Phosphinimine-borane combinations in frustrated Lewis pair chemistry

Article abstract of DOI:10.1039/c2dt30720k

The phosphinimines Ph₃PNR (R = Ph 1, C₆F ₅2, tBu 3) are combined with B(C₆F₅) ₃ in an effort to explore the frustrated Lewis pair (FLP) chemistry. While compound 1 is shown to form an adduc

Full text of DOI:10.1039/c2dt30720k

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An international journal of inorganic chemistry
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Volume 42 | Number 3 | 21 January 2013 | Pages 593–804
ISSN 1477-9226
COVER ARTICLE
Jiang and Stephan
Phosphinimine–borane combinations in frustrated Lewis pair chemistry

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Phosphinimine–borane combinations in frustrated
Lewis pair chemistry†
Cite this: Dalton Trans., 2013, 42, 630
Chunfang Jiang and Douglas W. Stephan*
The phosphinimines Ph3PNR (R = Ph 1, C6F5 2, tBu 3) are combined with B(C6F5)3 in an effort to explore
the frustrated Lewis pair (FLP) chemistry. While compound 1 is shown to form an adduct with the
borane, compounds 2 and 3 exhibit no apparent interaction. Nonetheless exposure of each of the three
combinations to H2 resulted in the formation of the corresponding salts [Ph3PN(H)R][HB(C6F5)3] (R = Ph
5, C6F5 6, tBu 7). Reaction of 1 or 2 with B(C6F5)3 and carbon dioxide afforded Ph3PN(R)COOB(C6F5)3 (R =
Ph 8, C6F5 9) while the corresponding reaction with 3 gave rise only to the tBuNCO and (Ph3PO)B(C6F5)3.
Reactions of 1–3 and B(C6F5)3 with PhCuCH proceeds to give either deprotonation or addition affording
products of the form [Ph3PN(H)R][PhCuCB(C6F5)3] or (Ph3PNR)(Ph)CvCH(B(C6F5)3). The factors govern-
ing the nature of the dominant products are considered.
Received 30th March 2012,
Accepted 12th April 2012
DOI: 10.1039/c2dt30720k
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Introduction
The advent of frustrated Lewis pairs (FLPs) in 2006 has
resulted in new strategy for the activation of small
a
molecules.1–5 The initial approach was based on the combi-
nation of a sterically encumbered Lewis acid and base.6,7 The
notion was that steric demands that preclude adduct for-
mation could then be exploited for further chemistry. Sub-
sequently it was shown that the formation of an adduct did
not preclude FLP reactivity as long as the adduct was soluble
and the FLP was accessible by an equilibrium.8 Perhaps most
notably of the substrates examined activated by FLPs to date is
dihydrogen as the activation of this substrate was previously
thought to be the limited perview of organometallic chem-
istry.6,7 Nonetheless, FLP chemistry has continued to broaden,
with reports of activations of olefins,9–11 acetylenes,11–21 disul-
fides,22 CO2,23–25 N2O,26 NO27 and most recently the CH bonds
of propene.28
In probing the chemistry of FLPs the majority of systems
examined have exploited boron-based Lewis acids although
more recent studies have employed C,29–34 Al,28,35–37 Zr,38,39
Si40 and P(V)41 based Lewis acids (Scheme 1). In terms of the
base component, phosphorus42–57 and nitrogen8,57–70 based
donors have dominated the FLP literature although the use of
carbenes and thioethers have also been reported. In a 2010
communication, Bercaw and coworkers71 described the
Department of Chemistry, University of Toronto, 80 St. George Street, Toronto,
Ontario, Canada, M5S 3H6. E-mail: dstephan@chem.utoronto.ca;
Tel: 01-416-946-3294
†CCDC reference numbers 873942–873947. For crystallographic data in CIF or
other electronic format see DOI: 10.1039/c2dt30720k
Scheme 1 Examples of donor–acceptor combinations in FLP chemistry.
630 | Dalton Trans., 2013, 42, 630–637
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combination of “Verkade’s superbase” and an alkylated 9-BBN
Synthesis of Ph3PNtBu (3). To a stirred solution of Ph3PBr2
Lewis acid in FLP reactions effecting the reduction of ReCO (2.11 g, 5 mmol) in dry CH2Cl2 (50 mL) was added tBuNH2
fragments. It appeared that the poorer Lewis acidity of the (0.36 g, 5 mmol) and dry NEt3 (7 mL) at room temperature.
9-BBN derivative was compensated for to some extent by the After 2 hours, cold water was added, the organic layer was
“super-basicity” of (iPr2N)3PNSiMe3. This finding prompted us dried over MgSO4 and the solvent was removed under vacuum.
to examine the more generalized reactivity of readily accessi- The crude product of [Ph3PNHtBu][Br] was washed with
ble, less basic phosphinimines in FLP activations of dihydro- hexane and dried in vacuum. K[N(SiMe3)2] (0.2 g, 1 mmol) in
gen, carbon dioxide and phenylacetylene. Herein, we THF solution was slowly added to
a THF solution of
demonstrate that neither adduct formation nor the inclusion [Ph3PNHtBu][Br] (0.42 g, 1 mmol) at room temperature. The
of electron withdrawing or sterically demanding substituents solution was allowed to stir overnight and the solvent then
precludes further FLP reactivity. The implications of this exten- removed in vacuo. The residue was extracted with pentane,
sion of FLP chemistry to include phosphinimine donors is compound 3 was obtained as a white solid. Yield: 0.17 g
considered.
