Iron catalysed Negishi cross-coupling using simple ethyl-monophosphines

Article abstract of DOI:10.1039/c5dt00112a

Monophosphines prepared by iron catalysed hydrophosphination have been used as pro-ligands in iron catalysed Negishi cross-coupling of alkyl bromides and diphenyl zinc reagents. The cross-coupling has been investigated with monophosphines with varying electronic properties and we find the simplest, unsubstituted phosphine to offer the optimum reaction conditions (both in terms of yield of diarylmethane product and cost-effectiveness of the phosphine). In situ catalyst generation from monophosphine and FeCl₂ was used in catalysis; however, preparation of a discrete homonuclear iron complex was also achieved and this four-coordinate iron-phosphine complex was isolated and used in catalysis.

Full text of DOI:10.1039/c5dt00112a

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DOI: 10.1039/C5DT00112A
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Cite this: DOI: 10.1039/c0xx00000x
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ARTICLE TYPE
Iron catalysed Negishi cross-coupling using simple ethyl-
monophosphines
a
b
a
a*
Caleb A. Brown, Terence A. Nile, Mary F. Mahon and Ruth L. Webster
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
5
DOI: 10.1039/b000000x
Monophosphines prepared by iron catalysed hydrophosphination have been used as pro-ligands in iron
catalysed Negishi cross-coupling of alkyl bromides and diphenyl zinc reagents. The cross-coupling has
been investigated with monophosphines with varying electronic properties and we find the simplest,
unsubstituted phosphine to offer the optimum reaction conditions (both in terms of yield of diarylmethane
1
0
product and cost-effectiveness of the phosphine). In situ catalyst generation from monophosphine and FeCl
2
was used in catalysis; however, preparation of a discrete homonuclear iron complex was also achieved and
this four-coordinate iron-phosphine complex was isolated and used in catalysis.
application for these phosphines. On top of this, the iron catalysed
Negishi cross-coupling of aryl zinc reagents and benzyl bromides
often relies on the use of diphosphines: although these are
commercially available, many such as dpbz are prohibitively
expensive and have limitations in terms of steric and electronic
Introduction
2
i
Catalysis with first row transition metals (FRTMs) is currently
undergoing a period of intense activity, with many elegant
transformations being directed towards the synthesis of small
50
1
2
2
3
3
4
4
5
0
5
0
5
0
5
variability. Elegant advances have been made with more simple
1
organic molecules. Justifiably the reasons for this attention rest
2r,6
diphosphines,
but reports of iron catalysed Negishi cross-
with the acute need to harness these inexpensive, environmentally
benign and non-toxic metals with a growing global focus on
sustainable green synthetic protocols. Catalytic C–C bond forming
reactions with the FRTMs is crucial, for example, the desire to
generate high value products by replacing transformations
traditionally carried out by the Platinum Group Metals (PGMs) is
a key target, however, tuning a FRTM catalyst to undertake a two-
electron process rather than the more favourable one-electron
transformation is a challenge. Traditional PGM cross-couplings
are used on an industrial scale and as a result, their mechanistic
details are generally well-understood, in contrast mechanistic
understanding of FRTM catalysis is exacting, not least because
reactions with metals such as iron invariably proceed with
paramagnetic pre-catalysts or paramagnetic reactive intermediates.
However, the FRTMs often undertake catalysis complimentary to
that of the PGMs. A classic example is iron catalysed cross-
coupling of organometallic reagents and alkyl halides:2 alkyl
halides containing halogen-substituted aromatic rings are also
coupling with monophosphines is limited and, given the principal
rationale for developing iron catalysis is often based on cost
effectiveness, we envisaged that use of an inexpensive phosphine
ligand would enhance the field. We herein report the extended
scope of this synthetic methodology using simple
monophosphines.
5
5
tolerated by iron catalysts whereas the palladium catalysed 60 Scheme 1. a) We have previously demonstrated that a simple, air-stable Fe
reaction is likely to lead to competitive aryl-aryl bond forming
(III) complex (1) can catalyse the hydrophosphination of styrenes; b)
preliminary results showing phosphine 2 can be employed as a ligand for
Fe-catalysed Negishi cross-coupling.
3
reactions.
