New aryloxo allylpalladium complexes

Article abstract of DOI:10.1016/S0277-5387(99)00105-9

Treatment of the di-μ-chloride allyl palladium complex [(η³-C₄H₇)Pd(μ-Cl) ₂Pd(η³-C₄H₇)] with [NBu₄]OH (1:2 molar ratio) in methanol, followed by addition of phenol or

Full text of DOI:10.1016/S0277-5387(99)00105-9

Polyhedron 18 (1999 2281–2285
New aryloxo allylpalladium complexes
*
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´
´
´
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Jose Ruiz, Jose M. Martı, Felix Florenciano, Gregorio Lopez
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Departamento de Quımica Inorganica, Universidad de Murcia, 30071 Murcia, Spain
Received 1 March 1999; accepted 20 April 1999
Abstract
Treatment of the di-m-chloride allyl palladium complex [(h3-C4H7)Pd(m-Cl)2Pd(h3-C4H7)] with [NBu4]OH (1:2 molar ratio) in
methanol, followed by addition of phenol or para-substituted phenol ArOH (1:2 molar ratio), allows the preparation of dimeric aryloxo
complexes of the type [(h3-C4H7)Pd(m-OAr)2Pd(h3-C4H7)] (Ar5Ph 1, C6H4Me-p 2, C6H4Cl-p 3, C6H4Br-p 4). The addition of
p-nitrophenol or pentafluorophenol to complex 1 results in quantitative substitution of the phenoxide anion to give the di-m-aryloxo
palladium complexes [(h3-C4H7)Pd(m -OAr)2Pd(h3-C4H7)] (Ar5C6H4NO2-p 5 or C6F5 6). Complexes 1, 5 and 6 react with PPh3 to
give the monomeric aryloxo complexes [(h3-C4H7)Pd(OAr)(PPh3)] (Ar5Ph 7, C6H4NO2-p 8, C6F5 9). The identity of these complexes
has been established by partial elemental analyses and NMR (1H, 19F, 13C and 31P) spectroscopy.
rights reserved.
1999 Elsevier Science Ltd. All
Keywords: Palladium; Aryloxo complexes; Allyl complexes
1. Introduction
type [NBu4]2[hM(C6F5)2(m-OR)j2] (M5Ni, Pd or Pt)
[22–26] and mononuclear aryloxo metal complexes of the
type [NBu4][hM(C6F5)2(OAr)L] (M5Pd, L5PPh3; Pt, L5
PPh3, CO) [26], which have been used as intermediates for
the synthesis of other transition-metal complexes [27,28].
In this paper we describe an easy route for the synthesis of
a number of di-m-aryloxo allylpalladium complexes and
their reactivity towards the neutral ligand triphenylphos-
phine. The synthesis of the related dinuclear allylnickel
aryloxides has been reported recently [29].
The role of h3-allylpalladium compounds in several
palladium-catalysed organic syntheses is now well estab-
lished [1–5]. The chemistry of late transition metal alkox-
ides or aryloxides [6] is recently attracting growing
attention partly because of their relevance to organic
synthesis where late-transition-metal alkoxides are
believed to be involved [4,7,8] and partly because of their
recently discovered unique chemical reactivities such as
CO insertion into metal alkoxide bonds [9–12] and adduct
formation with alcohols through strong hydrogen bonding
[13–20]. Unfortunately, the synthesis and reactivity of
palladium and platinum alkoxide and aryloxide complexes
have been little explored, probably because it was thought
that Pd–O and Pt–O bonds would be weak due to an
unfavorable interaction between the ‘hard’ alkoxide ligand
and the ‘soft’ metal centre [21]. The thermochemical
studies of Bryndza and Bercaw have shown that this is a
misconception [6,11].
