Reactivity of ammonium and iminium tetraphenylborates towards Pd(0)-complexes: Selective allyl or proton transfer to Pd(0). Evidence of formation of the species [HPd(dppe)2][BPh4]

Article abstract of DOI:10.1016/S0022-328X(02)01897-1

The reactivity of ammonium- and iminium-BPh₄ salts, [CH₂=CHCH₂NH₃]BPh₄, [(CH₂=CHCH₂)HN=CMe₂]BPh₄ and [(PhCH₂)HN=CMe₂]BPh₄,

Full text of DOI:10.1016/S0022-328X(02)01897-1

Journal of Organometallic Chemistry 662 (2002) 112ꢁ119
/
www.elsevier.com/locate/jorganchem
Reactivity of ammonium and iminium tetraphenylborates towards
Pd(0)-complexes: selective allyl or proton transfer to Pd(0).
Evidence of formation of the species [HPd(dppe)2][BPh4]
Michele Aresta a, Eugenio Quaranta a,b,
*
a Dipartimento di Chimica, Campus Universitario, 70126 Bari, Italy
b ICCOM-CNR, Dipartimento di Chimica, Campus Universitario, 70126 Bari, Italy
Received 27 June 2002; accepted 12 August 2002
Abstract
The reactivity of ammonium- and iminium-BPh4 salts, [CH2ꢀ
[(PhCH2)HNꢀCMe2]BPh4, towards Pd(0)-complexes, [Pd(dppe)(dba)] and [Pd(dppe)2] (dppeꢀ
dbaꢀdibenzylideneacetone), has been investigated. Allyl-ammonium and -iminium tetraphenylborates [CH2ꢀ
and [(CH2ꢀCHCH2)HNꢀ
CMe2]BPh4 react with [Pd(dppe)(dba)] to afford, under mild conditions (293 K), [(h3-
C3H5)Pd(dppe)][BPh4], through selective oxidative transfer of allyl group from the ammonium or iminium cation to the Pd center.
Pd(dppe)2][BPh4], that, under the reaction conditions, has poor
/
CHCH2NH3]BPh4, [(CH2ꢀ
1,2-bis(diphenylphosphino)ethane;
CHCH2NH3]BPh4
/
CHCH2)HNꢀ
/
CMe2]BPh4 and
/
/
/
/
/
/
[(PhCH2)HNꢀ
/
CMe2]BPh4 reacts with [Pd(dppe)2] to afford [Hꢁ
/
stability as it undergoes hydride transfer to the iminium ion present in the reaction medium, affording [Pd(dppe)2][BPh4]2.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Pdꢁ
/
allyl complexes; Pdꢁ
/
hydrido complexes; Allyl transfer; Proton transfer; Alkylammonium tetraphenylborates; Iminium
tetraphenylborates
[(h3-C3H5)Ni(PCy3)(NH3)][BPh4]ꢂPCy3 ꢂCO2 (1)
[(Cy3P)2NiNNNi(PCy3)2]ꢂ2[CH2ꢀCHCH2NH3]BPh4
1. Introduction
Recently [1], we have reported on the reactivity of
anhydrous N-alkylammonium and N-alkyl-monosub-
293 K; THF; N2
2[(h3-C3H5)Ni(PCy3)(NH3)][BPh4]
stituted-iminium BPh4 salts ([RNH3]BPh4 and [RHNꢀ
CMe2]BPh4, respectively; Rꢀalkyl) [2,3], towards
Ni(0)ꢁphosphine complexes [4,5a] and shown that either
CꢁN or HꢁN selective cleavage can take place. In fact,
[CH2ꢀCHCH2NH3]BPh4 (1) and [(CH2ꢀCHCH2)HNꢀ
CMe2]BPh4 (2) oxidatively add to Ni(0)ꢁphosphine
complexes (Eqs. (1)ꢁ(3)) through selective activation
of the NꢁC allyl bond to give new asymmetric cationic
/
ꢂ2PCy3 ꢂN2
[(Cy3P)2NiNNNi(PCy3)2]ꢂ
(2)
/
/
293 K; toluene; N2
/
/
2[(CH2ꢀCHCH2)HNꢀCMe2]BPh4
2[(h3-C3H5)Ni(PCy3)(h1(N)ꢁHNꢀCMe2)][BPh4]
ꢂ2PCy3 ꢂN2
/
/
/
/
(3)
/
/
Conversely, N-benzylisopropylidene-iminium cation
of [(PhCH2)HNꢀCMe2]BPh4 (3) selectively reacts with
[(Cy3P)2NiNNNi(PCy3)2], via activation of the Nꢁ
bond, to afford a new terminal cationic Niꢁhydride
complex, PhCH2Nꢀ
[trans-(H)Ni(PCy3)2(h1(N)ꢁ
p-allyl complexes bearing both P- and N-ligands in the
/
coordination sphere of Ni [4,5a].
/H
/
[(Cy3P)2Ni(h2-CO2)]ꢂ[CH2ꢀCHCH2NH3]BPh4
/
/
CMe2)][BPh4] (Eq. (4)), fully characterized both in
253 K; THF; CO2 or N2 (0:1 MPa)
solution and in the solid state [4].
[(Cy3P)2NiNNNi(PCy3)2]ꢂ2[(PhCH2)HNꢀCMe2]BPh4
* Corresponding author. Tel./fax: ꢂ
/
39-080-5442083
293 K; THF; N2
E-mail address: quaranta@chimica.uniba.it (E. Quaranta).
