10.1002/chem.201803477
Chemistry - A European Journal
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C6D6, 300K): δ 7.53 – 7.62 (m, 2 H, ortho-H), 7.21 – 7.3 (m, 3 H, meta/para-
H), 2.06 (ds, 2 H, J = 7.2, 1.6 Hz, CH), 1.16 (dd, 6 H, J = 14.8, 7.2 Hz,
CH3), 1.00 (dd, 6 H, J = 14.8, 7.2 Hz, CH3). 13C NMR (100 MHz, C6D6,
300K): δ 135.3 (d, quaternary-C), 134.6 (d, ortho-C), 128.6 (s, para-C),
127.8 (d, meta-C), 22.8 (d, CH), 19.7 (d, CH3), 18.6 (d, CH3). 31P{1H} NMR
(162 MHz, C6D6, 300K): δ 10.35 (s).
seen for the dimethyl substituted phenylphosphine and aniline
substrates respectively, while predominately meta-magnesiation
was observed for the other diethyl and diisopropyl substrates.
These findings were in agreement with the theoretically calculated
pKas indicating little to no variation in the relative aciditys of the
ortho- meta- and para-ring protons across all substrates.
Highlighting the cooperative effect of bimetallic base 1, mono-
metallic studies (NaTMP) on the diethlyphenylphosphine and
aniline substrates lead to no ring metallation and a competitive
ethene elimination pathway. In summary, this reactivity study has
shown exchanging the nitrogen for a softer phosphorus centre
results in more selective metallation outcomes, eliminating
competitive regioisomer mixtures seen predominately for their
nitrogen analogues.
General Procedure (GP): nBuNa (0.16 g, 2 mmol) was suspended in 10
mL of dry hexane. To this suspension TMP(H) (0.68 mL, 4 mmol) was
added dropwise and the reaction allowed to stir at room temperature for at
least 30 minutes. Next Mg(CH2SiMe3)2 (0.4 g, 2 mmol) was introduced with
subsequent addition of TMEDA (0.3 mL, 2 mmol) affording a pale yellow,
transparent solution which was used in situ. If clumps of solid remain in
solution following addition of TMEDA, the solution was sonicated until
complete dissolution occurred.
Synthesis of [(TMEDA)Na(TMP)(CH2PCH3Ph)Mg(TMP)] 2: To a stirred
solution of GP, 0.28 mL of P,P-dimethylphenylphosphine was added
dropwise at room temperature. The resulting solution was stirred overnight,
resulting in the formation of a large amount of white precipitate. This was
isolated by filtration and transferred to an argon glovebox for storage. X-
ray quality crystals were obtained upon recrystallisation from n-hexane.
Crystalline yield = 0.67 g, 58 %. 1H NMR (400 MHz, C6D6, 300K): 7.65 (t,
2 H, J = 6.84 Hz ortho-H), 7.27 (t, 2 H, J = 7.36 Hz, meta-H), 7.12 (t, 1 H,
J = 7.24 Hz, para-H), 1.95 (m (br), 4 H, γ-CH2, TMP), 1.74 (s (br), 12 H,
CH3 TMEDA), 1.68 (s (br), 4 H, CH2 TMEDA), 1.55 - 1.65 (m (br), 24 H,
CH3 TMP), 1.45 – 1.41 (m (br), 4 H, β-CH2 TMP) 1.40 (s, 3 H, CH3), 1.36 -
1.30 (m (br), 4 H, β-CH2 TMP), 0.60 (t, 1 H, J = 9.6 Hz, CH2Mg), -0.23 (d,
1 H, J = 10 Hz, CH2Mg). 13C NMR (100 MHz, C6D6, 300K): δ 150.25 (d,
ipso-C), 130.4 (ortho-C), 127.1 (para-C), 57.4 (CH2-TMEDA), 46.4 (CH3-
TMEDA), 42.8 (β-C TMP), 36.21 (CH3 TMP), 20.66 (γ-C TMP), 18.78 (CH3),
8.0 (CH2-Mg) Note: meta-C signal appears under the C6D6 residual peak
(as determined by HSQC experiment). 31P{1H} NMR (162 MHz, C6D6,
300K): δ -28.58 (s (br)), δ -29.68 (s (br)). Microanalysis: Calculated for
C32H62N4MgNaP: C, 66.14; H, 10.75; N, 9.64. Found: C, 65.88; H, 10.53;
N, 9.45. [(TMEDA)Na(TMP)(p-PMe2Ph)Mg(TMP)] 2a: 1H NMR (400 MHz,
C6D6, 300K): δ 8.83 (s (br), 0.5 H), 7.30 (m, 0.3 H), 1.40 (s, 1.3 H, CH3).
Experimental Section
All reactions (unless otherwise stated) were completed under an
atmosphere of dinitrogen and anhydrous conditions using standard
Schlenk-line techniques. Water and oxygen were removed from n-hexane
and diethylether using a MBRAUN SPS-800 solvent purification system
and were stored over 4 Å molecular sieves under a dinitrogen atmosphere.
TMEDA and TMP(H) were dried by reflux over CaH2 and stored over 4 Å
molecular sieves. 1H and 13C NMR spectra were recorded on Bruker DRX
400 MHz or 600 MHz Cryo spectrometers with chemical shifts internally
referenced to C6D6 or CDCl3. Microanalysis were carried out at the Science
Centre, London Metropolitan University, with samples prepared in air-tight
sealed glass ampules. nBuNa,[60] Mg(CH2SiMe3)2
[20]
and N,N-
diisopropylaniline[61] were prepared according to literature procedures.
