Preparation and reactions of palladium(0)-olefin complexes with iminophosphine ligands

Article abstract of DOI:10.1016/S0022-328X(98)00472-0

The complexes [Pd(η²-ol){o-(Ph₂P)-C₆H₄-CH=NR}] [ol, dimethyl fumarate (dmf), 1,4-naphtoquinone (nq), fumaronitrile (fn); R=C₆H₄OMe-4, CMe₃, Me, bornyl] can be prepared in good yields from the reaction of the allyl derivatives [Pd(η³-C₃H₅) {o-(Ph₂P)-C₆H₄-CH=NR}]BF₄ with an excess of NHEt₂ in the presence of the activated olefin ol. The complex [Pd(η²-ma){o-(Ph₂P)-C₆H₄-CH=NC₆H₄OMe-4}] (ma, maleic anhydride) is more conveniently obtained via olefin substitution from [Pd(η²-dmf){o-(Ph₂P)-C₆H₄-CH=NC₆H₄OMe-4}]. The α-diimine ligand of [Pd(η²-fn)(py-2-CH=NC₆H₄OMe-4)] is quantitatively displaced by the appropriate iminophosphine to give [Pd(η²-fn){o-(Ph₂P)-C₆H₄-CH=NC₆H₄OMe-4}]. The new zerovalent complexes with P-N ligands are characterized by multinuclear NMR spectroscopy. In solution, olefin rotation or olefin exchange are generally slow. The compound [Pd(η²-fn){o-(Ph₂P)-C₆H₄-CH=NC₆H₄OMe-4}] reacts with a second molecule of iminophosphine yielding [Pd(η²-fn){o-(Ph₂P)-C₆H₄-CH=NC₆H₄OMe-4}₂] in which the iminophosphines act essentially as P-monodentate ligands. [Pd(η²-dmf) {o-(Ph₂P)-C₆H₄-CH=NC₆H₄OM e-4}] undergoes fast oxidative addition of allyl chloride to [Pd(η³-C₃H₅){o-(Ph₂P)-C₆H₄-CH=NC₆H₄OMe-4}]⁺.

Full text of DOI:10.1016/S0022-328X(98)00472-0

Journal of Organometallic Chemistry 560 (1998) 137–146
Preparation and reactions of palladium(0)–olefin complexes with
iminophosphine ligands
Simonetta Antonaroli, Bruno Crociani *
Dipartimento di Scienze e Tecnologie Chimiche, Uni6ersita’ di Roma ‘Tor Vergata’, Via della Ricerca Scientifica, 00133 Roma, Italy
Received 26 November 1997
Abstract
The complexes [Pd(p2-ol){o-(Ph2P)–C6H4–CHꢀNR}] [ol, dimethyl fumarate (dmf), 1,4-naphtoquinone (nq), fumaronitrile ( fn);
R=C6H4OMe-4, CMe3, Me, bornyl] can be prepared in good yields from the reaction of the allyl derivatives [Pd(p3-C3H5)-
{o-(Ph2P)–C6H4–CHꢀNR}]BF4 with an excess of NHEt2 in the presence of the activated olefin ol. The complex [Pd(p2-ma){o-
(Ph2P)–C6H4-CHꢀNC6H4OMe-4}] (ma, maleic anhydride) is more conveniently obtained via olefin substitution from [Pd(p2-
dmf){o-(Ph2P)–C6H4–CHꢀNC6H4OMe-4}]. The h-diimine ligand of [Pd(p2-fn)(py-2-CHꢀNC6H4OMe-4)] is quantitatively
displaced by the appropriate iminophosphine to give [Pd(p2-fn){o-(Ph2P)–C6H4–CHꢀNC6H4OMe-4}]. The new zerovalent
complexes with P–N ligands are characterized by multinuclear NMR spectroscopy. In solution, olefin rotation or olefin exchange
are generally slow. The compound [Pd(p2-fn){o-(Ph2P)–C6H4–CHꢀNC6H4OMe-4}] reacts with a second molecule of iminophos-
phine yielding [Pd(p2-fn){o-(Ph2P)–C6H4–CHꢀNC6H4OMe-4}2] in which the iminophosphines act essentially as P-monodentate
ligands. [Pd(p2-dmf) {o-(Ph2P)–C6H4–CHꢀNC6H4OMe-4}] undergoes fast oxidative addition of allyl chloride to [Pd(p3-C3H5){o-
(Ph2P)–C6H4–CHꢀNC6H4OMe-4}]+. © 1998 Elsevier Science S.A. All rights reserved.
Keywords: Palladium; Alkene complexes; Olefin rotation; Oxidation addition
1. Introduction
(R=H, Me; ol=dimethyl fumarate, fumaronitrile,
maleic anhydride) which involves a phenyl transfer
from BPh4− to the allyl group to form allylbenzenes
and the palladium(0)-olefin derivative [3]. This is a
particular case of the general tendency of cationic allyl-
palladium(II) complexes to undergo nucleophilic attack
by a large variety of nucleophiles, thereby yielding
substituted allyl products and palladium(0) species,
which may be stabilized by coordination of a y-accept-
ing olefin, as in reaction (1), or may be reoxidized to
the starting cationic compounds in the presence of
allylic halides or esters, as in the palladium-catalyzed
allylic substitutions [4].
