Planar-chiral imidazole-based phosphine ligands derived from [2.2]paracyclophane

Article abstract of DOI:10.1039/b923716j

Two planar chiral heteroaryl monophosphines have been synthesised and studied. The phosphines are readily prepared from 4-imidazole[2.2]paracyclophane by selective deprotonation and reaction with the appropriate dialkylchlorophosphines. The planar chiral imidazole was constructed in four steps from readily available [2.2]paracyclophane. The 2-phosphino-N-[2.2] paracyclophanes were active in the Suzuki-Miyaura coupling of aryl bromides and chlorides. Coordination studies indicate P,N-chelation in the solid-state. These studies lay the foundations for asymmetric couplings.

Full text of DOI:10.1039/b923716j

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Planar-chiral imidazole-based phosphine ligands derived from
[2.2]paracyclophane†
Richard J. Seacome,a Martyn P. Coles,a Jean E. Glover,b Peter B. Hitchcocka and Gareth J. Rowlands*a,b
Received 11th November 2009, Accepted 8th February 2010
First published as an Advance Article on the web 25th February 2010
DOI: 10.1039/b923716j
Two planar chiral heteroaryl monophosphines have been synthesised and studied. The phosphines are
readily prepared from 4-imidazole[2.2]paracyclophane by selective deprotonation and reaction with the
appropriate dialkylchlorophosphines. The planar chiral imidazole was constructed in four steps from
readily available [2.2]paracyclophane. The 2-phosphino-N-[2.2]paracyclophanes were active in the
Suzuki–Miyaura coupling of aryl bromides and chlorides. Coordination studies indicate P,N-chelation
in the solid-state. These studies lay the foundations for asymmetric couplings.
Building upon chemistry previously developed within our
Introduction
laboratory,10,14,15 we have synthesised a new class of planar-
Bulky, electron-rich phosphines have been successfully used to
chiral imidazole-based phosphine ligands. We present preliminary
results of their behaviour in the Suzuki–Miyaura reaction and the
date, much of the work has concentrated on biaryl monophos-
structural characterisation of a representative Pd(II) compound
stabilise active palladium species for cross-coupling reactions.1 To
phines (e.g. 1; Fig. 1),2 for which it has been postulated that
a secondary interaction with the lower arene ring results in
a pseudo-bidentate coordination of the ligand.3 An alternative
that confirms bidentate coordination at the metal.
Results and discussion
ligand class that promotes high reactivity is the 2-phosphino-N-
aryl imidazoles (e.g. 2).4-7 Structurally characterised examples of
isolated palladium(II) compounds incorporating 2 show unusual
four-membered metallacycles generated through P,N-chelation of
the ligand.5,7,8
Due to the success of Buchwald’s biaryl monophosphines 1,
the initial target was an analogue of JohnPhos (1; R = t-Bu;
R1 = H), in which the lower arene ring has been replaced
by [2.2]paracyclophane (e.g. 7; Z = lone pair; Scheme 1). To
this end, 4-(2-bromophenyl)[2.2]paracyclophane 6a (Y = Br)
was prepared from 4-bromo[2.2]paracyclophane 4 by Roche’s
methodology.16 The low yield was a result of unproductive
consumption of 1,2-dibromobenzene under the reaction con-
ditions. The chloride 6b (X = Cl) was prepared by Suzuki–
Miyaura aryl coupling of [2.2]paracyclophan-4-yl triflate 5 and
2-chlorophenylboronic acid. Unfortunately, it proved impossi-
ble to substitute either halide 6a/b for a phosphine moiety;
conversion to the organolithium species or Grignard reagent
resulted in the recovery of 4-phenyl[2.2]paracyclophane 6c whilst
attempts at palladium-mediated C–P bond formation17 gave
either unreacted starting material or 6c. Aryl coupling of
Fig.
1 Various monophosphine ligands and [2.2]paracyclophane
numbering.
The singular structure of [2.2]paracyclophane (3,
R
=
H) bestows unique electronic and steric properties on its
derivatives, making them excellent scaffolds for a range of
applications.9,10 Many derivatives exhibit planar chirality and
have found use as chiral ligands for enantioselective catalysis.11
Of these chiral compounds, the most successful is 4,12-
bis(diphenylphosphino)[2.2]paracyclophane (PhanePhos), a com-
mercially available diphosphine that is employed in catalytic asym-
metric reductions.12 A number of other mono- and diphosphines
derived from [2.2]paracyclophane have also been reported.13
Scheme 1 Attempted synthesis of phosphine 7. Reagents and conditions:
i. (a) t-BuLi (2.05 eq.), B(OMe)3 (2.5 eq.), THF; (b) Pd(PPh3)4 (0.06 eq.),
1,2-Br2C6H4 (1.3 eq.), K2CO3 (2.7 eq.), tol/H2O, reflux, 13% (6a; Y = Br);
ii. Pd2dba3 (0.03 eq.), SPhos (0.06 eq.), 2-ClC6H4B(OH)2 (2 eq.), K3PO4
(3 eq.), toluene, reflux, 55% (6b; Y = Cl); iii. Failed with combinations
of n-BuLi, t-BuLi, Mg, Bu2iPrMgLi, R2PCl, R2P(O)Cl and Pd(OAc)2,
DiPPF, t-BuOK, HPCy2.
aDepartment of Chemistry, University of Sussex, Falmer, UK BN1 9QJ.
E-mail: m.p.coles@sussex.ac.uk
bInstitute of Fundamental Sciences - Chemistry, Massey University, Private
Bag 11 222, Palmerston North, New Zealand. E-mail: g.j.rowlands@
massey.ac.nz; Fax: +64 6 350 5682; Tel: +64 6 356 9099 extn 3566
† CCDC reference numbers 753893–753896. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b923716j
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(2-bromophenyl)dicyclohexylphosphine oxide with 4 employing
either Roche’s conditions or a Negishi coupling also failed to yield
the desired compound. Whilst the latter couplings failed due to
the steric bulk of [2.2]paracyclophane, the failure of 6a/b in simple
anion chemistry is less understandable.
followed by reaction with chlorophosphines R2PCl (R = t-Bu,
Cy) to afford ( )-11a and ( )-11b in moderate yields. Extensive
attempts to improve the yields by varying temperature, solvent
and co-solvent were unsuccessful. Compounds ( )-11 are air-stable
crystalline solids that can be handled and stored in air but slowly
oxidise in solution. The phosphine oxides ( )-12 were prepared by
oxidation with hydrogen peroxide. Non-racemic monophosphines
((Rp)-11) were prepared from enantiomerically enriched amine
(Rp)-4, formed via either classic resolution20 or by our own
sulfoxide-based methodology.15 Yields were, of course, comparable
to the racemic system. All the subsequent studies were performed
on racemic ( )-11a/b.
