Synthesis and characterisation of novel o-xylene-based P,E ligands

Article abstract of DOI:10.1039/c3ob42244e

A range of novel hybrid ligands of the type, o-C₆H ₄(CH₂PBu^t₂)(CH₂E) (E = P(C₆F₅)₂, SBu^t, SPh, S(O)Bu ^t, NR₂, SiPh₂H), have been synthesised in two or three steps from the common substrate, o-C₆H₄{CH ₂PBu^t₂(BH₃)}(CH₂Cl). The initial step involved treatment of the substrate with the appropriate nucleophilic reagent, or preparation of a Grignard reagent from o-C ₆H₄{CH₂PBu^t₂(BH ₃)}(CH₂Cl) and reaction with the appropriate electrophile. In most cases, this versatile strategy produced air-stable crystalline ligand precursors. Phosphine deprotection was achieved via one of three methods, dependent upon the properties of the second functional group. An alternative synthesis of the known ligand, o-C₆H₄(CH ₂PBu^t₂)(CH₂PPh₂), is also presented.

Full text of DOI:10.1039/c3ob42244e

Organic &
Biomolecular Chemistry
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PAPER
Synthesis and characterisation of novel o-xylene-
based P,E ligands†
Cite this: Org. Biomol. Chem., 2014,
12, 956
Kathryn M. Allan and John L. Spencer*
A range of novel hybrid ligands of the type, o-C6H4(CH2PBut2)(CH2E) (E = P(C6F5)2, SBut, SPh, S(O)But,
NR2, SiPh2H), have been synthesised in two or three steps from the common substrate,
o-C6H4{CH2PBut2(BH3)}(CH2Cl). The initial step involved treatment of the substrate with the appropriate
nucleophilic reagent, or preparation of a Grignard reagent from o-C6H4{CH2PBut2(BH3)}(CH2Cl) and reac-
tion with the appropriate electrophile. In most cases, this versatile strategy produced air-stable crystalline
ligand precursors. Phosphine deprotection was achieved via one of three methods, dependent upon
the properties of the second functional group. An alternative synthesis of the known ligand,
o-C6H4(CH2PBut2)(CH2PPh2), is also presented.
Received 12th November 2013,
Accepted 11th December 2013
DOI: 10.1039/c3ob42244e
www.rsc.org/obc
known examples of heterobidentate P,E ligands containing
o-xylene backbones.
Introduction
Phosphine ligands are ubiquitous in the field of homogeneous
We recently reported the synthesis of a potentially versatile
catalysis, and there are many examples of phosphine ligands new substrate for the production of unsymmetrical dipho-
as integral components of industrial catalysts. One example of sphine ligands, o-C6H4{CH2PBut2(BH3)}(CH2Cl) (1).21 In this
this is the chelating diphosphine ligand o-C6H4(CH2PBut2)2 paper we use compound 1 to present an alternative methodo-
(dbpx), which was instrumental in the development of a palla- logy for the production of unsymmetrical diphosphine
dium catalyst for the methoxycarbonylation of ethene on a ligands, and also for the synthesis of a number of novel com-
multi-tonne scale.1–3 As a result of this commercial success, a pounds for use as phosphine–thioether, phosphine–sulfoxide,
lot of interest has been generated in diphosphine ligands con- phosphine–amine and phosphine–silane hybrid ligands.
taining o-xylene backbones. A number of patents have sub-
Unlike the currently used methodology,13 which depends
sequently been granted for catalytic processes that utilise upon two sequential nucleophilic substitution steps, com-
dbpx,4–8 and the use of phosphine substituents other than pound 1 does not require the availability of a second nucleo-
t-butyl groups has also been investigated.9–12 There are also phile to produce unsymmetrical ligands. The reactivity of the
recent examples of unsymmetrical diphosphine ligands of this benzyl chloride moiety in 1 can be reversed by conversion to a
type, where the substituents on each phosphorus atom are Grignard reagent, which can then be reacted with electrophilic
different.13–18
reagents to synthesise compounds that would otherwise be
inaccessible. In most cases, the route from compound 1 also
has the benefit of providing air-stable, crystalline ligand pre-
cursors, which can be easily stored for many months without
decomposition.
Another area of active investigation is that of hybrid P,E
ligands,19,20 due to the ability of these ligands to produce
different chemical environments trans to the donor atoms
in metal complexes, and their potential for hemilability.
However, to the best of our knowledge, there are currently no
Results and discussion
P,P compounds
The known ligand o-C6H4(CH2PBut2)(CH2PPh2) (3) has been
synthesised from 1 in two steps (Scheme 1). Compound 1 was
treated with lithium diphenylphosphide–borane and the
product (2) crystallised in 57% yield. Borane protection of
both phosphines renders this material completely air-stable
and allows compound 2 to be stored under ambient conditions
for long periods of time. The 31P{1H} NMR spectrum of this
School of Chemical and Physical Sciences, Victoria University of Wellington,
Wellington, New Zealand. E-mail: john.spencer@vuw.ac.nz; Fax: +64 4 463 5241;
Tel: +64 4 463 5119
†Electronic supplementary information (ESI) available: 1H and 13C NMR spectra
of all compounds. See DOI: 10.1039/c3ob42244e
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Scheme 1 Reagents and conditions: (i) LiPPh2(BH3), THF, −78 °C → rt, overnight, 57% yield; (ii) morpholine, 100 °C, 1 h, 82% yield.
deprotection, nucleophilic aromatic substitution occurred at
the para position of each pentafluorophenyl group, producing
a clean sample of novel compound 6 (Scheme 3). This type
of nucleophilic aromatic substitution has previously been
shown to occur between pentafluorophenyl substituents of
various compounds and morpholine;24–26 however, this is the
first example of nucleophilic aromatic substitution at the para
position of a pentafluorophenylphosphine by a secondary
amine.
Scheme 2 Reagents and conditions: (i) Mg powder, (C6F5)2PBr, THF,
0 °C → rt, overnight, 32% yield.
compound displays broad peaks (due to boron coupling)
centred at 47.7 and 18.5 ppm, indicative of benzyldi-t-butyl-
phosphine–borane and benzyldiphenylphosphine–borane moi-
eties respectively.22
P,S compounds
For a long time, sulfur compounds were not considered viable
Compound 2 was easily deprotected by heating to 100 °C ligands for use in homogeneous catalysis, as they were widely
for one hour in excess morpholine, to give ligand 3 after work believed to poison catalysts.27,28 More recently they have
up in good yield and high purity. Complete disappearance of become the focus of research in catalysis29 and other areas,30
the broad peaks in the 31P{1H} NMR spectrum, and appear- nevertheless they remain relatively unexplored compared with
ance of sharp doublets (5JPP = 1.4 Hz) at 24.5 and −15.6 ppm other donor atom types.31
for the deprotected PBut2 and PPh2 groups respectively, is in
The synthesis of phosphine–thioether compounds with an
o-xylene backbone is quite straightforward. Compound 1 was
agreement with the published NMR data for compound 3.15
In some instances, the above synthetic route is not viable as treated with an excess of the appropriate sodium thiolate pre-
the appropriate nucleophilic reagent to produce the desired cursor to produce compounds containing either an electron-
compound is unavailable. For example, the bis(pentafluoro- rich (7a) or electron-poor (7b) thioether moiety in good yield
phenyl)phosphide anion is unstable even at low tempera- (Scheme 4). 11B{1H} NMR spectra of these compounds was col-
tures.23 In order to synthesise a molecule containing a bis- lected, displaying peaks with doublet coupling (1JPB ≈ 48 Hz)
(pentafluorophenyl)phosphine group (i.e. compound 4), the centred at −40.4 and −40.7 ppm for compounds 7a and 7b
ortho-substituted benzyl chloride compound 1 was treated with respectively.
