New open tetraaza nickel(II) and palladium(II) complexes. Different reactivity of the electrogenerated M(0) species toward difunctional substrates

Article abstract of DOI:10.1021/om9707026

A series of neutral and cationic Ni(II) and Pd(II) complexes with the open tetraaza ligand bisoxazoline bisamine N₄, were prepared and characterized. Neutral complexes presented dimeric structures of stoichiometry [M₂(μ-N₄)X₄] (M = Ni (1), Pd (2)) and underwent slow decomplexation in coordinating solvents. Cationic monomeric [M(N₄)]Y₂ (M = Ni (3), Pd (4)) compounds were stable in solution and were efficient catalysts in electrochemical reactions involving difunctional substrates, unsaturated o-haloaryl and o-halobenzyl ethers. [Ni(N₄)]²⁺-catalyzed reactions led to intramolecular cyclization products via initial oxidative addition on the C-X bond, whereas [Pd(N₄)]²⁺-catalyzed processes involved the cleavage of the C-O bond. Furthermore, organometallic σ-Ni(II) (7a,b) and π-allylpalladium(II) (8a,b) complexes were prepared in order to study the intermediate species proposed in the catalytic cycles.

Full text of DOI:10.1021/om9707026

5900
Organometallics 1997, 16, 5900-5908
New Op en Tetr a a za Nick el(II) a n d P a lla d iu m (II)
Com p lexes. Differ en t Rea ctivity of th e Electr ogen er a ted
M(0) Sp ecies tow a r d Difu n ction a l Su bstr a tes
Montserrat Go´mez, Guillermo Muller,* David Panyella, and Merce` Rocamora
Departament de Qu´ımica Inorga`nica, Universitat de Barcelona, Diagonal 647,
08028-Barcelona, Spain
Elisabet Dun˜ach* and Sandra Olivero
Laboratoire de Chimie Moleculaire, Associe´ au CNRS, URA 426, Universite´ de Nice-Sophia
Antipolis, Parc Valrose, 06108 Nice Cedex 2, France
J ean-Claude Clinet
Institut de Chimie Mole´culaire, CNRS, URA 1497, Universite´ Paris Sud, 91405 Orsay, France
Received August 11, 1997X
A series of neutral and cationic Ni(II) and Pd(II) complexes with the open tetraaza ligand
bisoxazoline bisamine N4, were prepared and characterized. Neutral complexes presented
dimeric structures of stoichiometry [M2(µ-N4)X4] (M ) Ni (1), Pd (2)) and underwent slow
decomplexation in coordinating solvents. Cationic monomeric [M(N4)]Y2 (M ) Ni (3), Pd
(4)) compounds were stable in solution and were efficient catalysts in electrochemical
reactions involving difunctional substrates, unsaturated o-haloaryl and o-halobenzyl ethers.
[Ni(N4)]2+-catalyzed reactions led to intramolecular cyclization products via initial oxidative
addition on the C-X bond, whereas [Pd(N4)]2+-catalyzed processes involved the cleavage of
the C-O bond. Furthermore, organometallic σ-Ni(II) (7a ,b) and π-allylpalladium(II) (8a ,b)
complexes were prepared in order to study the intermediate species proposed in the catalytic
cycles.
In tr od u ction
raazacyclotetradecane) allows access to the otherwise
unstable Ni(III)6 and Ni(I)7 oxidation states. It has been
shown that any modification of the ligand structure
(ring size, ring substituents, unsaturations, etc.) may
influence the catalytic activity of the resulting com-
plexes.8 On the other hand, little information has
appeared on the formation and reactivity of palladium
complexes with macrocyclic ligands.9
We have focused our attention on the particular case
of open tetraaza ligands and on how the metal ion is
held in the eventual macrocyclic cavity. The ligand N4
(1,4-bis[2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)phenyl]-
piperazine) (eq 1) has been chosen as an open-chain
analog of certain cyclam derivatives, containing both
oxazoline and amine donor groups. The use of oxazo-
In the past decade, the use of polydentate nitrogen
compounds as donor ligands for coordination complexes
has grown in the field of organometallic chemistry and
catalysis.1 Among these ligands, azacrown ethers and
cryptands are strong selective complexing agents for
metal cations and other charged and uncharged guest
molecules.2 These ligating compounds present several
applications in organic synthesis and catalysis,3 me-
dicinal chemistry,4 and analysis.5 Much of the current
interest in macrocyclic coordination chemistry stems
from the hope that unusual geometric relationships
imposed on the metal ions by the macrocyclic donor may
be transformed into unusual bonding situations and
novel reactivity. Thus, a Ni(II) center encircled by a
tetraamine macrocycle such as cyclam (1,4,7,11-tet-
X Abstract published in Advance ACS Abstracts, December 1, 1997.
(1) (a) Togni, A.; Venanzi, L. M. Angew. Chem., Int. Ed. Engl. 1994,
33, 497. (b) Van Veggel, F. C. J . M.; Verboom, W.; Reinhoult, D. N.
Chem. Rev. 1994, 94, 794.
(2) (a) Lindoy, L. F. The Chemistry of Macrocyclic Ligand Complexes;
Cambridge University Press: London, 1989. (b) Suh, M. P. Adv. Inorg.
Chem. 1996, 44, 93. (c) Lee, D.; Suh, M. P.; Lee, J . W. J . Chem. Soc.,
Dalton Trans. 1997, 577.
(1)
(3) Beley, M.; Collin, J . P.; Ruppert, R.; Sauvage, J . P. J . Am. Chem.
Soc. 1986, 108, 7461.
(4) Lauffer, R. B. Chem. Rev. 1987, 87, 901.
(5) Hui-Zhi, C.; Kaden, T. A. Helv. Chim. Acta 1994, 77, 383 and
references therein.
lines as ligands in organometallic catalysis has seen an
(6) Kinneary, J . F.; Albert, J . S.; Burrows, C. J . J . Am. Chem. Soc.
1988, 110, 6124. Ali, M.; Zilberman, I.; Cohen, H.; Shames, A. I.;
Meyerstein, D. Inorg. Chem. 1996, 35, 5127.
(7) De Santis, G.; Fabrizzi, L.; Lichelli, M.; Sardone, N.; Velders, A.
H. Chem. Eur. J . 1996, 2, 1243.
(8) (a) Fujita, E.; Haff, J .; Sanzenbacher, R.; Elias, H. Inorg. Chem.
1994, 33, 4627. (b) Abba, F.; De Santis, G.; Fabrizzi, L.; Lichelli, M.;
Manotti Lanfredi, A. M.; Pallavicini, P.; Poggi, A.; Ugozoli, F. Inorg.
