previously reported arylpalladium complexes having one
phosphine and one amine ligand,23 the trans disposition
of the PR3 (R ) Ph and Me) and Et2NH ligands in
complexes 13 and 14, as represented in Chart 1, was
deduced. Various amine-coordinated (â-aminoacyl)-
palladium complexes have been previously prepared,
and mutual cis arrangement of the coordinated amine
and the acyl groups has been confirmed.24
(22) Two types of isomers arising from a different arrangement of
the two (phenylacetyl)palladium moieties in the dimers 11 and 12 can
be observed in the 31P NMR at -40 °C as two singlets at 27.3 and 26.6
ppm in a 3:1 ratio for 11 and at -5.8 and -6.4 ppm in a 2:3 ratio for
12. At higher temperatures, these peaks coalesce to a broad singlet at
- 9 °C for 11 and at 2 °C for 12. From the Eyring equation, ∆Gq
)
264K
50.5 ( 0.2 kJ /mol for 11 and ∆Gq
) 52.7 ( 0.2 kJ /mol for 12 were
275K
derived. The values indicate easier interconversion between the trans
and cis isomers for the PPh3-coordinated complex 11 than for the PMe3-
coordinated complex 12.
(24) (a) Hegedus, L. S.; Siirala-Hanse´n, K. J . Am. Chem. Soc. 1975,
97, 1184. (b) Hegedus, L. S.; Anderson, O. P.; Zetterberg, K.; Allen,
G.; Siirala-Hanse´n, K.; Olsen, D. J .; Packard, A. B. Inorg. Chem. 1977,
16, 1887. (c) Ozawa, F.; Nakano, M.; Aoyama, I.; Yamamoto, T.;
Yamamoto, A. J . Chem. Soc., Chem. Commun. 1986, 382.
(23) (a) Paul, F.; Patt, J .; Hartwig, J . F. Organometallics 1995, 14,
3030. (b) Widenhoefer, R. A.; Zhong, H. A.; Buchwald, S. L. Organo-
metallics 1996, 15, 2745.

Pd-Catalyzed Carbonylation Processes
Organometallics, Vol. 17, No. 16, 1998 3471
Ta ble 2. Rea ction s of Alcoh ols tow a r d 8 a n d 9 in
th e P r esen ce of Ter tia r y Am in esa
The nature of the secondary amine as a nucleophile
also affects the reaction. Piperidine, having a pKa value
(of its conjugate acid in aqueous solution)25 of 11.123
similar to 11.02 of HNEt2, reacts with 8 in 1 day at room
temperature, giving the phenylacetyl piperidine (16) in
84 mol %/Pd (entry 6, Table 1), whereas less basic
morpholine (pKa ) 8.33) yields phenylacetyl morpholine
(17) in 68 mol %/Pd in 1 day, leaving 22 mol % of 8
unreacted (entry 7). When an equimolar mixture of
piperidine and morpholine was allowed to react with 8,
the reactivity of piperidine was found to be higher than
that of morpholine, giving 16 as the major product (eq
5).
additives (10 mol/Pd)
PhCH2COOR
entry
complex
HOR
NR3
(mol %/Pd)b
1
2
3
4
5
8
8
8
9
9
HOMe
HOEt
HOEt
HOMe
HOEt
NEt3
NEt3
proton sponge
NEt3
87c
79d
6
trace(43)c,e
0(10)c,e
NEt3
a
Reaction conditions: the palladium complex (0.03 mmol) in
CD2Cl2 was treated with alcohol (0.30 mmol) and amine (0.30
b
1
mmol) at room temperature. Determined by H NMR after 24 h
(PhSiMe3 as an internal reference). c A trace of PhCH2COO- was
detected. PhCH2COO- (5%) was detected. e The data in the
d
parentheses are the yields measured after the reaction for 3 days
at room temperature.
strongly basic but bulkier tertiary amine, proved to be
much less effective (entry 3).
In the course of reaction of the P2-type (phenylacetyl)-
palladium halide complexes with secondary amines,
displacement of part of the phosphine ligands with the
secondary amine is a probable process. In fact, forma-
tion of the amine-coordinated complex 13 as a transient
intermediate was observed in the reaction of the P2-
type complex 8 with HNEt2.
(3) Com p etitive Rea ction s of Secon d a r y Am in es
a n d Alcoh ols t ow a r d (P h en yla cet yl)p a lla d iu m
Com p lexes. To compare the relative abilities of sec-
ondary amines and alcohols toward (phenylacetyl)-
palladium halides, we have treated the P1- and P2-type
acylpalladium complexes with mixtures of EtOH and
HNEt2 at room temperature for 1 day in the absence
and presence of added PPh3 (Table 3).
The amine-coordinated complex 13 was found to be
decomposed in CD2Cl2 at room temperature to give
amide 15 in 41 mol %/Pd in 3 days. The reaction was
accompanied by formation of (PhCH2)2 (8 mol %),
indicating occurrence of decarbonylation from 13 fol-
lowed by coupling of the benzyl moiety. When 10 mol
of NEt3 was added per 1 mol of palladium in 13, the
yield of the amide was increased to 80 mol %/Pd. On
the other hand, employment of a more bulky proton
sponge proved to be less effective, giving 43 mol % of
the amide/Pd. Complex 14, the PMe3-coordinated ana-
logue of 13, was less susceptible to decomposition and
released the amide in 15 mol %/Pd in 3 days at room
temperature with 45 mol % of 14 remaining undecom-
posed. In addition to the amide, (PhCH2)2 (6 mol %/Pd)
and PhCH2Cl (8 mol %/Pd) together with the P2-type
complex 9 (6 mol %/Pd) were formed in the reaction
system.
The reaction of the 1:1 EtOH/Et2NH mixture with the
P1-type bridged dimer 11 gave ethyl phenylacetate 19
in 74 mol %, affording only a trace of the amide 15
(entry 1, Table 3). Addition of 1 mol of PPh3/Pd to 11
caused an increase in the yield of the amide at the cost
of the ester (entry 2). A higher yield of the amide was
obtained on treatment of the P2-type complex 8 without
additional PPh3 at the cost of the ester (entry 3). A
further increase in the amount of extra PPh3 added led
to production of the amide as the predominant product,
yielding only minor amounts of the ester (entries 4-6).