We have recently demonstrated the synthetic utility of an Fe(III)
salen complex (1) in the hydrophosphination (HP) of styrenes
4
Results and discussion
(
Scheme 1a). During these studies we proved that the ethyl-
monophosphine product (2) is a useful pro-ligand for iron-
catalysed Negishi cross-coupling (Scheme 1b). To our surprise,
although the synthesis of ethyl-monophosphines is routinely used
65
Tertiary phosphine 2 was prepared on a large scale using the HP
techniques developed in our laboratory. In our hands, we find this
to be the most convenient, reproducible and cleanest route to this
5
as a synthetic benchmark in TM catalysed HP chemistry, to the
class of phosphine. Attempted S
bromoethyl)benzene in the absence and presence of base often led
N
2 reaction of HPPh
2
7
with (2-
best of our knowledge, we are the first to develop a synthetic
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to low yield of product and/or complex mixtures. Using controlled
5, along with the inexpensive nature of the unsubstituted styrene
drop-wise addition, varying the order of addition, using low 60 used to make 2, we proceeded to optimise the reaction conditions
temperatures and/or reducing reactions times did not reduce the
complexity of the product mixture. Use of a stoichiometric amount
using 2. Although the predominant aim of this research is to
develop an application for a commonly synthesised yet largely
ignored phosphorus motif, we proceeded to test common
phosphines in order to illustrate wider options in this area of
5
0
5
0
of LiHMDS, HPPh
giving 72% of 2 after 4 h at RT, however, the need for a
stoichiometric organometallic reagent, which results in
2
and (2-bromoethyl)benzene was effective
a
65 Negishi cross-coupling. PCy
3
is a poor ligand in the standard
stoichiometric amount of waste by-product, is somewhat less
attractive. Our HP route led to high isolated yield of product on a
large scale (90%; 4.8 mmol diphenylphosphine and 6.7 mmol
styrene) and the catalyst loading could be further lowered from 0.5
mol% to 0.2 mol% with the reaction still being carried out at RT.
Increasing the scale of the reaction is also beneficial in removing a
reaction (Entry 10), whilst PPh
is in stark contrast to results obtained with PPh
3
is comparable to 2 (Entry 11). This
2
i
3
/Fe(acac)3.
1
1
2
Table 1: Optimisation of iron-catalysed Negishi cross-coupling
70
8
minor impurity observed to co-elute with 2.
Following the optimised synthesis of 2, we decided to explore the
potential of other phosphines to facilitate this transformation.
Three additional phosphines (3 to 5) with variable electronic
properties were prepared using the Fe-catalysed HP methodology
with little deviation in yield (Figure 1).
a
Entry Phosphine
Solvent
Spec. Yield (%)
1
2
3
4
5
6
7
8
9
1
1
0.3 mmol 2
0.3 mmol 2
0.3 mmol 2
0.3 mmol 2
0.15 mmol 2
0.3 mmol 3
0.3 mmol 4
0.3 mmol 5
ligand-free
THF
18
8
THF with pre-reduction
toluene
toluene, Hg
toluene
toluene
toluene
toluene
toluene
toluene
toluene
74
71
49
37
51
76
16
29
71
b
2
5
0
1
0.3 mmol PCy
0.3 mmol PPh
3
3
General reaction conditions: PhMgBr (670 μL, 2 mmol, 2 eq; 3 M in Et
ZnCl (136 mg, 1 mmol) in THF (0.5 mL) then solvent (4 mL) and benzyl
bromide (1 mmol, 1 eq). FeCl (6 mg, 5 mol%) and phosphine in solvent
3 mL). Determined by H NMR using 1,3,5-trimethoxybenzene as an
analytical standard (see experimental section for methodology). Three
drops of Hg added to the reaction mixture (~1.5 mmol).
2
O),
Fig. 1. Phosphines prepared using HP catalysed by 1 for use in Fe-
2
catalysed Negishi cross-coupling. HP carried out on a 4.8 mmol HPPh
scale.
