Reactions of phosphines with electron deficient boranes

Article abstract of DOI:10.1039/b814486a

A series of classical B(C₆F₅)₃-phosphine adducts are shown to be reactive molecules. Reaction of (THF)B(C ₆F₅)₃ with phosphines are shown to effect ring-opening of THF affording the zwitter

Full text of DOI:10.1039/b814486a

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PAPER
www.rsc.org/dalton | Dalton Transactions
Reactions of phosphines with electron deficient boranes†
Gregory C. Welch,a Roberto Prieto,a Meghan A. Dureen,b Alan J. Lough,b Oijsamola A. Labeodan,a
Thorsten Ho¨ltrichter-Ro¨ssmanna and Douglas W. Stephan*b
Received 20th August 2008, Accepted 7th November 2008
First published as an Advance Article on the web 19th January 2009
DOI: 10.1039/b814486a
A series of classical B(C6F5)3-phosphine adducts are shown to be reactive molecules. Reaction of
(THF)B(C6F5)3 with phosphines are shown to effect ring-opening of THF affording the zwitterionic
phosphonium-borate species of the form R2PH(C4H8O)B(C6F5)3 and R3P(C4H8O)B(C6F5)3.
Alternatively, treatment of (THF)B(C6F5)3 with a lithium phosphide (R2PLi, R = tBu, Ph Mes) affords
species of the form [Li(THF)x][R2P(C4H8O)B(C6F5)3]. Additionally, double THF ring-opening is also
demonstrated to give species of the form [Li(THF)x][R2P(C4H8OB(C6F5)3)2]. In addition a series of
classical borane-phosphine adducts are also shown to undergo thermal rearrangement reactions to give
the zwitterionic products of aromatic substitution R2PH(C6F4)BF(C6F5)2 and R3P(C6F4)BF(C6F5)2.
The mechanism of these substitutions is considered. A series of crystallographic studies of
phosphine-borane adducts, THF ring-opened zwitterions and para-attack zwitterionic phosphonium
borates are reported and discussed.
Introduction
Lewis acidic reagents play important roles in a variety of sto-
ichiometric and catalytic reactions. In the case of polymeriza-
tion catalysis, Lewis acid reagents such as the triorganoborane
B(C6F5)3 or the carbocation analog [Ph3C]+ (trityl) are powerful
co-catalysts as these species are used to generate catalytically active
cationic early metal alkyl complexes as a result of the vacant 2p-
orbitals on boron and carbon, respectively.1–3 Amines, pyridines
and phosphines have been shown to form simple Lewis acid–
base adducts with B(C6F5)3 and trityl cation.7–15 In the case
4–6
of trityl cation, recent work in our research group has shown
that sterically demanding phosphines are too large to interact
with the central carbon of the carbocation and instead effect
nucleophilic aromatic substitution at a position para to the central
carbon.16 While such chemistry was both unexpected and unique,
the resulting cylcohexadienyl and benzylhydryl-phenyl species are
robust (Scheme 1). Similarly, the unusual rearrangement of the
ylide-borane adduct (Ph3PCHPh)B(C6F5)3 to give the zwitterion
p-(Ph3PCHPh)(C6F4)BF(C6F5)2 has been reported by Erker and
co-workers (Scheme 1).17 These reactions demonstrate the non-
conventional reactivity of simple Lewis acid–base adducts. We
have previously communicated that sterically bulky phosphines
react with (THF)B(C6F5)3 to effect the ring-opening of THF
affording the zwitterions R3P(C4H8O)B(C6F5)3.18 Similarly, bulky
phosphines were shown to undergo para-attack of the C6F5 aryl
ring of B(C6F5)3 to give zwitterionic phosphonium borates of
the form R3P(C6F4)BF(C6F5)2.19 Related zwitterions of the form
Scheme 1 Non-conventional reactivity of the Lewis acids B(C6F5)3 and
Ph3C+.
catalyst activators; however, they were synthesized via traditional
Grignard routes. In this full report of this chemistry, we broaden
and explore the range of phosphines that exhibit both THF
ring-opening and para-aromatic substitution of a phosphine for
fluoride on a C6F5 ring on B(C6F5)3 and other related electron
deficient boranes.
Experimental
General data
All preparations were done under an atmosphere of dry, O2-free
N2 employing both Schlenk line techniques and an Innovative
Technologies or Vacuum Atmospheres inert atmosphere glove
box. Solvents (pentane, hexanes, toluene, and CH2Cl2) were
purified employing a Grubbs’ type column system manufactured
by Innovative Technology and stored over molecular sieves
20
21
p-R2EH(C6F4)B(C6F5)3 and p-R2EH(C6H4)B(C6F5)3 (E = N,
P) have been claimed in the patent literature as polymerization
˚
˚
(4 A). Molecular sieves (4 A) were◦ purchased from Aldrich
Chemical Company and dried at 140 C under vacuum for 24 h
prior to use. Uninhibited THF was purchased from EMD and
distilled from sodium/benzophenone. Deuterated solvents were
dried over Na/benzophenone (C6D6, C7D8, THF-d8) or CaH2
(CD2Cl2, C6D5Br). All common organic reagents were purified
aDepartment of Chemistry & Biochemistry, University of Windsor, Windsor,
Ontario, Canada N9B 3P4
bDepartment of Chemistry, University of Toronto, 80 St. George St., Toronto,
Ontario, Canada M5S 3H6. E-mail: dstephan@chem.utoronto.ca
† CCDC reference numbers 698991–699003. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b814486a
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 1559–1570 | 1559
©

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1
by conventional methods unless otherwise noted. H, 13C, 11B,
1
1
7 Hz, Me). 11B{ H} NMR (C6D5Br): -13.5 (bs). 13C{ H} NMR
19F and 31P nuclear magnetic resonance (NMR) spectra are
recorded on a Bruker Avance-300 spectrometer at 300 K unless
otherwise noted. 1H and 13C NMR spectra are referenced to
SiMe4 using the residual solvent peak impurity of the given
solvent. 31P, 11B and 19F NMR spectra are referenced to 85%
H3PO4, BF3(OEt2), and CFCl3, respectively. 7Li NMR spectra are
referenced to LiCl in D2O. Chemical shifts are reported in ppm
and coupling constants in Hz as absolute values. DEPT and 2-D
1H/13C correlation experiments were completed for assignment
of the carbon atoms. Combustion analyses were performed
in-house employing a Perkin Elmer CHN Analyzer. B(C6F5)3
was generously donated by NOVA Chemicals Corporation. All
phosphines were purchased from Aldrich or Strem and used as
received unless otherwise noted. Mes2PH22 and tBu(Mes)PH23
were prepared as reported in the literature. Paratone-N oil
was purchased from Hampton Research. (Cy2PH)B(C6F5)3
3,24 (Ph2PH)B(C6F5)3 6,24 (Me3P)B(C6F5)3 8,25–27 (Ph3P)B(C6F5)3
11,28,29 tBu2PH(C6F4)BF(C6F5)2 24, Mes2PH(C6F4)BF(C6F5)2
26, iPr3P(C6F4)BF(C6F5)2 30, Cy3P(C6F4)BF(C6F5)2 32,30 and
PhB(C6F5)2 3631 were prepared by published methods.
1
1
(C6D5Br): 148.3 (dm, JCF = 240 Hz, CF), 139.5 (dm, JCF
=
252 Hz, CF), 136.91 (dm, 1JCF = 254 Hz, CF), 115.93 (br, quat),
25.3 (d, 3JCP = 5 Hz, CH2), 23.9 (d, 2JCP = 11 Hz, CH2), 20.1 (d,
1JCP = 30 Hz, CH2), 12.8 (s, Me). 19F NMR (C6D5Br): -129.3 (d,
3
3
6F, JFF = 20 Hz, o-C6F5), -156.0 (t, 3F, JFF = 23 Hz, p-C6F5),
-163.0 (m, 6F, 3JFF = 24 Hz, m-C6F5). 31P { H} NMR (C6D5Br):
1
-0.6 (bs). Anal. calcd. for C30H27BF15P: C, 50.44; H, 3.81. Found:
C, 50.24; H, 3.75.
4. Yield 94%. Crystals suitable for X-ray diffraction were
grown via slow evaporation of a concentrated bromobenzene
solution at 25 ◦C. 1H NMR (C6D5Br): 4.42 (dm, 1H, JHP
=
1
2
410 Hz, PH), 0.90 (dm, 4H, JHP = 132 Hz, CH2), 0.45 (dt, 6H,
3JHP = 16 Hz, 3JHH = 18 Hz Me). 11B{ H} NMR (C6D5Br): -16.2
1
(d, JBP = 95 Hz). 13C{ H} NMR (C6D5Br) partial: 148.3 (dm,
1
1
1JCF = 240 Hz, CF), 140.1 (dm, 1JCF = 240 Hz, CF), 137.1 (dm,
1JCF = 250 Hz, CF), 115.8 (br s, quat), 11.91 (d, JCP = 36 Hz,
1
CH2), 10.9 (d, 2JCP = 8 Hz, Me). 19F NMR (C6D5Br): -130.4 (s, 6F,
o-C6F5), -155.6 (t, 3F, 3JFF = 20 Hz, p-C6F5), -162.9 (m, 6F, 3JFF
20 Hz m-C6F5). 31P NMR (C6D5Br): 5.7 (dq, 1JPH = 412 Hz, 1JPB
=
=
92 Hz). Anal. calcd. for C22H11BF15P: C, 43.98; H, 1.84. Found: C,
44.20; H, 2.05.
Synthesis of (CyPH2)B(C6F5)3 1, ((C5H9)2PH)B(C6F5)3 2,
(Cy2PH)B(C6F5)3 3, (Et2PH)B(C6F5)3 4, (Et3P)B(C6F5)3 9,
(n-Bu3P)B(C6F5)3 10
9. Yield 86%. Crystals suitable for X-ray diffraction were
grown via slow evaporation of a concentrated THF solution at
25 ◦C. 1H NMR (THF-d8): 1.94–1.88 (br m, 6H, CH2), 1.24–1.14
These compounds were prepared in a similar fashion and thus
only one preparation is detailed. To a clear solution of B(C6F5)3
(0.100 g, 0.20 mmol) in toluene (5 mL) was added (C5H9)2PH
(0.034 g, 0.20 mmol). The reaction was allowed to stir for 1 h at
25 ◦C. The solvent was removed in vacuo to give the product 2 as
a white solid.
(m, 9H, Me). 11B{ H} NMR (THF-d8): -13.4 (d, JBP = 75 Hz).
1
1
13C{ H} NMR (THF-d8): 149.2 (dm, 1JCF = 239 Hz, CF), 140.92
1
(dm, 1JCF = 249 Hz, CF), 138.4 (dm, 1JCF = 254 Hz, CF), 117.6
1
2
(br s, quat), 14.6 (d, JCP = 35 Hz, CH2), 8.6 (d, JCP = 8 Hz,
Me). 19F NMR (THF-d8): -130.2 (d, 6F, JFF = 22 Hz, o-C6F5),
3
-158.7 (m, 3F, 3JFF = 22 Hz, p-C6F5), -165.3 (m, 6F, 3JFF = 22 Hz,
m-C6F5). 31P { H} NMR (THF-d8): 5.6 (dm, 1JPB = 80 Hz). Anal.
1
1. Yield 0.230 g (93%). 1H NMR (C6D5Br): 4.65 (d, 2H, 1JHP
=
calcd. for C24H15BF15P: C, 45.75; H, 2.40. Found: C, 46.20; H,
2.55%.
393 Hz, PH2), 1.68 (br s, 1H, PCy), 1.43–1.36 (br m, 5H, PCy),
0.95–0.84 (br m, 5H, PCy). 11B{ H} NMR (C6D5Br): -17.5 (br).