Chem. 1994, 33, 1366. (c) Mochizuki, K.; Manaka, S.; Takeda, I.; Kondo,
T. Inorg. Chem. 1996, 35, 5132.
S0276-7333(97)00702-4 CCC: $14.00 © 1997 American Chemical Society

New Open Tetraaza Ni(II) and Pd(II) Complexes
Organometallics, Vol. 16, No. 26, 1997 5901
Sch em e 1
exponential growth in the past few years, essentially
due to the accessibility of chiral oxazolines for asym-
metric catalysis.10,11 However, the use of electron-rich
amino oxazolines has been limited to pyridine oxazolines
or to bisoxazolines,12 and apart from our studies, no
example of the use of such compounds as ligands in
electrochemical reactions has been described. We present
here our results on the characterization and reactivity
of ionic and neutral Ni(II) and Pd(II) complexes associ-
ated with the bisoxazoline bisamine tetradentate ligand
N4. The chemical and electrochemical reactivity of these
complexes has been examined, particularly in NiN4-
catalyzed intramolecular cyclizations. A preliminary
communication on the electrochemical activity has been
published.13
F igu r e 1. Temperature dependence of øMT for 1a .
with the complexes [NiCl2py2] and [NiCl2(PEt2Ph)2].
Preparation of compounds 1 failed from mixtures of
anhydrous NiX2 with N4. The [Pd2(µ-N4)Cl4] complex
2 was directly obtained from [PdCl2(cod)] and N4 as an
orange solid in 76% isolated yield (Scheme 1).
In the reactions of N4 with [MX2L2]-type starting
complexes, only dinuclear Ni(II) or Pd(II) aggregates
were formed. No evidence for the presence of mono-
nuclear neutral species of stoichiometry [MX2(N4)] could
be obtained. These results are in contrast with those
described in the case of cyclam as the ligand, for which
the [NiCl2(cyclam)] or [NiBr2(cyclam)] complexes are
easily obtained.16 Most probably, the rigid square-
planar arrangement of the four sp3 nitrogen atoms in
the cyclam stabilizes the octahedral complex.
Resu lts a n d Discu ssion
A. Syn th esis of th e N4 Liga n d . The two-step
synthesis of N4 (eq 1) started from commercial o-
bromobenzoic acid, by treatment with thionyl chloride,
followed by the addition of 2-amino-2-methylpropan-1-
ol and further dehydration with thionyl chloride, ac-
cording to the method of Meyers et al.14
Further treatment of the bromooxazoline with bis-
lithiated piperazine15 led directly to N4 in 64% isolated
yield (80% based on recovered bromooxazoline). The
forward synthesis of N4 presents sufficient flexibility for
the further elaboration of other derivatives, differing in
either their bisamino or their oxazoline moieties: such
a modulation constitutes an interesting feature for the
control of the physical and chemical properties of the
derived transition metal complexes.
B. Syn th esis of Neu tr a l Com p ou n d s [M2(µ-N4)-
X4] (M ) Ni, P d ). The neutral complexes [Ni2(µ-N4)-
X4] (1a , X ) Cl, and 1b, X ) Br) were prepared by
reaction of [NiX2L2] derivatives with low-basicity L
ligands in CH2Cl2 at room temperature. Thus, with a
phosphine ligand such as PEtPh2, 1a was obtained as
a purple solid in 87% yield. Starting from [NiBr2-
(PPh3)2], 1b was obtained in 88% yield (Scheme 1).
When the basicity of L was increased, the substitution
reaction with N4 did not take place, as was also the case
The new compounds 1a , 1b, and 2 are air-stable solids
and can be stored under nitrogen for several months.
Complexes 1 and 2 are soluble only in coordinating
solvents, although decoordination of N4 is observed.
Both Ni(II) complexes 1a and 1b are purple and
paramagnetic. In contrast, the palladium dinuclear
complex 2 is a diamagnetic orange solid. These com-
plexes were characterized by elemental analysis, infra-
1
red spectroscopy, H NMR (2), and magnetic suscepti-
bility (1a , 1b).
The measurements of the magnetic susceptibility for
1a and 1b were carried out at variable temperature.
The measured µeff ) 4.98 µB at 296 K was in the range
of the expected values for a molecular system with four
electrons (2 + 2), in two independent nickel atoms in a
tetrahedral environement, µeff (spin-only) ) 4.0 µB, that
large orbital contribution is usually shown.17 No sig-
nificant coupling was observed upon decreasing the
temperature (Figure 1).
C. Syn th esis of Ion ic Com p ou n d s [M(N4)]Y2 (M
) Ni, P d ). Although we were unable to obtain neutral
mononuclear [MX2(N4)] complexes starting from Ni(II)
or Pd(II) halides or via substitution reactions and only
dinuclear complexes were isolated, the cationic mono-
nuclear complexes could be obtained selectively in high
yields starting from nickel and palladium BF4-, ClO4
,
-
(9) (a) McAuley, A.; Whitcombe, T. W. Inorg. Chem. 1988, 27, 3090.
(b) Lilie, J .; Waltz, W. L.; Chandrasekhar, S. Inorg. Chim. Acta 1996,
246, 59.
(10) (a) Gant, T. G.; Meyers, A. I. Tetrahedron 1994, 50, 2297. (b)
Pfaltz, A. Acc. Chem. Res. 1993, 26, 339.
(11) Pfaltz, A. Acta Chem. Scand. 1996, 50, 189 and references
therein.
(12) Bolm, C. Angew. Chem., Int. Ed. Engl. 1991, 30, 542 and
references therein.
-
or PF6 salts.
Thus, the reaction of N4 with either nickel(II) tet-
rafluoroborate or perchlorate led to the ionic compounds
[Ni(N4)](BF4)2 (3a ) and [Ni(N4)](ClO4)2 (3b), respectively
(Scheme 2). From a mixture of palladium(II) acetate,
(13) Clinet, J . C.; Dun˜ach, E. J . Organomet. Chem. 1995, 503, C48.
(14) Meyers, A. I.; Temple, D. L.; Haidukewych, D.; Mihelich, E. D.
J . Org. Chem. 1974, 39, 2787.
(15) Meyers, A. I.; Gabel, R. A. J . Org. Chem. 1977, 42, 2653. Meyers,
A. I.; Reuman, M.; Gabel, R. A. J . Org. Chem. 1981, 46, 783.
(16) Bosnich, B.; Poon, C. K.; Tobes, M. L. Inorg. Chem. 1965, 4,
1102.
(17) (a) Donoghue, J . T.; Drago, R. S. Inorg. Chem. 1996, 1, 866. (b)
Goodgame, D. M. L.; Goodgame, M.; Cotton, F. A. J . Am. Chem. Soc.