2
7
5
2
3
0
a
1
(
b
Using the coupling of diphenyl zinc (prepared by the
transmetallation of phenylmagnesium bromide with zinc chloride)
and benzyl bromide as our standard Negishi reaction we first
investigated the effect of solvent. In situ catalyst preparation was
also used in the first instance. Similar to other reports in the
literature, use of THF as the principal solvent is deleterious to
We questioned whether a discrete, mononuclear iron complex
could be synthesised using phosphine 2. Reaction of two
equivalents of 2 with FeCl ·THF1.5 in dry, degassed acetone leads
2
to the formation of a white powder which is confirmed to have the
structure 7 by X-ray crystallography (Figure 2) and elemental
analysis. The single crystal X-ray structure of 7 shows an
approximate C2V arrangement of two phosphine and two chloride
ligands around the metal centre. It is a highly air-sensitive solid
which can only be prepared in acetone, where attempted synthesis
80
3
4
4
5
5
5
0
5
0
5
2
d
reactivity, giving only 18% diphenylmethane product (6a, Table
, Entry 1). Pre-reduction, whereby FeCl and the phosphine are
first added to the ZnCl solution followed by PhMgBr, with benzyl
1
2
8
9
9
5
0
5
2
bromide added last, further lowers the yield of 6a to 8% (Entry 2).
5
In our preliminary report, toluene was used as the solvent of
in THF or CH
iron. Interestingly, once synthesised and isolated, complex 7 is
stable in CH Cl and X-ray quality crystals can be grown by slow
2 2
Cl simply leads to precipitation of nanoparticulate
choice and an unoptimised loading of 30 mol% 2, it is clear that
toluene is best suited for this reaction based on these results and
[
2d,i,q]
2
2
other reports in the area.
The use of 30 mol% phosphine also
evaporation of this solvent. Bond angles around the metal centre
are 129.51(3)° for Cl1–Fe1–Cl2 and 116.50(2)° for P1–Fe1–P2.
There is an unsymmetrical bonding angle observed at the
phosphines where P1–Fe1–Cl1 is 96.48(2)° and P2–Fe1–Cl1 is
substantially wider at 103.04(2)°. In contrast the bond angles at Cl2
are far more symmetrical (P1–Fe1–Cl2 is 106.90(3)° and P2–Fe1–
Cl2 is 105.16(2))°. There is also a slight lengthening of the Fe1–
Cl2 bond (2.2513(6) Å versus 2.2340(7) Å for Fe1–Cl1). The Fe–
Cl and Fe–P bond lengths are consistent with those observed for
proves to be fundamental to the formation of 6a: the spectroscopic
yield of 6a drops to 49% when the ligand loading is halved to 15
mol% (compare Entries 3 and 5). A mercury drop test demonstrates
that the reaction mixture is not heterogenous in nature, with only a
9
minor reduction in yield being observed (Entry 4). With optimised
solvent conditions in hand we note that the electronic properties of
the phosphine also have an effect on catalysis: use of an electron
rich phosphine (3) leads to a reduction in spectroscopic yield of 6a
to 37% (Entry 6). A moderately electron poor phosphine (4, Entry
1
00 similar four-coordinate Fe (II) complexes reported in the literature.
7
) provides a modest yield of 6a, but is still lower than that
observed with 2. Introduction of a strongly electron withdrawing
p-CF group increases the yield of 6a further (Entry 8), but does
1
0
3
not offer any substantial benefits over unsubstituted variant 2. Due
to the minor difference in yield when comparing phosphines 2 and
2
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catalysis is further demonstrated by substrates containing β-
protons; allyl and isopropyl bromides couple to benzyl bromide in
good yield (Entries 8 to 10) without undergoing β-hydride
elimination (a major deactivation pathway observed during
palladium catalysis). Unfortunately, steric bulk proves to be
limiting when tert-butyl bromide is used in catalysis, with no
product being formed.
45
50
Table 2: Alkyl bromide substrate scope in the iron-catalysed Negishi
cross-coupling
Spec.
Entry
Bromide
Product
Yield
a
(%)
1
6a
6b
74
Fig. 2. X-ray crystal structure of complex 7 (thermal ellipsoids set at 50%).
Selected bond lengths (Å) Fe1–Cl1 2.2340(7); Fe1–Cl2 2.2513(6); Fe1–P1
2
3
4
5
51
60
67
51
2
1
.4415(7); Fe1–P2 2.4656(8); P1–C1 1.828(2); P1–C7 1.829(2); P1–C13
.832(2); P2–C21 1.831(2); P2–C27 1.824(2); P2–C33 1.833(2); C13–C14
5
0
5
0
5
0
5
0
1.534(4); C33–C34 1.534(3). Selected bond angles (°): Cl2–Fe1–Cl1
6c
6d
6e
1
1
29.51(3); Cl2–Fe1–P1 106.90(3); Cl1–Fe1–P2 103.04(2); Cl2–Fe1–P2
05.16(2); Cl1–Fe1–P1 96.48(2); P2–Fe1–P1 116.50(2).
