N-Heterocyclic carbene adducts of orthopalladated triarylphosphite complexes

Article abstract of DOI:10.1039/b506286a

Carbene adducts of orthopalladated triarylphosphite complexes have been synthesised and characterised. The structures of three of these complexes were determined by single-crystal X-ray analysis. The complexes are active in the Suzuki coupling of a range of aryl bromide substrates. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b506286a

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F U L L P A P E R
N-Heterocyclic carbene adducts of orthopalladated
triarylphosphite complexes
Robin B. Bedford,*a Michael Betham,a Michael E. Blake,b Robert M. Frost,b Peter N. Horton,c
Michael B. Hursthousec and Rosa-Mar´ıa Lo´pez-Nicola´sd
a School of Chemistry, University of Bristol, Cantock’s Close, Bristol, UK BS8 1TS.
E-mail: r.bedford@bristol.ac.uk
b Department of Chemistry, University of Exeter, Exeter, UK EX4 4QD
c EPSRC National Crystallography Service, Department of Chemistry, University of
Southampton, Highfield Road, Southampton, UK SO17 1BJ
d Grupo de Quimica Organometalica, Departamento de Quimica Inorganica, Facultad de
Quimica, Universidad de Murcia, Apdo. 4021, 30071, Murcia, Spain
Received 5th May 2005, Accepted 30th June 2005
First published as an Advance Article on the web 15th July 2005
Carbene adducts of orthopalladated triarylphosphite complexes have been synthesised and characterised. The
structures of three of these complexes were determined by single-crystal X-ray analysis. The complexes are active in
the Suzuki coupling of a range of aryl bromide substrates.
Introduction
Palladium catalysed carbon–carbon and carbon–heteroatom
bond forming reactions are widely used and powerful tools in
Scheme 1 The Buchwald–Hartwig amination of aryl chlorides.
organic synthesis.1 The inception and development of coupling
reactions of aryl chloride substrates has been the focus of much
3 could also be employed in amination.5 Further, Caddick and
recent research.2 This is because aryl chlorides tend to be cheaper
Kofie demonstrated the efficacy of palladium catalysts based on
and more widely available than bromides or iodides and as such
2b (formed in situ by deprotonation of the imidazolium salt) in
are valuable starting materials. Since the ease of the first step
intramolecular Heck couplings of aryl chloride substrates.6
of any coupling reaction – the oxidative addition of the C–X
While the choice of appropriate ligand is often crucial for the
bond of the aryl halide – is dependent on the carbon–halogen
activation of aryl chloride substrates,7 the correct selection of the
bond strength, it follows that aryl chlorides are more difficult to
palladium precursor can lead to a considerable enhancement
activate than their bromide or iodide counterparts.3
in performance. For instance Beller and co-workers showed
Generally, the best palladium catalysts for aryl chloride
that the pre-formed, zero-valent complexes 4 show substantially
coupling reactions incorporate strongly electron-donating phos-
improved activity in the Suzuki coupling of aryl chlorides
phine ligands with two or three alkyl substituents. The resultant
(Scheme 2) compared with the use of the more conventional
high electron density on the zero-valent active catalysts facili-
palladium source, palladium acetate, with the same ligands.8
tates the oxidative addition step. Typically, the phosphine ligands
that are employed include PtBu3, PCy3, PR2(o-biphenyl) and
related ligands.2
Scheme 2 The Suzuki coupling of aryl chlorides.
Activity is not limited to catalysts with phosphine ligands:
unsaturated N-heterocyclic carbene ligands 1 have also proved
to be effective in the coupling of aryl chloride substrates.2
The analogous saturated carbenes 2 also show promise in this
regard. Hartwig and co-workers demonstrated that 2b could
be used in the room-temperature Buchwald–Hartwig amination
(scheme 1) of non-activated aryl chlorides,4 while Caddick,
Cloke and co-workers showed that the preformed complexes
Palladacyclic precursors with either phosphine or carbene
co-ligands can also show enhanced activity. Thus the carbene
adduct 5 can be used to good effect in amination of aryl chlorides
and the a-arylation of ketones (Scheme 3).9
2 7 7 4
D a l t o n T r a n s . , 2 0 0 5 , 2 7 7 4 – 2 7 7 9
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
©

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Scheme 3 The a-arylation of ketones.
We have shown that the phosphine adducts of orthopalla-
dated triarylphosphite complexes, 6, show far higher activity
than equivalent adducts with N-based palladacycles in the
Suzuki coupling of aryl chloride substrates.10 In view of this
it may be anticipated that N-heterocyclic carbene adducts
of orthopalladated phosphite complexes would display good
activity in coupling reactions with not only aryl bromide but
also aryl chloride substrates. To this end we have synthesised
such complexes and tested their catalytic activity in the Suzuki
reaction and the results are presented below.