1
13C{ H} NMR (C6D5Br) partial: 147.9 (dm, 1JCF = 242 Hz, CF),
1
1
10. Yield 97%. H NMR (C6D5Br): 1.77 (m, 2H, CH2), 1.34
140.3 (dm, 1JCF = 250 Hz, CF), 137.1 (dm, 1JCF = 246 Hz, CF),
114.8 (quat), 31.4 (d, 3JCP = 6 Hz, PCy), 27.7 (d, 1JCP = 33 Hz PCy),
(m, 2H, CH2), 1.63 (m, 2H, CH2), 0.75 (t, 3H, 3JHH = 7 Hz, Me).
11B{ H} NMR (C6D5Br): -13.5 (br). 13C{ H} NMR (C6D5Br):
1
1
26.1 (d, JCP = 12 Hz PCy), 24.8 (s, PCy). 19F NMR (C6D5Br):
2
148.3 (dm, 1JCF = 240 Hz, CF), 139.5 (dm, 1JCF = 252 Hz, CF),
-130.5 (s, 6F, o-C6F5), -155.3 (t, 3F, 3JFF = 21 Hz, p-C6F5), -162.3
136.9 (dm, 1JCF = 254 Hz, CF), 115.9 (br s, quat), 25.3 (d, 3JCP
=
(m, 6F, JFF = 20 Hz m-C6F5). 31P NMR (C6D5Br): -30.0 (br t,
3
2
1
5 Hz, CH2), 23.9 (d, JCP = 11 Hz, CH2), 20.1 (d, JCP = 30 Hz,
1JPH = 392 Hz).
CH2), 12.0 (s, Me). 19F NMR (C6D5Br): -129.3 (d, 6F, JFF
=
3
20 Hz, o-C6F5), -156.0 (t, 3F, 3JFF = 23 Hz, p-C6F5), -163.0 (m,
2. Yield 95%. Crystals suitable for X-ray diffraction were
grown via slow diffusion of pentane into a CH2Cl2/toluene
solution at 25 ◦C. 1H NMR (CD2Cl2): 5.60 (d, 1H, 1JHP = 408 Hz,
6F, 3JFF = 24 Hz, m-C6F5). 31P { H} NMR (C6D5Br): -0.58 (bs).
1
Anal. calcd. for C30H27BF15P: C, 50.44; H, 3.81. Found: C, 50.24;
H, 3.75.
PH), 2.16 (m, 2H, P(C5H9)), 1.95 (m, 2H, P(C5H9)), 1.69–1.35
(br m, 14H, P(C5H9)). 11B{ H} NMR (CD2Cl2): -15.9 (d, 1JBP
=
1
80 Hz). 13C{ H} NMR (CD2Cl2) partial: 148.7 (dm, 1JCF = 240 Hz,
CF), 140.5 (dm, 1JCF = 254 Hz, CF), 138.0 (dm, 1JCF = 254 Hz,
CF), 117.4 (br s, quat), 32.5 (s, P(C5H9)2), 30.3 (br m, P(C5H9)2),
1
Generation of (tBu2PH)B(C6F5)3 5
An NMR tube was charged with B(C6F5)3 (0.050 g, 0.098 mmol)
and CD2Cl2 (0.75 mL). The NMR tube was capped with a rubber
septum, wrapped with parafilm, and cooled to -78 ◦C in a dry
ice/acetone bath. Using a syringe, tBu2PH (18 mL, 0.097 mmol)
was added to the NMR tube. The NMR tube was then inserted
into an NMR spectrometer pre-cooled to -60 ◦C. Crystals could
only be isolated at low temperature as this species proved to be
29.8 (s, P(C5H9)2), 26.2 (d, 2JCP = 8 Hz, P(C5H9)2), 25.7 (d, 2JCP
=
8 Hz, P(C5H9)2). 19F NMR (CD2Cl2): -129.7 (s, 6F, o-C6F5), -157.9
(t, 3F, 3JFF = 20 Hz, p-C6F5), -164.1 (m, 6F, 3JFF = 20 Hz m-C6F5).
31P NMR (CD2Cl2): 11.2 (dq, 1JPH = 402 Hz, 1JPB = 80 Hz). Anal.
calcd. for C28H19BF15P: C, 49.30; H, 2.81. Found: C, 49.20; H,
2.75.
thermally unstable. 1H NMR (CD2Cl2, 213 K): 5.58 (d, 1H, 1JHP
=
3. Yield 135 mg (97%). 1H NMR (C6D5Br): 1.77 (m, 2H,
397 Hz, PH), 1.19 (d, 18H, 1JHP = 14 Hz, PtBu}. 11B{ H} NMR
1
CH2), 1.34 (m, 2H, CH2), 1.63 (m, 2H, CH2), 0.75 (t, 3H, 3JHH
=
(CD2Cl2, 213 K): -12.8 (br). 13C{ H} NMR (CD2Cl2, 213 K)
1
1560 | Dalton Trans., 2009, 1559–1570
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The Royal Society of Chemistry 2009
©

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partial: 148.2 (dm, 1JCF = 250 Hz, CF), 147.2 (dm, 1JCF = 245 Hz,
CF), 139.4 (dm, 1JCF = 245 Hz, CF), 139.0 (dm, 1JCF = 250 Hz,
2,6)2), 1.62 (m, 2H, CH2CH2O), 1.23 (m, 2H, PCH2CH2). 11B
1
1
NMR (C6D6): -2.8. 13C{ H} NMR (C6D6): 149.0 (dm, JCF
=
1
CF), 138.9 (dm, JCF = 245 Hz, CF), 118.5 (quat), 114.9 (quat),
246 Hz, CF), 146.1 (s, p-C6H2), 143.36 (d, 2JCP = 11 Hz, o-C6H2),
139.28 (dm, 1JCF = 252 Hz, CF), 137.5 (dm, 1JCF = 257 Hz, CF),
1
36.8 (d, JCP = 22 Hz, PtBu), 30.3 (s, PtBu). 19F NMR (CD2Cl2,
3
2
213 K): -126.4 (m, 2F, o-C6F5), -128.7 (d, 2F, JFF = 26 Hz,
132.2 (d, JCP = 11 Hz, m-C6H2), 125.0 (quat, C6F5), 112.1 (d,
o-C6F5), -131.3 (m, 2F, o-C6F5), -156.4 (m, 1F, 3JFF = 22 Hz, p-
1JCP = 80 Hz, quat, C6H2), 65.6 (s, CH2O), 30.9 (s, PCH2CH2),
C6F5), -158.8 (t, 2F, 3JFF = 24 Hz, p-C6F5), -163.7 (m, 2F, 3JFF
=
24.9 (d, JCP = 58 Hz, PCH2CH2), 24.0 (s, CH2CH2O), 21.8 (d,
1
26 Hz, m-C6F5), -164.1 (m, 2F, m-C6F5), -164.7 (m, 2F, m-C6F5).
31P NMR (CD2Cl2, 213 K): 17.4 (d, 1JPH = 394 Hz, PH).
3JCP = 8 Hz, C6H2Me-2,6), 21.1 (s, C6H2Me-4). 19F NMR (C6D6):
-133.9 (d, 3JFF = 23 Hz, 6F, o-C6F5), -162.2 (s, 3F, p-C6F5), -165.9
1
(s, 6F, m-C6F5). 31P { H} NMR (C6D6): -12.0. Anal. calcd. for
Synthesis of (Mes2PH)B(C6F5)3 7
C40H31BF15OP: C, 56.23; H, 3.66. Found: C, 56.48; H, 3.83.
A clear yellow solution of B(C6F5)3 (1.50 g, 2.93 mmol) and
dimesityl phosphine (0.800 g, 2.96 mmol) in toluene (10 mL) was
prepared. The reaction was cooled to -35 ◦C and allowed to stir
for 12 h during which time the solution turned red and a white
precipitate formed. Pentane (10 mL) was added and the mixture
filtered. The resulting red filtrate was evaporated to dryness to
15. Yield 302 mg (98%). Crystals suitable for X-ray diffraction
were grown from a conce◦ntrated solution in CH2Cl2/toluene
1
layered with pentane at 25 C. H NMR (CD2Cl2): 3.21 (m, 2H,
CH2O), 2.46–2.40 (br m, 2H, PCH2), 2.23–2.15 (m, 3H, Cy),
1.89–1.80 (br m, 12H, Cy), 1.72–1.66 (m, 2H, PCH2CH2), 1.65
(m, 2H, CH2CH2O), 1.50–1.41 (br m, 6H, Cy), 1.36–1.26 (br m,
1
give the product as a pink solid. Yield 0.475 g (20%). H NMR
1
1
12H, Cy). 11B{ H} NMR (CD2Cl2): -2.1. 13C{ H} NMR (CD2Cl2)
(CD2Cl2): 6.88 (s, 4H, P(C6H2)2), 6.64 (bs, 1H, PH), 2.26 (s, 6H,
partial: 148.6 (dm, 1JCF = 240 Hz, CF), 138.8 (dm, 1JCF = 250 Hz,
1
P(C6H2Me-4)2), 2.15 (s, 12H, P(C6H2Me-2,6)2). 11B{ H} NMR
1
CF), 137.0 (dm, JCF = 245 Hz, CF), 125.9 (br s, quat), 63.8 (s,
1
(CD2Cl2): 23.6 (bs). 13C{ H} NMR (CD2Cl2, partial): 148.9 (dm,
3
1
CH2CH2O), 32.8 (d, JCP = 17 Hz, CH2CH2O), 30.5 (d, JCP
=
1
1JCF = 245 Hz, CF), 143.0 (dm, JCF = 250 Hz, CF), 142.9 (d,
42 Hz, Cy), 27.5 (s, Cy), 27.2 (d, 3JCP = 11 Hz, Cy), 25.9 (s, Cy).
21.9 (s, PCH2CH2), 16.2 (d, 1JCP = 44 Hz, PCH2CH2). 19F NMR
2JCP = 9 Hz, o-C6H2), 140.9 (s, p-C6H2), 138.1 (dm, 1JCF = 250 Hz,
3
1
CF), 130.3 (d, JCP = 5 Hz, m-C6H2), 120.7 (d, JCP = 80 Hz,
P-C6H2), 23.1 (d, 3JCP = 17 Hz, C6H2Me-2,6), 21.2 (s, C6H2Me-4).
19F NMR (CD2Cl2): -128.0 (s, 6F, o-C6F5), -151.5 (s, 3F, p-C6F5),
3
(CD2Cl2): -134.5 (d, 6F, JFF = 23 Hz, o-C6F5), -163.8 (t, 3F,
3JFF = 23 Hz, p-C6F5), -167.4 (t, 6F, JFF = 20 Hz, m-C6F5).
3
31P{ H} NMR (CD2Cl2): 32.1. Anal. calcd. for C40H41BF15OP: C,
1
1
-163.0 (s, 6F, m-C6F5). 31P { H} NMR (CD2Cl2): -67.7 (br). Anal.
55.57; H, 4.78. Found: C, 56.10; H, 4.98. Mp: 200–205 ◦C.
calcd. for C36H23BF15P: C, 55.27; H, 2.96. Found: C, 55.34; H, 3.24.
Synthesis of Et3P(C4H8O)B(C6F5)3 14
Synthesis of tBu2PH(C4H8O)B(C6F5)3 12,
Mes2PH(C4H8O)B(C6F5)3 13, Cy3P(C4H8O)B(C6F5)3 15
(Et3P)B(C6F5)3 (0.100 g, 0.16 mmol) was dissolved in THF (10 mL)
and transferred to a 50 mL reaction bomb. The solution was heated
to 80 ◦C for 5 h. Upon cooling all volatiles were removed in vacuo
to give the ring-opened product as a white solid. Yield 90 mg
(81%). Crystals suitable for X-ray diffraction were grown from a
concentrated solution in CH2Cl2/toluene layered with pentane at
These compounds were prepared in a similar fashion and thus only
one preparation is detailed. To a faint yellow solution of B(C6F5)3
(0.350 g, 0.684 mmol) in THF (4 mL) was added tBu2PH (0.100 g,
0.684 mmol) via syringe and the reaction mixture was left to stir
for 72 h at 25 ◦C. All volatiles were removed in vacuo and the
resulting white solid was dried under vacuum for 12 h.