(51%). 1H NMR (400 MHz, C6D6): 7.89–7.84 (m, 6H, Ph-H),
7.06–7.04 (m, 9H, Ph-H), 1.36 (s, 9H, CH3). 31P{1H} NMR
(162 MHz, C6D6): −14.7. 13C{1H} NMR (100 MHz, C6D6): 136.5
(d, JC–P = 96 Hz), 132.8 (d, JC–P = 10 Hz), 130.3 (d, JC–P = 3 Hz),
128.0 (d, JC–P = 12 Hz), 51.9, 35.9 (d, JC–P = 10 Hz).
Experimental
General considerations
Synthesis of Ph3PN(Ph)B(C6F5)3 (4). To a solution of 1
All preparation were done under nitrogen atmosphere in a (0.07 g, 0.2 mmol) dissolved in toluene (5 mL) was added
glovebox or using standard Schlenk techniques. Solvents (hexane, B(C6F5)3 (0.10 g, 0.2 mmol). The reaction mixture was allowed
pentane, toluene, diethyl ether, THF and methylene chloride) to stir for 30 min and the volatiles were removed in vacuum.
were purified with a Grubbs-type column system manufactured Pentane was added and the mixture filtrated and washed with
1
by Innovative Technology and stored over 4 Å molecular sieves. pentane to give the orange solid. Yield: 0.16 g (94%). H NMR
3
Deuterated solvents were dried over Na/benzophenone (C6D6, (400 MHz, C6D6): 7.38–7.33 (m, 6H, Ph-H), 7.27 (d, JH–H
=
1
3
C7D8) or CaH2 (CD2Cl2) and vacuum distilled prior to use. H, 7 Hz, 2H, Ph-H), 6.92 (t, JH–H = 7 Hz, 2H, Ph-H), 6.74 (m, 9H,
19F, 11B, 31P and 13C spectra were recorded at 25 °C on Varian Ph-H), 6.66 (br, 1H, Ph-H). 19F NMR (376 Hz, C6D6): −127.1 (s,
400 MHz and Bruker 400 MHz spectrometers. 1H and 13C 6F, o-C6F5), −159.5 (s, 3F, p-C6F5), −166.2 (s, 6F, m-C6F5). 11B
spectra are referenced to SiMe4 using the residual solvent peak {1H} NMR (128 MHz, C6D6): −4.0. 31P{1H} NMR (162 MHz,
impurity of the given solvent. 31P, 11B and 19F is referenced to C6D6): 37.2. 13C{1H} NMR (100 MHz, C6D6) partial: 148.7 (dm,
1
85% H3PO4, BF3·OEt2 and CFCl3, respectively. Chemical shifts 1JC–F = 240 Hz, o-C6F5), 137.1 (dm, JC–F = 250 Hz, p-C6F5),
1
are reported in ppm and coupling constants in Hz as absolute 137.8, 133.9 (dm, JC–F = 250 Hz, m-C6F5), 133.5 (d, JC–P
=
values. Combustion analyses were performed inhouse employ- 12 Hz), 130.3 (d, JC–P = 15 Hz), 130.0 (d, JC–P = 12 Hz), 129.1,
ing a Perkin-Elmer CHN Analyzer. 128.4, 128.3, 126.9, 125.6. Anal. Calcd for C42H20BF15NP: C,
Synthesis of Ph3PNR R = Ph (1), C6F5 (2). Ph3PNPh and 58.29; H, 2.33; N, 1.62. Found: C, 58.01; H, 2.73; N, 1.53.
Ph3PNC6F5 were prepared following modified literature Synthesis of [Ph3PN(H)Ph][HB(C6F5)3] (5). To a solution of 1
methods.72 To a stirred solution of Ph3PBr2 (2.11 g, 5 mmol) (0.07 g, 0.2 mmol) dissolved in toluene (5 mL) was added
in dry toluene (50 mL) was added C6H5NH2 (0.46 g, 5 mmol) B(C6F5)3 (0.10 g, 0.2 mmol). The solution was freeze-pump
and dry NEt3 (7 mL) at room temperature. The mixture was thawed for three cycles and backfilled with H2 (4 atm). The
then refluxed under nitrogen for 4 h, the resulting suspension solution was allowed to stir overnight at 80 °C and the volatiles
was filtrated and the filtrate was evaporated to dryness. The were removed in vacuo. Pentane was added and the mixture fil-
crude product was washed with hexane, and dried under trated and washed with pentane to give the white solid. Yield:
vacuum.
0.15 g (88%). Crystals for X-ray diffraction were grown from the
1
(1): White powder, Yield: 1.32 g (75%). H NMR (400 MHz, benzene–hexane layer. 1H NMR (400 MHz, CD2Cl2): 7.90 (m,
3
C6D6): 7.81–7.76 (m, 6H, Ph-H), 7.25 (d, JH–H = 7 Hz, 2H, Ph- 2H, Ph-H), 7.80–7.71 (m, 12H, Ph-H), 7.29–7.15 (m, 4H, Ph-H),
3
3
H), 7.19 (t, JH–H = 7 Hz, 2H, Ph-H), 7.04–6.95 (m, 9H, Ph-H), 6.87 (d, JH–H = 8 Hz, 2H, Ph-H), 5.93 (br, 1H, N-H), 3.60 (br,
6.82 (t, 3JH–H = 7 Hz, 1H, Ph-H). 31P{1H} NMR (162 MHz, C6D6): 1H, B-H). 19F NMR (376 Hz, CD2Cl2): −133.7 (d, JF–F = 22 Hz,
3
−1.3. 13C{1H} NMR (100 MHz, C6D6) partial: 152.0, 132.8 (d, 6F, o-C6F5), −164.2 (t, 3JF–F = 20 Hz, 3F, p-C6F5), −167.2 (t, 3JF–F
=
JC–P = 10 Hz), 131.7, 131.4, 129.1, 128.5 (d, JC–P = 12 Hz), 124.0, 20 Hz, 6F, m-C6F5). 11B{1H} NMR (128 MHz, CD2Cl2): −23.8.