1961, 83, 4161.

5902 Organometallics, Vol. 16, No. 26, 1997
Go´mez et al.
Ta ble 1. Selected NMR Da ta (δ in p p m ) for th e
Decoor d in a tion Rea ction of 2 in p y-d 5, w ith
Cou p lin g Con sta n ts (Hz) a n d Mu ltip licitya in
P a r en th eses
Sch em e 2
Me
1.70
CH2-N
3.70
CH2-O
H1
N4
2b
4.42
(s, 4H)
8.30
Sch em e 3
(s, 12H)
(s, 8H)
(dd, 2H)
(1.5, 7.6)
8.89
1.66
3.20
4.14
(s, 12H)
(s, 8H)
(s, 4H)
(br d, 2H)
(7.0)
2i
2.36
(s, 12H)
3.92
(br s, 8H)
4.83
(s, 4H)
9.91 dd
(dd, 2H)
(1.75, 7.75)
8.28
2ii
1.75
3.67
4.44
(s, 6H)
2.32
(s, 6H)
(br s, 8H)
(s, 2H)
4.78
(s, 2H)
(dd, 1H)
(1.5, 7.5)
9.89
(dd, 1H)
(1.75, 7.5)
a
b
Multiplicity: br, broad; s, singlet; d, doublet; t, triplet. Sol-
vent was CDCl3 + 10% py-d5.
N4, and ammonium hexafluorophosphate, mononuclear
cationic complex 4 was isolated as a pale orange solid
(Scheme 2). Compounds 3 and 4 are highly soluble in
common organic solvents. These complexes are dia-
magnetic, and their analytical data are in agreement
with the stoichiometry [M(N4)]Y2.
The solid state IR spectrum (KBr pellet) of the ligand
N4 shows four strong absorptions in the range 1638-
1038 cm-1. However, when the ligand is coordinated
to the metal (1-4), the relative intensity of the bands
changes, and only one very strong absorption in the
range 1650-1625 cm-1 is observed.
D. NMR An a lysis of 2-4. The proton NMR spectra
for the ionic complexes 3 and 4 are well defined, and no
decoordination of the N4 ligand was observed. However,
the neutral complex 2 gave broad NMR signals and
showed a great tendency to dissociate N4 in solution,
the process being slower for the Pd(II) than for the Ni-
(II) complexes. N4 decoordination took place in the
usual coordinating solvents (acetonitrile, acetone, py-
ridine, dimethylformamide). The ligand dissociation
reaction was monitored by 1H NMR in the case of
complex 2 when py-d5 (py*) was added or used as
solvent (Scheme 3 and Table 1). The time-dependent
spectra are shown in Figure 2. The complex 2 was not
soluble in CDCl3, but, in the presence of 10% of py*,
the spectrum showed a mixture of 2 and 2i (spectrum
A, Figure 2). When py* was used as solvent, evolution
from 2 to free ligand was completed in 3.5 h (spectra B,
C, and D). The proton signals corresponding to H1 (H1′)
as well as the CH2O, CH2N, and CH3 groups showed
the consecutive formation of the species involved in the
decoordination process.
1
F igu r e 2. Time-dependent H NMR spectra of [Pd2(µ-N4)-
Cl4] (2). #, solvent impurities (py-d5), §, 1 cm3 of CDCl3 +
0.1 cm3 of py*; [, 2; b, 2i; 2, 2ii; 9, N4, following Scheme
3.
solutions containing n-tetrabutylammonium tetrafluo-
roborate as supporting electrolyte presented two ir-
reversible reducing peaks at -1.2 and -1.7 V vs Ag/
E. Electr och em ica l Stu d ies. Electr och em ica l
Beh a vior of 3a . Cyclic voltammograms of 3a in DMF

New Open Tetraaza Ni(II) and Pd(II) Complexes
Organometallics, Vol. 16, No. 26, 1997 5903
roborate in a two-compartment cell, we observed a small
charge transfer before passivation occurred. Analysis
of the reaction mixture revealed the presence of unre-
acted 5, together with traces of 2-bromophenol arising
from the cleavage of the O-C bond of the allyl group.
In contrast, when the electrolysis of a 1:3 mixture of 3a
and 5 was carried out at -1.8 V under the same
conditions, the cyclized compound 3-methyldihydroben-
zofuran (6) was obtained in 30% yield, together with
unreacted 5 after the passage of 3 F/mol of 5 (eq 2).
These results indicate that the electrogenerated “NiN4”
complex at -1.2 V shows a very low reactivity toward
5, but, at lower potentials, the Br-C(aryl) bond of 5 can
be activated, and the reaction is followed by an intramo-
lecular cyclization.
In order to obtain more efficient cyclization reactions
from a preparative point of view, the reaction was
carried out using a sacrificial anode in a single-compart-
ment cell.19 This electrochemical methodology enables
electrolyses to run under intensiostatic conditions and
allows the straightforward scale-up of the electrochemi-
cal reactions. The electrolysis of 5 under a one-
compartment cell procedure was catalytic in Ni(II). The
reactions were carried out using a magnesium anode
and a carbon fiber cathode, with a catalytic amount of
3a (10 molar % with respect to 5), in DMF at room
temperature, with a low concentration of supporting
electrolyte (nBu4N+BF4-, 5 × 10-3 M). The reductive
cyclization to 6 occurred selectively in 80% yield (eq 2).
Thus, in the presence of a magnesium anode in one-
compartment cells, involving the continuous generation
of Mg2+ ions in solution, the [NiN4]2+-catalyzed in-
tramolecular cyclization of 5 becomes highly selective,
compared to the electrolysis results in two-compartment
cells (absence of Mg2+ ions). The presence of the
magnesium ions plays an active role in enhancing the
reactivity and the selectivity. Under the one-compart-
ment cell procedure, no reaction was observed in the
absence of electricity, and a nonselective reduction of 5
occurred in the absence of the nickel complex.
When the same one-compartment cell electrolysis was
carried out with neutral 1b as the catalyst, the reduc-
tion of 5 gave a mixture of products (cyclized 6, phenol,
2-bromophenol, unreacted 5, isomerized 1-propenyl
ether, dimeric compounds) without any selectivity. This
result, similar to that obtained in the noncatalyzed
process, can be explained by the fast ligand decomplex-
ation of 1b in DMF solution, involving a cathodic
deposition of metallic nickel upon electrochemical re-
duction.
A series of substrates related to model compound 5
were prepared and further electrolyzed,13 in reactions
catalyzed by 3a , under the single-compartment cell
conditions. The results are summarized in Table 2.