Experience within our group indicated that formation of a
planar chiral analogue of 2 would be more achievable.18 Racemic
4-amino[2.2]paracyclophane ( )-9 was prepared in 2 steps from
4-bromo[2.2]paracyclophane ( )-4 (Scheme 2). First, lithium–
halogen exchange followed by reaction with tosyl azide gave
( )-8, which was then reduced with NaBH4 under phase transfer
conditions to give ( )-9. Whilst it is possible to reduce the crude
4-azo[2.2]paracyclophane ( )-8, higher, and more reproducible
yields are obtained when ( )-8 is purified prior to reduction.15
The optimal conditions for the conversion of ( )-9 into imidazole
( )-10 were found to be treatment with paraformaldehyde,
ammonium chloride, glyoxal and catalytic phosphoric acid in
THF/dioxane at reflux.19 All other conditions gave low yields
with polymeric material predominating. It is important to basify
(pH = 8–11) the reaction mixture prior to extraction of ( )-
10 as the protonated imidazole shows surprisingly high water
solubility. Selective functionalisation of the imidazole ring was
achieved by deprotonation with n-butyllithium in THF/TMEDA,
The 1H NMR spectrum of 11a reveals the effect of planar
chirality with the diastereotopic tert-butyl groups exhibiting very
different chemical shifts (0.79 and 1.35 ppm). Both molecules show
characteristic high field resonances for the ortho (H5) hydrogen of
the paracyclophane ring (6.32 ppm for 11a and 6.36 for 11b) and
the syn C1 and C2 hydrogens (2.89–2.84 and 2.77–2.71 ppm for
11a and 2.77–2.72 for 11b). The electronic and steric environment
of the phosphorus appears similar to the achiral phosphines 2;
31P NMR of 11a = 8.74 ppm and 11b = -20.8 ppm compared to
values of 10.2 ppm and -23.3 ppm reported for 2a and 2b (R1 =
iPr) respectively.4 There is an inverse relationship between the
magnitude of the 77Se–31P coupling constant and the s-basicity.21
To ascertain the relative s-basicity of 11a and 11b they were
converted to the corresponding phosphine selenides 13a and 13b
1
on an NMR scale using elemental selenium.‡ The JSeP coupling
constants (13a 730 Hz; 13b 753 Hz) suggest lower s-basicity than
in compounds 2, for which corresponding values of 726 Hz and
732 Hz were reported for 2a and 2b (R1 = iPr), respectively.4
X-Ray diffraction data (Tables 1 and 2) confirm 11a and 11b as
the triorganophosphines, with pyramidal phosphorus atoms and
C–P–C angles in the range 100.34(11)–111.47(13) and 98.63(19)–
103.66(18), respectively (Fig. 2). The bonds to the phosphino
and [2.2]paracyclophane substituents are approximately coplanar
with the imidazole ring [P–C17–N1–C4 torsion angles (a): 11a,
5.22(33)◦; 11b, 0.36(58)◦], with bond lengths consistent with other
2-phosphino-N-substituted imidazoles.5,22 The C2 bridgehead
methylene group prevents the imidazole ring and the substituted
“top” deck of the [2.2]paracyclophane from adopting a coplanar
arrangement [angle between C3N2- and C6-least squares planes (b):
11a, 56.91(8)◦; 11b 45.42(19)◦], preventing effective p-conjugation
between these two units.
The molecular structure of phosphine oxide 12a has also
been determined by X-ray diffraction (Fig. 2). We note that
conversion to the P(V) analogue has negligible effect on the bond
lengths compared with phosphine 11a (Table 2), and the overall
conformation of the molecule remains very similar [a = -1.09(33)◦
and b = 51.80(08)◦, Fig. 3]. This suggests a stable arrangement of
the paracyclophane, imidazole and phosphine substituents in the
solid-state for 11a.
We investigated the potential of ( )-11a and ( )-11b in the palla-
dium mediated coupling of 4-bromotoluene and 4-chlorotoluene
with phenylboronic acid (Table 3). In both cases, the di-tert-butyl
derivative 11a gave better results, with yields of 90% and 53% for
Scheme 2 Synthesis of 2-phosphino-N-[2.2]paracyclophane imidazoles.
Reagents and conditions: i. (a) n-BuLi (1.05 eq.), THF, -78 ◦C; (b)
TsN3 (1.05 eq.), -78 ◦C to rt, 60%; ii. NaBH4 (11 eq.), n-Bu4NI (1 eq.),
THF–H2O, rt, 97%; iii. (CH2O)n (2.5 eq.), NH4Cl (2.5 eq.), C2H2O2
(2.5 eq.), H3PO4 (2 drops), dioxane/H2O, reflux, 63%; iv. (a) n-BuLi
(1.0 eq.), TMEDA (1.05 eq.), THF, -78 ◦C; (b) ClPR2 (1.05 eq.), -78 ◦
C
‡ Reactions performed on an NMR scale and compounds not purified.
Selected analytical data: 13a 31P NMR (202 MHz, CDCl3): d 62.2 (d, J
730). 13b 31P NMR (202 MHz, CDCl3): d 41.9 (d, J 753).
to rt, 49% (R = t-Bu), 44% (R = Cy); v. H2O2 (xs), CDCl3, rt, 89% (R =
t-Bu), 100% (R = Cy); vi. Se, CDCl3, 50 ◦C.