123.8, 117.7.
31P{1H} NMR (162 MHz, CD2Cl2): 34.4. 13C{1H} NMR
1
1
(2): White powder, Yield: 1.55 g (70%). H NMR (400 MHz, (100 MHz, CD2Cl2) partial: 148.6 (dm, JC–F = 240 Hz, o-C6F5),
C6D6): 7.74–7.69 (m, 6H, Ph-H), 7.04–6.94 (m, 9H, Ph-H). 19F NMR 137.9 (dm, JC–F = 250 Hz, p-C6F5), 136.7 (dm, JC–F = 250 Hz,
1
1
(282 Hz, C6D6): −154.7 (m, 2F, o-C6F5), −168.3 (t, 3JF–F = 21 Hz, 2F, m-C6F5), 136.4 (d, JC–P = 3 Hz), 133.9 (d, JC–P = 10 Hz),
m-C6F5), −175.5 (m, 1F, p-C6F5). 31P{1H} NMR (162 MHz, C6D6): 130.8 (d, JC–P = 15 Hz), 130.2, 129.4, 128.6, 125.9, 122.0 (d,
7.0. 13C{1H} NMR (100 MHz, C6D6) partial: 143.3 (dm, JC–F
240 Hz, o-C6F5), 138.7 (dm, 1JC–F = 240 Hz, p-C6F5), 132.5 (d, JC–P
10 Hz), 132.2, 131.8, 131.2, 128.6 (d, JC–P = 12 Hz).
=
JC–P = 6 Hz), 119.6 (d, JC–P = 102 Hz). Anal. Calcd for
C42H22BF15NP: C, 58.16; H, 2.56; N, 1.61. Found: C, 58.73; H,
2.79; N, 1.53.
1
=
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Synthesis of [Ph3PN(H)R][HB(C6F5)3] R = C6F5 (6), tBu 136.6 (dm, 1JC–F = 250 Hz, m-C6F5), 135.2 (d, JC–P = 3 Hz), 134.1
(7). These two compounds were prepared in a similar fashion (d, JC–P = 12 Hz), 130.6 (d, JC–P = 15 Hz), 130.0, 129.5, 129.1,
and thus only one preparation is detailed. To a solution of 2 120.9, 119.9. Anal. Calcd for C43H20BF15NO2P: C, 56.79; H,
(0.089 g, 0.2 mmol) dissolved in toluene (5 mL) was added 2.22; N, 1.54. Found: C, 57.12; H, 2.22; N, 1.74.
B(C6F5)3 (0.10 g, 0.2 mmol). The solution was freeze-pump
(9) Yield: 0.16 g (80%). 1H NMR (400 MHz, CD2Cl2):
thawed for three cycles and backfilled with H2 (4 atm). The 7.85–7.35 (m, 15H, Ph-H). 19F NMR (376 Hz, CD2Cl2): −135.9
3
3
solution was allowed to stir overnight at room temperature and (d, JF–F = 22 Hz, 6F, o-C6F5), −142.5 (d, JF–F = 20 Hz, 2F,
the volatiles were removed in vacuo. Pentane was added and o-C6F5), −150.6 (t, JF–F = 22 Hz, 1F, p-C6F5), −160.7 (t, JF–F
the mixture filtrated and washed with pentane to give the 22 Hz, 3F, p-C6F5), −161.8 (t, JF–F = 20 Hz, 2F, m-C6F5), −166.4
3
3
=
3
3
white solid.
(t, JF–F = 22 Hz, 6F, m-C6F5). 11B{1H} NMR (128 MHz, CD2Cl2):
(6) Yield: 0.14 g (74%). Crystals for X-ray diffraction were −2.8. 31P{1H} NMR (162 MHz, CD2Cl2): 44.7. 13C{1H} NMR
grown from the benzene–hexane layer. 1H NMR (400 MHz, (100 MHz, CD2Cl2) partial: 148.0 (dm, JC–F = 250 Hz, o-C6F5),
1
3
1
1
CD2Cl2): 7.92 (t, JH–H = 7 Hz, 3H, Ph-H), 7.80–7.70 (m, 12H, 144.7 (dm, JC–F = 244 Hz, o-C6F5), 141.2 (dm, JC–F = 245 Hz,
Ph-H), 6.42 (br, 1H, N-H), 3.52 (br, 1H, B-H). 19F NMR (376 Hz, p-C6F5), 137.5 (dm, JC–F = 244 Hz, p-C6F5), 136.3 (dm, JC–F
=
1
1
3
3
CD2Cl2): −135.0 (d, JF–F = 22 Hz, 6F, o-C6F5), −144.7 (d, JF–F
=
250 Hz, m-C6F5), 134.8, 134.4 (d, J = 3 Hz), 133.4 (d, J = 10 Hz),
3
20 Hz, 2F, o-C6F5), −153.6 (t, JF–F = 22 Hz, 1F, p-C6F5), −162.0 130.3 (d, J = 14 Hz), 129.9 (d, J = 14 Hz), 129.3 (d, J = 14 Hz),
3
3
(t, JF–F = 20 Hz, 2F, m-C6F5), −165.1 (t, JF–F = 22 Hz, 3F, 128.5, 125.5 (d, J = 109 Hz). Anal. Calcd for C43H15BF20NO2P:
3
p-C6F5), −168.2 (t, JF–F = 22 Hz, 6F, m-C6F5). 11B{1H} NMR C, 51.68; H, 1.51; N, 1.40. Found: C, 51.94; H, 1.76; N, 1.54.