A plot of the respective yields of the ester and amide
against the molar ratio of the PPh3 ligands to palladium
is given in Figure 1, which clearly shows that an
increase in the P2-type complex hinders the formation
of the ester and favors the formation of the amide. A
retardation effect in the production of an ester by
addition of free phosphine was previously observed in
the Pd-catalyzed carbonylation of aryl iodides in the
presence of alcohol and tertiary amine7a and in the
reductive elimination of aryl esters from acyl(aryloxy)-
palladium complexes.16a
(2) Rea ction s w ith Alcoh ols in th e P r esen ce of
Ter tia r y Am in es. Table 2 summarizes the results of
the reactions of the acylpalladium complexes 8 and 9
with mixtures of alcohols and tertiary amines. The
treatment of the PPh3-coordinated P2-type complex 8
with methanol and ethanol, respectively, in combination
with NEt3 afforded the methyl and ethyl phenylacetates
(18 and 19) in high yields (eq 6 and entries 1 and 2 in
Table 2). In contrast, the reactivity of the PMe3-
coordinated acylpalladium complex 9 toward the alco-
hols and NEt3 was much less (entries 4 and 5).26
The PMe3-coordinated P2-type (phenylacetyl)palla-
dium halide was found to be quite inactive, and the
reaction of 9 with the 1:1 mixture of EtOH/Et2NH gave
only a small amount of the ester in 3 days (entry 7,
Table 3), whereas the P1-type complex 12 gave the ester
In contrast to NEt3, which proved effective as a base
in the reactions of 8 with alcohols, the proton sponge, a
(26) While the present results show the much lower reactivity of
the PMe3-coordinated (phenylacetyl)palladium complex 9 than the
PPh3-coordinated complex 8 with the alcohols and NEt3 at room
temperature, the yields can be increased on prolonged reaction time.
Quantitative ester formation was reported on heating 9 with MeOH
and NEt3 at 80 °C for 1 h, see ref 11a.
(25) Lide, D. R. CRC Handbook of Chemistry and Physics, 76th ed.;
CRC Press: New York, 1995; pp 8-47.

3472 Organometallics, Vol. 17, No. 16, 1998
Lin and Yamamoto
Ta ble 3. Rea ction s of (P h en yla cetyl)p a lla d iu m
Com p lexes w ith 1:1 Mixtu r es of Et2NH a n d EtOH
Ta ble 4. Com p etitive Rea ction of Am in es a n d
Alcoh ols tow a r d tr a n s-P d Cl(COCH2P h )(P P h 3)2 (8)a
a
in th e P r esen ce a n d Absen ce of P P h 3
additives (10 mol/Pd)
products (mol %/Pd)b
products (mol %/Pd)b
2
2
entry
HOR1
HNR2
PhCH2COOR1 PhCH2CONR2
PPh3
molar
added
ratio PhCH2COOEt PhCH2CONEt2
1
2
3
4
5
6
7
8
9
HOMe
HNEt2
HNEt2
HNEt2
HNEt2
80
56
52
6
87
86
51
60
11
59
16
0
tracec
38c
42c
81c
5c
entry complex (mol/Pd) P/Pd
(19)
(15)
HOEt
HOPr
HOiPr
1
2
3
4
5
6
11
11
8
8
8
0
1
0
2
4
1
1.5
2
4
6
74
trace
17
60
56
26
18
10
38c
60c
67c
75c
HOCH2CF3 HNEt2
HOPh
HOEt
HOEt
HOiPr
HOEt
HOEt
HOEt
HNEt2
7c
HNPr2
28c
20c
71c
40c
60c,d
0
HNiPr2
8
10
12
HNiPr2
7
8
9
9
12
10
0
0
0
2
1
2
trace(5)
47(62)
76
0(0)d,e
0(0)d,f
9
10
11
12
piperidine
morpholine
HNPh2
a
Reaction conditions: the palladium complex (0.04 mmol in Pd)
a
Reaction conditions: the palladium complex 8 (0.03 mmol) in
in CD2Cl2 (0.5 mL) was treated with a 1:1 mixture of Et2NH (0.40
CD2Cl2 was treated with amine (0.30 mmol) and alcohol (0.30
b
mmol) and EtOH (0.40 mmol) at room temperature. Determined
b
1
mmol) at room temperature. Determined by H NMR after 24 h
by 1H NMR after 24 h (PhSiMe3 as an internal reference). c A trace
(PhSiMe3 as an internal reference). c A trace of PhCH2COO- was
detected. Unreacted 8 (6 mol %) was found.
d
of PhCH2COO- was detected. The data in the parentheses are
d
the yields measured after the reaction for
3 days at room
temperature. e (PhCH2)2 (3%) was detected after 3 days. f trans-
PdCl(COCH2Ph)(PMe3)2 (9) was formed (26 mol %) in 3 days.
coordinated species 13 were negligibly small. The
reactions monitored by NMR indicated that both forma-
tion of ester and amide were slowed by addition of 2
mol extra of PPh3 to the system, with retardation of
formation of ester being more severe than that of amide.
We have further examined the reactions of the P2-
type complex 8 toward 1:1 mixtures of various alcohols
and amines at room temperature in CD2Cl2. The results
summarized in Table 4 show that acidic alcohols such
as trifluoroethanol and phenol give higher ester yields
and that usage of bulkier alcohols such as isopropyl
alcohol is less favorable for the ester formation in
comparison with less bulky alcohols such as methanol,
ethanol, and n-propyl alcohol.
In the competition of an alcohol and a secondary
amine for the (phenylacetyl)palladium complex 8, the
nature of the secondary amines also affect the reaction.
Comparison of the effect of piperidine with that of less
basic morpholine, both having a similar steric bulkiness,
showed that more basic piperidine is favored for the
ester formation (entries 10 and 11, Table 4). Less basic
diphenylamine proved to be inactive for the formation
of the ester and the amide (entry 12). Employment of
the bulkier i-Pr2NH somewhat disfavored the amide
formation and favored the formation of the ethyl ester
than less bulky n-Pr2NH (entries 7 and 8).
F igu r e 1. Effect of the PPh3 ligands on the relative
amounts of the ester and amide formed in reactions of 1:1
mixtures of Et2NH and EtOH with (phenylacetyl)palladium
complexes
in 47 mol % yield in a day and 62 mol % in 3 days (entry
8). The dppe-coordinated complex 10 behaved differ-
ently from the PMe3-coordinated complex and yielded
the ester as the major product (entry 9).