0022-328X/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 3 2 8 X ( 0 2 ) 0 1 8 9 7 - 1

M. Aresta, E. Quaranta / Journal of Organometallic Chemistry 662 (2002) 112ꢁ
/119
113
[Pd(dppe)(dba)]ꢂ[(CH2ꢀCHCH2)HNꢀCMe2]BPh4
2[trans-(H)Ni(PCy3)2(h1(N)ꢁPhCH2NꢀCMe2)][BPh4]
ꢂN2 (4)
THF; 293 K[(h3-C3H5)Pd(dppe)][BPh4]ꢂdbaꢂHNꢀCMe2
The examples reported above confirm the potential of
alkyl-ammonium and -iminium tetraphenylborate salts
as suitable reagents for the synthesis of new cationic
transition metal complexes. Alkylammonium tetraphe-
(6)
spectroscopy (see Section 4). [(h3-C3H5)Pd(dppe)]ꢂ
cation, albeit well known in the literature [9], was never
isolated as having BPhꢃ4 as counterion. Table 1 shows a
few selected NMR data for complex 6 which agree very
well with those reported in the literature for [(h3-
C3H5)Pd(dppe)][PF6] [9a] and [(h3-C3H5)Pd(dppe)][BF4]
[9e] in the same solvent, CDCl3.
nylborates have been used as protolytic agents of Mꢁ
bonds in alkyl or aryl transition-metal complexes [6].
Allylammonium salts [CH2ꢀCRCH2NHnEt3ꢃn]X (Rꢀ
H, nꢀ0,1; RꢀMe, nꢀ0; XꢀClO4, BPh4) have been
/
C
/
/
/
/
/
/
shown to react with Pt(0) precursors to afford cationic
p-allyl Pt(II) complexes [7]. As for the reactivity of
iminium cations towards transition metal centers [8], it is
known that N,N-dialkylsubstituted iminium ions can
coordinate to low valent metal centers through either
The reactivity shown in Eqs. (5) and (6) resembles that
observed with Ni(0) systems [4,5a]. Reaction (5) has
character of novelty as allyl transfer from a primary
allylammonium cation to Pd(0) complexes has never
been documented before, as quaternary allylammonium
the Cꢁ
N bond (h2(C,N)) [8a,8b,8c,8f] or the electro-
/
philic iminium carbon atom (h1(C)) [8b,8f]. (h2(C,N)
coordinated iminium cations are supposed to be inter-
mediates in a few metal promoted reactions of tertiary
amines [8g]. Low valent transition metal complexes can
also promote the transformation of iminium groups into
carbenes [8b] or induce oxidative [8e] or reductive [8f]
coupling reactions.
cations (/
RNEtꢂ3 ; Rꢀ
allyl) were used so far [10]. Also,
/
reaction (6) represents the first documented example of
oxidative allyl transfer from an iminium ion to a metal
center. Our data clearly demonstrate that (using primary
allyl-ammonium or -iminium cations) the allyl group
transfer, by far, remains the preferred process with
respect to proton transfer. In fact, the 31P-NMR (202
MHz, 293 K) spectrum of the reaction solution obtained
by dissolving 4 (one equivalent) and 2 (one equivalent)
in THF-d8 showed only a singlet, at d 57.87 ppm,
assigned to 6. Accordingly, no signals were evident in
As a continuation of previous work [4,5a] on the
reaction of ammonium- and iminium-BPh4 salts with
metal centers in a low oxidation state, we have extended
our investigation to Pd(0)-based systems. In this report
we focus on the reactivity of alkyl-ammonium and -
iminium BPh4 salts 1ꢁ3 towards diphosphine-complexes
/
1
of Pd(0). We describe the oxidative transfer of allyl
group from a primary allylammonium or N-allylimi-
nium cation to [Pd(dppe)(dba)] (4) and present spectro-
the hydride region of the H-NMR (500 MHz, 293 K)
spectrum of the reaction mixture. Under the working
conditions, the signals due to the syn and anti protons
of allyl group of 6 were very broad resonances approxi-
mately located at d 4.8 and 3.2 ppm. As a result of syn-
anti proton exchange, the resonance due to Hmeso is a
scopic evidence for the formation of the cationic Pd(II)ꢁ
/
hydrido complex [HPd(dppe)2][BPh4] (5). The reaction
of salt 3 with [Pd(dppe)(dba)] has been reported else-
where [5b,5c].
quintet at d 5.63 ppm (Jꢀ
assigned to 6 were found at d 2.51 (d, Jꢀ
CH2CH2), 6.68 (tr, Jꢀ7.20 Hz, Hpara;BPh ); 6.82 (tr, Jꢀ
7.35 Hz, Hmeta;BPh ); 7.30 (m, Hortho;BPh ); 47.36ꢁ
7.60 ppm
(m, HPh,dppe).
/
10.66 Hz). The other signals
/
18.32 Hz,
/
/
/
2. Results and discussion
4
4
Cationic p-allyl Pd(II) complexes are of interest in
homogeneous catalysis and are, traditionally, prepared
from neutral p-allyl Pd(II) complexes via halide abstrac-
tion [11]. A different synthetic approach implies the
transfer of allyl group to Pd(0) precursors from ally-
lesters [12] or salts of allyl derivatives [9d,9e,10,13].