3688 | Dalton Trans., 2010, 39, 3687–3694
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Table 1 Crystal structure and refinement data for 11a, 11b, 12a and 14a
11a
11b
12a
14a
Formula
Formula weight
T/K
C27H35N2P
418.54
173(2)
C31H39N2P
470.61
173(2)
C27H35N2OP, 0.5(C6H12)
476.62
173(2)
C27H35Cl2N2PPd, CH2Cl2
680.77
173(2)
˚
Wavelength/A
0.71073
0.71073
0.71073
0.71073
Crystal size/mm
Crystal system
Space group
0.30 ¥ 0.05 ¥ 0.02
0.20 ¥ 0.05 ¥ 0.02
Monoclinic
P21/c (No. 14)
10.7792(3)
15.7625(8)
15.3052(7)
90
97.193(3)
90
2580.00(19)
4
0.35 ¥ 0.10 ¥ 0.10
0.30 ¥ 0.20 ¥ 0.10
Monoclinic
P21 (No. 4)
7.7953(2)
13.8315(3)
13.0449(3)
90
91.366(2)
90
1406.11(6)
2
Triclinic
Triclinic
¯
¯
P1 (No. 2)
P1 (No. 2)
˚
a/A
8.4500(6)
11.6495(9)
12.9271(8)
109.719(4)
90.305(5)
98.638(3)
1182.17(14)
2
1.18
0.13
3.54 to 25.93
16 283
9.1186(3)
11.6152(3)
13.9871(4)
105.127(1)
105.574(2)
102.542(2)
1310.24(7)
2
1.21
0.13
3.61 to 26.02
18 924
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
3
˚
V/A
Z
Dc/Mg m-3
1.21
0.13
3.48 to 26.00
39 349
1.61
1.12
3.41 to 26.07
16 669
Absorption coefficient/mm-1
q range for data collection/◦
Reflections collected
Independent reflections
Reflections with I > 2s(I)
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2s(I)]
4541 [Rint = 0.091]
5049 [Rint = 0.230]
5112 [Rint = 0.043]
5426 [Rint = 0.044]
3240
2851
4188
5243
4541/0/277
1.039
5049/0/307
1.111
5112/0/313
1.045
5426/3/320
1.045
R1 = 0.060
wR2 = 0.122
R1 = 0.097
wR2 = 0.140
0.21 and -0.28
R1 = 0.095
wR2 = 0.141
R1 = 0.185
wR2 = 0.168
0.31 and -0.34
R1 = 0.054
wR2 = 0.143
R1 = 0.069
wR2 = 0.153
0.87 and -0.69
R1 = 0.038
wR2 = 0.105
R1 = 0.040
wR2 = 0.107
0.99 and -0.83
R indices (all data)
3
˚
Largest diff. peak/hole/e A
Fig. 2 Thermal elliposid (30%) plots of 11a, 11b and 12a (hydrogen atoms omitted).
bromide even in the absence of phosphine ligand. Interestingly,
a lower ratio of palladium to ligand gave better results for the
tert-butylphosphine 11a (entries 5 vs. 6; entries 7 vs. 8) with the
opposite trend noted for the dicyclohexylphosphine 11b (entries 1
vs. 2; entries 3 vs. 4). Coupling of the aryl chloride benefited from
an increased ratio of Pd : 11a/b; the best results were achieved with
either a 1 : 10 ratio of Pd(OAc)2 : 11a (entry 16) although this could
be lowered if an alternative source of Pd was employed (entry 20).
To examine ligand/metal interactions with these phosphines,
the reaction between 11a and PdCl2(COD) was performed. The
product, 14a, was isolated as pale pink crystals, which analysed as
the monophosphine complex [PdCl2(11a)](Fig. 4). Single crystal
X-ray diffraction confirmed P,N-chelation of the ligand,5,7,8 with
a distorted square planar metal [angles in the range 70.68(11)–
99.96(5)◦] in which the bite angle of the ligand forms the smallest
Fig. 3 Overlay of 11a (yellow) and 12a (blue) mapping the imidazole ring
and phosphorus positions.
the bromide and chloride, respectively. The best conditions for the
coupling of 4-bromotoluene employed a 1 : 1 mixture of THF and
water (entry 10), whilst dioxane gave better results for the chloride.
It should be noted that Pd(OAc)2 catalyses the coupling of the
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◦
˚
Table 2 Selected bond lengths (A) and angles ( ) for 11a, 11b and 12a
11a
11b
12a
P–C17
P–C20
P–C24
P–C26
P–O
N1–C17
N2–C17
N1–C4
1.828(2)
1.893(3)
1.883(3)
—
1.828(4)
1.860(4)
—
1.855(4)
—
1.384(5)
1.327(5)
1.439(5)
1.825(2)
1.857(2)
1.859(2)
—
1.4841(15)
1.381(3)
1.323(3)
1.438(3)
—
1.386(3)
1.329(3)
1.435(3)
C17–P–C20
C17–P–C24
C20–P–C24
C17–P–C26
C20–P–C26
O–P–C17
O–P–C20
O–P–C24
C4–N1–C17
C4–N1–C19
C17–N1–C19
C17–N2–C18
100.34(11)
102.69(12)
111.47(13)
—
—
—
—
—
127.5(2)
125.2(2)
106.5(2)
105.7(2)
100.55(19)
—
—
98.63(19)
103.66(18)
—
—
—
127.8(3)
125.1(3)
106.9(3)
105.8(3)
103.49(10)
104.67(10)
114.69(11)
—
Fig. 4 Thermal elliposid (30%) plot of 14a (dichloromethane solvate and
hydrogen atoms omitted).
—
113.85(9)
109.85(10)
110.16(10)
129.53(18)
124.07(18)
106.23(18)
105.7(2)
Conclusions
In conclusion, we have developed a route to planar chiral
imidazole-based phosphine ligands, that chelate to metals with
P,N-coordination. Palladium catalysts derived from these ligands
promote the Suzuki–Miyaura reaction of aryl bromides and
chlorides. Whilst the present results do not match the best
ligands reported, they are promising. Further studies are currently
being undertaken in order to optimise the reaction conditions
for the coupling of more substituted aryl moieties and thus
permit enantiomerically pure variants of 11a/b to be screened in
atroposelective coupling reactions. These results will be published
in due course.
Table 3 Summary of results from Suzuki–Miyaura coupling of 4-
bromotoluene and 4-chlorotoluene employing 11a or 11b as a ligand source
X
Ligand Pd source
% Pd Pd : ligandSolvent
Yielda
1b Br
2b Br
3b Br
4b Br
5b Br
6b Br
7b Br
8b Br
11b
11b
11b
11b
11a
11a
11a
11a
—
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd2(dba)3
Pd2(dba)3
0.01 1 : 2
0.01 1 : 10
1 : 2
1 : 10
0.01 1 : 2
0.01 1 : 10
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
39
63
52
67
58
41
73
59
0.1
0.1
Experimental
General information
0.1
0.1
0.5
0.5
0.5
1.0
0.1
0.1
0.1
0.1
0.5
1.0
1.0
1 : 2
1 : 10
—
1 : 3
1 : 3
—
1 : 2
1 : 10
1 : 2
1 : 10
1 : 3
1 : 2
1 : 2
1 : 4
All reaction glassware was oven dried and reactions performed
under an inert atmosphere of nitrogen or argon where applicable.
Solvents were dried via the following methods: diethyl ether and
THF were heated at reflux over fresh sodium wire in the presence
9c
Br
THF–H2O 51
THF–H2O 74
THF–H2O 90
10c Br
11c Br
12d Cl
13d Cl
14d Cl
15d Cl
16d Cl
17e Cl
18f Cl
19g Cl
20h Cl
11b
11a
—
Toluene
Toluene
Toluene
Toluene
Toluene
2
4
13
33
49
˚
11b
11b
11a
11a
11a
11a
11a
11a
of benzophenone indicator. Toluene was dried over 4 A molecular
sieves or by reflux over calcium chloride. Dioxane was stored over
˚
sodium wire and DMF was stored over 4 A molecular sieves. NMR
THF–H2O 22
solvents were stored over molecular sieves and triethylamine and
N,N,N¢,N¢-tetramethylethylenediamine were freshly distilled over
sodium hydroxide pellets. Solvents were purchased from Fisher
or Acros. Palladium metal catalysts were purchased from Strem
or Sigma-Aldrich. Other reagents were purchased from Avocado,
Acros or Sigma-Aldrich.