The complexes [M(p2-ol)(NꢁN%)] (M, Pd or Pt; ol,
olefin; NꢁN%, bidentate nitrogen-donor ligand of the
h-diimine type, such as 1,2-bis(imino)ethanes, 2-(imi-
nomethyl)pyridines, 2,2-bipyridines, 1,10-phenanthroli-
nes, bis(arylimino)acenaphtenes and bis(phenylimino)
camphane) are generally prepared from olefinic zerova-
lent precursors via displacement reactions with the ap-
propriate ligands [1,2]. If this appears to be the best
synthetic route for [Pt(p2-ol)(N–N%)] ([1]c), [2], many
palladium analogs can be also prepared by reaction (1):
[Pd(p3-2-RC3H4)(N–N%)]+
In order to extend the synthetic application of nucle-
ophilic attack on allyl palladium(II) substrates, we re-
port herein the preparation of the complexes [Pd(p2-ol)
(P–N)] (P–N, bidentate iminophosphine ligand of
the N-(2-(diphenylphosphino)benzylidene)amine type),
+ol
+BPh4 “ [Pd(p2-ol)(N–N%)]+PhCH2CRꢀCH2
−
−BPh
3
(1)
* Corresponding author.
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00472-0

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S. Antonaroli, B. Crociani / Journal of Organometallic Chemistry 560 (1998) 137–146
Table 1
Elemental analysis and selected IR data
Compound
Analysisa
C
IR bandsb
H
N
w(CꢂN)
w(CꢀO)
w(CꢀN)
o-(Ph2P)–C6H4–CHꢀNR
R
C6H4OMe-4
79.1
(78.97)
79.7
(79.97)
79.3
5.7
(5.61)
7.1
(7.00)
6.1
(5.98)
7.7
3.5
(3.54)
3.9
(4.06)
4.5
(4.62)
3.3
1615 ms
1630 ms
1638 ms
1630 ms
CMe3
Me
(79.19)
81.3
bornyl
(81.85)
(7.58)
(3.29)
[Pd(p2-ol){o-(Ph2P)–C6H4–CHꢀNR}]
ol
R
1a
1b
1c
1d
2a
2b
3a
4b
dmf
C6H4OMe-4
58.9
(59.50)
61.8
(62.13)
65.0
(65.51)
59.6
(60.06)
58.7
(58.44)
59.9
(61.20)
56.0
(56.38)
64.9
4.5
(4.68)
4.0
(4.17)
4.4
(4.28)
3.9
(4.03)
5.6
(5.41)
4.8
(4.95)
4.8
(4.73)
5.7
2.1
(2.17)
7.1
(7.25)
2.1
(2.12)
2.2
(2.33)
2.3
(2.35)
7.8
(7.93)
2.6
(2.53)
6.6
1689 s, 1670 s
1612 m
1617 m
1615 ms
1608 m
1625 m
1616 m
1634 m
1607 m
fn
C6H4OMe-4
C6H4OMe-4
C6H4OMe-4
CMe3
2198 ms
nq
1630 m, 1590 m
1784 s, 1756 m, 1714 s(br)
1686 s(br)
ma
dmf
fn
CMe3
2202 ms, 2192 s
2203 ms, 2190 s
dmf
fn
Me
1694 s, 1667 s
bornyl
(64.97)
(5.62)
(6.89)
a Calculated values in parentheses.
b As Nujol nulls.
the appropriate primary amine in a CH2Cl2/MeOH (1:3
v/v) mixture at r.t.:
which is essentially based on the amination of the
corresponding [Pd(p3-C3H5)(P–N)]+ cations by diethy-
lamine in the presence of activated olefins.
Recently, the palladium(0) derivative [Pd(PNN)],
containing the terdentate N–(2-(diphenylphosphino)
benzylidene)(2-(2-pyridyl)ethyl) amine (PNN) has been
synthetized by reacting [Pd(C3H5)(PNN)]+ with pyrro-
lidine [5]. On the other hand, some [Pd(p2-ol)(P–N)]
complexes with chiral (aminoferrocenyl)phosphine lig-
ands have been prepared by displacement reactions
from [Pd2(dba)3]·CHCl3 (dba, dibenzylideneacetone)
[6].
(2)
(R=C6H4OMe-4, Me, CMe3, bornyl1)
Under these conditions, the reaction proceeds
smoothly to completion and does not require any heat-
ing at higher temperature (e.g. refluxing ethanol [8]), or
the presence of a drying agent (e.g. molecular sieves
[5,9]), or the use of a large excess of the amine (e.g. neat
tert-butylamine [10]).
