Cyclopalladated Compounds with Polyhalogenated Benzylphosphanes for the Mizoroki-Heck Reaction

Article abstract of DOI:10.1002/ejic.202000288

Nine partially halogenated benzylphosphanes Ar_XCH₂PR₂ (Ar_X = 3,6-dichlorophenyl, 3,6-difluorophenyl and 3,4,5-trifluorophenyl; R = Ph, Cy, iPr) have been prepared and reacted with palladium acetate to obtain the

Full text of DOI:10.1002/ejic.202000288

European Journal of Inorganic Chemistry
Accepted Article
Title: Cyclopalladated Compounds with Polyhalogenated
Benzylphosphanes for the Mizoroki-Heck Reaction
Authors: Cristina López-Mosquera, Arnald Grabulosa, Mercè
Rocamora, Mercè Font-Bardia, and Guillermo Muller
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.202000288
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01/2020

10.1002/ejic.202000288
European Journal of Inorganic Chemistry
Cyclopalladated Compounds with Polyhalogenated Benzylphosphanes
for the Mizoroki-Heck Reaction
Cristina López-Mosquera,a Arnald Grabulosa,a,b,* Mercè Rocamora,a Mercè Font-
Bardia,c and Guillermo Mullera
aDepartament de Química Inorgànica i Orgànica, Secció de Química Inorgànica, Universitat de Barcelona,
b
Martí i Franquès, 1-11, E-08028, Barcelona, Spain. Institut de Nanociència i Nanotecnologia (IN2UB),
c
Universitat de Barcelona, E-08028, Barcelona, Spain. Unitat de Difracció de RX, Centres Científics i
Tecnològics de la Universitat de Barcelona (CCiTUB), Solé i Sabarís 1-3, E-08028, Barcelona, Spain.
Abstract
Nine partially halogenated benzylphosphanes ArXCH2PR2 (ArX = 3,6-dichlorophenyl, 3,6-
difluorophenyl and 3,4,5-trifluorophenyl; R = Ph, Cy, i-Pr) have been prepared and reacted with
palladium acetate to obtain the cyclometallated dimers [Pd(µ-OAc)(k2-C,P-ArXCH2PR2)]2. The
acetate bridge has been exchanged by bromide using lithium bromide and the obtained dimers
have been thoroughly characterised. The dimers with the non-halogenated phosphanes PhCH2PR2
(R= Ph, i-Pr) have also been prepared. Treatment with norbornadiene in the presence of silver
tetrafluoroborate has furnished the cationic mononuclear complexes [Pd(k2-C,P-
ArXCH2PR2)(nbd)]BF4 as stable solids. These complexes and some of the bromide dimers have
been used as catalytic precursors in the Mizoroki-Heck reaction between bromobenzene and butyl
acrylate. The complexes efficiently catalyse this transformation and important differences of
activity are found depending on the ligand. In general, fluorinated phosphanes give more active
systems than chlorinated analogues.
Introduction
In 2010, Richard F. Heck, Ei-ichi Negishi and Akira Suzuki were awarded with the Nobel Prize
in Chemistry “for palladium-catalyzed cross couplings in organic synthesis”. The currently
known as Mizoroki-Heck, Negishi and Suzuki-Miyaura reactions revolutionised the field of
organic synthesis by allowing the formation of C–C bonds under mild conditions.[1] The three
1
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10.1002/ejic.202000288
European Journal of Inorganic Chemistry
reactions are efficiently catalysed by Pd(0) species and have been used to prepare countless
molecules of industrial or pharmacological interest and remain central in the synthetic toolkit.
The Mizoroki-Heck (M-H) reaction is the coupling between an aryl halide or tosylate with an
alkene, catalysed by Pd(0) in the presence of a base (Scheme 1).[2]
R
[Pd]
R
+
Ar–X
Ar
Base, –HX
Scheme 1. The Mizoroki-Heck reaction.
Compared to the Negishi or the Suzuki-Miyaura couplings, the M-H reaction is particular
because: 1) was the first to be discovered and paved the way to the discovery of the other cross-
coupling reactions; 2) it is mechanistically distinct compared to the other cross-coupling reactions
and 3) uses cheap and widely available unfunctionalised alkenes as coupling partners. The last
reason is particularly important and explains the intense interest in the M-H reaction in both
academia and industry, a research effort that has given tens of thousands of publications and
patents and has been collected in many reviews.[3]
The generally accepted mechanism of the M-H reaction involves a Pd(0)/Pd(II) catalytic
cycle[3d,3h] although usually the more stable Pd(II) systems are used as precatalysts. Simple
palladium(II) salts such as palladium acetate or chloride,[2b,4] molecular complexes and
organometallics[3b,5] as well as heterogeneous catalysts or “heterogenized” molecular species[6]
have been used in the M-H reaction.
Among the many systems studied, Herrmann’s[4a,5,7] cyclometallated dimeric complexes with
phosphanes (Figure 1) were found to produce exceptionally active systems for the reaction[8] and
remain a landmark in the area.
Xn
R
R
R
R
R
R
o-Tol
o-Tol
P
O
O
P
P
P
Br
Br
Br
Br
Pd
Pd
Pd
Pd
Pd
Pd
Pd
P
O
O
o-Tol
P
P
BF4
o-Tol
R
R
R
R
Xn
Xn
Herrmann et al., 1995
Cole-Hamilton et al., 2001
Present work
Figure 1. Catalytic precursors for the M-H reaction developed by the groups of Herrmann,[7] Cole-
Hamilton[9] and those described in the present work.
2
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10.1002/ejic.202000288
European Journal of Inorganic Chemistry
These systems were discovered when exploring the use of o-tolylphosphanes in M-H reactions,
with palladium acetate as metallic precursor. Under catalytic conditions the methyl group of the
o-tolyl substituent is activated forming the dimeric Herrmann’s catalyst, with acetate bridges.
Inspired by these results, a few years later Cole-Hamilton and coworkers[9] reported metallated
complexes of palladium with simple benzylphosphanes (Figure 1), which were also found to be
very active in M-H reactions and also in Suzuki-Miyaura couplings.
Cyclopalladated compounds with benzylphosphanes have indeed a long history. As early as 1975
Shaw and coworkers[10] showed that complexes trans-[PdCl2L2] (L = PBn2(t-Bu) and PBn(t-
Bu2)2) undergo internal metallation, with certain difficulty, to give complexes of the type [Pd(µ-
Cl)(k2-C,P-PBnRR’)]2. It was found that the bulkier PBn(t-Bu2)2 is metallated more readily than
PBn2(t-Bu). The bridging chlorides could be replaced by bromide or iodide and the bridges split
by various ligands to give mononuclear species. A few years later, Vrieze and coworkers[11]
reacted PBnR2 (R = Cy, t-Bu) with [Rh(cod)Cl]2, [Ir(cod)Cl]2, PdCl2 and PtCl2(benzonitrile)2,
obtaining the corresponding cyclometallated compounds. It was found that steric effects have a
large influence on the rates of the reactions. Hiraki and coworkers[12] were the first to
cyclopalladate benzyldiphenylphosphane with palladium acetate, giving the dimeric acetate-
bridged complex, which could be converted to the corresponding chloro-bridged analogue by a
metathesis reaction with lithium chloride. Much more recently, Leung and coworkers[13]
demonstrated that steric shielding greatly favours the palladation of benzylphosphanes and found
that bis(tert-butyl)(diphenylmethyl)phosphane readily palladates even under conditions known to
disfavour the reaction. Interestingly, Gatineau et al.[14] explored the cyclometallation of PBn(t-
Bu)(o-tolyl) with palladium acetate and found that the o-tolyl group not the benzyl, was
palladated, proving that often C(sp3)–H bonds are activated more easily than C(sp2)-H.
We reasoned that modification of the Cole-Hamilton systems by introduction of halogen atoms
in the ortho-metallated benzyl substituent would result in stronger Pd-Caryl bonds and could give
more robust catalysts. In addition, we also envisaged the preparation of mononuclear, cationic
versions of the Cole-Hamilton’s catalysts, stabilised by a norbornadiene to obtain more active
catalysts, since the dimeric systems are thought to give mononuclear complexes under catalytic
3
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10.1002/ejic.202000288
European Journal of Inorganic Chemistry
conditions. The results on the synthesis and characterisation of the polyhalogenated phosphanes
and their derived cyclopalladated compounds and the applications of the complexes in the M-H
reaction are described in the present paper.
Results and discussion
The cyclometallated dimers of Cole-Hamilton and coworkers[9] (Figure 1) were obtained by
oxidative addition of o-bromobenzylphosphanes with the Pd(0) precursor [Pd2(dba)3]. Although
very efficient, this method requires a bromo substituent to be installed in the benzylphosphane,
which would make the synthesis of the desired polyhalogenated phosphanes rather difficult.
Therefore, the direct palladation of the polyhalogenated benzylphosphanes by C–H activation
with palladium acetate was studied, following a method used for simple benzylphosphanes.
Benzylphosphanes
The synthesis of di- and trihalogenated benzylphosphanes was explored by two methods (Scheme
2): the alkylation of secondary phosphanes with benzyl bromides in the presence of base (A)[15]
and the treatment of chlorophosphanes with benzylic Grignard reagents (B).
Ph Ph
P
Ph Ph
P
A
Br
BH3
Cl
Cl
Cl
HPPh2, NEt3
BH3·SMe2
Toluene, rt, 1 h
Cl
Cl
Cl
1a
1a’
R
R
R
R
B
Br
P
P
BH3
1) Mg, Et2O, rt, 1h
BH3·SMe2
X
X
X
2) ClPR2, Et2O, 0 ºC, 1 h
X
X
X
X = F, Cl
R = Ph (a), Cy (b), i-Pr (c)
X = Cl; 1a, 1b, 1c
X = F; 2a, 2b, 2c
X = Cl; 1a’ (69%), 1b’ (49%), 1c’ (68%)
X = F; 2a’ (36%), 2b’ (68%), 2c' (61%)
R
R
R
R
Br
P
P
BH3
1) Mg, Et2O, rt, 1h
2) ClPR2, Et2O, 0 ºC, 1 h
BH3·SMe2
F
F
F
F
F
F
F
F
F
3a, 3b, 3c
3a’ (53%), 3b’ (24%), 3c’ (42%)
4
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10.1002/ejic.202000288
European Journal of Inorganic Chemistry
Scheme 2. Synthesis of benzylphosphanes, phosphane-boranes and overall yields of the latter.