Poorly stable allyloxophosphoniun salts [13], or N-allyl-
2,4,6-triphenylpyridinium tetrafluoroborates [9d,9e] or
allyltriethylammonium and N-allylpyridinium perchlo-
rates [10] have been employed to this end. The use of
allyl-ammonium or -iminium tetraphenylborates may
have a synthetic relevance for the direct synthesis of
cationic p-allyl Pd(II) complexes due to the fact that the
ammonium salts are safe, stable and very reactive and
2.1. Reactivity of [CH2ꢀ
[(CH2ꢀCHCH2)HNꢀCMe2]BPh4 towards
[Pd(dppe)(dba)]
/
CHCH2NH3]BPh4 and
/
/
Allyl-ammonium or -iminium tetraphenylborate salts
1 and 2 react with the coordinatively unsaturated species
[Pd(dppe)(dba)] (4), in THF, at room temperature (293
K), to give the cationic p-allyl complex [(h3-
C3H5)Pd(dppe)][BPh4] (6) (Eqs. (5) and (6)). Complex
6 was isolated and fully characterized in solution by
NMR
[Pd(dppe)(dba)]ꢂ[CH2ꢀCHCH2NH3]BPh4
THF; 293 K[(h3-C3H5)Pd(dppe)][BPh4]ꢂdbaꢂNH3 (5)
can be obtained in a straightforward way [2ꢁ5].
/

114
M. Aresta, E. Quaranta / Journal of Organometallic Chemistry 662 (2002) 112ꢁ119
/
Table 1
a
Selected 1H- and 31P-NMR data (d) for 6, [(h3-C3H5)Pd(dppe)][BF4] and [(h3-C3H5)Pd(dppe)][PF6]
b
Compound
1H-NMR dH (ppm)
31P-NMR dP (ppm)
Hsyn
Hanti
3.09
Hmeso
c,d
c,d
c,d
c,e
[(h3-C3H5)Pd(dppe)][BPh4] (6)
[(h3-C3H5)Pd(dppe)][BF4]
[(h3-C3H5)Pd(dppe)][PF6]
4.65
m
m
5.39
m
51.88
f,h
51.7
f,g
f,g
f,g
4.80}4.85 m
4.84 m, broad
3.29}3.40
3.32 m, broad
m
5.72}5.83
m
i,j
i,j
i,j
k
5.82
m
a
Solvent is CDCl3.
Versus H3PO4.
This work.
b
c
d
Experimental conditions: 293 K, at 500 MHz. See also Section 4.
Experimental conditions: 293 K, at 202 MHz.
Data from Ref. [9e].
e
f
g
h
i
At 250 MHz.
At 162 MHz.
Data from Ref. [9a].
Experimental conditions: 307 K, at 60 MHz.
dP (for the dppe ligand): 52.1 ppm, in (CD3)2SO [9b].
j
k
2.2. Reactivity of [(PhCH2)HNꢀ
/
CMe2]BPh4 towards
In CD2Cl2 solution 7 shows, as expected, a single
resonance at d 30.86 ppm. Upon addition of one
equivalent of the iminium salt 3, a singlet immediately
appears at d 32.98 ppm in the 31P{1H} spectrum. The
proton-coupled 31P spectrum shows that the new signal
[Pd(dppe)2]
At 293 K, in CH2Cl2, [(PhCH2)HNꢀCMe2]BPh4 (3)
reacts with the coordinatively saturated species
/
[Pd(dppe)2] (7) to afford the cationic five-coordinated
hydrido complex [HPd(dppe)2][BPh4] (5), as demon-
has a doublet structure (term separationꢀ52.4 Hz)
because of coupling of P nuclei with the hydride proton
[14].
Reaction (7) is a rare example of proton transfer from
a protonated imine to a transition metal center. As a
matter of fact, when C-substituted N,N?-dialkyliminium
cations have been used [8d], the transfer of an a proton
to CpFe(CO)ꢃ2 to give CpFe(CO)2H has been observed
with formation of an enamine (Eq. (8)). In the present
work, the intermediate formation of enamine
/
Pdꢁ
/
strated by NMR (1H, 31P) spectroscopy. In fact, the 1H-
NMR (500 MHz, CD2Cl2, 293 K) spectrum of the
reaction mixture [Pd(0) to BPh4 molar ratioꢀ
measured soon after (15 min) mixing the reactants,
shows, in addition to the signals of 7 [d 2.09 (m, CH2ꢁ
CH2), 7.04 (tr, Jꢀ7.45 Hz, Hmeta,Pd(0)), 7.14 (tr, Jꢀ
7.27 Hz, Hpara,Pd(0)), 7.36 ppm (m, Hortho,Pd(0))] and
BPhꢃ4 anion [d 6.85 (tr, Jꢀ
7.12 Hz, Hpara;BPh ); 7.00 (tr,
Jꢀ7.46 Hz, Hmeta;BPh ); 7.36 (m, Hortho;BPh )]; new signals
at d ꢃ
/
1:1.06],
/
/
/
/
4
/
(PhCH2)HNꢁ
/
C(Me)ꢀ/CH2 has not been observed by
4
4
/
7.37 (quintet, Jꢀ53.7 Hz), 2.30 (unresolved
/
NMR.
triplet), 7.20 (m) and 7.36 ppm (the latter masked by the
signals of Hortho,Pd(0) and Hortho;BPh ) with relative
CpFe(CO)2)ꢃ2 ꢂ[(R1)(R2HC)CꢀN(R2)2]ꢂ
0 CpFe(CO)2HꢂR2CꢀC(R1)N(R2)2
4
intensity 1:8:32:8. The quintet at d ꢃ7.37 ppm is
/
(8)
indicative of the presence of a hydride proton coupled
with four equivalent phosphorous nuclei and the whole
set of these new signals is consistent with the formation
Complex 5 is an unprecedented example of five-
coordinate cationic mononuclear Pdꢁhydrido complex
[15] of the tipe [HM(L2)2]ꢂ (L2ꢀ
diphosphine) that are
/
of the cationic five-coordinate Pdꢁhydride species
/
/
[HPd(dppe)2]ꢂ according to reaction (7).
well known in the literature for Ni(II) and Pt(II) [16].
