Reactivity of hydroxo complexes of palladium(II) towards nitriles: Formation of carboxamide and imino ether derivatives of palladium(II)

Article abstract of DOI:10.1039/a903262b

The binuclear hydroxo complexes [Pd₂(C,N)₂(μ-OH)₂] [C,N = 2-(dimethylaminomethyl)phenyl (dmba) or 2-(phenylazo)phenyl (az)] have been prepared by addition of 2 equivalents of NBu₄OH to the corresponding di-μ-acetate complexes in acetone. The reactions of both hydroxo complexes with a number of nitriles, RCN, led to the formation of the carboxamide complexes [Pd₂(C,N)₂(μ-NHC(R)O)₂] (R = Me, Ph or CH₂=CH) as well as the succinonitrile derivatives [(C,N)Pd{NHC(O)CH₂CH₂C(O)NH}Pd(C,N)]. The complexes [Pd₂(C,N)₂(μ-NHC(Me)O)₂] can also be prepared by reaction of [Pd₂(C,N)₂(μ-OH)₂] with acetamide. The hydroxo complex [Pd₂(C₆F₅)₄(μ-OH) ₂]^2- reacted with nitriles in methanol or ethanol to give the imino ether complexes [Pd(C₆F₅)₂{NH=C(OR′)R}₂] (R = Ph, R′ = Me or Et; R = Me, R′ = Me or Et) which in acetone solution are present as mixtures of EE, EZ and ZZ isomers. Similar reactions with 2-cyanopyridine and succinonitrile gave [Pd(C₆F₅)₂{NC₅H ₄C(OR′)NH-2}] and [Pd(C₆F₅)₂{NHC(OR′)CH₂CH ₂NH(OR′)}] (R′ = Me or Et) and the reaction with 2-cyanopyridine in acetone yielded [Pd(C₆F₅)₂{NC₅H ₄C(=O)NH-2}]. The crystal structures of [Pd₂(dmba)₂(μ-NHC(Ph)O)₂] and [Pd(C₆F₅)₂{NH=C(OMe)Me}₂] have been determined by single-crystal X-ray diffraction.

Full text of DOI:10.1039/a903262b

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Reactivity of hydroxo complexes of palladium(II) towards nitriles:
formation of carboxamide and imino ether derivatives of
palladium(II)
José Ruiz,a Natalia Cutillas,a Venancio Rodríguez,a José Sampedro,a Gregorio López,*a
Penny A. Chalonerb and Peter B. Hitchcockb
a Departamento de Química Inorgánica, Universidad de Murcia, 30071 Murcia, Spain.
E-mail: gll@fcu.um.es
b School of Chemistry, Physics and Environmental Sciences, University of Sussex, Brighton,
UK BN1 9QJ
Received 23rd April 1999, Accepted 13th July 1999
The binuclear hydroxo complexes [Pd2(C,N)2(µ-OH)2] [C,N = 2-(dimethylaminomethyl)phenyl (dmba) or
2-(phenylazo)phenyl (az)] have been prepared by addition of 2 equivalents of NBu4OH to the corresponding
di-µ-acetate complexes in acetone. The reactions of both hydroxo complexes with a number of nitriles, RCN, led
to the formation of the carboxamide complexes [Pd (C,N) (µ-NHC(R)O) ] (R = Me, Ph or CH ᎐CH) as well
᎐
2
2
2
2
as the succinonitrile derivatives [(C,N)Pd{NHC(O)CH2CH2C(O)NH}Pd(C,N)]. The complexes [Pd2(C,N)2-
(µ-NHC(Me)O)2] can also be prepared by reaction of [Pd2(C,N)2(µ-OH)2] with acetamide. The hydroxo
complex [Pd2(C6F5)4(µ-OH)2]2Ϫ reacted with nitriles in methanol or ethanol to give the imino ether complexes
[Pd(C F ) {NH᎐C(ORЈ)R} ] (R = Ph, RЈ = Me or Et; R = Me, RЈ = Me or Et) which in acetone solution are
᎐
6
5
2
2
present as mixtures of EE, EZ and ZZ isomers. Similar reactions with 2-cyanopyridine and succinonitrile gave
[Pd(C6F5)2{NC5H4C(ORЈ)NH-2}] and [Pd(C6F5)2{NHC(ORЈ)CH2CH2NH(ORЈ)}] (RЈ = Me or Et) and the reaction
with 2-cyanopyridine in acetone yielded [Pd(C F ) {NC H C(᎐O)NH-2}]. The crystal structures of [Pd (dmba) -
᎐
6
5
2
5
4
2
2
(µ-NHC(Ph)O) ] and [Pd(C F ) {NH᎐C(OMe)Me} ] have been determined by single-crystal X-ray diffraction.
᎐
2
6
5
2
2
Considerable attention has been focused on reactions involving
nucleophilic attack on co-ordinated nitriles in metal complexes
and this field of synthetic chemistry is extensively documented.1
Examples include reactions with hydroxide2–9 and alkoxide to
form amidates and imino ethers,10–15 respectively (Scheme 1). In
particular, the hydrolysis of nitriles in the co-ordination sphere
of a transition metal has been known for a long time;16 the
hydrolysis of metal-bound nitriles proceeds fairly easily com-
pared with that of unco-ordinated nitriles, due to the Lewis-
acid activation of the metal. Labile complexes serve as catalysts,
the main advantage over acids and bases being their selectivity,
because in the presence of transition-metal complexes amides
are not converted into caboxylic acids.17 From a biological
perspective, the nitrile hydratases are important, little studied
metalloenzymes which catalyse the hydration of nitriles in
vivo18,19 and recent interest in the chemistry of platinum–imino
ether compounds arises from the discovery that some of these
compounds have antitumour activity.20
Organometallic benzonitrile complexes cis-[MR2(PhCN)2]
(R = C6F5, C6F3H2 or C6Cl5; M = Ni, Pd or Pt) have been used
as labile complexes for the synthesis of a variety of compounds.