Not only the product ratios of the ester/amide were
changed on addition of the free PPh3 to the acylpalla-
dium complexes, but also the rate of reaction was
considerably decreased by addition of PPh3 to 8. The
rate of the reaction of 8 with 10 equiv each of EtOH
and Et2NH was found to be first order in 8. In the
absence of added PPh3, the reaction proceeds rapidly
Rea ction s of th e Ben zyl- a n d (P h en yla cetyl)-
p a lla d iu m Com p lexes w ith HNEt2 u n d er CO P r es-
su r e. To examine the feasibility of achieving catalytic
carbonylation and double carbonylation of benzylic
substrates in the presence of a secondary amine and to
get information concerning the reaction mechanism of
formation of amide, reactions of the benzyl- and (pheny-
acetyl)palladium halide complexes 1a , 1b, and 8 having
the PPh3 ligands toward HNEt2 were conducted under
various CO pressures (Table 5).
On reactions with HNEt2 (10 mol/Pd) in the presence
of CO, these complexes were smoothly transformed into
amide 15 and N,N-diethylphenylpyruvamide (20) at
room temperature in 1 day (eq 7).
For the three complexes examined, an increase in the
CO pressure led to an increase in the yield of the R-keto
amide 20 at the cost of the amide 15. The relative yields
of the R-keto amide to the amide are listed in the last
column in Table 5, which clearly indicates that higher
and is complete in 100 min, with the rate constant being
20°C
kobs
) (2.4 ( 0.1) × 10-4 s-1 based on complex 8.
During the course of the reaction of 8, the Et2NH-
coordinated P1-type complex was observed as a tran-
sient intermediate by NMR.
When 2 mol of PPh3 per 1 mol of palladium was added
to the reaction system containing 8 and 10 mol each of
EtOH and Et2NH, the rate constant of the reaction of 8
with EtOH/Et2NH at room temperature to give ester
and amide was dropped to (5.4 ( 0.1) × 10-5 s-1
compared to the case without added PPh3. The NMR
signals arising from the transient intermediate Et2NH-

Pd-Catalyzed Carbonylation Processes
Organometallics, Vol. 17, No. 16, 1998 3473
Ta ble 5. Rea ction of Ben zyl- a n d
(P h en yla cetyl)p a lla d iu m Com p lexes w ith CO in
th e P r esen ce of Et2NHa
Discu ssion
Rea ction Cou r ses of (P h en yla cetyl)p a lla d iu m
Com p lexes w ith Secon d a r y Am in es a n d Alcoh ols
in t h e Absen ce of CO. In the Introduction we
discussed the possible reaction courses of the acyl-
palladium complexes with nucleophiles to produce
amides or esters in Scheme 2. Among the three courses
we considered, course c involving the direct reductive
elimination of phenylacetyl halide from the (phenyl-
acetyl)palladium halide was found operative in the HI-
promoted palladium-catalyzed carbonylation to liberate
phenylacetic acid.15 However, the operation of this
course is unlikely in the reactions of (phenylacetyl)-
palladium halide with nucleophiles under basic condi-
tions on the following grounds. First, if phenylacetyl
chloride is produced on reductive elimination, amides
should be formed in preference to esters in the competi-
tive reactions of alcohols and secondary amines with the
acyl halide whereas esters were in fact formed as the
main reaction product at lower PPh3/Pd ratios (Figure
1). Second, if the direct reductive elimination of acyl
halide is operative, the influence of added phosphine
ligands on relative yields of amides and esters would
not be observed.
products (%)b,c
entry complex CO (atm) solvent 20 15
21
ratio 20/15
1
2
3
4
5
6
7
8
9
1a
1a
1a
1a
1a
1a
1b
1b
8
10
20
40
60
20
60
20
60
20
60
20
20
THF
THF
THF
THF
49 25 27
2.0
2.6
3.2
3.9
2.0
5.1
1.2
1.9
2.1
4.4
0.1
5.4
54 21 24
60 19 20
67 17 19
CHCl3 61 30 26
CHCl3 77 15 15
CHCl3 53 43 trace
CHCl3 63 33
6
CHCl3 64 31 32
CHCl3 75 17 13
10
11
12
8
1a
8
noned
noned
6
73 21
54 10 19
a
Reaction conditions: a mixture of the palladium complex (0.13
mmol), solvent (2 mL), and Et2NH (1.30 mmol) under CO pressure
b
was stirred at room temperature for 24 h. Respective yields in
mol %/Pd were determined by 1H NMR and GC (PhSiMe3 as an
internal reference). c Et2NH2+X- was found in the reaction mix-
tures as identified by 1H NMR. The amount of Et2NH2+I- was
smaller than that of Et2NH2+Cl-. The reaction was carried out
d
in neat Et2NH (26.0 mmol).
To unequivocally establish the reaction course of the
liberated acyl chloride with a mixture of nucleophiles,
we have examined the reaction of 0.04 mmol of phenyl-
acetyl chloride with a mixture of 0.4 mol each of ethanol
and diethylamine (eq 8). The reaction gave only amide
CO pressure favors the R-keto amide formation. The
benzyl- and (phenylacetyl)palladium complexes show a
similar reactivity pattern in giving the R-keto amide and
amide (entries 5, 6 vs 9, 10). The results suggest that
the reactions proceed through a common (phenylacetyl)-
palladium species regardless of the starting complex,
whether it is benzyl or phenylacetyl. The amount of
N,N-diethyloxamide (21) produced as the byproduct was
found to decrease upon increasing the CO pressure.
without giving any ester, excluding the possibility of
liberation of phenylacetyl chloride by reductive elimina-
tion from the (phenylacetyl)palladium chloride complex.
Course a involving the direct attack of the nucleophile
on the phenylacetyl ligand is the generally accepted
course and is compatible with the intuitive reasoning
based on the knowledge of organic chemistry without
involvement of a transition-metal catalyst. However,
if this reaction is operative, we would expect formation
of the amide as the predominant product in the com-
petitive reaction of the (phenylacetyl)palladium complex
with a 1:1 mixture of alcohol and secondary amine.
Formation of the ester as the main product is difficult
to explain, if we assume that the simple competition of
free secondary amine and alcohol toward the carbonyl
group in the phenylacetyl ligand determines the product
ratio. The assumption of formation of a minute amount
of a free alkoxide anion having a much greater nucleo-
philicity toward the acyl carbonyl group than free amine
is not reasonable either on the basis of the experiment
in eq 8.
On the other hand, formation of a free alkoxide on
interaction of an alcohol with a tertiary amine and the
subsequent attack of the alkoxide on the acylpalladium
complex, as proposed by Moser et al. in the reaction of
a benzoylpalladium complex with mixtures of methanol
and various tertiary amines, is a process worth consid-
eration.12 However, employment of a proton sponge, the
highly efficient deprotonation agent having a great
bulkiness, proved to be much less effective than that of
Quite different results were obtained when the car-
bonylation was carried out in HNEt2 without using any
other solvent. In neat HNEt2, the amide 15 was
obtained as the major product when the benzylpalla-
dium complex was carbonylated, whereas the R-keto
amide 20 was the predominant product in the treatment
of the (phenylacetyl)palladium complex (entries 11 and
12).