Flash chromatography was performed using Fischer Davisil
60 silica gel and t.l.c was carried out using glass backed pre-
coated silica plates (Merck 60 silica). Visualisation techniques
employed included using ultraviolet light (254 nm), potassium
permanganate, dinitropyridine, ethanolic phosphomolybdic acid
or ninhydrin when applicable.
Toluene
Dioxane
Dioxane
10
15
53
PdCl2(PPh3)2 1.0
a Average of 2 runs. b Conditions: K3PO4 (2 eq.), p-TolBr (1.0 eq.),
PhB(OH)2 (1.5 eq.), reflux. c K3PO4 (3 eq.), p-TolBr (1.0 eq.), PhB(OH)2
(1.5 eq.), reflux. d K3PO4 (2 eq.), p-TolCl (1.0 eq.), PhB(OH)2 (1.5 eq.),
reflux. e K3PO4 (3 eq.), p-TolCl (1.0 eq.), PhB(OH)2 (1.5 eq.), reflux.
f K3PO4 (2 eq.), p-TolCl (1.0 eq.), PhB(OH)2 (1.5 eq.), reflux. g K3PO4
(2 eq.), p-TolCl (1.0 eq.), PhB(OH)2 (1.5 eq.), reflux. h K3PO4 (2 eq.), p-
TolCl (1.0 eq.), PhB(OH)2 (1.5 eq.), reflux.
angle. The main conformational difference in the phosphine upon
complexation is a rotation about the P–C17 bond such that the
lone pairs on P and N2 interact with the metal. As a consequence,
t-Bu groups point towards the [2.2]paracyclophane substituent in
14a, effectively crowding one side of the metal coordination sphere.
In addition, the torsion between substituents of the imidazole is
considerably larger [a = -19.84(89)◦] and the interplane angle b
increases to 61.64(15)◦.
Optical rotation was recorded on a Perkin Elmer 241 polarime-
ter using the sodium lamp, emitting at 589 nm. All samples
were measured in chloroform (c = 1) in a 10 cm cell and an
average taken of 10 readings. Average temperature was 27 ◦C. Gas
chromatography was carried out on a Perkin Elmer Autosystem
XL using a Supelco MDN-5S, 30 m ¥ 0.25 mm ¥ 0.25 um
column. The injector temperature was set to 200 ◦C and detector
(flame ionization detector) set to 300 ◦C with a temperature
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◦
ramp of 15 C min-1. Data was recorded via PowerchromTM
16 h. The reaction was cooled to room temperature then poured
into H2O (25 mL) and extracted with Et2O (3 ¥ 25 mL). The com-
bined organic layers were dried (MgSO4) and concentrated. The
residue was purified via flash column chromatography (5 : 1 60/80
petroleum ether : Et2O) and recrystallised from n-heptane/CH2Cl2
to give 4-(2-chlorophenyl)[2.2]paracyclophane as white crystals
(170 mg, 55%); Rf 0.59 (5 : 1 60/80 petroleum ether/Et2O); m.p. =
and transferred into MS excel for processing. Melting points
were recorded on a Gallenkamp melting point apparatus and are
uncorrected.
NMR spectroscopy was carried out on a Bruker 400 MHz,
Bruker 300 MHz, Varian 500 MHz or Varian 400 Mhz. Fre-
quencies used for measurements were 400 MHz and 500 MHz
for proton; 75 MHz and 125 MHz for carbon; 161.7 MHz for
phosphorus. All spectra were run in deuterated chloroform unless
otherwise stated. Chemical shifts are in ppm and referenced to the
NMR solvent. Coupling constants are given in Hz. Multiplicities
are described as follows: s = singlet, d = doublet, t = triplet, q =
quartet, dd = double doublet, ddd = double double doublet, m =
multiplet, br = broad. Infrared spectroscopy was carried out on
a Perkin-Elmer 1600 Fourier Transform spectrometer as either
thin film (DCM) or solid. Mass spectra and exact mass data were
recorded by Dr Ali Abdul-Sada at University of Sussex or by the
EPSRC national mass spectrometry service, Swansea.
◦
139–140 C; IR 3054, 2986, 2932, 1421, 896 cm-1; dH (CDCl3,
300 MHz) 7.68 (1H, d, J 6.6, H6¢), 7.46 (2H, t and d, J 8.1 and
7.8, H3¢, H4¢), 7.30 (1H, t, J 7.2, H5¢), 6.69–6.46 (7H, m, H5,
H7, H8, H12, H13, H15, H16), 3.13–2.89 (6H, m, H1, H2, 2 ¥
H9, 2 ¥ H10), 2.86–2.80 (2H, m, H1, H2); dC (CDCl3, 75 MHz)
140.0 (C), 139.5 (C), 139.1 (C), 137.2 (C), 134.5 (CH), 133.9 (CH),
133.5 (CH), 133.3 (CH), 133.0 (CH), 132.3 (CH), 132.2 (CH),
131.4 (CH), 129.7 (CH), 129.5 (CH), 128.2 (CH), 127.0 (CH),
35.5 (CH2), 35.2 (CH2), 35.2 (CH2), 34.0 (CH2); MS (EI+): m/z
318 [M]+, 208, 213, 181, 178, 104, 78 (Found: [M + Na]+, 341.1074,
C22H19Cl35Na requires [M + Na]+, 341.1067).