The reductive cyclization procedure enabled the prepa-
ration of differently substituted bicyclic derivatives in
good yields. Allyl aryl ethers afforded dihydrobenzofu-
ran products in a selective reaction, without the pres-
ence of six-membered ring cyclization isomers. It is
noteworthy that not only bromo but also iodo and, more
interestingly, chloro aryl derivatives (entries 2, 3)
underwent efficient cyclization. A dihydro-1-benzopy-
ran compound (entry 4) could be prepared upon elec-
F igu r e 3. Cyclic voltammograms of 3a (curve a) in DMF
solutions containing n-tetrabutylammonium tetrafluorobo-
rate as supporting electrolyte. Curve b, 5/3a ) 0.5; curve
c, 5/3a ) 5.
AgCl, as shown in Figure 3, curve a. Reduction of the
free ligand N4 occurred at less than -2.3 V, at which
potential we observed the reduction of the solvent. The
electrochemical behavior of 3a was different from that
described for [Ni(cyclam)]2+, for which a one-electron
reduction process has been described as occurring at
-1.5 V in MeCN solutions.18 In the case of 3a , “NiIN4”
and “Ni0N4” species are presumably generated under
the electrochemical conditions, stabilized by the tetraaza
ligand.
We examined the reactivity of electrogenerated “NiN4”
species with organic halides. As a model compound we
chose the aromatic allyl 2-bromophenyl ether (5) (eq 2),
which possesses an olefin function as unsaturated side
chain. This substrate should faciliate the study of the
(2)
reactivity of the aryl-bromide bond, as well as the
possibilities of intramolecular radical-type reactions
involving the side chain.
The cyclic voltammetry behavior of 3a in the presence
of halide 5 is shown in Figure 3 (curves b and c). No
modification of the reduction peak of 3a at -1.2 V was
observed upon addition of 0.5 molar equiv of substrate
(curve b), the peak being irreversible. The peak at -1.7
V appeared wider. With a 1:1 or a 5:1 ratio of 5 to 3a
(curve c), no additional wave change was observed.
P r epar ative-Scale Electr or edu ctive Cyclization s
of 5 Ca ta lyzed by 3a . When 3a was electrolyzed in
the presence of bromide 5 in a 1:5 molar ratio at a
controlled potential of -1.2 V, in a DMF solution
containing 10-1 M n-tetrabutylammonium tetrafluo-
(19) Chaussard, J .; Folest, J . C.; Ne´de´lec, J . Y.; Pe´richon, J .; Sibille,
S.; Troupel, M. Synthesis 1990, 5, 369.
(18) Olson, D. C.; Vasilevski, J . Inorg. Chem. 1969, 8, 1611.

5904 Organometallics, Vol. 16, No. 26, 1997
Go´mez et al.
Ta ble 2. Electr och em ica l Cycliza tion of o-Ha loa r yl
a n d o-Ha loben zyl Eth er s Ca ta lyzed by 3a
Sch em e 5
tive formation of tributylamine, issued from the am-
monium salt decomposition, was confirmed by GC
analysis.
The results of the aryl halide cyclizations are largely
parallel to those described with [Ni(cyclam)]2+ in elec-
trochemical reactions, for which a radical-type reaction
has been suggested.21 However, in the case of nickel-
cyclam complexes, a mechanism involving the electro-
chemical Ni(II) reduction to Ni(I) has been proposed.22
Electr och em ica l Beh a vior of 4. The cyclic volta-
mmetry of 4 on a carbon fiber microelectrode showed
an irreversible (two-electron) reduction process at -0.9
V vs Ag/AgCl. Upon the addition of the substrate 5 (in
1:1 and 5:1 ratios of 5:4), a slight enhancement in the
reduction peak at -0.9 V could be observed.
Sch em e 4
P r ep a r a tive-Sca le Electr och em ica l Clea va ge of
th e Allyl Gr ou p of 5, Ca ta lyzed by 4. The bulk
electrolysis of substrate 5 in a Pd-catalyzed reaction by
4 under a single-compartment cell procedure in the
presence of a magnesium anode led, after 1 F/mol, to a
50% conversion of 5, with the formation of only 2-bro-
mophenol. After 2.1 F/mol electrolysis, the complete
consumption of 5 was attained, with 95% of bromophe-
nol present (eq 3). If the electrolysis was continued,
trolysis of a homoallylic ether, and a dihydro-2-ben-
zopyran analog (entry 5) was obtained from an allyl
benzyl ether. The bulk electrolyses catalyzed by 3a
proceed with a consumption of 2-4 F/mol of halide.
According to cyclic voltammetry and controlled po-
tential experiments, a two-electron reduction of 3a to
“NiN4” at -1.7 V is necessary to obtain the intramo-
lecular cyclization reaction. The process may be inter-
preted by a first oxidative addition of 5 over the
electrogenerated Ni(0) species, followed by an olefin
insertion in the σ(Ni-C) bond (Scheme 4). The last step
involves the protonation of the Ni-C bond assisted by
the Mg2+ ions. The proton sources were shown to be
the supporting electrolyte and the DMF solvent.20
Moreover, in a stoichiometric one-compartment cell
cyclization of 5 in the presence of 1 molar equiv of
n-tetrabutylammonium tetrafluoroborate, the quantita-
(3)
dehalogenation took place, and phenol was formed
progressively; thus, after 3 F/mol electrolysis, a mixture
of 2-bromophenol (63%) and phenol (32%) was obtained.
In the presence of the palladium catalyst 4, a highly
selective cleavage of the O-C(allyl) bond of 5 occurred.
The reaction presumably involves an initial electrogen-
eration of “Pd0N4” species, which reacts with the organic
substrate to form a π-allyl Pd(II) intermediate (Scheme
5). Under the electrochemical conditions, and in the
(21) (a) Olivero, S.; Dun˜ach, E. Tetrahedron Lett. 1995, 36, 4429.
(b) Ozaki, S.; Matsushita, H.; Ohmori, H. J . Chem. Soc., Chem.
Commun. 1992, 1120. (c) Ozaki, S.; Horiguchi, I.; Matsushita, H.;
Ohmori, H. Tetrahedron Lett. 1994, 35, 725.
(20) De´rien, S.; Dun˜ach, E.; Pe´richon, J . J . Am. Chem. Soc. 1991,
113, 8447.
(22) (a) Gosden, C.; Pletcher, D. J . Organomet. Chem. 1980, 186,
401. (b) Healy, K. P.; Pletcher, D. J . Organomet. Chem. 1978, 161, 109.