For gaining information concerning the mechanism
of the formation of R-keto amide and comparing the
reactivities of the phenylacetyl and CO ligands toward
nucleophiles, the reaction of HNEt2 (10 mol/Pd) with
the cationic CO-coordinated (phenylacetyl)palladium
complex 7 at room temperature under 10 atm of CO was
examined. The reaction released the R-keto amide 20
and amide 15 in a molar ratio of 2.5:1, accompanied by
formation of a black precipitate of Pd metal and
Et2NH2+PF6-, as confirmed by NMR. The results
indicate that the amide as well as the R-keto amide can
be produced from the CO-coordinated (phenylacetyl)-
palladium complex.

3474 Organometallics, Vol. 17, No. 16, 1998
Lin and Yamamoto
Sch em e 3. P r op osed Mech a n ism for th e
F or m a tion of Am id e
gives the (phenylacetyl)palladium alkoxide that reduc-
tively eliminates the ester (Scheme 4). The ineffective-
ness of the strongly basic proton sponge for the ester
formation may be an indication that too bulky base is
not a suitable agent for the deprotonation. A similar
mechanism was proposed previously to account for the
formation of esters in the reaction of benzoylpalladium
complexes with alcohols and amine bases.7a
In the competitive reactions of alcohols and secondary
amines with 8 and 11 in the absence of added tri-
phenylphosphine to give esters as the main product, a
similar mechanism may be operative (Scheme 5).
In the reaction of the triphenylphosphine-coordinated
acylpalladium complexes 8 and 11, coordination of
diethylamine will take place first to give the amine-
coordinated P1-type complex 13.
triethylamine (entry 3 in Table 2). The result is not
compatible with the idea of simple deprotonation of
methanol by tertiary amines and suggests that consid-
eration of a steric effect is necessary to account for the
striking ineffectiveness of the proton sponge. The effect
of suppression of formation of carboxylic esters on
increase of the amount of triphenylphosphine added to
the (phenylacetyl)palladium complex resulting in an
increase of the amount of amide is also difficult to
explain by the mechanism involving the attack of free
alkoxide on the carbonyl group in the (phenylacetyl)-
palladium complex.
The alcohol and the amine will coordinate to complex
13 to form an equilibrium mixture of the amine- and
alcohol-coordinated complexes. Deprotonation of the
coordinated alcohol from the alcohol-coordinated species
(I) will give the acylpalladium ethoxide intermediate (II)
that produces the ester 19 on reductive elimination,
whereas migration of the coordinated amine to the acyl
ligand as discussed in Scheme 3 will give the amide 15.
If deprotonation from the coordinated alcohol is favored
over the migration of the coordinated amine to the
phenylacetyl ligand, the ester will be produced through
the (phenylacetyl)palladium alkoxide intermediate (II).
A difficulty in the present mechanism is in assuming
the coordination of alcohol forming a five-coordinate
complex in Schemes 4 and 5. It is not unreasonable,
however, to assume the coordination of alcohol to the
Pd(II) center and the subsequent slow deprotonation
process to give the alkoxide intermediate. In fact, the
formation of ester in a high yield in the reaction of the
dppe-coordinated complex 10 with ethanol and Et2NH
seems to support the involvement of a five-coordinate
intermediate. Examples of alcohol coordination to
tertiary phosphine-coordinated palladium complexes are
known.28 Furthermore, the result that the bulky iso-
propyl alcohol is less favorable than linear alcohols for
the ester formation may reflect the difficulty in coordi-
nation of a sterically demanding alcohol (entries 4 and
9, Table 4).
The higher yields of esters with alcohols of higher
acidities are compatible with the mechanism where
deprotonation is a key step in the ester formation. The
route through formation of a free alkoxide is not
compatible with the results that employment of a bulky
base such as a proton sponge is ineffective in giving the
esters as we previously discussed.
In the presence of added phosphine to form the P2-
type complexes, the coordination site for the nucleophile
to palladium is blocked and the nucleophile will ap-
proach from the fifth coordination site. In this case, the
competition for coordination to the palladium center
between the amine and alcohol to be followed by
deprotonation is favorable for the amine to yield the
amide 15 preferentially.
Since both routes a and c in Scheme 2 do not seem to
accommodate a reasonable explanation of the experi-
mental results, we now discuss the mechanisms of
aminolysis and alcoholysis (course b in Scheme 2) in
the reactions of the (phenylacetyl)palladium complexes
with secondary amines or alcohols. Both processes
should involve deprotonation from the neutral nucleo-
phile HNu at a certain stage to give the esters and the
amides. The results shown in Tables 1, 3, and 4 on the
reactions of the (phenylacetyl)palladium complexes with
secondary amines and alcohols suggest that the mech-
anism to give amides is different from the mechanism
to give esters; a more basic amine is preferred to give
the amides, whereas a less basic alcohol is favored for
giving the esters.
For the amide formation from the (phenylacetyl)-
palladium chloride 8 and 11 on reaction with diethyl-
amine, we propose the mechanism shown in Scheme 3.
From either the P2- or P1-type complexes 8 or 11, the
monoamine-coordinated complex 13 is formed first, as
observed experimentally. Direct deprotonation from the
coordinated HNEt2 to give (phenylacetyl)palladium
amide is not the likely course to give phenylacetamide,
since the less basic morpholine is less reactive than
piperidine (eq 5). Therefore, migration of the amine to
the carbonyl group in the phenylacetyl ligand is as-
sumed to take place with the resultant formation of the
amide 15 by deprotonation with the aid of a base.
In the ester formation from the (phenylacetyl)palla-
dium complexes on reaction with alcohols and a tertiary
amine (Table 2), the palladium complexes will also be
coordinated by the amine first. Trogler prepared vari-
ous amine-coordinated cationic methylpalladium com-
plexes and measured the binding constants of the
amines.27 Coordination of the alcohol will follow, and
deprotonation of the coordinated alcohol by the base
The much lower reactivity of the PMe3-coordinated
P1- and P2-type (phenylacetyl)palladium complexes
(27) Seligson, A. L.; Trogler, W. C. J . Am. Chem. Soc. 1991, 113,
2520.
(28) Davies, J . A.; Hartley, F. R.; Murray, S. G. J . Chem. Soc., Dalton
Trans. 1980, 2246.