4-(2-Bromophenyl)[2.2]paracyclophane 6a
( )-4-Azo[2.2]paracyclophane ( )-8
To
a
solution of ( )-4-bromo[2.2]paracy◦clophane (4.1 g,
n-Butyllithium (2.5 M in hexanes; 17.9 mL, 36.64 mmol, 1.05 eq.)
was added dropwise to ( )-4-bromo[2.2]paracyclophane (10.0 g,
34.9 mmol, 1.0 eq.) in THF (160 mL) at -78 ◦C over 5 min, turning
the solution blood red then yellow. After 1 h at -78 ◦C, p-tosylazide
(7.33 g, 36.64 mmol, 1.05 eq.) in THF (40 mL, 0.92 M) was added
dropwise turning the solution dark purple. The reaction mixture
was then allowed to room temperature over 14 h. The reaction
mixture was poured into sat. NH4Cl(aq) (250 mL) and extracted
with Et2O (2 ¥ 100 mL). The combined organic phase was dried
(MgSO4) and solvent removed. The crude solid was purified via
flash chromatography on silica gel (DCM–hexane gradient) to
isolate the product as pale brown solid (5.22 g, 60%); Rf 0.35
(60/80 petroleum ether); m.p = 84–86 ◦C; IR 2929, 2852 (C–H),
14.4 mmol, 1.0 eq.) in THF (144 mL) at -78 C was added tert-
butyllithium (1.7 M in pentane; 17.3 mL, 29.5 mmol, 2.05 eq.)
dropwise over 5 min to produce a blood red solution. After
5 min B(OMe)3 (4.1 mL, 36.0 mmol, 2.5 eq.) was added. The
resulting yellow solution was warmed to room temperature over
6 h. Pd(PPh3)4 (1.0 g, 0.9 mmol, 6 mol%) and 1,2 dibromobenzene
(2.2 mL, 18.7 mmol, 1.3 eq.) in toluene (100 mL) were added,
followed by potassium carbonate (5.4 g, 38.3 mmol, 2.7 eq.)
and water (3.0 mL). The reaction mixture was heated to reflux
for 5 days. After cooling to room temperature, the reaction
mixture was poured into water (150 mL) and extracted with
Et2O (3 ¥ 100 mL). The combined organic layers were dried
(MgSO4) and concentrated. The crude material was purified by
flash column chromatography (Et2O–hexane gradient) to give
4-(2-bromophenyl)[2.2]paracyclophane as a white solid (0.62 g,
13%); Rf 0.7 (10 : 1 60/80 petroleum ether : Et2O); m.p. = 144–
=
=
2104 (N N N), 1593, 1559 (C–N), 1493, 1410 (C–C alkane), 890,
861, 798, 719, 646 (aromatic C–H) cm-1; dH (CDCl3, 500 MHz)
6.89 (1H, d, J 8.0, HAr), 6.54 (1H, d, J 8.0, HAr), 6.47 (1H, d, J
8.0, HAr), 6.44–6.41 (3H, m, HAr), 5.98 (1H, s, HAr), 3.35 (1H, ddd,
J 15.0, 9.0, 3.0, CHH), 3.38–3.02 (6H, m, CH2), 2.69–2.63 (1H,
m, CHH); dC (CDCl3, 125 MHz) 142.0 (C), 139.8 (C), 139.0 (C),
138.9 (C), 135.6 (CH), 133.7 (CH), 133.0 (CH), 131.6 (CH), 133.1
(CH), 131.2 (C), 129.0 (CH), 128.8 (CH), 124.5 (CH), 35.7 (CH2),
35.4 (CH2), 34.0 (CH2), 31.9 (CH2); MS (EI+): m/z 249 [M]+, 221,
206, 119, 104 (Found: [M]+, 249.1259, C16H15N3 requires [M]+,
249.1260).
◦
146 C; IR 3056, 2987, 2922, 2894, 1422, 1071, 1037, (Ar C–Br)
and 896 cm-1; dH (CDCl3, 300 MHz) 7.72 (1H, d, J 7.0, H6¢), 7.65
(1H, d, J 7.5, H3¢), 7.53 (1H, t, J 7.5, H4¢), 7.24 (1H, t, J 8.0, H5¢),
6.70 (1H, d, J 7.5, H13), 6.65 (1H, d, J 8.0, H8), 6.61 (1H, d, J 8.0,
H7), 6.53 (3H, d, J 7.5, H12, H15, H16), 6.45 (1H, s, H5), 3.18–
3.10 (4H, m, H1, H2, H9, H10), 3.06–3.02 (1H, m, H10), 2.98–2.91
(1H, m, H2), 2.88–2.85 (2H, m, H1, H9); dC (CDCl3, 125 MHz)
140.1 (C), 139.6 (C), 139.5 (C), 139.1 (C), 139.0 (C), 134.6 (CH),
133.6 (CH), 133.0 (CH), 132.3 (CH), 132.2 (CH), 131.4 (C), 129.5
(C), 129.5 (CH), 128.3 (CH), 35.7 (CH2), 35.4 (CH2), 35.3 (CH2),
35.1 (CH2); MS (EI+): m/z 364 [M]+, 257, 208, 179, 104 (Found:
[M]+, 362.0662, C22H19Br79 requires [M]+, 362.0665).
( )-4-Amino[2.2]paracyclophane ( )-9
To a flask charged with tetrabutylammonium iodide (8.83 g,
23.89 mmol, 1.0 eq.) and sodium borohydride (9.89 g, 261.4 mmol,
11.0 eq.) was added 4-( )-azo[2.2]paracyclophane (5.90 g,
23.7 mmol, 1.0 eq.) in THF (158 mL) followed by water (128 mL).
The reaction mixture was left to stir at room temperature for
3 days. A further portion of sodium borohydride was added (5.29 g,
139.83 mmol, 5.85 eq.) and stirred at room temperature for a
further 24 h. After this time, the reaction mixture was poured
into water (250 mL) and extracted with Et2O (3 ¥ 250 mL). The
combined organic phase was dried (MgSO4) and solvent removed
to give a light brown solid (5.17 g, 97%); Rf 0.45 (1 : 1 60/80
4-(2-Chlorophenyl)[2.2]paracyclophane 6b
To a flask charged with tris(dibenzylideneacetone)dipalladium(0)
(24.5 mg, 0.03 mmol, 3 mol%), SPhos (21.9 mg, 0.05 mmol,
6 mol%), boronic acid (278 mg, 1.78 mmol, 2.0 eq.) and tripotas-
sium phosphate (0.57 g, 2.67 mmol, 3 eq.) was added a solution
of [2.2]paracyclophan-4-yl triflate (300 mg, 0.89 mmol, 1.0 eq.)
in toluene (6 mL). The reaction mixture was heated to reflux for
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petroleum ether : Et2O); m.p. = 222–224 ◦C (lit. value 239–241 ◦C);
IR 3388 (NH), 2922, 2852 (C–H alkyl), 1614 (NH), 1498, 1425,
1286, 912, 864, 795, 718 cm-1; dH (CDCl3, 500 MHz) 7.17 (1H,
d, J 7.5, HAr), 6.59 (1H, d, J 8.0, HAr), 6.40 (2H, d, J 8.0, HAr),
6.27 (1H, d, J 7.5, HAr), 6.13 (1H, d, J 7.5, HAr), 5.38 (1H, s, HAr),
3.47 (s, broad, NH2), 3.15–2.96 (6H, m, CH2), 2.86–2.80 (1H, m,
CHH), 2.71–2.65 (1H, m, CHH); dC (CDCl3, 125 MHz): 144.9
(C), 141.0 (C), 138.9 (C), 138.9 (C), 135.2 (CH), 133.4 (CH), 132.4
(CH), 131.4 (CH), 126.8 (CH), 124.5 (C), 122.8 (CH), 122.3 (CH),
35.4 (CH2), 34.9 (CH2), 33.0 (CH2), 32.2 (CH2). In agreement with
literature.20
(Rp)-(–)-4-Imidazole[2.2]paracyclophane (Rp)-10
Carried out as above except employing enantiomerically enriched
(Rp)-4-amino[2.2]paracyclophane as starting material to yield the
product as a light brown powder (391.1 mg, 1.425 mmol, 44.3%);
[a]D = -39.6 (c = 0.2, CHCl3); all data as above.