These include mononuclear21 complexes, R2ML2, as well as
heterobimetallic complexes, [R2Pd(µ-X)2ML2] (M = Ni, Pd or
Pt).22 Interestingly, the metathesis of PhCN by OHϪ to syn-
thesize the hydroxo complexes [M2(C6F5)4(µ-OH)2]2Ϫ was
shown to be metal dependent.23 When M = Ni or Pd metathesis
of PhCN by OHϪ takes place, and binuclear hydroxo complexes
are obtained, eqn. (1).24,25 However, for the more kinetically
2 cis-[M(C6F5)2(NCPh)2] ϩ 2 OHϪ →
[M2(C6F5)4(µ-OH)2]2Ϫ ϩ 4 PhCN (1)
(M = Ni or Pd)
inert benzonitrileplatinum complex26 the nucleophilic attack
by OHϪ is faster than the substitution reaction, and the aqua–
η1-amidate complex is produced, eqn. (2). On heating this
cis-[Pt(C6F5)2(NCPh)2] ϩ OHϪ ϩ H2O →
Scheme 1 Nucleophilic attack of OHϪ and ROϪ on co-ordinated
nitrile.
cis-[Pt(C F ) {η1(N)-NHC(᎐O)Ph}(H O)]Ϫ ϩ PhCN (2)
᎐
6
5
2
2
J. Chem. Soc., Dalton Trans., 1999, 2939–2946
2939

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compound the co-ordinated water is lost and the bis(µ-η2-
amidate) complex is formed, eqn. (3). With methanol the
2 [Pt(C F ) {η1(N)-NHC(᎐O)Ph}(H O)]Ϫ ϩ heat →
᎐
6
5
2
2
[Pt (C F ) {µ-η2(N,O)-NHC(᎐O)Ph} ]2Ϫ ϩ 2 H2O (3)
᎐
2
6
5
4
2
bis(iminoether) [Pt(C F ) {NH᎐C(Ph)OMe} ] is directly ob-
᎐
6
5
2
2
tained.26
In summary, the previous results mentioned above indicate:
(i) Ni–NCPh and Pd–NCPh can be metathetically transformed
into Ni–OH and Pd–OH by reaction with OHϪ; (ii) Pt–NCPh,
however, is prone to nucleophilic attack by OHϪ (or MeOϪ)
yielding the amidate complex Pt–NHC(᎐O)Ph (or the imino
᎐
ether complex Pt–N᎐C(OMe)Ph). These different results may
᎐
easily be interpreted on the basis of the well known inertness of
platinum complexes towards substitution reactions. Once the
outcome of the reaction palladium nitrile ϩ free OHϪ was
known the reaction between M–OH and free nitrile following
remained unsolved. In binuclear complexes, {M(µ-OH)2M},
the enhanced nucleophilicity of the OH bridges is manifested
by their high-field proton resonances (δ Ϫ5.74 (Ni), Ϫ2.84 (Pd)
and Ϫ1.21 (Pt), respectively, for [M2(C6F5)4(µ-OH)2]2Ϫ).† Con-
sequently, it was to be expected that the reaction between
hydroxo complexes and nitriles should yield, under appropriate
conditions, the respective amidate and imino ether complexes,
which has been confirmed by the present study. The reactions
of the hydroxo complexes [Pd2(C6F5)4(µ-OH)2]2Ϫ and [Pd2-
(C,N)2(µ-OH)2] (C,N = 2-[(dimethylamino)methyl]phenyl-C1N
(dmba) or 2-phenylazophenyl-C1,N (az)) with a number of
nitriles have been studied.
Scheme 2 (i) 2 OHϪ.
Results and discussion
The anionic complex [Pd2(C6F5)4(µ-OH)2]2Ϫ was prepared as
described25 and the neutral cyclopallated complexes [Pd2-
(C,N)2(µ-OH)2] (C,N = dmba 1 or az 2) were conveniently pre-
pared by simple metathesis on the corresponding di-µ-acetate
complexes28,29 by addition of 2 equivalents of NBu4OH
(Scheme 2). The reactions take place in acetone at ambient
temperature and both complexes are precipitated by addition
of water. Although complex 1 was previously prepared,30 a less
convenient route was used, i.e. the hydrolysis of a dioxygen-
bridged complex, and no spectroscopic data were reported.
The analytical data are consistent with the proposed formu-
lae as are the IR and 1H NMR data (Table 1) with the presence
of hydroxide as bridging ligand,25,31,32 with an IR band at
ca. 3560 cmϪ1 due to the O–H stretching vibration and with a
high-field 1H resonance at δ Ϫ2.40 and Ϫ1.13, respectively.
1
Furthermore, the H NMR spectrum of complex 1 (Table 1)
shows the chemical shift equivalence of the CH2N and NMe2
protons of co-ordinated dmba.
The hydroxo-complexes 1 and 2 react with nitriles to give
the corresponding di-µ-amidate complexes 3–10 shown in
Scheme 3. The 1H NMR spectra of 3, 5, 7 and 9 (Table 1) show
that both the N-methyl and the CH2 groups of the dmba are
diastereotopic, two separate signals being observed for the
former and an AB quartet for the latter. Therefore there is no
plane of symmetry in the palladium co-ordination plane. A
folded ‘basket’ structure related to that observed in acetato-
bridged dimers is likely.33
Since both C6H4CH2NMe2 and RCONH are unsymmetrical,
there are five possible diastereomers for the dimeric complex,
two with head-to-head and the other three with head-to-tail
Scheme 3 (i) 2 RCN; (ii) NCC2H4CN.