Given the optimum ligand stoichiometry necessary for the Negishi
cross-coupling (six equivalents per iron centre, Table 1, Entry 3),
we attempted to prepare the octahedral complex (8) where four
1
1
2
2
3
3
4
2
equivalents of phosphine are used per equivalent of FeCl ·THF1.5.
This would allow us to evaluate the effectiveness of in situ catalyst
preparation versus the use of a pre-synthesised complex.
Formation of the octahedral complex is not conclusive: a complex
forms within minutes in dry, degassed acetone and is recrystallized
to give an off-white powder, with micro-analytical data of the bulk
sample consistent with formation of the desired octahedral
complex, however, after several single crystal X-ray analyses the
structure is consistently revealed to be identical to that of 7. This
result is perhaps unsurprising as, to the best of our knowledge, no
examples of octahedral Fe(II) complexes exist which are ligated by
6
7
6f
72
85
6g
1
1
four PR
3
ligands and two chlorides. Investigation of the
efficiency with which complex 7 carries out the cross-coupling of
benzyl bromide and diphenyl zinc reinforces that the quantity of
phosphine in the catalytic mixture is important even with a discrete
mononuclear complex: only 32% 6a forms with 5 mol% complex
8
9
6h
6i
43
47
7
.
We next proceeded to explore the substrate scope using 2 as the
pro-ligand. We also continued to use in situ catalyst generation
(Table 1, Entry 3) due to ease of handling and inability to
conclusively form complex 8. A range of benzyl bromides are
tolerated in the reaction including electron donating (Table 2,
Entries 2 and 6) and electron withdrawing substrates (Table 2,
Entry 5). The power of the iron catalysed Negishi cross-coupling
is demonstrated by halogen-substituted benzyl bromides (Entries 4
and 7), where under palladium catalysed cross-coupling we would
anticipate transfer of the aryl group from the diaryl zinc to the
aromatic fragment of the benzyl bromide, thus forming a biaryl
motif. With iron catalysis we observe complementary reactivity,
where there is no evidence for biaryl formation and no indication
that dehalogenation is taking place. The elegant nature of iron
1
1
0
1
6j
44
60
6k
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instruments in CDCl
3
at 293 K and referenced to residual protic
1
2
solvent or TMS. Spectroscopic yields were calculated from the
distinctive methylene peak of the products (~ 4 ppm) using 0.1
mmol of 1,3,5-trimethoxybenzene as the analytical standard. UV-
6
l
0
45
2 2
vis spectrum was collected using a 10 μM solution of 7 in CH Cl .
General reaction conditions: PhMgBr (670 μl, 3 M solution in Et
2
O), ZnCl
2
(
(
136 mg, 1 mmol) in THF (0.5 mL) then toluene (4 mL) and alkyl bromide
1 mmol). FeCl (6 mg, 5 mol%) and 2 (87 mg, 30 mol%) in toluene (3
General method for the synthesis of 1.
2
a
1
[4]
mL), 45 °C, 14 h. Determined by H NMR using 1,3,5-trimethoxybenzene 50 Following the literature method, Fe(OAc)
as an analytical standard, see experimental section for methodology and
isolated yield.
2
(109 mg, 0.6 mmol,
5
1
eq) was weighed into a flask and dissolved in ethanol (5 mL). A
solution of N,N’-bis(salicylidene)ethylenediamine (200 mg, 0.7
mmol, 1.2 eq) in ethanol (10 mL) was then added forming a red
solution. The mixture was then stirred at 80 °C for 2 h. The flask
Varying the electronic properties was also investigated (Scheme
2
). It is interesting to note that when synthesising 6b and 6f, 55 was allowed to cool to RT before filtering the solid and subsequent
1
1
2
0
5
0
irrespective of whether the methoxy or fluoride group originates
from the benzyl bromide or diaryl zinc reagent, the spectroscopic
yields are very similar (compare Table 2, Entries 2 and 6 to Scheme
washing with ethanol. The dark red solid was dried under vacuum
for 2 hours.