Results and discussion
Complex synthesis
In the first instance we examined the formation of carbene
adducts of the bulky orthopalladated triarylphosphite complex
7a, reasoning that if this proves successful then analogous
syntheses with smaller precursors should be facile. The reaction
of 7a with the free carbene ligand 2a – prepared in situ by
deprotonation of the corresponding imidazolium salt11 – in
THF at room temperature did not proceed cleanly when the
stoichiometry was held at 1 : 1 but rather gave a mixture of
compounds as determined by 31P NMR. This may be due to
partial decomposition of the free carbene. When the reaction was
repeated with a large (ten-fold) excess of 2a the 31P NMR
spectrum of the resultant mixture showed a single peak at
134.4 ppm corresponding to the desired complex 8a (Scheme 4).
However, the yield of the isolated product proved to be
low (20%). Waymouth, Hedrick and co-workers very recently
showed that the 2-(pentafluorophenyl)imidazolidine 9a can be
used as a simple, air-stable precursor for the synthesis of
the carbene adducts of allyl palladium chloride under mild
thermolytic conditions, via loss of pentafluorobenzene.12 We
wondered whether 9a could be used in an analogous fashion
to produce 8a and were pleased to find that the reaction worked
well to produce 8a in 68% yield (Scheme 4).
Scheme 4 Synthesis of carbene adducts. Reagents and conditions:
(i) THF, r.t., 2 h; (ii) complex 7a (0.5 equiv.), toluene, 80 ◦C, 2 h;
(iii) C6F5CHO, HOAc, 30 min, r.t.; (iv) [{Pd(l-Cl){j2-P,C-
P(OC6H4)(OPh)2}}2], 7b, (0.5 equiv.), toluene, 80 ◦C, 18 h.
The 13C NMR spectrum of 8a shows a doublet at 152.5 ppm
2
with a 28.7 Hz JPC cis coupling for the metallated carbon of
the phosphite ligand. The carbene carbon is seen as a doublet
2
at 212.3 ppm with a large JPC of 213.6 Hz, indicating that the
carbene ligand is trans to the P-donor. The 31P NMR spectrum
of pure 8a formed under these conditions shows only the peak at
134.4 ppm, while a spectrum of the crude reaction mixture also
shows a small peak at 136.4 ppm, which may correspond to the
formation of some of the second possible isomer in which the
carbene is cis to the phosphite P-atom. This peak is not seen in
the reaction of 7a with excess free carbene, presumably because
the reaction is performed at a lower temperature and the second
isomer is less favoured on both steric and electronic grounds.
It is possible to produce the even more encumbered analogue
8b by the same method (Scheme 1). The organic precursor 1,3-
bis(2,6-diisopropylphenyl)-2-(pentafluorophenyl)imidazolidine,
9b, was synthesised in good yield in an analogous manner
to 9a, by the reaction of the 1,2-(diarylamino)ethane with
pentafluorobenzaldehyde.12 Unlike 9a, the more hindered
species 9b proved to be slightly thermally sensitive in solution,
with partial decomposition apparent by 1H NMR within
48 h. As a solid 9b is stable at room temperature (weeks). In
contrast, over a similar timescale, compound 9a shows signs
of decomposition in the solid state. The reaction of 9b with
complex 7a gives the desired complex 8b in 53% yield. The
31P NMR spectrum of 8b shows a singlet at 135.0 ppm, very
close to that for 8a. The 13C NMR shows doublets for the
orthometallated carbon and the carbene carbon at 154.49 and
212.0 ppm, respectively, with 2JPC couplings of 29 and 216 Hz.
These data are close to those of 8a indicating that the structures
are very similar.
The less bulky phosphite dimer 7b readily reacts with the car-
bene precursor 9b to generate the carbene-containing complex 8c
in 93% yield within 2 h, provided that an excess of 9b is employed.
When the stoichiometry of 9b : Pd is held at 1 : 1 a mixture of the
desired product and the starting complex 7b is observed by 31
P
NMR after 2 h, but when the reaction is heated overnight pure
8c is isolated in 83% yield. This implies the reaction is slower
when the bulk of the phosphite is reduced. This may indicated
that the carbene adduct forms via a dissociative process, where
the rate-determining step is fission of the chloride bridged
dimer, a process that may be expected to be slower with smaller
orthometallated phosphites. The major isomer observed is again
that in which the carbene ligand is trans to the phosphite P-atom.
The 31P NMR shows this isomer as a singlet at 136.8 ppm. As
before, a second small peak is apparent at 137.2 ppm which
may correspond to the second possible isomer. The 13C NMR
shows the expected doublets at 158.6 and 213.5 ppm for the
orthometallated carbon and carbene carbon, with 2JPC couplings
of 30 and 214 Hz, respectively. The putative second isomer is at
D a l t o n T r a n s . , 2 0 0 5 , 2 7 7 4 – 2 7 7 9
2 7 7 5

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◦
˚
Table 1 Selected bond lengths (A) and angles ( ) for complexes 8a–c
8a
8b
8c
Pd–C(carbene)
Pd–C(aryl)
Pd–P
2.0661(16)
2.0352(15)
2.1976(5)
2.3840(5)
2.061(3)
2.046(3)
2.2124(8)
2.3784(8)
2.066(4)
2.030(4)
2.1868(10)
2.3739(10)
Pd–Cl
C(carbene)–Pd–C(aryl)
C(carbene)–Pd–Cl
C(carbene)–Pd–P
C(aryl)–Pd–P
C(aryl)–Pd–Cl
P–Pd–Cl
94.00(6)
94.59(5)
172.73(5)
79.42(5)
170.41(4)
91.76(2)
90.09(12)
95.92(8)
167.36(8)
80.09(9)
167.63(9)
95.26(3)
93.16(14)
98.16(10)
173.33(10)
80.88(11)
168.51(11)
87.91(4)
too low a concentration for the carbene carbon to be observed
by 13C NMR, even after protracted scan times.