arrangements of the bridging MeCONH ligands, but only one
isomer is present in solution at room temperature, perhaps due
to the fact that the ligand dmba exerts very different trans
influences through its C and N atoms.34 A facile head-to-tail
to head-to-head rearrangement has been observed in cis-[M2-
(NH3)4(µ-C2H4NO)2]2ϩ (M = Pd or Pt).35 The observation of a
† In fact these complexes have been used as Brönsted bases in a variety
of reactions. For example, the reaction between [(C6F5)2Ni(µ-OH)2-
Ni(C6F5)2]2Ϫ and malononitrile (1:2 ratio) yields the µ-η2(N,N)-
malonitrilate complex [(C6F5)2Ni(µ-NCCHCN)2Ni(C6F5)2]2Ϫ
,
and
catalytic cyclotrimerization to 2,4-diamino-6-cyanomethyl-3,5-pyrid-
inedicarbonitrile occurs when an excess of malononitrile is used.27
2940
J. Chem. Soc., Dalton Trans., 1999, 2939–2946

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Table 2 Selected distances (Å) and angles (Њ) for complex 5
Table 1 1H NMR data (δ, J in Hz) for the palladium complexes 1–10
(in CDCl3, reference SiMe4)
Pd(1)–C(1)
Pd(1)–N(1)
Pd(1)–Pd(2)
Pd(1)–N(3)
Pd(1)–O(1)
1.916(3)
2.079(3)
3.0054(5)
2.013(3)
2.130(3)
Pd(2)–C(24)
Pd(2)–N(2)
Pd(2)–N(4)
Pd(2)–O(2)
1.963(3)
2.017(3)
2.087(3)
2.118(3)
Complex
1
6.9 (m, 8 H, aromatics)
3.77 (s, 4 H, NCH2)
2.70 (s, 12 H, NMe2)
Ϫ2.40 (s, 2 H, OH)
7.9–7.0 (m, 18 H, aromatics)
Ϫ1.13 (s, 2 H, OH)
7.0–6.8 (m, 8 H, aromatics)
4.9 (s, 2 H, NH)
C(1)–Pd(1)–N(3)
C(1)–Pd(1)–N(1)
N(3)–Pd(1)–O(1)
N(1)–Pd(1)–O(1)
95.45(14)
82.76(14)
88.49(12)
92.74(12)
C(24)–Pd(2)–N(2)
C(24)–Pd(2)–N(4)
N(2)–Pd(2)–O(2)
N(4)–Pd(2)–O(2)
95.78(13)
82.37(13)
87.50(12)
94.10(12)
2
3
3.43 (d, 2 H, NCH2, J 13.6)
3.02 (s, 2 H, NCH2, J 13.6)
2.63 (s, 6 H, NMe2)
2.10 (s, 6 H, NMe2)
2.02 (s, 6 H, CH3CONH)
7.6 (d, 2 H, J 7.6)
7.43 (d, 4 H, J 7.6)
7.30 (m, 6 H)
7.04 (dd, 2 H, J ≈ JЈ 7.6)
6.8 (dd, 2 H, J 7.6)
6.6 (d, 2 H, J 7.6)
5.0 (s, 2 H, NH)
1.94 (s, 6 H, CH3CONH)
7.8–7.3 (m, 10 H, C6H5)
7.0–6.9 (m, 8 H, aromatics dmba)
5.74 (s, 2 H, NH)
4
5
3.5 (d, 2 H, NCH2, J 13.6)
3.1 (d, 2 H, NCH2, J 13.6)
2.7 (s, 6 H, NMe2)
2.1 (s, 6 H, NMe2)
7.6–6.6 (m, 28 H, aromatics)
5.91 (s, 2 H, NH)
6
7
7.0–6.8 (m, 8 H, aromatics)
6.19 (dd, 2 H, CH᎐CH2, J 16.9, JЈ 10.0)
᎐
Fig. 1 Perspective view of the molecular structure of complex 5.
5.85 (dd, 2 H, CH᎐CH2(a), J 16.9, JЈ 1.7)
᎐
5.25 (dd, 2 H, CH᎐CH2(b), J 9.7, JЈ 1.7)
᎐
5.1 (s, 2 H, NH)
aware this is the first dipalladium species bridged by two benz-
amidate ligands to be structurally characterized. The two
palladium atoms are crystallographically inequivalent,
although the bond lengths and angles about each are not
markedly different. Co-ordination at palladium is approxi-
mately square planar with the two co-ordination planes inclined
at 35.50(11)Њ to each other giving a basket-shaped 8-membered
ring. The cyclometallated rings are puckered with the nitrogen
atom significantly out of the plane defined by the palladium
and carbon atoms, a feature which is quite commonly observed
in cyclometallated dmba complexes.
8
7.68 (dd, 2 H, J 7.6, JЈ 1.4)
7.47 (d, 4 H, J 7.2)
7.30 (m, 6 H)
7.06 (ddd, 2 H, J ≈ JЈ 7.4, JЉ 1.2)
6.71 (ddd, 2 H, J ≈ JЈ 7.3, JЉ 1.4)
6.55 (ddd, 2 H, J ≈ JЈ 7.7, JЉ 1.3)
6.21 (dd, 2 H, CH᎐CH2, J 16.9, JЈ 9.7)
᎐
6.02 (dd, 2 H, CH᎐CH2(a), J 16.9, JЈ 2.1)
᎐
5.41 (dd, 2 H, CH᎐CH2(b), J 9.7, JЈ 2.1)
᎐
5.37 (s, 2 H, NH)
9
7.0–6.8 (m, 8 H, aromatics dmba)
4.9 (s, 2 H, NH)
A number of cyclometallated dmba complexes with nitrogen
and oxygen ligands have been structurally characterized. In all
instances, both with chelating and non-chelating ligands, the
nitrogen atoms occupy trans sites at the metal with oxygen trans
to carbon, as indeed is observed for 5. The Pd–N(sp3) distances
in 5, 2.079(3) and 2.087(3) Å, are comparable with those
3.50 (d, 2 H, NCH2, J 13.8)
3.05 (d, 2 H, NCH2, J 13.6)
2.6 (s, 6 H, NMe2)
2.5 (m, 4 H, C2H4)
2.06 (s, 6 H, NMe2)
7.69 (d, 2 H, J 7.3)
7.3 (m, 8 H)
7.06 (ddd, 2 H, J ≈ JЈ 7.2, JЉ 1.7)
6.70 (m, 4 H)
10
in [(dmba)Pd–OC(᎐O)CHRNHRЈ]37 (R = CH2CH2SMe or
᎐
CH2Ph, RЈ = protected sugar; 2.079(6), 2.052(6) Å), [Pd(dmba)-
(OC6H4NMe2-2)]38 (2.075(2) Å) and [Pd(dmba){OC6H4-
5.19 (s, 2 H, NH)
2.5 (m, 4 H, C2H4)
CH᎐NPh-2}]39 (2.090(10) Å). Two related complexes in which
᎐
the N- and O-ligands are not part of a chelate have also been
1
unique resonance for the MeCO and NH protons in the H
spectrum of complex 3 (Table 1), together with the observed
C6H4CH2NMe2 resonances, is consistent with only the head-
to-tail structures (Scheme 3) containing the central core Pd-
{µ-OC(Me)NH}{µ-NHC(Me)O}Pd. Furthermore, we should
expect that the O atom would be trans to the carbon atom of
the C6H4CH2NMe2 chelate by analogy to the imidate complexes
[{Pd(C,N)(µ-NCOC2H4CO)}2] (C,N = o-C6H4CH2NMe2 or o-
studied, [Pd(dmba)(bquin)(OH2)][ClO4]40 (bquin = benzo[h]-
quinoline) and the ylid derivative [Pd(dmba)(py){OC(Me)᎐
᎐
CHPPh3}][ClO4]ؒCH2Cl2.41 The Pd–NMe2 distances (2.06(1)
and 2.074(3) Å) in these species are also comparable with those
in 5. The Pd–C distances in 5 (1.961(3), 1.963(3) Å) also lie
within the range normal for palladium dmba complexes.