2. Experimental
The C, H, N analyses were performed with a Carlo Erba
model EA 1108 microanalyzer. Decomposition tempera-
tures were determined with a Mettler TG-50 thermobal-
ance at a heating rate of 58C min21 and the solid sample
under nitrogen flow (100 ml min21). The 1H, 19F and
31P-NMR spectra were recorded on a Bruker AC 200E or
Varian Unity 300 spectrometer, using SiMe4, CFCl3 and
H3PO4 as standards, respectively. Infrared spectra were
recorded on a Perkin–Elmer 16F PC FT–IR spec-
trophotometer using Nujol mulls between polyethylene
sheets. Solvents were dried by the usual methods. The
We have recently reported on the syntheses of binuclear
hydroxo-, methoxo- and aryloxo-metal complexes of the
*Corresponding author. Fax: 134-68-364-148.
E-mail address: gll@fcu.um.es (G. Lopez)
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0277-5387/99/$ – see front matter
PII: S0277-5387(99)00105-9
1999 Elsevier Science Ltd. All rights reserved.

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J. Ruiz et al. / Polyhedron 18 (1999) 2281–2285
starting complex [(h3-allyl)Pd(m-Cl)2Pd(h3-allyl)] (allyl5
C4H7) was prepared by the procedure described elsewhere
[30].
constant stirring at room temperature for 30 min to afford a
suspension from which solvent was partially evaporated
under reduced pressure. The yellow (5) or white (6) solids
were filtered off and air-dried. complex 5: Yield 80%. M.p.
1248C (dec). IR (Nujol, cm21) 1288 n(C–O). Anal. Calcd.
for C20H22N2O6Pd2: C, 40.1; H, 3.7; N, 4.7. Found: C,
39.8; H, 3.7; N, 4.7. Complex 6: Yield 60%. M.p. 1008C
(dec). IR (Nujol, cm21) 1348 n(C–O). Anal. calcd. for
C20H14F10O2Pd2: C, 34.8; H, 2.1. Found: C, 34.7; H, 2.0.
2.1. Preparation of the complexes
2.1.1. Complexes 1–4
To a suspension of the di-m-chloride allyl complex
[(h3-C4H7)Pd(m-Cl)2Pd(h3-C4H7)] (100 mg, 0.25 mmol)
in methanol (9 cm3) was added 20% [NBu4]OH (aq) (0.67
cm3, 0.51 mmol) to yield a yellow solution to which the
corresponding phenol ArOH (0.51 mmol) was added, with
constant stirring at room temperature for 1 h. After partial
evaporation of the solvent under reduced pressure, addition
of water caused the precipitation of yellowish solids which
were filtered-off and air-dried. Complex 1: Yield 85%;
m.p. 1178C (dec). IR (Nujol, cm21) 1258 n(C–O). Anal.
Calcd. for C20H24O2Pd2: C, 47.2; H, 4.8. Found: C, 46.8;
H, 4.7. Complex 2: Yield 79%. M.p. 1108C (dec). IR
2.1.3. Complexes 7–9
To a solution of [(h3-C4H7)Pd(m-OAr)2Pd(h3-C4H7)]
(Ar5C6H5, p-NO2C6H4 or C6F5) (0.17 mmol) in di-
chloromethane (15 cm3) was added triphenylphosphine
PPh3 (90 mg, 0.34 mmol) with stirring at room tempera-
ture for 1 h to yield an orange solution. The solvent was
completely evaporated under vacuum and the residue
treated with hexane, then filtered off and air-dried. Com-
plex 7: Yield 61%. M.p. 1088C (dec). IR (Nujol, cm21
)
(Nujol, cm21
)
1251 n(C–O). Anal. Calcd. for
1298 n(C–O). Anal. Calcd. for C28H27OPPd: C, 65.1; H,
5.3. Found: C, 64.7; H, 5.3. Complex 8: Yield 90%. M.p.
131 8C (dec). IR (Nujol, cm21) 1296 n(C–O). Anal.
Calcd. for C28H26NO3PPd: C, 59.9; H, 2.5; N, 4.7. Found:
C, 59.6; H, 2.4; N, 4.6. Complex 9: Yield 80%. M.p. 119
8C (dec). IR (Nujol, cm21) 1302 n(C–O). Anal. Calcd. for
C28H22F5OPPd: C, 55.4; H, 3.7. Found: C, 55.7; H, 3.5.