Pd-Catalyzed Carbonylation Processes
Organometallics, Vol. 17, No. 16, 1998 3475
Sch em e 4. P r op osed Mech a n ism for th e F or m a tion of Ester in th e P r esen ce of Ter tia r y Am in e
Sch em e 5. P r op osed Mech a n ism for th e
F or m a tion of Ester in th e P r esen ce of HNEt2
en ce of CO. On the basis of the fundamental infor-
mation on the reactivities of the (phenylacetyl)palladium
complexes with various nucleophiles, we now discuss
the reactivities of the benzyl- and (phenylacetyl)palla-
dium complexes toward Et2NH under CO pressures.
As shown in Table 5, upon increasing the CO pressure
from 20 to 60 atm in CHCl3, a similar increase in the
amount of the R-keto amide 20 at the cost of the amide
15 and oxamide 21 was observed for the both benzyl-
and (phenylacetyl)palladium complexes. The results
may be taken as an indication that under CO pressure
all of the benzylpalladium complexes are converted into
(phenylacetyl)palladium prior to the reaction of the CO-
coordinated benzylpalladium complex with the amine
and that the R-keto amide and amide may arise from
the common (phenylacetyl)palladium complex. Previ-
ously, arylpalladium complexes have been converted
into R-keto amides and amides under CO pressure on
reaction with secondary amines.29 The enhancement in
the selectivity of R-keto amide over amide on increasing
the CO pressure was ascribed to promotion of the course
through path b and the intermediate G in Scheme 1
with suppression of the reaction course through path a
involving the aryl(carbamoyl)palladium complex.29 The
difference of the previous results on the arylpalladium
complex from the present one is partly ascribed to the
difference in the reactivities between the aryl- and
benzylpalladium complexes toward CO insertion and
toward the attack of a nucleophile at the coordinated
CO. The other important factor is that the reaction of
the arylpalladium complex with the amine under CO
to give the amide was carried out in neat amine. The
presence of the large excess of the amine in the system
would favor its attack on the coordinated CO before the
CO insertion occurs. In fact, in the present study, the
reaction of the benzylpalladium complex 1a with CO (20
atm) in neat Et2NH at room temperature also produced
the amide 15 as the major product (entry 11 in Table
5), indicating the occurrence of the attack of amine on
the CO coordinated to the benzylpalladium species. On
the other hand, the reaction of the (phenylacetyl)-
palladium complex 8 in neat Et2NH under similar
conditions produced the R-keto amide 20 as the main
product.
than the PPh3- and dppe-coordinated complexes toward
Et2NH (Table 1) and alcohol mixed with tertiary amine
base (Table 2) suggests that the electrophilicity of the
acylpalladium center toward a nucleophile is very
important in determining the production of the organic
carbonylation product. The result that the dppe-
coordinated (phenylacetyl)palladium chloride complex
10 reacted smoothly with HNEt2 to give the amide as
well as the reaction of 10 with a 1:1 mixture of EtOH
and HNEt2 to give the ester as the main product implies
that the assumption of the approach of a nucleophile
from the fifth coordination site is not unreasonable.
Rea ction s of Ben zyl- a n d (P h en yla cetyl)p a lla -
d iu m Ha lid e Com p lexes w ith Et2NH in th e P r es-
The proposed course of R-keto amide formation from
the benzyl- and (phenylacetyl)palladium complexes is
shown in Scheme 6, which is comprised of (a) CO
(29) Ozawa, F.; Sugimoto, T.; Yusas, Y.; Santra, M.; Yamamoto, T.;
Yamamoto, A. Organometallics 1984, 3, 683.

3476 Organometallics, Vol. 17, No. 16, 1998
Lin and Yamamoto
ses were performed on a Hitachi 263-50 equipped with an SE-
30 column, using N2 as the carrier gas.
Sch em e 6. P r op osed Mech a n ism for th e
F or m a tion of r-Keto Am id ea
Solvents were dried and distilled before use by standard
methods. Amines and alcohols were commercially available
and dried by MS 4A before use. Benzyl iodide was prepared
by the reaction of benzyl chloride with excess of LiI. The
palladium complexes, Pd(PPh3)4,30 Pd(CH2Ph)Cl(PPh3)2 (1a ),17
Pd(CH2Ph)I(PPh3)2 (1b ),15b Pd(CH2Ph)Cl(PMe3)2 (2),15b
(η3-benzyl)bis(triphenylphosphine)palladium hexafluorophos-
phate (3),15b (η3-benzyl)bis(trimethylphosphine)palladium
hexafluorophosphate (4),15b and Pd(COCH2Ph)Cl(PPh3)2 (8),18
were synthesized as reported in the literature.
a
L ) tertiary phosphine; X ) halide.
P r ep a r a tion of tr a n s-P d (COCH2P h )Cl(P Me3)2 (9). To
a white turbid mixture of trans-PdCl(COCH2Ph)(PPh3)2 (1.0
g, 1.27 mmol) and toluene (30 mL) was added PMe3 (0.394 mL,
3.81 mmol) at room temperature under an atmosphere of
argon. After the mixture was stirred for 20 min at room
temperature, it was concentrated to 5 mL. Ether (30 mL) was
added to the solution to yield a white precipitate, which was
filtered, washed with ether, and dried. Recrystallization of
the above solid from CH2Cl2/Et2O gave a white powder of 9
(0.41 g, 78%). 1H NMR (CD2Cl2, δ, 270 MHz, 298 K): 7.3 (m,
5H, Ph), 3.86 (s, 2H, PhCH2), 1.24 (s br, 18H, PMe3). 31P NMR
insertion into the benzyl-Pd bond; (b) CO coordination
to the phenylacetyl complex; (c) attack of Et2NH on the
coordinated CO to give (phenylacetyl)(carbamoyl)palla-
dium species; and (d) the reductive elimination of the
phenylacetyl and carbamoyl groups to give 20 after
trans to cis isomerization. The amide 15 may be formed
by the reaction of the (phenylacetyl)palladium complex
with Et2NH as we previously discussed.
These results suggest that employment of a high CO
pressure and a limited amount of a secondary amine is
favorable for achieving double carbonylation to give an
R-keto amide. In fact, the palladium-catalyzed double
carbonylation was realized using allylic chlorides, high
CO pressure, and a limited amount of Et2NH.3
(CD2Cl2, δ, 109.4 MHz, 298 K): -18.7 (s). υCdO 1661 cm-1
.
Anal. Calcd for C14H25ClOP2Pd: C, 40.70; H, 6.10. Found:
C, 40.52; H, 6.07.