◦
1
25 C. H NMR (CD2Cl2): 3.23 (m, 2H, CH2CH2O), 2.59–2.49
(br m, 2H, PCH2CH2), 2.11–1.99 (dq, 6H, 3JHP = 12 Hz, 3JHH
=
12. Yield 0.404 g (81%). Crystals suitable for X-ray diffraction
8 Hz, CH2), 1.83 (m, 2H, PCH2CH2), 1.66 (m, 2H, CH2CH2O),
were grown from a layered THF/C6D6/pentane solution at 25 ◦C.
3
3
1
1.32–1.23 (dt, 9H, JHP = 18 Hz, JHH = 8 Hz, Me). 11B{ H}
1
3
1H NMR (THF-d8): 5.60 (dt, 1H, JHP = 453 Hz, JHH = 4 Hz,
NMR (CD2Cl2): -2.9. 13C{ H} NMR (CD2Cl2): 148.5 (dm, 1JCF
240 Hz, CF), 138.7 (dm, 1JCF = 246 Hz, CF), 137.2 (dm, 1JCF
250 Hz, CF), 124.9 (br s, quat), 63.1 (s, CH2CH2O), 31.9 (d, 3JCP
=
=
=
=
1
PH), 3.24 (t, 2H, 3JHH = 5 Hz, CH2O), 2.64 (m, 2H, PCH2), 1.99
(m, 2H, PCH2CH2), 1.67 (m, 2H, CH2CH2O), 1.45 (d, 18H, 3JHP
=
16 Hz, tBu). 11B NMR (C6D6): -2.9. 13C{ H} NMR (C6D6): 149.2
1
14 Hz, CH2CH2O), 20.2 (d, 2JCP = 7 Hz, PCH2CH2), 17.8 (d, 1JCP
(dm, 1JCF = 230 Hz, CF), 139.3 (dm, 1JCF = 244 Hz, CF), 137.4
47 Hz, PCH2CH2), 12.3 (d, JCP = 50 Hz, CH2), 5.7 (s, Me). 19F
NMR (CD2Cl2): -134.8 (d, 6F, 3JFF = 20 Hz, o-C6F5), -163.5 (m,
3F, 3JFF = 20 Hz, p-C6F5), -167.3 (m, 6F, 3JFF = 20 Hz, m-C6F5).
1
1
(dm, JCF = 237 Hz, CF), 125.7 (quat, C6F5), 64.4 (s, CH2O),
1
3
33.6 (d, JCP = 35.9 Hz, quat, PtBu), 32.79 (d, JCP = 11 Hz,
1
CH2CH2O), 27.1 (s, tBu), 26.93 (m, PCH2CH2), 15.0 (d, JCP
=
31P{ H} NMR (CD2Cl2): 38.7. Anal. calcd. for C28H23BF15OP: C,
1
39 Hz, PCH2CH2). 19F NMR (C6D6): -133.9 (d, 3JFF = 23 Hz, 6F,
47.89; H, 3.30. Found: C, 48.11; H, 3.52. Mp: 165–170 ◦C.
o-C6F5), -164.78 (t, 3JFF = 11 Hz, 3F, p-C6F5), -168.02 (t, 3JFF
=
20 Hz, 6F, m-C6F5). 31P NMR (C6D6): 50.9 (1JHP = 453 Hz). Anal.
calcd. for C30H27BF15OP: C, 49.34; H, 3.73. Found: C, 48.85; H,
3.58.
Generation of [Li(THF)2][tBu2P(C4H8O)B(C6F5)3] 16
Method A. The species 12 (0.207 g, 0.283 mmol) was dissolved
in THF (5 mL) and cooled to -35 ◦C. To this reaction mixture was
added tBuLi in hexanes (0.18 mL, 0.301 mmol) via syringe. The
mixture became pale yellow and then colorless and was allowed
to warm to room temperature over 30 min, during which time the
solution again became pale yellow. The reaction was stirred for a
13. Yield 0.497 g (79%). Crystals suitable for X-ray diffraction
◦
1
were grown from a concentrated solution in C6D6 at 25 C. H
NMR (C6D6): 7.33 (dt, 1H, 1JHP = 531 Hz, 3JHH = 7 Hz, PH), 6.40
(d, 4JHP = 4 Hz, 4H, P(C6H2)), 3.48 (m, 2H, CH2O), 2.85 (m, 2H,
PCH2CH2), 1.90 (s, 6H, P(C6H2Me-4)2), 1.87 (s, 12H, P(C6H2Me-
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further 2 h. All volatiles were removed in vacuo and the resulting
white solid was dried under vacuum for 12 h. Yield 0.180 g (73%).
was left to stir for 24 h at 25 ◦C. All volatiles were removed in
vacuo and the resulting cream-colored solid was washed with Et2O
(2 mL) and pentane (2 mL) and then dried under vacuum for 24 h.
Method B. LiPtBu2 (0.100 g◦, 0.657 mmol) was dissolved in
THF (4 mL) and cooled to -78 C in a dry ice/acetone bath. A
solution of B(C6F5)3 (0.340 g, 0.664 mmol) in THF (2 mL) was then
added to the phosphide via syringe over the course of 15 min. The
yellow solution was warmed to room temperature over the course
of 6 h and then further stirred at room temperature overnight. All
volatiles were removed in vacuo to give a white sticky solid. The
residue was triturated with hexanes (10 mL), the solvent decanted
and the residual solvent removed in vacuo three times. The resulting
off-white solid was dried under vacuum overnight. Yield 0.350 g
(65%).1H NMR (THF-d8): 4.02 (m, 2H, CH2CH2O), 3.60 (s, 8H,
18. Yield 0.188 g (62%). 1H NMR (C6D6): 7.28 (m, 4H, PPh2),
3
7.05 (m, 6H, PPh2), 3.38 (t, JHH = 7 Hz, 2H, CH2CH2O), 3.25
3
(m, 8H, THF), 1.85 (t, JHH = 7 Hz, 2H, PCH2CH2), 1.42 (m,
2H, CH2CH2O), 1.26 (m, 2H, PCH2CH2), 1.19 (s, 8H, THF). 11
B
NMR (C6D6): -2.7. 13C{ H} NMR (C6D6) partial: 148.7 (dm,
1JCF = 232 Hz, CF), 139.59 (dm, 1JCF = 237 Hz, CF), 137.22 (dm,
1JCF = 249 Hz, CF), 133.41, 132.75, 131.57, 128.81 (quat, C6H5),
1
3
68.37 (s, THF), 65.13 (s, CH2CH2O), 31.96 (d, JCP = 10 Hz,
CH2CH2O), 27.59 (d, 1JCP = 10 Hz, PCH2CH2), 25.15 (s, THF),
22.56 (d, 2JCP = 15 Hz, PCH2CH2). 19F NMR (C6D6): -137.5 (d,
3JFF = 14 Hz, 6F, o-C6F5), -159.1 (t, 3JFF = -20 Hz, 3F, p-C6F5),
THF), 2.18 (m, 2H, PCH2CH2), 1.84 (m, 2H, CH2CH2O), 1.90
3
(s, 8H, THF), 1.75 (m, 2H, PCH2CH2), 1.46 (d, 18H, JHP
=
1
3
-164.2 (t, JFF = 20 Hz, 6F, m-C6F5). 31P NMR (C6D6): -18.9.
11 Hz, tBu). H NMR (C6D6): 3.55 (s, 8H, THF), 3.45 (m, 2H,
CH2CH2O), 1.75 (s, 8H, THF), 1.40 (m, 2H, PCH2CH2), 1.29 (m,
Anal. calcd. for C42H32BF15LiO3P: C, 54.81; H, 3.72. Found: C,
54.77; H, 4.01.
3
2H, CH2CH2O), 1.08 (m, 2H, PCH2CH2), 0.96 (d, 18H, JHP
=
11 Hz, tBu). 11B NMR (THF-d8): -2.9. 13C{ H} NMR (THF-d8):
1
149.3 (dm, 1JCF = 235 Hz, CF), 139.2 (dm, 1JCF = 242 Hz, CF),
19. Yield 0.844 g (80%). Crystals suitable for X-ray diffraction
were grown from a layered CH2Cl2/pentane solution at 25 ◦C. 1H
NMR (CD2Cl2): 6.75 (s, 4H, C6H2), 3.72 (s, 8H, THF), 3.22 (m,
2H, CH2CH2O), 2.33 (m, 2H, PCH2CH2), 2.20 (s, 18H, Me), 1.85
(s, 8H, THF), 1.49 (m, 2H, CH2CH2O), 1.14 (m, 2H, PCH2CH2).
1
137.2 (dm, JCF = 244 Hz, CF), 126.61 (quat, PC6F5), 64.5 (s,
1
3
CH2CH2O), 35.4 (d, JCP = 30 Hz, quat, tBu), 31.8 (d, JCP
=
=
20 Hz, CH2CH2O), 30.42 (d, 2JCP = 9 Hz, tBu), 28.31 (d, 1JCP
26 Hz, PCH2CH2), 22.38 (d, 2JCP = 20 Hz PCH2CH2). 19F NMR
3
(THF-d8): -136.7 (m, 6F, o-C6F5), -159.6 (t, JPF = 20 Hz, 3F,
1
11B NMR (CD2Cl2): -3.1. 13C{ H} NMR (CD2Cl2): 148.4 (dm,
p-C6F5), -164.1 (s, 6F, m-C6F5). 31P NMR (THF-d8): 27.4. Anal.
calcd. for C40H42BF15O3PLi: C, 53.12; H, 4.68. Found: C, 53.00;
H, 4.83.
1JCF = 240 Hz, CF), 142.2 (d, 2JCP = 13 Hz, o-C6H2), 139.7 (dm,
1JCF = 240 Hz, CF), 138.1 (s, p-C6H2), 137.3 (dm, 1JCF = 240 Hz,
CF), 130.4 (s, m-C6H2), 122.5, 118.0 (quat, C6F5, C6H2), 68.9 (s,
THF), 65.6 (s, CH2CH2O), 33.4 (d, 2JCP = 14 Hz, PCH2CH2), 28.2
(d, 1JCP = 14 Hz, PCH2CH2), 25.9 (s, THF), 23.9 (s, CH2CH2O),
23.2 (d, 3JCP = 14 Hz, C6H2Me-2,6), 21.0 (s, C6H2Me-4). 19F NMR
Generation of [Li][tBu2P(C4H8O)B(C6F5)3] 17
The species 12 (0.200 g, 0.274 mmol) was slurried in toluene
◦
(CD2Cl2): -137.6 (d, 3JFF = 20 Hz, 6F, o-C6F5), -161.0 (t, 3JFF
=
(8 mL) and cooled to -35 C. To this mixture was added tBuLi
20 Hz, 3F, p-C6F5), -165.6 (t, 3JFF = 20 Hz, 6F, m-C6F5). 31P NMR
(CD2Cl2): -21.4. Anal. calcd. for C48H46BF15LiO3P: C, 57.39; H,
4.62. Found: C, 57.57; H, 5.25.
in hexanes (0.16 mL, 0.274 mmol) via syringe. The reaction was
◦
allowed to warm to 25 C over 30 min, at which time all solids
dissolved. The reaction was stirred for a further 2 h. All volatiles
were removed in vacuo and the resulting solid was dried under
vacuum for 12 h, giving the product as an off-white solid. Yield
0.180 g (89%). 1H NMR (toluene-d8): d 3.18 (br s, 2H, CH2CH2O),
1.35 (m, 2H, PCH2CH2), 1.30 (m, 2H, PCH2CH2CH2CH2O), 0.95
Synthesis of [Li][tBu2P(C4H8OB(C6F5)3)2] 20
To a faint yellow solution of B(C6F5)3 (0.673 g, 1.314 mmol)
in THF (2 mL) was added LiPtBu2 (0.100 g, 0.657 mmol) in
THF (4 mL) and the reaction mixture was left to stir for 12 h
at 25 ◦C. All volatiles were removed in vacuo and the resulting
white solid was dried under vacuum for 24 h. Yield 0.776 g (89%).