New Open Tetraaza Ni(II) and Pd(II) Complexes
Organometallics, Vol. 16, No. 26, 1997 5905
presence of Mg2+ ions issued from anodic oxidation,
2-bromophenolate ion is formed by metal exchange, the
allyl moiety being protonated by the reaction medium.20
The [Pd(N4)]2+ complex can be liberated and recycled
by continuous reduction.
The oxidative addition of 5 was not observed with [Ni-
(cod)2], with or without additional phosphine as stabiliz-
ing ligand, and no reaction products of the organic
halide could be detected. The oxidative addition of 5 to
[Ni(PPh3)4] at room temperature gave small amounts
of [NiBr(2-(OCH2CHdCH2)C6H4)(PPh3)2] (7a ), as could
be monitored by 31P NMR of the solution reaction.
However, this complex was not isolated, and only PPh3
and OPPh3 could be recovered. The analysis of the
reaction solution showed the presence of unreacted 5,
the coupling compound [2-(OCH2CHdCH2)C6H4]2, and
o-bromophenol. These results suggest that the oxidative
addition of 5 is a competitive process between the Br-C
and O-C bonds. Similar product mixtures were ob-
tained by electrochemical reduction of neutral complex
1b in the presence of 5.
The syntheses of [NiBr(2-(OCH2CHdCH2)C6H4)(P)2]
(where P ) PPh3 (7a ) and PEt2Ph (7b)) were achieved
from reactions of [NiBr2P2] and BrMg(2-(OCH2CHd
CH2)C6H4) in very low yields. The coupling product (2-
(OCH2CHdCH2)C6H4)2 from the decomposition of the
organometallic compound,25 allyl phenyl ether, and an
unexpected compound o-(OCH2CHdCH2)(CH2CHdCH2)-
C6H4, were observed, as well as the corresponding
phosphine and its oxide (eq 4). Addition of N4 to the
The ability of Pd(0) complexes to form π-allyl Pd(II)
species with allyl esters or carbonates is a well-known
reaction,23 with various applications in the field of
asymmetric alkylations.24 In the example with sub-
strate 5, the cleavage concerns an allyl ether and takes
place without interference to the aryl-bromide bond.
The difference in reactivity observed for 3 and 4
toward difunctional 5 in one-compartment cells is note-
worthy: nickel complex 3 chemoselectively orientates
the reactivity toward activation of the aryl-bromide
bond, whereas the electroreduction of the palladium
complex 4 specifically activates the allyl ether moiety.
F . In ter m ed ia te “MN4” Sp ecies. The results ob-
served by cyclic voltammetry for Ni(II) (3) and Pd(II)
(4) complexes showed the formation of Ni(I), Ni(0), and
Pd(0) species. We were interested in the chemical
preparations of such intermediates, in order to study
their behavior and stability, and to get some compara-
tive features concerning their chemical and electro-
chemical reactivity.
Thus, when N4 was added to a toluene or THF
solution of [Ni(cod)2] at room temperature, only decom-
posed black metallic nickel could be recovered. Alter-
natively, when N4 was added to [Ni(cod)2] in toluene
solution in the presence of PPh3 in a 1:1:2 molar ratio,
no mixed compounds [Ni(PPh3)2(N4)] were detected, and
only [Ni(PPh3)4] was obtained. The same process oc-
curred upon adding dppe instead of PPh3, with obtention
of [Ni(dppe)2]. However, when N4 was added to [Ni-
(cod)2] in a DMF solution, no decomposition to black Ni-
(0) was observed. Therefore, the solvent plays a fun-
damental role in the stabilization of the “Ni(0)N4”
species.
Since the cyclization reaction has been observed from
Ni(I)-cyclam-type species21 and we have observed the
same Ni(I) species in the cyclic voltametry, we have
tried to isolate the “NiIN4” complexes. Attempts to
prepare NiIN4 species were performed from mixtures of
[NiCl(PPh3)3] and N4. In toluene, no ligand exchange
reaction occurred. However, stable orange solutions
were obtained in DMF, although it was not possible to
characterize pure solid compounds from these solutions.
On standing for several days, the disproportionation
reaction took place, and 1a could be recovered.
A Ni(0)/Ni(II) comproportionation reaction was at-
tempted by adding [Ni(cod)2], [Ni(N4)](ClO4)2, and N4
in an equimolar ratio in toluene, but no NiIN4 species
could be cleanly isolated. The direct chemical reduction
of [Ni(N4)](ClO4)2 with Na/Hg amalgam in DMF was
monitored by EPR, but no Ni(II) reduction was observed,
and 3b was recovered.
(4)
solutions of complexes 7 did not induce the substitution
of coordinated phosphines.
The preparation of neutral mononuclear organome-
tallic complexes containing the N4 ligand was unsuc-
cessfully attempted via substitution reactions starting
from [NiCl(2,4,6-Me3C6H2)(PPh3)2] and [PdBr(o-MeC6H4)-
(PPh3)2] with N4. The action of Grignard reagents such
as BrMg(2,4,6-Me3C6H2) on the neutral coordination
complexes [M2(µ-N4)X4] also failed to produce [M2X2R2-
(µ-N4)] or [MXR(N4)] compounds.
In the case of the catalytic reaction of 5 with [Pd-
(N4)]2+, a π-allylpalladium species has been proposed
(Scheme 5) as intermediate. Therefore, neutral (8a ) and
ionic (8b) allyl dinuclear complexes were obtained in
quantitative yields (eq 5). The proton NMR spectrum
(5)
The intramolecular cyclization observed with 5 in-
duced by the electrochemical reduction in the presence
of the cationic [Ni(N4)]2+ species could not be reproduced
in stoichiometric reactions starting from [Ni(cod)2] or
[NiCl(PPh3)3] complexes in the presence of the N4
ligand, either in toluene or in DMF.
of 8b was well defined, whereas for the neutral complex
8a the signals were broad in the range 223-323 K,
probably due to the fast substitution exchange of the
(23) Pregosin, P. S.; Salzmann, R. Coord. Chem. Rev. 1996, 155, 35.
(24) (a) Trost, B. M.; van Vranken, D. L. Chem. Rev. 1996, 96, 395.
(b) Frost, C. G.; Howarth, J .; Williams, J . M. J . Tetrahedron: Asym-
metry 1992, 3, 1089.
(25) Anto´n, M.; Muller, G.; Sales, J . Transition Met. Chem. 1983, 8,
79.

5906 Organometallics, Vol. 16, No. 26, 1997
Go´mez et al.