magnesium powder in THF to generate an ortho-substituted
Synthesis of the equivalent phosphine–sulfoxide com-
benzyl Grignard reagent. This solution was then combined pounds is more difficult, as standard peroxide-based oxidising
with (C6F5)2PBr to produce the borane-protected unsymmetric agents are known to deprotect and oxidise trialkylphosphine–
diphosphine compound 4 (Scheme 2). The 31P{1H} NMR spec- boranes,32,33 and nucleophilic sulfoxide reagents are not avail-
trum of this compound displays the characteristic broad di-t- able. However, a PCC derivative, 3-carboxypyridinium chloro-
butylphosphine–borane peak at 49.4 ppm, and a bis(penta- chromate (CPCC), is known to selectively oxidise thioethers to
fluorophenyl)phosphine quintet at −50.5 ppm. Deprotection sulfoxides in the presence of functional groups.34 In this case,
of compound 4 was achieved by treatment with tetrafluoro- CPCC oxidised compound 7a to the racemic borane-protected
boric acid (Scheme 3), giving novel ligand 5 in moderate yield. phosphine–sulfoxide 8 in a 58% yield (Scheme 5). As the
Again, the presence of a sharp doublet and quintet of doublets sulfur atom in compound 8 is a chiral centre, the methylene
(at 25.2 and −50.9 ppm respectively) in the 31P{1H} NMR protons and phosphine t-butyl groups are rendered diastereo-
1
spectrum of compound 5 confirmed complete removal of the topic, which is reflected in the doubling of H and 13C NMR
borane protecting group.
signals for these atoms when compared with the precursor.
Deprotection of compound 4 was also attempted with
Again, these phosphine–borane compounds were easily
excess morpholine. Interestingly, along with the desired deprotected by heating to 100 °C for one hour in excess
Scheme 3 Reagents and conditions: (i) HBF4·Et2O, CH2Cl2, rt, 1 h, NaHCO3, H2O, rt, 30 min, 51% yield; (ii) morpholine, 100 °C, 1 h, 86% yield.
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reagent contained bulkier ethyl substituents (Scheme 7). The
1H NMR spectra of these compounds display very broad peaks
centred around 2.2 and 1.2 ppm, for the amine–borane and
phosphine–borane protons respectively. The 11B{1H} NMR
spectra of these compounds also display two peaks, a singlet
for the amine–borane and the expected doublet for the phos-
phine–borane.
Scheme 4 Reagents and conditions: (i) NaSR, EtOH, rt, overnight,
75–80% yield.
These phosphine–amine compounds also require
a
different deprotection strategy, as morpholine does not
efficiently deprotect the amine–borane moiety. An effective
deprotection strategy for compounds 11a–c involves treatment
with tetrafluoroboric acid, followed by sodium hydrogen car-
bonate, to give novel ligands 12a–c in moderate to good yield
with high purity (Scheme 7). Deprotection of both the phos-
phorus and nitrogen atoms was established by the complete
absence of any broad peaks associated with BH3 protons in the
1H NMR spectra of the ligands.
Scheme 5 Reagents and conditions: (i) CPCC, AlCl3, MeCN, reflux, 2 h,
58% yield.
P,Si compounds
Over recent decades, silyl ligands have attracted interest as
they are considered to have a great impact on the various para-
meters of transition metal complexes, which may lead to inter-
esting and beneficial reactivity patterns.39 However, metal–
silicon bonds are highly reactive. One method of reducing this
unwanted reactivity is to employ the chelate effect, for example
through the use of P,Si chelating ligands.
In general, secondary silyl anions are unstable. The only
known examples are LiSiMes2H and LiSiPh2H (produced in
low yield).40 For this reason, a better route to phosphine–
silane compounds such as 14 is via an in situ benzyl Grignard
reagent. Compound 1 was combined with excess magnesium
turnings and chlorodiphenylsilane in THF under anhydrous
Scheme 6 Reagents and conditions: (i) Morpholine, 100 °C,
69–92% yield.
1 h,
morpholine, producing novel ligands 9a, 9b and 10 with high
purity and moderate to good yield (Scheme 6). The complete
deprotection of these compounds was again established by the
appearance of sharp singlet peaks in the 31P{1H} NMR spectra
between 25.0 and 25.9 ppm.
P,N compounds
Both phosphorus and nitrogen donor atoms are widely used in conditions and stirred at room temperature overnight, to give
coordination chemistry. The combination of the two to form the borane-protected phosphine–silane compound 13, as
hybrid P,N ligands has recently attracted a great deal of interest shown in Scheme 8. The 31P{1H} NMR spectrum of compound
in the field, due to their interesting coordination behav- 13 displayed the expected broad peak centred at 48.6 ppm, and
iour35,36 and catalytic applications.35,37
the existence of a triplet peak at 5.10 ppm with silicon satel-
1
As the addition of a lithium amide reagent to compound 1 lites (1JSiH = 197.3 Hz) in the H NMR spectrum confirmed the
would result in deprotection of the phosphine–borane, it is presence of the Si–H bond.
necessary to borane-protect the amine prior to reaction with
Removal of the borane protecting group from compound 13
compound 1. Lithium N,N-dialkylaminoborohydride (LAB) was attempted with morpholine but resulted in a mixture of
reagents are well-known reducing agents when utilised at products, and as Si–H bonds are known to undergo acid hydro-
room temperature or above; however, at or below 0 °C, LAB lysis,41 an alternative deprotection method was required. To
reagents can react with benzyl halides to produce tertiary this end, compound 13 and DABCO were dissolved in toluene
amine–boranes.38 Using this methodology, compounds 11a–c and heated to 60 °C overnight (Scheme 8). This procedure gave
were synthesised in yields of over 80%, even when the LAB ligand 14 in 69% yield with high purity. Again, the presence of
Scheme 7 Reagents and conditions: (i) LiNR2(BH3), THF, −5 °C, 1 h, 80–89% yield; (ii) HBF4·Et2O, CH2Cl2, rt, 1 h, NaHCO3, H2O, rt, 30 min, 60–85%
yield.
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Scheme 8 Reagents and conditions: (i) Mg turnings, I2, Ph2SiHCl, THF, rt, overnight, 34% yield; (ii) DABCO, toluene, 60 °C, overnight, 69% yield.
with the CH2E protons are also dependent upon the identity of
E, varying from 2.93 ppm in compound 13 to 4.61 ppm in
compound 8. The 31P{1H} NMR signals associated with these
phosphine–borane compounds do not show the expected
1 : 1 : 1 : 1 quartet due to 11B coupling, but rather broad multi-
plet coupling. The peak shape changes with temperature,
suggesting a dynamic process may exist, but this phenomenon
has not been further investigated.