C22H28O2Pd2: C, 49.2; H, 5.3. Found: C, 48.8; H, 5.4.
Complex 3: Yield 83%. M.p. 1278C (dec). IR (Nujol,
cm21) 1254 n(C–O). Anal. Calcd. for C20H22Cl2O2Pd2:
C, 41.5; H, 3.8. Found: C, 41.1; H, 3.6. Complex 4: Yield
89%. M.p. 1108C (dec). IR (Nujol, cm21) 1256 n(C–O).
Anal. Calcd. for C20H22Br2O2Pd2: C, 36.0; H, 3.3. Found:
C, 36.0; H, 3.3.
2.1.2. Complexes 5 and 6
3. Results and discussion
To
a
solution of [(h3-C4H7)Pd(m-OC6H5)2Pd(h3-
C4H7)] (200 mg, 0.39 mmol) in methanol (20 cm3) was
Treatment of a suspension of the di-m-chloride allylpal-
ladium complex [(h3-C4H7)Pd(m-Cl)2Pd(h3-C4H7)] in
added p-NO2C6H4OH or C6F5OH (0.79 mmol) with
Scheme 1.

J. Ruiz et al. / Polyhedron 18 (1999) 2281–2285
2283
Table 1
1H, 19F and 31P NMR dataa (J in Hz) for the palladium complexes (in CDCl3)
Complex
1H d (SiMe4)
19F d (CFCl3)
31P d (H3PO4)
1
7.07 (pseudotriplet, 4 H, Hm, J 7.5)
6.91 (d, 4 H, Ho, J 7.5)
6.63 (t, 2 H, Hp, J 7.5)
3.18 (s, 4 H, Hsyn
)
2.52 (s, 4 H, Hanti
)
2.12 (s, 6 H, CH3)
2
3
4
5
6.81 (m, 8 H, Ho1Hm)
3.15 (s, 4 H, Hsyn
)
2.50 (s, 4 H, Hanti
)
2.21 (s, 6 H, CH3 allyl)
2.11 (s, 6 H, CH3 of ArO)
6.90 (d, 4 H, Hm, J 8.8)
6.82 (d, 4 H, Ho, J 8.8)
3.16 (s, 4 H, Hsyn
)
2.52 (s, 4 H, Hanti
)
2.12 (s, 6 H, CH3)
7.13 (d, 4 H, Hm, J 8.4)
6.77 (d, 4 H, Ho, J 8.4)
3.15 (s, 4 H, Hsyn)
2.51 (s, 4 H, Hanti
)
2.11 (s, 6 H, CH3)
8.03 (d, 4 H, Hm, J 8.9)
6.82 (d, 4 H, Ho, J 8.9)
3.37 (s, 4 H, Hsyn
)
2.62 (s, 4 H, Hanti
)
2.15 (s, 6 H, CH3)
3.06 (s, 4 H, Hsyn
2.40(s, 4 H, Hanti
2.10 (s, 6 H, CH3)
7.36 (m, 15 H, PPh3)
6.95 (m, 2 H, Hm)
6
7
)
)
2161.0 (d, 4 Fo, J 18.3)
2167.1 (m, 4 Fm)
2175.1 (t, 2 Fp, J 21.4)
23.67 (s)
6.66 (m, 2 H, Ho)
6.40 (m, 1 H, Hp)
4.39 (dd, 1 H, Hd, JdP 6.3, Jad 2.4)
3.64 (d, 1 H, Hc, JcP 9.6)
2.72 (d, 1 H, Ha, Jad 2.4)
2.47 (s, 1 H, Hb)
2.05 (s, 6 H, CH3)
8
7.79 (d, 2 H, Hm, J 9.0)
7.31 (m, 15 H, PPh3)
6.32 (d, 2 H, Ho, J 9.0)
4.38 (dd, 1 H, Hd, JdP 6.3, Jad 2.4)
3.61 (d, 1 H, Hc, JcP 9.9)
2.84 (d, 1 H, Ha, Jad 2.4)
2.56 (s, 1 H, Hb)
25.35 (s)
2.04 (s, 6 H, CH3)
9
7.37 (m, 15 H, PPh3)
4.38 (dd, 1 H, Hd, JdP 6.3, Jad 2.4)
3.71 (d, 1 H, Hc, JcP 9.6)
2.71 (d, 1 H, Ha, Jad 2.4)
2.55 (s, 1 H, Hb)
2167.7 (m, 2 Fo)
2170.2 (m, 2Fm)
2183.9 (m, 1 Fp)
24.56 (s)
2.06 (s, 6 H, CH3)
a Chemical shifts from TMS (1H), from CFCl3
doublets. Assignments:
( (
19F) or from H3PO4 31P). Abbreviations: s, singlet; d, doublet; t, triplet; m, multiplet; dd, doublet of

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J. Ruiz et al. / Polyhedron 18 (1999) 2281–2285
methanol with 20% [NBu4]OH(aq) (in 1:2 molar ratio),
which gives a yellow solution, followed by addition of
phenol or p-substituted phenol ArOH (1:2 molar ratio)