(128 MHz, CD2Cl2): −24.1. 31P{1H} NMR (162 MHz, CD2Cl2):
[Ph3PN(H)R][PhCuCB(C6F5)3] R = Ph (10), tBu (12). All
42.1. 13C{1H} NMR (100 MHz, CD2Cl2) partial: 148.0 (dm, JC–F these compounds were prepared in a similar fashion and thus
1
1
= 250 Hz, o-C6F5), 144.7 (dm, JC–F = 244 Hz, o-C6F5), 141.2 only one preparation is detailed. To a solution of 1 (0.035 g,
(dm, 1JC–F = 245 Hz, p-C6F5), 137.5 (dm, 1JC–F = 244 Hz, p-C6F5), 0.2 mmol) dissolved in toluene (5 mL) was added B(C6F5)3
136.3 (dm, 1JC–F = 250 Hz, m-C6F5), 136.4 (d, JC–P = 3 Hz), 133.6 (0.051 g, 0.2 mmol) and PhCuCH (0.01 g, 0.1 mmol). The
(d, JC–P = 12 Hz), 130.3 (d, JC–P = 14 Hz), 124.3, 119.3 (d, JC–P
=
solution was allowed to stir for 2 h at room temperature and
102 Hz), 110.5. Anal. Calcd for C42H17BF20NP: C, 52.69; H, the filtrated. The residue was washed with pentane and dried
1.79; N, 1.46. Found: C, 52.44; H, 2.06; N, 1.52.
under vacuum.
(7) Yield: 0.12 g (72%). 1H NMR (400 MHz, CD2Cl2):
(10) Yield: 0.08 g (82%). Crystals for X-ray diffraction were
7.90–7.72 (m, 15H, Ph-H), 3.63 (br, 1H, B-H), 3.35 (br, 1H, grown from the toluene–hexane layer. 1H NMR (400 MHz,
N-H), 1.30 (s, 9H, CH3). 19F NMR (376 Hz, CD2Cl2): −134.9 (d, CD2Cl2): 7.92–7.89 (m, Ph-H), 7.76–7.68 (m, Ph-H), 7.60–7.50
3
3JF–F = 22 Hz, 6F, o-C6F5), −165.2 (t, JF–F = 22 Hz, 3F, p-C6F5), (m, Ph-H), 7.27–7.15 (m, Ph-H), 6.91–6.87 (m, Ph-H), 5.68 (br,
3
3
−168.4 (t, JF–F = 22 Hz, 6F, m-C6F5). 11B{1H} NMR (128 MHz, N-H). 19F NMR (376 Hz, CD2Cl2): −132.8 (d, JF–F = 20 Hz, 6F,
CD2Cl2): −24.9. 31P{1H} NMR (162 MHz, CD2Cl2): 33.4. 13C{1H} o-C6F5, 10b), −133.1 (d, JF–F = 20 Hz, 6F, o-C6F5, 10b), −133.7
3
1
3
3
NMR (100 MHz, CD2Cl2) partial: 148.2 (dm, JC–F = 248 Hz, (d, JF–F = 22 Hz, 6F, o-C6F5, 10a), −164.8 (t, JF–F = 20 Hz, 3F,
1
1
3
o-C6F5), 137.4 (dm, JC–F = 244 Hz, p-C6F5), 136.3 (dm, JC–F
=
p-C6F5, 10a), −165.0 (t, JF–F = 20 Hz, 3F, p-C6F5, 10b), −165.4
3
3
250 Hz, m-C6F5), 135.5, 133.4 (d, JC–P = 12 Hz), 130.3 (d, JC–P
=
(t, JF–F = 20 Hz, 3F, p-C6F5, 10b), −168.2 (t, JF–F = 20 Hz, 6F,
3
14 Hz), 121.2 (d, JC–P = 102 Hz), 124.2, 56.5, 31.3. Anal. Calcd m-C6F5, 10a), −168.8 (t, JF–F = 20 Hz, 6F, m-C6F5, 10b), −168.9
for C40H26BF15NP: C, 56.69; H, 3.09; N, 1.65. Found: C, 56.92; (t, JF–F = 20 Hz, 6F, m-C6F5, 10b). 11B{1H} NMR (128 MHz,
3
H, 3.13; N, 1.64.
Ph3PN(R)COOB(C6F5)3 R = Ph (8), C6F5 (9). These two com- 38.4(10b), 34.6 (10a). 13C{1H} NMR (100 MHz, CD2Cl2) partial:
pounds were prepared in a similar fashion and thus only one 148.5 (dm, JC–F = 240 Hz, o-C6F5), 137.2 (dm, JC–F = 250 Hz,
CD2Cl2): −16.5 (br), −20.9 (s). 31P{1H} NMR (162 MHz, C6D6):
1
1
1
preparation is detailed. To a solution of 1 (0.089 g, 0.2 mmol) p-C6F5), 136.3 (dm, JC–F = 250 Hz, m-C6F5), 136.5 (d, JC–P = 3
dissolved in toluene (5 mL) was added B(C6F5)3 (0.10 g, Hz), 134.9, 133.8 (d, JC–P = 12 Hz), 131.5, 130.9 (d, JC–P = 15
0.2 mmol). The solution was freeze-pump thawed for three Hz), 129.9, 129.7, 128.4, 126.0, 121.5 (d, JC–P = 6 Hz), 119.3 (d,
cycles and backfilled with CO2 (1 atm). The solution was JC–P = 102 Hz). Anal. Calcd for C50H26BF15NP: C, 62.07; H, 2.71;
allowed to stir 1 h at room temperature and the volatiles were N, 1.45. Found: C, 62.53; H, 2.76; N, 1.53.
removed in vacuo. Pentane was added and the mixture filtrated
and washed with pentane to give the white solid.