The iminophosphines are characterized by elemental
analysis, IR spectra (Table 1) and by multinuclear
NMR spectra (Tables 2 and 3). The NMR spectra of
o-(Ph2P)–C6H4CHꢀNR (R=bornyl) indicate the pres-
ence of a minor isomer in solution (ca. 9%), which may
be due either to an exo structure of the N-substituent
or to a Z configuration of the aldimine group in
2. Results and discussion
2.1. Preparation and characterization of the
iminophosphine ligands
The
N-(2-(diphenylphosphino)benzylidene)amines
are synthetized in high yield from the condensation
reaction of 2-(diphenylphosphino)benzaldehyde [7] with
1 bornyl, endo-(IR)-1,7,7-trimethylbicyclo [2.21]hept-2-yl.

S. Antonaroli, B. Crociani / Journal of Organometallic Chemistry 560 (1998) 137–146
139
Table 2
Selected 1H- and 31P-{1H}-NMR dataa
Compound
Iminophosphine protons
Olefin protons
31P resonances
NꢀCH
N–CH
C(CH3)3 OCH3
ꢀCH
OCH3
o-(Ph2P)–C6H4–CHꢀNR
R
C6H4OMe-4
9.06 d
(4.4)b
3.78 s
−15.56 s
−14.50 s
−16.83 s
−14.97 s
CMe3
Me
8.77 d
1.04 s
(4.2)b
8.92 d 3.37 s
(3.7)b
bornyl
8.73 d 3.29 m
(5.3)b
8.71c
3.06c
m
−16.68c
s
[Pd (p2-ol){o-(Ph2P)–C6H4–
CHꢀNR}]
ol
R
1a
1b
dmf C6H4OMe-4
8.11 d
(4.0)
3.81 s
3.81 s
4.23 d,
(9.9)e
3.22d dd 3.32 s, 3.14 s
19.24 s
18.24 s
(9.9)b
fn
C6H4OMe-4
8.18 d
3.22 dd,
2.46d dd
(9.8)b
(3.2)b
(9.8)e
(3.3)b
1c
1d
nq
C6H4OMe-4
C6H4OMe-4
8.05 d
(4.3)b
3.86 s
3.83 s
4.83 d,
4.48d dd
24.12 s
21.57 s
(4.5)e
4.24 dd,
(4.1)e
(10.0)b
ma
8.11 d
3.61d dd
(10.4)b
(3.9)b
(3.2)b
2a
2b
3a
4b
dmf CMe3
fn CMe3
dmf Me
fn bornyl
8.08 d
(3.5)b
8.11 s
1.28 s
1.28 s
4.12 d,
(10.2)e
3.13 d,
(10.0)e
4.22, d
(10.1)e
3.12 d,
(9.6)e
3.69d dd 3.54 s, 3.14 s
(10.2)b
2.65d dd
(10.0)b
3.89d dd 3.66 s, 3.15 s
(10.1)b
22.61 s
20.71 s
17.99 s
19.41 s
8.15 s
3.93 s
8.21 d 3.60 m
(2.7)b
2.77d dd
(9.6)b
(3.4)b
8.29f d 4.42f m
(2.2)b
mk,
2.58d,f dd
9.6)b
(9.6)e
a In CDCl3 at 30°C; satisfactory integration values were obtained; coupling constants in Hz; mk, masked; s, singlet; d, doublet; dd, doublet of
doublets; m, multiplet.
b J(PH).
c Minor isomer (see text).
d Trans to phosporus.
e J(HH).
f Minor diasteroisomer (see text).
equilibrium with the more stable E isomer [11]. Inspec-
tion of the H-NMR spectrum of the commercial (R)-
gest the E–Z isomerism to be the more likely explana-
tion for the solution behaviour of the uncoordinated
iminophosphine ligand. The larger size of the bornyl
group, compounded with the bulkiness of the o-Ph2P
substituent, seems to play an important role in stabiliz-
ing the Z isomer in line with the steric effects observed
for ortho-substituted aryl aldimines [11].
1
(+)-bornylamine, used in the synthesis of the ligand,
shows that the endo-(1R) form is predominant in
CDCl3 solution (ca. 97%). On the other hand, no
isomeric species attributable to an exo structure of the
N-bornyl fragment is observed in the 1H- and 31P-
NMR spectra of the complex [PtCl2{o-(Ph2P)–C6H4–
CHꢀNR}] (R=bornyl) in which the aldimine function
is forced by chelation to assume exclusively the E
configuration. These pieces of evidence therefore sug-
The 2D 1H-NMR spectrum of o-(Ph2P)–C6H4–
CHꢀNMe in CDCl3 shows an intense NOE between the
imino proton and the NMe protons, in accordance with
an E configuration of the imino function, and two

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S. Antonaroli, B. Crociani / Journal of Organometallic Chemistry 560 (1998) 137–146
141
2.2. Preparation and characterization of the complexes
[Pd(p2-ol)(P–N)]
These complexes are prepared by reactions (3–6) of
Scheme 1.