The formation of complexes 3–10 may be explained by initial
formation of an intermediate hydroxonitrile complex ([(C,N)-
C H CH᎐NPh).36 This point has been confirmed by X-ray
Pd(µ-OH)2Pd(C,N)] ϩ 2 RCN
2 [Pd(C,N)(OH)(NCR)])
᎐
6
4
determination of the crystal structure of the benzamidato
complex 5.
Suitable crystals of complex 5 were grown from dichloro-
methane–hexane. The structure of 5 is shown in Fig. 1 and
selected bond lengths and angles in Table 2. So far as we are
and subsequent nucleophilic attack of OHϪ on the co-
ordinated nitrile and migration of Hϩ to the nitrogen atom
bound to palladium. The conversion of acetonitrile into acet-
amide in the co-ordination sphere of cis- and trans-MII(amine)2
(M = Pd or Pt) has been reported.36 The reaction of complexes
J. Chem. Soc., Dalton Trans., 1999, 2939–2946
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1 or 2 with the fairly weak acid acetamide also yields complex 3
or 4, respectively (Scheme 4). This is a consequence of the con-
IR spectra show the characteristic absorptions of the C6F5
group46 at 1630, 1490, 1450, 1050, 950 and a split band at ca.
800 cmϪ1 which is derived from the so-called X-sensitive mode
in C6F5–halogen molecules. This is characteristic of the pres-
ence of the cis-Pd(C6F5)2 fragment47 and behaves like a ν(M–C)
band.48 The bands at ca. 3360 and 1645 cmϪ1 provide evidence
for the NH and C᎐N groups of the imino ether.49
᎐
The NMR data for the bis(imino ether) complexes 11–14
(Table 3) showed that they are present in (CD3)2CO solution in
three isomeric forms, with EE, EZ and ZZ conformations of
the ligands (Chart 1 for complex 11) in approximately 8:5:1
Scheme 4 (i) 2 CH3CONH2.
Chart 1
siderable basicity of the OH bridges in 1 and 2, as expected
from the high field proton resonances. The basic character of
the hydroxo complexes [M2(C6F5)4(µ-OH)2]2Ϫ (M = Ni, Pd or
Pt) has allowed the preparation of new binuclear or mono-
nuclear complexes by reaction with the corresponding protic
electrophile (HX = azoles,24,25,42,43 β-diketones,25,26 malono-
nitrile,27 amines44 or thiols45) with the concomitant release of
water.
ratio for 11 and 12, and 12:6:1 for 13 and 14, respectively.
On leaving the mixture of 11 in solution for 1 d no change was
observed. The conformation of the imino ether ligands (E or
Z) could be assigned on the basis of the H NMR data.50 In
1
Chart 1 it is shown for complex 11 how the ortho protons of the
phenyl, or, alternatively, the methyl protons of the methoxy
group, are arranged about the palladium atom depending upon
the E or Z configuration of the imino ether ligand. As a con-
sequence of this a downfield shift is expected for the ortho pro-
tons of the phenyl group, in the case of the E conformation,
and for the methyl protons of the methoxy group, in the case of
the Z conformation. These shifts have been attributed to an
induced anisotropic paramagnetic contribution to the molecu-
lar susceptibility. The magnitude of the shift is predicted to
become greater the closer the protons approach to the
metal.51,52 Furthermore, the EZ isomer is expected to show two
resonances for the methyl protons of the methoxy groups of
equal intensities. As noted in Table 3 the chemical shift separ-
ation between the methyl protons of the methoxy group of the
EE and ZZ isomers of complex 11 is more than 1 ppm.
The hydroxo complex [Pd2(C6F5)4(µ-OH)2]2Ϫ reacts with
nitriles in methanol or ethanol to give the corresponding imino
ether derivatives 11–18 shown in Scheme 5. All these com-
In (CD ) CO the isomerization about the C᎐N double bond
᎐
3
2
is fast enough to prevent us from separating species with differ-
ent conformations of the imino ether ligands (E or Z). In fact,
redissolution in (CD3)2CO of white crystals of the EE isomer
of complex 13 grown from dichloromethane–hexane gives the
1
same H NMR spectrum with the three isomers in the same
ratio. The three isomeric forms have also been found in the
related bis(imino ether) platinum derivative cis-[PtCl {HN᎐
᎐
2
C(OMe)Ph}2], where the E conformation is preferred over Z,
though the isomerization about the C᎐N double bond was slow
᎐
enough in this case to allow separation of species with different
conformations of the imino ether ligands. The related complex
cis-[Pt(C6F5)2{HN=C(OMe)Ph}2] was found in solution as a
unique form, the EE isomer.26
The 19F NMR spectra of the imino ether derivative 15 or 16
reveal the presence of two inequivalent C6F5 groups (trans to
NH group and trans to N of the pyridine group). The same
pattern is observed for the EZ isomers of complexes 11 and 12
(the corresponding resonances for the EZ isomers of 13 and 14
are overlapped with those of the other isomers).