Crystals suitable for X-ray di◦ffraction were grown from a layered
THF/pentane solution at 25 C. 1H NMR (THF-d8): 3.22 (t, 4H,
3JHH = 5 Hz, CH2CH2O), 2.51 (m, 4H, PCH2CH2CH2CH2O),
1.92 (m, 4H, PCH2CH2), 1.65 (m, 4H, CH2CH2O), 1.35 (d, 18H,
3
(m, 2H, PCH2CH2), 0.88 (d, 18H, JHP = 11.60 Hz, tBu). 11B
1
NMR (toluene-d8): -2.9. 13C{ H} NMR (toluene-d8): 148.9 (dm,
1JCF = 235 Hz, CF), 140.11 (dm, 1JCF = 250 Hz, CF), 137.98 (dm,
1JCF = 238 Hz, CF), 126.0 (quat, CF), 64.1 (s, CH2CH2O), 31.7
1
3
(d, JCP = 32 Hz, quat, tBu), 30.9 (d, JCP = 7 Hz, CH2CH2O),
2
1
29.5 (d, JCP = 10 Hz, tBu), 22.7 (d, JCP = 17 Hz, PCH2CH2),
19.6 (s, PCH2CH2). 19F NMR (toluene-d8): -139.2 (s, 6F, o-C6F5),
-158.3 (t, 3JFF = 20 Hz, 3F, p-C6F5), -163.3 (t, 3JFF = 20 Hz, 6F,
m-C6F5). Li NMR (toluene-d8): 1.3–0.5 (dm, JLiP = 75 Hz). 31P
7
1
3JHP = 14 Hz, tBu). 11B NMR (THF-d8): -2.9. 13C{ H} NMR
NMR (toluene-d8): 26.7 (q, JPLi = 75 Hz).
1
1
(THF-d8): 149.2 (dm, JCF = 246 Hz, CF), 139.2 (dm, JCF
=
244 Hz, CF), 137.5 (dm, 1JCF = 245 Hz, CF), 126.22 (quat, C6F5),
Synthesis of [Li(THF)2][Ph2P(C4H8O)B(C6F5)3] 18,
[Li(THF)2][Mes2P(C4H8O)B(C6F5)3] 19
1
64.5 (s, CH2CH2O), 35.3 (d, JCP = 38 Hz, quat, PtBu), 33.4 (d,
3JCP = 12 Hz, CH2CH2O), 27.5 (s, tBu), 26.6 (m, PCH2CH2), 17.8
1
These compounds were prepared in a similar fashion and thus
one preparation is detailed. To a faint yellow solution of B(C6F5)3
(0.200 g, 0.391 mmol) in toluene (2 mL) was added THF (0.16 mL,
1.97 mmol). LiPPh2 (0.075 g, 0.390 mmol) in toluene (2 mL) and
THF (0.16 mL, 1.97 mmol) was added and the reaction mixture
(d, JCP = 40 Hz, PCH2CH2). 19F NMR (THF-d8): -133.9 (d,
3JFF = 23 Hz, 12F, o-C6F5), -165.2 (t, 3JFF = 11 Hz, 6F, p-C6F5),
-168.2 (t, 3JFF = 20 Hz, 12F, m-C6F5). 31P NMR (THF-d8): 45.3.
Anal. calcd. for C52H34B2F30LiO2P: C, 47.30; H, 2.60. Found: C,
47.58; H, 2.89.
1562 | Dalton Trans., 2009, 1559–1570
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Synthesis of [Li(THF)4][Mes2P(C4H8OB(C6F5)3)2] 21
23. Yield 0.510 g (73%). 1H NMR (CD2Cl2): 6.50 (d, 1H,
1JHP = 480 Hz, PH), 3.80 (m, 2H, PCy2), 2.09–1.27 (br m,
To a faint yellow solution of B(C6F5)3 (0.200 g, 0.391 mmol) in
THF (5 mL) was added dropwise an orange solution of LiPMes2
(0.054 g, 0.195 mmol) in THF (5 mL). The reaction mixture
immediately went colorless followed by a gradual color change
to red. The reaction mixture was allowed to stir for 12 h, at which
time all volatiles were remove in vacuo. Pentane (5 mL) was added
and the reaction stirred for 10 min. All volatiles were removed in
vacuo and the residue dried under vacuum for 24 h yielding the
1
1
20H, PCy2). 11B{ H} NMR (CD2Cl2): -0.2 (br). 13C{ H} NMR
1
(CD2Cl2) partial: 149.3 (dm, JCF = 250 Hz, CF), 148.37 (dm,
1JCF = 240 Hz, CF), 146.3 (dm, 1JCF = 250 Hz, CF), 139.4 (dm,
1JCF = 250 Hz, CF), 137.2 (dm, 1JCF = 250 Hz, CF), 129.1, 122.7,
1
87.1 (quat), 33.3 (d, JCP = 41 Hz, PCy2), 28.3 (s, PCy2), 27.2 (s,
PCy2), 26.4 (s, PCy2), 26.2 (d, 3JCP = 15 Hz, PCy2), 25.2 (s, PCy2).
19F NMR (CD2Cl2): -129.2 (s, 2F, C6F4), -131.9 (s, 2F, C6F4),
-135.8 (d, 4F, 3JFF = 19 Hz, o-C6F5), -161.6 (t, 2F, 3JFF = 20 Hz,
p-C6F5), -166.6 (t, 4F, 3JFF = 20 Hz, m-C6F5), -191.5 (br, 1F, BF).
1
product as a tan solid. Yield 0.844 g (80%). H NMR (CD2Cl2):
4
6.99 (d, JHP = 4 Hz, 4H, C6H2), 3.69 (s, 16H, THF), 3.15 (m,
1
31P { H} NMR (CD2Cl2): 11.5 (m). Anal. calcd. for C30H23BF15P:
4H, CH2CH2O), 2.75 (m, 4H, PCH2CH2), 2.32 (s, 6H, C6H2Me-
4), 2.17 (s, 12H, C6H2Me-2,6), 1.85 (s, 16H, THF), 1.48 (m, 4H,
CH2CH2O), 1.36 (m, 4H, PCH2CH2). 11B NMR (CD2Cl2): -3.0.
C, 50.73; H, 3.26. Found: C, 50.65; H, 3.22.
27. Heated to reflux in toluene for 24 h. Yield 0.510 g (77%).
1H NMR (CD2Cl2): 7.98–7.89 (m, 3H, P(C6H5)), 7.76–7.69 (m,
1
1
13C{ H} NMR (CD2Cl2): 148.4 (dm, JCF = 240 Hz, CF), 145.8
2
1
1
(s, p-C6H2), 142.2 (d, JCP = 10 Hz, o-C6H2), 139.3 (dm, JCF
=
=
2H, P(C6H5)), 7.39 (d, 1H, JHP = 487 Hz, PH), 1.54 (d, 9H,
1
3
1
1JHP = 21 Hz, PtBu). 11B NMR (CD2Cl2): 0.4 (d, JBF = 63 Hz).
240 Hz, CF), 137.3 (dm, JCF = 240 Hz, CF), 133.5 (d, JCP
10 Hz, m-C6H2), 123.4 (quat, C6F5), 117.1 (d, 1JCP = 88 Hz, quat,
C6H2), 68.7 (s, THF), 64.8 (s, CH2CH2O), 32.3 (d, 2JCP = 13 Hz,
1
13C{ H} NMR (CD2Cl2) partial: 149.9 (dm, 1JCF = 246 Hz, C6F4),
147.9 (dm, 1JCF = 240 Hz, C6F5), 145.5 (dm, 1JCF = 250 Hz, C6F5),
140.0 (dm, 1JCF = 240 Hz, C6F4), 137.0 (dm, 1JCF = 246 Hz, C6F5),
136.9 (s, Ph), 134.4 (d, 3JCP = 11 Hz, Ph), 131.3 (d, 2JCP = 12 Hz,
Ph), 112.41 (d, 1JCP = 82 Hz, PPh), 35.0 (d, 1JCP = 40 Hz, PtBu),
26.0 (s, tBu). 19F NMR (CD2Cl2): -128.7 (s, 2F, C6F4), -130.3 (m,
2F, C6F4), -135.8 (m, 4F, o-C6F5), -161.5 (t, 2F, 3JFF = 20 Hz, p-
C6F5), -166.6 (t, 4F, 3JFF = 22 Hz, m-C6F5), -191.4 (br s, 1F, BF).
1
PCH2CH2), 27.2 (d, JCP = 44 Hz, PCH2CH2), 25.9 (s, THF),
23.5 (d, 3JCP = 14 Hz, C6H2Me-2,6), 21.2 (s, C6H2Me-4), 21.0 (s,
CH2CH2O). 19F NMR (CD2Cl2): -136.1 (s, 12F, o-C6F5), -161.8
(s, 6F, p-C6F5), -166.0 (m, 12F, m-C6F5). 31P NMR (CD2Cl2): 30.9.
Anal. calcd. for C78H70B2F30LiO6P: C, 54.06; H, 4.07. Found: C,
53.58; H, 3.89.
1
31P { H} NMR (CD2Cl2): 14.7 (m). Anal. calcd. for C28H15BF15P:
C, 49.59; H, 2.23. Found: C, 49.50; H, 2.33.
Synthesis of (C5H9)2PH(C6F4)BF(C6F5)2 22,
Cy2PH(C6F4)BF(C6F5)2 23, (tBu)(Ph)PH(C6F4)BF(C6F5)2 27,
(tBu)(Mes)PH(C6F4)BF(C6F5)2 28, nBu3P(C6F4)BF(C6F5)2 31,
Ph3P(C6F4)BF(C6F5)2 33, (p-FC6H4)3P(C6F4)BF(C6F5)2 34,
(o-C6H4OMe)3P(C6F4)BF(C6F5)2 35
28. Heated to reflux in toluene for 24 h. Yield 0.450 g
(64%). Crystals suitable for X-ray diffraction were grown via slow
diffusion of pentane into a CH2Cl2/toluene solution of the product
at 25 ◦C (open to air in wet solvents). 1H NMR (THF-d8): 8.21 (d,
1H, 1JHP = 505 Hz, PH), 7.17 (d, 4JHP = 7 Hz, 2H, P(C6H2)), 2.47
(br s, 6H, P(C6H2Me-2,6)), 2.32 (s, 3H, P(C6H2Me-4)), 1.61 (d, 9H,
3JHP = 21 Hz, PtBu). 11B NMR (THF-d8): 0.4 (d, 1JBF = 59 Hz).
These compounds were prepared in a similar fashion and thus
one preparation is detailed. Minor modifications are indicated.
To a clear yellow solution of B(C6F5)3 (0.556 g, 1.09 mmol) in
toluene (20 mL) was added (C5H9)2PH (0.199 g, 1.18 mmol) in
toluene (5 mL) via syringe. The reaction was heated to 130 ◦C
in a sealed glass bomb with a Teflon cap for 24 h. During such
time the reaction turned yellow in color and a white precipitate
formed. Pentane (40 mL) was added and the mixture filtered,
washed with pentane (3 ¥ 10 mL), and dried in vacuo for 1 h.
The product was collected as a white solid. Yield 0.560 g (76%).
Crystals suitable for X-ray diffraction were grown from a layered
dichloromethane/benzene/pentane solution at 25 ◦C.