Sch em e 6
sociated with the 2,2′-bipy ligand induced the allyl-O
cleavage reaction on 5.27
Exp er im en ta l Section
Rea gen ts a n d Ch em ica ls. All manipulations of the
complexes in solution were carried out using Schlenk tech-
niques under a nitrogen atmosphere. All solvents were dried
and degassed by standard methods. [PdCl2(cod)] was prepared
as reported.28 Allyl 2-bromophenyl ether (5) (and other allyl
ethers) was prepared from 2-bromophenol by treatment with
allyl chloride and potassium carbonate on DMF.
In str u m en ta tion a n d Cells. 1H, 31P, and 13C NMR
spectra were obtained using Varian Gemini-200, Unity 300,
and Bruker DRX 250 spectrometers. Solvents used were
CDCl3, acetonitrile-d3, acetone-d6 benzene-d6, or py-d5. Infra-
red spectra were recorded as KBr disks on a Nicolet 520 FT-
IR spectrometer. Microanalyses were performed by the In-
stitut de Qu´ımica Bio-Orga`nica de Barcelona (CSIC) and by
the Serveis Cient´ıfico-Te`cnics de la Universitat de Barcelona.
Conductivity measurements were taken with a Radiometer
CDM3 instrument in 10-3 M acetone or acetonitrile solutions
at 20 °C. Magnetic measurements were carried out at variable
temperature (300-4 K) on polycrystalline samples with a
pendulum-type magnetometer (Manics DSM8) equipped with
a Drusch EAF 16UE electromagnet. The magnetic field was
approximately 1.5 T. Diamagnetic corrections were estimated
from Pascal’s tables.
ligands. In order to stabilize π-allylpalladium interme-
diates with 5, we studied the stoichiometric reaction to
prepare the dimeric allylic palladium complexes follow-
ing the published conditions (eq 6).26 The analysis of
(6)
the products showed the formation of 2-bromophenol
and the dimeric allylic complex in low yields. This
would seem to suggest that the π-allylpalladium inter-
mediate (Scheme 5) is a dinuclear species stabilized by
the tetraaza ligand.
Cyclic voltammetry experiments and controlled potential
electrolyses were performed with the aid of PAR scanning
potentiostat Model 362 equipment and were carried out at 25
°C by utilizing Pt or carbon fiber microelectrodes (Tacussel).
All potentials were quoted with respect to Ag/AgCl electrode
at room temperature. Intensiostatic electrolyses were carried
out by using a stabilized constant-current supply (Sodilec, EDL
36.07). The electrochemical one-compartment cell is a cylin-
drical glass vessel of ∼40 cm3 volume, already described,19
equipped with a carbon fiber cathode (20 cm2) and a magne-
sium rod anode immersed to 3 cm. In the two-compartment
cell, the two compartments are separated by a sintered glass
(no. 4); the anodic compartment has a Pt wire as the anode,
and the cathodic compartment is equipped with a carbon fiber
cathode and a Ag/AgCl electrode.29
N4. In a 500 cm3, three-necked flask, dried and flushed with
argon, 2.15 g of dry piperazine was introduced, followed by
250 cm3 of anhydrous THF. The resulting mixture was stirred
for 20-30 min in order to obtain a homogeneous medium. This
solution was then brought to -10 °C (ice/brine bath), and 33.5
cm3 of a 1.5 N n-BuLi solution in hexane (0.05 mol) was added
into the flask via a canula, keeping the temperature under 0
°C. There was an immediate precipitate of the dilithiated
piperazine. The mixture was stirred for 30 min at -10 °C,
and then a solution of 12.7 g of the 2-(2′-bromophenyl)-4,4-
dimethyloxazoline14 (0.05 mol) in 100 cm3 of anhydrous THF
was introduced dropwise via a canula. The reaction was
exothermal, and the medium quickly turned to a dark red
color. The resulting solution was then stirred for 12 h. The
solvent was evaporated, and the residue was taken in a
mixture of 100 cm3 water and 200 cm3 chloroform. The phases
were separated. The aqueous phase was extracted twice with
chloroform (100 cm3). Then, the joined organic phases were
washed three times with 100 cm3 of clear water. The organic
phase was dried over potassium carbonate and then concen-
trated under reduced pressure. The residue was stirred in
diethyl ether to give a white precipitate, which was then
recrystallized in a mixture of dichloromethane and ether. A
total 13.8 g of a white solid was isolated in a 64% yield. The
remaining oil of the recrystallization was essentially consti-
Con clu sion
For the neutral complexes [M2(µ-N4)X4] (M ) Ni (1a ,
1b), Pd (2a )), the potential tetradentate ligand acts only
in a bidentate form, giving dinuclear compounds, where
decomplexation of N4 was observed in solution of
coordinating solvents, as was established by NMR
spectroscopy. However, the ligand N4 acts as a tet-
radentate ligand in the monomeric ionic complexes
[M(N4)]Y2 (M ) Ni (3), Pd (4)). These complexes remain
stable in coordinating solvents and present very differ-
ent electrochemical reactivity toward difunctional or-
ganic substrates such as allyl 2-bromophenyl ether (5).
The difference in reactivity observed for complexes
[M(N4)]Y2 (3 and 4) toward difunctional 5 in one-
compartment cells is noteworthy: nickel complex 3
chemoselectively orientates the reaction toward activa-
tion of the aryl-bromide bond, whereas the electrore-
duction of the palladium complex 4 specifically activates
the allyl ether moiety (Scheme 6).
The attemps to prepare the intermediate species with
different oxidation states of the proposed cycles (Schemes
4 and 5) allowed us to confirm the activation of the
C-Br bond by formation of σ(Ni-C) complexes (7a ,b)
and the activation of the C-O bond by formation of
π-allylpalladium complexes (8a ,b). Furthermore, the
effect of the solvent is also important, both in the
stabilization of the M(0) intermediate species and in
providing the hydrogen neccesary to cleave the M-C
bond.
The role of the ligand and oxidation state of the Ni
complexes is also essential in determining the selectiv-
ity. Thus, with [Ni(cyclam)]2+, the same intramolecular
cyclization products were obtained from 5, but in a
process involving Ni(I) species. In contrast, Ni(0) as-
(26) Tatsuno, Y.; Yoshida, T.; Otsuka, S. Inorg. Synth. 1990, 28, 342.
(27) Olivero, S.; Dun˜ach, E. J . Chem. Soc., Chem. Commun. 1995,
2497.
(28) Drew, D.; Doyle, J . R. Inorg. Synth. 1990, 28, 346.
(29) Garnier, L.; Rollin, Y.; Pe´richon, J . New J . Chem. 1989, 13, 53.

New Open Tetraaza Ni(II) and Pd(II) Complexes
Organometallics, Vol. 16, No. 26, 1997 5907
tuted by 2-bromooxazoline, 2.5 g of which was recovered by
vacuum distillation. The final yield based on the consumed
bromooxazoline was 80%, mp ) 178 °C.
obtained as reported above, was added slowly to a suspension
of [NiBr2(PPh3)2] (1.5 g, 2 mmol) in THF (10 cm3) at -78 °C.