Scheme 5 (i) RCN/RЈOH; (ii) 2-CNpy/RЈOH; (iii) NCCH2CH2CN/
RЈOH.
pounds behave as non-electrolytes in acetone solution and their
analytical data are consistent with the proposed formulae. The
Nucleophilic attack of alcohols on nitrile complexes of
platinum or nickel in the presence of a catalytic amount of base
2942
J. Chem. Soc., Dalton Trans., 1999, 2939–2946

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Table 3 The 1H and 19F NMR data (δ, J in Hz) for the palladium complexes 11–19 (in (CD3)2CO)
Complex
1H (SiMe4)
19F (CFCl3)
11
8.73 (d, Ho, C6H5, EZ, J 7.4)
8.69 (d, Ho, C6H5, EE, J 7.4)
7.73–7.14 (other aromatics)
6.72 (br, NH)
5.01 (s, CH3O, ZZ)
4.87 (s, CH3O, EZ)
Ϫ115.8 (m, Fo, EE and EZ)
Ϫ116.6 (d, Fo, ZZ, J 24.6)
Ϫ116.9 (d, Fo, EZ, J 24.6)
Ϫ163.8 (t, Fp, EZ, J 19.8)
Ϫ164.0 (t, Fp, EZ, J 19.8)
Ϫ164.2 (t, Fp, EZ, J 19.8)
Ϫ164.4 (t, Fp, EE, J 19.8)
Ϫ166.0 (m, Fm, EE, EZ and ZZ)
Ϫ115.9 (m, Fo, EE and EZ)
Ϫ116.6 (d, Fo, ZZ, J 24.6)
Ϫ116.9 (d, Fo, EZ, J 24.6)
Ϫ164.1 (t, Fp, ZZ, J 19.8)
Ϫ164.2 (t, Fp, EZ, J 19.8)
Ϫ164.2 (t, Fp, EZ, J 19.8)
Ϫ164.4 (t, Fp, EE, J 19.8)
Ϫ166.0 (m, Fm, EE, EZ and ZZ)
4.00 (s, CH3O, EZ)
3.32 (s, CH3O, EE)
12
8.76 (d, Ho, C6H5, EZ, J 7.4)
8.65 (d, Ho, C6H5, EE, J 7.4)
7.74–7.13 (other aromatics)
6.60 (br, NH)
5.68 (q, CH2O, ZZ, J 7.0)
5.52 (q, CH2O, EZ, J 7.0)
4.28 (q, CH2O, EZ, J 7.0)
3.41 (q, CH2O, EE, J 7.0)
1.54 (t, CH3CH2O, ZZ, J 7.0)
1.48 (t, CH3CH2O, EZ, J 7.0)
1.36 (t, CH3CH2O, EZ, J 7.0)
1.16 (t, CH3CH2O, EE, J 7.0)
7.36 (br, NH)
4.49 (s, CH3O, ZZ)
4.47 (s, CH3O, EZ)
3.72 (s, CH3O, EZ and EE)
2.39 (s, CH3, EZ)
2.36 (s, CH3, EE)
2.12 (s, CH3O, EZ and ZZ)
7.28 (br, NH)
5.06 (q, CH2O, ZZ, J 7.0)
5.00 (q, CH2O, EZ, J 7.0)
4.02 (q, CH2O, EZ and EE, J 7.0)
2.37 (s, CH3, EZ)
13
14
Ϫ115.9 (m, Fo)
Ϫ164.4 (m, Fp)
Ϫ166.3 (m, Fm)
Ϫ115.9 (m, Fo)
Ϫ164.6 (m, Fp)
Ϫ166.3 (m, Fm)
2.35 (s, CH3, EE)
2.12 (s, CH3, EZ)
2.11 (s, CH3, ZZ)
1.33 (t, CH3CH2O, ZZ, J 7.0)
1.32 (t, CH3CH2O, EZ, J 7.0)
1.22 (t, CH3CH2O, EZ and EE, J 7.0)
8.34 (m, 1 H, H5)
15
16
Ϫ114.7 (d, 4 Fo, Jom 26.8)
Ϫ115.1 (d, 4 Fo, Jom 26.8)
Ϫ162.7 (t, 2 Fp, Jmp 19.5)
Ϫ163.7 (t, 2 Fp, Jmp 19.8)
Ϫ164.7 (m, 4 Fm)
Ϫ115.1 (d, 4 Fo, Jom 27.4)
Ϫ115.5 (d, 4 Fo, Jom 27.4)
Ϫ163.1 (t, 2 Fp, Jmp 19.8)
Ϫ164.1 (t, 2 Fp, Jmp 19.8)
Ϫ165.2 (m, 4 Fm)
8.17 (d, 1 H, H6, J 7.0)
8.09 (d, 1 H, H3, J 5.1)
7.82 (m, 1 H, H4)
4.20 (s, 3 H, CH3O)
8.97 (br, 2 H, NH)
8.34 (m, 1 H, H5)
8.19 (d, 1 H, H6, J 7.4)
8.09 (d, 1 H, H3, J 5.1)
7.80 (m, 1 H, H4)
4.52 (q, 4 H, CH2O, J 7.0)
1.51 (t, 6 H, CH3CH2O, J 7.0)
7.35 (br, 2 H, NH)
3.75 (s, 6 H, CH3O)
3.24 (s, 4 H, CH2)
7.27 (br, 2 H, NH)
4.04 (q, 4 H, CH2O, J 7.0)
3.24 (s, 4 H, CH2)
17
18
Ϫ116.1 (d, 4 Fo, Jom 22.9)
Ϫ164.4 (t, 2 Fp, Jmp 19.8)
Ϫ166.2 (m, 4 Fm)
Ϫ111.5 (d, 4 Fo, Jom 24.3)
Ϫ159.8 (t, 2 Fp, Jmp 19.8)
Ϫ161.7 (m, 4 Fm)
1.24 (t, 6 H, CH3CH2O, J 7.0)
19
8.03 (m, 1 H, H5)
Ϫ113.9 (m, 4 Fo)
7.95 (d, 1 H, H6, J 6.1)
7.83 (d, 1 H, H3, J 5.1)
7.44 (m, 1 H, H4)
Ϫ165.0 (t, 2 Fp, Jmp 19.8)
Ϫ165.7 (t, 2 Fp, Jmp 20.0)
Ϫ166.9 (m, 4 Fm)
4.91 (br, 1 H, NH)
3.43 (m, 8 H, NCH2)
1.80 (m, 8 H, NCH2CH2)
1.40 (m, 8 H, CH2CH3)
0.90 (m, 12 H, CH3, J 7.3)
have been described.10,11,26,53 The reaction of the previously
reported21a complex cis-[Pd(C6F5)2(PhCN)2] with methanol in
the presence of NaOMe (see Experimental section) yields the
bis(imino ether) complex 11 with isomers also in the ratio 8:5:1
(see above). This suggests that, after facile heterolysis of the
palladium hydroxo complex [(C6F5)2Pd(µ-OH)2Pd(C6F5)2]2Ϫ in
alcoholic solvents when nitrile ligands are present, outer-sphere
attack of alcohol on nitrile bound to palladium takes place in
the above reactions. The synthesis of the related methoxo-
platinum complex [(C6F5)2Pt(µ-OMe)2Pt(C6F5)2]2Ϫ by reaction
of the corresponding hydroxoplatinum complex with methanol
has also been described.43
Finally, although the reaction of the labile cis-[Pd(C6F5)2-
(PhCN)2] with NBu4OH (aq) in acetone solution is a conven-
ient route25 for the synthesis of the di-µ-hydroxo complex
[Pd2(C6F5)4(µ-OH)2]2Ϫ, and the nucleophilic attack of OHϪ on
J. Chem. Soc., Dalton Trans., 1999, 2939–2946
2943

View Article Online
Table 4 Selected distances (Å) and angles (Њ) for complex 13
distances in 13 (2.108(3), 2.108(4) Å) lie within the range
reported for Pd–N in these complexes (2.064–2.131 Å), despite
the fact that the sp2 nitrogens involved are of different types.