1
13C{ H} NMR (THF-d8) partial: 149.9 (dm, 1JCF = 230 Hz, CF),
1
149.0 (dm, JCF = 240 Hz, CF), 148.1 (s, p-C6H2), 146.6 (dm,
1JCF = 240 Hz, CF), 145.1 (d, 2JCP = 11 Hz, o-C6H2), 139.8 (dm,
1
1JCF = 245 Hz, CF), 137.3 (dm, JCF = 275 Hz, CF), 132.6 (d,
3JCP = 10 Hz, m-C6H2), 110.6 (d, 1JCP = 77 Hz, P-C6H2), 37.8 (d,
1JCP = 40 Hz, PtBu), 26.4 (s, tBu), 22.7 (d, 3JCP = 7 Hz, C6H2Me-
2,6), 21.0 (s, C6H2Me-4). 19F NMR (THF-d8): -123.0 (br s, 4F,
3
C6F4), -135.2 (m, 4F, o-C6F5), -163.4 (t, 2F, JFF = 20 Hz, p-
C6F5), -167.8 (t, 4F, 3JFF = 23 Hz, m-C6F5), -193.2 (br s, 1F, BF).
1
31P { H} NMR (THF-d8): -2.9 (m). Anal. calcd. for C31H21BF15P:
22. 1H NMR (THF-d8): 7.24 (d, 1H, 1JHP = 508 Hz, PH), 3.11
C, 51.69; H, 2.94. Found: C, 51.36; H, 3.20.
(m, 2H, P(C5H9)), 2.25 (m, 2H, P(C5H9)), 2.07 (m, 2H, P(C5H9)),
1.86–1.68 (br m, 12H, P(C5H9)). 11B{ H} NMR (THF-d8): -0.1
31. Heated at 125 ◦C for 2 days. Yield 205 mg (74%). Crystals
suitable for X-ray diffraction were grown via slow diffusion of
pentane into a CH2Cl2/toluene solution at 25 ◦C. 1H NMR
(C6D5Br): 2.22 (m, 6H, CH2), 1.25 (m, 12H, CH2CH2), 0.74
1
1
1
(d, JBF = 54 Hz). 13C{ H} NMR (THF-d8) partial: 148.8 (dm,
1JCF = 255 Hz, CF), 148.1 (dm, 1JCF = 240 Hz, CF), 146.3 (dm,
1JCF = 255 Hz, CF), 138.9 (dm, 1JCF = 252 Hz, CF), 136.6 (dm,
1
1
1
1JCF = 252 Hz, CF), 123.3 (br m, quat), 92.1 (m, JCP = 70 Hz,
(m, 9H, Me). 11B{ H} NMR (C6D5Br): -0.8 (bs). 13C{ H} NMR
quat), 30.6 (d, 1JCP = 45 Hz, P(C5H9)2), 29.9 (s, P(C5H9)2), 29.7 (s,
P(C5H9)2), 27.2 (d, 3JCP = 12 Hz, P(C5H9)2), 26.4 (d, 3JCP = 12 Hz,
P(C5H9)2). 19F NMR (THF-d8): -129.8 (s, 2F, C6F4), -133.5 (s,
2F, C6F4), -135.3 (m, 4F, o-C6F5), -163.4 (t, 2F, 3JFF = 20 Hz, p-
C6F5), -167.9 (t, 4F, 3JFF = 20 Hz, m-C6F5), -193.3 (br m, 1F, BF).
(C6D5Br) partial: 149.2 (dm, JCF = 250 Hz, CF), 148.2 (dm,
1
1JCF = 240 Hz, CF), 146.5 (dm, 1JCF = 250 Hz, CF), 139.2 (dm,
1JCF = 245 Hz, CF), 137.0 (dm, JCF = 250 Hz, CF), 92.4 (dt,
1
1JCP = 78 Hz, 2JCF = 20 Hz, quat), 23.6 (br m, CH2CH2), 20.0 (d,
1JCP = 50 Hz, CH2), 13.0 (s, Me). 19F NMR (C6D5Br): -129.2 (s,
2F, C6F4), -133.5 (m, 2F, C6F4), -135.1 (m, 4F, o-C6F5), -160.5
1
31P{ H} NMR (THF-d8): 12.7 (m). Anal. calcd. for C28H19BF15P:
3
C, 49.30; H, 2.81. Found: C, 48.76; H, 2.93.
(t, 2F, JFF = 20 Hz, p-C6F5), -166.0 (m, 4F, m-C6F5), -190.3
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©

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unidentified. 1H NMR (CD2Cl2): 7.9–7.4 (m, 10H, Ph), 7.5 (d, 1H,
1
(br s, 1F, BF). 31P { H} NMR (C6D5Br): 33.1 (br). Anal. calcd. for
1
PH). 11B{ H} NMR (CD2Cl2): -1.0 (br s). 19F NMR (CD2Cl2):
C30H27BF15P: C, 50.44; H, 3.81. Found: C, 50.24; H, 3.63.
-129.3 (m, 2F, C6F4), -132.5 (m, 2F, C6F4), -135.8 (m, 4F, o-
C6F5), -160.7 (m, 2F, p-C6F5), -166.1 (m, 4F, m-C6F5), -194.8
33. Heated at 125 ◦C for 2 days. Yield 110 mg (73%). Crystals
suitable for X-ray diffraction were grown via slow evaporation
1
(br s, 1F, BF). 31P { H} NMR (CD2Cl2): 6.5.
◦
1
of a concentrated bromobenzene solution at 25 C. H NMR
(C6D5Br): 7.44–7.14 (m, 3H, Ph), 7.28–7.23 (m, 12H, Ph). 11B{ H}
1
Generation of Et3P(C6F4)BF(C6F5)2 29
NMR (C6D5Br): -0.3 (br s). 13C{ H} NMR (C6D5Br) partial:
1
149.5 (dm, 1JCF = 245 Hz, CF), 148.5 (dm, 1JCF = 240 Hz, CF),
146.4 (dm, 1JCF = 250 Hz, CF), 139.3 (dm, 1JCF = 245 Hz, CF),
136.5 (dm, 1JCF = 250 Hz, CF), 135.5 (d, 4JCP = 3 Hz, Ph), 133.5
In a re-sealable J.Young NMR tube (Et3P)B(C6F5)3 (0.050 mg,
0.056 mmol) was dissolved in C6D5Br (0.75 mL) and heated to
120 ◦C for 24 h. Quantitative product formation was observed
by NMR spectroscopy although this species was not isolated in
(d, 3JCP = 11 Hz, Ph), 130.2 (d, 2JCP = 14 Hz, Ph), 117.0 (d, 1JCP
=
92 Hz, quat Ph). 19F NMR (C6D5Br): -127.9 (m, 2F, C6F4), -128.0
(m, 2F, C6F4), -133.6 (m, 4F, o-C6F5), -160.7 (t, 2F, 3JFF = 20 Hz,
1
analytically pure form. H NMR (C6D5Br): 2.04–1.93 (m, 6H,
2JHP = 20 Hz, 3JHH = 7 Hz, CH2), 0.85–0.76 (dt, 9H, 3JHP = 21 Hz,
p-C6F5), -165.5 (m, 4F, m-C6F5), -193.0 (br s, 1F, BF). 31P{ H}
1
1
1
3JHH = 7 Hz, Me). 11B{ H} NMR (C6D5Br): 0.5 (br). 13C{ H}
1
NMR (C6D5Br): 15.1. Anal. calcd. for C36H15BF15P: C, 55.84; H,
1.95. Found: 55.65; H, 1.87.
NMR (C6D5Br) partial: 149.7 (dm, JCF = 248 Hz, CF), 148.21
(dm, 1JCF = 240 Hz, CF), 146.3 (dm, 1JCF = 255 Hz, CF), 139.3
1
1
◦
(dm, JCF = 248 Hz, CF), 137.0 (dm, JCF = 250 Hz, CF), 91.0
34. Heated at 125 C for 12 h. Yield 122 mg (75%). Crystals
suitable for X-ray diffraction were grown via slow evaporation
1
2
1
(dt, JCP = 80 Hz, JCF = 18 Hz, quat), 13.7 (d, JCP = 48 Hz,
CH2), 5.3 (d, JCP = 5 Hz, Me). 19F NMR (C6D5Br): -129.8 (m,
2
◦
1
of a concentrated bromobenzene solution at 25 C. H NMR
2F, C6F4), -134.0 (m, 2F, C6F4), -135.8 (m, 6F, 3JFF = 20 Hz, o-
(C6D5Br): 7.25–7.15 (ddd, 6H, 3JHF = 13 Hz, 3JHH = 8 Hz, 4JHP
=
C6F5), -161.1 (m, 3F, 3JFF = 21 Hz, p-C6F5), -166.2 (m, 6F, 3JFF
=
5 Hz, Ph), 6.85–6.78 (ddd, 6H, 3JHP = 8 Hz, 3JHH = 8 Hz, 4JHF
=
20 Hz, m-C6F5), -192.2 (br s, 1F, BF). 31P { H} NMR (C6D5Br):
1
3 Hz, Ph). 11B{ H} NMR (C6D5Br): -0.2 (br s). 13C{ H} NMR
1
1
39.1.
(C6D5Br) partial: 167.3 (d, 1JCF = 260 Hz, CF), 149.9 (dm, 1JCF
245 Hz, CF), 148.7 (dm, 1JCF = 235 Hz, CF), 139.9 (dm, 1JCF
=
=
=
1
2
Synthesis of Cy3P(C6F4)BF(C6F5)(Ph) 37
246 Hz, CF), 137.1 (dm, JCF = 247 Hz, CF), 137.0 (dd, JCP
13 Hz, 3JCF = 11 Hz, Ph), 118.6 (dd, 2JCF = 16 Hz, 3JCP = 13 Hz,
Ph), 113.04 (d, 1JCP = 97 Hz, quat Ph). 19F NMR (C6D5Br): -97.8
(s, 3F, F-C6H4), -128.1 (m, 4F, C6F4), -134.9 (m, 4F, o-C6F5),
A clear yellow solution of 36 (0.100 g, 0.237 mmol) and Cy3P
(0.067 g, 0.240 mmol) in toluene (20 mL) was allowed to stir for
12 h at25 ◦C duringwhichtime a whiteprecipitate formed. Pentane
(10 mL) was added and the mixture filtered and dried in vacuo for
1 h. The product was collected as a white solid. Yield 0.110 g (80%).
Crystals suitable for X-ray diffraction were grown from a layered
dichloromethane/pentane solution at 25 ◦C. 1H NMR (CD2Cl2):
3
-160.4 (t, 2F, JFF = 20 Hz, p-C6F5), -165.4 (m, 4F, m-C6F5),
-192.3 (br s, 1F, BF). 31P { H} NMR (C6D5Br): 14.1 (s). Anal.
1
calcd. for C36H12BF18P: C, 52.21; H, 1.46. Found: C, 53.05; H,
2.10.
3
3
7.40 (d, 2H, JHH = 7 Hz, Ph), 7.16 (d, 2H, JHH = 7 Hz, Ph),
35. Heated to reflux in toluene for 6 h. Yield 400 mg (76%).
Crystals suitable for X-ray diffraction were grown from a layered
dichloromethane/pentane solution at 25 ◦C. 1H NMR (CD2Cl2):
7.77–7.72 (m, 3H, Ph), 7.50–7.45 (m, 3H, Ph), 7.19–7.09 (m, 3H,
7.10 (m, 1H, 3JHH = 7 Hz, Ph), 2.92 (m, 3H, 3JHH = 12 Hz, PCy),
1.95–1.27 (br m, 30H, PCy). 11B{ H} NMR (CD2Cl2): 2.2 (br).