Table 1 Overall yields of P,E ligands from compound 1
Ligand
E
Yield (%)
3
5
PPh2
P(C6F5)2
47
16
27
74
52
38
68
53
58
23
6
P{(C6F4)N(CH2CH2)2O}2
9a
9b
10
12a
12b
12c
14
SBut
SPh
S(O)But
NMe2
N(CH2)4
NEt2
A number of dissimilarities in the 1H and 31P NMR data are
observed upon removal of the borane protecting groups to give
the o-C6H4(CH2PBut2)(CH2E) (P,E) ligands (Table 3). The great-
est difference is seen in the 31P NMR spectra, where the broad
signals of the formerly PBut2(BH3) moieties (ca. 49 ppm) are
replaced by sharp singlets at ca. 25 ppm, corresponding to the
free di-t-butylphosphine groups. Deprotection of the phos-
SiPh2H
1
a triplet peak at 5.22 ppm in the H NMR spectrum, also with
silicon satellites, confirmed the Si–H bond remained intact.
The overall yields of all P,E ligands synthesised in two or
three steps from compound 1 are shown in Table 1.
2
phine also has a significant effect on the JPH coupling con-
stant of the signal associated with the CH2P protons. These
coupling constants are reduced from ca. 12 Hz in the phos-
phine–borane compounds, to <3 Hz in the free phosphines. In
fact, in many cases no 2JPH coupling is observed. However, in a
NMR comparison
Common 1H and 31P NMR data for the novel
o-C6H4{CH2PBut2(BH3)}(CH2E) compounds is shown in
Table 2. The signals corresponding to the PBut2(BH3) moieties
show little variation, for example the broad 31P NMR signals
range from 47.7 ppm (E = PPh2(BH3)) to 49.8 ppm (E =
NMe2(BH3), NEt2(BH3)), and the t-butyl 1H NMR signals vary
by only 0.20 ppm over the nine compounds. The shifts associ-
ated with the CH2P groups are somewhat more influenced by
the identity of substituent E, from δH 2.69 in compound 13
5
number of the deprotected P,E ligands a long-range JPH coup-
ling of up to 3.5 Hz is seen between the CH2E protons and the
di-t-butylphosphine. This feature is not present in the 1H NMR
spectra of any of the borane-protected compounds.
Conclusions
(E = SiPh2H) to δH 4.07 in compound 8 (E = S(O)But). The AB In summary, a number of novel diphosphine, phosphine–
system associated with the CH2P protons of compound 8 is thioether, phosphine–sulfoxide, phosphine–amine and phos-
2
also the outlier in terms of the JPH coupling constants, with phine–silane hybrid ligands containing an o-xylene backbone
values of 9.0 and 15.0 Hz, as compared to J ≈ 12.0 Hz for all were synthesised in two or three steps from the common sub-
the other borane-protected P,E compounds. As would be strate 1. This versatile substrate was treated with a nucleophilic
expected, the 1H NMR chemical shifts of the signals associated reagent or, where the appropriate nucleophile was unavailable,
Table 2 Selected 31P and 1H NMR shifts (in ppm) and couplings (in Hz) of borane-protected P,E compounds in benzene-d6
PBut
CH2P
CH2E
δH
a
Compound
E
δP
δH
3JPH
δH
2JPH
2b
4
PPh2(BH3)
P(C6F5)2
SBut
47.7
49.4
47.9
48.0
48.0
49.8
49.6
49.8
48.6
1.23
1.09
1.12
1.05
1.06 & 1.19
1.08
1.13
1.12
1.03
12.3
12.2
12.5
12.0
12.5 & 12.5
12.0
12.5
12.5
12.2
3.11
3.29
3.27
3.20
3.04 & 4.07
3.55
3.69
3.82
2.69
11.8
11.9
12.0
12.0
15.0 & 9.0
12.0
12.0
12.0
12.0
3.93
4.23
3.99
4.40
3.63 & 4.61
3.98
4.10
4.02
2.93
7a
7b
8
11a
11b
11c
13
SPh
S(O)But
NMe2(BH3)
N(CH2)4(BH3)
NEt2(BH3)
SiPh2H
a Broad multiplet coupling. b Spectra recorded in chloroform-d.
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Table 3 Selected 31P and 1H NMR shifts (in ppm) and couplings (in Hz) of P,E ligands in benzene-d6
PBut
CH2P
CH2E
Ligand
E
δP
δH
3JPH
δH
2JPH
δH
5JPH
3
5
6
9a
9b
10
12a
12b
12c
14
PPh2
P(C6F5)2
24.5
25.2
25.4
25.0
25.9
25.2
24.5
24.6
23.8
25.2
1.09
1.07
1.12
1.13
1.07
1.06 & 1.14
1.13
1.14
1.14
10.5
10.8
10.7
10.6
10.8
10.9 & 10.8
10.7
10.5
10.8
3.09
3.07
3.20
3.09
3.06
2.99 & 3.37
3.16
3.16
3.12
—
—
—
1.2
—
2.0 & –
2.4
2.7
2.7
1.5
3.92
4.27
4.53
4.05
4.51
3.85 & 4.25
3.60
3.82
3.69
—
—
—
—
2.2
1.4 & 3.5
—
—
—
P{(C6F4)N(CH2CH2)2O}2
SBut
SPh
S(O)But
NMe2
N(CH2)4
NEt2
SiPh2H
1.05
10.5
2.65
3.10
1.5
converted to a Grignard reagent and reacted with an electro- referenced to H3PO4, CFCl3 and BF3·Et2O respectively. 13C,
phile. In most cases, the borane-protected ligand precursors 31P, 19F and 11B NMR spectra were measured with 1H-de-
formed from this procedure were crystalline and air-stable. coupling. J values are given in Hz. Electrospray ionisation mass
Deprotection of the phosphine moiety was achieved by treat- spectrometry was recorded using an Agilent 6530 Q-TOF mass
ment with morpholine, tetrafluoroboric acid or DABCO, spectrometer or performed by the Carbohydrate Chemistry
dependent upon the properties of the second functional Group at Industrial Research Limited, Lower Hutt, using a
group, producing a range of novel P,E ligands in moderate to Waters Q-TOF Premier Tandem mass spectrometer.
good yield.