The only palladium iminoether complex which has previously
Pd–C(1)
Pd–C(7)
Pd–N(1)
2.001(4)
2.003(4)
2.108(3)
Pd–N(2)
N(2)–C(16)
2.108(4)
1.341(7)
been characterized is cis-[PdCl {NH᎐CCH CH CH O}(PPh )]ؒ
᎐
2
2
2
2
3
0.5CH2Cl2.14 This species contains two crystallographic in-
dependent molecules with palladium–nitrogen bond lengths
2.026(9) and 2.042(10) Å. The shorter distances here may result
from a slightly less crowded molecule, but the authors did note
that these bond lengths lay at the extreme of established Pd–
N(sp2) distances. The cyclic nature of the imino ether here
makes it difficult to compare bond lengths in the ligand with
those in 13. The C6F5 rings in 13 show typical55 distortions at
C1 and C7 with C(2)–C(1)–C(6) 114.4(4) and C(12)–C(7)–C(8)
115.0(4)Њ.
C(1)–Pd–C(7)
C(7)–Pd–N(1)
C(1)–Pd–N(2)
87.4(2)
91.4(2)
92.6(2)
N(1)–Pd–N(2)
C(13)–N(1)–Pd
C(16)–N(2)–Pd
88.68(14)
126.2(4)
125.8(4)
Experimental
The analyses (C, H, N) were performed with a Carlo Erba
model EA 1108 microanalyser. Decomposition temperatures
were determined on a Mettler TG-50 thermobalance with a
heating rate of 5 ЊC minϪ1 and the solid sample under nitrogen
flow. Conductance measurements were made with a Crison 525
conductimeter in acetone solutions (c ≈ 5 × 10Ϫ4 mol LϪ1).
Infrared spectra were recorded on a Perkin-Elmer 1430 spec-
trophotometer using Nujol mulls between polyethylene sheets,
the NMR spectra on a Bruker AC 200E or a Varian Unity 300
spectrometer, using SiMe4 and CFCl3 as standards, respec-
tively. The precursors [{Pd(C,N)(µ-OAc)}2] (C,N = o-C6H4-
28
CH2NMe2 and o-C H N᎐NPh29) and [NBu ] [Pd (C F ) -
᎐
6
4
4 2
2
6
5 4
Fig. 2 Perspective view of the molecular structure of complex 13.
(µ-OH)2]25 were prepared as described. Solvents were dried by
the usual methods.
co-ordinated benzonitrile is not detected,‡ the reaction of
[Pd2(C6F5)4(µ-OH)2]2Ϫ with 2-cyanopyridine in acetone yields
the carboxamide derivative 19 (Scheme 6). The IR spectrum
Preparations
Complexes 1 and 2. A 20% solution of NBu4OH (aq) (1.102
mmol) was added to an acetone (4 cm3) solution of the corre-
sponding di-µ-acetate complex [{Pd(C,N)(µ-OAc)}2] (0.501
mmol). After stirring at room temperature for 10 min a white
(1) or brown (2) solid was collected by filtration, washed with
acetone and water, and air dried. Complex 1: yield 90% (Found:
C, 42.0; H, 5.2; N, 5.4. C9H13NOPd requires C, 42.0; H, 5.1; N,
5.4%), mp 168 ЊC (decomp.); IR (Nujol, cmϪ1) 3560 (ν(OH)).
Complex 2: yield 98% (Found: C, 47.0; H, 3.4; N, 9.0.
C12H10N2OPd requires C, 47.3; H, 3.3; N, 9.2%), mp 162 ЊC
(decomp.); IR (Nujol, cmϪ1) 3575 (ν(OH)).
Scheme 6 (i) 2-CNpy in acetone.
shows ν(NH) and ν(C᎐O) bands at 3225 and 1630 cmϪ1, respect-
᎐
ively. An alternative iminoenol formulation is excluded by the
absence of ν(OH) bands at ca. 3500 cmϪ1. In acetone solution
19 behaves as a 1:1 electrolyte.54 Again heterolysis of the pal-
ladium hydroxo complex in the presence of the good ligand 2-
cyanopyridine might take place, and in this case nucleophilic
attack of OHϪ on co-ordinated 2-cyanopyridine is favourably
competitive.
A single isomer of complex 13 (the EE isomer), presumably
the least soluble one, could be isolated from CH2Cl2–hexane as
crystals suitable for a diffraction study. The structure is shown
in Fig. 2, and selected bond lengths and angles given in Table 4.
The co-ordination at palladium is close to square planar, with
a small deviation towards tetrahedral, and the C6F5 groups are
cis.