The solid-state structures of the complexes 8a–c were deter-
mined by single-crystal X-ray analyses. The molecules are shown
in Figs. 1–3, while selected data are presented in Table 1.
Fig. 3 The molecular structure of [PdCl{j2-P,C-P(OC6H4)(OPh)2}-
{C(CN(2,6-iPr2C6H3)CH2)2}], 8c.
considerable steric encumbrance around the periphery of the
approximately square planar complexes. In all cases the plane
of the carbene is approximately orthogonal to the square plane
(71.4, 70.8 and 80.4◦ for complexes 8a–c, respectively). The Pd–
C bond lengths of the orthometallated phosphite ligands are
slightly longer than that of the parent complex 7a (1.998(6)
A),13 possibly as a result of the high steric profile of the carbene
˚
ligands. The Pd–P bond lengths are also longer than that in 7a
˚
((2.1668(17) A). There are no significant differences between the
Pd–C(carbene) bond lengths of the complexes 8 and that of the
related unsaturated carbene N-palladacyclic complex 5 (Ar =
C6H3-2,6-iPr2).9
The complex 8c reacts with silver hexafluoroantimonate
in acetonitrile solution to generate the cationic complex 10
(Scheme 5). The 31P NMR spectrum of 10 shows a singlet
at 129.9 ppm, slightly up-field of the neutral parent complex
8a. The 13C NMR spectrum shows a doublet at 207.9 ppm
corresponding to the carbene carbon, which has shifted upfield
compared with that in 8a. The magnitude of the coupling to
the P-donor, 145 Hz, indicates that the carbene is trans to the
phosphite group, as in complex 8a. Complex 10 can also be
synthesised in good yield by the reaction of the cationic bis-
acetonitrile complex 11 with the carbene precursor 9a.
Fig. 1 The molecular structure of [PdCl{j2-P,C-P(OC6H2-2,4-tBu2)-
(OC6H3-2,4-tBu2)2}{C(CNMesCH2)2}], 8a.
Scheme 5 Reagents and conditions: (i) AgSbF6, MeCN, r.t., 4 h; (ii) 9a,
toluene, 100 ◦C, 3 h; (iii) Ag[SbF6], MeCN, r.t., 4 h.
Fig. 2 The molecular structure of [PdCl{j2-P,C-P(OC6H2-2,4-tBu2)-
(OC6H3-2,4-tBu2)2}{C(CN(2,6-iPr2C6H3)CH2)2}], 8b.
Catalysis
We investigated the Suzuki coupling of aryl halides substrates
using 1,4-dioxane as solvent and caesium carbonate as base
(non-optimised conditions). The results from this study are
As can be seen the molecules are highly crowded with both
the carbene and orthometallated phosphite ligands presenting
2 7 7 6
D a l t o n T r a n s . , 2 0 0 5 , 2 7 7 4 – 2 7 7 9

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Table 2 Suzuki coupling of aryl halides with phenylboronic acid catalysed by complexes 8a and 8ba
Entry
Aryl halide
Product
Catalyst
Conv.b (%)
1
2
8a
8b
84
83
3
4
8a
8b
80
76
5
6
8a
8b
87
58
7
8
8a
8b
67
40
9
10
8a
8b
57
34
11
12
8a
8b
91
80
13
14
8a
8b
15
8
15
8a
0
a Reagents and conditions: Aryl halide (1.0 mmol), PhB(OH)2 (1.5 mmol), Cs2CO3 (3.0 mmol), 1,4-dioxane, 110 ◦C (external temperature). b Conversion
to coupled product determined by GC (hexadecane standard).
summarised in Table 2. As can be seen, catalyst 8a shows
reasonable activity with both activated and non-activated aryl
bromide substrates (entries 1, 3 and 5). Lower activity is observed
with electronically deactivated aryl bromides (entries 7 and
9) while little and no activity is seen with non-activated and
deactivated aryl chlorides, respectively (entries 13 and 15). In all
cases tested, the bulkier catalyst 8b showed poorer activity.