Although both methods allowed the synthesis of the desired ligands, method B provided slightly
higher yields and much better reproducibility and therefore was selected as default. As the free
phosphanes turned out to be very air-sensitive, they were immediately either coordinated or
protected with borane for storage and complete characterisation. For comparison purposes, non-
halogenated phosphanes benzyldiphenylphosphane (4a) and benzyldiisopropylphosphane (4c)
were also considered. Phosphane 4a is commercially available while 4c was prepared by method
B employing commercially available benzylmagnesium chloride solution and following a
literature procedure.[16]
The free phosphanes were characterised by 31P{1H} NMR spectroscopy while their borane
1
adducts were characterised by 31P{1H}, H and 13C{1H} NMR spectroscopy, IR spectroscopy,
mass spectrometry and chemical analysis. The most relevant NMR data is given in Table 1.
Table 1. Selected NMR data of benzylphosphanes and their borane adducts.
Free phosphanes
Phosphane-boranes
d 31P{1H}
d 31P{1H}a (1JPB) d 1Ha PCH2Ar (2JPH)
(4JPF)
–12.8
+2.6
1ab
1bc
1cc
1a’
1b’
1c’
2a’
2b’
2c’
+17.9 (q, 56)
3.77 (d, 12.0)
+29.7 (br)
+37.5 (q, 59)
+17.7 (q, 72)
+30.0 (q, 67)
+36.1 (q, 58)
+17.2 (q, 63)
+27.7 (q, 59)
+34.6 (q, 51)
+19.3 (d, 65)
–
3.16 (d, 11.9)
3.11 (d, 12.0)
3.53 (d, 11.6)
3.00 (d, 11.2)
3.03 (d, 11.2)
3.50 (d, 11.6)
2.94 (d, 11.6)
2.95 (d, 11.6)
3.61 (d, 12.0)
–
+10.1
2ab
2bc
2cc
–11.5 (d, 12.1)
+2.4 (d, 9.5)
+10.6 (d, 10.5)
–9.9
3ab
3bc
3cc
3a’
3b’
3c’
+2.1
+10.6
4a[17]
4c
–10.0
4a’[15a]
–
+9.9[18]
Chemical shifts in ppm, coupling constants in Hz; 31P{1H} (101,1 MHz, 298 K) and 1H (400
a
b
MHz, 298 K). Multiplicity and JPB and JHP in parenthesis. Recorded in CDCl3, recorded in
diethylether with an external reference (1% P(OMe)3 in C6D6); recorded in toluene with an
c
external reference (1% P(OMe)3 in C6D6).
As expected, 31P chemical shifts strongly depended on the identity of the phosphane groups, with
only a minor influence of the substitution in benzyl group. Diphenylphosphanes (a) appeared at
the highest field followed by dicyclohexylphosphanes (b) and finally diisopropylphoshines (c).
5
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10.1002/ejic.202000288
European Journal of Inorganic Chemistry
It was possible to grow crystals of phosphane-boranes 2a’ and 3c’ by slow diffusion of ethanol
into concentrated dichloromethane solutions of the corresponding phosphane-boranes, at 4 ºC.
The molecular structures are shown in Figure 2 along with a selection of bond distances and
angles.
Figure 2. Representation of the molecular structure of phosphane-boranes 2c’ (left) and 3c’ (right), with
ellipsoids shown at 50% probability level and hydrogen atoms omitted for clarity. Selected distances (Å)
and angles (º): for 2c’ P–C7, 1.842(4), P–C9, 1.807(4), P–C12, 1.862(4), P–B, 1.890(5), C9–P–C7
107.75(18), C7–P–C12 101.9(2), C9–P–C12 105.91(17), C7–P–B 113.8(2), C9–P–B 113.2(3), C12–P–B
113.3(2). For 3c’: P–C7, 1.821(3), P–C9, 1.842(3), P–C12, 1.859(3), P–B, 1.914(4), C9–P–C7
103.03(15), C7–P–C12 104.28(14), C9–P–C12 108.06(15), C7–P–B 110.72(16), C9–P–B 114.83(17),
C12–P–B 114.77(17).
No significant differences in bond distances and angles were found for adducts 2c’ and 3c’, which
show similar values to previously reported benzylphosphane-boranes.[14,19]
Neutral palladium complexes
In the present work, with the aim of obtaining cyclometallated complexes the reaction of
benzylphosphanes and palladium acetate was studied in detail in toluene due to increased stability
of phosphanes in this solvent.
Palladium acetate has been known to be particularly effective to palladate phosphanes.[12,14,20]
When the reaction was performed at room temperature, palladium coordination complexes
([Pd(OAc)nP2]) were obtained and could be unequivocally identified upon conversion to trans-
[PdBr2P2] by treatment with lithium bromide in acetone. An increase of the temperature was
necessary to observe the C(sp2)-H activation of the benzyl substituent of the phosphane. From
temperatures in the range 50-60 °C it was already possible to detect cyclometallated complexes.
6
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10.1002/ejic.202000288
European Journal of Inorganic Chemistry
The addition of a base like NaOAc was convenient to favour the C–H activation and improve the
yield of the palladium dimer and the reproducibility of the reaction.
Palladium dimers [Pd(μ-OAc)(k2-PC)]2 (6c, 7b, 8a) containing the desired five-membered PdPC
ring were obtained at 60 ºC in 12 h while heating at 80 ºC allowed the formation of the
cyclometallated dimers for all the phosphanes (Scheme 3).
R
R
X
X
R
R
R
R
P
P
O
O
P
Br
Br
X
X
Pd(OAc)2, NaOAc
Pd
LiBr
Pd
Pd
X
Pd
X
X
O
O
P
Toluene, 80 ºC, 12 h
Acetone, 25 ºC, 2 h
P
R
R
R
X
R
X
X
X = Cl; 1a, 1b, 1c
X = F; 2a, 2b, 2c
X = H; 4a, 4c
X = Cl; 5a, 5b, 5c
X = F; 6a, 6b, 6c
X = H; 11a, 11c
X = Cl; 8a (40%), 8b (30%), 8c (26%)
X = F; 9a (69%), 9b (28%), 9c (20%)
X = H; 12a (55%), 12c (19%)
F
F
R
R
F
F
R
F
F
R
R
R
P
P
P
O
O
Br
Br
Pd
Pd
Pd(OAc)2, NaOAc
Pd
LiBr
Pd
P
O
O
P
Toluene, 80 ºC, 12 h
Acetone, 25 ºC, 2 h
R
R
F
F
R
F
F
R
F
F
F
F
F
3a, 3b, 3c
7a, 7b, 7c
10a (27%), 10b (65%) , 10c (34%)
Scheme 3. Preparation of dimeric cyclometallated acetate-bridged complexes (not isolated) and the
isolated bromide-bridged complexes. The overall yields are given for the latter.
The cyclopalladation of the benzylic phosphanes could be monitored by 31P{1H} NMR
spectroscopy. In all cases different amounts (10 – 30%) of coordination compounds [Pd(OAc)nP2]
were also detected as well as small amounts of starting palladium acetate and palladium black.
The reaction mixture containing the palladium dimer was filtered through celite and the crude
toluene solution was evaporated to dryness. The reaction of the solid residue with LiBr in acetone
at room temperature for two hours led to the substitution of the acetate bridge and to the formation
of the dimeric compounds [{Pd(k2-PC)}(μ-Br)]2 (8, 9, 10 and 12).[8b,12,14,20] In some occasions the
coordination compound trans-[PdBr2P2] was also obtained and was separated by precipitation or
column chromatography.
In some cases, like with phosphane 2b or if the reaction was carried out without adding sodium
acetate, the formation of other compounds was observed (Scheme 4).
7
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10.1002/ejic.202000288
European Journal of Inorganic Chemistry
Cy
Cy
F
Cy
Cy
Cy
Cy
P
P
P
(2,5-F2Ph)CH2Cy2P
+
O
O
OAc
OAc
F
Pd(OAc)2, NaOAc
Pd
Pd
Pd
Pd
F
F
F
+
PCy2CH2(2,5-F2Ph)
AcO
O
O
PCy2CH2(2,5-F2Ph)
P
Toluene, 60 ºC, 12 h
F
Cy
Cy
F
F
2b
6b
6b’
LiBr, acetone
25 ºC, 2 h
F
Cy
Cy
Cy
Cy
P
(2,5-F2Ph)CH2Cy2P
+
P
Br
Br
Br
F
Pd
Pd
Pd
Pd
F
F
+
PCy2CH2(2,5-F2Ph)
Br
Br
PCy2CH2(2,5-F2Ph)
P
Cy
9b
Cy
F
F
9b’
Scheme 4. Mixture of complexes formed by reaction of 2b with palladium acetate.
In this case the reaction of 2b with palladium acetate yields the expected dimer 6b but also the
monomeric species 6b’ resulting from the splitting of this dimer with another equivalent of 2b
and the coordination compound [Pd(2b)2(OAc)2]. The ratio between the three species was
1.0:0.7:0.5 approximately. It could be observed that when mixtures of the metallated dimers and
the corresponding coordination compounds [Pd(PR2CH2ArX)2(OAc)2] are left at 80 ºC in the
presence of sodium acetate for long periods of time, the monomeric complexes [PdBr((k2-
PC)(PR3)]] and unidentified decomposition products are obtained. 31P{1H} NMR spectroscopy
was an invaluable tool to analyse this kind of mixtures. As an example, Figure 3 shows the
31P{1H} NMR spectrum of complexes of Scheme 4.
8
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10.1002/ejic.202000288
European Journal of Inorganic Chemistry
Figure 3. 31P{1H} NMR spectrum of a mixture of brominated complexes obtained from 2b.
Complexes 10 showed low solubility in common organic solvents such as dichloromethane,
toluene or THF and all are stable as solids under nitrogen atmosphere. The new palladium
complexes obtained [Pd(k2-PC)(μ-Br)]2 (8, 9, 10, 11 and 12) were characterized by elemental
1
analysis, infrared spectroscopy and multi-nuclear (31P{1H}, H, 19F and 13C{1H}) NMR
spectroscopy. The metallated dimers with acetate bridge showed broad signals in both the 31P{1H}
1
and H NMR spectra, in particular those with the diphenylphoshino group (a) and only the
31P{1H} spectra are presented. This is due to the fluxional character of the compounds and to the
possible existence of an equilibrium between the monomer and the dimer, owing to the weakly
bound acetate anions.[5] Relevant NMR data is summarized in Table 2.