In contrast to the corresponding reaction with
[Pd(p3-C3H5)(N–N%)]ClO4 (N–N%=h-diimine) [3], the
phenylation of the allyl complexes [Pd(p3-C3H5)(P–
N)]BF4 by NaBPh4 in the presence of activated olefins
[Eq. 3] requires heating at 60–70°C to proceed at
reasonable rate. At that temperature, however, partial
decomposition of the products to metallic palladium
reduces considerably the yield in [Pd(p2-ol)(P–N)]. The
latter compounds are more conveniently obtained from
amination of [Pd(p3-C3H5)(P–N)]BF4 by diethylamine
according to reaction (4), which occurs rapidly at ambi-
ent temperature when a moderate excess of the amine is
used. This method, however, cannot be applied for the
preparation of palladium(0) derivatives with p2-bound
maleic anhydride due to the reactivity of this ligand
towards NHEt2. The ma complex 1d is therefore syn-
thetized from the substitution reaction (5) involving the
preformed dmf derivative 1a. On the other hand, reac-
tion (6) provides another synthetic route through dis-
placement of h-diimine ligands from zerovalent palla-
dium complexes by iminophosphines. As indicated by
1H-NMR spectra, the 2-(iminomethyl)pyridine ligand
of [Pd(p2-fn)(py-2-CHꢀNC6H4OMe-4)] [3] is rapidly
and quantitatively displaced by o-(Ph2P)–C6H4–CHꢀ
NC6H4OMe-4 when the reactants are mixed in a 1:1
molar ratio in CDCl3 solution.
Fig. 1. Perspective view of the most stable conformation for o-
(Ph2P)–C6H4–CHꢀNMe, with phenyl carbon numbering scheme and
some selected atomic distances and torsion angles.
1
The elemental analyses and some selected IR, H-,
31P- and 13C-NMR data of complexes 1a–4b are listed
in the Tables 1–3.
weaker NOEs of the imino proton with the H(6) proton
of the 1,2-disubstituted phenyl group and with the ortho
protons of the Ph2P phenyl groups. These findings may
be interpreted in terms of a predominant conformation
of type I:
According to X-ray structural data, the complexes
[Pd(p2-ol)L2] have a trigonal planar coordination
around the palladium center as in structure II:
in which the plane passing through palladium and the
olefinic carbons is almost coplanar with the PdL2 plane
([1]c) [6,12]. In view of the chelating properties of the
iminophosphine ligands [5] ([8]b,c) [10], a structure of
type II is assumed to be extant also for the [Pd(p2-
where the imino group lies on the side opposite to the
phosphorus lone pair (relative to the P–C(2) bond) and
the imino C–H bond is on the side opposite to the
C(6)–H(6) bond. In this conformation, the imino pro-
ton may be at relatively short distance from the Ph2P
ortho protons, comparable with that from the H(6)
proton.
1
ol)(P–N)] compounds. The H- and 13C-NMR spectra
are in fact consistent with the planar geometry III:
Interestingly, model calculations have shown that
conformations similar to I are predominant also for the
isolated molecule. The most stable of these conforma-
tions is reported in Fig. 1, along with some selected
atomic distances and torsion angles.

142
S. Antonaroli, B. Crociani / Journal of Organometallic Chemistry 560 (1998) 137–146
Scheme 1.
as suggested by the larger J(PC) and J(PH) coupling
constants of the olefinic ꢀCH fragment trans to phos-
phorus relative to those of the cis=CH moiety. In the
complexes 1a–4b the 31P signals of the PPh2 group and
at 1725 cm−1 for dmf, at 1650 cm−1 for nq, at 1850,
1792 and 1780 cm−1 for ma, and the w(CꢂN) band at
2244 cm−1 for fn]. In contrast, the w(CꢀN) absorptions
of the imino group are scarcely affected by coordina-
tion, in line with the observation that the CꢀN bond
distances of h-diimines undergo only a slight lengthen-
ing in the coordination to palladium(II) and palla-
dium(0) centers ([1]c) [13]. Thus, y back-donation from
the electron rich metal center to the activated alkene
appears to be the predominating factor in stabilizing
the zerovalent complexes [Pd(p2-ol)(P–N)], as was ear-
lier reported for [Pd(p2-ol)(N–N%)] (N–N%=h-diimine)
[1b–1d, 3]. Accordingly, the electron accepting abilities
of the olefin are important for the preparation of stable
complexes: attempts to isolate complexes of type
[Pd(p2-ol)(P–N)] with less y-accepting olefins, such as
methyl acrylate or acrylonitrile, were unsuccessful.
In contrast to the solution behaviour of [Pd(p2-
ol)(N–N%)] (N–N%=h-diimine) ([1]c) [3], for the
[Pd(p2-ol)(P–N)] analogs the dynamic processes, such
as olefin rotation or olefin dissociation-association, are
slow, if they occur, on the NMR time scale at 30°C in
CDCl3. In the 1H and 13C-NMR spectra, the non-
equivalent hydrogens and carbons of the p2-bound
1
the H and 13C signals of the imino group –CHꢀNR
are generally shifted downfield if compared to the cor-
responding signals of the uncoordinated iminophines,
indicating that | donation predominates in the P–N
bonding. A noticeable exception is given by the imino
proton resonance which undergoes an upfield shift of
0.6–1.0 ppm, probably due to a conformational change
of the ligand upon chelation.