The low activity of the catalysts 8a and 8b, particularly with
regards the activation of chloride substrates, is perhaps surpris-
ing given the high activities associated with the notionally related
catalyst systems 5 and 6.9,10 The fact that the catalysts are able
to couple aryl bromides substrates demonstrates that, from a
steric perspective, the catalysts are competent, but that the active
species are not sufficiently electron-rich to facilitate the oxidative
addition of aryl chlorides. This is particularly surprising in view
of the very high activity associated with the complexes 6 because
N-heterocyclic carbenes are typically considered to be more
electron donating than di- and trialkylphosphines.14 It is possible
that the carbene ligand is not actually present in the active species
– these ligands have been shown to be reasonably labile on both
Pd(0) and Pd(II) centres.5,15 This would mean that the active
catalyst would only contain phosphite ligands which tend to
give poor performances with all but electronically activated aryl
chlorides.16 However, this is militated against by the fact that
phosphite-based palladacycles show vastly better activity in the
coupling of aryl bromides.10c,12
Perhaps unsurprisingly, given its lack of activity in the Suzuki
coupling of aryl chlorides, the Buchwald–Hartwig amination
reaction of 4-chlorotoluene with morpholine in toluene at 110 ◦C
with K3PO4 as base and 8a as pre-catalyst (1 mol%) did not yield
any of the coupled product, N-(4-tolyl)morpholine after 17 h.
In conclusion, the compounds 9 make excellent precursors
for the generation of both neutral and cationic carbene adducts
of phosphite-based palladacycles in good yields. The neutral
complexes formed show, somewhat surprisingly, only modest
activity in the Suzuki coupling of aryl bromides and poor activity
with aryl chlorides. We are currently investigating the use of
cationic complexes in a range of Lewis-acid catalysed reactions
and this work will be reported at a later date.
Experimental
General
All reactions and manipulations of air-sensitive materials were
carried out under nitrogen either in a glove-box or using
standard Schlenk techniques. Solvents were dried and freshly
distilled prior to use. All other chemicals were used as received.
Compounds 7a, 7b and 9b were prepared according to literature
methods.12,17 GC analyses were performed on a Varian 3800 GC
fitted with a 25 m CPSil 5CB column and data were recorded on
a Star workstation.
D a l t o n T r a n s . , 2 0 0 5 , 2 7 7 4 – 2 7 7 9
2 7 7 7

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Synthesis
1,3-Bis(2,6-diisopropylethylphenyl)-2-(pentafluorophenyl) imi-
Ar), 142.13, 145.78, 148.44, 148.48, 148.75 (s, C, Ar), 154.49
2
2
(d, JPC = 29 Hz, metallated C of phosphite), 212.0 (d, JPC
=
216 Hz, carbene C).
dazolidine, 9b. Pentafluorobenzaldehyde (0.125 g, 1.06 mmol)
was dissolved in a minimal amount of glacial acetic acid, N,Nꢀ-
bis(2,6-diisopropylphenylamino)ethane (0.240 g, 0.64 mmol)
was added and the resultant mixture was stirred at room temper-
ature for 30 min. The precipitate was washed with cold methanol,
dissolved in CH2Cl2 and forced through a short silica plug that
had been previously treated with triethylamine. Evaporation of
the CH2Cl2 solution afforded the product as a colourless solid.
Yield: 0.260 g (73%). Anal. Calc. for C33H39F5N2: C, 70.95; H,
i
[PdCl{j2-P,C-P(OC6H4)(OPh)2}{C(CN(C6H3-2,6-Pr2)CH2)2}],
8c. A mixture of 9b (0.136 g, 0.244 mmol) and complex 7a
(0.110 g, 0.244 mmol) was heated in toluene (10 mL) at 100 ◦C
for 18 h. The solvent was removed in vacuo, and the colourless
solid was recrystallised from Et2O. Yield 0.166 g, (81%). Anal.
Calc. for C45H52ClN2O3PPd: C, 64.26; H, 6.66; N, 3.32. Found:
1
C, 64.13; H, 6.18; N, 3.07%. H NMR (300 MHz, CDCl3): d
3
i
3
0.24 (d, 6H, JHH = 6 Hz, Pr CH3), 1.05 (d, 6H, JHH = 6 Hz,
1
7.04; N, 5.01. Found: C, 71.04; H, 7.36; N, 5.13%. H NMR
iPr CH3), 1.12 (d, 6H, JHH = 6 Hz, Pr CH3), 1.38 (d, 6H,
3JHH = 6 Hz, iPr CH3), 3.27 (m, 2H, 3JHH = 6 Hz, iPr CH), 3.54
3
i
(300 MHz, CDCl3): d 0.71 (d, 6H, 3JHH = 9 Hz, iPr CH3), 0.95 (d,
6H, 3JHH = 9 Hz, iPr CH3), 1.21 (d, 6H, 3JHH = 9 Hz, iPr CH3),
3
i
(m, 2H, JHH = 6 Hz, Pr CH), 4.04 (m, br, 4H, CH2), 6.63 (d,
2H, 3JHH = 9 Hz, Ar), 6.92 (m, 6H, Ar), 6.97 (m, 6H, Ar), 7.19
(m, 3H, Ar), 7.30 (m, 3H, Ar). 31P NMR (121.5 MHz, CDCl3):
d 136.8 (s). 13C NMR (75 MHz, CDCl3): d 26.64, 27.53, 28.76,
29.33 (s, iPr), 54.86 (d, 4JPC = 7 Hz, CH2), 111.41, 111.67 (s, CH,
Ar), 121.95 (d, JPC = 5 Hz, CH, Ar), 122.54, 124.85, 125.11,
126.49, 129.45, 129.76 (s, CH, Ar), 134.47, 136.27 (s, C, Ar),
3
i
1.33 (d, 6H, JHH = 9 Hz, Pr CH3), 3.45 (virtual heptet, 4H,
i
3JHH = 9 Hz, Pr CH), 3.55 (m, 2H, CH2), 3.82 (m, 2H, CH2),
6.23 (s, 1H, C6F5CH), 6.94 (m, 2H), 7.08 (m, 4H). 19F NMR
(282.4 MHz, CDCl3): d −136.05, −147.45, −156.11, −162.71,
−163.34 (s). 13C NMR (75 MHz, CDCl3): d 24.16, 24.48, 24.66,
25.81, 26.33, 27.06, 27.15, 29.20 (s, iPr), 53.57 (s, CH2N), 66.29
(s, CH(C6F5), 124.01, 124.63, 125.00, 125.42, 127.17, 127.76,
138.83, 149.63, 151.69.