( )-4-(1-Di-tert-butyl)imidazole[2.2]paracyclophane phosphine
( )-11a
n-Butyllithium (2.5 M in hexanes; 1.45 mL, 2.97 mmol, 1.05 eq)
was added dropwise to ( )-4-imidazole[2.2]paracyclophane
(0.81 g, 2.96 mmol, 1.0 eq.) in THF (15 mL) and TMEDA
(0.47 mL, 3.10 mmol, 1.05 eq.) at -78 ◦C. After 1 h at -78 ◦C,
chloro-di-tert-butylphosphine (0.54 g, 3.00 mmol, 1.01 eq.) in
THF (1.5 mL) was added to the dark red solution and the reaction
mixture allowed warmed to room temperature over 18 h. The
reaction mixture was then poured into water (50 mL) and extracted
with Et2O (3 ¥ 30 mL). The combined organic extracts were dried
(MgSO4) and solvent removed. The residue was purified via flash
chromatography (50 : 50 Et2O/hexanes) to yield the product as
a white powder (0.61 g, 48.8%); Rf 0.70 (1 : 1 60/80 petroleum
ether/Et2O); m.p. = 160–162 ◦C; IR 2932, 2894, 2858, 2214,
1596, 1560, 1497, 1471, 1425, 1178, 1148, 1097 cm-1; dH (CDCl3,
500 MHz) 7.56 (1H, s, H18), 7.49 (1H, s, H19), 6.72 (2H, t, J 7.0,
H15, H16), 6.67 (1H, d, J 8.5, H13), 6.58 (1H, d, J 8.0, H8), 6.54
(1H, d, J 8.0, H7), 6.46 (1H, d, J 8.0, H12), 6.32 (1H, s, H5),
3.14–2.96 (6H, m, CH2), 2.89–2.84 (1H, m, CHH), 2.77–2.71 (1H,
m, CHH), 1.35 (9H, d, J 12.5, tert-butyl), 0.79 (9H, d, J 12.0,
tert-butyl); dC (CDCl3, 125 MHz) 148.6 (C, d, JPC 26), 140.0 (C),
139.9 (CH), 139.4 (CH), 136.8 (C), 136.1 (C), 136.1 (C), 135.7
(CH), 134.2 (CH), 133.5 (CH), 132.3 (CH), 130.2 (CH), 129.8
(CH), 129.3 (CH), 121.9 (C), 35.3 (CH2), 34.9 (CH2), 34.4 (C, d,
(Rp)-(-)-4-Amino[2.2]paracyclophane (Rp)-920
(1S)-(+)-10-Camphor sulfonic acid (5.21 g, 22.41 mmol, 1.0 eq.)
was placed under vacuum then flushed with nitrogen (¥3). To this
was added ( )-4-amino[2.2]paracyclophane (5.0 g, 22.42 mmol,
1.0 eq.) in EtOAc (163 mL) and the reaction mixture stirred at 4 ◦C
for 2 days. The solid formed was filtered off over a high porosity
scinter and placed in a clean round bottomed flask. The solid was
re-dissolved in EtOAc (20 mL) then (1S)-(+)-10-camphor sulfonic
acid (5.21 g, 22.41 mmol, 1.0 eq.) added. The reaction mixture was
stirred at 4 ◦C for a further 2 days. After this time, the solid formed
was filtered off over a high porosity scinter, washed with sodium
hydroxide (0.1M; 200 mL + 150 mL). The collected solid was
re-dissolved in the minimum amount of MeOH–DCM and dried
(MgSO4). The solid (1.11 g) was purified via flash chromatography
(hexane–ethyl acetate, neutralized silica gel) to give a pale orange-
brown solid (767.5 mg, 15.3%); [a]D= -72 (c = 0.078, CHCl3)
(lit. value -83.5);20 all other data as above. The amine was also
prepared as previously reported.15
( )-4-Imidazole[2.2]paracyclophane ( )-10
J
J
PC 18.4), 32.7 (C, d, JPC 17.5), 32.5 (CH2, d, JPC 6.8), 30.7 (CH3, d,
PC 24.8), 29.8 (CH3, d, JPC 13.6); dP (CDCl3, 161.7 MHz) 8.74; MS
( )-4-Amino[2.2]paracyclophane (1.12 g, 5.03 mmol, 1.0 eq.),
paraformaldehyde (388 mg, 12.81 mmol, 2.5 eq.) and NH4Cl
(672 mg, 12.58 mmol, 2.5 eq.) were suspended in dioxane
(20 mL) and water (20 mL). To this was added glyoxal (1.80 mL,
12.58 mmol, 2.5 eq.) and 2 drops of phosphoric acid added. The
reaction mixture heated to reflux for 18 h. After this time the
dark green reaction mixture was cooled to room temperature and
poured into sodium hydroxide (3.0 M; 30 mL). The aqueous phase
was extracted with Et2O (3 ¥ 20 mL), combined, dried (MgSO4)
and solvent removed to give a brown powder. Purification via flash
chromatography (50 : 50 ethyl acetate–hexane, neutralized silica
gel) to yield a light brown powder (870.8 mg, 63.1%); Rf 0.02 (1 : 1
60/80 petroleum ether : Et2O); m.p = 156–158 ◦C; IR 3369 (broad,
(EI+): m/z 418 [M]+, 361, 306, 201, 187 (Found: [M]+, 418.2530,
C27H35N2P requires [M]+, 418.2532).
(Rp)-4-(1-Di-tert-butyl)imidazole[2.2]paracyclophane phosphine
(Rp)-11a
Reaction performed as above except using enantiomerically en-
riched imidazole. All data as above; [a]D = 88.2 (c = 0.9, CHCl3).