α-(Di-t-butylphosphino)-α′-(diphenylphosphino)-o-xylene–
diborane (2)
A solution of freshly prepared diphenylphosphine–borane
(0.136 g, 0.68 mmol) in THF (5 mL) was cooled to 0 °C and a
solution of n-butyllithium (0.35 mL, 2.0 M in cyclohexane,
Experimental
General methods
All reactions were carried out using degassed solvents and 0.70 mmol) was added dropwise with stirring. The mixture was
standard Schlenk techniques under a nitrogen or argon atmos- stirred at room temperature for 2 h, cooled to −78 °C and a
phere unless stated otherwise. Starting materials were solution of compound 1 (0.180 g, 0.60 mmol) in THF (4 mL)
obtained from Sigma-Aldrich or Merck Chemical Companies. added. The mixture was stirred at room temperature overnight,
DABCO was sublimed under reduced pressure, and other the solvent removed under reduced pressure, and the resulting
amines and thiols were dried and distilled before use. off-white solid stirred in toluene (25 mL) for 1 h in the air. Fil-
Diphenylphosphine–borane,42 α-(di-t-butylphosphino)-α′-chloro- tration and solvent removal under reduced pressure gave crude
o-xylene–borane (1),21 bis(pentafluorophenyl)bromophosphine,43 compound 2, which was recrystallised from 1 : 3 toluene–
3-carboxypyridinium chlorochromate,34 pyrrolidine–borane44 n-hexane. Air-stable white crystals (0.158 g, 57%). Anal. found:
and diethylamine–borane45 were synthesised using literature C, 73.0; H, 9.0; calc. for C28H42B2P2: C, 72.8; H, 9.2%. IR νmax
/
methods. Tetrahydrofuran (THF) and diethyl ether (Et2O) were cm−1: 2349–2386 (BH), 2869–3079 (CH). NMR δH (600 MHz;
distilled under a nitrogen or argon atmosphere from sodium CDCl3): 0.2–1.2 (6H, br, BH3), 1.23 (18H, d, J 12.3, PBut), 3.11
benzophenone ketyl immediately prior to use. All other sol- (2H, d, J 11.8, CH2PBut), 3.93 (2H, d, J 11.8, CH2PPh), 6.51 (1H,
vents used were of analytical grade, and were degassed and d, J 7.6, Ar), 6.90 (1H, t, J 7.4, Ar), 7.10 (1H, t, J 7.6, Ar), 7.42
dried over molecular sieves. Elemental analysis was performed (5H, m, Ar & PPh), 7.50 (2H, m, PPh), 7.59 (4H, m, Ar); δC
at the Campbell Microanalytical Laboratory at Otago Univer- (150 MHz; CDCl3): 23.54 (d, J 23.5, CH2PBut), 28.55 (s, PCMe3),
sity, Dunedin. Infrared spectra were obtained using a Perkin- 31.88 (d, J 31.1, CH2PPh), 33.15 (d, J 24.8, PCMe3), 126.50 (t, J
Elmer Spectrum One FT-IR spectrophotometer (resolution 2.6, Ar), 126.88 (dd, J 3.2, 1.9, Ar), 128.81 (d, J 10.2, PPh),
4 cm−1) in absorbance mode, as films from CH2Cl2. All spec- 129.10 (d, J 54.0, PPh), 131.41 (d, J 1.9, PPh), 131.60 (dd, J 3.8,
tral data were obtained at ambient temperature. Nuclear mag- 1.9, Ar), 131.78 (t, J 3.8, Ar), 132.03 (t, J 3.2, Ar), 132.80 (d, J 8.9,
netic resonance (NMR) spectra were recorded using a Varian PPh), 134.66 (t, J 4.5, Ar); δP (121 MHz; CDCl3): 18.52 (br, PPh),
Unity Inova spectrometer operating at 300, 121 and 282 MHz 47.69 (br, PBut). HRMS found: m/z 485.2848; calc. for
for 1H, 31P and 19F spectra respectively, a Varian Unity Inova C28H42B2NaP2 [M + Na]+: 485.2850.
spectrometer operating at 500, 125 and 96 MHz for 1H,
α-(Di-t-butylphosphino)-α′-{bis(pentafluorophenyl)-
phosphino}-o-xylene–borane (4)
13C and 11B spectra respectively, and a Varian DirectDrive
spectrometer operating at 600 and 150 MHz for 1H and
13C spectra respectively. All direct-detected 1H and 13C chemical Flame-dried magnesium powder (1.20 g, 49 mmol) and THF
shifts, δ (ppm), were referenced to the residual solvent peak of (5 mL) were combined in a Schlenk tube, 1,2-dibromoethane
the deuterated solvent.46 31P, 19F and 11B NMR spectra were (0.05 mL) added and the mixture heated until bubbles
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appeared. After reaction was complete, the solvent was dec- H, 9.4; S, 8.5; calc. for C22H34BPS: C, 71.0; H, 9.2; S, 8.6%.
anted and fresh THF (5 mL) added. A solution of compound 1 IR νmax/cm−1: 2381 (BH), 2870–3059 (CH). NMR δH (500 MHz;
(0.40 g, 1.34 mmol) in THF (5 mL) was added and the mixture C6D6): 0.9–1.7 (3H, br, BH3), 1.05 (18H, d, J 12.0, PBut), 3.20
stirred for 2 h. The resulting green solution was decanted and (2H, d, J 12.0, CH2P), 4.40 (2H, s, CH2S), 6.92 (2H, m, Ar &
added dropwise to a solution of bis(pentafluorophenyl)bromo- SPh), 7.01 (4H, m, Ar & SPh), 7.32 (2H, d, J 8.5, SPh), 7.61
phosphine (0.30 mL, 1.34 mmol) in THF (5 mL) at 0 °C. The (1H, d, J 8.0, Ar); δC (125 MHz; C6D6): 22.31 (d, J 22.9, CH2P),
solution was stirred at room temperature overnight and the 28.31 (d, J 1.0, PCMe3), 32.99 (d, J 24.4, PCMe3), 38.50
solvent removed under reduced pressure giving a sticky solid. (s, CH2S), 126.52 (s, SPh), 127.33 (d, J 2.0, Ar), 127.51 (d, J 1.4,
The mixture was triturated with n-hexane (40 mL), filtered Ar), 129.17 (s, SPh), 130.11 (s, SPh), 131.57 (d, J 1.5, Ar), 132.20
through a plug of alumina and the solvent removed under (d, J 3.4, Ar), 134.67 (d, J 3.4, Ar), 136.61 (d, J 4.3, Ar), 137.21
reduced pressure. The resulting cloudy oil was washed with (s, SPh); δP (121 MHz; C6D6): 47.97 (br); δB (96 MHz; C6D6):
methanol (2 × 5 mL) giving compound 4. Air-sensitive white −40.65 (d, J 48.4). HRMS found: m/z 395.2116; calc. for
powder (0.27 g, 32%). NMR δH (500 MHz; C6D6): 0.9–1.6 (6H, C22H34BNaPS [M + Na]+: 395.2110.
br, BH3), 1.09 (18H, d, J 12.2, PBut), 3.29 (2H, d, J 11.9,
CH2PBut), 4.23 (2H, d, J 4.6, CH2P(C6F5)), 6.64 (1H, d, J 7.6, Ar),
α-(Di-t-butylphosphino)-α′-(t-butylsulfinyl)-o-xylene–borane (8)
6.69 (1H, t, J 7.6, Ar), 6.86 (1H, t, J 7.6, Ar), 7.51 (1H, d, J 7.8,
Compound 7a (1.00 g, 2.84 mmol), 3-carboxypyridinium chlor-
Ar); δC (125 MHz; C6D6): 23.22 (dd, J 22.1, 9.1, CH2PBut), 28.29
ochromate (0.74 g, 2.84 mmol) and aluminium trichloride
(s, PCMe3), 30.20 (m, CH2P(C6F5)), 33.08 (d, J 24.0, PCMe3),
(0.38 g, 2.84 mmol) were combined in acetonitrile (50 mL) in
108.60 (m, P(C6F5)), 127.34 (t, J 2.4, Ar), 127.45 (dd, J 3.4, 1.5,
the air, and heated to reflux for 2 h. The resulting mixture was
Ar), 130.91 (d, J 8.6, Ar), 132.74 (t, J 2.9, Ar), 134.02 (dd, J 5.8,
separated by centrifugation and the solid washed with aceto-
4.3, Ar), 134.44 (t, J 3.8, Ar), 137.76 (dm, J 254.3, P(C6F5)),
nitrile (2 × 40 mL). The combined purple solutions were
142.50 (dm, J 257.2, P(C6F5)), 147.96 (dm, J 246.6, P(C6F5)); δP
passed through a plug of alumina, which was then washed
(121 MHz; C6D6): −50.47 (quin, J 22.2, P(C6F5)), 49.38 (br,
through with further acetonitrile (30 mL). Solvent evaporation
PBut); δF (282 MHz; C6D6): −160.32 (4F, m, P(m-C6F5)), −149.37
under reduced pressure gave the crude product. Recrystallisa-
(2F, tt, J 21.8, 4.0, P(p-C6F5)), −130.11 (4F, m, P(o-C6F5)). HRMS
tion from hot toluene gave desired compound 7a. Hygroscopic
found: m/z 627.1597; calc. for
627.1599.