1
13C{ H} NMR (CD2Cl2) partial: 145.0 (dm, 1JCF = 250 Hz, CF),
1
148.5 (dm, 1JCF = 240 Hz, CF), 147.6 (dm, 1JCF = 255 Hz, CF),
Ph), 7.06–7.01 (m, 3H, Ph), 3.52 (br s, 9H, OMe). 11B{ H} NMR
1
139.2 (dm, 1JCF = 240 Hz, CF), 137.6 (dm, 1JCF = 245 Hz, CF),
(CD2Cl2): -0.5 (br). 13C{ H} NMR (CD2Cl2) partial: 162.1 (quat
1
1
1
1
131.98 (s, Ph), 127.17 (s, Ph), 125.41 (s, Ph), 88.73 (dm, JCP
=
PhOMe), 149.4 (dm, JCF = 250 Hz, CF), 148.5 (dm, JCF
240 Hz, CF), 148.9 (dm, 1JCF = 240 Hz, CF), 139.5 (dm, 1JCF
=
=
70 Hz, PC6F4), 33.2 (d, 1JCP = 40 Hz, PCy3), 28.0 (s, PCy3), 27.5
(d, 3JCP = 14 Hz, PCy3), 25.9 (s, PCy3). 19F NMR (CD2Cl2): -126.9
(m, 2F, C6F4), -132.1 (m, 2F, C6F4), -133.6 (d, 2F, 3JFF = 16 Hz,
250 Hz, CF), 137.8 (Ph), 135.8 (dm, 1JCF = 250 Hz, CF), 135.1 (d,
3JCP = 11 Hz, Ph), 122.39 (d, 2JCP = 16 Hz, Ph), 113.2 (d, 3JCP
=
o-C6F5), -162.9 (t, 1F, 3JFF = 20 Hz, p-C6F5), -166.8 (t, 2F, 3JFF
=
5 Hz, Ph), 106.4 (d, JCP = 106 Hz, quat Ph), 56.4 (s, OMe). 19F
NMR (CD2Cl2): -127.9 (br, 1F, C6F4), -131.4 (br s, 2F, C6F4),
-136.0 (m, 5F, C6F4, o-C6F5), -162.2 (t, 2F, 3JFF = 20 Hz, p-C6F5),
1
20 Hz, m-C6F5), -193.4 (br s, BF). 31P{ H} NMR (CD2Cl2): 41.2.
Anal. calcd. for C36H38BF10P: C, 54.91; H, 2.45. Found: C, 54.55;
H, 2.45.
1
3
-165.5 (m, 4F, JFF = 20 Hz, m-C6F5), -192.8 (br m, 1F, BF).
31P { H} NMR (CD2Cl2): 10.9. Anal. calcd. for C39H21O3BF15P:
1
X-Ray data collection, reduction, solution and refinement
C, 54.91; H, 2.45. Found: C, 54.85; H, 2.10. Preliminary X-ray:
¯
˚
˚
˚
triclinic P1, a = 12.041 A, b = 12.245 A, c = 14.757 A, a =
Single crystals were mounted in thin-walled capillaries either
under an atmosphere of dry N2 in a glove box and flame sealed
or coated in paratone-N oil. The data were collected using the
SMART software package32 on a Siemens SMART System CCD
diffractometer using a graphite monochromator with MoKa
99.370◦, b = 111.626◦, g = 90.521◦.
Generation of Ph2PH(C6F4)BF(C6F5)2 25
In a re-sealable J.Young NMR tube the adduct Ph2PH-B(C6F5)3
(0.050 mg, 0.072 mmol) was dissolved in C6D5Br (0.75 mL) and
heated to 140 ◦C for 24 h. Near quantitative product formation was
observed by NMR. NMR resonances for the major product are
reported. Other minor products were observed (>15%) and were
˚
radiation (l = 0.71073 A). A hemisphere of data was collected
in 1448 frames with 10 second exposure times unless otherwise
noted. Data reduction was performed using the SAINT software
package33 and an absorption correction applied using SADABS.34
1564 | Dalton Trans., 2009, 1559–1570
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The structures were solved by direct methods using XS and refined
by full-matrix least-squares on F2 using XL as implemented
in the SHELXTL suite of programs.35 All non-hydrogen atoms
were refined anisotropically. Carbon-bound hydrogen atoms were
placed in calculated positions using an appropriate riding model
and coupled isotropic temperature factors. Phosphorus-bound
hydrogen atoms were located in the electron difference map and
their positions refined isotropically. In the case of compound
5, constraints were imposed on the disordered toluene solvate.
Disordered CH2Cl2 solvent molecules were removed using the
‘squeeze’ command in PLATON for compounds 28 and 34. In
the case of compound 37 the disordered CH2Cl2 was modelled.
Crystal data and structure refinement parameters are given in
Table 1.†
Results and discussion
Classical Lewis adducts
Following published procedures, a range of phosphines were
combined in toluene with B(C6F5)3 and stirred for 1 hour at
25 ◦C. Concentration of the solvent afforded the series of adducts,
(CyPH2)B(C6F5)3 1, ((C5H9)2PH)B(C6F5)3 2, (Cy2PH)B(C6F5)3
3,24 (Et2PH)B(C6F5)3 4, (Ph2PH)B(C6F5)3 6,24 (Mes2PH)B(C6F5)3
7, (Me3P)B(C6F5)3 8,25–27 (Et3P)B(C6F5)3 9, (n-Bu3P)B(C6F5)3 10
and (Ph3P)B(C6F5)3 1128,29 (Scheme 2). All products were readily
1
characterized by 1H, 11B,13C{ H}, 19F and 31P NMR spectroscopy
(Table 2). These adducts exhibit a gap in the 19F NMR resonances
attributable to the meta and para fluorine atoms and a 11B chemical
shift that is characteristic of a four-coordinate boron center.36–41 In
addition, the solid state structures of 4, 5, 6 and 9 were determined
Scheme 2 Synthesis of compounds 1–35.
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Table 2 Chemical shifts and structural data for free phosphine, (phosphine)B(C6F5)3 adducts and R2PR¢(C6F4)BF(C6F5)2
Phosphine
B(C6F5)3 adduct
R2PR¢(C6F4)BF(C6F5)2
31P(1JPH
)
Cmpd
31P(1JPH
)
11B
P–B/A
Cmpd
31P(1JPH
)
11B
˚
H3P
tBuPH2
PhPH2
2.046(8)59
2.015(3)60
2.039(3)61
a
CyPH2
-110.1(184)
-35.2(191)
-27.5(192)
-55.5(190)
20.1(199)
-40.1(215)
-92.7(229)
-5.3(208)
-49.1(214)
-63.3
1
2
3
4
5
6
7
-30.0(392)
11.2(408)
9.3(406)
5.7(412)
17.4(394)
0.9(411)
-67.7
-17.5
-15.9
-13.5
-16.2
-12.8
-9.4
(C5H9)2PHb
Cy2PHc,27
Et2PHc,24
tBu2PHc
Ph2PH
2.0243(3)
2.0270(14)24
2.036(4)
2.094(7)
2.098(3)
22
23
12.7(508)
11.5(480)
-0.1
-0.2
24
25
26
27
28
34.2(465)
6.5(500)
-37.7(503)
14.7(487)
-2.9(505)
0.8
-1.0
0.4
0.4
0.4
Mes2PHc
tBuPhPHb
tBuMesPHd
Me3P24
23.6
8
9
-6.1
5.6
-14.7
-13.4
2.061(4)25
2.081(4)
Et3Pc
-19.1
29
30
31
32
33
34
35
39.1
53.2
33.1
41.6
15.1
14.1
10.9
0.5
-0.9
-0.8
-0.7
-0.3
-0.2
-0.5
iPr3P24
19.3
-31.6
11.1
nBu3Pc
10
11
-0.6
-5.2
-13.5
-2.5
Cy3Pc
Ph3Pc
-4.6
2.180(6)17
(p-C6H4F)3Pc
(o-C6H4OMe)3Pc
-9
-29.3
a C6D5Br solvent for NMR spectra. b CD2Cl2 solvent for NMR spectra. c C6D6 solvent for NMR spectra. d THF solvent for NMR spectra.
by X-ray crystallography (Fig. 1, Table 1), while those of 2, 3,24
825 and 1029 had been previously determined. As expected the
geometries at the B and P atoms are both pseudo-tetrahedral in
each case. In the present compounds, the P–B bond distances
These NMR data support the notation that Mes2PH forms a weak
adduct with B(C6F5)3 at 25 C and at low temperatures exhibits
◦
PH ◊ ◊ ◊ FC interactions rendering the inequivalence of fluorine
atoms. A similar phenomenon has been previously observed for
amine-B(C6F5)3 adducts.42 Similarly, weak P–B interactions were
observed between tBu(Mes)PH and B(C6F5)3 and thus an adduct
was not isolated. In such crowded systems, the steric interactions
have been rationalised in terms of the sum of repulsive Pauli and
attractive electrostatic and van der Waals interactions by Erker,
Grimme and co-workers.43
In the case of tBu2PH, evidence of formation of adduct
(tBu2PH)(B(C6F5)3 5 was observed on cooling of solutions of the
phosphine in the presence of B(C6F5)3 to -60 ◦C. Such solutions
gave rise to a broad 31P NMR resonance at 17.4 ppm and a 11B
NMR signal at -12.8 ppm. The 19F NMR spectrum of 5 shows
eight signals consistent with inequivalent C6F5 ring environments.
Nonetheless, the adduct 5 was not stable as alternate chemistry
occurs on warming to 25 ◦C (vide infra).
˚
range from 2.024(3) to 2.180(6) A (Table 2) and appear to vary
with both the relative steric bulk and basicity of the phosphine.
The bulky phosphine adduct 7 was isolated, but only as a minor
product. The 31P and 11B NMR spectra of 7 are very broad signals
at -67 and 23 ppm, respectively, while the 19F NMR spectrum
exhibits three broad resonances for the ortho, meta and para
fluorine atoms of the C6F5 rings. Upon cooling to -70 ◦C, the
three broad fluorine resonances split into 13 sharp peaks with 2 of
double intensity, corresponding to 15 inequivalent fluorine atoms.
Larger phosphines such as (o-C6H3Me2)3P, (o-C6H4Me)3P,
(C6H2Me3)3P or tBu3P appear to effect no reaction with B(C6F5)3
in toluene-d8 or CD2Cl2 in the temperature range of 25 ◦C to
◦
1
-70 C as evidenced by H, 31P, 11B, and 19F NMR spectroscopy.
Such mixtures of Lewis acids and Lewis bases, where steric
demands preclude quenching of the Lewis acidity and basicity,
have been described as ‘frustrated Lewis pairs’ and have been
shown to exhibit unique reactivity with small molecules.44–48 As
noted previously, the combination of Mes3P and B(C6F5)3 gave
rise to a violet solution; in contrast to combinations of Ph2MeN
and B(C6F5)3 where formal electron transfer is proposed,4 reaction
mixtures of Mes3P and B(C6F5)3 were found to be EPR silent.
THF ring-opening
Intuitively an alternative to the procedure above to gener-
ate B(C6F5)3 adducts involves the displacement of THF from
Fig. 1 POV-ray drawings of (a) 4 (b) 5 (c) 6 (d) 9.
1566 | Dalton Trans., 2009, 1559–1570
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(THF)B(C6F5)3. Indeed this approach has been employed to
obtain 3 and 6.24 However, the analogous reactions employing
tBu2PH, Mes2PH and Cy3P do not proceed in this fashion;
rather, reaction of (THF)B(C6F5)3 with these phosphine effects
the ring-opening of THF affording the products 12, 13, and
15 in 81, 79 and 98% yields, respectively. The 11B NMR
spectra revealed single resonances at ca. -2.1 to -2.8 ppm
indicative of four-coordinate boron centers, while the 31P NMR
spectra gives rise to downfield resonances. The 1H NMR
data are consistent with the presence of four methylene reso-
nances. These NMR data are consistent with the formulation
of the products as the THF ring-opened phosphonium borates
tBu2PH(C4H8O)B(C6F5)3 12, Mes2PH(C4H8O)B(C6F5)3 13 and
Cy3P(C4H8O)B(C6F5)3 15 (Scheme 2). In a similar fashion, the
species [Li][tBu2P(C4H8OB(C6F5)3)2] 20 and [Li(THF)4][Mes2P-
(C4H8OB(C6F5)3)2] 21. The X-ray structures of 19 and 20 have
been previously communicated.18 It should be noted that 20 is
observed in preparations of 16 performed at room temperature,
while 16 is generated cleanly at -78 ◦C, consistent with the ability
of 16 to effect also THF ring-opening.