Table 2. Selected NMR data of cyclopalladated complexes 5-12.a
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10.1002/ejic.202000288
European Journal of Inorganic Chemistry
31P{1H}
1H PCH2Ar (2JPH)
13C{1H} PCH2Ar (1JCP)
d
µ
k2
d
d
[Pd( -X)( -PC)]2
Ph
Ph
5a
8a
48.4
–
–
P
Pd
Cl
X
2
53.1
4.09 (d, 11.6)
–
43.0 (d, 36.8)
Cl
Cy
Cy
66.3, 65.3
3:1
5b
–
P
Pd
Cl
X
2
8b
5c
8c
6a
78.7
60.2
87.1
3.31 (d, 10.4)
35.3 (d, 24.5)
Cl
–
–
P
Pd
Cl
X
2
3.33 (d, 10.4)
–
26.0 (d, 25.3)
–
Cl
Ph
59.3, 57.9
2:3
Ph
P
Pd
F
59.9, 59.0
3:1
X
2
9a
3.92 (d, 12.0)
38.9 (d, 36.7)
F
Cy
Cy
6b
9b
69.3
85.1
–
–
P
Pd
F
X
2
3.19 (d, 10.2)
35.2 (d, 25.0)
F
6c
9c
78.0
94.8
–
–
P
Pd
F
X
2
3.20 (d, 10.4)
25.9 (d, 25.0)
F
Ph
Ph
46.1, 46.0
9:1
54.4, 54.3
9:1
P
7a
–
–
Pd
X
2
F
F
10a
7b
3.88 (d, 12.0)
–
44.1 (d, 41.4)
–
F
Cy
Cy
P
65.2
82.1
74.4
91.0
51.2
Pd
X
2
10b
7c
3.19 (d, 10.8)
35.1 (d, 25.7)
F
F
F
–
–
P
Pd
X
2
10c
11a
12a
11c
12c
3.20 (d, 11.2)
25.8 (d, 20.1)
F
F
F
Ph
Ph
–
–
P
Pd
55.9. 56.4
2:3
X
2
3.86 (d, 12.0)
–
43.4 (d, 36.9)
–
76.0
P
Pd
91.0, 89.7
1:2
X
3.11-3.19 (m)
32.6 (d, 32.2)
2
aChemical shifts in ppm, coupling constants in Hz; 31P{1H} (101,1 MHz, 298 K), 1H (400 MHz,
298 K) and 13C{1H} (101 MHz, 298 K). Recorded toluene for X = OAc and in CDCl3 for X =
Br.
10
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10.1002/ejic.202000288
European Journal of Inorganic Chemistry
As expected, 13P{1H} NMR spectra showed a shift towards lower fields in all the complexes with
respect to free phosphane. The ring contribution effect[21] is very important as reflected for
example in the spectrum of complex 9b’ (Table 3) with the same phosphane in the
cyclometallated compound (d = +71.5 ppm) and as simply P-coordinated ligand (d = +28.4 ppm).
The shift values followed the order –PiPr2 (c) > –PCy2 (b) > –PPh2 (a) for each benzyl group, and
the sequence –2,5-F2Ph > –Ph > –3,4,5-F3Ph > –2,5-Cl2Ph for each –PR2 moiety. Furthermore,
the mixture of the two possible isomers (cis and trans) was observed in the acetate bridge
complexes 5b, 6a and 7a, and in the bromide bridge for complexes 9a, 10a, 12a and 12c.
19F{1H}, 13C{1H} and 1H NMR spectra of 5-12 showed less significant variations when forming
the metallacycles. The values of the signals of the complexes bearing –PiPr2 and –PCy2 moieties
are similar, in accordance with their comparable steric and electronic characteristics. It is
interesting to note that the methyl groups of the isopropyl moiety in complexes derived from
phosphanes c are not equivalent and appear as doublet of doublet sets.
Free phosphanes 2 containing the difluorobenzyl group showed a 4JPF of about 10 Hz, however
in the dimeric palladacycles 5 and 8 this coupling was not observed at the same 101.1 MHz field.
However, in the case of mononuclear complexes 6b’ and 9b’ (Table 3) the coupling constant
reappears at the coordinated phosphane with values around 30 Hz, but here there are two fluorine
atoms in the same four bonds range 4JPF. In order to ascertain the origin of the P-F coupling the
splitting of the dinuclear complex 9c with PCy3 was performed to obtain complex 13c (Scheme
5).
F
P
P
Br
Br
Br
F
Pd
Pd
PCy3
Pd
F
F
PCy3
P
Toluene, 25 ºC, 1 h
F
F
9c
13c
Scheme 5. Preparation of mononuclear complex 13c.
To a toluene solution of 9c a slight excess of tricyclohexylphosphane was added at room
temperature, the complete splitting of the dimer was observed by 31P{1H} NMR after one hour of
reaction. The neutral compound 13c was readily obtained and characterized by standard methods.
11
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10.1002/ejic.202000288
European Journal of Inorganic Chemistry
The spectra were obtained in CDCl3 and it showed small amounts of the product of the Pd-Br/Cl
halogen exchange, leading to the duplication of signals both in the 1H and 31P{1H} NMR.
Table 3. Selected NMR data of cyclopalladated complexes 6b’, 9b’ and 13c.a
2JPP’
4JP’F
1
k2
d 31
k2
[PdBr( -PC)P’]2
P{ H} -PC
31P{1H} P’
d
Cy
Cy
F
P
OAc
Pd
F
Cy
6b’
70.7, d
71.5, d
77.5, d
32.3, dd
409.2
34.4
P
Cy
F
F
Cy
Cy
F
P
Br
Pd
F
Cy
9b’
13c
28.4, dd
23.7, dd
414.9
414.0
32.8
27.4
P
Cy
F
F
P
Br
Pd
F
PCy3
F
aChemical shifts in ppm, coupling constants in Hz; 31P{1H} (101,1 MHz, 298 K) and 1H (400
MHz, 298 K).
The 31P{1H} NMR signals are consistent with the presence of only the trans isomer (2JPP = 414.0
Hz) of 13c. Furthermore, the coupling between the phosphorus atom of the PCy3 and the fluorine
atom in ortho position of the phenyl ligand was observed (4JPF = 27.4 Hz). This means that the
4JPF observed in the mononuclear complexes 6b’ and 9b’ in the signal of the monodentate
phosphane could be assigned to the same coupling with the fluorine in ortho position of the phenyl
ligand. The exclusive formation of the trans isomer can be justified on steric arguments although
electronic factors could also play a role.[22]
Despite many attempts, single crystals suitable for X-ray diffraction could not be obtained for any
of complexes with the halogenated phosphanes. Fortunately, single crystals could be obtained for
dimers 12a and 12c, containing the simple benzylphosphanes 4a and 4c respectively. The
structures of the dimers are shown in Figure 4.
12
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10.1002/ejic.202000288
European Journal of Inorganic Chemistry
Figure 4. Molecular views of complexes 12a (left) and 12c (right) with ellipsoids drawn at 50%
probability level and H atoms removed for clarity. Selected distances (Å) and angles (º) for 12a: Pd1-C1
1.996(4); Pd1-Br1 2.5324(5); Pd1-P1 2.1930(11); Br1-Pd1-Br1 86.186(18); Br1-Pd1-C1 97.66 (11); C1-
Pd1-P1 82.41(11); P1-Pd1-Br1 93.91(3). For 12c: Pd1-C1 2.0281(18); Pd1-Br1 2.5490(3); Pd1-P1
2.2007(11); Br1-Pd1-Br1 85.524(9); Br1-Pd1-C1 98.47 (5); C1-Pd1-P1 82.10(6); P1-Pd1-Br1
94.010(15).
The structures contain the expected dimeric complexes with square-planar geometries around the
Pd atoms. Both structures correspond to the transoid isomers and have a crystallographic
inversion centre and hence the {Pd2Cl2} moiety is completely flat. The cyclometallation forces a
much smaller P-Pd-C1 angle compared to the others around the metal centre. Interestingly,
coordination bonds of 12a are slightly shorter than those of 12c, probably due to less steric
requirements of 4a compared to 4c. Rather surprisingly, the structures of 12a and 12c are the first
to be reported for bromo-bridged dimers with cyclometallated benzylphosphanes. Indeed, there
are only a few structures of chloro-bridge dimers,[20,23] including chloro-analogue of 12a,
described by Smoliakova and coworkers.[23] The parameters of 12a and 12b are similar to those
reported structures except the Pd–Br distances which as expected are longer than the Pd–Cl.
Ionic palladium complexes
Reaction of a dichloromethane solution of the palladium dimers 8c, 9c, 10a-c, 12a and 12c (1 eq.)
with a slight excess of norbornadiene and silver tetrafluoroborate (3 eq.) afforded the ionic
palladium complexes of general formulae [Pd(k2-PC)(norbornadiene)]BF4 (Scheme 6). The new
compounds were obtained as pure solids after separation of the silver bromide by filtration
through a celite pad.
13
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10.1002/ejic.202000288
European Journal of Inorganic Chemistry
X
R
R
R
R
P
P
Br
Br
AgBF4
X
Pd
Pd
+
Pd
X
X
CH2Cl2, 25 ºC
P
R
R
BF4
X
X
8c, 9c, 12a, 12c
R = Ph (a), i-Pr (c)
F
R = i-Pr, X = Cl, 14c; X = F, 15c; X = H, 16c
R = Ph, X = H, 17a
F
F
R
R
R
R
P
P
Br
AgBF4
+
Pd
Pd
Pd
CH2Cl2, 25 ºC
Br
P
R
R
BF4
F
F
F
F
F
F
18a, 18b, 18c
10a, 10b, 10c
R = Ph (a), Cy (b), i-Pr (c)
Scheme 6. Preparation of cationic complexes with a norbornadiene ligand.