139.29 (s, CH, Ar), 146.98, 148.35, 150.21 (s, C, Ar), 158.6 (d,
2
2JPC = 30 Hz, metallated C of phosphite), 213.54 (d, JPC
=
[PdCl{j2 -P,C -P(OC6H2 -2,4-tBu2 )(OC6H3 -2,4-tBu2 )2}{C-
(CNMesCH2)2}], 8a. A mixture of 1,3-bis(2,4,6-trimethyl-
phenyl)-2-(pentafluorophenyl)imidazolidine, 9a, (0.065 g,
0.14 mmol) and complex 7a (0.101 g, 0.06 mmol) was heated
in toluene (5 mL) at 80 ◦C for 2 h. The solvent was removed
in vacuo, cold ether (5 mL) was added to induce crystallisation
and the colourless solid was recrystallised from Et2O–pentane.
Yield: 0.095 g (72%). Anal. Calc. for C63H89ClN2O3PPd·C4H10O:
C, 68.82; H, 8.53; N, 2.40. Found: C, 68.87; H, 8.77; N, 2.15%.
1H NMR (300 MHz, CDCl3): d 0.96 (s, 9H, tBu), 1.27 (s, 18H,
tBu), 1.29 (s, 18H, tBu), 1.33 (s, 9H, tBu), 2.24 (s, 6H, CH3), 2.30
(s, 6H, CH3), 2.54 (s, 6H, CH3), 4.02 (m, 4H, NCH2CH2N),
214 Hz, carbene carbon).
[Pd{j2-P,C-(P(OC6H2-2,4,-tBu2)(OC6H3-2,4-tBu2)2}(NCMe)2]-
[SbF6], 11. Complex 7a (0.196 g, 0.248 mmol) was suspended
in MeCN (10 mL) and Ag[SbF6] (0.085 g, 0.248 mmol) in MeCN
(5 mL) was added. The mixture was stirred at room temperature
for 4 h, during which time a fine grey precipitate began to
form. The solution was filtered through Celite and the solvent
removed under reduced pressure to give an off white powder.
Yield: 0.254 g (95%). Anal. Calc. for C46H68F6N2O3PPdSb: C,
51.63; H, 6.40; N, 2.62. Found: C, 51.81; H, 6.27; N, 2.31%. 1H
NMR (CDCl3, 300 MHz): d 1.08 (s, 9H, tBu), 1.23 (s, 18H, tBu),
t
t
3
4
1.24 (s, 9H, Bu), 1.36 (s, 18H, Bu), 2.22 (br s, 6H, NCCH3),
6.73 (dd, 2H, JHH = 9 Hz, JHH = 3 Hz, non-orthometallated
phosphite ring), 6.78 (s, br, 2H, mesityl), 6.87 (s, br, 2H,
mesityl), 6.99 (virtual t, br, 1H, J = 3 Hz, orthometallated
7.07 (d, 1H, 4JHH = 3 Hz, Ar), 7.15 (m, 4H, Ar), 7.38 (br s, 2H,
Ar). 31P{ H} NMR (CDCl3, 121.5 MHz): d 118.9 (s). 13C NMR
1
3
(75 MHz, CDCl3): d 2.74 (NCCH3), 29.79, 30.59, 31.79, 31.97
phosphite ring), 7.12 (dd, 2H, JHH = 9 Hz, J = 2.5 Hz,
t
t
(s, Bu), 35.13, 35.30, 35.38, 35.45 (s, C, Bu), 64.97, 119.42 (d,
non-orthometallated phosphite ring), 7.19 (virtual t, br, 1H,
4JHH = 3 Hz, orthometallated phosphite ring), 7.23 (d, br, 2H,
4JHH = 3 Hz, non-orthometallated phosphite ring). 31P NMR
(121.5 MHz, CDCl3): d 134.4. 13C NMR (75 MHz, CDCl3): d
19.15, 19.65, 20.07 (s, CH3), 28.44, 29.44, 30.39, 30.46 (s, tBu),
JPC = 8 Hz, CH, Ar), 124.36, 124.68, 125.79, 131.62 (d, JPC
=
4 Hz, C, Ar), 133.20, 135.00, 135.27, 139.47 (d, JPC = 7 Hz, C,
Ar), 147.08, 147.58 (d, JPC = 7 Hz, C, Ar), 149.05, 151.12 (d,
JPC = 28 Hz, C, Ar).