For Pd(II), they have been described so far as extremely
reactive and have neither been isolated, nor spectro-
scopically detected in solution [16]. Table 2 collects some
selected spectral data for cation [HPd(dppe)2]ꢂ (5ꢂ)
and a few related [HM(diphosphine)2]ꢂ complexes of
platinum and nickel. As data in Table 2 indicate, along
the series [HNi(dppe)2]ꢂ, [HPd(dppe)2]ꢂ and
[HPt(dppe)2]ꢂ, the 31P resonance due to the dppe
ligands in [HM(dppe)2]ꢂ cations is progressively upfield
shifted ([HNi(dppe)2]ꢂ (42.5 ppm), [HPd(dppe)2]ꢂ
(32.98 ppm), [HPt(dppe)2]ꢂ (20.4 ppm)). However, in
[(PhCH2)HNꢀCMe2]BPh4 ꢂ[Pd(dppe)2]
? [HPd(dppe)2][BPh4]ꢂ(PhCH2)NꢀCMe2
(7)
In the 1H-NMR spectrum other signals are also
evident at d 4.27 (s), 1.94 (s) and 1.91 ppm (s), with
relative intensity 2:3:3, which can be assigned, respec-
tively, to the methylene and methyl protons of the
species (PhCH2)Nꢀ
/
CMe2 and [(PhCH2)HNꢀ
/
CMe2]ꢂ,
that may undergo a rapid proton exchange.
The formation of the hydrido species 5 is also
supported by 31P-NMR (81 MHz, 293 K) experiments.
5ꢂ, the hydride ligand is less shielded (ꢃ
7.37 ppm) than
/

M. Aresta, E. Quaranta / Journal of Organometallic Chemistry 662 (2002) 112ꢁ
/119
115
Table 2
Selected 1H- and 31P-NMR data for [HꢁM(diphosphine)2]ꢂ complexes (MꢀNi, Pd, Pt)
a
Complex
Solvent
1H-NMR HꢁM
dH (ppm)
31P{1H}-NMR diphosphine
Reference
b
2JHꢁMꢁP (Hz)
dP (ppm)
[HNi(dmpe)2]PF6
[HNi(depe)2]PF6
[HNi(dppv)2]BF4
[HNi(dppe)2]PF6
[HPd(dppe)2]BPh4
[HPt(dppe)2]PF6
[HPt(dmpe)2]PF6
[HPt(depe)2]PF6
CD3CN
CD3NO2
CD3CN
CD2Cl2
CD2Cl2
CD3NO2
CD3CN
CD3CN
ꢃ14.02
ꢃ14.16
ꢃ11.87
ꢃ12.87
8.5 (quintet)
(s)
10 (quintet)
24.6
46.2
[16a,16d]
[16a]
[16e]
56.71
42.5
c
2.4
53.7 (quintet)
[16a]
This work
[16a]
ꢃ7.37
32.98
20.4
d
d
ꢃ11.55
ꢃ12.12
30 (quintet)
29 (quintet)
ꢃ7.3
22.1
[16a,16d]
[16a,16d]
a
dmpeꢀ1,2-bis(dimethylphosphino)ethane; depeꢀ1,2-bis(diethylphosphino)ethane; dppvꢀ1,2-bis(diphenylphosphino)ethylene.
Versus H3PO4.
b
c
Multiplicity not reported.
Not reported.
d
in [HPt(diphosphine)2]ꢂ (ꢃ
[HNi(diphosphine)2]ꢂ (ꢃ
12}
/
11}
/
ꢃ
/
12 ppm) and
/
/
ꢃ14 ppm) complexes
/
2
and, furthermore, the JHꢁPdꢁP coupling constant (53.7
2
Hz) largely exceeds the JHꢁMꢁP values observed for
related [HPt(diphosphine)2]ꢂ (29ꢁ
/30 Hz) and
[HNi(diphosphine)2]ꢂ (0ꢁ
/10 Hz) cations.
Under the working conditions, the stability of 5 is
quite modest. In the 31P-NMR spectrum (81 MHz,
CD2Cl2, 293 K) of the reaction mixture (Eq. (7)); Pd(0)
to BPh4 salt molar ratioꢀ1:1) a new resonance becomes
/
clearly evident within 30 min at d 57.07 ppm, suggesting
the formation of cation [Pd(dppe)2]2ꢂ [17]. The forma-
tion of this species is also supported by the appearance
in the proton spectrum (500 MHz, CD2Cl2, 293 K; Pd(0)
Scheme 1.
[Pd(dppe)2][BPh4]2 8 (as for the characterization, see
Section 4) [18] together with variable amounts of the
starting Pd(0)-complex 7.