For the p2–bound olefins, upfield shifts of 2.5–3.8
ppm for the alkenic protons, and of 75–97 ppm for the
1
alkenic carbons are observed in the H- and 13C-NMR
spectra, respectively, in comparison to the correspond-
ing signals of the free ligands, which occur at 6.86 (1H)
and 133.9 (13C) ppm for dmf, at 6.99 and 138.6 ppm for
nq, at 6.29 and 119.8 ppm for fn, and at 7.04 and 137.1
ppm for ma, in CDCl3. These changes clearly arise from
extensive electron donation from the d10 palladium
center to the olefin, which is also reflected by the
low-frequency shifts of the alkenic w(CꢀO) and w(CꢂN)
bands in the IR spectra of 1a–4b [cf. the w(CꢀO) bands

S. Antonaroli, B. Crociani / Journal of Organometallic Chemistry 560 (1998) 137–146
143
CHꢀCH olefinic unit appear as two distinct and sharp
signals. The low rate (or absence) of olefin dissociation
can be also inferred by the detection of two diastereoiso-
mers for complex 4b, containing the chiral o-(Ph2P)–
C6H4–CHꢀNR (R=bornyl) ligand, in the ratio of ca.
1:7.8:
reported for analogous olefin substitutions on [Pd(p2-
ol)(N–N%)] (N–N%=bis(arylimino)acenapthenes or
bis(phenylimino)camphane ([1]c) and 2-(iminomethyl)
pyridines ([1]d)), and provide further evidence to the
increasing stabilization of the zerovalent palladium–
Owing to the trans geometry of fumaronitrile, inter-
conversion of these isomers can occur only through
olefin (or P–N ligand) dissociation-association
equilibria.
olefin compounds with increasing electron accepting
abilities of the olefinic ligands.
In the presence of free olefin, the h-diimine complexes
[Pd(p2-ol)(N–N%)] undergo fast exchange (on the NMR
time scale) between free and coordinated olefin, the rate
of which decreases with decreasing concentration of the
reactants and with increasing steric demand of both the
h-diimine and olefinic ligands, in agreement with an
essentially associative mechanism analogous to that
proposed for olefin substitutions ([1]c), ([1]d).
The lack of dissociation–association equilibria of this
type has been also reported for the related complexes
[Pd(p2-ol)(P–N)] with ol=ma, dmf and P–N=chiral
(aminoferrocenyl)phosphine [6]. For the latter com-
pounds, however, rotation of the coordinated olefin was
1
observed with coalescence of the alkenic H resonances
generally occurring at rather high temperatures (313–
373 K). In our case, the study of the fluxional behaviour
at higher temperatures was hampered by partial decom-
position of the complexes to palladium metal (which was
particularly extensive for the dmf derivatives).
For
equimolar
[Pd(p2-ol){o-(Ph2P)–C6H4–
CHꢀNC6H4OMe-4}]/ol solutions in CDCl3, such ex-
change was found to occur at considerably reduced rates,
even at 30°C and with complex and olefin concentrations
as high as 2.5×10−2 mol dm−3. In the 1H-NMR
spectra, the exchange brings about only some broadening
of the signals for the free and coordinated olefin, without
any coalescence or significant change in chemical shifts,
relative to those of CDCl3 solutions containing the olefin
or the complex alone. The broadening is more pro-
nounced for cis olefins, nq and ma, than for trans olefin,
dmf and fn, suggesting a slightly higher exchange rate for
the former ligands. In terms of the proposed associative
mechanism through a labile 18-electron intermediate
2.3. Reactions of the complexes [Pd(p2-ol)(P–N)]
2.3.1. Ligand exchange and substitution
The reactions involving olefin exchange or substitu-
tion occur according to the equilibrium (7):
[Pd(p2-ol)(P–N)]+ol% = [Pd(p2-ol%)(P–N)]+ol
(7)
where the entering olefin ol% may be identical to or
different from the coordinated olefin ol in the starting
compound.
[Pd(p2-ol)2(P–N)], these findings may be rationalized if
one considers the greater steric demand of the
As indicated by 1H-NMR spectra in CDCl3, the
p2-bound dmf ligand of 1a is readily and quantitatively
substituted by 1 equivalent of any of the other olefins.
