Palladium(II) aminoiminophosphoranate complexes as cross-coupling catalysts

Article abstract of DOI:10.1007/s11172-014-0739-8

The Tsuji-Trost reaction between diethyl malonate and allyl acetate catalyzed by palladium(II) NPN-aminoiminophosphoranate complexes yields mono- and diallylation products in the ratios depending on the complex used. The Suzuki-Miyaura cross-coupling of 4-bromoacetophenone with phenylboronic acid catalyzed by these palladium complexes proceeds with 66-99.5% conversions.

Full text of DOI:10.1007/s11172-014-0739-8

Russian Chemical Bulletin, International Edition, Vol. 63, No. 10, pp. 2305—2308, October, 2014
2305
Palladium(II) aminoiminophosphoranate complexes
as crossꢀcoupling catalysts*
T. A. Peganova,a A. M. Kalsin,a N. A. Ustynyuk,a and A. A. Vasil´evb
aA. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 6471. Eꢀmail: kalsin@ineos.ac.ru
bN. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 5328. Eꢀmail: vasiliev@ioc.ac.ru
The Tsuji—Trost reaction between diethyl malonate and allyl acetate catalyzed by
palladium(II) NPNꢀaminoiminophosphoranate complexes yields monoꢀ and diallylation prodꢀ
ucts in the ratios depending on the complex used. The Suzuki—Miyaura crossꢀcoupling of
4ꢀbromoacetophenone with phenylboronic acid catalyzed by these palladium complexes proꢀ
ceeds with 66—99.5% conversions.
Key words: palladium(II) aminoiminophosphoranate complexes, crossꢀcoupling catalysts,
Tsuji—Trost reaction, Suzuki crossꢀcoupling.
In recent years, transition metal complexes with hetꢀ
eronuclear chelate NNNꢀ (triazenide), NCNꢀ (amidꢀ
inate), and NPNꢀ (aminoiminophosphoranate) ligands are
topical in organometallic and coordination chemistry1 due
to ongoing search for innovative catalysts for crossꢀcouꢀ
pling applications. In this regard, the chemistry and cataꢀ
lytic properties of amidinate complexes are more studied2
in contrast to complexes bearing aminophosphoranꢀ
ate moieties as heteronuclear (NPN) ligands. However,
the latter attracts more and more attention due to their
promising applications as precatalysts in a number of
transformations of alkenes: cyclopropanation,3 aziridinaꢀ
tion,4 polymerization,5 and oligomerization.6 These works
deal mostly with NPNꢀcomplexes of chromium, copper
and nickel. Until 2009, the data on the synthesis of
palladium and platinum NPN complexes were limited
to only two examples, i.e., ethyleneꢀplatinum comꢀ
plex Cl(2ꢀC2H4)Pt[Me2P(NMe)2]7 and allylpalladiꢀ
um complex (3ꢀC3H5)Pd[(Me3Si)2NP(CH2CH=CH2)ꢀ
(NSiMe3)2].5a In 2009, we synthesized a series of platiꢀ
num and palladium NPN complexes with different auxilꢀ
iary ligands [{Ph2P(NC6H4Priꢀp)2}MLx] (Lx = PPh3, Cl;
NPN; C2H4, Cl).8 It was found that NPN ligand
has a zwitterionic structure R2P+(NR´–)2. Later, the
molecular and electronic structure of the NPN complexꢀ
es was evaluated on the example of allylpalladium and
allylplatinum complexes [{Ph2P(NC6H4Rꢀp)2}M(3ꢀ
C3H5)] (R = Pri, Me, OMe, COOEt) by Xꢀray diffracꢀ
tion and DFT calculations.9,** It should be noted that
NPN ligands are strong  and  donors10 and thus can
be used for the stabilization of electronꢀdeficient organoꢀ
metallic complexes. Consequently, the evaluation of
the catalytic activity of transition metal complexes with
NPN ligands is a great challenge of the modern organic
chemistry.
In the present work, we describe the catalytic perꢀ
formance of three recently synthesized palladium(II)
NPNꢀcomplexes in the Tsuji—Trost allylation1a,11,12 and
the Suzuki—Miyaura crossꢀcoupling.13,14
Results and Discussion
We studied catalytic activity of palladium NPN comꢀ
plexes 1—3 differing in the auxiliary ligands and the
aryl substituents at the nitrogen atoms. Compounds 1—3
were earlier synthesized8,9 in our research group. Their
complete structure elucidation was performed by
spectroscopy, microanalysis, and Xꢀray diffraction. In
compounds 1—3, the palladium atom is in the 2+ oxidaꢀ
tion state and the phosphorus atom has an azaphosꢀ
phorane nature and is not involved in the coordination
with metal.
* Dedicated to Academician of the Russian Academy of Sciencꢀ
es Yu. N. Bubnov on the occasion of his 80th birthday and the
60th anniversary of the foundation of A. N. Nesmeyanov Instiꢀ
tute of Organoelement Compounds of the Russian Academy
of Sciences.
** T. A. Peganova, M. G. Peterleitner, P. V. Petrovskii, K. A.
Lyssenko, I. V. Fedyanin, O. V. Gusev, A. M. Kalsin, Eur. J.
Inorg. Chem. (in press).
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2305—2308, October, 2014.
1066ꢀ5285/14/6310ꢀ2305 © 2014 Springer Science+Business Media, Inc.