(12) Yield: 0.085 g (89%). Crystals for X-ray diffraction were
grown from the toluene–hexane layer. 1H NMR (400 MHz,
(8) Yield: 0.15 g (83%). Crystals for X-ray diffraction were CD2Cl2): 7.90–7.86 (m, 3H, Ph-H), 7.83–7.72 (m, 12H, Ph-H),
grown from the benzene–hexane layer. 1H NMR (400 MHz, 7.34–7.31 (m, 2H, Ph-H), 7.22–7.12 (m, 3H, Ph-H), 3.22 (d, 3JP–H
=
CD2Cl2): 7.79–7.75 (m, 3H, Ph-H), 7.66–7.57 (m, 12H, Ph-H), 8 Hz, N-H), 1.28 (s, 9H, CH3). 19F NMR (376 Hz, CD2Cl2):
7.23–7.18 (m, 3H, Ph-H), 7.14–7.11 (m, 2H, Ph-H). 19F NMR −133.6 (d, 3JF–F = 22 Hz, 6F, o-C6F5), −164.8 (t, 3JF–F = 22 Hz, 3F,
3
3
(376 Hz, CD2Cl2): −136.4 (d, JF–F = 20 Hz, 6F, o-C6F5), −162.6 p-C6F5), −168.3 (t, JF–F = 20 Hz, 6F, m-C6F5). 11B{1H} NMR
3
3
5
(t, JF–F = 20 Hz, 3F, p-C6F5), −167.8 (td, JF–F = 20 Hz, JF–F
=
(128 MHz, CD2Cl2): −20.9. 31P{1H} NMR (162 MHz, CD2Cl2):
9 Hz, 6F, m-C6F5). 11B{1H} NMR (128 MHz, CD2Cl2): −3.6. 33.4. 13C{1H} NMR (100 MHz, CD2Cl2) partial: 148.4 (dm,
31P{1H} NMR (162 MHz, CD2Cl2): 41.9. 13C{1H} NMR 1JC–F = 244 Hz, o-C6F5), 138.7 (dm, JC–F = 242 Hz, p-C6F5),
1
1
1
(100 MHz, CD2Cl2) partial: 148.2 (dm, JC–F = 240 Hz, o-C6F5), 136.7 (dm, JC–F = 242 Hz, m-C6F5), 136.0, 133.6 (d, JC–P
=
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10 Hz), 131.5, 130.7 (d, JC–P = 14 Hz), 128.2, 126.1, 121.5 (d, methods using XS and refined by full-matrix least-squares on
JC–P = 102 Hz), 56.9, 32.0. Anal. Calcd for C48H30BF15NP: C, F2 using XL as implemented in the SHELXTL suite of pro-
60.84; H, 3.19; N, 1.48. Found: C, 60.59; H, 3.19; N, 1.46.
grams.73 All non-hydrogen atoms were refined anisotropically.
(Ph3PN(H)C6F5)(Ph)CvC(H)B(C6F5)3 (11). This species was Carbon-bound hydrogen atoms were placed in calculated posi-
prepared in an analogous fashion to that described for 10 and tions using an appropriate riding model and coupled isotropic
12 above.
temperature factors (see ESI†).
(11) Yield: 0.092 g (87%). Crystals for X-ray diffraction were
grown from the toluene–hexane layer. 1H NMR (400 MHz,
CD2Cl2): 7.83–7.73 (m, Ph-H), 7.70–7.56 (m, Ph-H), 7.20–7.17
(m, Ph-H), 7.13–7.07 (m, Ph-H), 6.94–6.84 (m, Ph-H), 6.64 (br,
Results and discussion
Z-CvCH), 5.50 (br, E-CvCH). 19F NMR (376 Hz, CD2Cl2): The phosphinimines Ph3PNR (R = Ph 1, C6F5 2) were prepared
3
3
−133.2 (d, JF–F = 22 Hz, 6F, Z-o-C6F5), −133.7 (d, JF–F = 22 Hz, by a modified literature preparation via reactions of Ph3PBr2
3
6F, E-o-C6F5), −139.2 (d, JF–F = 20 Hz, 2F, Z-o-C6F5), −144.5 (d, and the corresponding arylamine. The related species
3JF–F = 22 Hz, 2F, E-o-C6F5), −151.8 (t, JF–F = 22 Hz, 1F, Z-p- Ph3PNtBu 3 was prepared in an analogous manner although
3
3
3
C6F5), −152.9 (t, JF–F = 22 Hz, 1F, E-p-C6F5), −161.3 (t, JF–F
=
the intermediate product [Ph3PNHtBu][Br] required use of
3
20 Hz, 2F, E-m-C6F5), −163.0 (t, JF–F = 20 Hz, 2F, Z-m-C6F5), K[N(SiMe3)2] to afford 3. To probe the potential of these phos-
3
3
−164.6 (t, JF–F = 22 Hz, 3F, E-p-C6F5), −164.9 (t, JF–F = 22 Hz, phinimines in FLP reactions, these species were first reacted
3
3F, Z-p-C6F5), −166.7 (t, JF–F = 22 Hz, 6F, Z-m-C6F5), −168.2 (t, with B(C6F5)3. In the case of 1 combination with B(C6F5)3
3JF–F = 20 Hz, 6F, E-m-C6F5). 11B{1H} NMR (128 MHz, CD2Cl2): resulted in the formation of an orange solid which was iso-
−16.7 (Z), −20.9 (E). 31P{1H} NMR (162 MHz, CD2Cl2): 42.3 (E), lated in 94% yield. This product 4 exhibits a 11B{1H} NMR
41.8 (Z). 13C{1H} NMR (100 MHz, CD2Cl2) partial: 148.4 (dm, resonance at −4.0 ppm and 19F NMR signals at −127.1, −159.5
1JC–F = 240 Hz, o-C6F5), 137.0, 135.7, 134.9 (d, JC–P = 10 Hz), 134.0 and −166.2 ppm. These data are consistent with the presence
(d, JC–P = 12 Hz), 131.5, 130.8 (d, JC–P = 14 Hz), 130.1 (d, JC–P = 14 of four coordinated boron. The 31P{1H} NMR spectrum shows
Hz), 129.4, 128.8, 128.5, 128.3, 127.7, 126.3, 125.5, 119.8 (d, JC–P a peak at 37.2 ppm significantly downfield from the precursor
1
= 100 Hz), 118.3 (d, JC–P = 14 Hz). Anal. Calcd for C50H21BF20NP: phosphinimine. These together with the H and 13C{1H} NMR
C, 56.79; H, 2.00; N, 1.32. Found: C, 57.24; H, 2.05; N, 1.31.