C28H28BF10P2 [M −
H]+:
white powder (0.61 g, 58%). Anal. found: C, 65.1; H, 10.6; S,
−1
8.4; calc. for C20H38BOPS: C, 65.2; H, 10.4; S, 8.7%. IR νmax/cm
:
1028 (SO), 2391 (BH), 2870–3052 (CH). NMR δH (500 MHz;
C6D6): 0.8–1.6 (3H, br, BH3), 1.06 (9H, d, J 12.5, PBut), 1.09
(9H, s, SBut), 1.19 (9H, d, J 12.5, PBut), 3.04 (1H, t, J 15.0,
CH2P), 3.63 (1H, d, J 13.5, CH2S), 4.07 (1H, dd, J 15.0, 9.0,
CH2P), 4.61 (1H, d, J 13.5, CH2S), 7.06 (3H, m, Ar), 7.36 (1H, d,
J 7.5, Ar); δC (150 MHz; C6D6): 22.95 (s, SCMe3), 23.33 (d, J 22.7,
CH2P), 28.51 (d, J 0.9, PCMe3), 28.53 (d, J 1.1, PCMe3), 32.99
(d, J 25.0, PCMe3), 33.01 (d, J 24.1, PCMe3), 52.19 (d, J 1.2,
CH2S), 53.44 (s, SCMe3), 127.43 (d, J 2.0, Ar), 127.55 (d, J 2.2,
Ar), 132.39 (d, J 2.0, Ar), 132.56 (d, J 3.9, Ar), 134.34 (d, J 3.6,
Ar), 136.47 (d, J 3.9, Ar); δP (121 MHz; C6D6): 47.98 (br). HRMS
found: m/z 391.2376; calc. for C20H38BNaOPS [M + Na]+:
391.2372.
General procedure for synthesis of α-(di-t-butylphosphino)-α′-
thio-o-xylene–borane compounds (7)
Sodium metal (0.164 g, 7.1 mmol) and ethanol (50 mL) were
combined and after reaction was complete, the appropriate
thiol (7.5 mmol) was added and resulting solution stirred for
1 h. Compound 1 (1.05 g, 3.5 mmol) was added and the
mixture stirred overnight, followed by solvent evaporation
under reduced pressure. The resulting white solid was dis-
solved in toluene (50 mL) in the air, filtered and the solvent
evaporated under reduced pressure leaving crude product,
which was recrystallised from n-hexane.
α-(Di-t-butylphosphino)-α′-(t-butylthio)-o-xylene–borane (7a).
White powdery crystals (0.98 g, 80%). Anal. found: C, 68.0; H,
11.1; S, 9.0; calc. for C20H38BPS: C, 68.2; H, 10.9; S, 9.1%.
IR νmax/cm−1: 2383 (BH), 2902–3051 (CH). NMR δH (500 MHz;
C6D6): 1.0–1.8 (3H, br, BH3), 1.12 (18H, d, J 12.5, PBut), 1.29
General procedure for synthesis of α-(di-t-butylphosphino)-
α′-(dialkylamino)-o-xylene–diborane compounds (11)
(9H, s, SBut), 3.27 (2H, d, J 12.0, CH2P), 3.99 (2H, s, CH2S), A solution of dialkylamine–borane (1.6 mmol) in THF (5 mL)
6.99 (1H, t, J 7.5, Ar), 7.04 (1H, t, J 7.5, Ar), 7.23 (1H, d, J 7.0, was cooled to 0 °C and a solution of n-butyllithium (1.0 mL,
Ar), 7.79 (1H, d, J 8.0, Ar); δC (125 MHz; C6D6): 22.43 (d, J 23.5, 1.6 M in hexanes, 1.6 mmol) was added dropwise with stirring.
CH2P), 28.38 (d, J 1.0, PCMe3), 30.98 (s, SCMe3), 32.93 The mixture was stirred at room temperature for 1 h, then
(s, CH2S), 33.08 (d, J 24.8, PCMe3), 42.67 (s, SCMe3), 127.22 added dropwise to a solution of 1 (0.42 g, 1.4 mmol) in
(d, J 1.5, Ar), 127.37 (d, J 1.9, Ar), 131.69 (d, J 1.4, Ar), 132.16 THF (5 mL) at −5 °C and stirred at this temperature for 1 h.
(d, J 3.3, Ar), 134.67 (d, J 3.4, Ar), 137.17 (d, J 4.8, Ar); δP The solvent was evaporated under reduced pressure, and the
(121 MHz; C6D6): 47.94 (br); δB (96 MHz; C6D6): −40.37 resulting white solid was stirred in distilled water (10 mL) in
(d, J 47.6). HRMS found: m/z 374.2462; calc. for C20H38BNaPS the air for 1 h, filtered and recrystallised from 1 : 2 toluene–
[M + Na]+: 374.2459.
n-hexane.
α-(Di-t-butylphosphino)-α′-(phenylthio)-o-xylene–borane (7b).
α-(Di-t-butylphosphino)-α′-(dimethylamino)-o-xylene–diborane
White plate-like crystals (0.98 g, 75%). Anal. found: C, 71.0; (11a). White needle-like crystals (0.36 g, 80%). Anal. found:
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C, 67.4; H, 12.1; N, 4.4; calc. for C18H38B2NP: C, 67.3; H, 11.9; again removed under reduced pressure. Elution through an
N, 4.4%. IR νmax/cm−1: 2278–2380 (BH), 2871–2988 (CH). NMR alumina column with 1% ethyl acetate in n-hexane gave pure
δH (500 MHz; C6D6): 0.8–1.6 (3H, br, PBH3), 1.08 (18H, d, compound 13 (RF = 0.33). Air-stable clear oil (75 mg, 34%).