The ionic complexes were characterized by elemental analysis, infrared spectroscopy and multi-
nuclear NMR spectroscopy. There are no significant changes in the NMR of the metallacycle
(Table 4 and Figure 5).
Table 4. Selected NMR data of cationic cyclopalladated complexes.a
Ha
Hb
13C{1H}
1H
d
CH=CH
cis, trans
d
1H PCH2Ar
(2JPH)
d
d
k2
[Pd( -PC)(nbd)]BF4
PCH2Ar
31P{1H}
1H Ha,b
(1JCP)
d
(2JHH)
P
7.60-7.80
(bs)
86.6 (s)
92.5 (s)
3.41 (bs)
24.9 (d, 22.7)
28.2 (d, 34.1)
2.21 (m)
14c
Pd
Cl
BF4
Cl
P
2.26 (d, 8.8)
2.31 (d; 9.2)
3.31 (d, 10.8)
3.36 (d, 10.8)
4.22 (d, 13.2)
7.11, 7.57
Pd
15c
16c
17a
F
BF4
F
P
95.5 (s)
56.3 (s)
31.3 (d, 34.6)
40.6 (d, 39.1)
1.28 (br)
1.92 (br)
–
Pd
BF4
Ph
Ph
P
Pd
6.74, 7.08
BF4
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European Journal of Inorganic Chemistry
P
Pd
88.7 (s)
3.39 (d, 11,6)
41.2 (d, 37.5)
2.24-2.33 (m)
7.06, 7.55
18c
BF4
F
F
F
Cy
Cy
P
Pd
81.3 (s)
57.3 (s)
3.35 (d, 11,4)
4.15 (d, 13,6)
33.6 (d, 35.2)
41.2 (d, 35.2)
2.21 (m)
6.95, 7.46
6.30, 7.41
18b
18a
BF4
F
F
F
Ph
Ph
P
Pd
2.09 (br)
2.20 (d, 9.2)
BF4
F
F
F
aChemical shifts in ppm, coupling constants in Hz; 31P{1H} (101,1 MHz, 298 K) and 1H (400 MHz,
298 K).
2xCH3, iPr
2xCH3, iPr
CH=CHnbd, cis
2xCHnbd
CH2, bn
CH=CHnbd, trans
CHa,b, nbd
2xCHiPr
2xCHAr
Figure 5. 1H NMR (CDCl3) spectrum of 15c.
Interestingly, the 1H NMR spectra shows the splitting of the signal of the methylene group of the
norbornadiene ligand. In addition, the signals of the olefinic protons differ markedly due to the
distinct ligands in trans position, phosphorus or carbon. The contacts observed in the NOESY
spectrum of 15c (Figure 5) allowed to assign the signal at lower fields to the double bond trans
to the phosphorus atom.
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10.1002/ejic.202000288
European Journal of Inorganic Chemistry
The molecular structure of 17a could be obtained by X-ray diffraction methods and it is
represented in Figure 6.
Figure 6. Molecular view of complex 17a with ellipsoids drawn at 50% probability level. H atoms and the
tetrafluoroborate anion have been removed for clarity. Selected distances (Å) and angles (º): Pd1-P1
2.2561(6); Pd1-C8 2.020(2); Pd1-C1 2.300(2); Pd1-C2 2.275(2); Pd1-C6 2.301(3); Pd1-C7 2.316(2); C1-
C2 1.344(4); C6-C7 1.352(4); C8-Pd1-P1 79.56(7).
The molecular structure confirms the identity of 17a as a mononuclear complex with the Pd atom
containing the cyclometallated ligand 4a and a norbornadiene coordinated by the two double
bonds. The distances between the Pd atom and 4a are slightly longer than in 12a and the
norbornadiene ligand is coordinated in slightly asymmetric fashion because the C1-C2 bond is
closer to the Pd than the C6-C7 bond. To the best of our knowledge, the structure of 17a is the
first one ever reported to contain a palladium coordinated to a metallated phosphane and a diene.
In the reported structures of [PdCl2(nbd)][24] and [PdBr2(nbd)][25] the distances between the Pd and
the diene are considerably shorter. In contrast, other structures containing the palladium
embedded in a palladacyclopentadiene[26] present similar Pd-nbd distances than in 17a. This
suggests that the cyclometallated phosphane exerts a strong s-donation that weakens the bonds
of Pd with the nbd in trans as does in palladacyclopentadienes.
Mizoroki-Heck reactions
To test the performance of the cyclopalladated compounds, the M-H reaction between
bromobenzene and butyl acrylate (Scheme 7) was chosen.
16
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10.1002/ejic.202000288
European Journal of Inorganic Chemistry
O
O
Br
Base, [Pd]
O
+
O
DMF, 130 ºC
Scheme 7. M-H reaction between bromobenzene and butyl acrylate.
The palladium complexes 9c and 15c, containing the same phosphane ligand 2c, were selected to
establish the optimal reaction conditions. In order to study the stability of these complexes, some
melting point determinations were carried out, but decomposition was found instead. The
fluorinated neutral dimeric complex 9c decomposed to palladium black at approximately 225 ºC
while the cationic counterpart 15c did the same at 165 ºC. For the non-fluorinated complexes 12a
and 17a, the decomposition temperatures were approximately 215 and 160 ºC respectively.
The initial catalytic experiments were carried out with 15c and sodium acetate as base. The ratio
Pd/PhBr/butyl acrylate was set to 1/1000/1500 (0.1% catalyst loading) while the PhBr/NaOAc
ratio was set to 1/1.1. Under these conditions, no formation of the M-H product was observed at
80 ºC, and the temperature was gradually increased in intervals of 10 ºC until at 120 ºC some
product could be detected after 1 h of reaction time. Therefore, a compromise temperature of 130
ºC was selected because it was high enough to have an active system, but well below the
decomposition temperature of the complexes. In the literature, temperatures in the range 115-165
ºC are commonly used in M-H reactions using cyclopalladated compounds as catalytic
precursors.[27]
Under these conditions, N,N-dicyclohexylmethylamine, sodium acetate and caesium carbonate
were tested as a base. After 20 h, the conversions using precursor 15c were 3, 13 and 80%
respectively so caesium carbonate was selected as by default base.
Then the effect of the amount of catalytic precursor was studied. When the relative amount of the
palladium complex (15c) was duplicated to 0.2% (Pd/PhBr/butyl acrylate = 2/1000/1500), the
rate of the reaction decreased, achieving a TOF value of 70 h–1 at 1 h, compared to 260 h–1 with
Pd/PhBr/butyl acrylate = 1/1000/1500. The rate reduction is significant because with 0.1%
catalyst loading, the 50% conversion time was attained after approximately 3 h, while doubling
the loading of the precatalyst delayed this time until 4 h. For this reason, the catalyst loading was
17
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10.1002/ejic.202000288
European Journal of Inorganic Chemistry
set to 0.1%. The use of an excess of olefin was also detrimental on the rate because with a
Pd/PhBr/butyl acrylate = 1/1000/3000 the TOF was 110 h–1. It seems, therefore, that the activity
does not depend on the total amount of palladium. Evolution of the catalytic precursor to colloidal
Pd(0) species could justify this behavior.[27-28]
The effect of the concentration was also studied. Halving the concentration from 0.67 to 0.38 M
led to similar conversions and TOF values. However, the reproducibility of the reaction was better
at higher dilution, probably because the formation of palladium agglomerates is less favoured.
The cationic complex 15c showed a higher initial activity at 1 h (TOF = 260 h–1) than the neutral
dimer 9c (TOF = 180 h–1) but at longer reaction times both precursors led to the same results.
This may indicate the opening of dimer 9c forming active, mononuclear species over time.
After having optimised the reaction conditions, we performed the systematic screening of the
cyclometallated complexes in the M-H reaction between bromobenzene and butyl acrylate (Table
5).
Table 5. M-H coupling reactions catalysed by cyclometallated Pd complexes.a
TOF/h–1 (1
h)
TOF/h–1 (6
h)
Entry
Catalytic precursor
Conversion/% (6 h)
1
2
3
4
5
6
7
8
9
9c (2F, iPr, dimeric)
12a (2H, Ph, dimeric)
12c (2H, iPr, dimeric)
180
307
316
250
260
11
321
44
107
160
270
132
149
162
90
110
22
153
38
28
81
90
97
55
65
13
92
25
17
34
63
14c (2Cl, iPr, monomeric)
15c (2F, iPr, monomeric)
16c (2H, iPr, monomeric)
17a (2H, Ph, monomeric)
18a (3F, Ph, monomeric)
18b (3F, Cy, monomeric)
18c (3F, iPr, monomeric)
15c (2F, iPr, dimeric)
10
60
106
11b
aReaction conditions: bromobenzene (10 mmol), butyl acrylate (15 mmol), Cs2CO3 (11 mmol),
Pd complex (0.1% of Pd with respect to bromobenzene) in 20 mL of DMF at 130 ºC. bStyrene
instead of butyl acrylate was used.
The conversions and selectivities (which were found to be > 95% towards the M-H product) were
determined by GC. In a few cases, Pd black could be observed in the reaction flasks after the
consumption of the reagents. It was found that the precursors were active, giving good
conversions in most cases towards the M-H product after 6 h of reaction time. There were,
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10.1002/ejic.202000288
European Journal of Inorganic Chemistry
however, important differences in reaction rates depending on the phosphane substituents,
especially at 1 h reaction times.
There is not a clear trend when comparing the performance between monomeric and dimeric
precursors with the same ligand. In the case of ligand 2c (entries 1 and 5) and 4a (entries 2 and
7) the differences are relatively minor suggesting the formation of the same mononuclear
catalytically active species from dimers.[29] In contrast, monomeric complex 16c (entry 6)
unexpectedly gives very low conversions and TOFs regardless of the reaction time while its
dimeric counterpart 12c (entry 3) is one of the most active. These differences show that the ligand
influences the active species formed under catalytic conditions. It seems that sometimes the
monomeric and dimeric complexes lead to the same catalytically active species and sometimes
not, or less efficiently.
In some cases, the activity of the precursors increases with the electronegativity of the substituents
of the cyclometallated aryl ring. This can be clearly seen comparing entries 6 (2H in the aryl) 4
(2Cl) and 5 (2F) and may be due to the stronger Caryl–Pd bond in halogenated phosphanes, as
originally reasoned when the halogenated benzylphosphanes were designed. This is however not
general: ligand 3c (entry 10) gives a less active system than ligand 2c (entry 5) despite the former
having a trifluorinated aryl ring compared to a difluorinated ring for the latter.