The reactivity of 3 towards 7 is affected by the nature
of solvent. In CD2Cl2 (Eq. (7)); Pd(0) to BPh4 salt molar
to BPh4 salt molar ratioꢀ1:1.06) of an unresolved
/
triplet at d 2.03 ppm. In the 1H spectrum, a weak signal
also appears at d 4.65 ppm due to formation of H2,
which has been further confirmed by GC analysis of the
gas in equilibrium with the solution. Furthermore, new
ratioꢀ1:1.06), at 293 K, after a reaction time of 15 min,
/
the 5 to 7 molar ratio, determined by integration of the
signals at d 7.20 (due to 5) and 7.04 ppm (due to 7), was
equal to 1.12:1, from which a lower limit of the
resonances, with relative intensity 2:1:6, are found at d
3
3.61 (s), 2.81 (septet, JHH
ꢀ6.1 Hz) and 1.05 ppm (d,
/
3JHH
tion of the amine PhCH2NH(CHMe2). The latter species
has been unambiguously identified, together with the
ꢀ6.1 Hz), respectively, which support the forma-
/
conversion a can be calculated (aꢀ
ently from what observed in CD2Cl2, the 1H-NMR (500
MHz, 293 K) spectrum of a THF-d8 solution of 7 (1.5ꢄ
10ꢃ2 mol lꢃ1) and 3 (3ꢄ10ꢃ2 mol lꢃ1) did not show
any evidence of the typical hydride signal around d ꢃ
/
53%) [19]. Differ-
/
imine PhCH2Nꢀ
reaction mixture. An analogous reactivity was observed
for a higher BPh4 saltꢁPd(0) molar ratio (2.09:1). These
data show that 5 can interact with iminium cation
[(PhCH2)HNꢀ
CMe2]ꢂ to give either molecular hydro-
gen and the imine (PhCH2)NꢀCMe2, or, by hydride
/
CMe2, by a GCꢁ
/
MS analysis of the
/
/7
/
ppm. Nevertheless, the presence of 5 in the reaction
solution, although in much lower concentration than in
CD2Cl2, can be inferred by the immediate appearance of
a new very weak signal at d 2.3 ppm (unresolved triplet),
assigned to the CH2CH2 protons of 5 [20]. However,
also in THF, 5 further reacts with 3 according to what
reported in Scheme 1.
The problem of the solution structure of cation 5ꢂ is
quite puzzling. The NMR (1H, 31P) spectra, at room
temperature (293 K), do not allow to distinguish among
a square pyramidal structure and lower-symmetry
coordination geometries (trigonal bipyramid or capped
/
/
transfer to the electrophilic iminium carbon, the amine
PhCH2NH(CHMe2) (Scheme 1).
Several attempts have been carried out to isolate
complex 5 in a pure form from the reaction mixture,
using both different Pd(0)ꢁBPh4 salt molar ratios (from
/
3:1 to 1:2) and a variety of experimental conditions,
without success. Work-up of the reaction mixture
allowed to isolate in a pure form only the new salt

116
M. Aresta, E. Quaranta / Journal of Organometallic Chemistry 662 (2002) 112ꢁ119
/
tetrahedron), which may undergo a fast fluxional
process on the NMR time scale, at room temperature.
VT-NMR [1H(200 MHz), 31P(81 MHz)] experiments in
CD2Cl2 did not help to solve the problem as no
complete decoalescence but only significant broadening
of both quintuplet terms in the proton spectrum and the
31P resonance of 5ꢂ (see Table 3) were observed upon
temperature lowering (down to 178 K [21]), as already
observed by other authors for the relevant Ni and Pt
complexes [16d]. It is worth noting that line broadening
is marked only for 5, while it is very modest for 7 and 8.
This behavior suggests that 5ꢂ is fluxional, but does not
provide any clear indication about the structure of the
cation in solution.
[22] and stored under N2. Tetraphenylborate salts 1ꢁ
/
3
were prepared as previously reported [2ꢁ4,5a].
/
[Pd(dppe)(dba)] was synthesized as described in the
literature [23].
IR spectra were obtained with a PerkinꢁElmer 883
/
spectrophotometer. NMR spectra were run on a Varian
XL-200 or a Bruker AM 500 instrument, as specified in
1
the text. H and 13C chemical shifts are in ppm versus
Me4Si and referenced to the solvent peak. 31P reso-
nances are reported in ppm versus H3PO4. GCꢁMS
/
analyses were carried out with a Shimadzu GC-17A
linked to a Shimadzu GCMS-QP5050 selective mass
detector (capillary column: 60 mꢄ0.25 mm Supelco
/
MDN-5S, 0.25 mm film thickness). Gas analyses were
performed using a Carlo Erba Fractovap instrument.
3. Conclusions
4.2. Synthesis of [Pd(dppe)2]
The reactivity of ammonium- and iminium-BPh4 salts
[Pd(dppe)2] was synthesized according to the litera-
ture procedure [17]. Below we report the NMR spectra
of a pure sample of 7 in the solvents (CD2Cl2, THF-d8)
used in this work for studying reaction (7). H-NMR
(THF-d8, 500 MHz, 293 K): d 2.08 (m, 8H, CH2CH2),
towards low-valent Pdꢁ
investigated. The allyl salts [CH2ꢀ
CMe2]BPh4 react with
/diphosphine complexes has been
/CHCH2NH3]BPh4
1
and [(CH2ꢀ
/
CHCH2)HNꢀ
/
[Pd(dppe)(dba)] to afford the new salt [(h3-
C3H5)Pd(dppe)][BPh4], through selective oxidative
transfer of allyl group from the primary ammonium or
iminium cation to the metal center.
6.99 (tr, 16H, Jꢀ
/
7.52 Hz, Hmeta), 7.08 (tr, 8H, Jꢀ7.50
/
1
Hz, Hpara), 7.38 (m, 16H, Hortho). H-NMR (CD2Cl2,
500 MHz, 293 K): d 2.09 (m, 8H, CH2CH2), 7.04 (tr,
An
[(PhCH2)HNꢀ
decribed, which gives a rare five-coordinated cationic
Pdꢁhydride, [HPd(dppe)2][BPh4], spectroscopically de-
unprecedented
proton
transfer
from
16H, Jꢀ
H
/
7.48 Hz, Hmeta), 7.15 (tr, 8H, Jꢀ
/
7.50 Hz,
para), 7.38 (m, 16H, Hortho). 31P-NMR (CD2Cl2, 81
/CMe2]BPh4 to Pd(dppe)2 has been also
MHz, 293 K): d 30.86 (vs. dP 30.6 ppm, in CH2Cl2 as
solvent; see Ref. [17]).