( )-4-(1-Dicyclohexyl)imidazole[2.2]paracyclophane phosphine
( )-11b
n-Butyllithium (2.5 M in hexanes; 0.58 mL, 1.19 mmol, 1.0
eq) was added dropwise to ( )-4-imidazole[2.2]paracyclophane
(0.32 g, 1.19 mmol, 1.0 eq.) in THF (6.0 mL) and TMEDA
(0.19 mL, 1.27 mmol, 1.05 eq.) at -78 ◦C. After 1 h at -78 ◦C,
chlorodicyclohexylphosphine (0.29 g, 1.25 mmol, 1.05 eq.) in THF
(1.0 mL) was added to the dark red solution and the reaction
mixture warmed to room temperature over 3 days. The reaction
mixture was then poured into water (25 mL) and extracted with
Et2O (3 ¥ 20 mL). The combined organic extracts were dried
(MgSO4) and solvent removed. The residue was purified via flash
chromatography (Et2O) to yield the product as a white powder
(0.25 g, 44.2%); Rf 0.89 (Et2O); m.p. = 194–196 ◦C; IR 3369, 2927,
2851, 2205, 1596, 1560, 1497, 1447, 1428, 1179, 1146, 1098 cm-1;
=
N), 3116, 3010, 2931, 2855, 2214, 1597, 1500, 1454, 1436, 1423,
907, 839, 822, 731, 663 cm-1; dH (CDCl3, 500 MHz) 7.74 (1H, s,
H17), 7.26 (1H, s, H19), 7.20 (1H, s, H18), 6.66 (1H, d, J 8.0,
HAr), 6.64–6.57 (4H, m, HAr), 6.51 (1H, d, J 8.0, HAr), 6.41 (1H, s,
HAr), 3.23 (1H, t, J 9.0, CHH), 3.15 (3H, s, CH2), 3.04 (1H, t, J
13.5, CHH), 2.94–2.88 (2H, m, CHH), 2.71 (1H, t, J 9.5, CHH);
dC (CDCl3, 125 MHz) 141.9 (CH), 139.4 (CH), 139.3 (C), 136.8
(C), 136.7 (CH), 136.5 (C), 133.4 (CH), 133.0 (CH), 132.9 (C),
132.7 (C), 132.7 (CH), 131.9 (CH), 129.9 (CH), 129.3 (CH), 127.0
(CH), 119.5 (C), 35.3 (CH2), 34.9 (CH2), 34.6 (CH2), 32.5 (CH2);
MS (EI+): m/z 274 [M]+, 169, 143, 104 (Found: [M]+, 274.1465,
C19H18N2 requires [M]+, 274.1465).
3692 | Dalton Trans., 2010, 39, 3687–3694
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dH (CDCl3, 500 MHz) 7.51 (1H, s, H18), 7.46 (1H, s, H19), 6.70
(1H, d, J 8.0, H13), 6.68 (2H, dd, J 8.0, 8.0, H15, H16), 6.59
(1H, d, J 8.0, H8), 6.55 (1H, d, J 8.0, H7), 6.47 (1H, d, J 7.5,
H12), 6.36 (1H, s, H5), 3.19–2.77 (7H, m, CH2), 2.75–2.72 (1H,
m, CHH), 2.55–2.53 (1H, m, P–CH), 1.85 (1H, d, J 12.0, P–CH),
1.75–1.71 (4H, m, Cy), 1.54–1.13 (11H, m, Cy), 1.04–0.94 (2H,
m, Cy), 0.89–0.84 (1H, m, Cy), 0.78–0.70 (1H, m, Cy), 0.38–0.33
(1H, m, Cy); dC (CDCl3, 125 MHz) 147.6 (C, d, J 20.0), 140.4
(CH), 140.0 (CH), 139.3 (C), 135.8 (C), 135.6 (C), 133.4 (CH),
132.4 (CH), 132.3 (CH), 130.7 (CH), 129.7 (C), 128.7 (CH), 122.0
(CH), 35.5 (CH, d, JPC 13), 35.4 (CH2), 35.1 (CH2), 35.0 (CH2),
32.6 (CH, d, JPC 9.2), 32.0 (CH2, d, J 5.6), 30.5 (CH2, d, JPC 5.3),
30.4 (CH2, d, JPC 7.4), 29.3 (CH2, d, JPC 16.0), 28.1 (CH2), 27.0
(CH2), 26.9 (CH2), 26.8 (CH2), 26.6 (CH2), 26.2 (CH2); dP (CDCl3,
161.7 MHz) -20.8; MS (EI+) m/z 469 [M]+, 361, 306, 201, 187
(Found: [M]+, 470.2844, C31H39N2P requires [M]+, 470.2845).
6.54 (1H, d, J 8.0, H7), 6.44 (1H, d, J 8.0, H12), 6.37 (1H, s, H5),
3.15–2.92 (6H, m, CH2), 2.90–2.85 (1H, m, CHH), 2.82–2.76 (1H,
m, CHH), 2.45–2.36 (1H, m, CH), 1.94–1.84 (3H, m, Cy), 1.71–
1.26 (13H, m, Cy), 1.02–0.87 (4H, m, Cy), 0.51–49 (1H, m, Cy);
dC (CDCl3, 125 MHz) 140.3 (C, d, JPC 116.1), 140.1 (CH), 139.4
(CH), 139.3 (C), 138.0 (C), 135.4 (CH), 134.8 (C), 134.6 (CH),
133.6 (CH), 132.5 (CH), 132.0 (CH), 130.1 (C, d, JPC 14.1), 129.4
(CH), 128.2 (CH), 124.0 (C, d, J 1.8), 42.6 (Cy), 38.2 (Cy), 37.6
(Cy), 36.0 (Cy), 35.4 (Cy), 35.3 (CH2), 35.2 (CH2), 34.9 (CH2),
32.0 (CH2), 29.7 (Cy), 26.3 (Cy, d, J 3.5), 26.2 (Cy, t, J 4.0), 26.1
(Cy, d, J 3.7), 25.9 (Cy), 25.7 (Cy), 25.2 (Cy, d, J 2.4), 24.6 (Cy,
d, J 3.4), 24.3 (Cy, d, J 2.2); dP (CDCl3, 161.7 MHz) 42.6; MS
(EI+) m/z 487.5 [M]+, 275.3 (Found: [M]+, 487.2875, C31H39N2PO
requires [M]+, 487.2873).