As mentioned before, such a reaction has been used for
the preparation of the ma derivative 1d [Eq. (5) of
Scheme 1]. Similarly, a quantitative substitution of the
p2-bound nq ligand takes place in the reactions of 1c
with 1 equivalent of fn or ma.
iminophosphine
o-(Ph2P)–C6H4–CHꢀNC6H4OMe-4
compared to that of an h-diimine such as py-2-
CHꢀNC6H4OMe-4, and the greater steric interaction
between the p2-bound trans olefins in the intermediate IV
compared to that of the p2-bound cis olefins in V:
Both reactions of the fumaronitrile complex 1b with
ma (1:1 molar ratio) and of the maleic anhydride
complex 1d with fn (1:1 molar ratio) lead to the same
equilibrium mixture in CDCl3, in which a 1b:1d ratio of
1:1.6 is observed. These results closely parallel those

144
S. Antonaroli, B. Crociani / Journal of Organometallic Chemistry 560 (1998) 137–146
2.3.2. Oxidati6e addition of allyl chloride
The dmf complex 1a undergoes a fast oxidative addi-
The reactions involving exchange of the iminophos-
tion of allyl chloride at ambient temperature, yielding
phine ligands occur according to equilibrium (8):
the cationic complex [Pd(p3-C3H5){o-(Ph2P)-C6H4–
−
CHꢀNC6H4OMe-4}]+ which was isolated as BF4 salt
[Pd(p2-ol)(P–N)]+P–N = [Pd(p2-ol)(P–N)2]
(8)
1
and identified by comparing its H-NMR with that of
an authentic sample independently prepared.
These reactions have been studied for the fumaroni-
trile complexes 1b and 2b in the presence of 1 equiva-
lent of the corresponding P–N ligand. The exchange
rate and the equilibrium position depend markedly on
3. Experimental
1
the nitrogen substituent. The H-NMR spectra of an
1
The H-, 13C-{1H}- and 31P-{1H}-NMR spectra were
equimolar 1b/o-(Ph2P)–C6H4–CHꢀNC6H4OMe-4 solu-
tion in CDCl3 show a fast exchange (on the NMR time
scale) with the equilibrium being almost completely
shifted to the right. At 30°C, time-avered signals are
detected for both the iminophosphine (e.g. a single
broad resonance for the imino protons at 8.73 ppm)
and the olefin (a single broad resonance for the olefinic
protons at 2.70 ppm). At −40°C (the lowest tempera-
ture explored), the signals sharpen but no appreciable
amount of the reactants 1b and free iminophosphine is
observed. For this reason, the product [Pd(p2-fn) {o-
(Ph2P)–C6H4–CHꢀNC6H4OMe-4}2] can be isolated
and characterized (see Section 3). The multinuclear
NMR spectra of this compound suggest that the olefin
is p2-bound to the metal [l(ꢀCH) as a broad singlet at
2.70 ppm, and l(ꢀCH) as a broad singlet at 36.5 ppm],
while the iminophosphines very likely act as P-
monodentate ligands [l(31P) as a singlet at 17.5 ppm;
l(NꢀCH) as a broad singlet at 8.73 ppm, l(NꢀCH)
and l(N–C) as broad singlets at 156.0 and 144.5 ppm,
respectively]. If compared with the imino function reso-
nances of the free o-(Ph2P)–C6H4–CHꢀNC6H4OMe-4
[Tables 2 and 3], the imino proton signal in the complex
appears to be shifted upfield of 0.33 ppm, while the
carbon signals are nearly coincident.
recorded on a Bruker AM400 spectrometer, operating
at 400.13, 100.61 and 161.98 MHz, respectively. Chem-
ical shifts (ppm) are given relative to TMS (1H-, 13C-
NMR) and 85% H3PO4 (31P-NMR). The 1H 2D
ROESY spectrum of o-(Ph2P)–C6H4–CHꢀNMe in
CDCl3 was obtained in the phase-sensitive mode using
the TPPI phase cycle with the ROESY pulse sequence,
modified to eliminate the offset dependence of cross-
peak intensity [15]. A total of 128 transients on a size of
2K were accumulated for 512 experiments. A spinlock
period corresponding to a transverse mixing time of 0.3
s was applied. Data were processed with the 2-D NMR
program TRITON, licensed by the University of
Utrecht, The Netherlands. A sine bell apodization func-
tion, shifted by y/3, was applied in both dimension as
to obtain a 1K×1K real matrix. We thank Fabio
Bertocchi for technical support in running the NMR
spectra.
The IR spectra of solid samples were recorded in the
range 4000–200 cm−1 on a Perkin-Elmer 983 G instru-
ment using CsI windows.
Model calculations were performed with version 5.0
of the HyperChem package (Hypercube, Waterloo, On-
tario) running on a Pentium Pro-133 MHz micropro-
cessor. The geometry of the model compound
o-(Ph2P)–C6H4–CHꢀNMe, with an E configuration for
the imine function, was optimized by the AM1 method
[16] implemented in HyperChem, up to a RMS gradient
1
The H-NMR spectra of an equimolar 2b/o-(Ph2P)–
C6H4–CHꢀNCMe3 solution in CDCl3 at 30°C show
that the exchange rate is slow and, when the equi-
librium is reached, the mixture consists of a 1:1:9.5
molar ratio of 2b, P–N and [Pd(p2-fn) (P–N)2], respec-
tively. The latter complex was not isolated, but was
−1
˚
50.01 kcal A
mol−1 (heat of formation=123.93
kcal mol−1). The conformational search for finding low
energy conformations of the molecule was carried out
by varying of 30° the dihedral angles concerning the
rotation of the phenyl planes around the phosphorus–
phenyl bonds, and the rotation of the imino group
plane (–CHꢀN–Me) around its bond to the C6H4
fragment. We thank M.L. Di Vona of Dipartimento di
Scienze e Tecnologie Chimiche, Universita’ di Roma
‘Tor Vergata’, for running the model calculations.