Complexes 3–8. On addition of the corresponding nitrile
(1.164 mmol) to a suspension of complex 1 or 2 (0.116 mmol) in
benzene (5 ml) a clear solution resulted. After boiling under
reflux for 2 h the solution was concentrated under reduced pres-
sure and the addition of hexane caused the precipitation of a
white (3, 5, 7) or dark green (4, 6, 8) solid, which was collected
by filtration and air dried. Alternatively, 3 and 4 were prepared
by addition of MeCONH2 (0.230 mmol) to a solution of 1 or 2
(0.115 mmol) in CH2Cl2 (5 cm3). After stirring at room tem-
perature for 30 min the solution was concentrated under
reduced pressure and addition of hexane caused the precipit-
ation of a solid, which was collected by filtration, washed with
water and air dried (75–80% yield). Complex 3: yield 80%
(Found: C, 44.5; H, 5.6; N, 9.5. C11H16N2OPd requires C, 44.3;
H, 5.4; N, 9.4%), mp 197 ЊC (decomp.); IR (Nujol, cmϪ1) 3340,
The structures of a small number of {(C6F5)2PdN2} moieties
have been previously determined. The Pd–C bond lengths in
complex 13, 2.001(4) and 2.003(4) Å, are quite similar to those
in [Pd(C6F5)2(terpy)]55 (2.011(7) and 1.994(7) Å), [Pd(C6F5)2-
3300 (ν(NH)), 1570 (ν(C᎐O)). Complex 4: yield 70% (Found: C,
᎐
48.2; H, 3.6; N, 11.9. C14H13N3OPd requires C, 48.6; H, 3.8; N,
{PhP(᎐O)C H N-2} ]ؒ2CHCl (2.015(4), 2.010(3) Å)56 and
12.2%), mp 201 ЊC (decomp.); IR (Nujol, cmϪ1) 3380, 3295
᎐
5
4
2
3
[NBu4][Pd(C6F5)2(pz ؒ ؒ ؒ H ؒ ؒ ؒ pz)].46 The palladium–nitrogen
(ν(NH)), 1570 (ν(C᎐O)). Complex 5: yield 60% (Found: C, 53.1;
᎐
H, 4.9; N, 8.0. C16H18N2OPd requires C, 53.3; H, 5.0; N, 7.8%),
mp 215 ЊC (decomp.); IR (Nujol, cmϪ1) 3390, 3370 (ν(NH)),
‡ When a mixture of benzonitrile (0.714 mol) and [NBu4]2[Pd2(C6F5)4-
(µ-OH)2] (0.074 mol) was boiled under reflux in benzene (12 ml) for
2 h the solid recovered by precipitation with hexane was identified as
unchanged [NBu4]2[Pd2(C6F5)4(µ-OH)2] (0.043 mol).
1600 (ν(C᎐O)). Complex 6: yield 65% (Found: C, 55.2; H, 3.9;
᎐
N, 10.0. C19H18N3OPd requires C, 56.0; H, 3.7; N, 10.3%), mp
251 ЊC (decomp.); IR (Nujol, cmϪ1) 3340 (ν(NH)), 1570
2944
J. Chem. Soc., Dalton Trans., 1999, 2939–2946

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Table 5 Crystal data and structure refinement for complexes 5 and 13
5
13
Formula
Formula weight
C32H36N4O2Pd2
721.5
C18H14F10N2O2Pd
584.7
Crystal system
Space group
a/Å
b/Å
Monoclinic
P21/c (no. 14)
15.487(2)
10.811(4)
18.249(3)
91.540(10)
3054.3(13)
4
Monoclinic
P21/n (non-standard no. 14)
9.243(3)
14.634(6)
15.865(3)
94.71(2)
2138.7(12)
4
c/Å
β/Њ
V/Å3
Z
T/K
293
9161
1.21
293
6541
0.97
Reflections collected
µ/mmϪ1
Independent reflections
Final R1, wR2 [I > 2σ(I)]
(all data)
8875 [R(int) = 0.0250]
0.040, 0.088
0.070, 0.103
6204 [R(int) = 0.0219]
0.047, 0.101
0.089, 0.121
(ν(C᎐O)); 1H NMR (CDCl ) δ 7.6–6.6 (m, 28 H, aromatics) and
(ν(NH)), 1645 (ν(C᎐N)), 795, 785 (Pd–C F ). Complex 17: yield
᎐
6 5
᎐
3
5.91 (s, 2 H, NH). Complex 7: yield 69% (Found: C, 46.3; H, 5.0;
N, 9.0. C12H16N2OPd requires C, 46.4; H, 5.2; N, 9.0%); mp
173 ЊC (decomp.); IR (Nujol, cmϪ1) 3360, 3305 (ν(NH)), 1640
89% (Found: C, 37.0; H, 1.9; N, 4.7. C18H12F10N2O2Pd requires
C, 37.0; H, 2.1; N, 4.8%), mp 213 ЊC (decomp.); IR (Nujol,
cmϪ1) 3365 (ν(NH)), 1665 (ν(C᎐N)), 795, 780 (Pd–C F ). Com-
᎐
6
5
(ν(C᎐C)), 1565 (ν(C᎐O)). Complex 8: yield 65% (Found: C,
plex 18: yield 73% (Found: C, 39.4; H, 3.0; N, 4.7. C20H16F10-
᎐
᎐
50.2; H, 3.6; N, 11.6. C15H13N3OPd requires C, 50.4; H, 3.7; N,
N2O2Pd requires C, 39.2; H, 2.6; N, 4.6%), mp 208 ЊC
11.7%), mp 194 ЊC (decomp.); IR (Nujol, cmϪ1) 3270 (ν(NH)),
(decomp.); IR (Nujol, cmϪ1
) 3380, 3340 (ν(NH)), 1660
1635 (ν(C᎐C)), 1560 (ν(C᎐O)).
(ν(C᎐N)), 790, 780 (Pd–C F ).
᎐
6 5
᎐
᎐
Reaction of [Pd(C6F5)2(NCPh)2] with NaOMe. To a solution
of [Pd(C6F5)2(NCPh)2] (100 mg, 0.155 mmol) in MeOH (8 mL)
was added Na[OMe] (83.7 mg, 1.55 mmol). The resulting solu-
tion was stirred at room temperature for 4 h and concentrated
under vacuum. The addition of water caused the precipitation
of a white solid which was collected by filtration, washed with
water and hexane, air-dried, and characterized as complex 11
(yield 59%).