t
4
33.36, 33.61, 33.76, 33.80 (s, C, Bu), 51.20 (d, JPC = 7 Hz,
CH2), 118.80 (d, JPC = 9 Hz, CH, Ar), 120.93, 122.03, 122.84,
127.79, 129.09 (s, CH, Ar), 131.94, 132.18, 134.41 (s, C, Ar),
134.91 (s, CH, Ar), 135.24, 136.43, 136.87 (s, C, Ar), 137.73
(d, JPC = 5 Hz, C, Ar), 140.65, 144.60 (s, C, Ar), 147.75 (d,
[Pd{j2-P,C-P(OC6H2-2,4-tBu2)(OC6H3-2,4-tBu2)2}(NCMe)-
{C(CNMesCH2)2}][SbF6], 10, Method A. Complex 8a (0.151 g,
0.113 mmol) was suspended in MeCN (5 mL) and Ag[SbF6]
(0.039 g, 0.113 mmol) in MeCN (5 mL) was added. The mixture
was stirred at room temperature for 4 h, during which time a
fine grey precipitate began to form. The solution was filtered
through Celite and the solvent removed under reduced pressure
2
JPC = 4 Hz, C, Ar), 152.52 (d, JPC = 29 Hz, metallated C of
phosphite), 212.32 (d, 2JPC = 214 Hz, carbene C).
[PdCl{j2 -P,C -P(OC6H2 -2,4-tBu2 )(OC6H3 -2,4-tBu2 )2 }{C-
(CN(C6H3-2,6-iPr2)CH2)2}], 8b. As for complex 8a with 9b
(0.368 g, 0.65 mmol) and complex 7a (0.485 g, 0.31 mmol).
The colourless product was recrystallised from dichloro-
methane–pentane. Yield: 0.386 g (53%). Anal. Calc. for
C69H100ClN2O3PPd: C, 70.33; H, 8.55; N, 2.38. Found: C, 70.10;
to give a white solid. Yield: 0.134 g (89%). H NMR (CDCl3,
1
t
t
300 MHz): d 0.95 (s, 9H, Bu), 1.12 (s, 18H, Bu), 1.14 (s, 9H,
tBu), 1.23 (s, 18H, Bu), 2.09 (s, 6H, CH3), 2.20 (s, 6H, CH3),
t
2.26 (s, 6H, CH3), 3.98 (m, 2H, NCH2), 4.09 (m, 2H, NCH2),
6.62 (br s, 2H, Ar), 6.69 (dd, 2H, 4JHH = 3 Hz, 4JHP = 9 Hz, Ar),
6.84 (dd, 2H, 4JHH = 3 Hz, 4JHP = 9 Hz, Ar), 6.88 (br s, 2H, Ar),
1
4
H, 8.95; N, 2.13%. H NMR (300 MHz, CDCl3): d 0.40 (d,
6.96 (br s, 2H, Ar), 7.05 (br s, 2H, Ar), 7.28 (br d, 2H, JHH
=
3
i
t
1
6H, 2CH3, JHH = 6 Hz, Pr CH3), 0.93 (s, 9H, Bu), 1.11–1.17
3 Hz, Ar). 31P{ H} NMR (CDCl3, 121.5 MHz): d 129.9 (s).
13C NMR (75 MHz, CDCl3): d 2.62 (s, NCMe), 18.74, 20.31,
20.94 (s, CH3), 29.39, 30.15, 30.26, 31.48 (s, tBu), 34.40, 34.63,
i
t
i
(m, br, 48H, Pr CH3 and Bu), 1.34 (m, br, 15H, Pr CH3 and
tBu), 3.48 (m, br, 4H, Pr CH), 4.09 (m, br, 4H, 2CH2), 6.52
i
3
t
(br d, 2H, JHH = 9 Hz, Ar), 6.95 (br s, 1H, Ar) 7.08 (m, 4H,
34.80, 34.88 (s, C, Bu), 52.40 (s, CH2), 119.29 (d, JPC = 5 Hz,
Ar), 7.15 (m, 3H, Ar), 7.30 (m, 4H, Ar). 31P NMR (121.5 MHz,
CH, Ar), 123.08 (s, CH, Ar), 123.65 (s, CH, Ar), 124.19 (s, CH,
Ar), 124.85 (s, CH, Ar), 128.85 (s, CH, Ar), 129.76 (s, CH, Ar),
130.13 (s, CH, Ar), 135.40, 135.42 (s, CH, Ar), 138.50, 139.34,
CDCl3): d 135.0 (s). 13C NMR (75 MHz, CDCl3): d 23.59,
i
t
24.58, 26.53, 27.68 (s, Pr), 30.11, 30.71, 31.97, 32.13 (s, Bu),
t
4
2
35.34, 35.25, 35.01, 34.84, (s, C, Bu), 54.88 (d, JPC = 7 Hz,
CH2), 120.39 (d, JPC = 10 Hz, CH, Ar), 123.00, 124.00, 124.14,
125.29, 125.43, 129.47, 133.18 (s, CH, Ar), 133.94 (d, 17 Hz,
C, Ar), 135.74, 136.78 (s, C, Ar), 138.75 (d, JPC = 4.5 Hz, C,
143.81, 147.15, 147.91, 152.18 (d, JPC = 21 Hz, metallated
2
C of phosphite), 207.88 (d, JPC = 145 Hz, carbene carbon).