The complexes [PtCl2(COD)] (COD=1,5-cycloocta-
diene) [17] [Pd(v-Cl) (p3-C3H5)]2 [18] and [Pd(p2-fn)(py-
2-CHꢀNC6H4OMe-4)] [3] were prepared by literature
methods. The commercial p-anisidine was sublimed at
low pressure before use. All other chemicals and sol-
vents were reagent grade, and were used without fur-
ther purification.
1
identified from its H-NMR spectrum, characterized by
the signals of the imino proton (a sharp singlet at 8.65
ppm), of the p2-bound olefin (a sharp doublet at 2.66
ppm with J(PH) of 3.7 Hz) and of the CMe3 group (a
sharp singlet at 0.93 ppm). The corresponding integra-
tion values are in agreement with the proposed formu-
lation. Also for [Pd(p2-fn){o-(Ph2P)–C6H4–CHꢀNC-
1
Me3}2] the H imino function resonances are close to
those of the free iminophosphine (Table 2), suggesting a
P-monodentate coordination for this ligand.
A P-monodentate coordination of the rigid ligand
1-(dimethylamino)-8-(diphenylphosphino)naphtalene
(PAN) in trans-[PdCl2(PAN)2] was demonstrated by an
X-ray structural determination [14].

S. Antonaroli, B. Crociani / Journal of Organometallic Chemistry 560 (1998) 137–146
145
3.1. Preparation of the iminophosphines
o-(Ph2P)–C6H4–CHꢀNR
data were obtained: molar conductivity, 96.5 ohm−1
cm2 mol−1 for a 10−3 mol dm−3 MeOH solution at
25°C; analysis (Found: C, 55.2; H, 4.3; N, 2.1.
C29H27BF4NOPPd calcd.: C, 55.31; H, 4.32; N, 2.22%);
The 2-(diphenylphosphino)benzaldehyde [7] (1.16 g, 4
mmol) and the required amount of the appropriate
amine RNH2 were dissolved in 200 cm3 of a MeOH/
CH2Cl2 mixture (3:1 v/v) under N2. For R=
C6H4OMe-4 and Me, an aldehyde/amine molar ratio of
1:1.1 was used, whereas for the more sterically demand-
ing bornyl and CMe3 substituents the ratio was in-
creased to 1:1.5 and 1:3, respectively. In the case of
MeNH2, 0.38 cm3 of a 40% acqueous solution of the
amine was used. The progress of the reaction was
monitored by IR spectroscopy, following the decay of
the aldehyde w(CꢀO) band at 1695 cm−1. The comple-
tion was reached in ca. 2 h for R=Me, 3–4 h for
R=C6H4OMe-4 and bornyl, and 7 h for R=CMe3.
After standing overnight at r.t., the solution was con-
centrated to small volume (ca. 5 cm3) and kept at
−20°C for 24 h. The microcrystalline solids were
filtered off and washed with cold methanol. For the
more soluble iminophosphines (R=bornyl and CMe3),
the mother liquor resulting from filtration and MeOH
washing was concentrated and cooled at −20°C to give
a second crop of solid product. The yields were in the
range 76–92%.
IR spectrum as Nujol mull [w(CꢀN) at 1612 cm−1
,
1
w(B–F) at 1060 cm−1]; H- and 31P-NMR spectra in
CDCl3 [P–N protons, l 8.33 (d, J(PH)=2.8 Hz, N=
CH), 3.81 (s, OCH3); allyl protons, trans to phospho-
rus: l 4.06 (dd, J(HH)=J(PH)=6.7 Hz, Hsyn), 3.65
(dd, J(HH)=14.2 and J(PH)=9.5 Hz, Hanti), trans to
nitrogen: l 3.45 (d(br), J(HH)=5.0, Hsyn), 2.96 (d(br),
J(HH)=12.1, Hanti); d(31P), 22.07(s)].
3.4. Preparation of [Pd(p2-ol)(P–N)] (1a–4b)
3.4.1. Allylic amination
A moderate excess of NHEt2 (2.5 mmol) was added
to a solution of [Pd(p3-C3H5)(P–N)]BF4 (0.5 mmol)
and the olefinic ligand ol (0.6 mmol) in CH2Cl2 (20
cm3). After standing for 2 h at r.t., the solvent was
evaporated to dryness. The solid residue was repeatedly
washed with water, dried under vacuum and redis-
solved in CH2Cl2 (20 cm3). Upon treatment with acti-
vated charcoal and filtration, the resulting solution was
washed with ca. 50 cm3 of a 0.1 mol dm−3 aqueous
solution of Na2CO3 and then with ca. 50 cm3 of water
to remove the residual traces of ammonium salts. After
drying over Na2SO4, the CH2Cl2 solution was concen-
trated to small volume and diluted with n-hexane/di-
ethyl ether (1:1 v/v) to precipitate the palladium(0)
products, which were recrystallized from the same sol-
vent mixture (yields in the range 78–90%).