For the trifluorinated aryl ring it is found that the diphenylphosphanes produce less active
precursors compared to diisopropyl or dicyclohexylphosphanes (entries 8-10), but in contrast the
most active system overall, 17a (entry 7) is the simple benzyldiphenylphosphane, in accordance
with the results of Cole-Hamilton and coworkers.[9] With precursor 15c the M-H with styrene was
also tested (entry 11) giving very similar results than with butyl acrylate (entry 5).
In order to explore the usefulness of catalysts based on halogenated phosphanes in the M-H of
other aryl bromides, a few experiments were also carried out with the reaction of butyl acrylate
with electron-poor 4-bromobenzaldehyde and with electron-rich 4-bromoanisol (Table 6).
Table 6. M-H reactions of butyl acrylate with 4-bromobenzaldehyde and 4-bromoanisol.a
Entry
Catalytic precursor
Aryl bromide TOF/h–1 (1 h)
Conversion/%
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14c (2Cl, iPr,
monomeric)
Br
1
610
100 (2 h)
O
2
3
15c (2F, iPr, monomeric)
18c (3F, iPr, monomeric)
850
350
100 (2 h)
72 (3 h)
H
Br
4
15c (2F, iPr, monomeric)
145
52 (6 h)
MeO
aReaction conditions: aryl bromide (10 mmol), butyl acrylate (15 mmol), Cs2CO3 (11 mmol),
Pd complex (0.1% of Pd with respect to the aryl bromide) in 20 mL of DMF at 130 ºC.
As expected, the reactions with 4-bromobenzaldehyde (entries 1-3) proceeded much faster than
with bromobenzene, due to the weaker nature of the C–Br bond, which favours oxidative addition
to Pd(0). In spite of this, the tendencies with this substrate were the same as those observed in
Table 5. Unsurprisingly, 4-bromoanisol (entry 4) was a poorer substrate than bromobenzene
(Table 5, entry 5) due to the stronger C–Br bond.
Conclusions
This paper has described the systematic preparation of new benzylphosphanes partially
halogenated at the phenyl group, showing that the reaction of benzylmagnesium reagents with
chlorophosphanes is the best method to prepare such compounds. The tendency of
benzylphosphanes to form cyclopalladated compounds has been used to prepare acetate-bridged
and bromide-bridged complexes as pure stable solids. Bromide scavenging by silver
tetrafluoroborate has allowed the obtention of cationic, nbd-stabilised mononuclear complexes.
The use of 0.1% loading of palladium complexes in the Mizoroki-Heck reaction between
bromobenzene and butyl acrylate has provided good conversions after a few hours for several
systems. The results are in the same range that those obtained by other palladacycles[27,30] under
similar conditions and confirm that cyclopalladated complexes are an excellent choice for M-H
reactions.[5,8a,8c,31]
Although the original idea that halogenated benzylphosphanes would give cyclopalladated
compounds with stronger Pd-Caryl bonds and hence more robust and active precursors has been
observed in a few cases, in general the halogenated precursors have not provided better systems
than simple, non-halogenated benzylphosphanes.
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The palladated phosphane has an important influence in the catalytic outcome but so far it has not
been possible to rationalise the results of individual catalytic precursors and find clear structure-
activity relationships using simple parameters of the metallated phosphane. This stems from the
deficient knowledge of the nature of the catalytically active species formed from cyclometallated
compounds under M-H conditions despite many efforts.[4a,27,29,32]
Experimental section
General data
All compounds were prepared under a purified nitrogen atmosphere using standard Schlenk and
vacuum-line techniques. The solvents were purified by a solvent purification system or by
standard procedures[33] and kept under nitrogen. Unless otherwise noted, all reagents were
purchased from commercial sources and were used without further purification. Benzyl bromides
must be handled with care, manipulated in an efficient hood, wear protective gloves and eye
protection because they may cause skin, eye and respiratory track irritation. 1H, 13C{1H}, 31P{1H}
and 19F{1H} NMR spectra were recorded at room temperature with 250, 300 and 400 MHz
1
spectrometers using CDCl3 as solvent unless otherwise specified. H-1H NOESY spectra were
recorded in 500 MHz spectrometers. Chemical shifts are reported in ppm relative to residual
solvent peaks. IR spectra were recorded in KBr and the main absorption bands are expressed in
cm–1. Mass spectrometry (MS) and high-resolution mass (HRMS) analyses were carried out in a
time-of-flight instrument using electrospray ionisation. The microanalyses given are the best that
could be obtained. The discrepancies observed are probably due to the presence of residual
1
solvents (as observed by H NMR), which were impossible to remove despite leaving the
complexes under high vacuum for several hours. Gas chromatography analyses of the catalytic
runs were performed using a gas chromatograph, equipped with a FID detector, and a capillary
column.
Synthesis of phosphane-boranes
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10.1002/ejic.202000288
European Journal of Inorganic Chemistry
To a mixture of 1 mmol of the appropriate benzyl bromide and 1.2 mmol of previously ground
magnesium turnings, 5 mL of diethyl ether were added, and the mixture was stirred at room
temperature for 1 h. The reaction was moderately exothermic, and during the formation of the
Grignard reagent, the solution turned to a dark grey colour. The solution was then cooled to 0 ºC
and 1 mmol of ClPR2 in 10 ml of diethyl ether were added dropwise. The mixture was stirred for
1 h, allowing the reaction to warm up to room temperature and 1.5 mL of borane-dimethyl sulfide
solution (1 M in THF) were added. 10 mL of a degassed solution of 10% NH4Cl was added and
the mixture was stirred for 30 min to allow hydrolysis of the unreacted magnesium turnings. The
diethyl ether was removed under reduced pressure and the resulting aqueous mixture was washed
with dichloromethane (3 x 5 mL). The organic layer was filtered and dried over anhydrous
Na2SO4 and the resulting solution was concentrated to dryness. The crude product was purified
as detailed for each compound.
under vacuum to half its volume, and absolute ethanol was added until appearance of turbidity.
Storing the mixture at –20 ºC for 24 h resulted in the precipitation of the phosphane-borane
adduct, which was filtered off and dried under vacuum.
(2,5-Dichlorobenzyl)diphenylphosphane-borane (1a’)
The preparation was carried out according to the general procedure. The crude product was
purified by column chromatography (hexane/ethyl acetate mixtures) to obtain the phosphane-
borane as a colourless resin (0.247 g, 69% yield).
1H NMR: 3.77 (d, 2H; J = 12.0 Hz, CH2(Bn)); 6.90-7.10 (m, 3H, CH(Ar)); 7.30-7.60 (m, 10H,
CH(Ph)). 13C{1H} NMR: 30.8 (d, J = 31.6 Hz, CH2(Bn)); 128.6 (s, CH); 128.8 (d, J = 9.6 Hz, CH);
130.5 (s, CH); 131.7 (s, CH); 131.8 (d, J = 3.2 Hz, CH); 132.2 (m, C); 132.3 (d, J = 3.8 Hz, C);
132.6 (m, C); 132.8 (d, J = 8.9 Hz, CH); 133.1 (d, J = 5.7 Hz, C). 31P{1H} NMR: 17.9 (d, J = 55.7
Hz). IR: 3084, 3058, 2924, 2395, 2361, 2341 n(B–H), 1640, 1619, 1431, 1099, 1053, 742, 690.
HRMS: 355.0385 [M–3H]+.
Dicyclohexyl(2,5-dichlorobenzyl)phosphane-borane (1b’)
The preparation of this compound was carried out according to the general procedure and was
purified by recrystallisation in dichloromethane/pentane, affording the phosphane-borane as a
white powder (0.181 g, 49% yield).
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10.1002/ejic.202000288
European Journal of Inorganic Chemistry
1H NMR (–0.03)-0.80 (br; 3H; J ≈ 10 Hz; BH3); 1.10-1.90 (m; 22 H; CH(Cy) + CH2(Cy)); 3.16 (d;
2H; J = 11.9 Hz; CH2(Bn)); 7.14 (d; 1H; J = 8.7 Hz; CH(Ar)); 7.27 (d; 1H; J = 8.7 Hz; CH(Ar)); 7.52
(m; 1H; CH(Ar)). 13C{1H} NMR: 24.5 (d, J = 26.8 Hz; CH2 (Bn)); 26.0 (s; CH2); 26.9 (m; CH2); 27.0
(d; J = 1.5 Hz; CH2); 27.1 (d; J = 1.9 Hz; CH2); 32.2 (d; J = 30.6 Hz; CH); 128.4 (d; J = 2.3 Hz;
CH); 130.5 (d, J = 1.5 Hz; CH); 132.2 (d, J = 4.5 Hz; C); 132.5 (d, J = 2.3 Hz; CH); 132.7 (d; J
31
= 2.5 Hz; C); 134.1 (d; J = 3.8 Hz; C). P{1H} NMR: 29.7 (m). IR: 3081, 3061, 2927, 2854,
2384, 2375, 2331 n(B–H), 1465, 1448, 1096, 1038, 893, 817. Anal. Calcd for C19H30BCl2P C
61.49%, H 8.15%; found C 61.48%, H 9.15%. HRMS: 367.1312 [M–3H]+, 369.1373 [M–H]+.
(2,5-Dichlorobenzyl)diisopropylphosphane-borane (1c’)
The preparation of this compound was carried out according to the general procedure. The crude
product was recrystallised in dichloromethane/ethanol to obtain the phosphane-borane as a white
powder (0.198 g, 68% yield).