Aromatic substitution
In the majority of cases, the classical borane-phosphine adducts
were found to undergo rearrangement reactions, yet requiring
prolonged heating in some cases. For example, heating 2 in a
sealed reaction bomb to 125 ◦C for 24 h in toluene resulted
in the formation of a white precipitate. Subsequent workup
afforded 22 as a white solid in 73% yield (Scheme 2). The 11B
NMR signal for 22 was observed at -0.2 ppm, which is shifted
dramatically from that seen for 2 (-13.5 ppm). Similarly, the
31P NMR resonance shifted downfield slightly to 11.5 ppm and
◦
adduct 9 was dissolved in THF and heated to 80 C for 6 hours
to give a white solid formulated as Et3PC4H8OB(C6F5)3 14 in 81%
yield. It is noteworthy that prolonged heating of 4 in THF to
80 ◦C showed no such rearrangement. This presumably reflects
the stronger P–B bond in 4 relative to that in 9. The formulations
of the zwitterions above were also supported by X-ray data for
12, 13,18 14 and 15 (Fig. 2). The THF ring-opening reaction
1
notably exhibited a JPH coupling constant of 480 Hz typical
of a phosphonium salt. A new 19F NMR signal was observed
at -191.5 ppm attributable to a B–F unit, while resonances at
-129.2 and -131.9 ppm confirmed the presence of a 1,4-di-
substituted C6F4 aryl ring. Collectively, these data are consistent
with the formulation of 22 as (C5H9)2PH(C6F4)BF(C6F5)2. In a
similar fashion, the adducts 3, 6, 8, 9, 10 and 11 underwent
similar thermal rearrangements to give the corresponding zwitte-
rionic species Cy2PH(C6F4)BF(C6F5)2 23, Ph2PH(C6F4)BF(C6F5)2
25, Mes2PH(C6F4)BF(C6F5)2 26, Et3P(C6F4)BF(C6F5)2 29,
nBu3P(C6F4)BF(C6F5)2 31 and Ph3P(C6F4)BF(C6F5)2 33, in near
quantitative yields, respectively (Scheme 2). Although such rear-
rangements of Lewis acid–base adducts have only rare precedent,17
the nucleophilic substitution of at the para-position of a pentaflu-
orophenyl ring is well known.51,52
˚
products exhibit B–O bond lengths of 1.415(18)–1.459(4) A,
which are in the range seen for the related compound tBuNTe(m-
49
˚
NtBu)2TeN(tBu)(CH2)4OB(C6F5)3 (1.444(4) A) and are shorter
than that found in the anion [HOB(C6F5)3]- (B–O = 1.480(11)
50
˚
A). The remaining metric parameters are unexceptional.
In the case of bulky basic phosphine, the attack of the
fluorinated aromatic rings is even more facile. For example
and as mentioned above, isolation of the B(C6F5)3 adduct of
tBu2PH is challenging; however, on stirring at room temper-
ature, attack at a para-carbon atom proceeds easily to give
tBu2PH(C6F4)BF(C6F5)2 24. Similarly, monitoring the reaction of
Cy3P and B(C6F5)3 showed no evidence of the formation of the
adduct, but rather the rapid formation of Cy3P(C6F4)BF(C6F5)2
32. In the same fashion, the species (tBu)(Ph)PH(C6F4)BF(C6F5)2
27, (tBu)(Mes)PH(C6F4)BF(C6F5)2 28, iPr3P(C6F4)BF(C6F5)2 30
and (o-C6H4OMe)3P(C6F4)BF(C6F5)2 35, were prepared and iso-
lated (Scheme 2). The spectral data for these zwitterionic species
are all similar to those described above for 22, each exhibiting the
1
characteristic 31P, 11B, 19F and H NMR resonances (Table 2).
In each case, the sterically congested environment about the
phosphorus atom disfavors coordination to boron thus prompting
nucleophilic aromatic substitution at the electrophilic para-carbon
atom of an arene ring followed by fluoride transfer to boron.
X-Ray structural data for 27, 28, 31, 33 and 34 are reported
herein (Fig. 3 and 4) confirming the zwitterionic nature of these
species. In each species the phosphorus and boron centers are
pseudo-tetrahedral. The B–F bond lengths range from 1.413(4)
Fig. 2 POV-ray drawings of (a) 14 (b) 15.
Related anionic phosphine-borates are readily derived from 12
via treatment with tBuLi or, alternatively, by treating B(C6F5)3 with
a lithium phosphide (R2PLi, R = tBu, Ph Mes) to afford 16–19 in
THF. These approaches, depending on the solvent used, afford
the species [Li(THF)2][tBu2P(C4H8O)B(C6F5)3] 16, [Li][tBu2P-
(C4H8O)B(C6F5)3] 17, [Li(THF)2][Ph2P(C4H8O)B(C6F5)3] 18 and
[Li(THF)2][Mes2P(C4H8O)B(C6F5)3] 19 as confirmed by NMR
data (Scheme 2). Indeed this latter approach can be ex-
tended to a 2 : 1 reaction, as treatment of (THF)B(C6F5)3
with two equivalents of a lithium phosphide affords the
˚
˚
A to 1.436(6) A and compare well to those found in the
17
˚
zwitterions 1,4-Ph3PCH2(C6F4)BF(C6F5)2 (1.392(12) A), 1,4-
Ph2MeP(C6H4)BF(Mes)2 (1.467(4) A),53 and the anions (C6F5)3BF
˚
(1.428 A), and (o-(C6F5)C6F4)3BF (1.472 (11) A),55 while they are
54
˚
˚
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Fig. 3 POV-ray drawings of two adjacent molecules of 28. The dashed
lines indicate the close approach of the BF and PH fragments.
longer than those found in the diarylboranes Mes2BF (1.339(2)
56
˚
˚
A) and (o,p-C6H3(CF3)2)2BF (1.313(3) A). In the solid state, the
molecules of 28, like 24, pack in a head-to-tail fashion accom-
˚
modating intermolecular P–H ◊ ◊ ◊ F–B interactions of 2.55(3) A
and 2.20(2) A respectively (Fig. 4). This orientation also provides
˚
parallel yet offset p-stacking of the phosphorus and boron
substituted (PC6F4B) arene rings. Additionally the PH moiety is
orientedparallel toan o-fluorine of the bridging C6F4 unit resulting
˚
in intramolecular P–H ◊ ◊ ◊ F–C contacts of 2.50(3) A and 2.47(2)
57
˚
A for 24 and 28, respectively. The remaining metric parameters
were unexceptional and similar to those communicated for 22,
24, 26, 30 and 32. It should be noted that recently, Royo and
co-workers have reported the formation of a related zwitterion
Ph3P(C6F4)BMe(C6F5)2 as a by-product of a mixture of Ph3P a◦nd
1
the ion pair [Zr{C5H3[SiMe2(h -NtBu)]2}][RB(C6F5)3] left at 80 C
for one week.58
While the aromatic substitution seems to tolerate a variety of
substituents on phosphorus, it is noteworthy that no reaction was
observed wit◦h prolonged heating of the solutions of adducts 1, 4
and 8 to 140 C for several days.62 The inability of these adducts to
undergo thermal rearrangement demonstrates that small, highly
basic phosphines form strong P–B bonds with B(C6F5)3 that
are thermally stable. This notion is consistent with the relatively
short P–B bond lengths seen in 4 and 8 in comparison to those
determined for 6 to 9 for which thermal rearrangement does
proceed (Table 2). In the case of 1 and 4, secondary H ◊ ◊ ◊ F contacts
analogous to those seen for amine adducts24 also strengthen the
Lewis acid–base interaction. Short inter- and intra-molecular
CH ◊ ◊ ◊ F contacts have been described for 725 and are thought
to contribute to its poor solubility in organic solvents. Short
intramolecular CH ◊ ◊ ◊ F and PH ◊ ◊ ◊ F and intermolecular CH ◊ ◊ ◊ F
Fig. 4 POV-ray drawings of (a) 27 (b) 31 (c) 33 (d) 34.
Interestingly, the solid state structure of the adduct 6 exhibits a
57
˚
short intramolecular PH ◊ ◊ ◊ F contact of 2.27(2) A, yet it still
thermally rearranges to give the zwitterions 25, albeit only at
a higher temperature. Hence while such secondary interactions
may play a role, clearly the sterics and basicity of the phosphine
dominate in determining the strength of the P–B bond.
To examine the impact of alternative substitution at the boron
atom the species PhB(C6F5)2 36,31 known to have a diminished
degree of Lewis acidity63,64 compared to B(C6F5)3, was prepared.
Crystals of PhB(C6F5)2 were obtained and the solid-state structure
determined by X-ray diffraction (Fig. 5(a)). The structure is planar
ꢀ
= 360◦) and exhibits a propeller shape with the
˚
contacts less than the sum of the van der Waals radii (<2.55 A)
at B (
C–B–C
are found in 4.57 Bradley et al.60 have attributed the strength of the
adduct (tBuPH2)B(C6F5)3 vs. (H3P)B(C6F5)3 to both short inter-
and intra-molecular H ◊ ◊ ◊ F interactions present in the former.
In each case, the CH ◊ ◊ ◊ F and/or PH ◊ ◊ ◊ F interactions are not
retained in solution as determined using 19F NMR spectroscopy,
indicating that such interactions are significantly weaker than sim-
ilar NH ◊ ◊ ◊ F contacts, which are typically observed in solution.24
two C6F5 rings turned 43◦ and 50◦ out of the BC3 plane and
the C6H5 ring rotated 24◦ out of the BC3 plane as is typical for
related triarylboranes.56,65–71 Upon addition of Cy3P to a toluene
solution of PhB(C6F5)2 at 25 ◦C, a white solid precipitated and was
identified as the phosphonium borate Cy3P(C6F4)BF(Ph)(C6F5) 37
(Fig. 5(b)). The 31P NMR spectrum is very similar to that of 32,
while the 11B NMR resonance is shifted downfield 3 ppm from
1568 | Dalton Trans., 2009, 1559–1570
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is not limited to simple adduct formation. Instead, novel phos-
phonium borate zwitterions derived from THF ring-opening and
nucleophilic aromatic substitution are accessible depending on the
conditions. Extremely bulky tertiary phosphines do not react at all
with B(C6F5)3 thus yielding ‘frustrated Lewis pairs’. We continue
to examine the chemistry of each class of these products. While
we are currently exploring the potential of these two classes of
zwitterions as ligands, we also continue to explore the fundamental
reactivity of Lewis acids and bases and in particular that of
‘frustrated Lewis pairs’.
Acknowledgements
Financial support from NSERC of Canada and NOVA Chemicals
Corporation is gratefully acknowledged. G. C. W. is grateful for
the award of an NSERC-postgraduate scholarship. M. A. D. is
grateful for the award of an Ontario graduate scholarship.
References
1 W. E. Piers and T. Chivers, Chem. Soc. Rev., 1997, 26, 345–354.
2 E. Y.-X. Chen and T. J. Marks, Chem. Rev., 2000, 100, 1391–1434.
3 J. C. W. Chien, W. M. Tsai and M. D. Rausch, J. Am. Chem. Soc., 1991,
113, 8570–8571.
4 W. E. Piers, Adv. Organomet. Chem., 2005, 52, 1–76.
5 F. Focante, P. Mercandelli, A. Sironi and L. Resconi, Coord. Chem.
Rev., 2006, 250, 170–188.
6 G. Erker, Dalton Trans., 2005, 1883–1890.
7 X. G. Fang, B. L. Scott, K. D. John, G. J. Kubas and J. G. Watkin,
New J. Chem., 2000, 24, 831–833.