data are consistent with the formulation of 4 as the phosphini-
mine–borane adduct Ph3PN(Ph)B(C6F5)3. In contrast, com-
pounds 2 and 3 in combination with B(C6F5)3 show no
apparent reaction. The resulting mixtures are best described as
FLPs and presumably result from the diminished donor ability
of 2 and the increased steric demands of 3.
X-ray data collection, reduction, solution and refinement
Single crystals were coated in Paratone-N oil in the glovebox,
mounted on a MiTegen Micromount and placed under an N2
stream. The data were collected on a Bruker Apex II diffracto-
meter (see Table 1). The data were collected at 150( 2) or
293( 2) K for all crystals. Data reduction was performed using
Reactions with hydrogen
the SAINT software package and an absorption correction Despite the ability of 1 to react with B(C6F5)3, the addition of
applied using SADABS. The structures were solved by direct dihydrogen to a solution of 4 and stirring of the mixture at
Table 1 Crystallographic data
5
6
8
10
11
12
Formula
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
C48H28BF15NP
945.49
C42H17BF20NP
957.35
Monoclinic
P21/n
11.7826(7)
16.5070(10)
19.9076(13)
90.00
94.530(2)
90.00
3859.8(4)
4
C49H26BF15NO2P
987.49
Monoclinic
P21/n
9.1433(8)
17.7446(16)
26.879(3)
90.00
92.266(3)
90.00
4357.6(7)
4
C50H26BF15NP
967.50
Monoclinic
P21/n
10.7176(5)
24.4998(11)
15.8572(7)
90.00
97.100(2)
90.00
4131.8(3)
4
C55.25H27BF20NP
1126.56
Monoclinic
P21/c
23.6597(5)
19.1776(4)
24.7362(5)
90.00
117.8180(10)
90.00
9926.6(4)
8
C48H30BF15NP
947.51
Triclinic
Triclinic
ˉ
ˉ
P1
P1
10.1234(5)
11.7781(6)
17.6664(9)
82.839(2)
83.646(2)
83.741(2)
2067.47(18)
2
10.1999(8)
17.1867(13)
24.1364(19)
89.968(4)
80.171(4)
83.358(4)
4140.3(6)
4
α (°)
β (°)
γ (°)
V (Å3)
Z
d (calc) (g cm−3
)
1.519
0.172
1.647
0.203
1.505
0.170
1.555
0.174
1.508
0.171
1.520
0.172
μ (mm−1
)
Total data
32 322
7265
5733
594
0.0410
0.1108
1.025
34 172
8872
5638
594
0.0514
0.1336
0.997
37 373
9946
7243
622
0.0576
0.1616
1.046
68 246
9497
6714
613
0.0401
0.1127
0.873
83 412
22 636
13 976
1402
0.0587
0.1980
1.058
69 928
18 865
13 852
1197
0.0403
0.1082
1.037
Unique data
Fo2 > 2σ (Fo
Variables
R1
)
2
wR2
GOF
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Scheme 2 Synthesis of 5–7.
Fig. 2 POV-ray depiction of 6. Of the hydrogen atoms, only the BH and NH
protons are shown. C: black; F: pink; B: green; P: orange; N: blue; H: turquoise.
distance in 6 was found to be 1.645(2) Å. Again, the B–H⋯H–N
separation was short being 2.01 Å, suggestion the presence of
dihydrogen bonding in the solid state.
Reactions with carbon dioxide
The combinations of the phosphinimine Lewis bases 1 or 2
with B(C6F5)3 also react with carbon dioxide at room tempera-
ture to give the white solids 8 and 9 in 83 and 80% yields
respectively. Compound 8 exhibits 19F NMR signals at −136.4,
−162.6 and −167.8 ppm and a 11B{1H} NMR resonance at
−3.6 ppm. The 31P{1H} NMR spectrum of 8 shows a resonances
at 41.9 ppm. These data are very similar to those observed for
9 and infer the formulation of these products as Ph3PN(R)C(O)-
OB(C6F5)3 R = Ph 8, C6F5 9 (Scheme 3). (8) In the case of 8 this
Fig. 1 POV-ray depiction of 5. Of the hydrogen atoms, only the BH and NH
protons are shown. C: black; F: pink; B: green; P: orange; N: blue; H: turquoise.
80 °C overnight resulted in the formation of a new product 5.