/
tected (by NMR), for the first time, in solution. Under
the working conditions, [HPd(dppe)2][BPh4] is not stable
as it acts as a hydride transfer agent towards the
4.3. Synthesis of [(h3-C3H5)Pd(dppe)][BPh4] by
reaction of [CH2ꢀ
/
CHCH2NH3]BPh4 with
iminium cation [(PhCH2)HNꢀ
/
CMe2]ꢂ to afford the
[Pd(dppe)(dba)]
new salt [Pd(dppe)2][BPh4]2.
BPh4 salt 1 (0.05475 g, 0.145 mmol) was added to a
THF (4 ml) solution of [Pd(dppe)(dba)] (0.106 g, 0.144
mmol). The resulting solution, stirred at 293 K for 2 h,
4. Experimental
slowly turned from red to yellowꢁorange. The gas
/
4.1. General
phase, periodically analyzed by GC throughout the
reaction time, did not show detectable amounts of H2.
The reaction mixture was concentrated in vacuo and
30 ml of Et2O were layered. After cooling to 253 K
overnight, the sticky oil separated was isolated by
removing the mother solution with a syringe and washed
Unless otherwise stated, all reactions and manipula-
tions were conducted under a dinitrogen atmosphere (as
specified in the text), by using vacuum line techniques.
All solvents were dried according to literature methods
Table 3
Reaction of [(PhCH2)HNꢀCMe2]BPh4 (3) with [Pd(dppe)2] (7). VT-31P{1H}-NMR (CD2Cl2, 81 MHz; 7 to 3 molar ratioꢀ1:1; see Section 4)
T (K)
[HPd(dppe)2][BPh4]
[Pd(dppe)2]
[Pd(dppe)2][BPh4]2
dP (ppm)
w1/2 (Hz)
dP (ppm)
w1/2 (Hz)
dP (ppm)
w1/2 (Hz)
293
223
193
178
32.96
33.49
33.73
33.91
7
9
30.86
31.73
32.21
32.44
3
4
5
6
57.08
57.13
57.37
57.53
3
3
5
6
30
68

M. Aresta, E. Quaranta / Journal of Organometallic Chemistry 662 (2002) 112ꢁ
/119
117
with Et2O (3ꢄ
/
10 ml). Upon drying in vacuo an orange
4.5. Reaction of [(PhCH2)HNꢀ
/
CMe2]BPh4 with
[Pd(dppe)2]: isolation and characterization of
[Pd(dppe)2][BPh4]2
solid was obtained and identified as 6. Yield: 0.100 g,
80%. Anal. Found: C, 73.29; H, 5.69; P, 7.28; Pd, 12.25.
Calc. for C53H49BP2Pd: C, 73.58; H, 5.71; P, 7.17; Pd,
12.30%. As for the spectroscopic characterization, see
below.
To a CH2Cl2 (10 ml) solution of 7 (0.13000 g, 0.144
mmol) the BPh4 salt 3 (0.13965 g, 0.299 mmol),
previously dissolved in 10 ml of the same solvent, was
added. The system was stirred at room temperature (293
K) for 6 h. Upon addition of n-C5H12 (20 ml) and
cooling to 253 K, a beige microcrystalline solid was
4.4. Synthesis of [(h3-C3H5)Pd(dppe)][BPh4] by
reaction of [(CH2ꢀ
[Pd(dppe)(dba)]
/
CHCH2)HNꢀ/CMe2]BPh4 with
obtained, isolated by filtration, washed with C6H6 (2ꢄ
/
10 ml), dryed in vacuo and characterized as
[Pd(dppe)2][BPh4]2. Yield: 0.155 g, 70%. Anal. Found:
C, 77.79; H, 5.97; P, 7.98; Pd, 6.88. Calc. for
To a THF (4 ml) solution of 4 (0.108 g, 0.146 mmol)
the BPh4 salt 2 (0.064 g, 0.153 mmol), dissolved in THF
(3 ml), was added and the resulting solution was stirred
at 293 K for 2 h. The initially red solution turned to
deep red, then to orange and finally to deep yellow. The
GC analysis of the gas phase, periodically monitored
throughout the reaction time, did not show any evidence
of H2 evolution.
C
100H88B2P4Pd: C, 77.90; H, 5.75; P, 8.04; Pd, 6.90%.
IR (Nujol, KBr, cmꢃ1): 3055 (m-w), 3030 (m-w), 1575
(m-w), 1475 (m), 1430 (m), 1310 (w), 1300 (w), 1260 (w),
1100 (m), 1060 (w), 1025 (w), 995 (m-w), 870 (w), 838
(w), 810 (m-w), 740 (m), 730 (m-s), 703 (s), 685 (m-s),
650 (w), 620 (w), 610 (m), 530 (m-s), 510 (m), 475 (m).
1H-NMR (Me2SO-d6, 500 MHz, 293 K): d 2.97
To the reaction mixture, concentrated in vacuo, Et2O
(30 ml) was added. By cooling to 253 K, an orange oil
separated, from which an orange solid was obtained (see
above) and identified as 6. Yield: 0.107 g, 85%. Anal.