2
). Moderate yields of di-functionalised diarylmethane motif are
General method for the synthesis of phosphines 2 to 5.
obtained when using a 4-methoxy diaryl zinc reagent (Scheme 2, 60 1 (8 mg, 0.2 mol%) was weighed into a Schlenk tube under an inert
9a and 9b). It should also be noted that when alkyl zinc reagents
were used, for example diethyl zinc and allyl zinc, no coupling to
benzyl bromide occurs (only unreacted benzyl bromide is observed
3
atmosphere. CH CN (5 mL) was added followed by styrene (0.86
mL, 7.5 mmol, 1 eq) and diphenylphosphine (1.04 mL, 6 mmol,
0.8 eq). After stirring at RT for 48 h, the Schlenk tube was placed
under vacuum to remove the excess styrene and solvent. The
1
by H NMR spectroscopy). In these cases, the zinc reagent was
added to the iron solution at low temperature (addition at both −78 65 product was isolated by column chromatography (2%
°C and 0 °C was attempted), along with RT and 45 °C (closed
system) reactions for 14 h.
EtOAc/pentane). The phosphines have been isolated and analysed
5
previously.
General method for Negishi reaction to form cross-coupled
products 6a to 6k.
7
7
8
8
9
0
5
0
5
0
PhMgBr (670 μL, 2 mmol, 3 M solution in Et
solution of ZnCl (136 mg, 1 mmol) in THF (0.5 mL) and stirred
under N for 30 min. Toluene (4 mL) was added, followed by the
appropriate benzyl bromide (1 mmol). The mixture was transferred
by cannula to a stirred solution of FeCl (6 mg, 5 mol%) and
phosphine (0.3 mmol) in toluene (1 mL), washing the ZnPh
solution through with toluene (2 mL). The reaction was stirred at
5 °C for 14 h, quenched with H O, extracted into EtOAc and dried
over MgSO . 1,3,5-Trimethoxybenzene (0.1 mmol, 10 mol%) was
2
O) was added to a
2
2
2
2
Scheme 2: Negishi cross-coupling varying the diaryl zinc reagent
(spectroscopic yield, see experimental section for isolated yield).
4
2
4
added to the dried, filtered EtOAc solution, this was then
concentrated and an NMR sample prepared by diluting the whole
2
5
Conclusions
sample with 1 mL CDCl
diluted with CDCl
3
, an aliquot was removed and further
prior to analysis by H NMR. Compounds were
We have prepared simple monophosphines using HP methodology
developed in our own laboratory. These phosphines, in the
presence of FeCl , competently catalyse the Negishi cross-
2
1
3
isolated by column chromatography (100% pentane to 5%
EtOAc/pentane).
coupling of alkyl bromides and diaryl zinc reagents. This is a rare
example of a monophosphine being used to carry out such a
3
0
General method for the synthesis of 7 and 8.
FeCl ·THF1.5 (17 mg, 0.064 mmol) and 2 (0.128 mmol or 0.257
2
mmol) were mixed in a vial in an argon filled glovebox. Dry,
degassed acetone (1 mL) was added and the reaction mixture
stirred for 4 h. During this time the solution turned yellow followed
by precipitation of an off-white solid. The solution was cooled to
transformation and indeed we have demonstrated that PPh
3
in the
presence of FeCl is similarly proficient. In situ catalyst
2
preparation proves to be the easiest method to facilitate the
transformation, however, the air-sensitive four-coordinate
complex 7 was also isolated and characterised by X-ray
crystallography.
3
5
−
30 °C for 15 minutes then the supernatant was removed, the
precipitate was washed with a further 2 × 1 mL cold acetone then
95 dissolved in CH Cl , filtered through a pipette plugged with glass
Experimental
2
2
paper and crystals grown by slow evaporation of the solvent. NMR
data are consistent with the formation of paramagnetic complexes.
General considerations
Reagents were purchased from Sigma Aldrich and used without
4
0
2
further purification. Solvents were dried over CaH or Na (reflux),
Analysis data for products
00 Compound 6a, Table 2, Entry 1
distilled and then degassed using three freeze-pump-thaw cycles.