( )-4-Imidazolyl(17-di-tert-butylphosphino-P-N2-
palladium(0)dichloride)-N1-[2.2]paracyclophane phosphine
( )-14a
(Rp)-4-(1-Dicyclohexyl)imidazole[2.2]paracyclophane phosphine
(Rp)-11b
( )-4-N-Imidazolyl(17-di-tert-butylphosphine)[2.2]paracyclophane
(50 mg, 0.119 mmol, 1.0 eq.) was dissolved in DCM (1.0 mL)
and added to dichloro(1,5-cyclooctadiene)palladium(II) (34.0 mg,
0.119 mmol, 1.0 eq.), Et2O added (0.5 mL) and the reaction
mixture evaporated slowly to form orange crystals. dH (CD2Cl2,
500 MHz) 7.78 (1H, s, H18), 7.67 (1H, s, H19), 6.80 (1H, d, J
5.0, H13), 6.74 (2H, t, J 7.5, H7, H8), 6.69 (2H, d, J 10.0, H16),
6.66 (1H, d, J 8.3, H15), 6.55 (2H, br s, H5, H12), 3.20–2.98 (7H,
m, CH2), 2.63–2.56 (1H, m, H2), 1.50 (9H, d, J 20.0, t-Bu), 1.06
(9H, d, J 15.0, t-Bu); dC (CD2Cl2, 125.7 MHz) 148.8 (C, d, JPC
26.3), 143.4 (C), 140.6 (C), 139.5 (C), 137.5 (CH), 137.1 (CH),
136.4 (C), 134.2 (CH), 133.3 (CH), 132.7 (CH), 130.4 (CH), 130.4
(CH), 129.2 (C, d, JPC 7.5), 124.8 (CH), 117.7 (C), 38.9 (C, t, J
10.6), 35.9 (CH2), 35.5 (CH2), 35.1 (CH2), 32.7 (CH2), 31.6 (C),
30.0 (CH3, d, J 5.0), 29.4 (CH3, d, J 3.8); dP (CD2Cl2, 161.7 MHz)
41.7; Elemental analysis calcd. (%) for C27H35Cl2N2PPd: C 54.42,
H 5.92, N 4.70; found: C 54.39, H 5.88, N 4.67.
Experiment performed as above. All data as above; [a]D = 70.4
(c = 1, CHCl3).
( )-4-(1-Di-tert-butyl)imidazole[2.2]paracyclophane phosphine
oxide ( )-12a
Hydrogen peroxide (0.015 mL, excess, 37% in water) was added
to ( )-4-(1-di-tert-butyl)imidazole[2.2]paracyclophane phosphine
(10.0 mg, 0.02 mmol, 1.0 eq.) in CDCl3 (1.0 mL) and shaken at
room temperature for 10 min. DCM (5 mL) was added and the
organic phase dried (MgSO4), the solvent was then removed to
give a white solid (9.3 mg, 0.021 mmol, 89.0%); m.p. 220–222 ◦C;
IR 3252, 2928, 2855, 2325, 1597, 1563, 1474, 1428, 1365, 1299,
1170, 1120, 1081 cm-1; dH (CDCl3, 500 MHz) 7.60 (1H, t, J 1.5,
H18), 7.43 (1H, t, J 1.5, H19), 6.73 (1H, dd, J 10.5, 1.5, H13),
6.67 (2H, br d, J 10.5, H15, H16), 6.55 (1H, d, J 10.0, H8), 6.52
(1H, dd, J 10.0, 2.5, H7), 6.42 (1H, dd, J 10.5, 2.5, H12), 6.32 (1H,
d, J 2.0, H5), 3.15–2.97 (6H, m, CH2), 2.90–2.82 (1H, m, CHH),
2.76–2.69 (1H, m, CHH), 1.42 (9H, d, J 18.0, t-Bu), 0.89 (9H,
d, J 18.0, t-Bu); dC (CDCl3, 125 MHz) 140.2 (C, d, JPC 125.0),
140.1 (CH), 139.4 (CH), 138.9 (C), 138.0 (C), 135.4 (C), 135.1
(CH), 134.5 (CH), 133.6 (CH), 132.4 (CH), 132.0 (CH), 129.6 (C,
d, JPC 17.1), 129.4 (CH), 128.4 (CH), 123.8 (C, d, JPC 2.5), 37.8
(C, d, JPC 28.1), 37.2 (C, d, JPC 27.3), 35.3 (2 ¥ CH2), 34.8 (CH2),
31.8 (CH2), 27.0 (CH3), 26.2 (CH3); dP (CDCl3, 161.7 MHz) 51.7;
MS EI+) m/z 435.5 [M]+ (Found: [M]+, 435.2560, C27H35N2PO
requires [M]+, 435.2560).
X-Ray diffraction data
Crystals were covered in oil and suitable single crystals were
selected under a microscope and mounted on a Kappa CCD
diffractometer. The structures were refined with SHELXL-97.23
Details of the crystal data, intensity collection and refinement are
listed in Table 1. Selected bond lengths are presented in Table 2
(11a, 11b and 12a) and Table 4 (14a). Additional features of note
are listed below:
◦
˚
Table 4 Selected bond lengths (A) and angles ( ) for 14a
( )-4-(1-Dicyclohexyl)imidazole[2.2]paracyclophane phosphine
oxide ( )-12b
Pd1–N2
P–C17
P–C24
2.028(4)
1.824(5)
1.855(5)
1.342(6)
Pd1–P
2.2671(11)
1.856(4)
1.356(6)
1.447(6)
P–C20
N1–C17
N1–C4
Hydrogen peroxide (0.5 mL, excess, 37% in water) was added
to ( )-4-(1-dicyclohexyl)imidazole[2.2]paracyclophane phosphine
(16.0 mg, 0.03 mmol, 1.0 eq.) in CDCl3 (1.6 mL) and shaken at
room temperature for 10 min. DCM (5 mL) was added and the
organic phase dried (MgSO4). The solvent was then removed to
give an oily pale yellow solid (25.2 mg, 100%); IR 2924, 2852, 1596,
1498, 1448, 1427, 1298, 1213, 1174, 1144, 1080 cm-1; dH (CDCl3,
500 MHz) 7.59 (1H, s, H18), 7.45 (1H, s, H19), 6.72 (1H, d, J
7.5, H13), 6.68 (2H, d, J 7.5, H15, H16), 6.57 (1H, d, J 7.5, H8),
N2–C17
P–Pd1–N2
70.68(11)
95.64(11)
81.86(14)
114.87(15)
111.7(2)
127.0(4)
106.8(4)
144.8(3)
P–Pd1–Cl1
99.96(5)
93.79(5)
117.10(15)
107.8(2)
117.4(2)
126.2(4)
104.7(3)
108.9(4)
N2–Pd1–Cl2
C17–P–Pd1
C24–P–Pd1
C17–P–C24
C4–N1–C17
C17–N1–C19
C18–N2–Pd1
Cl1–Pd1–Cl2
C20–P–Pd1
C17–P–C20
C20–P–C24
C4–N1–C19
C17–N2–Pd1
C17–N2–C18
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14a. The dichloromethane solvate was restrained to have C–Cl
distances initially set at 1.75 A; the carbon atom was left isotropic.
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3694 | Dalton Trans., 2010, 39, 3687–3694
This journal is
The Royal Society of Chemistry 2010
©