P r ep a r a tion of P d Cl(COCH2P h )(d p p e) (10). To a sus-
pension of trans-PdCl(COCH2Ph)(PPh3)2 (0.079 g, 0.1 mmol)
in CH2Cl2 (5 mL) was added dppe (0.080 g, 0.2 mmol). The
mixture was stirred for 1 h at room temperature under an
atmosphere of argon. Addition of ether (20 mL) to the mixture
gave a white precipitate, which was filtered and recrystallized
from CH2Cl2 (2 mL)-Et2O (4 mL) twice to give a white powder
of 10 (0.040 g, 61%). 1H NMR (CD2Cl2, δ, 270 MHz, 298 K):
7.82 (dd, J ) 7, 3 Hz, 4H, Ph2PCH2CH2PPh2), 7.61 (dd, J )
11, 7 Hz, 4H, Ph2PCH2CH2PPh2), 7.45 (s br, 12H, Ph2PCH2-
CH2PPh2), 7.05 (s br, 3H, Ph), 6.68 (s br, 2H, Ph), 3.85 (s, 2H,
PhCH2), 2.45 (dm, J ) 26, 6 Hz, 2H, Ph2PCH2CH2PPh2), 2.09
(ddt, J ) 26, 13, 6 Hz, 2H, Ph2PCH2CH2PPh2). 31P NMR (CD2-
Cl2, δ, 109.4 MHz, 298 K): 38.5 (d, J ) 44, Ph2PCH2CH2PPh2),
22.7 (d, J ) 44, Ph2PCH2CH2PPh2). 13C NMR (CD2Cl2, 67.9
MHz, δ, 298 K): 238.2 (d br, J ) 12 Hz, COCH2Ph), 58.7 (dd,
J ) 37, 19 Hz, COCH2Ph), 29.4 (dd, J ) 33, 22 Hz, Ph2PCH2-
CH2PPh2), 22.6 (dd, J ) 24, 11 Hz, Ph2PCH2CH2PPh2). υCdO
1693 cm-1. Anal. Calcd for C34H31ClOP2Pd: C, 61.93; H, 4.74.
Found: C, 61.66; H, 4.75.
Con clu sion
Examination of the reactivities of benzyl- and (phen-
ylacetyl)palladium complexes toward various nucleo-
philes has shed light on the detailed courses of the
reactions of these complexes with amines and alcohols.
More acidic and less bulky alcohols have been found to
be more favorable to give esters in reactions of the
(phenylacetyl)palladium complexes in the presence of
a base. On the other hand, operation of two processes
to give the phenylacetamide has been established. One
involves formation of an amine-coordinated (phenyl-
acetyl)palladium complex in which amine migration to
the acyl group takes place in the absence of CO, whereas
the other involves the nucleophilic attack of an excess
of Et2NH on the coordinated CO to give benzyl(carbam-
oyl)palladium, which liberates amide on reductive elimi-
nation. The R-keto amide formation is considered to
proceed via the route involving nucleophilic attack of
amine on the CO-coordinated (phenylacetyl)palladium
complex followed by reductive elimination of the phen-
ylacetyl and the carbamoyl ligands. The attempted
catalytic double carbonylation of benzylic substrates has
not been realized yet, but various pieces of fundamental
information obtained in the present study should pro-
vide a basis to eventually realize the catalytic processes.
P r ep a r a tion of [P d Cl(COCH2P h )(P P h 3)]2 (11). To a
CH2Cl2 (20 mL) solution of trans-PdCl(COCH2Ph)(PPh3)2
(0.800 g, 1.018 mmol) was added PdCl2(PhCN)2 (0.195 g, 0.509
mmol). Immediately, a yellow precipitate was formed. After
the mixture was stirred for 20 min at room temperature, the
precipitate was filtered off and the filtrate was concentrated
to give an orange residue. Addition of ether followed by
filtration and drying gave a yellowish-orange solid of 11 (0.46
g, 86%). Purification can be achieved by recrystallization from
CH2Cl2-Et2O. 1H NMR (CD2Cl2, δ, 270 MHz, 298 K): 7.67
(m, 12H, PPh3), 7.40 (m, 18H, PPh3), 7.10 (d, J ) 6 Hz, 6H,
m-, p-Ph), 6.64 (d, J ) 6 Hz, 4H, o-Ph), 3.76 (s, 4H, PhCH2).
31P NMR (CD2Cl2, δ, 109.4 MHz, 298 K): 27.0 (s). 13C NMR
(CD2Cl2, 67.9 MHz, 298 K): δ 219.2 (s br, COCH2Ph), 57.5 (d,
Exp er im en ta l Section
J ) 24, COCH2Ph). υCdO 1712 cm-1. Anal. Calcd for C52H44
Cl2O2P2Pd2: C, 59.68; H, 4.24. Found: C, 59.78; H, 4.22.
-
All manipulations were carried out under an atmosphere
of argon. Infrared spectra were recorded on a Hitachi 295
spectrometer using KBr pellets. 1H, 13C, and 31P NMR spectra
were recorded on a J EOL EX-270 spectrometer. Chemical
shifts are reported in δ units (parts per million, ppm) downfield
P r ep a r a tion of [P d Cl(COCH2P h )(P Me3)]2 (12). To a
CH2Cl2 (10 mL) solution of trans-PdCl(COCH2Ph)(PMe3)2
(0.280 g, 0.678 mmol) was added PdCl2(PhCN)2 (0.130 g, 0.339
mmol). Immediately, a white precipitate was formed. After
the mixture was stirred for 20 min at room temperature, ether
(ca. 30 mL) was added to the mixture until no more precipitate
1
from Me4Si for H and 13C and H3PO4 (85% in aqueous solution,
external reference) for 31P. Carbon, hydrogen, and nitrogen
analyses were carried out on a Perkin-Elmer PE 2400II
Elemental Analyzer. Mass spectra were analyzed on a J EOL
AUTOMASS spectrometer. Gas chromatographic (GC) analy-
(30) Hegedus, L. S. In Organometallics in Synthesis: A Manual;
Schlosser, M., Ed.; Wiley: New York, 1994; p 383.

Pd-Catalyzed Carbonylation Processes
Organometallics, Vol. 17, No. 16, 1998 3477
formed. Filtration gave a white solid and a pale yellow filtrate.
The white solid was dissolved in CH2Cl2 (10 mL), and ether
was added to the mixture until no more precipitate formed.