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Peganova et al.
Table 1. Palladium catalyzed Tsuji—Trost allylaꢀ
tion of diethyl malonate 4 with allyl acetate
Catalyst
Reaction mixture composition* (%)
4
5
6
1
2
3
10
23
11
22
77
91
78
10
18
* GC data.
catalytic performance than complex 1. Indeed, the  allylꢀ
palladium complexes are the intermediates of the
Tsuji—Trost reaction.1a,11 We suggest that true catalysts
in this reaction is the Pd0ꢀbased complexes generated via
the reduction of precatalysts 1—3 under reaction condiꢀ
tions. Since thiphenylphosphine unit favors the stabilizaꢀ
tion of these Pd0 complexes, complex 1 shows the stronger
catalytic effect.
R = OMe (2), COOEt (3)
The Tsuji—Trost reaction of diethyl malonate (4) with
allyl acetate was performed at room temperature under
phase transfer conditions in DMF using K2CO3 as a base
following the known procedure12a,b (Scheme 1, Table 1).
Compounds 1—3 were also studied as catalysts for
Suzuki—Miyaura crossꢀcoupling13,14 of highly reactive
4ꢀbromoacetophenone (7) with phenylboronic acid. The
reaction was carried out under typical aqueous Suzuꢀ
ki—Miyaura conditions15 in 1,2ꢀdimethoxyethane in the
presence of Na2CO3 as a base (Scheme 2). This procedure
accommodates a wide range of bromoꢀ and iodoarenes as
well as arylboronic acids. In our reactions catalyzed by
complex 1, the yield of biaryl 8 was almost quantitative;
however, on going to complexes 2 and 3 the conversions
of bromide 7 were noteably below 100%. In all cases,
the precipitation of palladium black is observed indicating
cessation of the reaction. This fact suggests both the deꢀ
composition of complexes 1—3 and the absence of the
species capable of palladium stabilizing in the reaction
media. Thus, compounds of the type of complexes 1—3
though being able to catalyze the Suzuki—Miyaura crossꢀ
couplings cannot be regarded as powerful catalysts.
Scheme 1
Conditions: 1, 2 or 3 (2 mol.%), K2CO3, DMF, 20 C, 15 h.
Compound 1 turned to be the most efficient catalyst
among the tested complexes. It provides complete conꢀ
version of substrate 4 to give diallyl derivative 6 as a major
product. On using complexes 2 and 3, the major product is
monoallyl derivative 5, while diallylation does not occur
to any significant extent and the conversion of malonate 4
was incomplete. Complex 3 bearing electronꢀwithꢀ
drawing substituents is more active than complex 2.
Note that complex 2 can be regarded as a catalyst for
selective monoallylation of diethyl malonate. The attemptꢀ
ed prenylation of malonate 4 with less active sterically
hindered prenyl acetate in the presence of complexes 1—3
failed (cf. Ref. 12a).
Scheme 2
Catalyst
Yield of 8 (%)
99.5
1
2
3
66.0
86.0
It should be noted that the use of the conventional
phosphineꢀ or diamidophophiteꢀbased Pd0 catalysts in the
absence of unfavorable factors gives rise to diallyl derivaꢀ
tive 6.12a,d In our case, complexes 2 and 3 show a lower
Conditions: 1, 2 or 3 (3 mol.%), Na2CO3, 1,2ꢀdimethoxyethane,
water, 90 C, 6 h.

Palladium aminoiminophosphoranate complexes
Russ.Chem.Bull., Int.Ed., Vol. 63, No. 10, October, 2014
2307
diluted with water, and extracted with toluene. After drying with
CaCl2, the extracts were analyzed by GC. The GC chromatoꢀ
grams contained predominantly peaks of compounds 7 and 8
(the retention times coincided with the retention times of the
reference samples). In some cases, small amounts of biphenyl
(the product of homocoupling of phenylboronic acid, which was
discarded on GC data calculations) were detected. It was asꢀ
sumed that compounds 7 and 8 are chemically stable and do not
undergo resinification upon reaction, therefore, the yield of comꢀ
pound 8 was considered equal to the conversion of the starting
compound 7 (see Scheme 2).
In summary, we first examined the catalytic efficienꢀ
cy of PdII aminoiminophosphoranate complexes in the
Tsuji—Trost allylation and Suzuki—Miyaura crossꢀcouꢀ
pling reactions. The moderate product yields can be exꢀ
plained by the fact that these reactions should be favored
by the Pd0ꢀbased catalytic systems containing ligands
effectively stabilizing the palladium intermediates in the
solutions. However, the obtained results are of interest for
fundamental understanding of the crossꢀcoupling processꢀ
es. Finally, the possibility of raising the efficiency of
complexes 1—3 by their use in combination with other
stabilizing ligands cannot be excluded.
This work was financially supported by the Russian
Foundation for Basic Research (Project Nos 14ꢀ03ꢀ00345
and 08ꢀ03ꢀ00086).
Experimental
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Received June 6, 2014;
in revised form July 7, 2014