8 J. B. Lambert and J. H. So, J. Org. Chem., 1991, 56, 5960–5962.
9 G. Bidan and M. Genies, Tetrahedron Lett., 1978, 2499–2502.
10 R. A. Jones, G. Wilkinson, M. B. Hursthouse and K. M. A. Malik,
J. Chem. Soc., Perkin Trans. 2, 1980, 117–120.
11 J. R. Sanders, J. Chem. Soc., Dalton Trans., 1973, 743–747.
12 Y. Okamoto and Y. Shimakaw, J. Org. Chem., 1970, 35, 3752.
13 H. Hoffmann and P. Schellen, Chem. Ber. Recl., 1966, 99, 1134.
14 R. Damico and C. D. Broaddus, J. Org. Chem., 1966, 31, 1607.
15 G. Briegleb, W. Ruttiger and W. Jung, Angew. Chem., Int. Ed. Engl.,
1963, 2, 545–546.
Fig. 5 POV-ray drawings of (a) 36 (b) 37.
that of 32, while the gap between the meta- and para-resonances
(Dp-m = 4 ppm) is slightly smaller than in 32 (Dp-m = 5 ppm). The
solid-state structure of 37 was determined by X-ray diffraction.
While the metric parameters are as expected and unexceptional,
the structure confirms the preferential attack of the phosphine at
the electron deficient C6F5 ring. This is consistent with experiments
where mixtures of Ph3B and Cy3P or tBu2PH showed no evidence
of aromatic substitution at 125 ◦C by 11B or 31P NMR spectroscopy.
In line with this, no reactivity was observed between Cy3P and the
borane B(m-C6H3(CF3)2)3.
Mechanistic insights
Dissociation of (phosphine)B(C6F5)3 adducts permits attack at
the para-carbon of a C6F5 ring on B(C6F5)3 to give zwitterions of
the form R¢R2P(C6F4)BF(C6F5)2. Mechanistically it is thought
that the first step in the reaction involves nucleophilic attack
by phosphine at a para-carbon atom forming a dearomatized
intermediate. This step is followed by fluoride transfer to the
boron atom. The strength of the newly formed P–C and B–
F bonds renders the reaction irreversible. A similar mecha-
nism was described by Erker and co-workers17 for the gen-
eration of (Ph3PCHPh)C6F4BF(C6F5)2. Similarly, the reaction
of tertiary phosphines with trityl cation proceeds in a similar
16 L. Cabrera, G. C. Welch, J. D. Masuda, P. Wei and D. W. Stephan,
Inorg. Chim. Acta, 2006, 359, 3066–3071.
17 S. Do¨ring, G. Erker, R. Fro¨hlich, O. Meyer and K. Bergander,
Organometallics, 1998, 17, 2183–2187.
18 G. C. Welch, J. D. Masuda and D. W. Stephan, Inorg. Chem., 2006, 45,
478–480.
19 G. C. Welch, R. R. San Juan, J. D. Masuda and D. W. Stephan, Science,
2006, 314, 1124–1126.
20 G. Rodriguez, Fluorinated Zwitterionic Cocatalysts for Olefin Poly-
merization, US Pat., WO 02/36639 A2, 2002.
21 M. W. Holtcamp and T. H. Pham, Catalyst system and its use in a
polymerization process, US Pat., WO 02/102857, 2002.
22 R. A. Bartlett, M. M. Olmstead, P. P. Power and G. A. Sigel, Inorg.
Chem., 1987, 26, 1941–1946.
23 W. McFarlane and C. T. Regius, Polyhedron, 1997, 16, 1855–1861.
24 S. J. Lancaster, A. J. Mountford, D. L. Hughes, M. Schormann and M.
Bochmann, J. Organomet. Chem., 2003, 680, 193–205.
25 P. A. Chase, M. Parvez and W. E. Piers, Acta Crystallogr., Sect. E, 2006,
62, O5181–O5183.
26 L. H. Doerrer, A. J. Graham and M. L. H. Green, J. Chem. Soc., Dalton
Trans., 1998, 3941–3946.
27 G. S. Hair, R. A. Jones, A. H. Cowley and V. Lynch, Organometallics,
2001, 20, 177–181.
28 A. G. Massey and A. J. Park, J. Organomet. Chem., 1964, 2, 245–250.
29 H. Jacobsen, H. Berke, S. Do¨ring, G. Kehr, G. Erker, R. Fro¨hlich and
O. Meyer, Organometallics, 1999, 18, 1724–1735.
30 G. C. Welch, L. Cabrera, P. A. Chase, E. Hollink, J. D. Masuda, P. R.
Wei and D. W. Stephan, Dalton Trans., 2007, 3407–3414.
31 A. Sundararaman and F. Ja¨kle, J. Organomet. Chem., 2003, 681, 134–
142.
fashion, initially giving the (4-benzhydrylidene-cyclohexa-2,5-
+
=
dienyl)phosphonium cations [R3P(C6H5) CPh2] and subsequent
(p-benzhydryl)phenylphosphonium cations [R3P(C6H4)CHPh2]+
(Scheme 1).16 Efforts to observe a dearomatized intermediate in the
reaction of phosphine and B(C6F5)3 by NMR spectroscopy were
unsuccessful. Nonetheless, the general trend in reactivity seems to
parallel steric bulk, consistent with the proposed mechanism; small
phosphines form robust adducts, larger phosphines rearrange
to give aromatic substitution under thermal duress, larger still
phosphines form weak adducts and effect aromatic substitution
rapidly, while very large phosphines show no reactivity at all
towards B(C6F5)3.
In summary, it has been demonstrated that the reactivity
between Lewis basic phosphines and the Lewis acid B(C6F5)3
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View Article Online
32 SMART, Bruker AXS Inc, Madison, WI, 2001.
33 SAINT, Bruker AXS Inc., Madison, WI, 2003.
56 S. M. Cornet, K. B. Dillon, C. D. Entwistle, M. A. Fox, A. E. Goeta,
H. P. Goodwin, T. B. Marder and A. L. Thompson, Dalton Trans.,
2003, 4395–4405.
57 The P–H bond distances reported were experimentally determined.
X-Ray data are known to underestimate these distances and thus the
intramolecular distances P–H ◊ ◊ ◊ F–C are over estimated (see refs 72
and 73).
34 SADABS, Bruker AXS Inc., Madison, WI, 2003.
35 G. M. Sheldrick, Bruker AXS Inc., Madison, WI, 2000.
36 P. A. Chase, L. D. Henderson, W. E. Piers, M. Parvez, W. Clegg and
M. R. J. Elsegood, Organometallics, 2006, 25, 349–357.
37 P. A. Chase, P. E. Romero, W. E. Piers, M. Parvez and B. O. Patrick,
Can. J. Chem., 2005, 83, 2098–2105.
38 J. M. Blackwell, W. E. Piers and R. McDonald, J. Am. Chem. Soc.,
2002, 124, 1295–1306.
39 J. M. Blackwell, W. E. Piers and M. Parvez, Org. Lett., 2000, 2, 695–698.
40 A. D. Horton and J. deWith, Organometallics, 1997, 16, 5424–5436.
41 A. D. Horton, J. de With, A. J. Van Der Linden and H. van de Weg,
Organometallics, 1996, 15, 2672–2674.
58 J. Cano, M. Sudupe, P. Royo and M. E. G. Mosquera, Angew. Chem.,
Int. Ed., 2006, 45, 7572–7574.
59 D. C. Bradley, M. B. Hursthouse, M. Motevalli and D. H. Zheng,
J. Chem. Soc., Chem. Commun., 1991, 7–8.
60 D. C. Bradley, I. S. Harding, A. D. Keefe, M. Motevalli and D. H.
Zheng, J. Chem. Soc., Dalton Trans., 1996, 3931–3936.
61 J.-M. Denis, H. Forintos, H. Szelke, L. Toupet, T.-N. Pham, P.-J. Madec
and A.-C. Gaumont, Chem. Commun., 2003, 54–55.
62 Prolonged heating above 150 ◦C in the presence of excess phosphine
results in partial decomposition of the adduct to give a mixture of
unidentifiable species with some exhibiting characteristic P–F coupling.
The nature of these products is currently under investigation.
63 D. J. Morrison and W. E. Piers, Org. Lett., 2003, 5, 2857–2860.
64 R. F. Childs, D. L. Mulholland and A. Nixon, Can. J. Chem., 1982, 60,
801–808.
42 A. J. Mountford, S. J. Lancaster, S. J. Coles, P. N. Horton, D. L. Hughes,
M. B. Hursthouse and M. E. Light, Inorg. Chem., 2005, 44, 5921–5933.
43 P. Spies, R. Fro¨hlich, G. Kehr, G. Erker and S. Grimme, Chem.–Eur. J.,
2008, 14, 333–343.
44 P. A. Chase, T. Jurca and D. W. Stephan, Chem. Commun., 2008, 1701–
1703.
45 P. A. Chase, G. C. Welch, T. Jurca and D. W. Stephan, Angew. Chem.,
Int. Ed., 2007, 46, 8050–8053.
46 J. S. J. McCahill, G. C. Welch and D. W. Stephan, Angew. Chem., Int.
Ed., 2007, 46, 4968–4971.
47 D. W. Stephan, Org. Biomol. Chem., 2008, 6, 1535–1539.
48 G. C. Welch and D. W. Stephan, J. Am. Chem. Soc., 2007, 129, 1880–
1881.
49 T. Chivers and G. Schatte, Eur. J. Inorg. Chem., 2003, 3314–3317.
50 A. A. Danopoulos, J. R. Galsworthy, M. L. H. Green, L. H. Doerrer, S.
Cafferkey and M. B. Hursthouse, Chem. Commun., 1998, 2529–2560.
51 G. M. Brooke, J. Fluorine Chem., 1997, 86, 1.
52 C. E. Smith, P. S. Smith, R. L. Thomas, E. G. Robins, J. C. Collings,
C. Y. Dai, A. J. Scott, S. Borwick, A. S. Batsanov, S. W. Watt, S. J.
Clark, C. Viney, J. A. K. Howard, W. Clegg and T. B. Marder, J. Mater.
Chem., 2004, 14, 413–420.
65 S. A. Cummings, M. Iimura, C. J. Harlan, R. J. Kwaan, I. V. Trieu, J. R.
Norton, B. M. Bridgewater, F. Ja¨kle, A. Sundararaman and M. Tilset,
Organometallics, 2006, 25, 1565–1568.
66 G. J. P. Britovsek, J. Ugolotti and A. J. P. White, Organometallics, 2005,
24, 1685–1691.
67 L. Li, C. L. Stern and T. J. Marks, Organometallics, 2000, 19, 3332–
3337.
68 S. Toyota, M. Asakura, M. Oki and F. Toda, Bull. Chem. Soc. Jpn.,
2000, 73, 2357–2362.
69 W. V. Konze, B. L. Scott and G. J. Kubas, Chem. Commun., 1999,
1807–1808.
70 F. Zettler, H. D. Hausen and H. Hess, J. Organomet. Chem., 1974, 72,
157–162.
53 M. H. Lee, T. Agou, J. Kobayashi, T. Kawashima and F. P. Gabbai,
Chem. Commun., 2007, 1133–1135.
71 M. Hutching, C. Maryanof and K. Mislow, J. Am. Chem. Soc., 1973,
95, 7158–7159.
54 R. Taube, S. Wache and J. Sieler, J. Organomet. Chem., 1993, 459,
335–347.
55 M. H. Hannant, J. A. Wright, S. J. Lancaster, D. L. Hughes, P. N.
Horton and M. Bochmann, Dalton Trans., 2006, 2415–2426.
72 P. S. Bryan and R. L. Kuczkowski, Inorg. Chem., 1972, 11, 553.
73 T. L. Clark, J. M. Rodezno, S. B. Clendenning, S. Aouba, P. M.
Brodersen, A. J. Lough, H. E. Ruda and I. Manners, Chem.–Eur. J.,
2005, 11, 4526–4534.
1570 | Dalton Trans., 2009, 1559–1570
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The Royal Society of Chemistry 2009
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