After filtration, the white solid was repeatedly recrystallized
from CH2Cl2 and ether. The filtrates and washings were
combined and concentrated to give a white precipitate, which
was filtered, washed with ether, and dried to afford a white
powder of 12 (0.14 g, 56%). 1H NMR (CD2Cl2, δ, 270 MHz,
298 K): 7.41 (d, J ) 7 Hz, 4H, o-Ph), 7.34 (t, J ) 7 Hz, 4H,
m-Ph), 7.25 (t, J ) 7 Hz, 2H, p-Ph), 4.02 (s, 4H, PhCH2), 1.16
(d, J ) 11 Hz, 18H, PMe3). 31P NMR (CD2Cl2, δ, 109.4 MHz,
tube was added HNEt2 (0.041 mL, 0.40 mmol) and PhSiMe3
(0.0068 mL, 0.04 mmol, as an internal reference) at room
temperature under an atmosphere of argon. After 1 day, the
1
reaction was analyzed by H NMR and GC-MS (Table 1).
The same procedure as described above was used in the
reactions of complexes 9-12 with HNEt2, piperidine, and
morpholine, respectively (Table 1).
Decom p osition of P d Cl(COCH2P h )(P R3)(NHEt2) (R )
P h , Me). A CD2Cl2 (0.6 mL) solution of 13 (0.024 g, 0.04
mmol) was placed in an NMR tube at room temperature under
an atmosphere of argon. PhSiMe3 (0.0068 mL, 0.04 mmol) was
added as an internal reference. After 3 days at room temper-
ature, the solution was analyzed by 1H and 31P NMR and GC-
MS to reveal the formation of 15 (41%), (PhCH2)2 (8%), a small
amount of phenylacetic acid anion, and an unidentified
compound (6%).
The same procedure was used for the decomposition experi-
ment of 14 (0.016 g, 0.04 mmol). After the CD2Cl2 solution of
14 was allowed to stand at room temperature for 3 days, the
solution was found to be composed of a mixture of the
undecomposed complex 14 (45 mol %/Pd), 15 (15 mol %/Pd),
PhCH2Cl (8 mol %/Pd), (PhCH2)2 (6 mol %/Pd), 9 (6 mol %/Pd),
and a small amount of phenylacetic acid anion.
298 K): -6.8 (s). υCdO 1696 cm-1
Cl2O2P2Pd2: C, 39.20; H, 4.78. Found: C, 38.93; H, 4.76.
. Anal. Calcd for C22H32-
Syn th esis of P d Cl(COCH2P h )(P P h 3)(NHEt2) (13). To
a CH2Cl2 solution (8 mL) of [PdCl(COCH2Ph)(PPh3)]2 (0.105
g, 0.10 mmol) cooled to -20 °C was added HNEt2 (0.026 mL,
0.25 mmol) under an atmosphere of argon. After the mixture
was stirred at -20 °C for 20 min, a light-yellow solution was
obtained, which was concentrated under reduced pressure at
-20 °C to give a pale yellow residue. Addition of pentane (10
mL) gave a pale yellow precipitate. After filtration, washing
with cooled pentane (2 × 10 mL), and careful vacuum-drying
at low temperature (-30 °C), a pale yellow solid of 13 was
obtained (0.107 g, 90%), which was stored in a refrigerator
(-30 °C). 1H NMR (CD2Cl2, δ, 270 MHz, 253 K): 7.68 (m, 6H,
PPh3), 7.41 (m, 9H, PPh3), 7.09 (s br, 3H, Ph), 6.40 (s br, 2H,
Ph), 3.60 (s br, 1H, HNEt2), 3.57 (s, 2H, PhCH2), 2.63 (s br,
4H, HN(CH2CH3)2), 1.62 (t, J ) 7 Hz, 6H, HN(CH2CH3)2). 31P
NMR (CD2Cl2, δ, 109.4 MHz, 253 K): 26.9 (s). 13C NMR
(CD2Cl2, δ, 67.9 MHz, 253 K): 231.3 (d, J ) 3 Hz, COCH2Ph),
57.7 (d, J ) 21 Hz, COCH2Ph), 47.0 (d, J ) 8 Hz, HN(CH2-
CH3)2)), 15.9 (s, HN(CH2CH3)2). IR: 3216, 1671 cm-1. Anal.
Calcd for C30H33ClNOPPd: C, 60.41; H, 5.58; N, 2.35. Found:
C, 59.49; H, 5.56; N, 2.19.
Syn th esis of P d Cl(COCH2P h )(P Me3)(NHEt2) (14). To
a CH2Cl2 solution (5 mL) of [PdCl(COCH2Ph)(PMe3)]2 (0.067
g, 0.10 mmol) cooled to -30 °C was added HNEt2 (0.026 mL,
0.25 mmol) under an atmosphere of argon. After the mixture
was stirred at -30 °C for 20 min, the colorless solution
obtained was concentrated under reduced pressure at -30 °C
to give a pale yellow oily residue. Addition of pentane (5 mL)
and HNEt2 (0.026 mL) to the residue and stirring gave a white
precipitate. After filtration and careful vacuum-drying at low
temperature (-50 °C), a white solid of 14 was obtained (0.078
g, 95%), which was stored in a refrigerator (-30 °C). 1H NMR
(CD2Cl2, δ, 270 MHz, 253 K): 7.28 (t, J ) 7 Hz, 2H, Ph), 7.23
(t, J ) 7 Hz, 1H, Ph), 7.15 (d, J ) 7 Hz, 2H, Ph), 3.96 (s, 2H,
PhCH2), 2.98 (s br, 1H, HNEt2), 2.62 (m, 4H, HN(CH2CH3)2),
1.47 (t, J ) 7 Hz, 6H, HN(CH2CH3)2), 1.26 (d, J ) 11 Hz, 9H,
PMe3). 31P NMR (CD2Cl2, δ, 109.4 MHz, 253 K): -7.4 (s). IR:
3232, 1680 cm-1. Anal. Calcd for C15H27ClNOPPd: C, 43.92;
H, 6.63; N, 3.41. Found: C, 43.57; H, 6.67; N, 3.60.
Rea ction of 8 w ith AgP F 6. To a CD2Cl2 (2 mL) solution
of AgPF6 (0.036 g, 0.142 mmol) was added trans-PdCl(COCH2-
Ph)(PPh3)2 (8) (0.112 g, 0.142 mmol) under an atmosphere of
argon. A white precipitate formed immediately. After 10 min,
the mixture was filtered through kieselgur to give a light
yellow solution, which was analyzed by 1H and 31P NMR. The
solution was found to contain only (η3-benzyl)bis(triphenylphos-
phine)palladium hexafluorophosphate (3). Evaporation of the
solvent and addition of ether gave a yellow solid. The infrared
spectrum indicated the disappearance of the acyl υ(CO) band.