Found: C, 73.30; H, 5.82; P, 7.27; Pd, 12.38. Calc. for
C53H49BP2Pd: C, 73.58; H, 5.71; P, 7.17; Pd, 12.30%. IR
(Nujol, KBr, cmꢃ1): 3050 (m-w), 3030 (m-w), 1575 (m-
w), 1475 (m), 1430 (m), 1328 (w), 1300 (w), 1260 (w),
1175 (w), 1098 (m), 1060 (w), 1025 (w), 995 (m-w), 965
(w), 870 (w), 838 (w), 815 (m-w), 740 (m), 732 (m-s), 705
(s), 690 (m-s), 648 (w), 620 (w), 610 (m), 523 (m-s), 485
(unresolved triplet, 8H, CH2CH2), 6.77 (tr, 8H, Jꢀ
/
7.17 Hz, Hpara;BPh ); 6.90 (tr, 16H, Jꢀ7.40 Hz,
/
4
Hmeta;BPh ); 7.17 (m, 16H, Hortho;BPh ); 7.25 (m, 16H,
H
4
4
ortho,dppe), 7.34 (tr, 16H, Jꢀ
/
7.56 Hz, Hmeta,dppe),
7.50 (tr, 8H, Jꢀ7.45 Hz, H
/
para,dppe). 13C-NMR
(Me2SO-d6, 125 MHz, 293 K): d 28.90 (m, broad,
CH2CH2), 121.48 (s, Cpara;BPh ); 125.26 (quartet,
4
3JCB
singlets, aromatic Cdppe), 135.51 (unresolved multiplet,
ꢀ2.6 Hz, Cmeta;BPh ); 129.18, 132.74, 133.39 (all
/
4
1
Cortho;BPh ); 163.33 (quartet, JCB
ꢀ
/
49.3 Hz, Cipso;BPh ):/
4
4
1
4.6. Reactivity of [(PhCH2)HNꢀ
/CMe2]BPh4 with
(m), 475 (m). H-NMR (CD2Cl2, 500 MHz, 293 K): d
2.52 (m, 4H, CH2CH2), 3.26 (m, 2H, Hanti), 4.84 (m, 2H,
[Pd(dppe)2]: NMR experiments
H
syn), 5.64 (septet, 1H, Jꢀ
Jꢀ7.20 Hz, Hpara;BPh ); 6.98 (tr, 8H, Jꢀ
Hmeta;BPh ); 7.30 (m, 8H, Hortho;BPh ); 7.35ꢁ
/
7 Hz, Hmeso), 6.83 (tr, 4H,
4.6.1. 1H-NMR (CD2Cl2, 500 MHz, 293 K; 7 to 3 molar
ratioꢀ1:1.06)
Compounds 7 (0.01875 g, 0.0208 mmol) and 3
(0.01030 g, 0.0220 mmol) were dissolved in 0.5 ml of
CD2Cl2, respectively. After mixing, the resulting solu-
tion was transferred into a NMR tube, and the spectrum
was recorded after 15 min, 1 h and 3 h. The gas phase
was analyzed by GC (H2 was detected in the gas phase)
/
/7.42 Hz,
4
/
/7.64 (m, 20H,
4
4
H
supported by decoupling experiments from which the
Ph,dppe). The assignment of the allyl protons was
3
3
values of JH
(7.33 Hz) and JH
(13.6 Hz)
mesoꢁHanti
mesoꢁHsyn
were obtained. 13C-NMR (CD2Cl2, 125 MHz, 293 K): d
27.35 (virtual triplet, Jꢀ22.8 Hz, CH2CH2), 71.36
(virtual triplet, Jꢀ15.4 Hz, terminal allyl carbon
5.83 Hz,
2.8 Hz, Cmeta;BPh ); 130.09
/
/
and the reaction solution by GCꢁ
/
MS. The GCꢁMS
/
atoms), 122.07 (s, Cpara;BPh ); 123.54 (tr, JCP
ꢀ
/
4
analysis showed the presence of the imine (PhCH2)Nꢀ
/
meso), 125.95 (quartet, 3JCB
ꢀ
/
CMe2 (m/z 147 [Mꢂ], 132, 117, 104, 91, 77, 69, 66, 56,
51, 42, 39) and confirmed (see Section 2) the formation
of the amine PhCH2NH(CHMe2) (m/z 149 [Mꢂ], 134,
91, 77, 65, 41, 39).
C
4
3
1
(d, JCP
Hz, Cipso,dppe), 132.66 (s, Cpara,dppe), 132.96 (d, JCP
ꢀ
/
11.42 Hz, Cmeta,dppe), 132.64 (d, JCP
ꢀ19.43
/
2
ꢀ
/
7.15 Hz, Cortho,dppe), 136.30 (s, C ); 164.40
(quartet, 1JCB
(CD2Cl2, 202 MHz, 293 K): d 53.65. 1H-NMR
(CDCl3, 500 MHz, 293 K): d 2.12 (m, 4H, CH2CH2),
3.09 (m, 2H, Hanti), 4.65 (m, 2H, Hsyn), 5.39 (m, 1H,
ortho;BPh4
ꢀ
/
49.65 Hz, Cipso;BPh ): 31P-NMR
4
4.6.2. 1H-NMR (CD2Cl2, 500 MHz, 293 K; 7 to 3 molar
ratioꢀ1:2.09)
/
Compounds 7 (0.02695 g, 0.0298 mmol) and 3
(0.02915 g, 0.0624 mmol) were dissolved, respectively,
in 0.5 ml of CD2Cl2. After mixing, the resulting solution
was analyzed as reported above. An analogous experi-
H
meso), 6.76 (tr, 4H, Jꢀ
Jꢀ7.42 Hz, Hmeta;BPh ); 7.20ꢁ
Ph,dppe). 31P-NMR (CDCl3, 202 MHz, 293 K): d 51.88.