NMR data was collected at 250, 300, 400 or 500 MHz on Bruker
1
4
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Dalton Transactions
1
-1
15
Colourless oil, 102 mg (61%). H NMR (250 MHz; 298 K; CDCl
3
)
2920, 1591, 1513, 1447 cm . Data matches literature reports.
δ 7.30-7.14 (m, 10H), 3.97 (s, 2H); 13C{ H} NMR (63 MHz; 298
1
60
K; CDCl
032, 2929, 1595, 1476 cm . Data matches that of a commercial
sample (CAS: 101-81-5).
3
) δ 141.2, 128.9, 128.5, 126.1, 41.9; IR (neat) ν 3060,
Compound 6i, Table 2, Entry 9
Colourless oil, 84 mg (45%). H NMR (250 MHz; 298 K; CDCl
-
1
1
3
3
)
1
3
1
5
δ 7.38-7.02 (m, 10H), 2.92 (s, 2H); C{ H} NMR (63 MHz; 298
K; CDCl ) δ 141.8, 128.4, 128.3, 125.9, 37.0; IR (neat) ν 3029,
3
-
1
6
7
7
8
5
0
5
0
2930, 1595, 1481 cm . Data matches that of a commercial sample
(CAS: 103-29-7).
Compound 6b, Table 2, Entry 2
1
Colourless oil, 98 mg (49%). H NMR (250 MHz; 298 K; CDCl
3
)
δ 7.33-7.29 (m, 2H), 7.28-7.22 (m, 3H), 7.16 (d, J 8.4 Hz, 2H),
1
Compound 6j, Table 2, Entry 10
1
1
2
2
3
3
4
4
5
5
0
5
0
5
0
5
0
5
0
5
6.87 (d, J 8.4 Hz, 2H), 3.94 (s, 2H), 3.79 (s, 3H); 13C{ H} NMR
63 MHz; 298 K; CDCl ) δ 157.9, 141.6, 133.3, 129.9, 128.8,
28.4, 126.0, 113.9, 55.3, 41.0; IR (neat) ν 3025, 2860, 1594, 1494,
1
Colourless oil, 48 mg (40%). H NMR (250 MHz; 298 K; CDCl
3
)
(
3
δ 7.33-7.18 (m, 5H), 6.06-5.93 (m, 1H), 5.13-5.05 (m, 2H), 3.40
1
1
1
3
1
-
1
12
(d, 2H, J 6.5 Hz); C{ H} NMR (63 MHz; 298 K; CDCl
3
) δ 148.8,
437 cm . Data matches literature reports.
1
28.3, 126.4, 125.8, 34.1, 24.0; IR (neat) ν 3028, 2902, 1639, 1494
-
1
cm . Data matches that of a commercial sample (CAS: 300-57-2).
Compound 6c, Table 2, Entry 3
1
Colourless oil, 88 mg (49%). H NMR (250 MHz; 298 K; CDCl
3
)
Compound 6k, Table 2, Entry 11
δ 7.42-7.32 (m, 2H), 7.32-7.22 (m, 3H), 7.22-7.12 (m, 4H), 4.03
1
1
3
1
Colourless oil, 68 mg (57%). H NMR (250 MHz; 298 K; CDCl
3
)
(
s, 2H), 2.40 (s, 3H); C{ H} NMR (63 MHz; 298 K; CDCl
3
) δ
δ 7.45-7.30 (m, 5H), 3.03 (septet, 1H, J 6.9 Hz), 1.40 (d, 6H, J 6.9
1
41.5, 138.1, 135.6, 129.2, 128.9, 128.9, 128.5, 126.1, 41.6, 21.1;
1
3
1
-
1
Hz); C{ H} NMR (63 MHz; 298 K; CDCl
3
) δ 140.0, 137.4,
IR (neat) ν 3022, 2850, 1595, 1491 cm . Data matches literature
reports.
2
i,8
128.6, 128.4, 126.0, 115.7, 40.1; IR (neat) ν 3028, 2960, 1494,
-
1
1464 cm . Data matches that of a commercial sample (CAS: 98-
2-8).
