Kinetic features of oxidative addition of organic halides to the organonickel σ-complex

Article abstract of DOI:10.1023/A:1023986118211

Electrochemically generated organonickel σ-complexes were used as model compounds to study the kinetics of oxidative addition of ArNi ^Ibpy to RX, the key stage of cross-coupling of organic halides (RX). The reaction rate constants were calculat

Full text of DOI:10.1023/A:1023986118211

Russian Chemical Bulletin, International Edition, Vol. 52, No. 3, pp. 567—569, March, 2003
567
Kinetic features of oxidative addition of organic halides
to the organonickel σꢀcomplex*
ꢀ
D. G. Yakhvarov, Yu. H. Budnikova, and O. G. Sinyashin
A. E. Arbuzov Institute of Organic and Physical Chemistry,
Kazan Research Center of the Russian Academy of Sciences,
8 ul. Akad. Arbuzova, 420088 Kazan, Russian Federation.
Fax: +7 (843 2) 75 2253. Eꢀmail: yulia@iopc.knc.ru
Electrochemically generated organonickel σꢀcomplexes were used as model compounds to
study the kinetics of oxidative addition of ArNiIbpy to RX, the key stage of crossꢀcoupling of
organic halides (RX). The reaction rate constants were calculated, and the sequence of relative
reactivity of RX toward the electrochemically generated MesNiIbpy complex was obtained.
Key words: nickel, 2,2´ꢀbipyridine, organic halide, metal complex, electrochemistry, caꢀ
talysis.
I
Studies of the mechanism of reductive transformaꢀ
tions of organic halides in the presence of electrochemiꢀ
cally generated lowꢀvalent transition metal complexes are
of value for the theory and practice of catalysis.1 We have
previously2,3 shown that the use of orthoꢀsubstituted aroꢀ
matic bromides makes it possible to establish the structure
of intermediates in RX dehalogenation by electrochemiꢀ
cally generated Ni0bpy complexes (bpy is 2,2´ꢀbipyridine).
Some intermediate organonickel compounds were isoꢀ
lated and characterized by physicochemical data, in parꢀ
ticular, the product of the first stage of the catalytic cycle
σꢀMesNibpyBr complex. It is the product of the oxidative
addition of MesBr to the electrochemically generated
Ni0bpy complex.2,3 This complex is stable in air and is
convenient for proving the occurrence of certain stages of
the catalytic cycle.
2
25 µA
0
1
–1
–2
–E/V
Fig. 1. CV curve for the MesNibpyBr complex (10–2 mol L–1) in
DMF against the background of Et4NBF4 (10–1 mol L–1) in the
absence (1, EA) and presence (2, EC) of RX.
The electrochemical behavior of MesNibpyBr was
studied in the absence and presence of different RX. The
CV curve for MesNibpyBr in DMF exhibits one oneꢀ
electron reversible cathodic peak at –1.80 V. In addition
to the anodic peak at –1.72 V related to this cathodic peak
of the substrate (iA/iC = 0.9), a small anodic peak is obꢀ
served at –1.50 V (see Fig. 1). Probably, the latter correꢀ
sponds to the oxidation of the MesNiIbpy—NiIMesbpy
dimer, which can form in the absence of RX.
It has been shown2,3 that the key stage of catalytic RX
dehalogenation resulting in crossꢀcoupling products is the
oxidative addition of RX to the electrochemically generꢀ
ated σꢀMesNiIbpy complex. The latter is formed by
oneꢀelectron reduction of the σꢀMesNibpyBr comꢀ
plex (Fig. 1).
Let us consider the shape of the CV curve for electroꢀ
reduction of the MesNibpyBr complex at different
amounts of RX. When RX is successively added to a soluꢀ
tion of MesNibpyBr, the reduction current of the comꢀ
The purpose of this work is to estimate the reactivity of
different RX toward the electrochemically generated
MesNiIbpy complex in crossꢀcoupling reactions using cyꢀ
clic voltammetry (CV).
plex increases to a certain limit. At low RX concentraꢀ
—
tions the plot of the current vs. √C RX is linear, while in an
excess of RX the current is independent of the concentraꢀ
tion of the added substrate (Fig. 2). For the most part of
substrates, the anodic component of the reduction peak
of the MesNibpyBr complex disappears, i.e., the electroꢀ
* Dedicated to Academician I. P. Beletskaya on the occasion of
her anniversary.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 545—547, March, 2003.
1066ꢀ5285/03/5203ꢀ567 $25.00 © 2003 Plenum Publishing Corporation