J 12.0, PBut), 1.9–2.8 (3H, br, NBH3), 2.09 (3H, s, NMe), 3.55 Anal. found: C, 75.3; H, 9.2; calc. for C28H40BPSi: C, 75.3; H,
(2H, d, J 12.0, CH2P), 3.98 (2H, s, CH2N), 6.74 (1H, d, J 8.0, Ar), 9.0%. NMR δH (500 MHz; C6D6): 1.0–1.8 (3H, br, BH3), 1.03
6.93 (1H, t, J 7.5, Ar), 7.09 (1H, t, J 7.5, Ar), 7.69 (1H, d, J 8.0, (18H, d, J 12.2, PBut), 2.69 (2H, d, J 12.0, CH2P), 2.93 (2H, d, J
Ar); δC (125 MHz; C6D6): 24.08 (d, J 22.5, CH2P), 28.43 (d, J 1.0, 3.4, CH2Si), 5.10 (1H, t, J 3.1, 1JSiH 197.3, SiH), 6.97 (3H, m, Ar),
PCMe3), 32.99 (d, J 24.4, PCMe3), 51.32 (s, NMe), 64.98 (s, 7.11 (6H, m, SiPh), 7.45 (4H, d, J 7.6, SiPh), 7.82 (1H, d, J 7.8,
CH2N), 126.23 (d, J 2.4, Ar), 128.62 (d, J 2.0, Ar), 132.02 (d, Ar); δC (125 MHz; C6D6): 21.71 (s, CH2Si), 22.91 (d, J 23.1,
J 4.3, Ar), 132.74 (d, J 3.8, Ar), 133.51 (d, J 1.4, Ar), 137.70 (d, CH2P), 28.34 (s, PCMe3), 32.97 (d, J 23.9, PCMe3), 125.20 (d, J
J 3.8, Ar); δP (121 MHz; C6D6): 49.80 (br); δB (96 MHz; C6D6): 1.9, Ar), 127.22 (d, J 1.9, Ar), 128.39 (s, SiPh), 130.19 (s, SiPh),
−40.83 (d, J 52.5, PBH3), −8.78 (s, NBH3). HRMS found: m/z 130.59 (d, J 1.5, Ar), 132.12 (d, J 2.9, Ar), 132.98 (d, J 3.3, Ar),
344.2832; calc. for C18H38B2NNaP [M + Na]+: 344.2832.
133.73 (s, SiPh), 135.67 (s, SiPh), 137.60 (d, J 4.8, Ar); δP
α-(Di-t-butylphosphino)-α′-pyrrolidino-o-xylene–diborane (11b). (121 MHz; C6D6): 48.57 (br). HRMS found: m/z 445.2643; calc.
White needle-like crystals (0.43 g, 89%). Anal. found: C, 69.1; for C28H39BPSi [M − H]+: 445.2652.
H, 11.7; N, 4.0; calc. for C20H40B2NP: C, 69.2; H, 11.6; N, 4.0%.
−1
IR νmax/cm
: 2279–2379 (BH), 2904–3052 (CH). NMR
General procedure for deprotection of compounds 2, 7 and 8,
and synthesis of compound 6
δH (500 MHz; C6D6): 0.8–1.6 (3H, br, PBH3), 1.13 (18H, d,
J 12.5, PBut), 1.8–2.6 (3H, br, NBH3), 1.19 (2H, m, NCH2CH2),
1.82 (2H, m, NCH2CH2), 2.31 (2H, m, NCH2CH2), 2.90 (2H, m, The appropriate phosphine–borane (50 mg) and morpholine
NCH2CH2), 3.69 (2H, d, J 12.0, CH2P), 4.10 (2H, s, ArCH2N), (1 mL) were combined in a sealed tube and heated to 100 °C
6.84 (1H, d, J 7.5, Ar), 6.99 (1H, t, J 7.5, Ar), 7.11 (1H, t, J 7.5, for 1 h. After cooling, the solvent was evaporated under
Ar), 7.66 (1H, d, J 7.5, Ar); δC (125 MHz; C6D6): 22.15 reduced pressure. The resulting white solid was extracted with
(s, NCH2CH2), 24.36 (d, J 22.9, CH2P), 28.50 (d, J 1.0, PCMe3), n-hexane (2 × 2 mL), filtered through a plug of alumina, and
33.06 (d, J 24.4, PCMe3), 59.93 (s, NCH2CH2), 63.18 (s, the solvent evaporated under reduced pressure, giving desired
ArCH2N), 126.39 (d, J 2.4, Ar), 132.71 (d, J 3.4, Ar), 132.79 (d, product.
J 1.9, Ar), 133.28 (d, J 3.8, Ar), 138.00 (d, J 3.9, Ar), other Ar
α-(Di-t-butylphosphino)-α′-(diphenylphosphino)-o-xylene (3).
obscured by solvent; δP (121 MHz; C6D6): 49.55 (br); δB (96 MHz; Highly air-sensitive white solid (39 mg, 82%). NMR δH
C6D6): −40.86 (d, J 47.8, PBH3), −11.44 (s, NBH3). HRMS found: (500 MHz; C6D6): 1.09 (18H, d, J 10.5, PBut), 3.09 (2H, s,
m/z 370.2981; calc. for C20H40B2NNaP [M + Na]+: 370.2990.
CH2PBut), 3.92 (2H, d, J 2.5, CH2PPh), 6.75 (1H, d, J 7.6, Ar),
α-(Di-t-butylphosphino)-α′-(diethylamino)-o-xylene–diborane 6.85 (1H, t, J 7.5, Ar), 7.00 (1H, t, J 7.6, Ar), 7.04 (6H, m, PPh),
(11c). White crystals (0.39 g, 80%). Anal. found: C, 68.9; 7.42 (4H, m, PPh), 7.50 (1H, d, J 7.9, Ar); δC (125 MHz; C6D6):
H, 12.2; N, 3.9; calc. for C20H42B2NP: C, 68.8; H, 12.1; N, 4.0%. 27.41 (dd, J 26.9, 6.7, CH2PBut), 30.10 (d, J 13.4, PCMe3), 32.12
−1
IR νmax/cm
: 2281–2366 (BH), 2872–2998 (CH). NMR (d, J 24.0, PCMe3), 34.63 (dd, J 17.0, 11.8, CH2PPh), 125.82
δH (500 MHz; C6D6): 0.6–1.6 (3H, br, PBH3), 0.88 (6H, t, J 7.0, (t, J 1.9, Ar), 126.28 (d, J 2.9, Ar), 128.59 (d, J 6.2, PPh), 128.77
NCH2Me), 1.12 (18H, d, J 12.5, PBut), 1.6–2.5 (3H, br, NBH3), (s, PPh), 131.45 (d, J 7.2, Ar), 131.74 (dd, J 10.6, 1.4, Ar), 133.51
2.50 (2H, sext, J 7.0, NCH2Me), 2.62 (2H, sext, J 7.0, NCH2Me), (d, J 18.2, PPh), 136.03 (dd, J 6.5, 2.2, Ar), 139.28 (d, J 16.3,
3.82 (2H, d, J 12.0, CH2P), 4.02 (2H, s, ArCH2N), 6.95 (1H, d, PPh), 139.60 (dd, J 8.7, 3.9, Ar); δP (121 MHz; C6D6): −15.61
J 7.5, Ar), 7.00 (1H, t, J 7.5, Ar), 7.10 (1H, t, J 7.5, Ar), 7.53 (1H, (d, J 1.4, PPh), 24.47 (d, J 1.4, PBut).
d, J 7.5, Ar); δC (125 MHz; C6D6): 8.75 (s, NCH2Me), 24.75 (d,
α-(Di-t-butylphosphino)-α′-{bis(p-N-morpholinotetrafluoro-
J 22.5, CH2P), 28.55 (s, PCMe3), 33.01 (d, J 24.8, PCMe3), 52.51 phenyl)phosphino}-o-xylene (6). Highly air-sensitive white
(s, NCH2Me), 60.35 (s, ArCH2N), 126.08 (d, J 2.4, Ar), 132.89 expanded oil (50 mg, 84%). NMR δH (500 MHz; C6D6): 1.12
(d, J 3.8, Ar), 133.07 (d, J 3.8, Ar), 133.18 (d, J 1.9, Ar), 138.35 (18H, d, J 10.7, PBut), 2.76 (8H, br s, CH2N), 3.20 (2H,
(d, J 3.8, Ar), other Ar obscured by solvent; δP (121 MHz; C6D6): s, CH2PBut), 3.36 (8H, br s, CH2O), 4.53 (2H, s, CH2P(C6F4)N),
49.80 (br); δB (96 MHz; C6D6): −40.97 (d, J 53.7, PBH3), −12.93 6.85 (1H, t, J 7.3, Ar), 6.98 (2H, m, Ar), 7.56 (1H, d, J 7.0, Ar);
(s, NBH3). HRMS found: m/z 372.3138; calc. for C20H42B2NNaP δC (125 MHz; C6D6): 27.11 (dd, J 27.3, 7.2, CH2PBut), 29.78
[M + Na]+: 372.3146.