The solution was allowed to warm to room temperature and
was then stirred for 30 min. After 12 h at 0 °C, the resulting
suspension was filtered, the solution was concentrated under
reduced pressure, and 20 cm3 of toluene was added. The
solution was washed with 15% NH4Cl aqueous solution. The
organic layer was separated and dried over anhydrous Na2-
SO4. The solvent was removed under vacuum. The oil
obtained was washed with hexane, and, after addition of
absolute ethanol, a yellow solid was precipitated. Yield: 0.2
g, 18%. 31P{1H} NMR (CDCl3, 240 K): δ 22.2. 1H NMR (C6D6,
308 K): δ 4.7 (CH2dCH-, t, 1H, J ) 7 Hz), 5.4 and 5.8
(CH2dCH-, d, 1H, J ) 5 Hz and d, 1H, J ) 8 Hz), 6.38 and
6.49 (CH2O, t, 1H, J ) 7.5 Hz and t, 1H, J ) 7.5 Hz), 7-8
(aromatic, m). Anal. Calcd for C45H39BrNiOP2: C, 67.87; H,
4.94. Found: C, 66.7; H, 4.9.
[NiBr (2-(CH2dCHCH2O)C6H4)(P Et2P h )2] (7b). A solu-
tion of 2-(allyloxy)benzene magnesium bromide (11 cm3, 1.5
mmol), obtained as reported above, was added slowly to a
suspension of [NiBr2(PEt2Ph)2] (0.45 g, 1 mmol) in toluene (15
cm3) at -78 °C. The solution was allowed to warm to room
temperature and was further stirred for 30 min. The solvent
was removed under reduced pressure. The solid obtained was
washed with water, dissolved in toluene, and dried over
anhydrous Na2SO4. The solvent was partially removed, and
hexane was added. A yellow solid was precipitated and filtered
off. Yield: 65 mg, 10%. 31P{1H} NMR (C6D6, 293 K): δ 11.0.
1H NMR (C6D6, 308 K): δ 1.6 and 2.2 (PCH2CH3, br, 4H and
1H NMR (CDCl3): δ 7.63 (d, 1H, J ) 7.6 Hz), 7.38 (dd, 1H,
J ) 7.4 and 7.6 Hz), 7.04 (d, 1H, J ) 8.0 Hz), 7.00 (dd, 1H, J
) 7.4 and 8 Hz), 4.07 (s, 4H), 3.22 (s, 8H), 1.37 (s, 12H). 13C
NMR (CDCl3): δ 163.3, 151.6, 131.7, 131.5, 122.0, 121.6, 118.2,
79.0, 67.4, 52.0, and 28.4. IR (Nujol): 1630, 1600, 1315, 1035
cm-1. Anal. Calcd for C26H32N4O2: C, 72.19; H, 7.47; N, 12.95.
Found: C, 71.98; H, 7.40; N, 12.54.
[Ni2(µ-N4)X4] X ) Cl (1a ), Br (1b). To a solution of the N4
ligand (0.11 g, 0.25 mmol) in THF (10 cm3) at room temper-
ature was added dropwise a solution of [NiX2L2] ([NiBr2-
(PPh3)2], 0.38 g, 0.50 mmol; [NiCl2(PEtPh2)2], 0.28 g, 0.5 mmol)
in 10 cm3 of THF. The mixture was stirred for 1 h under these
conditions, affording a purple solid. The precipitate was
filtered off, washed with ether and hexane, and dried under
vacuum. Data for 1a follow. Yield: 0.15 g, 87%. Anal. Calcd
for C26H32Cl4N4O2Ni2: C, 45.14; H, 4.66; N, 8.10. Found: C,
45.10; H, 4.25; N, 8.29. Data for 1b follow. Yield: 0.19 g, 88%.
Anal. Calcd for C26H32Br4N4O2Ni2: C, 35.91; H, 3.71; N, 6.44.
Found: C, 35.80; H, 3.65; N, 6.45.
[P d 2(µ-N4)Cl4] (2). A solution of the N4 ligand (0.11 g, 0.25
mmol) in CH2Cl2 (10 cm3) at room temperature was added
dropwise to a solution of [PdCl2(cod)] (0.14 g, 0.5 mmol) in CH2-
Cl2 (10 cm3). The mixture was stirred for 2 h under these
conditions, affording an orange solid. Then, the precipitate
was filtered off and washed with ether and hexane. Finally,
the solid was dried under vacuum. Yield: 0.15 g, 76%. Anal.
4H), 0.98 and 1.02 (PCH2CH3, both q, 6H and 6H, J H ≈ J P,P′
≈
Calcd for
Found: C, 39.90; H, 4.25; N, 7.18.
C26H32Cl4N4O2Pd2: C, 39.67; H, 4.10; N, 7.12.
8 Hz), 4.8 (CH2dCH-, t, 1H, J ) 7 Hz), 6.4 and 6.55 (CH2dCH-,
s, 1H and d, 1H, J ) 7 Hz), 6.8-6.9 (CH2O, m, 2H), 7-8
(aromatic, m). Anal. Calcd for C29H39BrNiOP2: C, 57.65; H,
6.51. Found: C, 57.2; H, 6.7.
[Ni(N4)]Y2 (Y ) BF 4 (3a ), ClO4 (3b)). A suspension of NiY2
(0.5 mmol; Y ) ClO4-, 0.16 g, Y ) BF4-, 0.14 g) in ethanol (20
cm3) at room temperature was added dropwise to a solution
of N4 (0.22 g, 0.5 mmol) in ethanol (10 cm3). The mixture was
stirred for 1 h under these conditions. The solvent was
partially removed under reduced pressure, and 20 cm3 of ether
was added, affording a white precipitate. The compounds 3
were separated by filtration, washed with ether and hexane,
and dried under vacuum. Data for 3a follow. Yield: 0.14 g,
84%. Molar conductivity (10-3 M, acetone): ΛM ) 190 cm2 Ω-1
mol-1. Anal. Calcd for C26H32B2F8N4O2Ni: C, 46.97; H, 4.10;
N, 7.12. Found: C, 47.00; H, 4.95; N, 8.50. Data for 3b follow.