This species was precipitated by addition of pentane as a white
solid in 88% yield. The 11B{1H} NMR spectrum showed a reso-
nance at −23.8 ppm while the 19F NMR spectrum showed
peaks at −133.7, −164.2 and −167.2 ppm, consistent with the
generation of the hydridoborate anion HB(C6F5)3. The 31P{1H}
NMR data showed a slightly shifted signal at 34.4 ppm. Reso-
nances at 5.93 and 3.60 ppm in the 1H NMR spectrum were
attributed to NH and BH fragments. These data infer that 5 is
[Ph3PN(H)Ph][HB(C6F5)3] (Scheme 2). This was subsequently
confirmed following the isolation of crystals for X-ray diffrac-
tion from the toluene–hexane (Fig. 1). The P–N distance was
1.641(2) Å. The remaining metric parameters are unexcep-
tional. The formation of 5 establishes that there is a small
equilibrium governing the formation of 4. A similar situation
in which an adduct exhibited FLP reactivity has been described
for the combination of lutidine and B(C6F5)3.8,65
formulation was confirmed via
a crystallographic study
(Fig. 3). The P–N and B–O bond lengths in 8 were found to be
1.671(2) Å and 1.526(3) Å, respectively while the terminal and
bridging C–O bond distances were determined to be 1.214(3) Å
and 1.288(3) Å, respectively. These C–O bond lengths are com-
parable to 1.2081(15)/1.2988(15) Å and 1.209(4)/1.284(4) Å
observed in tBu3P(CO2)B(C6F5)3 (C6H2Me3)2PCH2CH2B(C6F5)2-
(CO2), respectively.23 The B–O distance in 8 is slightly shorter
than the B–O distances of 1.5474(15) Å and 1.550(4) Å reported
in these two phosphine–borane–CO2 complexes.
The isolation of 8 and 9 is interesting given that com-
pounds 1–3 are known to react with CO2 on their own to
In a similar fashion, the phosphinimines 2 and 3 were com-
bined with B(C6F5)3 and stirred overnight under 4 atm of H2 at
25 °C. These reactions resulted in the formation of the white
salts [Ph3PN(H)R][HB(C6F5)3] R = C6F5 6 and tBu 7, respectively
(Scheme 2). These products were isolated in 74 and 72% yields
and the spectroscopic data of 6 and 7 were similar to those
described for 5. In the case of 6, the formulation was further
confirmed by X-ray diffraction studies (Fig. 2). The B–H and
N–H distances were similar to those found in 5, while the P–N Scheme 3 Synthesis and reactivity of 8 and 9.
634 | Dalton Trans., 2013, 42, 630–637
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Scheme 4 Synthesis of 10–12.
Fig. 3 POV-ray depiction of 8. No hydrogen atoms shown. C: black; F: pink; B:
green; P: orange; N: blue; O: red.
generate phosphine–oxide and the isocyanate RNCO derived
from the terminal imide fragment on the phosphinimine.74 In
contrast to 1 and 2, compound 3 together with B(C6F5)3 reacts
with CO2 rapidly to give Ph3PvOB(C6F5)3 and tBuNvCvO. No
intermediate CO2 species were intercepted in this case. This
may result in part from the stronger basicity of 3 compared to
the other phosphinimines. Presumably, in this case, the transi-
ent CO2 species is highly reactive and as a result of this
enhanced basicity, thus prompting rapid formation of phos-
phineoxide and isocyante. It is also noteworthy that com-
pounds 8 and 9 are not stable, and transform to Ph3PvOBC-
(C6F5)3 and R–NvCvO when left in solution for several days.
Alternatively heating to 60 °C for 30 min affords conversion of
8 and 9 to the borane adduct of the corresponding phosphine-
oxide and isocyanate.
Fig. 4 POV-ray depiction of 10a. Of the hydrogen atoms, only the NH proton is
shown. C: black; F: pink; B: green; P: orange; N: blue; H: turquoise.
Reactions with phenylacetylene
Reactions of the FLPs derived from 1–3 with B(C6F5)3 with phe-
nylacetylene generate new products 10–12, in 82, 87 and 89%
yields, respectively. In the case of 10, two isomers of the
product were observed in a 80 : 20 ratio as evidenced by the
31P{1H} NMR resonances at 34.6 (10a) and 38.4 (10b) ppm and
the sharp 11B{1H} NMR signal at −20.9 ppm and the broader
signal at −16.5 ppm. Similarly the 19F NMR spectrum showed
two sets of signals. In the case of 10a signals were observed at
−133.7, −164.8 and −168.2 ppm while for 10b the resonances
were seen at −132.8, −133.1, −165.0, −165.4, −168.8 and
−168.9 ppm. In the 1H NMR spectrum the most notable signal
is observed at 5.68 ppm which is indicative of phosphinimo-
nium salt. (br, N-H). Collectively these data infer the formation
of [Ph3PN(H)Ph][PhCuCB(C6F5)3] 10a as the major product
together with a minor amount of the addition product
(Ph3PNPh)(Ph)CvCH(B(C6F5)3) 10b (Scheme 4). The formu-
lation of 10a was subsequently confirmed via a crystallographic
study (Fig. 4). The metric parameters were unexceptional. The
formation of both 10a and 10b, albeit in a 80 : 20 ratio, is a
further demonstration of the two reaction pathways for the
reactions of FLPs with phenylacetylene.15,16
Fig. 5 POV-ray depiction of 11a. Of the hydrogen atoms, only the CH proton is
shown. C: black; F: pink; B: green; P: orange; N: blue; H: turquoise.
in contrast to 10, the 31P{1H} and 11B{1H} signals were more
similar for the two species giving signals at 42.3 and 41.8 ppm
and −20.9 and −16.7 ppm, respectively. These isomers were
attributed to the E (11a) and Z (11b) isomers of the addition
products. In addition to the other NMR data, this notion was
further supported by a crystallographic study (Fig. 5). The
newly formed N–C bond is found to be 1.433(2) Å, while the
olefinic bond is 1.387(3) Å. In the case of 11, the reduced basi-
city of the phosphinimine 2 results in the exclusive formation
The corresponding reaction that yielded 11 also showed the
formation of two isomers 11a and 11b in a 3 : 1 ratio. However
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3 D. W. Stephan, Chem. Commun., 2010, 46, 8526–8533.