8
Compound 6d, Table 2, Entry 4
1
White solid, 85 mg (34%). H NMR (250 MHz; 298 K; CDCl
3
) δ
7.48-7.16 (m, 9H), 3.94 (s, 2H); 13C{ H} NMR (63 MHz; 298 K;
1
Complex 7
Isolated as a white powder (35 mg, 77%). H NMR (500 MHz; 298
Cl ) δ 13.42 (br), 7.55 (br), 7.14 (br), 0.85 (br), 0.12 (br), -
1
CDCl
3
) δ 140.4, 139.9, 131.5, 130.6, 128.9, 128.5, 126.3, 119.8,
-
1
85 K; CD
2
2
4
1.6; IR (neat) ν 3025, 2920, 1598, 1484 cm . Data matches
1
3
1
2
i,8
0.92 (br); C{ H} NMR (125 MHz; 298 K; CD
2 2
Cl ) δ 173.4,
literature reports.
1
48.7, 135.1, 128.5, 128.3, 126.4, 31.6, 31.0, -0.5; elemental
analysis: C 67.9, H 5.4 (calcd); C 68.1, H 5.0 (obs.); m.p. 164 °C
(decomp.); IR (solid) ν 3054 (w), 3023 (w), 1602 (w), 1583 (w),
90 1484 (s), 1433 (s), 1238 (br), 1097 (s), 748 (s), 738 (s), 732 (s),
Compound 6e, Table 2, Entry 5
1
Colourless oil, 112 mg (47%). H NMR (250 MHz; 298 K; CDCl
3
)
δ 7.58 (d, J 8.0 Hz, 2H), 7.38-7.20 (m, 7H), 4.06 (s, 2H); 13C{ H}
NMR (63 MHz; 298 K; CDCl ) δ 145.3, 140.0, 129.2, 128.9,
28.7, 128.2 (q, J 33 Hz), 126.5, 125.4 (q, J 4 Hz), 124.4 (q, J 270
1
7
23 (s).
3
1
-
1
Crystal Data for C40H38Cl FeP (7).
2 2
Hz), 41.7; IR (neat) ν 3031, 2931, 1595, 1481 cm . Data matches
literature reports.2i,8
M = 707.39,  = 0.71073 Å, triclinic, space group P-1, a =
9.4059(4), b = 10.4593(5), c = 19.1213(8)Å, α = 89.049(4), 
9
5
o
3
=
1
0
c
84.880(4), γ = 68.014 , U = 1737.08(13) Å , Z = 2, D =
Compound 6f, Table 2, Entry 6
-3
-1
.352 g cm ,  = 0.708 mm , F(000) = 736. Crystal size =
.3550 × 0.2201 × 0.1414 mm, unique reflections = 7961 [R(int)
1
Colourless oil, 127 mg (69%). H NMR (500 MHz; 298 K; CDCl
3
)
δ 7.28 (t, J 7.3 Hz, 2H), 7.21-7.18 (m, 5H), 6.96 (t, J 8.8 Hz, 2H),
=
0.0294], observed reflections [I>2I)]
) δ 161.3 (d, 100 data/restraints/parameters = 7961/0/406. Observed data; R1 =
J 244.2 Hz), 140.7, 136.5 (d, J 2.9 Hz), 130.0 (d, J 7.6 Hz), 128.8,
0.0432, wR2 = 0.0814. All data; R1 = 0.0638, wR2 = 0.0886.
=
6167,
1
3
1
3
.93 (s, 2H); C{ H} NMR (125 MHz; 298 K; CDCl
3
-
3
1
1
28.5, 126.2, 115.4 (d, J 21.0 Hz), 41.0; IR (neat) ν 3035, 2944,
589, 1489 cm . Data matches literature report.
Max peak/hole = 0.443 and −0.341 eÅ , respectively. CCDC
1035920.
-
1
13
Compound 6g, Table 2, Entry 7
105 Compound 6b, Scheme 2
1
Colourless oil, 99 mg (50%). Data matches literature reports.11
Colourless oil, 155 mg (78%). H NMR (250 MHz; 298 K; CDCl
3
)
δ 7.30-7.12 (m, 6H), 6.79-6.70 (m, 3H), 3.91 (s, 2H), 3.71 (s, 3H);
1
3
1
C{ H} NMR (63 MHz; 298 K; CDCl
3
) δ 159.9, 142.9, 139.9,
Compound 6f, Scheme 2
Colourless oil, 117 mg (63%). Data matches literature reports.