3.2. Preparation of [PtCl2{o-(Ph2P)–C6H4–CHꢀNR}]
(R=bornyl)
A solution of the P–N ligand (0.14 g, 0.33 mmol) in
5 cm3 of benzene was added to a solution of
[PtCl2(COD)] (0.10 g, 0.27 mmol) in 5 cm3 of CH2Cl2.
After stirring for 2 h, the product separated as a white
solid. The precipitation was completed by dilution with
diethyl ether (0.16 g, 85.7 %). The complex was charac-
terized by elemental analysis (Found: C, 50.7; H, 4.7;
N, 2.0. C29H32Cl2NPPt calcd.: C, 50.37; H, 4.66; N,
2.03%), IR spectrum as Nujol mull [w(CꢀN) at 1620
3.4.2. Ligand substitution
1. Maleic anhydride (0.06 g, 0.6 mmol) was added to a
solution of 1a (0.26 g, 0.4 mmol) in CHCl3 (20 cm3).
After 0.5 h, the solution was concentrated to small
volume and diluted with diethyl ether to precipitate
the product [Pd(p2-ma){o-(Ph2P)–C6H4–CHꢀNC6-
H4OMe-4}] (1d), which was recrystallized from the
same solvent mixture (0.20 g, 83.3 %).
2. The ligand o-(Ph2P)–C6H4–CHꢀNC6H4OMe-4
(0.40 g, 1.01 mmol) was added to a solution of
[Pd(p2-fn)(py-2-CHꢀNC6H4OMe-4)] (0.40 g, 1.01
mmol) in CHCl3 (80 cm3). After 1h, the solution
was concentrated to small volume and diluted with
diethyl ether to precipitate the product 1b (0.54 g,
92.2 %).
cm−1; w(Pt–Cl) at 342 and 279 cm−1], H- and 31P-
NMR spectra in CDCl3 [l(NꢀCH) at 8.36 ppm with
J(PtH)=109 Hz; l(31P) at 2.05 ppm with J(PtP)=
3828 Hz].
1
3.3. Preparation of [Pd(p3-C3H5)(P–N)]BF4
These complexes were prepared from the reaction of
[Pd(v-Cl)(p3-C3H5)]2 (0.5 mmol) with the appropriate
iminophosphine P–N (1 mmol) in the presence of an
excess of NaBF4 (2 mmol), in the same way as de-
scribed for [Pd(p3-2-MeC3H4)(py-2-CHꢀNC6H4OMe-
4)]BF4 [19]. The products were isolated in high yields
(88–95%) and characterized by electric conductivity
measurements, elemental analysis, IR and multinuclear
NMR spectra. As an example, for [Pd(p3-C3H5){o-
(Ph2P)–C6H4–CHꢀNC6H4OMe-4}]BF4 the following
3.5. Preparation of
[Pd(p2-fn){o-(Ph2P)–C6H4–CHꢀNC6H4OMe-4)}2]
A
solution of the ligand o-(Ph2P)–C6H4–
CHꢀNC6H4OMe-4 (0.059 g, 0.15 mmol) and of 1b
(0.087 g, 0.15 mmol) in CH2Cl2 (30 cm3) was stirred for

146
S. Antonaroli, B. Crociani / Journal of Organometallic Chemistry 560 (1998) 137–146
[2] (a) V. De Felice, M. Funicello, A. Panunzi, F. Ruffo, J.
Organomet. Chem. 403 (1991) 243. (b)V. De Felice, A. De
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0.5 h at r.t.. Upon concentration and dilution with
diethyl ether, the product precipitated as a yellow pow-
der (0.123 g, 84%). This complex was characterized by
elemental analysis (Found: C, 69.2; H, 4.6; N, 5.7;
C56H46N4O2P2Pd calcd.: C, 68,96; H, 4.75; N, 5.74), IR
spectrum as Nujol mull [w(CꢂN) at 2203 cm−1; w(CꢀN)
1
at 1627 and 1613 cm−1], and by H-, 13C- and 31P-
NMR spectra in CDCl3 (see text).
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Allyl chloride (0.04 cm3, 0.5 mmol) was added to a
solution of 1a (0.16 g, 0.25 mmol) in CH2Cl2 (10 cm3)
under N2. The colour changed immediately from deep-
red to yellow–orange. The IR spectrum showed the
complete disappearance of 1a and the presence of unco-
ordinated dmf [w(CꢀO) at 1725 cm−1]. After stirring for
0.5 h, a solution of NaBF4 (0.06 g) in MeOH (5 cm3)
was added, and the mixture was worked up as for the
preparation of [Pd(p3-C3H5)(P–N)]BF4, to give [Pd(p3-
C3H5){o-(Ph2P)–C6H4–CHꢀNC6H4OMe-4}BF4 (0.13
g, 82.6 %).
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Financial support by the Italian Ministero per l’Uni-
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