Due to decomposition reproducible CHN analysis could not be
obtained.
2 7 7 8
D a l t o n T r a n s . , 2 0 0 5 , 2 7 7 4 – 2 7 7 9

View Article Online
[Pd(NCMe){j2-P,C-P(OC6H2-2,4-tBu2)(OC6H3-2,4-tBu2)2}{C-
(CNMesCH2)2}][SbF6], 10, Method B. A mixture of complex
11 (0.254 g, 0.237 mmol) and 1,3-bis(2,4,6-trimethylphenyl)-2-
(pentafluorophenyl)imidazolidine (0.113 g, 0.237 mmol) were
heated in toluene (15 mL) at 100 ◦C for 3 h. After this time the
solution was slightly cloudy, so it was filtered through Celite and
the solvent removed under reduced pressure to give a white
solid. Yield: 0.273 g (86%). Spectroscopic data as above.
(0.12 mL, 1.0 mmol), morpholine (0.13 mL, 1.5 mmol), K3PO4
(0.636 g, 3.0 mmol) and toluene (5 mL) were added and the
resultant mixture was heated at reflux temperature for 17 h.
The work-up employed was the same as described above for the
Suzuki reactions.
Acknowledgements
We thank the EPSRC (PDRAs for M. B. and M. E. B., Ad-
vanced Research Fellowship for R. B. B.), Kingston Chemicals
(R. M. F.) and the Ministerio de Educacio´n, Cultura y Deporte
(RMLN) for support and Johnson Matthey for the loan of
palladium salts.
Crystallography
Suitable crystals were selected and data collected on a Bruker
Nonius KappaCCD Area Detector at the window of a Bruker
˚
Nonius FR591 rotating anode (kMo-Ka = 0.71073 A) driven by
COLLECT18 and DENZO19 software at 120 K. Structures were
determined in SHELXS-9720 and refined using SHELXL-97.21
References
Crystal data for complex 8a. C67H98ClN2O4PPd, M =
1168.29, monoclinic, space group P21/n, a = 12.9482(13), b =
1 For C–C coupling reactions, see: (a) R. F. Heck, Palladium Reagents
in Organic Synthesis, Academic Press, New York, 1985; (b) J. P.
Collman, L. S. Hegedus, J. R. Norton and R. G. Finke, Principles and
Applications of Organotransition Metal Chemistry, University Science
Books, Mill Valley, CA, 1987; (c) B. M. Trost and T. R. Verhoven,
in Comprehensive Organometallic Chemistry, ed. G. Wilkinson,
F. G. A. Stone and E. W. Abel, Pergamon Press, Oxford, 1982,
vol. 8, pp. 799–938.
2 For recent reviews on the use of aryl chlorides as substrates, see:
(a) A. F. Littke and G. C. Fu, Angew. Chem., Int. Ed., 2002, 41, 4176;
(b) R. B. Bedford, C. S. J. Cazin and D. Holder, Coord. Chem. Rev.,
2004, 248, 2283.
3 For a discussion, see: V. V. Grushin and H. Alper, Chem. Rev., 1994,
94, 1047.
4 S. R. Stauffer, S. Lee, J. P. Stambuli, S. I. Hauck and J. F. Hartwig,
Org. Lett., 2000, 2, 1423.
5 L. R. Titcomb, S. Caddick, F. G. N. Cloke, D. J. Wilson and D.
McKerrecher, Chem. Commun., 2001, 1388.
◦
3
˚
˚
13.284(2), c = 37.944(8) A, b = 96.787(11) , U = 6480.9(18) A ,
T = 120(2) K, Z = 4, l(Mo-Ka) = 0.398 mm−1, 75355 reflections
measured, 14755 unique (Rint = 0.0289) which were used in all
calculations. Final R1 = 0.0296, wR2 = 0.0762 [F2 > 2r(F2)],
R1 = 0.0366, wR2 = 0.0800 (all data).
Crystal data for complex 8b. C69H100ClN2O3PPd, M =
1178.33, tetragonal, space group P41212, a = 21.0783(16), b =
3
˚
˚
21.0783(16), c = 29.741(3) A, U = 13214(2) A , T = 120(2) K,
Z = 8, l(Mo-Ka) = 0.390 mm−1, 91295 reflections measured,
15144 unique (Rint = 0.1204) which were used in all calculations.