(m, CH2P(C6F4)N), 30.00 (d, J 13.4, PCMe3), 32.11 (d, J 24.5,
PCMe3), 51.11 (t, J 3.4, CH2N), 67.05 (s, CH2O), 106.06 (m,
P(C6F4)N), 126.13 (s, Ar), 127.24 (d, J 3.4, Ar), 130.83 (d, J 8.7,
Ar), 132.00 (m, P(C6F4)N), 132.19 (dd, J 12.5, 2.4, Ar), 134.37
α-(Di-t-butylphosphino)-α′-(diphenylsilyl)-o-xylene–borane (13)
Flame-dried magnesium turnings (24 mg, 1.00 mmol), com- (dd, J 7.8, 2.1, Ar), 140.12 (dd, J 9.1, 4.3, Ar), 142.06 (dm,
pound 1 (150 mg, 0.50 mmol), chlorodiphenylsilane (0.15 mL, J 230.3, P(C6F4)N), 149.04 (dm, J 234.2, P(C6F4)N); δP (121 MHz;
0.75 mmol), a crystal of iodine and THF (12 mL) were com- C6D6): −51.73 (quind, J 23.7, 8.1, P(C6F4)N), 25.40 (d, J 8.1,
bined and stirred at room temperature overnight. The solvent PBut); δF (282 MHz; C6D6): −150.56 (4F, dd, J 20.9, 7.0, P(m-
was removed under reduced pressure, the resulting mixture C6F4)N), −132.47 (4F, td, J 22.8, 9.9, P(o-C6F4)N). HRMS found:
extracted into toluene (15 mL) in the air, filtered and solvent m/z 749.2659; calc. for C36H43F8N2O2P2 [M + H]+: 749.2667.
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α-(Di-t-butylphosphino)-α′-(t-butylthio)-o-xylene (9a). Highly PCMe3), 109.13 (m, P(C6F5)), 126.24 (dd, J 2.4, 1.9, Ar), 127.63
air-sensitive clear oil (44 mg, 92%). NMR δH (600 MHz; C6D6): (d, J 3.4, Ar), 130.50 (d, J 9.6, Ar), 132.36 (dd, J 11.1, 2.4, Ar),
1.13 (18H, d, J 10.6, PBut), 1.29 (9H, s, SBut), 3.09 (2H, d, J 1.2, 133.21 (dd, J 7.7, 1.9, Ar), 137.77 (dm, J 252.9, P(C6F5)), 139.97
CH2P), 4.05 (2H, s, CH2S), 7.01 (1H, t, J 7.3, Ar), 7.07 (1H, t, J (dd, J 8.6, 4.3, Ar), 142.46 (dm, J 257.2, P(C6F5)), 148.03 (dm,
7.7, Ar), 7.31 (1H, d, J 7.3, Ar), 7.68 (1H, d, J 7.3, Ar); J 246.6, P(C6F5)); δP (121 MHz; C6D6): −50.87 (quind, J 22.3,
δC (150 MHz; C6D6): 26.21 (d, J 26.0, CH2P), 30.07 (d, J 13.2, 11.9, P(C6F5)), 25.15 (d, J 12.6, PBut); δF (282 MHz; C6D6):
PCMe3), 31.00 (s, SCMe3), 32.01 (d, J 24.2, PCMe3), 32.25 −160.51 (4F, m, P(m-C6F5)), −149.81 (2F, tt, J 20.8, 4.0, P(p-
(d, J 8.7, CH2S), 42.57 (s, SCMe3), 126.18 (d, J 1.8, Ar), 127.20 C6F5)), −130.01 (4F, m, P(o-C6F5)).
(s, Ar), 131.14 (s, Ar), 131.63 (d, J 14.4, Ar), 136.58 (d, J 2.9, Ar),
α-(Di-t-butylphosphino)-α′-(dimethylamino)-o-xylene (12a).
140.06 (d, J 9.2, Ar); δP (121 MHz; C6D6): 24.99 (s).
Highly air-sensitive cloudy oil (35 mg, 85%). NMR
α-(Di-t-butylphosphino)-α′-(phenylthio)-o-xylene (9b). Highly δH (500 MHz; C6D6): 1.13 (18H, d, J 10.7, PBut), 2.11 (6H, s,
air-sensitive white solid (33 mg, 69%). NMR δH (500 MHz; NMe), 3.16 (2H, d, J 2.4, CH2P), 3.60 (2H, s, CH2N), 7.05 (1H, t,
C6D6): 1.07 (18H, d, J 10.8, PBut), 3.06 (2H, s, CH2P), 4.51 (2H, J 7.3, Ar), 7.15 (1H, t, J 7.6, Ar), 7.21 (1H, d, J 7.3, Ar), 7.77 (1H,
d, J 2.2, CH2S), 6.93 (2H, m, Ar & SPh), 6.99 (2H, t, J 7.6, SPh), d, J 7.3, Ar); δC (125 MHz; C6D6): 25.53 (d, J 25.5, CH2P), 30.02
7.03 (1H, t, J 7.3, Ar), 7.09 (1H, d, J 7.5, Ar), 7.30 (2H, d, J 7.0, (d, J 13.9, PCMe3), 31.95 (d, J 24.0, PCMe3), 45.46 (s, NMe),
SPh), 7.47 (1H, d, J 7.5, Ar); δC (125 MHz; C6D6): 26.79 63.46 (d, J 6.2, CH2N), 125.56 (d, J 1.9, Ar), 127.38 (s, Ar),
(d, J 27.4, CH2P), 29.99 (d, J 13.5, PCMe3), 32.04 (d, J 24.4, 131.08 (s, Ar), 131.54 (d, J 14.8, Ar), 137.54 (d, J 2.9, Ar), 141.20
PCMe3), 37.84 (d, J 12.9, CH2S), 126.19 (d, J 1.4, Ar), 126.35 (d, J 10.1, Ar); δP (121 MHz; C6D6): 24.53 (s).
(s, SPh), 127.57 (s, Ar), 129.06 (s, SPh), 130.23 (s, SPh), 131.18
(s, Ar), 131.91 (d, J 10.5, Ar), 135.65 (d, J 2.4, Ar), 137.50 air-sensitive clear oil (27 mg, 60%). NMR δH (500 MHz; C6D6):
(s, SPh), 140.16 (d, J 8.6, Ar); δP (121 MHz; C6D6): 25.93 (s).