/
7.1 Hz, Hpara;BPh ); 6.88 (tr, 8H,
4
/
/
7.54 (28H, Hortho;BPh and
4
4
H

118
M. Aresta, E. Quaranta / Journal of Organometallic Chemistry 662 (2002) 112ꢁ119
/
[3] M. Aresta, A. Dibenedetto, E. Quaranta, J. Chem. Soc. Dalton
Trans. (1995) 3359.
ment was also carried out using THF-d8 as solvent (see
Section 2).
[4] M. Aresta, E. Quaranta, A. Dibenedetto, P. Giannoccaro, I.
Tommasi, M. Lanfranchi, A. Tiripicchio, Organometallics 16
(1997) 834.
4.6.3. 31P-NMR (CD2Cl2, 81 MHz, 293 K; 7 to 3 molar
[5] (a) M. Aresta, A. Dibenedetto, E. Quaranta, M. Lanfranchi, A.
Tiripicchio, Organometallics 21 (2000) 4199;
(b) E. Amodio, Dr. Thesis, University of Bari, 2001;
(c) M. Aresta, I. Tommasi, A. Dibenedetto, E. Amodio, Eur. J.
Inorg. Chem. (2002) 2188.
ratioꢀ1:1.01)
/
Compound 7 (0.03170 g, 0.0351 mmol) was dissolved
in 3 g of CD2Cl2 and the 31P{1H} spectrum recorded
(see Section 4.2). To this solution 0.01660 g of 3 (0.0355
mmol), dissolved in 1 g of CD2Cl2, were added under a
N2 stream and the resulting solution analyzed by 31P-
NMR (see Section 2).
[6] (a) H.J. Heeres, A. Meetsma, J.H. Teuben, J. Organomet. Chem.
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(b) A.L. Seligson, W.C. Trogler, Organometallics 12 (1993) 744;
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(d) S.L. Borkowski, R.F. Jordan, J.D. Hinch, Organometallics 10
(1991) 1268;
ratioꢀ1:1.19)
/
(e) M. Bochmann, G. Karger, A.G.J. Jaggar, J. Chem. Soc.
Chem. Commun. (1990) 1038;
The reaction mixture was prepared by mixing 0.03715
g (0.0411 mmol) of 7, dissolved in 0.5 ml of CD2Cl2, and
0.02280 g (0.0488 mmol) of 3 dissolved in the same
solvent (0.5 ml). The spectrum of the reaction mixture
was, then, recorded at the following temperatures: 293,
233, 193 and 178 K. The quintet due to complex 5 (see
(f) Z. Lin, J.-F. Le Marechal, M. Sabat, T.J. Marks, J. Am. Chem.
Soc. 109 (1987) 4127.
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1100;
Section 2), originally located at d ꢃ
markedly broadened upon lowering temperature and
was found at ꢃ7.25 ppm at 233 K, ꢃ7.20 at 193 K and
7.16 at 178 K.
/
7.37 ppm at 293 K,
(c) D.J. Sepelak, C.J. Pierpont, E.K. Barefield, J.T. Budz, C.A.
Poffenberger, J. Am. Chem. Soc. 98 (1976) 6178;
(d) E.K. Barefield, D.J. Sepelak, J. Am. Chem. Soc. 101 (1979)
6542;
/
/
ꢃ
/
(e) E.K. Barefield, A.M. Carrier, D.J. Sepelak, D.G. Van Derveer,
Organometallics 1 (1982) 103;
4.6.5. VT-31P-NMR (CD2Cl2, 81 MHz; 7 to 3 molar
ratioꢀ1:1)
(f) E.K. Barefield, A.M. Carrier, D.J. Sepelak, D.G. Van Derveer,
Organometallics 4 (1985) 1395;
/
(g) S.-I. Murahashi, Angew. Chem. Int. Ed. Engl. 34 (1995) 2443.
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(b) R.S. Paonessa, A.L. Prignano, W.C. Trogler, Organometallics
4 (1985) 647;
The reaction solution was prepared by mixing 0.10605
g (0.117 mmol) of 7, dissolved in 2.5 ml of CH2Cl2, and
0.05465 g (0.117 mmol) of 3 dissolved in 1 g of CD2Cl2.
The spectrum of the reaction mixture was, then,
(c) H. Kumobayashi, S. Mitsuhashi, S. Akutagawa, S. Ohtsuka,
Chem. Lett. (1986) 157;
measured in the temperature range 293ꢁ178 K. Decreas-
/
(d) R. Malet, M. Moreno-Manas, R. Pleixats, Organometallics 13
(1994) 397;
ing temperature caused downfield shift of all signals and
marked broadening of the signal assigned to 5 (see Table
3).
(e) R. Malet, M. Moreno-Manas, R. Pleixats, Anales de Quimica
Int. Ed. 92 (1996) 25.
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Acknowledgements
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Tetrahedron Lett. 21 (1965) 1583;
We gratefully acknowledge financial support from the
Ministero dell’Universita` e della Ricerca Scientifica e
Tecnologica (MURST, Project MM03027791).
(b) J. Powell, B.L. Shaw, J. Chem. Soc. (A) (1968) 774.
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more precise value obtained from the 1H spectrum (53.7 Hz).
/
/
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/

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/
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