See ESI for full details of X-ray crystallographic information and
electrophilic quenching studies. X-ray crystallographic information files
(CIFS) for compounds 2, 3, 4, 5, 6 and 7 has been deposited with the
Cambridge Crystallographic Database with CCDC number 1831594,
1831592, 1831590, 1831593, 1850750 and 1831591 respectively.
Synthesis of [(TMEDA)Na(TMP)(m-C6H4NEt2)Mg(TMP)] 3: To a stirred
solution of GP, N,N-diethylaniline (0.32 mL, 2 mmol) was added dropwise
at room temperature. The resulting solution was stirred overnight, resulting
in the formation of a large amount of white precipitate. This was isolated
by filtration and transferred to an argon glovebox for storage. X-ray quality
crystals were obtained upon recrystallisation from n-hexane and slow
Synthesis of P,P-diethylphenylphosphine: Ethylmagnesium bromide
(25 mL, [3 M in diethyl ether], 75 mmol) was added dropwise to a stirred
solution of phenylphosphorus dichloride (5 mL, 37 mmol) in 60 mL of
diethyl ether at 0 °C over 60 minutes. After filtration, the reaction was
quenched with 5 mL of deoxygenated water. The aqueous layer was
removed via a gas-tight syringe, and the ethereal layer dried with
anhydrous magnesium sulphate. The solution was filtered, the solvent
removed under vacuum and the phosphine purified by vacuum distillation
(0.15 torr, 30 °C) to afford the product as a colourless air-sensitive liquid.
Typical yield 4.3 mL, 65 %. 1H NMR (400 MHz, C6D6, 300K): δ 7.56 (m, 2
H, ortho-H), 7.1 – 7.3 (m, 3 H, meta/para-H), 1.61 (m, 4 H, CH2), 1.05 (dt,
6 H, J = 7.6, 7.2 Hz, CH3). 13C NMR (100 MHz, C6D6, 300K): δ 139.1 (d,
quaternary-C), 132.4 (d, ortho-C), 128.4 (s, para-C), 128.2 (d, meta-C),
20.3 (d, CH2), 9.7 (d, CH3). 31P{1H} NMR (162 MHz, C6D6, 300K): δ -16.59
(s).
1
cooling in a hot oil bath. Yield = 0.77 g, 65 %. H NMR (600 MHz, C6D6,
300K): δ 7.45 (d, 1 H, J = 2.9 Hz), 7.12 (s, 1 H, C2), 7.11 (d, 1 H, J = 1.8
Hz), 6.48 (m, 1 H, meta’-H), 3.17 (q, 4 H, J = 7 Hz, Ethyl-CH2), 1.98 – 1.87
(m, 4 H, γ-CH2 TMP), 1.66 (s (br), 24 H, CH3 TMP), 1.63 (s (br), 12 H, CH3-
TMEDA), 1.55 (s, 6 H, CH2 TMEDA), 1.44 – 1.31 (m, 8 H, β-CH2-TMP),
1.04 (t, 6 H, J = 7 Hz, Ethyl-CH3). 13C NMR (151 MHz, C6D6, 300K): 173.41
(s, Mg-C), 147.22, 127.51, 126.03, 110.33 (meta’-C), 57.30 (CH2 TMEDA),
46.34 (CH3 TMEDA), 45.06 (CH3), 42.76 (β-CH2-TMP), 36.26 (CH3 TMP),
20.76 (γ-CH2 TMP), 13.48 (CH3). Despite multiple attempts, satisfactory
elemental analysis has not proved possible.
Synthesis of P,P-diisopropylphenylphosphine: Isopropylmagnesium
chloride (25 mL, [1 M in tetrahydrofuran], 25 mmol) was added dropwise
to a stirred solution of phenylphosphorus dichloride (1.65 mL, 12.34 mmol)
in 50 mL of anhydrous tetrahydrofuran at 0 °C over 60 minutes. After
stirring overnight, the reaction was quenched with 5 mL of deoxygenated
water. The aqueous layer was removed via a gas-tight syringe, and the
tetrahydrofuran was removed under vacuum and replaced with
diethylether. This solution was filtered, solvent removed and the phosphine
purified by vacuum distillation (0.15 torr, 46 °C) to afford the product as a
colourless air-sensitive liquid. Typical yield: 2 g, 81 %. 1H NMR (400 MHz,
Synthesis of [(TMEDA)Na(TMP)(m-C6H4PiPr2)Mg(TMP)] 4: To a stirred
solution of GP, P,P-diisopropylphenylphosphine (0.4 g, 2 mmol) was
added dropwise at room temperature. Upon addition, an immediate
formation of a bright yellow solution was observed. After stirring overnight,
the solution was filtered and its volume reduced in vacuo, where storage
at -30°C resulted in the deposition of a large crop of yellow, block crystals
Crystalline yield = 0.4 g, 31 %. 1H NMR (600 MHz, C6D6, 300K): δ 8.15
(dd, 1 H, J = 8.4, 1.2 Hz, H ), 7.83 (d, 1 H, J = 4.4 Hz, H4), 7.23 (m, 1 H,
H5), 7.17 (t, 1 H, J = 6.6 Hz, H2), 2.10 (septet, 2 H, J = 6.6 Hz, CH), 1.90 (t
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