1.14 (18H, d, J 10.5, PBut), 1.58 (4H, m, NCH2CH2), 2.40 (4H,
α-(Di-t-butylphosphino)-α′-pyrrolidino-o-xylene (12b). Highly
α-(Di-t-butylphosphino)-α′-(t-butylsulfinyl)-o-xylene (10). Highly m, NCH2CH2), 3.16 (2H, d, J 2.7, CH2P), 3.82 (2H, s, ArCH2N),
air-sensitive white solid (39 mg, 81%). NMR δH (500 MHz; 7.07 (1H, t, J 7.3, Ar), 7.16 (1H, t, J 7.6, Ar), 7.27 (1H, d, J 7.5,
C6D6): 1.06 (9H, d, J 10.9, PBut), 1.08 (9H, s, SBut), 1.14 (9H, d, Ar), 7.81 (1H, dd, J 7.6, 1.5, Ar); δC (125 MHz; C6D6): 23.90
J 10.8, PBut), 2.99 (1H, dd, J 14.8, 2.0, CH2P), 3.37 (1H, d, (s, NCH2CH2), 25.29 (d, J 25.0, CH2P), 30.00 (d, J 13.4, PCMe3),
J 14.9, CH2P), 3.85 (1H, dd, J 13.0, 1.4, CH2S), 4.25 (1H, dd, 31.95 (d, J 24.0, PCMe3), 54.31 (s, NCH2CH2), 59.64 (d, J 5.8,
J 13.0, 3.5, CH2S), 7.04 (2H, m, Ar), 7.23 (1H, d, J 8.1, Ar), 7.46 ArCH2N), 125.60 (d, J 1.9, Ar), 127.24 (s, Ar), 130.50 (s, Ar),
(1H, d, J 7.1, Ar); δC (125 MHz; C6D6): 22.99 (s, SCMe3), 27.59 131.35 (d, J 15.4, Ar), 138.15 (d, J 2.9, Ar), 140.87 (d, J 10.5, Ar);
(d, J 26.4, CH2P), 30.06 (d, J 13.0, PCMe3), 30.13 (d, J 13.0, δP (121 MHz; C6D6): 24.56 (s).
PCMe3), 32.04 (d, J 26.9, PCMe3), 32.22 (d, J 26.4, PCMe3),
α-(Di-t-butylphosphino)-α′-(diethylamino)-o-xylene (12c). Highly
50.89 (d, J 13.4, CH2S), 53.46 (s, SCMe3), 126.41 (d, J 1.5, Ar), air-sensitive clear oil (33 mg, 73%). NMR δH (500 MHz; C6D6):
128.00 (s, Ar), 131.79 (d, J 1.9, Ar), 132.04 (d, J 10.5, Ar), 132.54 0.97 (6H, t, J 7.1, NCH2Me), 1.14 (18H, d, J 10.8, PBut), 2.46
(s, Ar), 141.00 (d, J 7.7, Ar); δP (121 MHz; C6D6): 25.23 (s).
(4H, q, J 7.1, NCH2Me), 3.12 (2H, d, J 2.7, CH2P), 3.69 (2H, s,
ArCH2N), 7.08 (1H, t, J 7.3, Ar), 7.17 (1H, t, J 7.4, Ar), 7.33 (1H,
d, J 7.3, Ar), 7.95 (1H, dd, J 7.3, 2.9, Ar); δC (125 MHz; C6D6):
General procedure for deprotection of compounds 4 and 11
A solution of the appropriate phosphine–borane (0.14 mmol) 11.81 (s, NCH2Me), 25.17 (d, J 24.0, CH2P), 30.09 (d, J 13.5,
in dichloromethane (3 mL) was cooled to −10 °C, tetrafluoro- PCMe3), 32.00 (d, J 24.0, PCMe3), 46.89 (s, NCH2Me), 57.64 (d, J
boric acid–diethyl ether complex (0.24 mL, 85% solution, 3.9, ArCH2N), 125.55 (d, J 1.9, Ar), 127.16 (s, Ar), 130.88 (s, Ar),
1.4 mmol) added dropwise, and the resulting solution stirred 131.26 (d, J 18.2, Ar), 138.00 (d, J 3.3, Ar), 140.96 (d, J 11.0, Ar);
at room temperature for 1 h. Diethyl ether (4 mL) was added, δP (121 MHz; C6D6): 23.76 (s).
followed by saturated sodium hydrogen carbonate solution
(8 mL), and the mixture stirred for 30 min. The resulting layers
α-(Di-t-butylphosphino)-α′-(diphenylsilyl)-o-xylene (14)
were separated, the aqueous layer washed with diethyl ether Compound 13 (15 mg, 0.03 mmol) and DABCO (4 mg,
(2 × 4 mL), combined organic fractions washed with distilled 0.04 mmol) were combined in toluene (0.5 mL) and heated to
water (4 mL) and brine (4 mL), and solvent evaporated under 60 °C overnight. After cooling, the solvent was evaporated
reduced pressure. The resulting material was extracted into under reduced pressure. The resulting white solid was
n-hexane (6 mL), dried over magnesium sulfate and filtered extracted with n-hexane (2 × 1 mL), filtered through a plug of
through a plug of alumina. The solvent was evaporated under alumina, and the solvent evaporated under reduced pressure,
reduced pressure, giving desired product.
giving desired product 14. Highly air-sensitive white solid
α-(Di-t-butylphosphino)-α′-{bis(pentafluorophenyl)phosphino}- (9 mg, 69%). NMR δH (500 MHz; C6D6): 1.05 (18H, d, J 10.5,
o-xylene (5). Highly air-sensitive white solid (44 mg, 51%). PBut), 2.65 (2H, d, J 1.5, CH2P), 3.10 (2H, dd, J 3.4, 1.5, CH2Si),
NMR δH (500 MHz; C6D6): 1.07 (18H, d, J 10.8, PBut), 3.07 (2H, 5.22 (1H, t, J 3.7, 1JSiH 197.5, SiH), 6.95 (1H, m, Ar), 7.01 (2H, m,
s, CH2PBut), 4.27 (2H, s, CH2P(C6F5)), 6.69 (1H, d, J 7.8, Ar), Ar), 7.13 (6H, m, SiPh), 7.51 (4H, dd, J 7.5, 1.2, SiPh), 7.53 (1H, d,
6.74 (1H, t, J 7.3, Ar), 6.91 (1H, t, J 7.5, Ar), 7.41 (1H, d, J 7.6, J 7.8, Ar); δC (125 MHz; C6D6): 20.72 (d, J 8.6, CH2Si), 27.17 (d, J
Ar); δC (125 MHz; C6D6): 27.36 (dd, J 27.8, 6.7, CH2PBut), 29.29 26.4, CH2P), 30.03 (d, J 13.5, PCMe3), 31.97 (d, J 25.0, PCMe3),
(m, CH2P(C6F5)), 29.87 (d, J 13.4, PCMe3), 32.07 (d, J 24.0, 125.13 (s, Ar), 126.07 (d, J 2.0, Ar), 128.29 (s, SiPh), 130.01
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Organic & Biomolecular Chemistry
(s, SiPh), 130.44 (s, Ar), 131.71 (d, J 12.5, Ar), 134.23 (s, SiPh), 21 K. M. Allan and J. L. Spencer, Tetrahedron Lett., 2009, 50,
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