568
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 3, March, 2003
Yakhvarov et al.
n
Table 1. Apparent rate constants for oxidative addition of orꢀ
ganic halides to the electrochemically generated MesNiIbpy
complex
4
3
2
1
2
3
0
d
Substrate
(RX)
CRX
Ipk/Ip lg(χk)
χk
k1
/L mol–1 s–1
C 0
complex
5
PriI
1
1
1
1
2
1
2
5
1
2
5
1
2
5
1
1.82
1.80
1.77
1.52
1.71
1.42 –0.21
1.55 –0.25
1.81 –0.20
1.25 –0.51
1.35 –0.62
1.62 –0.53
1.27 –0.52
1.41 –0.53
1.64 –0.45
1.31 20.12
1.28 19.21
1.24 17.51
0.15
0.20
3950
3800
3450
280
310
120
110
120
60
50
60
60
60
4
6
7
iꢀC5H11
PhI
I
8
PhBr
1.41
1.58
0.62
0.56
0.63
0.32
0.25
0.31
0.32
0.31
0.36
3.16
—
5
10
15
√C RX•102/M1/2
4ꢀTolBr
MesBr
BuBr
Fig. 2. Number of electrons (n) transferred at potentials of the
reduction wave of MesNibpyBr as a function of √C RX: 1, PriI;
2, iꢀC5H11I; 3, PhI; 4, 2ꢀClTh; 5, PhBr; 6, 4ꢀTolBr; 7, BuBr;
and 8, MesBr.
—
chemically generated MesNiIbpy complex enters into an
irreversible chemical reaction, viz., either oxidative addiꢀ
tion or complexation with the substrate.
70
620
2ꢀClTh
1.62
0.53
the substrate.4 The calculated k1 values are presented in
—
Table 1. The slope of the plot I = a√C RX + b can characꢀ
terize the rate of the primary stage of the process: the
greater the slope, the higher the rate constant of the reacꢀ
tion of MesNiIbpy with RX.
We obtained the sequence of relative reactivity of the
substrates: MesBr < BuBr < oꢀBrTol < PhBr < 2ꢀClTh <
< PhI < iꢀC5H11I < PriI.
Thus, the use of the electrochemically synthesized
model σꢀMesNibpyBr aryl complex made it possible to
determine the key stage of crossꢀcoupling producing
MesR, viz., interaction of MesNiIbpy with RX, and to
estimate the rate constants of this reaction.
Subsequent reactions afford crossꢀcoupling products
if reductive elimination occurs rapidly. The current inꢀ
crease can be due to the catalytic reduction of intermediꢀ
ates of the cycle, which form upon elimination.
In the presence of MesBr, oꢀTolBr, and 2ꢀClTh (Th is
thiophene), the crossꢀcoupling reactions involving these
compounds occur, most probably, slowly and the current
increase of the cathodic peak (see Fig. 2) is caused by the
reversible electrochemical reduction of the intermediate
σꢀ[MesRNibpyX] complex, due to which the anodic comꢀ
ponent corresponding to this peak in the CV curve reꢀ
mains unchanged.
We made an estimate of the kinetics of the initial stage
of the process (interaction of the σꢀMesNiIbpy complex
with RX) under assumption that this stage is rateꢀdeterꢀ
mining. The k1 rate constant was calculated from changes
in the reduction current in the interval of RX concentraꢀ
Experimental
A stationary disk glassyꢀcarbon (GC) electrode with a surꢀ
face area of 3.14 mm2 was used as a working electrode in
CV studies. Voltammograms were recorded using a PIꢀ50ꢀ1
potentiostat with a PRꢀ49 programmer and an electrochemical
cell connected by the threeꢀelectrode scheme in DMF against
the background of Et4NBF4 (0.1 mol L–1) on a two coordinate
recorder with a sweep rate of 50 mV s–1. A reference electrode
was Ag/0.01 М AgNO3 in MeCN. A Pt wire 1 mm in diameter
was used as auxiliary electrode. Measurements were carried out
in an argon atmosphere in a cell thermostatted at 25 °C.
A required amount of RX was added into a solution of the
nickel complex (10–2 mol L–1) using a 10ꢀµL chromatographic
syringe.
The NiBr2bpy complex was synthesized from NiBr2 and
2,2´ꢀbipyridine in EtOH with stirring for 5 h. The precipitate
that formed was filtered off and dried in a desiccator at 30 °C for
24 h. Commercial organic halides (reagent grade) were purified
by distillation to unchanged physical constants.
tions in which the reduction current is proportional to
—
√C RX and the reaction has the first order with respect to

Kinetic features of oxidative addition to σꢀcomplex
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 3, March, 2003
569
Processing of CV data. The error of results of measuring
peak potentials was ≤10 mV. The number of electrons transꢀ
ferred from the electrode to the nickel complex was determined
by comparison of the currents in the peaks of the compounds
under study with the current of the first diffusion peak of benꢀ
zophenone reduction (1e) under similar conditions.
Methods for Creation and Target Synthesis of Subꢀ
stances with Specified Properties," and the INTAS (Grant
00ꢀ00018).
References
Rate constants of oxidative addition (k1) of organic halides
to the organonickel σꢀcomplex were calculated using a known
procedure4 from the calibrated curves for the excess factors
1. H. Lemkuhl, Synthesis, 1973, 377.
2. Y. H. Budnikova, J. Perichon, D. G. Yakhvarov, Y. M. Kargin,
and O. G. Sinyashin, J. Organomet. Chem., 2001, 630, 185.
3. D. G. Yakhvarov, E. G. Samieva, D. I. Tazeev, and Yu. G.
Budnikova, Izv. Akad. Nauk, Ser. Khim., 2002, 734 [Russ.
Chem. Bull., Int. Ed., 2002, 51, 796].
0
0
СS0/CM (where СS is the volume concentration of the subꢀ
0
strate, and CM is the volume concentration of the mediator)
based on the plot of the ratio of the catalytic (kinetic) to difꢀ
d
fusion currents Ipk/Ip vs. logχk, where χk is the kinetic paramꢀ
eter equal to k1CM0RT/(FV ).
4. S. U. Pedersen and B. Svensmark, Acta. Chem. Scand.,
1986, 9, 607.
This work was financially supported by the Russian
Foundation for Basic Research (Project Nos. 01ꢀ03ꢀ
33210ꢀa and 01ꢀ15ꢀ99353ꢀm) and the Complex Program
of the Russian Academy of Sciences "New Principles and
Received July 5, 2002;
in revised form December 6, 2002