1H NMR: 0.00-0.80 (br q; 3H; J ≈ 98 Hz; BH3); 1.06 (dd; 6H; J = 14.0, 7.2 Hz; 2xCH3(iPr)); 1.11
(dd; 6H; J = 14.4, 7.2 Hz; 2xCH3(iPr)); 2.01 (dht; 2H; J = 10.0, 7.2 Hz; CH(iPr)); 3.11 (d; 2H; J =
12.0 Hz; CH2Bn)); 7.08 (m; 1H; CH(Ar)); 7.20 (m; 1H; CH(Ar)); 7.50 (m; 1H; CH(Ar)). 13C{1H} NMR:
17.2 (d; J = 6.9 Hz; CH3); 22.4 (d; J = 30.6 Hz; CH2(Bn)); 24.3 (d; J = 26.8 Hz; CH); 128.5 (s;
CH); 130.6 (s; CH); 132.1 (d; J = 5.4 Hz; C); 132.3 (s; CH); 132.7 (s; C); 133.8 (d; J = 3.8 Hz;
C). 31P{1H} NMR: 37.5 (q; J = 58.8 Hz). IR: 3084, 2965, 2930, 2875), 2375, 2355, 2334 n(B-H),
1471, 1454, 1096, 1038, 884, 820, 803. Anal. Calcd for C13H22BCl2P C 53.66%, H 7.62%; found:
C 51.49%, H 8.12%. HRMS: 287.0688 [M–3H]+, 289.0708 [M–H]+.
Diphenyl(2,5-difluorobenzyl)phosphane-borane (2a’)
The preparation of this compound was carried out according to the general procedure and was
purified by recrystallisation in dichloromethane/pentane, affording the phosphane-borane as a
white powder (0.117 g, 36% yield).
1H NMR: 0.40-1.30 (br q; 3H; J ≈ 96 Hz; BH3); 3.53 (d; 2H; J = 11.6 Hz; CH2(Bn)); 6.70-6.80 (m;
3H; CH(Ar)); 7.35-7.38 (m; 4H; CH(Ar)); 7.39-7.44 (m; 2H; CH(Ar)); 7.54-7.61 (m; 4H; CH(Ar)).
13C{1H} NMR: 26.8 (d; J = 32.8 Hz; CH2(Bn)); 115.4 (dd; J = 23.8, 8.3 Hz; CH); 116.1 (dd; J =
25.7, 8.9 Hz; CH); 118.4 (d; J = 25.0 Hz; CH); 121.3 (m; C); 128.2 (d; J = 54.1 Hz; C); 128.9 (d;
J = 9.6 Hz; CH); 131.6 (s; CH); 132.6 (d; J = 9.0 Hz; CH); 156.9 (d; J = 240.1 Hz; CF); 158.1 (d;
J = 242.7 Hz; CF). 31P{1H} NMR: 17.7 (d; J = 71.6 Hz). 19F NMR: –121.4 (m; 1Fo); –118.6 (m;
1Fm). IR: 3078, 3052, 2962, 2921, 2406, 2398, 2352 n(B-H), 1637, 1614, 1433, 1096, 1050, 742,
692. Anal. Calcd for C19H18BF2P C 69.97%, H 5.56%; found C 68.30%, H 5.76%. HRMS:
323.1000 [M–3H]+, 329.0910 [M–(BH3)+(OH)]+.
Dicyclohexyl(2,5-difluorobenzyl)phosphane-borane (2b’)
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The preparation of this compound was carried out according to the general procedure and was
purified by recrystallisation in dichloromethane/pentane, affording the phosphane-borane as a
white powder (0.230 g, 68% yield).
1H NMR: 0.00-0.80 (br q; 3H; J ≈ 74 Hz; BH3); 1.10-1.90 (m; 22 H; CH(Cy) + CH2(Cy)); 3.00 (d;
2H; J = 11.2 Hz; CH2(Bn)); 6.89 (m; 1H; CH(Ar)); 6.98 (m; 1H; CH(Ar)); 7.13 (m; 1H; CH(Ar)).
13C{1H} NMR: 20.3 (d; J = 27.5 Hz; CH2(Bn)); 26.0 (m; CH2); 26.8-27.1 (m; 2xCH2); 32.2 (d; J =
30.6 Hz; CH); 115.1 (dd; J = 7.64, 22.9 Hz; CH); 116.2 (dd; J = 8.4, 25.2 Hz; CH); 118.8 (d; J =
24.5 Hz; CH); 123.0 (m; C); 156.8 (d; J = 236.0 Hz; CF); 158.3 (d; J = 243.0 Hz; CF). 31P{1H}
NMR: 30.0 (d; J = 67.0 Hz). 19F NMR: –123.1 (m; 1Fo); –118.6 (m; 1Fm). IR: 3073, 2927, 2849,
2363, 2337 n(B-H), 1497, 1451, 1207, 1064, 876, 809. Anal. Calcd for C19H30BF2P C 67.47%, H
8.94%; found C 67.19%, H 9.87%. HRMS: 335.1903 [M–3H]+.
(2,5-Difluorobenzyl)diisopropylphosphane-borane (2c’)
The preparation of this compound was carried out according to the general procedure. The crude
product was purified by column chromatography (hexane/ethyl acetate mixtures) to obtain the
phosphane-borane as a white powder (0.157 g, 61% yield).
1H NMR: 0.00-0.80 (br q; 3H; J ≈ 86 Hz; BH3); 1.15 (dd; 6H; J = 7.2, 1.6 Hz; CH3(iPr)); 1.19 (dd;
6H; J = 7.2, 1.6 Hz; CH3(iPr)); 2.04 (dht; 2H; J = 10.8, 7.2 Hz; CH(iPr)); 3.03 (d; 2H; J = 11.2 Hz;
CH2(Bn)); 6.86-6.94 (m; 1H; CH(Ar)); 6.95-7.20 (m; 1H; CH(Ar)); 7.14-7.20 (m; 1H; CH(Ar)). 13C{1H}
NMR: 17.0 (d; J = 4.6 Hz; CH3); 20.3 (d; J = 27.6 Hz; CH2(Bn)); 22.2 (d; J = 31.5 Hz; CH); 115.2
(ddd; J = 3.1, 8.3, 23.8 Hz; CH); 116.3 (ddd; J = 2.3, 9.1, 25.3 Hz; CH); 118.8 (dt; J = 3.0, 24.5
Hz; CH); 122.8 (m; C); 156.8 (d; J = 240.0 Hz; CF); 158.4 (d; J = 243.0 Hz; CF). 31P{1H} NMR:
36.1 (q, J = 58.5 Hz). 19F NMR: –122.9 (m; 1Fo); –118.6 (m; 1Fm). IR: 3090, 3070, 2979, 2962,
2936, 2875, 2378, 2346, 2369 n(B-H), 1503, 1463, 1213, 1192, 1067, 1038, 870, 820. Anal.
Calcd for C13H22BF2P C 60.50%, H 8.59%; found C 60.35%, H 8.80%. HRMS: 255.1287 [M–
3H]+.
Diphenyl(3,4,5-trifluorobenzyl)phosphane-borane (3a’)
The preparation of this compound was carried out according to the general procedure. The crude
product was purified by column chromatography (hexane/ethyl acetate mixtures) to obtain the
phosphane-borane as a white powder (0.182 g, 53% yield).
1H NMR: 0.40-1.40 (br q; 3H; J ≈ 112 Hz; BH3); 3.50 (d; 2H; J = 11.6 Hz; CH2(Bn)); 6.56 (m;
2xCH(Ar)); 7.40-7.80 (m; 10H; CH(Ph)). 13C{1H} NMR: 17.0 (d; J = 4.6 Hz; CH3); 20.3 (d; J = 27.6
Hz; CH2(Bn)); 22.2 (d; J = 31.5 Hz; CH); 115.2 (ddd; J = 3.1, 8.3, 23.8 Hz; CH); 116.3 (ddd; J =
2.3, 9.1, 25.3 Hz; CH); 118.8 (dt; J = 3.0, 24.5 Hz; CH); 122.8 (m; C); 156.8 (d; J = 240.0 Hz;
CF); 158.4 (d; J = 243.0 Hz; CF). 31P{1H} NMR: 17.2 (d; J = 62.9 Hz). 19F NMR: –162.1 (tdd; J
= 19.9; 13.2; 5.3 Hz; 1Fp); –134.4 (dd; J = 21.0; 8.5 Hz; 2Fm). IR: 3096, 3058, 2916, 2378, 2343
n(B-H), 1622, 1532, 1451, 1442, 1349, 1041, 861, 742, 707, 690. Anal. Calcd for C19H17BF3P C
24
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European Journal of Inorganic Chemistry
66.32%, H 4.98%; found C 65.30%, H 5.34%. HRMS: 341.0874 [M–3H]+, 347.0812 [M–
(BH3)+(OH)]+.
Dicyclohexyl(3,4,5-trifluorobenzyl)phosphane-borane (3b’)
The preparation of this compound was carried out according to the general procedure. The crude
product was purified by column chromatography (hexane/ethyl acetate mixtures) to obtain the
phosphane-borane as a white powder (0.085 g, 24% yield).
1H NMR: 0.00-0.80 (br q; 3H; J ≈ 112 Hz; BH3); 1.10-1.90 (m; 22 H; CH (Cy) + CH2 (Cy)); 2.94
(d; 2H; J = 11.6 Hz; CH2 (Bn)); 6.92 (t; 2H; J = 6.8 Hz; CH(Ar)). 13C{1H} NMR: 26.0 (s; CH2); 26.9
(m; 2xCH2); 27.5 (d; J = 27.6 Hz; CH2(Bn)); 32.0 (d; J = 29.8 Hz; CH2); 114.2 (d; J = 16.9 Hz;
CH); 130.3 (m; C); 138.9 (d; J = 254.0 Hz; CF); 151.0 (d; J = 254.0 Hz; CF). 31P{1H} NMR: 27.7
(d, J = 58.8 Hz). 19F NMR: –162.2 (td; J = 21.0, 3.7 Hz; 1Fp); –133.8 (dd; J = 19.9, 7.9 Hz; 2Fm).
IR: 2933, 2857, 2375, 2343 n(B-H), 1530, 1445, 1035, 870, 797. Anal. Calcd for C19H29BF3P C
64.06%, H 8.21%; found C 63.76%, H 8.94%. HRMS: 353.1812 [M–3H]+, 711.4023 [2M–H]+.
Diisopropyl(3,4,5-trifluorobenzyl)phosphane-borane (3c’)
The preparation of this compound was carried out according to the general procedure. The crude
product was first subjected to column chromatography (hexane/ethyl acetate mixtures) and
subsequently recrystallized in a mixture of dichloromethane/heptane to obtain the phosphane-
borane as a white powder (0.116 g, 42% yield).