Yield: 0.16 g, 87%. Molar conductivity (10-3 M, acetone): ΛM
[P d 2(µ-N4)(C3H5)2Br 2] (8a ). A solution of N4 (0.060 g, 0.14
mmol) in CH2Cl2 (10 cm3) at room temperature was added to
a solution of [Pd2(C3H5)2(µ-Br)2] (0.13 g, 0.28 mmol) in CH2Cl2
(10 cm3). The mixture was stirred overnight. Then, 25 cm3
of hexane was added, affording a yellow solid. The precipitate
was filtered off and washed with ether and hexane. Finally,
the solid was dried under vacuum. Yield: 0.10 g, 81%. Anal.
Calcd for C32H42Br2N4O2Pd2: C, 43.32; H, 4.77; N, 6.31.
Found: C, 42.70; H, 4.60; N, 5.95.
[P d 2(µ-N4)(C3H5)2](P F 6)2 (8b). A solution of 8a (0.089 g,
0.20 mmol) in ethanol (10 cm3) at room temperature was added
to a solution of NH4PF6 (0.066 g, 0.40 mmol) in the same
solvent (10 cm3). The mixture was stirred overnight, affording
a white solid. The precipitate was filtered off and washed with
degassed water (3 × 10 cm3). Finally, the solid was dried
under vacuum. Yield: 0.090 g, 88%. Molar conductivity (10-3
) 190 cm2 Ω-1 mol-1 1H NMR (CD3CN, 298 K): δ 1.6 (s, 12H,
.
Me), 3.40 (s, 8H, CH2-N), 4.75 (s, 4H, CH2-O), 7.45 (t, 2H, J )
7.5 Hz), 7.7 (d, 2H, J ) 7.5 Hz), 7.9 (t, 2H, J ) 7.5 Hz), 8.0 (d,
2H, J ) 7.5 Hz). Anal. Calcd for C26H32Cl2N4O10Ni: C, 45.25;
H, 4.56; N, 8.12. Found: C, 45.80; H, 4.56; N, 8.24.
[P d (N4)](P F 6)2 (4). A suspension of Pd(OAc)2 (0.11 g, 0.5
mmol) and NH4PF6 (0.16 g, 0.1 mmol) in CH2Cl2 (20 cm3) was
added dropwise to a solution of N4 (0.22 g, 0.5 mmol) in 10
cm3 of the same solvent. The solution was stirred at room
temperature for 2 h. Then, 20 cm3 of the solvent was removed
under reduced pressure, and 30 cm3 of hexane was added. The
solution was placed in the freezer overnight. The orange
precipitate formed was filtered and washed with degassed
water (3 × 10 cm3) and dried under vacuum. Yield: 0.3 g, 74%.
M, acetonitrile): ΛM ) 200 cm2 Ω-1 mol-1 1H NMR (CD3CN,
.
298 K): δ 1.44 (Me, s, 12H), 3.00 (HantiHCdCH-, d, 4H, J )
12.5 Hz), 3.51 (CH2-N, s, 8H), 4.03 (HsynHCdCH-, d, 4H, J )
7.0 Hz), 4.45 (CH2-O, s, 4H), 5.58 (CH2dCH-, 2H, J ) 12.5
and 7.0 Hz), 7.35 (t, 2H, J ) 7.6 Hz), 7.50 (br d, 2H, J ) 8.2
Hz), 7.70 (br t, 2H, J ) 7.5), 7.80 (dd, 2H, J ) 7.7 and 1.5 Hz).
Anal. Calcd for C32H42F12N4O2P2Pd2: C, 37.78; H, 4.16; N,
5.51. Found: C, 37.40; H, 4.20; N, 5.75.
Gen er a l P r oced u r e for On e-Com p a r tm en t Cell Elec-
tr olyses. A DMF solution containing 3a (0.3 mmol), 5 (or the
other ether derivatives, 3 mmol), and n-Bu4N+BF4- (0.2 mmol)
was placed in the cell and stirred at room temperature under
nitrogen atmosphere. A current of 60 mA was applied between
the electrodes connected to a dc power supply (apparent
current density of 0.3 A dm-2, applied voltage ca. 3-15 V).
The consumption of 5 was monitored by GC analysis of aliquots
withdrawn from the reaction mixture, and the electrolysis was
continued until the starting material was almost depleted, e.g.,
about 4-5 h. Generally, 3-4 F/mol of 5 was necessary to
achieve a complete conversion. The solution was hydrolyzed
with 50 cm3 of 0.1 N HCl solution and extracted with Et2O,
and the organic layer was washed with H2O, dried over MgSO4,
Molar conductivity (10-3 M, acetone): ΛM ) 195 cm2 Ω-1 mol-1
.
1H NMR (CDCl3, 298 K): δ 2.05 (s, 12H, Me), 3.31 (s, 8H, CH2-
N), 4.17 (s, 4H, CH2-O), 7.10 (t, 2H, J ) 7.5 Hz), 7.4 (t, 2H, J
) 7.5 Hz), 7.75 (d, 2H, J ) 7.5 Hz), 8.0 (d, 2H, J ) 7.5 Hz).
Anal. Calcd for C26H32F12N4O2P2Pd: C, 37.67; H, 3.89; N, 6.76.
Found: C, 37.02; H, 3.70; N, 6.50.
Solu tion of 2-(Allyloxy)ben zen e Ma gn esiu m Br om id e.
A mixture of allyl 2-bromophenyl ether (5, 0.86 g, 4 mmol) and
magnesium turnings (0.24 g, 10 mmol) in THF (30 cm3) was
stirred at room temperature for 2 h. GC analysis of hydrolyzed
drops of the solution showed the complete formation of
(allyloxy)benzene.
[NiBr (2-(CH2dCHCH2O)C6H4)(P P h 3)2] (7a ). A solution
of 2-(allyloxy)benzene magnesium bromide (22 cm3, 3 mmol),

5908 Organometallics, Vol. 16, No. 26, 1997
Go´mez et al.
and evaporated. The products were purified by column
chromatography on silica gel with pentane/Et2O mixtures as
eluent. The yields are quoted in Table 2. The products were
compared to authentic samples.
when the current was negligible. The workup was the same
as described above, the reaction being followed by GC.
Gen er a l P r oced u r e for Tw o-Com p a r tm en t Cell Elec-
tr olyses. Both compartments were filled with a DMF solution
Ack n ow led gm en t. We thank the Comisio´n Inter-
ministerial de Ciencia y Tecnologı´a and the Generalitat
de Catalunya (Grant Nos. QFN95-4708, 1995SGR 00199,
and HF1996-0034) and CNRS for financial support.
-
(30 cm3 each) of n-Bu4N+BF4 (1 g, 3 mmol) under inert
atmosphere. Complex 3a (0.1 mmol) and 5 (0.3 or 0.5 mmol)
were added to the cathodic compartment. The electrolyses
were run at 20 °C at the desired potential and were stopped
OM9707026