allows the preparation of the corresponding dimeric
aryloxo complexes 1–4 shown in Scheme 1. Complexes
1–4 were all obtained as yellowish precipitates by addition
of water. This formal metathesis reaction of Cl2 by ArO2
presumably implies the initial formation of a di-m-
methoxo and/or hydroxo palladium complex [31] that then
reacts with ArOH to yield the corresponding aryloxo
complex with the concomitant release of methanol.
In reactions with the stronger acids p-nitrophenol (pKa5
7.3) or pentafluorophenol (pKa55.5) [19,30] in 1:2 molar
ratio in methanol, complex 1 undergoes quantitative substi-
tution of the phenoxide anion (pKa59.9 for phenol) for
p-NO2C6H4O2 or C6F5O2 to afford the palladium com-
plexes 5 or 6 (Scheme 1).
Partial elemental analyses, yields and decomposition
temperatures of complexes 1–6 are shown in the Ex-
perimental section. The 1H-NMR spectra of the dimeric
complexes 1–6 (Table 1) at room temperature indicate that
they exist in solution as a unique isomer with only one set
of resonances for the methylallyl group, i.e. three singlet
resonances with the expected intensity ratio of 2:2:3
(mixtures of cis and trans isomers, depending on the
arrangements of allyl groups with respect to each other,
have been reported for the related aryloxo nickel complex-
es [Ni2(h3-allyl)2(m-OAr)2] [29] and thiolato palladium
complexes [hPd(h3-allyl)(m-SAr)j2] [32]). The anti
-protons of the terminal CH2 group are most shielded, and
no geminal coupling between the syn -periplanar and the
Scheme 2.
added to a CDCl3 solution of complex 7 in the NMR tube
(1:1 molar ratio) the following NMR data were obtained:
(i) H, d 7.6–6.8 (very complex multiplet, aromatic), 5.04
(s, 1H, CH25), 4.93 (s, 1H, CH25), 4.38 (s, 2H, -CH2-)
and 1.77 (s, 3H, Me), assigned to CH25C(Me)-CH2-OPh;
(ii) 13C: d 141.0 (C Me), 112.5 (CH25), 71.6 (-CH2-) and
19.3 (Me), in accordance with the signals of a genuine
sample of CH25C(Me)-CH2-OPh [35]; (iii) no signal
1
assignable
to
the
parent
compound
[(h3-
1
anti-periplanar protons is observed. The H-NMR spectra
C4H7)Pd(OPh)(PPh3)] 7 was observed in the 31P-NMR
spectrum, but three new resonances were found at d 32.6,
29.1 and 28.6 which may be attributed to Pd(0)–PPh3
complexes (metallic palladium was not formed in the NMR
tube). These results are summarized in Scheme 3; in the
presence of added PPh3 the reductive elimination of allyl
phenyl ether occurs with the concomitant formation of
Pd–PPh3 complex.
of complexes 1–5 (and the 19F NMR spectrum of complex
6) also show one set of sharp resonances from the two
m-aryloxide ligands (Table 1).