1H NMR: 0.00-0.80 (br q; 3H; J ≈ 90.4 Hz; BH3); 1.15 (dd; 6H; J = 7.2, 1.6 Hz; CH3(iPr)); 1.18
(dd; 6H; J = 7.2, 2.0 Hz; CH3(iPr)); 1.98 (dht; 2H; J = 10.4, 7.2 Hz; CH(iPr)); 2.95 (d; 2H; J = 11.6
13
Hz; CH2(Bn)); 6.94 (td; 2H; J = 6.8, 1.8 Hz; CH(Ar)). C{1H} NMR: 17.1 (s; CH3); 22.0 (d; J =
31.4 Hz; CH2(Bn)); 27.6 (d; J = 26.9 Hz; CH); 114.2 (m; CH); 130.0 (s; C); 138.9 (dt; J = 12.8,
251.0 Hz; CF); 151 (dd; J = 10.9, 251.0 Hz; CF). 31P{1H} NMR: 34.6 (q; J = 51.2 Hz). 19F NMR:
–162.3 (td; J = 20.3; 4.1 Hz; 1Fp); –133.8 (dd; J = 19.9; 7.9 Hz; 2Fm). IR: 3078, 3061, 3040, 2962,
2933, 2872, 2375, 2340, 2265 n(B-H), 1622, 1588, 1535, 1465, 1448, 1349, 1070, 1038, 861.
Anal. Calcd for C13H21BF3P C 56.56%, H 7.67%; found: C 56.00%, H 8.35%. HRMS: 273.1193
[M–3H]+.
Synthesis of palladium complexes
Cyclometallated palladium dimeric complexes with a bromide bridge were obtained by reaction
of the corresponding phosphane with Pd(OAc)2 followed by substitution of acetate by bromide.
Only the preparation of 1a/5a/8a is described in detail and the rest of the complexes were obtained
by the same protocol. Due to the easy oxidation of the phosphanes all operations must be carried
out under nitrogen. The final purification of the cyclometallated dimer is performed by
recrystallisation or column chromatography (DCM/hexane).
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European Journal of Inorganic Chemistry
Di-μ-bromo-bis{2-[(diphenylphosphano)methyl]-3,6-dichlorophenyl-C1,P}dipalladium(II)
(8a)
Preparation of phosphane 1a
To a solution of 0.38 g (1.60 mmol) of 2,5-dichlorobenzyl bromide in 10 mL of diethyl ether
0.045 g (1.80 mmol) of previously ground magnesium turnings were added. The mixture was
stirred at 20 °C for 1 h avoiding any temperature increase. The dark grey solution was cooled to
0 ºC and 0.330 g (1.5 mmol) of ClPPh2 in 5 ml of diethyl ether were added dropwise. The mixture
was stirred for 1 h, allowing the reaction to warm up to room temperature. The solvent was
removed under reduced pressure giving a crude resin, which was dissolved in 10 mL of toluene
and washed with deoxygenated water. The organic layer was separated and dried over anhydrous
Na2SO4 and filtered off. The solution of 1a (dP = –12.8 ppm) was used immediately without
further purification.
Preparation of palladium complexes 5a and 8a
The obtained phosphane solution was slowly added over a suspension of palladium acetate 0.314
g (1.40 mmol) and sodium acetate 0.254 g (1.80 mmol) in 10 mL of toluene at room temperature.
After 5 min of stirring, the reaction mixture was heated at 80 °C for 12 h. The disappearance of
the free phosphane was monitored by 31P{1H} NMR. The solution was filtered, and the solvent
removed under reduced pressure, giving crude 5a (dP = +48.4 ppm). This crude and lithium
bromide 0.155 g, (1.80 mmol) were dissolved in acetone (10 ml) and stirred for 2 h at room
temperature. The solvent was removed under reduced pressure, the solid dissolved in
dichloromethane (10 mL) and washed several times with water. The organic phase was dried over
anhydrous Na2SO4, filtered and after reducing the volume of dichloromethane, absolute ethanol
was added. After several hours in the freezer the resulting yellow complex 8a was filtered off.
The yield of calculated from the initial Pd(OAc)2: 0.30 g (40% yield).
1H NMR: 4.09 (d; 4H; J = 11.6 Hz; CH2(Bn)); 6.80-6.90 (m; 4H; CH(Ar)); 7.30-7.80 (m; 20H;
CH(Ph)). 13C{1H} NMR: 43.0 (d; J = 36.8 Hz; CH2(Bn)); 126.8 (s; CH); 128.8 (s; CH); 128.9 (d; J
= 5.3 Hz; CH); 129.5 (s; C); 130.0 (s; C); 131.9 (s; CH); 133.4 (d; J = 11.5 Hz; CH); 139.8 (s; C).
31P{1H} NMR: 53.1 (s). IR: 3077, 3055, 2950, 2925, 2847, 1433, 1419, 1381, 1165, 1148, 1123,
1104, 1051. Anal. Calc. for C38H28Br2Cl4P2Pd2 C 43.02%, H 2.66%; found C 44.12% H 2.99%.
HRMS: 525.8080 [(M/2)–2H]+.
Di-μ-bromo-bis{2-[(dicyclohexylphosphano)methyl]-3,6-dichlorophenyl-
C1,P}dipalladium(II) (8b)
The procedure was analogous to that employed for 8a but using 1b. The compound was obtained
as a yellow solid after column chromatography. The yield was calculated relative to the initial
Pd(OAc)2: 0.227 g (30%). dP(1b) = +2.6 ppm (s), dP(5b) = 65.3 (s), 66.3 (s) ppm; 1:3 ratio.
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European Journal of Inorganic Chemistry
1H NMR: 0.80-2.60 (m; 44 H; CH(Cy) + CH2(Cy)); 3.31 (d; 4H; J = 10.4 Hz; CH2(Bn)); 6.88 (d; 2H;
J = 8.4 Hz; CH(Ar)); 6.96 (d; 2H; J = 8.7 Hz; CH(Ar)). 13C{1H} NMR: 25.8 (s; CH2); 26.0 (d; J =
13.7 Hz; CH); 26.6 (d; J = 11.5 Hz; CH2); 28.2 (s; CH2); 28.9 (s; CH2); 34.4 (d; J = 34.5 Hz;
CH2); 35.3 (d; J = 24.5 Hz; CH2(Bn)); 126.2 (s; CH); 127.3 (d; J = 24.5 Hz; C); 128.7 (s; CH);
31
139.9 (s; C); 144.4 (d; J = 16.0 Hz; C); 152.9 (s; C). P{1H} NMR: 78.7 (s). IR: 3046, 2930,
2850, 2784, 1446, 1419, 1157, 1047, 851, 798. Anal. Calc. for C38H52Br2Cl4P2Pd2 C 42.06%, H
4.83%; found C 44.04%, H 5.01%. HRMS: 461.0183 [(M/2)–Br]+; 502.0452 [(M/2)–
Br+(CH3CN)]+, 1000.9545 [M–Br]+.
Di-μ-bromo-bis{2-[(diisopropylphosphano)methyl]-3,6-dichlorophenyl-
C1,P}dipalladium(II) (8c)
The procedure was analogous to that employed for 8a but using 1c. The compound was obtained
as a yellow solid after column chromatography. The yield was calculated relative to the initial
Pd(OAc)2: 0.168 g (26%). dP(1c) = +10.1 ppm (s), dP(5c) = 60.2 (s) ppm.
1H NMR: 0.95 (dd; 12H; J = 15.6; 7.2 Hz; CH3(iPr)); 1.46 (dd; 12H; J = 18.4; 7.2 Hz; CH3(iPr));
2.31 (dht; 4H; J = 9.6; 7.2; Hz; CH(iPr)); 3.33 (d; 4H; J = 10.4 Hz; CH2(Bn)); 6.90 (d; 2H; J = 8.4
Hz; CH(Ar)); 6.96 (d; 2H; J = 8.4 Hz; CH(Ar)). 13C{1H} NMR: δ: 18.0 (s; CH3); 19.2 (s; CH3); 26.0
(d; J = 25.3 Hz; CH2(Bn)); 33.8 (d; J = 33.7 Hz; CH); 126.5 (s; CH); 127.6 (d; J = 22.9 Hz; C);
128.9 (s; CH); 139.8 (s; C); 144.19 (d; J = 16.9 Hz; C); 152.4 (d; J = 3.8 Hz; C). 31P{1H}: 87.1
(s). IR: 3094, 3041, 2958, 2921, 2894, 2871, 1455, 1413, 1237, 1151, 1053, 1026, 878, 802. Anal.
Calc. for C26H36Br2Cl4P2Pd2 C 33.76%, H 3.92%; found C 34.02%, H 4.15%. HRMS: 380.9544
[(M/2)–Br]+, 421.9819 [(M/2)–Br+(CH3CN)]+.
Di-μ-bromo-bis{2-[(diphenylphosphano)methyl]-3,6-difluorophenyl-C1,P}dipalladium(II)
(9a)
The procedure was analogous to that employed for 8a but using 2a. The compound was obtained
as a yellow solid. The yield was calculated relative to the initial Pd(OAc)2: 0.480 g (69%). dP(2a)
= –11.5 ppm (d, J = 12.1 Hz), dP(6a) = 57.9 (s), 59.3 (s) ppm; 3:2 ratio.
1H NMR: 3.92 (d; J = 12.0 Hz; 4H; CH2(Bn)); 6.50-6.60 (m; 4H; CH(Ar)); 7.30-7.75 (m; 20H;
CH(Ph)). 13C{1H} NMR: 38.9 (d; J = 36.7 Hz; CH2(Bn)); 112.7 (dd; J = 24.4; 8.3; Hz; CH); 114.6
(dd; J = 32.8; 5.8; Hz; CH); 128.9 (d; J = 10.4 Hz; CH); 129.2 (s; C); 129.7 (s; C); 131.5 (s; C);
131.8 (s; CH); 133.3 (d; J = 11.6 Hz; CH); 154.9 (dd; J = 244.6; 24.4; Hz; CF); 161.7 (d; J =
236.2 Hz; CF). 31P{1H} NMR: 57.0 (s); 57.9 (s) (ratio 1:3). 19F NMR: –118.5 (m; 1Fo); –94.9 (m;
1Fm). IR: 3087, 3046, 2959, 2916, 1561, 1451, 1433, 1384, 1111, 1099, 969, 864. Anal. Calc. for
C38H28Br2F4P2Pd2 C 45.86%, H 2.84%; found C 45.54%, H 2.96%. HRMS: 416.9836 [(M/2)–
Br]+.