1
2
129.5, 128.9, 128.5, 126.2, 121.4, 114.9, 111.4, 55.1, 42.1; IR
-
1
(
neat) ν 3030, 2973, 1595, 1496 cm . Data matches literature 110
1
4
reports.
Compound 9a, Scheme 2
Colourless oil, 102 mg (48%). H NMR (500 MHz; 298 K; CDCl
1
3
)
Compound 6h, Table 2, Entry 8
δ 7.14-7.08 (m, 6H), 6.86-6.84 (m, 2H), 3.90 (s, 2H), 3.79 (s, 3H),
1
13
1
Colourless oil, 98 mg (40%). H NMR (250 MHz; 298 K; CDCl
3
)
3
2.33 (s, 3H); C{ H} NMR (125 MHz; 298 K; CDCl ) δ 157.7,
δ 7.57 (d, J 9.0 Hz, 1H), 7.37-7.01 (m, 8H), 4.12 (s, 2H); 13C{ H} 115 138.6, 135.1, 133.6, 129.7, 129.2, 128.8, 113.7, 55.0, 40.4,
1
1
1c
NMR (63 MHz; 298 K; CDCl
3
) δ 140.4, 139.6, 132.8, 131.1,
20.8. Data matches literature reports.
1
28.9, 128.5, 127.9, 127.6, 126.2, 124.9, 41.7; IR (neat) ν 3018,
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Page 6 of 7
Compound 9b, Scheme 2
White solid, 113 mg (41%). H NMR (500 MHz; 298 K; CDCl
d) J. Hassan, M. Sevignon, C. Gozzi, E. Schulz and M. Lemaire, Chem.
Rev. 2002, 102, 1359-1469; e) A. F. Littke and G. C. Fu, Angew. Chem.
Int. Ed. 2002, 41, 4176-4211.
1
3
) δ
7
3
.50 (d, J 8.3 Hz, 2H), 7.08-7.01 (m, 4H), 6.85 (d, J 8.3 Hz, 2H),
60
1
3
1
.84 (s, 2H), 3.78 (s, 3H); C{ H} NMR (125 MHz; 298 K;
) δ 158.4, 140.3, 132.6, 131.0, 130.1, 129.4, 119.4, 113.8,
4
5
6
K. J. Gallagher and R. L. Webster, Chem. Commun.2014, 50, 12109-
5
CDCl
5
3
1
2111.
1
6
4.8, 40.2; m.p. 88 °C. Data matches literature reports.
a) L. Rosenberg, ACS Catal. 2013, 2845-2855; b) V. Koshti, S.
Gaikwad and S. H. Chikkali, Coord. Chem. Rev. 2014, 265, 52-73.
R. B. Bedford, E. Carter, P. M. Cogswell, N. J. Gower, M. F. Haddow,
J. N. Harvey, D. M. Murphy, E. C. Neeve and J. Nunn, Angew. Chem.
Int. Ed. 2013, 52, 1285-1288.
Notes and references
65
a
Department of Chemistry, University of Bath, Claverton Down, Bath,
UK, BA2 7AY.Tel:+44(0)1225 386103 E-mail: r.l.webster@bath.ac.uk
Department of Chemistry and Biochemistry, University of North
b
1
1
2
0
5
0
7
8
9
M. T. Honaker, B. J. Sandefur, J. L. Hargett, A. L. McDaniel and R.
N. Salvatore, Tetrahedron Lett. 2003, 44, 8373-8377.
Carolina Greensboro, Greensboro, North Carolina, 27405, USA.
The participation of Caleb Brown (Home institution: Guilford College,
Greensboro, North Carolina, USA) was made possible by the support of
the National Science Foundation (Grant number 1262847) through its
Research Experiences for Undergraduates program, which is gratefully
acknowledged. The University of Bath is also thanked for additional
funding.
70
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Organometallics 1985, 4, 1819-1830.
†
Electronic Supplementary Information (ESI) available: cif file or
complex 7. See DOI: 10.1039/b000000x/
7
8
8
9
9
5
0
5
0
5
1
a) C. Bolm, J. Legros, J. Le Paih and L. Zani, Chem. Rev. 2004, 104,
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DOI: 10.1039/C5DT00112A
Reported is a rare example of the use of monophosphines in iron catalysed Negishi cross-
coupling. Substrate scope in terms of alkyl bromide and diaryl zinc reagent is explored.