Final R1 = 0.0531, wR2 = 0.0683 [F2 > 2r(F2)], R1 = 0.0864,
wR2 = 0.0750 (all data).
Crystal data for complex 8c. C49H62ClN2O4PPd, M =
6 S. Caddick and W. Kofie, Tetrahedron Lett., 2002, 43, 9347.
7 The use of highly donating ligands is not always essential-even
‘ligandless’ palladium systems have been shown to activate deacti-
vated aryl chlorides. See, for instance: R. B. Bedford, M. E. Blake,
C. P. Butts and D. Holder, Chem. Commun., 2003, 466.
8 M. G. Andreu, A. Zapf and M. Beller, Chem. Commun., 2002,
2475.
915.83, orthorhombic, space group Pbca, a = 12.9666(10), b =
3
˚
˚
17.766(2), c = 39.401(3) A, U = 9076.5(14) A , T = 120(2) K,
Z = 8, l(Mo-Ka) = 0.548 mm−1, 32776 reflections measured,
9335 unique (Rint = 0.0620) which were used in all calculations.
Final R1 = 0.0449, wR2 = 0.0898 [F2 > 2r(F2)], R1 = 0.1016,
wR2 = 0.1143 (all data).
9 M. S. Viciu, R. A. Kelly, E. D. Stevens, F. Naud, M. Studer and S. P.
Nolan, Org. Lett., 2003, 5, 1479.
CCDC reference numbers 271192–271194.
See http://dx.doi.org/10.1039/b506286a for crystallographic
data in CIF or other electronic format.
10 (a) R. B. Bedford, C. S. J. Cazin and S. L. Hazelwood, Angew. Chem.,
Int. Ed., 2002, 41, 4120; (b) R. B. Bedford, S. L. Hazelwood and
M. E. Limmert, Chem. Commun., 2002, 2610; (c) R. B. Bedford, S. L.
Hazelwood, M. E. Limmert, D. A. Albisson, S. M. Draper, P. N.
Scully, S. J. Coles and M. B. Hursthouse, Chem. Eur. J., 2003, 9,
3216.
Catalysis
General method for the Suzuki coupling reactions. The
appropriate catalyst (1 mol%) was introduced into the reaction
flask as a dichloromethane solution and then the solvent was
removed in vacuo. The aryl halide (1.0 mmol), Cs2CO3 (0.977 g,
3.0 mmol), PhB(OH)2 (0.183 g, 1.5 mmol) and 1,4-dioxane (5 ml)
were added and the resultant mixture heated at 110 ◦C (external
temperature) for the required time. The reaction mixture was
allowed to cool and then HCl(aq) (2 M, 5 mL) was added,
the mixture was extracted with CH2Cl2 (3 × 40 mL) and the
combined organic fraction was dried (MgSO4). The solvent
was removed on a rotary evaporator and then the residue
was redissolved in CH2Cl2 (5 mL) and hexadecane (0.068 M
in CH2Cl2, 1.00 mL, internal standard) was added and the
conversion to coupled product was determined by GC.
11 A. J. Arduergo, J. R. Goerlich and W. J. Marshall, J. Am. Chem. Soc.,
1995, 117, 11027.
12 G. W. Nyce, S. Csihony, R. M. Waymouth and J. L. Hedrick, Chem.
Eur. J., 2004, 10, 4073.
13 D. A. Albisson, R. B. Bedford, S. E. Lawrence and P. N. Scully, Chem.
Commun., 1998, 2095.
14 For a recent discussion and leading references, see: M. S. Sanford,
J. A. Love and R. H. Grubbs, J. Am. Chem. Soc., 2001, 123, 6543.
15 A. K. de K. Lewis, S. Caddick, F. G. N. Cloke, N. C. Billingham, P. B.
Hitchcock and J. Leonard, J. Am. Chem. Soc., 2003, 125, 10066.
16 Beller and Zapf have shown that non-orthometallated complexes of
triarylphosphites can couple activated aryl chlorides, see: A. Zapf
and M. Beller, Chem. Eur. J., 2000, 6, 1830.
17 A. Albinati, S. Affolter and P. S. Pregosin, Organometallics, 1990, 9,
379.
18 Collect: Data collection software, R. Hooft, Nonius B.V., 1998.
19 Z. Otwinowski and W. Minor, Methods Enzymol., 1997, 276, 307–
326.
20 G. M. Sheldrick, Acta Crystallogr., Sect. A, 1990, 46, 467.
21 G. M. Sheldrick, University of Go¨ttingen, Germany, 1997.
Attempted amination reaction. Complex 8b (11 mg) was
introduced into the reaction flask as a dichloromethane solu-
tion and the solvent was removed in vacuo. 4-Chlorotoluene
D a l t o n T r a n s . , 2 0 0 5 , 2 7 7 4 – 2 7 7 9
2 7 7 9