Di-μ-bromo-bis{2-[(dicyclohexylphosphano)methyl]-3,6-difluorophenyl-
C1,P}dipalladium(II) (9b)
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10.1002/ejic.202000288
European Journal of Inorganic Chemistry
The procedure was analogous to that employed for 8a but using 2b. The compound was obtained
as a yellow solid after column chromatography purification. The yield was calculated relative to
the initial Pd(OAc)2: 0.200 g (28%). dP(2b) = +2.4 ppm (d, J = 9.5 Hz), dP(6b) = 69.3 (s).
1H NMR: 0.80-2.50 (m; 44 H; CH (Cy)+CH2(Cy)); 3.19 (d; J = 10.2 Hz; 4H; CH2(Bn)); 6.64 (d; J =
5.8 Hz; 2H; CH(Ar)); 6.66 (d; J = 5.8 Hz; 2H; CH(Ar)). 13C{1H} NMR: 25.8 (s; CH2); 26.1 (d; J =
14.1 Hz; CH); 26.6 (d; J = 10.9 Hz; CH2); 28.1 (s; CH2); 28.8 (s; CH2); 29.8 (d; J = 33.5 Hz;
CH2); 35.2 (d; J = 25.0 Hz; CH2(Bn)); 112.0 (dd; J = 9.0; 24.4 Hz; CH); 114.2 (d; J = 7.6; 33.4 Hz;
CH); 134.1 (d; J = 14.8 Hz; C); 138.6 (d; J = 41.8 Hz; C); 154.3 (dd; J = 244.6; 24.4 Hz ; CF);
161.8 (d; J = 235.0 Hz; CF). 31P{1H} NMR: 85.1 (s). 19F NMR: –118.5 (m; 1Fo); –93.9 (bd; J =
19.6 Hz; 1Fm). IR: 3061, 2930, 2852, 1558, 1448, 1218, 977, 855. Anal. Calc. for
C38H52Br2F4P2Pd2 C 44.77%, H 5.14%; found: C 46.02%; H 5.52%. HRMS: 429.0777 [(M/2)–
Br]+, 470.1043 [(M/2)–Br+(CH3CN)]+.
Di-μ-bromo-bis{2-[(diisopropylphosphano)methyl]-3,6-difluorophenyl-
C1,P}dipalladium(II) (9c)
The procedure was analogous to that employed for 8a but using 2c. The compound was obtained
as a yellow solid. The yield was calculated relative to the initial Pd(OAc)2: 0.120 g (20%). dP(2c)
= +10.6 ppm (d, J = 10.5 Hz), dP(6c) = 78.0 (s).
1H NMR: 1.01 (dd; J = 15.6; 7.2 Hz; 12H; CH3(iPr)); 1.48 (dd; J = 18.0; 7.2 Hz; 12H; CH3(iPr));
2.35 (dht; J = 9.2; 7.2 Hz; 4H; CH(iPr)); 3.20 (d; J = 10.4 Hz; 4H; CH2(Bn)); 6.65 (d; J = 5.6 Hz;
2H; CH(Ar)); 6.67 (d; J = 5.6 Hz; 2H; CH(Ar)). 13C{1H} NMR: 17.9 (s; CH3); 19.1 (s; CH3); 25.9
(d; J = 25.3 Hz; CH2(Bn)); 29.0 (d; J = 32.9 Hz; CH); 112.4 (dd; J = 24.5; 9.1; Hz; CH); 114.4 (dd;
J = 32.9; 7.6; Hz; CH); 134.0 (s; C); 134.1 (s; C); 154.7 (d; J = 242.0 Hz; CF);162.0 (d; J = 234.0
31
19
Hz; CF). P NMR: 94.8 (s). F NMR: –118.3 (bd; J = 19.5 Hz; 1Fo); –94.8 (d; J = 17.3 Hz;
1Fm). IR: 3061, 2962, 2933, 2895, 2869, 1451, 1207, 971, 849, 806. Anal. Calc. for
C26H36Br2F4P2Pd2 C 36.35%, H 4.22%; found C 37.16%, H 4.42%. HRMS: 349.0143 [(M/2)–
Br]+, 390.0409 [(M/2)–Br+(CH3CN)]+.
Di-μ-bromo-bis{2-[(diphenylphosphano)methyl]-4,5,6-trifluorophenyl-
C1,P}dipalladium(II) (10a)
The procedure was analogous to that employed for 8a but using 3a. The compound was obtained
as a yellow solid. The yield was calculated relative to the initial Pd(OAc)2: 0.195 g (27%). The
compound showed low solubility in common organic solvents. dP(3a) = –9.9 ppm (s), dP(7a) =
46.0 (s), 46.1 ppm; 1:9 ratio.
1H NMR: 3.88 (d; 4H; J = 12.0 Hz; CH2(Bn)); 6.72 (m; 2H; J = 7.2 Hz; CH(Ar)); 7.30-7.80 (m;
13
20H; CH(Ph)). C{1H} NMR: 44.1 (d; J = 41.4 Hz; CH2 (Bn)); 108.23 (m; CH); 128.9 (m; CH);
131.9 (m; CH); 133.7 (d; J = 11.5 Hz; CH). 31P{1H} NMR: 54.3 (s); 54.4 (s) (ratio 1:9). 19F NMR:
–163.4 (t; J = 22.5 Hz; 1Fm); –140.1 (m; 1Fp); –109.8 (d; J = 22.5 Hz; 1Fo). IR: 3083, 3056, 2947,
2927, 2854, 1479, 1432, 1416, 1333, 1040, 821, 745. Anal. Calc. for C38H26Br2F6P2Pd2 C 44.26%;
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H 2.54%; found C 46.77%, H 3.30%. HRMS: 1031.2119 [M–Br+2CH3CN], 765.0521
[Pd(PC)P]+.
Di-μ-bromo-bis{2-[(dicyclohexylphosphano)methyl]-4,5,6-trifluorophenyl-
C1,P}dipalladium(II) (10b)
The procedure was analogous to that employed for 8a but using 3b. The compound was obtained
as a yellow solid. The yield was calculated relative to the initial Pd(OAc)2: 0.480 g (65%). The
compound showed low solubility in common organic solvents. dP(3b) = +2.1 ppm (s), dP(7b) =
65.2 (s).
1H NMR: 1.00-2.45 (m; 44 H; CH(Cy) + CH2(Cy)); 3.19 (d; 4H; J = 10.8 Hz; CH2(Bn)); 6.68 (d; 2H;
J = 6.8 Hz; CH(Ar)); 6.69 (d; 2H; J = 6.8 Hz; CH(Ar)). 13C{1H} NMR: 25.8 (s; CH2); 26.1 (d; J =
14.8 Hz; CH); 26.6 (d; J = 11.6 Hz; CH2); 28.2 (s; CH2); 28.8 (s; CH2); 29.8 (s; CH2); 35.1 (d; J
= 25.7 Hz; CH2 (Bn)). 31P{1H} NMR: 82.1 (s). 19F NMR: –163.9 (ddd; J = 23.7; 19.9; 5.3 Hz 1Fm);
–140.7 (m; J = 10.5 Hz; 1Fp); –108.9 (dd; J = 26.7; 6.3; Hz; 1Fo). IR: 3040, 2923, 2850, 2797 n;
1476; 1412; 1333; 1040; 825. Anal. Calc. for C38H50Br2F6P2Pd2 C 43.25%, H 4.78%; found: C
43.52%, H 4.83%. HRMS: 447.0684 [(M/2)–Br]+, 488.0951 [(M/2)–Br+(CH3CN)]+.
Di-μ-bromo-bis{2-[(diisopropylphosphano)methyl]-4,5,6-trifluorophenyl-
C1,P}dipalladium(II) (10c)
The procedure was analogous to that employed for 8a but using 3c. The compound was obtained
as a yellow solid. The yield was calculated relative to the initial Pd(OAc)2: 0.215 g (34%). The
compound showed low solubility in common organic solvents. dP(3c) = +10.6 ppm (s), dP(7c) =
74.4 (s).
1H NMR: 1.00 (dd; 12H; J = 15.2; 6.8 Hz; CH3(iPr)); 1.47 (dd; 12H; J = 18.0; 6.8 Hz; CH3(iPr));
2.34 (dht; 4H; J = 7.2 Hz; CH(iPr)); 3.20 (d; 4H; J = 11.2 Hz; CH2(Bn)); 6.72 (pt; 2H; J = 8.0 Hz;
CH(Ar)). 13C{1H} NMR: 18.0 (s; CH3); 19.1 (s; CH3); 25.8 (d; J = 20.1 Hz; CH2 (Bn)); 29.7 (d; J =
31
19
10.1 Hz; CH). P{1H} NMR: 91.0 (s). F NMR: –163.8 (ddd; J = 22.5; 7.5; 3.8 Hz; 1Fm); –
140.6 (dpt; J = 18.0; 8.6 Hz; 1Fp); –109.9 (dd; J = 26.3; 6.4 Hz; 1Fo). IR: 3086, 3038, 2955, 2927,
2865, 1474, 1458, 1410, 1330, 1040, 831, 819. Anal. Calc. for C26H34Br2F6P2Pd2: C 34.89%, H
3.83%; found C 35.37%, H 4.01%. HRMS: 367.0060 [(M/2)–Br]+, 408.0323 [(M/2)–
Br+(CH3CN)]+.
Di-μ-bromo-bis{2-[(diphenylphosphano)methyl]phenyl-C1,P}dipalladium(II) (12a)
The procedure was analogous to that employed for 8a but using 4a. The compound was obtained
as a brown solid. The yield was calculated relative to the initial Pd(OAc)2: 0.355 g (55%). dP(4a)
= –10.0 ppm (s), dP(11a) = 51.2 (s).
1H NMR: 3.86 (d; 4H; J = 12.0 Hz; CH2(Bn)); 6.82-7.10 (m, 7H); 7.32-7.45 (m, 12H), 7.69-7.83
13
31
(m, 9H). C{1H} NMR: 43.4 (d; J = 36.9 Hz; 2CH2(Bn)); 124.0-143.9 (C(Ar), CH(Ar)). P{1H}
29
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