4 D. W. Stephan, Dalton Trans., 2009, 3129–3136.
5 D. W. Stephan, Org. Biomol. Chem., 2008, 6, 1535–1539.
6 G. C. Welch and D. W. Stephan, J. Am. Chem. Soc., 2007,
129, 1880–1881.
7 G. C. Welch, R. R. S. Juan, J. D. Masuda and D. W. Stephan,
Science, 2006, 314, 1124–1126.
8 S. J. Geier, A. L. Gille, T. M. Gilbert and D. W. Stephan,
Inorg. Chem., 2009, 48, 10466–10474.
9 X. Zhao and D. W. Stephan, J. Am. Chem. Soc., 2011, 133,
12448–12450.
10 T. Voss, J. B. Sortais, R. Fröhlich, G. Kehr and G. Erker,
Organometallics, 2011, 30, 584–594.
11 T. Voss, C. Chen, G. Kehr, E. Nauha, G. Erker and
D. W. Stephan, Chem.–Eur. J., 2010, 16, 3005–3008.
12 C. A. Tanur and D. W. Stephan, Organometallics, 2011, 30,
3652–3657.
13 R. Liedtke, R. Fröhlich, G. Kehr and G. Erker, Organometal-
lics, 2011, 30, 5222–5232.
14 C. M. Mömming, G. Kehr, R. Fröhlich and G. Erker, Chem.
Commun., 2011, 47, 2006–2007.
15 M. A. Dureen, C. C. Brown and D. W. Stephan, Organo-
metallics, 2010, 29, 6594–6607.
16 M. A. Dureen and D. W. Stephan, J. Am. Chem. Soc., 2009,
131, 8396–8397.
17 C. M. Mömming, S. Fromel, G. Kehr, R. Fröhlich,
S. Grimme and G. Erker, J. Am. Chem. Soc., 2009, 131,
12280–12289.
18 C. F. Jiang, O. Blacque and H. Berke, Organometallics, 2010,
29, 125–133.
Fig. 6 POV-ray depiction of 12. Of the hydrogen atoms, only the NH proton is
shown. C: black; F: pink; B: green; P: orange; N: blue; H: turquoise.
of the addition products. The dominant E-isomer is consistent
with that observed for phosphine–borane additions to alkynes.
Interestingly no evidence was previous reported for formation
of the Z-addition products for related termolecular reactions.
Indeed, it is only in chelated FLP systems where cis-addition
products have been previously observed.12,37
The last of these reactions with phenylacetylene afforded
the product 12. In this case only a single product was observed
as it gave rise to a single 31P{1H} resonance at 33.4 ppm and a
11B{1H} signal at −20.9 ppm. The 1H NMR spectral data, in
particular the phosphorus coupled doublet at 3.22 (3JP–H = 8 Hz)
inferred the formation of a phosphinimonium salt and thus
the formulation of 12 as [Ph3PN(H)tBuR][PhCuCB(C6F5)3].
This was verified by a crystal structure of 12 (Fig. 6). It seems
clear that the increased basicity of 3 results in the exclusive
formation of the deprotonation product, the phosphinimo-
nium salt 12.
19 C. M. Mömming, G. Kehr, B. Wibbeling, R. Fröhlich,
B. Schirmer, S. Grimme and G. Erker, Angew. Chem., Int.
Ed., 2010, 49, 2414–2417.
20 C. Chen, R. Fröhlich, G. Kehr and G. Erker, Chem.
Commun., 2010, 46, 3580–3582.
21 M. Ullrich, K. S. H. Seto, A. J. Lough and D. W. Stephan,
Chem. Commun., 2009, 2335–2337.
Conclusions
The reactions described herein demonstrated that phosphin-
imines are effective base partners for FLP reactions. Even in
the case of 1 where a classical Lewis-acid–base adduct is iso-
lable, the combination of these phosphinimines of the form
Ph3PNR with B(C6F5)3 are capable of effecting the activation of
H2, CO2 and phenylacetylene. These findings serve to broaden
the range of acid–base combinations for FLP reactivity. We are
continuing probe new combinations of Lewis acids and bases
in the quest for more reactive FLP systems for the activation of
small molecules and applications in catalysis.
22 M. A. Dureen, G. C. Welch, T. M. Gilbert and
D. W. Stephan, Inorg. Chem., 2009, 48, 9910–9917.
23 C. M. Mömming, E. Otten, G. Kehr, R. Fröhlich,
S. Grimme, D. W. Stephan and G. Erker, Angew. Chem., Int.
Ed., 2009, 48, 6643–6646.
24 I. Peuser, R. C. Neu, X. X. Zhao, M. Ulrich, B. Schirmer,
J. A. Tannert, G. Kehr, R. Fröhlich, S. Grimme, G. Erker
and D. W. Stephan, Chem.–Eur. J., 2011, 17, 9640–9650.
25 X. Zhao and D. W. Stephan, Chem. Commun., 2011, 47,
1833–1835.
26 E. Otten, R. C. Neu and D. W. Stephan, J. Am. Chem. Soc.,
2009, 131, 9918–9919.
27 A. J. P. Cardenas, B. J. Culotta, T. H. Warren, S. Grimme,
A. Stute, R. Fröhlich, G. Kehr and G. Erker, Angew. Chem.,
Int. Ed., 2011, 50, 7567–7571.
Notes and references
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2 D. W. Stephan and G. Erker, Angew. Chem., Int. Ed., 2010, 29 B. Ines, S. Holle, R. Goddard and M. Alcarazo, Angew.
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636 | Dalton Trans., 2013, 42, 630–637
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Paper
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32 P. A. Chase, A. L. Gille, T. M. Gilbert and D. W. Stephan,
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