Complexes 9 and 10. To a suspension of complex 1 or 2 (0.116
mmol) in benzene (5 cm3) was added succinonitrile (1.164
mmol). The solution was boiled under reflux for 3 h, and then
concentrated to dryness under reduced pressure. Addition of
acetone–water (9) or MeOH (10) yielded a white (9) or red (10)
solid which was collected by filtration and air dried. Complex 9:
yield 73% (Found: C, 44.4; H, 4.9; N, 9.5. C13H18N3O2Pd
requires C, 44.4; H, 5.1; N, 9.4%), mp 275 ЊC (decomp.); IR
(Nujol, cmϪ1) 3355, 3250 (ν(NH)), 1580 (ν(C᎐O)). Complex 10:
᎐
Complex 19. 2-Cyanopyridine (14.87 mg, 0.1428 mmol) was
added to a solution of [NBu4][(C6F5)2Pd(µ-OH)2Pd(C6F5)2] (0.1
g, 0.0714 mmol) in acetone (8 mL). The solution was stirred at
room temperature. The solution was concentrated under
vacuum to dryness. The residue was then treated with diethyl
ether (6 mL) and the yellow complex was collected by filtration
and air-dried. Yield 94% (Found: C, 50.9; H, 5.0; N, 5.1.
C34H41F10N2O2Pd requires C, 50.8; H, 5.1; N, 5.2%), mp 267 ЊC
yield 43% (Found: C, 48.6; H, 3.6; N, 12.3. C16H15N4O2Pd
requires C, 48.8; H, 3.5; N, 12.2%), mp 275 ЊC (decomp.); IR
(Nujol, cmϪ1) 3250 (ν(NH)), 1560 (ν(C᎐O)).
᎐
Complexes 11–18. The appropriate nitrile RCN (benzonitrile
or acetonitrile, 7.14 mmol; 2-cyanopyridine or succinonitrile,
0.1428 mmol) was added to a solution of [NBu4][(C6F5)2-
Pd(µ-OH)2Pd(C6F5)2] (0.1 g, 0.0714 mmol) in methanol or
ethanol (8 mL). The solution was stirred at room temperature
for 2 h. After addition of dichloromethane (15 mL) the solution
was chromatographed on Florisil and the resulting solution was
concentrated under vacuum. On addition of water the white
complexes 11–18 precipitated, were collected by filtration, and
air-dried. Complex 11: yield 79% (Found: C, 47.7; H, 2.4; N,
4.0. C28H18F10N2O2Pd requires C, 47.3; H, 2.6; N, 3.9%), mp
180 ЊC (decomp.); IR (Nujol, cmϪ1) 3355 (ν(NH)), 1640
(decomp.); IR (Nujol, cmϪ1) 3225 (ν(NH)), 1630 (ν(C᎐O)),
᎐
795, 780 (Pd–C6F5).
Crystallography
Crystals of complexes 5 and 13 suitable for diffraction studies
were grown from dichloromethane–hexane. Single crystals of 5
(approximate dimensions 0.35 × 0.20 × 0.20) and 13 (0.25 ×
0.25 × 0.10) were mounted on an Enraf-Nonius CAD4
diffractometer equipped with a graphite monochromator for
Mo-Kα radiation. Details of data collection and refinement are
given in Table 5.
(ν(C᎐N)), 800, 780 (Pd–C F ). Complex 12: yield 76% (Found:
᎐
6
5
C, 48.7; H, 2.9; N, 3.8. C30H22F10N2O2Pd requires C, 48.8; H,
3.0; N, 3.8%), mp 180 ЊC (decomp.); IR (Nujol, cmϪ1) 3360
(ν(NH)), 1630 (ν(C᎐N)), 795, 780 (Pd–C F ). Complex 13: yield
75% (Found: C, 37.0; H, 2.3; N, 4.9. C18H14F10N2O2Pd requires
Accurate cell parameters were determined by least-squares
fitting of 25 high-angle reflections. Empirical Ψ scans absorp-
tion correction was made for complex 13. The structures were
refined by the full-matrix least-squares technique. For 5 all
non-H atoms were refined anisotropically. The H atoms were
included in riding mode with Uiso(H) = 1.2Ueq(C) or 1.5Ueq(C)
for methyl groups. For 13 all non-H atoms were refined aniso-
tropically, methyl groups were fixed at idealized geometry but
with the torsion angle defining the H atom positions refined
and Uiso(H) = 1.2Ueq(C).
᎐
6
5
C, 36.9; H, 2.4; N, 4.8%), mp 168 ЊC (decomp.); IR (Nujol,
cmϪ1) 3370 (ν(NH)), 1650 (ν(C᎐N)), 790, 780 (Pd–C F ). Com-
᎐
6
5
plex 14: yield 72% (Found: C, 39.3; H, 2.8; N, 4.7. C20H18F10-
N2O2Pd requires C, 39.1; H, 3.0; N, 4.6%), mp 186 ЊC
(decomp.); IR (Nujol, cmϪ1) 3360 (ν(NH)), 1650 (ν(C᎐N)),
᎐
795, 785 (Pd–C6F5). Complex 15: yield 90% (Found: C, 39.5; H,
1.3; N, 4.8. C19H8F10N2O2Pd requires C, 39.6; H, 1.4; N, 4.9%),
mp 252 ЊC (decomp.); IR (Nujol, cmϪ1) 3370 (ν(NH)), 1645
(ν(C᎐N)), 795, 785 (Pd–C F ). Complex 16: yield 57% (Found:
The largest difference peak and hole were 0.41 and Ϫ0.96
᎐
6
5
C, 40.9; H, 1.8; N, 4.7. C20H10F10N2O2Pd requires C, 40.7; H,
e ÅϪ3 for complex 5; in the case of 13 they were 0.74 and
1.7; N, 4.7%), mp 263 ЊC (decomp.); IR (Nujol, cmϪ1) 3395
Ϫ0.50 e ÅϪ3
.
J. Chem. Soc., Dalton Trans., 1999, 2939–2946
2945

View Article Online
25 G. López, J. Ruiz, G. García, C. Vicente, J. Casabó, E. Molins and
Programs used were Enraf-Nonius CAD 4 software for data
collection,57 SHELXS 86 for structure solution,58 SHELXL 93
for structure refinement,59 and CAMERON for interactive
graphics and final drawings.60
CCDC reference number 186/1574.
See http://www.rsc.org/suppdata/dt/1999/2939/ for crystallo-
graphic files in .cif format.
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Acknowledgements
Financial support from the Dirección General de Investigación
Científica y Técnica (project PB97-1036), Spain, is gratefully
acknowledged. V. R. thanks CajaMurcia, Spain, for a research
grant.
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Paper 9/03262B
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