Rea ction of 13 w ith P P h 3. To an NMR tube containing
a CD2Cl2 solution (0.6 mL) of PdCl(COCH2Ph)(PPh3)(NHEt2)
(13) (0.020 g, 0.0335 mmol) cooled at -20 °C was added PPh3
(0.009 g, 0.0335 mmol). The mixture was warmed to room
temperature and analyzed by 1H and 31P NMR to indicate the
quantitative formation of trans-PdCl(COCH2Ph)(PPh3)2 (8) and
free HNEt2.
Decom p osition of 13 in th e P r esen ce of a Ter tia r y
Am in e. A CD2Cl2 (0.6 mL) solution of 13, prepared in situ by
mixing 11 (0.021 mg, 0.02 mmol) with HNEt2 (0.0046 mL,
0.044 mmol), was placed in an NMR tube at room temperature
under an atmosphere of argon. NEt3 (0.055 mL, 0.4 mmol) or
proton sponge (0.086 g, 0.4 mmol) and PhSiMe3 (0.0068 mL,
0.04 mmol, as an internal reference) were added. The decom-
1
position reaction was analyzed by H NMR and GC-MS after
3 days to show the formation of 15 in a yield of 80 mol %/Pd
(NEt3) or 43 mol %/Pd (Proton Sponge).
Rea ction s of Com p lexes 8 a n d 9 w ith MeOH a n d EtOH
in th e P r esen ce of Et3N or P r oton Sp on ge. To a CD2Cl2
(0.6 mL) solution of 8 (0.04 mmol) in an NMR tube was added
alcohol (0.40 mmol), PhSiMe3 (0.0068 mL, 0.04 mmol, as an
internal reference), and a tertiary amine (0.40 mmol) at room
temperature under an atmosphere of argon. After 1 day, the
1
reaction was analyzed by H NMR and GC-MS (Table 2).
The same procedure as described above was used in the
reactions of complex 9 with alcohols (Table 2).
Rea ction s of Com p lexes 8-12 w ith HNEt2/EtOH. To
CD2Cl2 (0.6 mL) solution of a (phenylacetyl)palladium
a
complex (0.04 mmol/Pd) in an NMR tube was added a mixture
of HNEt2 (0.041 mL, 0.40 mmol) and EtOH (0.023 mL, 0.40
mmol), together with PhSiMe3 (0.0068 mL, 0.04 mmol, as an
internal reference) at room temperature under an atmosphere
of argon. After 1 and 3 days, the reaction mixtures were
1
analyzed by H NMR and GC-MS (Table 3).
In the reaction of 8 with HNEt2/EtOH, different ratios of
free PPh3 were added and the formation of ester 19 and amide
1
15 were analyzed by H NMR after 1 day (Table 3). Kinetic
studies on the reactions of 8 with HNEt2/EtOH in the absence
and presence of 2 equiv of PPh3 were performed and monitored
by 1H NMR by observing the decay of the benzyl signals of
complex 8 at room temperature.
Com p etitive Rea ction s of Com p lex 8 w ith Va r iou s
P a ir s of Alcoh ols a n d Secon d a r y Am in es. To a CD2Cl2
(0.6 mL) solution of 8 (0.03 mmol) in an NMR tube was added
amine (0.30 mmol) and alcohol (0.30 mmol), together with
PhSiMe3 (0.0051 mL, 0.03 mmol, as an internal reference) at
room temperature under an atmosphere of argon. After 1 day,
1
the reaction was analyzed by H NMR and GC-MS (Table 4).
Rea ction s of tr a n s-P d X(CH2P h )(P P h 3)2 (1a , X ) Cl; 1b,
X ) I) a n d tr a n s-P d Cl(COCH2P h )(P P h 3)2 (8) w ith CO a n d
Et2NH. Gen er a l P r oced u r e. In a typical experiment, a 100-
mL stainless steel autoclave was charged with trans-PdCl(CH2-
Ph)(PPh3)2 (1a ) (0.100 g, 0.13 mmol), THF or CHCl3 (2 mL),
and Et2NH (0.135 mL, 1.3 mmol) under an atmosphere of
argon. Carbon monoxide was introduced into the system, and
Rea ction s of Com p lexes 8-12 w ith Secon d a r y Am in es.
To a CD2Cl2 (0.6 mL) solution of 8 (0.04 mmol) in an NMR

3478 Organometallics, Vol. 17, No. 16, 1998
Lin and Yamamoto
the mixture was magnetically stirred at room temperature for
1 day. The yields of N,N-diethyl phenylacetamide (15), N,N-
diethyl phenylpyruvamide (20), and N,N-diethyl oxamide (21)
produced were measured using PhSiMe3 as an internal
standard by means of GC (Column: SE-30), GC-MS, and 1H
NMR after evaporation of solvent by comparison with authen-
tic samples. In addition, Et2NH2+X- was detected in the
mixture. NMR data assigned for 20: 1H NMR (CD2Cl2, δ, 270
MHz, 298 K) 7.4-7.2 (m, 5H, Ph), 4.01 (s, 2H, PhCH2), 3.29
(q, J ) 7.3 Hz, 2H, N(CH2CH3)(CH2′CH3′)), 2.97 (q, J ) 7.0
Hz, 2H, N(CH2CH3)(CH2′CH3′)), 1.03 (t, J ) 7.3 Hz, 3H,
N(CH2CH3)(CH2′CH3′)), 0.95 (t, J ) 7.0 Hz, 3H, N(CH2CH3)-
(CH2′CH3′)).
was prepared in situ by the reaction of 4 with 12CO as
described elsewhere.15b Et2NH (0.042 mL, 0.4 mmol) was
added to this solution at -20 °C under CO pressure by a
syringe, and the mixture was allowed to stand at room
temperature for 2 days. Compounds 15 and 20 were obtained
in a ratio of 1 to 2.5, as identified by 1H NMR and GC-MS.
The formation of Et2NH2+PF6 was confirmed by H and 31P
NMR, and a Pd metal black precipitate was found.
-
1
Ack n ow led gm en t. This work was supported by
Nippon Zeon Co., the Ministry of Education, Science,
Sports and Culture, and the J apan Society for Promo-
tion of Science (to Y.-S. Lin). Elemental analyses and
MS spectra measurement were performed at Materials
Characterization Central Laboratory, Waseda University.
The same procedure as for the carbonylation of 1a was
employed for the carbonylation of 1b and 8. The results are
summarized in Table 5.
Rea ction of tr a n s-[P d (COCH2P h )(CO)(P Me3)2]P F 6 (7)
w ith Et2NH in th e P r esen ce of CO. A CD2Cl2 solution of 7
OM980234F