The reaction of the dimeric complexes 1, 5 and 6 with
triphenylphosphine (1:2 molar ratio) in dichloromethane
yields the monomeric aryloxo palladium complexes 7–9
shown in Scheme 2. The related complex [Pd(h3-
C3H5)(OC6H4CN-p)(PCy3)] was prepared by Yamamoto
et al. by oxidative addition of the allyl ether CH25
CHCH2OC6H4CN to Pd(PCy3)2 [33].
The 1H NMR spectra of complexes 7–9 (Table 1)
indicate that the h3-ligand is rigid at room temperature as
they show a unique set of four resonances of equal
intensities for the allylic protons Ha, Hb, Hc and Hd (see
Table 1 for the allyl proton assignments) with a spin–spin
coupling pattern which is the same as that observed for the
chloride complex [(h3-C4H7)PdCl(PPh3)] [34], where
nuclei trans to PPh3 (Hd and Hc) are coupled to 31P. The
31Ph1Hj-NMR spectra of 7–9 show a singlet resonance
(Table 1). The 13C NMR data for complexes 1–9 are
shown in Table 2.
It is well known that monomeric complexes of the type
[(h3-C4H7)PdX(PPh3)] react with nucleophiles to afford
the corresponding allylated product [33]. When PPh3 was
Scheme 3.

J. Ruiz et al. / Polyhedron 18 (1999) 2281–2285
2285
Table 2
13C NMR data for the palladium complexes (in CDCl3)
Complex
ipso-C
m-C
C Me
o-C
p-C
CH2
CH3
o-C
p-C
m-C
Me
(OAr)
(OAr)
(C4H7)
(OAr)
(OAr)
(C4H7)
(C4H7)
(PPh3)
(PPh3)
(PPh3)
(OAr)
1
2
3
4
5
6
7
8
9
165.8
168.1
174.2
174.1
128.6
129.0
131.2
131.2
124.8
124.7
125.2
128.6
125.1
127.0
125.1
122.1
126.0
119.7
119.4
121.4
125.2
117.4
126.4
128.6
121.4
56.0
55.9
56.2
56.2
57.1
55.6
54.8
54.6
53.0
22.9
20.5
22.9
22.9
22.4
22.4
23.3
23.5
23.2
20.5
169.2
125.8
124.8
119.5
a
a
a
a
a
a
a
128.2
119.4
117.4
133.7 (d)
133.8 (d)
133.7 (d)
130.6
130.6
130.6
128.6 (d)
128.6 (d)
128.6 (d)
126.4
119.4
125.2
a
a
a
a Not observed.
[18] Y.-J. Kim, J.-C. Choi, K. Osakada, J. Organomet. Chem. 491 (1995)
97.
Acknowledgements
[19] P.L. Alsters, P.J. Baesjou, M.D. Janssen, H. Kooijman, A. Sicherer-
Roetman, A.L. Spekand, G. van Koten, Organometallics 11 (1992)
4142.
Financial support from the DGICYT (project PB97-
1036), Spain, is grateful acknowledged. J.M.M. and F.F.
´
thank the Fundacion ONCE of Spain and the University of
[20] G.M. Kapteijn, A. Dervisi, D.M. Grove, H. Kooijman, M.T. Lakin,
A.L. Spek, G. van Koten, J. Am. Chem. Soc. 117 (1995) 1039.
[21] R.G. Bergman, Polyhedron 14 (1995) 3277.
Murcia, respectively, for a research grant.
´
´
´
´
[22] G. Lopez, G. Garcıa, G. Sanchez, J. Garcıa, J. Ruiz, J.A. Hermoso,
´
A. Vegas, M. Martınez-Ripoll, Inorg. Chem. 31 (1992) 1518.
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